# What was the problem with the allison engine?



## davparlr (Jun 1, 2011)

I have been confused by the allison V-1710 engine. In 1940, It appears to roughly be equivalent to the Merlin and the DB-601A, around 1050-1150 hp, and in 1945 was generating 1600 hp in the P-38/P-82. But it was always associated with poor altitude performance. Wouldn't this be cured by an adequate compressor ala Merlin, and wouldn't this have corrected the problem, for, say, the P-51A? Why wasn't this accomplished?


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## Readie (Jun 1, 2011)

It was an inferior design to the Merlin. That's why the P51 received Britain's finest aero engine.
Cheers
John

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## fastmongrel (Jun 1, 2011)

Readie said:


> It was an inferior design to the Merlin. That's why the P51 received Britain's finest aero engine.
> Cheers
> John



There was nothing wrong with the Allison it was in no way inferior to the Merlin. Rolls Royce were able to use the genius of Stanley Hooker and build better and better superchargers and improve altitude performance but that was very nearly the only advantage the Merlin had. Allison was a relatively small company that was swamped by the work heaped on it, a lot of its time was spent getting the installation right on the P38.

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## Readie (Jun 1, 2011)

Allison had been leaning heavily towards exhaust-driven turbochargers instead of the more common mechanically-driven superchargers, feeling that their added performance more than made up for the added complexity. Thus little effort was invested in equipping the V-1710 with a reasonable supercharger, and when placed in aircraft designs like the P-39 or P-40 which lacked the room for a turbo the engine suffered tremendously at higher altitudes. It was for this reason in particular that the V-1710 was later removed from the P-51 Mustang and replaced with the Rolls-Royce Merlin.

The Merlin was a better developed aero engine and more appropriate for the needs of WW2 fighters. Mind you, the lack of power was not Allison's fault but,the US Army's thing about turbo chargers.

The Army had earlier decided to concentrate on turbosuperchargers for high altitude boost, believing that further development of turbochargers would allow their engines to outperform European rivals using superchargers. Turbosuperchargers are powered by the engine exhaust and so do not draw power from the engine crankshaft, whereas superchargers are connected directly by gears to the engine crankshaft. Turbosuperchargers do increase the exhaust back-pressure and thus do cause a decrease in engine power, but the power increase due to increased induction pressures more than make up for that decrease. Crankshaft-driven superchargers require an increasing percentage of engine power as altitude increases (the two-stage supercharger of the Merlin 60 series engines consumed some 230-280 horsepower at 30,000 ft). General Electric was the sole source for research and production of American turbosuperchargers during this period.
Turbosuperchargers were indeed highly successful in U.S. bombers, which were exclusively powered by radial engines. The P-47 fighter had the same combination of radial engine (R-2800) and turbosupercharger and was also successful, apart from its large bulk, which was caused by the need for the ductwork for the aft-mounted turbosupercharger.
However, mating the turbocharger with the Allison V-1710 proved to be problematic. As a result, designers of the fighter planes that utilized the V-1710 were invariably forced to choose between the poor high-altitude performance of the V-1710 versus the increased problems brought on by addition of the turbosupercharger. The fates of all of the V-1710 powered fighters of World War II would thus hinge on that choice.

Technically clever, the turbosupercharger.

The P-38 was the only fighter to make it into combat during World War II with turbosupercharged V-1710s. The operating conditions of the Western European air war – flying for long hours in intensely cold weather at 30,000 feet revealed several problems with the turbosupercharged V-1710. These had a poor manifold fuel-air distribution and poor temperature regulation of the turbosupercharger air, which resulted in frequent engine failures (detonation occurred in certain cylinders as the result of persistent uneven fuel-air mixture across the cylinders caused by the poor manifold design). The turbosupercharger had additional problems with getting stuck in the freezing air in either high or low boost mode; the high boost mode could cause detonation in the engine, while the low boost mode would be manifested as power loss in one engine, resulting in sudden fishtailing in flight. These problems were aggravated by suboptimal engine management techniques taught to many pilots during the first part of WWII, including a cruise setting that involves running the engine at a high RPM and low manifold pressure with a rich mixture. These settings can contribute to overcooling of the engine, fuel condensation problems, accelerated mechanical wear, and the likelihood of components binding or "freezing up." 
Details of the failure patterns were described in a report by General Doolittle to General Spatz in January 1944. In March 1944, the first Allison engines appearing over Berlin belonged to a group of P-38H pilots of 55FG, engine troubles contributing to a reduction of the force to half strength over the target. It was too late to correct these problems in the production lines of Allison or GE, and so the P-38s were steadily withdrawn from Europe until they were no longer used for bomber escort duty with the Eighth Air Force by October 1944. A few P-38s would remain in the European theater as the F-5 for photo reconnaissance.

If my life depended upon it, I would choose the reliable Merlin
Cheers
John

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## davebender (Jun 1, 2011)

> Allison had been leaning heavily towards exhaust-driven turbochargers instead of the more common mechanically-driven superchargers


I think this is the main problem. The U.S. Army Air Corps bet on the wrong horse. If they had emphasized mechanically driven superchargers as Britain and Germany did the Allison engine might have turned out just fine.


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## Shortround6 (Jun 1, 2011)

Oh boy, were to begin. 



Readie said:


> Allison had been leaning heavily towards exhaust-driven turbochargers instead of the more common mechanically-driven superchargers, feeling that their added performance more than made up for the added complexity.



Allison had very little to do with the exhaust-driven turbochargers, they were government specified equipment and government supplied equipment as were the turbo controls. The exhaust-driven turbochargers were supplied by General Electric. Both th exhaust turbines and the intake air compressor. GE had been supplying ALL US aircraft manufacturers with supercharger designs and parts until about 1937. Allison had done sub-contract work for GE making impellers and such but had no supercharger design staff of their own. The ARMY felt that the turbo was the way to go, Allison and other companies just did what the Army told them to do or paid them to do. See the Continental I-1430 and Lycoming O-1230 for a few other examples of the Army projects. 

edit>The turbo set up was a two stage supercharger, the turbo supplied sea level air pressure to the carburetor deck up to the rated altitude of the supercharger. the second impeller (compressor) in the system was between the carburetor and the intake manifold and was gear driven. 
P&W flies a two stage mechanical system in 1939 and is is adopted for use in the F4F-3 in late 1939 but production difficulties force some F4F-3s to be fitted with single stage engines as F4F-3As. 
Bristol has used a two stage system (mechanical driven) to set some worlds records in the late 1930s but aside from a few experimental Wellingtons no WW II production Bristol engine uses a two stage system. 
Rolls-Royce doesn't get the 60 series Merlin into production until 1942. 
For aircraft use two stage superchargers of any type (turbo or mechanical) were mighty scarce in the late 30s or even the first couple of years of the war. 
Hookers work on superchargers doesn't affect anything until the introduction of the Merlin XX and 45 engines.<edit



Readie said:


> Thus little effort was invested in equipping the V-1710 with a reasonable supercharger, and when placed in aircraft designs like the P-39 or P-40 which lacked the room for a turbo the engine suffered tremendously at higher altitudes.



With the entire US supercharger knowledge held by one company until 1937 it is rather amazing that the US did as good as it did in 1939-41 with superchargers. Allison, P&W and Wright all decided at different times in 1937-38 to design their own superchargers as it was becoming obvious that the GE designs weren't that good. The Supercharger on the Allison was actual just about equal to the supercharger used on the Merlin III or Merlin X. There were a few detail differences that kept the Allison from performing quite as well at altitude as the early Merlins but they had little to do with the actual supercharger itself. 




Readie said:


> It was for this reason in particular that the V-1710 was later removed from the P-51 Mustang and replaced with the Rolls-Royce Merlin.



This was done because R-R was the second company to get a 2 stage mechanical supercharger into production. Yes Allison was behind the curve in making a two stage mechanical supercharger. 


Readie said:


> The Merlin was a better developed aero engine and more appropriate for the needs of WW2 fighters. Mind you, the lack of power was not Allison's fault but,the US Army's thing about turbo chargers.



That is a rather simplistic way of looking at it. The Allison was perfectly capable of making power, it had trouble making power at altitude. At low altitudes using similar levels of boost there wasn't that much to chose between the two engines. 



Readie said:


> Turbosuperchargers were indeed highly successful in U.S. bombers, which were exclusively powered by radial engines. The P-47 fighter had the same combination of radial engine (R-2800) and turbosupercharger and was also successful, apart from its large bulk, which was caused by the need for the ductwork for the aft-mounted turbosupercharger.
> However, mating the turbocharger with the Allison V-1710 proved to be problematic. As a result, designers of the fighter planes that utilized the V-1710 were invariably forced to choose between the poor high-altitude performance of the V-1710 versus the increased problems brought on by addition of the turbosupercharger. The fates of all of the V-1710 powered fighters of World War II would thus hinge on that choice.



The P-38 gets a bit of a bum rap because it helped pioneer the turbo-superchager in combat. Turbo-ed P-43 with their radial engines had their share of turbo woes as did early B-17s. It took a while to straighten out the turbo in ALL US aircraft. 




Readie said:


> The P-38 was the only fighter to make it into combat during World War II with turbosupercharged V-1710s. The operating conditions of the Western European air war – flying for long hours in intensely cold weather at 30,000 feet revealed several problems with the turbosupercharged V-1710. These had a poor manifold fuel-air distribution and poor temperature regulation of the turbosupercharger air, which resulted in frequent engine failures (detonation occurred in certain cylinders as the result of persistent uneven fuel-air mixture across the cylinders caused by the poor manifold design). The turbosupercharger had additional problems with getting stuck in the freezing air in either high or low boost mode; the high boost mode could cause detonation in the engine, while the low boost mode would be manifested as power loss in one engine, resulting in sudden fishtailing in flight. These problems were aggravated by suboptimal engine management techniques taught to many pilots during the first part of WWII, including a cruise setting that involves running the engine at a high RPM and low manifold pressure with a rich mixture. These settings can contribute to overcooling of the engine, fuel condensation problems, accelerated mechanical wear, and the likelihood of components binding or "freezing up."
> Details of the failure patterns were described in a report by General Doolittle to General Spatz in January 1944. In March 1944, the first Allison engines appearing over Berlin belonged to a group of P-38H pilots of 55FG, engine troubles contributing to a reduction of the force to half strength over the target. It was too late to correct these problems in the production lines of Allison or GE, and so the P-38s were steadily withdrawn from Europe until they were no longer used for bomber escort duty with the Eighth Air Force by October 1944. A few P-38s would remain in the European theater as the F-5 for photo reconnaissance.



Part of the problem was change in the allowable "ingredients" for 100/130 fuel which changed it's volatility. This was known as a potential problem in the spring/summer of 1943 and Allison worked on a new intake manifold to help solve the problem, as it would affect ALL Allisons, not just the turbo-ed ones. It went into production in the fall of 1943 and was being fitted to new engines in Nov of 1943. Many manifolds were shipped overseas for refitting in service engines. 
The Army's initial design of turbo control was not well thought out, it sought to control the turbo by measuring the pressure in the exhaust ducts or close to the turbine. By maintaining a constant exhaust back pressure they thought this would regulate the intake boost. It was slow responding and subject to freezing, as anybody you has seen the plume of water vapor coming out of a tail pipe on a cold day might have guessed. The turbo control was changed to a system that measured the intake pressure and adjusted the turbo waste gates accordingly. Please note that this was an "Army" or government furnished piece of equipment and not supplied by either Allison (or any other engine maker) or even by GE. 
The problems had been sorted out/solved by the spring of 1944 and all new P-38s from Dec of 1943 on (which may take weeks or months to get to a combat theater) have most of the basic engine problems solved. Mis rigged turbo controls and bad piloting technique (against the directions of both Allison and Lockheed) do cause problems. Decision in favor of the P-51 is made before operational experience with corrected P-38s can be accumulated. It was still the right decision but given a few more weeks it might have been a bit tougher to make. The P-38H that made that flight over Berlin was being built side by side with P-38Js because of a shortage of the intercoolers used in the J. First Js are delivered in Sept of 1943. 

In post war civil use Merlins were fitted with an intake charge heater to solve a similar fuel mixture distribution problem in cruising flight.

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## V-1710 (Jun 1, 2011)

The above posts are correct. It really came down to most Allsions having a simple single stage centrifical blower, while the Merlin used a two-stage supercharger. The V-1710 was indeed designed to be used with a turbocharger for high altitude performance as it was in the YP-37, XP-39, YB-38 and the P-38's. Since the P-40 was intended to be a low altitude ground support fighter, a single stage non-turbo V-1710 was deemed sufficient. Also, when the role of the P-39 was changed from high altitude interceptor to ground attack, the turbocharger was deleted. Beyond that, the V-1710 was a fine design, very rugged and tolerated abuse better than most any water cooled aircraft engine. In fact, Allison powered P-40's were more reliable than the Merlin powered versions in North Africa because the Allison was less prone to damage from sand ingestion. Of course, the Allison's downdraft carburetor and intake mounted on top of the cowling helped, as opposed to the Merlin using an updraft carburetor and intorporating the air intake in the radiator air scoop, below the propellor.

Also, with regards to the P-38's performance over Europe, there was a problem with too low oil temperatures, cause bo too large an engine oil cooler. That was not an issue in the Pacific.

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## Shortround6 (Jun 1, 2011)

I would really, really like somebody to come up with some proof that the P-40 was designed or intended to be a "low altitude ground support fighter".
If was intended to be such a thing they did a remarkably poor job of it. The Army had already decided they wanted air-cooled engines in attack planes. Even the P-26 with it's 600hp Wasp engine had a bigger bomb load than the P-40 prototype and early production versions. Two cowl mounted .50 cal guns with 200rpg is a pretty poor ground attack armament. They used a version of the Allison with the highest possible gear ratio for the supercharger that Allison offered at the time, this cut available power at sea level in favor of power at 11,000-12,000ft and higher. Better "low altitude" performance could have been had by using the supercharger gears from early P-38s. 

The Mission of the P-39 was not changed. The original turbo charger installation was just plain bad with an inter-cooler that severaly limited performance. There was no room inside the aircraft for a proper inter-cooler set up and by switching to a NON-TURBO version the reduction in drag was good for an increase in speed of 30-40mph at all altitudes up to 15,000ft with the turbo plane only being faster at around 20,000ft and up. 

Just like the YP-37 and the P-40, the Army realized that SERVICE turboed p-39s were, if they were lucky, at least a year further down the road than the non-turboed planes. Considering the state of the USAAF and the types and numbers of planes in hand or likely to show up in the next year or two going for non-turboed aircraft meant having at least SOME SORT of MODERN fighter even if they weren't the best compared to a possibly great (or possibly not great) fighter still in testing if they had to go to war. 

Your choice, Going to war in P-40B&Cs with Es starting to show up and early P-39s (which had a LOT of troubles to begin with) or go to war with turbo P-39s/P-40s still in testing and service squadrons still using P-35s/ P-36s in hand fulls with some squadrons still using P-26s?


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## Shortround6 (Jun 2, 2011)

davebender said:


> I think this is the main problem. The U.S. Army Air Corps bet on the wrong horse. If they had emphasized mechanically driven superchargers as Britain and Germany did the Allison engine might have turned out just fine.


 
The German superchargers weren't much better (or worse) than anybody else's. Supercharger design did not stay static during the war. The performance of the supercharger, measured in pressure ratio achievable and efficiency, was improved buy most, if not all countries as the war went on. The German superchargers didn't offer any better performance than the allied ones except maybe for brief periods as advantages see-sawed back and forth as many other fields experienced.


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## MIflyer (Jun 2, 2011)

It's true that the lack of a suitable supercharger was the problem with the V-1710. And it is also true that the USAAF focused on turbosuperchargers as the answer to high altitude power following that famous GE Pike's Peak test in 1918. Turbos were excellent for bombers but you could not put a turbo in a small fighter aircraft, one of the main reasons being the incrased boost mandated a intercooler or aftercooler. 

But the inexplicable things are:

1. Once it became obvious from the XP-37 and the XP-39 that you could not count on turbos for fighters Allison could have made a two-speed supercharger for the V-1710 very easily. It might not have been as good as the Merlin's but it would have added valuable performance to the P-39, P-40, and P-51. In fact, Allison could have done this very easily because unlike the Merlin the crankcase, reduction gears, and supercharger accessory case of the Allison were separate parts. The supercharger accessory case for the V-1710 was great for production since the same one could be used in all of the versions and only a change in impeller and gear ratio had to be made. BUT by sticking with that one design Allison doomed the V-1710 to single speed. By 1941 everybody but everybody was going to at least two speed superchargers.

2. When Allison added an auxillary mechanical supercharger stage to the V-1710 they left out an intercooler or aftercooler. The reason is clear - it is too hard to fit one in a sleek fighter airframe IF you make it an air to air cooler like was used in everything else BUT the Merlin 60 series. Have you seen the intercooler of a B-17? It is large and buried in the wing - not that much of a problem for a big bomber. Have you seen the intercooler for a P-47? It is huge and buried in the fuselage where the 2nd seat of its ancestor was (the P-35 was virtually a 2 seat airplane). That was the clear incredible genius of Sir Stanley Hooker. He solved the problem of getting all that draggy air in and out of the aftercooler by going to a liquid to air cooler. The fact that Allison and no one else did not copy that stunningly obvious idea is simply incredible. Using a liquid cooler would have solved the P-38's intercooler problems, made the 2 stage V-1710 as used in the P-63 and F-82 a more viable powerplant, and would have been useful in otehr engine installations as well, for everything from the P-61 to the B-28 to the Republic Rainbow.

And you are right Shortround. The P-40, P-39 and Allsion P-51 were NOT meant to be low altitude fighters. Take a look at the performance curves and you will see that the superchargers were optimized for about 15,000 ft, that being a happy medium for a single speed supercharger. In contrast the V-1710 in the A-36A was optimized for around 5,000 ft. And the "cropped" Merlin 45's used in the Spitfire V LF versions were also optimized for low altitude and made that airplane what was described as the hottest Spitfire of all below 10,000 ft. 

And take a look at the performance data for the V-1650-7 and the V-1710 with turbo. The Allision was 400 pounds lighter (not counting the turbo) and put out more power at a higher altitude.

I was going to follow up my 2001 Airpower magazine article on WWII supercharging with one that explanined all of this but the mag went out of business. So thanks to y'all for letting me rant!

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## Shortround6 (Jun 2, 2011)

davparlr said:


> I have been confused by the allison V-1710 engine. In 1940, It appears to roughly be equivalent to the Merlin and the DB-601A, around 1050-1150 hp, and in 1945 was generating 1600 hp in the P-38/P-82. But it was always associated with poor altitude performance. Wouldn't this be cured by an adequate compressor ala Merlin, and wouldn't this have corrected the problem, for, say, the P-51A? Why wasn't this accomplished?


 
For an Allison to make 1600hp at 27,000ft it needed about 60in of manifold pressure. At 27,000ft the air pressure is 10.16in according to one old chart so you need a supercharger with a pressure ratio of 5.9 to one. This is beyond the capability of a single stage supercharger of any type. So you are into a two stage supercharger set up of some kind. And with that kind of pressure ratio you need an inter-cooler or after-cooler or the intake air will be too hot. 

The two stage Merlin was designed with an especially compact two stage supercharger in the same housing and it used a liquid after-cooler. The 1st stage was always turning and used power/heated the intake mixture even at low altitude were it wasn't needed. Air to air inter-coolers are larger and bulker but more resistant to combat damage. By placing the the 1st stage a bit further away from the engine it is possible to use a different drive system than the common shaft used by the Merlin 60 series. 
It is also possible to have the carburetter between the stages. This makes for a bulker installation but allows the first stage to be either de-clutched or idled freeing more power for take-off or low altitudes. 

Allison started work on a two stage mechanical system in 1938 but due to the small size of the staff and the pressure to produce what was already tested it had a low priority. It was also very much learn as you go because one of Hooker's claims to fame was that he recognized very early on that some of the formulas in text books about supercharger design were wrong. 

The P-51B had a 7in vertical splice in the fuselage to accommodate the Merlin and it's associated inter-cooler radiator and larger coolant radiator.

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## Shortround6 (Jun 2, 2011)

Nice post MIflyer.

One point needs a bit of clarification though.



MIflyer said:


> 1. Once it became obvious from the XP-37 and the XP-39 that you could not count on turbos for fighters Allison could have made a two-speed supercharger for the V-1710 very easily. It might not have been as good as the Merlin's but it would have added valuable performance to the P-39, P-40, and P-51. In fact, Allison could have done this very easily because unlike the Merlin the crankcase, reduction gears, and supercharger accessory case of the Allison were separate parts. The supercharger accessory case for the V-1710 was great for production since the same one could be used in all of the versions and only a change in impeller and gear ratio had to be made. BUT by sticking with that one design Allison doomed the V-1710 to single speed. By 1941 everybody but everybody was going to at least two speed superchargers.



Two speed superchargers don't do a lot for high altitude performance. This can be seen on a few Merlins. The Merlin III used an 8.588 gear for it's supercharger. The Merlin X with a two speed drive used a 6.389 gear for low speed and a 8.75 gear for high for the same supercharger as used on the III. Altitude performance improved about 1000-1500ft but take off power was improved from the 880hp of the III to 1075hp (a 22% improvement) on 87 octane fuel. Likewise while a Merlin 45 used a 9.089 gear the Merlin XX (with the same supercharger) used 8.15 and 9.49 gears. While altitude performance was slightly improved the low gear set allowed about another 100hp for take-off/low altitude flying at the same RPM and boost pressure. 

An estimate for the performance of the Allison with a two speed drive can be made by using the HP figures of the late Allison's with 9.60 drive ratio and for low altitude work the 7.88 gears. 

By my calculations (which could be wrong) the Allison impeller tips were moving at 1193 FPS with the 9.60 gears while the Merlin XX with 9.49 gears had an impeller tip speed of 1272fps. Perhaps more could be gotten out of the Allison by changing to a higher ratio (that takes more power to turn) but it wasn't going to do much for performance over 20,000ft no matter what ratio is used. The air pressure at 20,000ft is 13.75in and the Allison needed 44.5in to make 1125hp for a pressure ratio of 3.23 which is asking a lot of any single stage compressor.

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## renrich (Jun 2, 2011)

Dav, I appreciate you starting this thread. Many questions I have had for a long time are being answered by some well informed posters. Many thanks and keep up the good work, all!


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## tomo pauk (Jun 2, 2011)

When comparing 1710 with DB 601/605, it might be OK to note that 601/605 were ~35 liter engines, and have had a supercharger tailored for such working volume. V-1710 have had 25% less working volume, thus a similar deficit in power output is to be expected for contemporary engines.


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## Milosh (Jun 2, 2011)

Readie said:


> It was an inferior design to the Merlin. That's why the P51 received Britain's finest aero engine.
> Cheers
> John


 

You do know that Allison engine parts are put in Merlins today because those parts were better than the R-R parts.

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## V-1710 (Jun 2, 2011)

What was the arrangement on the P-63 and P-82?


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## Readie (Jun 2, 2011)

V-1710 said:


> What was the arrangement on the P-82?


 
On 27 February 1947, a P-82B 44-65168 named Betty Jo and flown by Colonel Robert E. Thacker made history when it flew nonstop from Hawaii to New York without refueling, a distance of 5,051 mi (8,129 km) in 14 hr 32 min (347.5 mph/559.2 km/h). This flight tested the P-82's range. The aircraft carried a full internal fuel tank of 576 gal, augmented by four 310 gal tanks for a total of 1,816 gal . Also, Colonel Thacker forgot to drop three of his external tanks when their fuel was expended, landing with them in New York.
To this day, it remains the longest nonstop flight ever made by a propeller-driven fighter, and the fastest such a distance has ever been covered in a piston-engined aircraft (the record for the longest unrefueled flight by a propeller-driven aircraft of any type is held by the Rutan Voyager). The aircraft chosen was an earlier "B" model powered by *Rolls-Royce Merlin engines *

Sense prevailed in the end with RR Merlins.

Cheers
John


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## Shortround6 (Jun 2, 2011)

Readie said:


> Sense prevailed in the end with RR Merlins.
> 
> Cheers
> John



Common sense did prevail, mainly because the first flight of an Allison powered F-82 was 10 days before the record setting flight. 

I would say that not trying a record setting long distance flight with an airframe engine combo that had only been flying a few days is common sense, aside from that it doesn't prove much of anything about the relative merits of the two "brands" of engines considering the vast number of different models and modifications both had.


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## davparlr (Jun 2, 2011)

renrich said:


> Dav, I appreciate you starting this thread. Many questions I have had for a long time are being answered by some well informed posters. Many thanks and keep up the good work, all!


 
Thanks. This certainly has been very informative.


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## Shortround6 (Jun 2, 2011)

V-1710 said:


> What was the arrangement on the P-63 and P-82?



The engines used in the P-63 and P-82 had a second supercharger spaced out to the rear of the engine and the original supercharger, a short drive shaft and variable speed hydraulic coupling took up some of the space The P-63 did not use an inter-cooler and I am not sure that the P-82 did. They did use water injection but against a plane using both an intercooler and water injection that still leaves it behind. The engines were about 22 in longer than a single stage engine. Some versions mounted the carburetor and the engine supercharger (auxiliary supercharge blew into the carburettor) and some had the carburettor on the outside of the auxiliary stage with the auxiliary stage sucking through the carburettor. The first system worked better. 
The P-63 engines were the so called "E" series just like the P-39 but had many changes including, on many P-63s a heavier crankshaft. The P-82s not only had the heavier crankshaft but different reduction gearing to the prop that allowed them to run at 3200rpm without overspeeding the prop tips. The P-82s used the "G" series Allison that was not used in any other production aircraft. The "G" series engines also used a 10 1/4 in impeller on the main supercharger instead of the 9 1/2 in impeller on the earlier engines.

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## Readie (Jun 2, 2011)

Had Allison's engineers been able to put the effort into gear-driven superchargers that Pratt and Whitney and Rolls-Royce did, it might have been a different story. As it was, there can be little doubt that the V-1710 had more potential than was actually exploited.

The V -1710 was an airship engine! Around the time that the Army was washing its hands of the Curtiss Conqueror, Allison began to develop its own engine, at the request of Allison General manager Norm Gilman. The target was 1,000 hp, and Allison intended that the engine should be large enough to deliver this power easily. A successful V-1710-A was test run in 1931 and delivered 650 hp at 2,400 RPM on 80-octane fuel. Development proceeded slowly until the Navy entered the picture. The Navy, while not losing its attachment to air-cooled power plants for airplanes, needed liquid cooling for dirigibles.

Power-to-weight ratio: 0.90 hp/lb

The Merlin/ PV12 was designed from the out set as a new generation fighter/bomber engine.

The Merlin was the most successful aircraft engines of the World War II era, and many variants were built by Rolls-Royce in Derby, Crewe and Glasgow,as well as by Ford of Britain in Trafford Park, near Manchester. The Packard V-1650 was a version of the Merlin built in the United States. Production ceased in 1950 after a total of almost 150,000 engines had been delivered, the later variants being used for airliners and military transport aircraft.
Also used in tanks.

Power-to-weight ratio: 0.96 hp/lb 

Very near the magic 100hp/Lb mark.

Allison V RR/Packard Merlin? No contest.

Cheers
John


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## gjs238 (Jun 2, 2011)

Readie said:


> The Navy, while not losing its attachment to air-cooled power plants for airplanes, needed liquid cooling for dirigibles.



Yeah, why was that?


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## Readie (Jun 2, 2011)

gjs238 said:


> Yeah, why was that?



Allison were asked to contact the Navy, who were working with the Hall Aluminium Aircraft Co on a flying boat, the XP2H-1. The Navy did talk with Allison on this project, but another angle was to emerge during these talks, that of the power units for airships. The Navy wanted an all-american engine available to replace the German Maybach power plants being used at the time. It gave Allison a contract for a single V1710-A engine, to develop 650hp at sea level. Ultimately, the airship engine supply position was not to materialise as the Macon was lost on the 12th February 1935, and with it went the Navy's airship programme.

Cheers
John


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## Shortround6 (Jun 2, 2011)

The Allison was not designed to be an airship engine. It was designed to fill a future market need for a 1000hp engine with high reliability and good fuel economy. The Army was mildly interested but had no money and suggested Allison see the Navy to see if they had any money/interest. Their only interest was as an airship engine so they funded one engine. The market for airship engines was rather small and would be a poor product for an engine maker just starting out. As a stepping stone to future developments and a chance to use somebody else's money for R&D it makes sense. 

The power to weight ratios you posted are worthless because they make no reference to which model or which year or even under what conditions they were calculated.


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## Readie (Jun 2, 2011)

Shortround6 said:


> The Allison was not designed to be an airship engine. It was designed to fill a future market need for a 1000hp engine with high reliability and good fuel economy. The Army was mildly interested but had no money and suggested Allison see the Navy to see if they had any money/interest. Their only interest was as an airship engine so they funded one engine. The market for airship engines was rather small and would be a poor product for an engine maker just starting out. As a stepping stone to future developments and a chance to use somebody else's money for R&D it makes sense.
> 
> The power to weight ratios you posted are worthless because they make no reference to which model or which year or even under what conditions they were calculated.


Shortround, please see my post above.
However you stoutly defend the Allison it simply was not as good as the Merlin. We could speculate till the cows come home but, facts are facts and Allison missed the mark in WW2.
The Merlin would also have gone up a blind alley if the evaporative cooling system had not be changed.

Doubtlessly you will scoff at these :
http://www.outlawpulling.com/PDF/Allison Aircraft Engine.pdf
Typo, it was 92 not 90.

Specifications for the Merlin 61.
Data from Jane's[96]
General characteristics
Type: 12-cylinder, supercharged, liquid-cooled, 60° "Vee", piston aircraft engine.
Bore: 5.4 in (137.16 mm)
Stroke: 6.0 in (152.4 mm)
Displacement: 1,647 cu in (27 L)
Length: 88.7 in (225.3 cm)
Width: 30.8 in (78.1 cm)
Height: 40 in (101.6 cm)
Dry weight: 1,640 lb (744 kg)[nb 13]
Components
Valvetrain: Overhead camshaft, two intake and two exhaust valves per cylinder, sodium-cooled exhaust valve stems.
Supercharger: Two-speed, two-stage. Boost pressure automatically linked to the throttle, coolant-air aftercooler between the second stage and the engine.
Fuel system: Twin-choke updraught Rolls-Royce/S.U. carburettor with automatic mixture control. Twin independent fuel pumps.
Fuel type: 100/130 Octane petrol.
Oil system: Dry sump with one pressure pump and two scavenge pumps.
Cooling system: 70% water and 30% ethylene glycol coolant mixture, pressurised. Supercharger intercooler system entirely separate from main cooling system.[80]
Reduction gear: 0.42:1
Performance
Power output:
1,290 hp (962 kW) at 3,000 rpm at take-off.
1,565 hp (1,167 kW) at 3,000 rpm at 12,250 ft (3,740 m, MS gear)[nb 14]
1,580 hp (1,178 kW) at 3,000 rpm at 23,500 ft (7,200 m, FS gear)
Specific power: 0.96 hp/cu in (43.6 kW/L)
Compression ratio: 6:1
Fuel consumption: Minimum 39 Imp gal/h (177 L/h), maximum 88 Imp gal/h (400 L/h)[nb 15]
Power-to-weight ratio: 0.96 hp/lb (1.58 kW/kg) at maximum power.

Cheers
John


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## Shortround6 (Jun 2, 2011)

Readie said:


> Shortround, please see my post above.
> However you stoutly defend the Allison it simply was not as good as the Merlin. We could speculate till the cows come home but, facts are facts and Allison missed the mark in WW2.
> The Merlin would also have gone up a blind alley if the evaporative cooling system had not be changed.
> 
> ...



I don't believe I am defending the Allison. I am correcting a lot of misapprehensions you seem to have about it though. And some rather blatant examples of not evidence like the record flight. A great achievement by both the Pilots and and the Merlin engines but they didn't "choose" the Merlins over the Allison at the time because the Allison powered version of the plane was undergoing preliminary flight trials.

You might also want to read your own sources a bit better. 

" The Allison Division of General Motors began developing the ethylene glycol-cooled 
engine in 1929 to meet a US Army need for a modern, 1000 hp (750 kW), engine to fit 
into a new generation of streamlined bombers and fighters. To ease production the new 
design could be equipped with different propeller gearing systems and superchargers, 
allowing a single production line to build engines for everything from fighters to 
bombers. 
The U.S. Navy purchased the first V-1710s, the B model (the only V-1710 that did not 
have a gear driven supercharger) in 1931 and installed them on the airship aircraft 
carriers the Akron and Macon." 
Navy doesn't purchase an Allison engine until 2 years after the project starts and the yet the Allison was designed as an "airship" engine?

By the way, that web site has the wrong diameter impeller for that model Allison and if you divide 1325hp by 1445lbs you get 0.9169, not 0.90. of course the 1325hp figure is the wrong figure for a -85 engine also.

A lot of my "facts" come from the Book "Vees for Victory" by Danial Whitney. He may have gotten a few things wrong or had a few typos but I want something more than just a website before I throw out his data.

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## gjs238 (Jun 2, 2011)

gjs238 said:


> Yeah, why was that?


What I meant was, why the need for liquid cooled engines on dirigibles?
Or, what's the matter with air cooled engines on dirigibles?


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## Lighthunmust (Jun 2, 2011)

I seem to recall that the Allison was superior to the Merlin in North Africa due to less maintenance issues from the environmental conditions. I am going to check Bodie, but I think they did a study on using Merlins in the P-38 that surprisingly indicated a significant weight gain and no increase or possibly a decrease in overall performance. Have either of you read anything about these issues.


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## V-1710 (Jun 2, 2011)

It is true, Allison engined P-40's fared better than their Merlin engined counterparts in North Africa. It seemed that the Allison was more tolerant of ingesting sand then the Merlin was. The fact that the Allison used downdraft carburetors (with the intake above the propeller) probably kept more sand out of the engine than the Merlin's updraft carburetors did. Some Merlin powered P-40's in North Africa were re-engined with Allisons.

'Vees For Victory' covers the Merlin powered P-38 proposal. It appeared that there would have been no improvement in performance, and of course there was a heavy demand for Merlins in other aircraft.


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## Shortround6 (Jun 2, 2011)

gjs238 said:


> What I meant was, why the need for liquid cooled engines on dirigibles?
> Or, what's the matter with air cooled engines on dirigibles?



At the time (late 20s/early 30s) air-cooled engines had a higher fuel consumption per horsepower hour than the liquid cooled engines did. With flight times measured in days instead of hours this fuel consumption difference more than canceled out the higher weight per horsepower of the liquid cooled engines. Since arrangements were made to service the engines in flight (mechanic access) most liquid cooled leaks could be reached and repaired. Dirigibles also liked to be able to recapture the moisture in the exhaust to use as ballast. Some dirigible engines were actually constructed that could be reversed in rotation, if not while actually running, in just a few seconds in order to give reverse thrust (including the early Allison v-1710 airship engine) . Reversible pitch propellers not being available yet. 
Allison had worked on a airship engine from 1927 on till 1929 or a bit later when the project was transfered to the GM Detroit Diesel division. It was a 6 cylinder inline two stroke diesel engine with a roots supercharger. Planned HP was 900. Allison did other airship work including remote shafts and gear boxes that allowed the propellers to be rotated 90 degrees for forward thrust or vertical lift.

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## Lighthunmust (Jun 2, 2011)

V-1710 said:


> It is true, Allison engined P-40's fared better than their Merlin engined counterparts in North Africa. It seemed that the Allison was more tolerant of ingesting sand then the Merlin was. The fact that the Allison used downdraft carburetors (with the intake above the propeller) probably kept more sand out of the engine than the Merlin's updraft carburetors did. Some Merlin powered P-40's in North Africa were re-engined with Allisons.
> 
> 'Vees For Victory' covers the Merlin powered P-38 proposal. It appeared that there would have been no improvement in performance, and of course there was a heavy demand for Merlins in other aircraft.



That is what I remember now that you mentioned it. Could it also be that GM design and manufacturing philosophy encouraged looser parts tolerances than Rolls Royce? I also recall that the Hawker Hurricanes had problems in Africa for the same reason.


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## Shortround6 (Jun 2, 2011)

Lighthunmust said:


> That is what I remember now that you mentioned it. Could it also be that GM design and manufacturing philosophy encouraged looser parts tolerances than Rolls Royce? I also recall that the Hawker Hurricanes had problems in Africa for the same reason.



I really doubt that Allison's had looser parts tolerances than Rolls-Royce, at least enough looser to eat dirt and sand without wrecking the engine. All of these aircraft engines were, compared to even car engines of the 60s, 70s and 80s, lightly built and highly stressed, engines that will tolerate 12-15lb of boost for minutes on end do not have sloppy, ill fitting rings. The blowby into the crankcase would be tremendous. A leaking intake valve could spell disaster. Backfires into the intake manifold could and did wreck intake manifolds, superchargers, carburetors and in some cases blew parts of the intake duct off the aircraft. Sloppy main bearings on a 5 foot long crankshaft in a 1000-1400hp engine would make for a might short lived engine also.


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## Lighthunmust (Jun 2, 2011)

Shortround6 said:


> I really doubt that Allison's had looser parts tolerances than Rolls-Royce, at least enough looser to eat dirt and sand without wrecking the engine. All of these aircraft engines were, compared to even car engines of the 60s, 70s and 80s, lightly built and highly stressed, engines that will tolerate 12-15lb of boost for minutes on end do not have sloppy, ill fitting rings. The blowby into the crankcase would be tremendous. A leaking intake valve could spell disaster. Backfires into the intake manifold could and did wreck intake manifolds, superchargers, carburetors and in some cases blew parts of the intake duct off the aircraft. Sloppy main bearings on a 5 foot long crankshaft in a 1000-1400hp engine would make for a might short lived engine also.


 
Loose is a relative term. I certainly get your point about what too loose can do. Whether looser tolerances did or did not contribute to reliability in desert conditions; you have more faith in GM than I do. Rolls Royce had a history of making tight engines for air racers, not so much GM. Remember the GM design and manufacturing philosophy is what birthed the P-75.


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## V-1710 (Jun 3, 2011)

I think GM was capable of manufacturing most any precision device to whatever tolerance the specifications called for, be it an aircraft engine, a diesel engine, a complete aircraft, or a gun. And I think GM was without peer when it came to manufacturing percision devices in quantity. Vast, almost unimaginable quantities. If the Allison was 'looser' than a Merlin, it was certainly designed that way, not the result of haphazard manufacturing. 

I have been told that at low altitudes the Allison powered P-51 and P-51A would outperform the later Merlin powered models. I would imagine the lighter weight of the early P-51 would come into play if in fact this is true. I don't have any data to back that claim up, perhaps one of you has more details?


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## Shortround6 (Jun 3, 2011)

Lighthunmust said:


> Loose is a relative term. I certainly get your point about what too loose can do. Whether looser tolerances did or did not contribute to reliability in desert conditions; you have more faith in GM than I do. Rolls Royce had a history of making tight engines for air racers, not so much GM. Remember the GM design and manufacturing philosophy is what birthed the P-75.



GM is a large corporation, just because on Division of GM made a mistake or or one division made stamped sheet metal parts of rather loose tolerances doesn't mean that ALL their divisions couldn't make quality products. This is also 1940 GM as a corporation is 22 years old with many fits and starts, I am not sure there was time for a GM "design and manufacturing philosophy" to take root. Cadillac at the time was one of the quality car companies in the world, It took another 15-25 years for them to coast on that reputation. 
Without a break down of the actual clearances used and tolerances allowed it is rather pointless to comment on which was looser. In some cases they didn't measure things the same way.
I have found out that R-R allowed (at least at overhaul) a maximum weight variation of 1 OZ between the pistons in one engines. Allison allowed 0.030lb or just under 1/2 ounce. 
Piston to cylinder fit isn't specified the same way. 
Allison has min and max dimensions at top and bottom of the cylinder (.015-.019 and .030-.034) while The Merlin has specifications for measuring at 90 degrees to gudgeon pin at the top of the piston (0.030-0.034 new-0.045 worn) and in line with gudgeon pin at the bottom of the piston (0.020-0.024 -0.035 worn).

Most figures are from the "Aircraft handbook" by Fred Colvin McGraw-Hill 1942, 5th edition. If somebody else wants to go through a 1/2 dozen pages of tables of allowable tolerances to PROVE the Allison was looser be my guest.

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## Shortround6 (Jun 3, 2011)

V-1710 said:


> I think GM was capable of manufacturing most any precision device to whatever tolerance the specifications called for, be it an aircraft engine, a diesel engine, a complete aircraft, or a gun. And I think GM was without peer when it came to manufacturing percision devices in quantity. Vast, almost unimaginable quantities. If the Allison was 'looser' than a Merlin, it was certainly designed that way, not the result of haphazard manufacturing.
> 
> I have been told that at low altitudes the Allison powered P-51 and P-51A would outperform the later Merlin powered models. I would imagine the lighter weight of the early P-51 would come into play if in fact this is true. I don't have any data to back that claim up, perhaps one of you has more details?



It was not just the weight, the P-51B had a 7in vertical splice in the fuselage and so had more frontal area and more skin drag. Scoop on the bottom was a bit bigger too.


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## Lighthunmust (Jun 3, 2011)

Shortround6 said:


> GM is a large corporation, just because on Division of GM made a mistake or or one division made stamped sheet metal parts of rather loose tolerances doesn't mean that ALL their divisions couldn't make quality products. This is also 1940 GM as a corporation is 22 years old with many fits and starts, I am not sure there was time for a GM "design and manufacturing philosophy" to take root. Cadillac at the time was one of the quality car companies in the world, It took another 15-25 years for them to coast on that reputation.
> Without a break down of the actual clearances used and tolerances allowed it is rather pointless to comment on which was looser. In some cases they didn't measure things the same way.
> I have found out that R-R allowed (at least at overhaul) a maximum weight variation of 1 OZ between the pistons in one engines. Allison allowed 0.030lb or just under 1/2 ounce.
> Piston to cylinder fit isn't specified the same way.
> ...



Great reply! That probably settles the issue of loose tolerances. Even in 1940 I believe Rolls Royce had a better reputation for precision. Didn't the Allison also have less parts than the Merlin? If true perhaps that was a factor also.


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## MIflyer (Jun 3, 2011)

The Merlin built by RR tended to be assembled using the "Master craftsman" approach, where components such as pistons were closely matched. A teacher I had in college flew P-51's in WWII and he said his personal airplane had a RR Merlin rather than a Packard one and that it made a big difference.

Or so he said anyway. One day I had flown my Ercoupe into Kissimmee, Florida and a man visiting from Scotland came over to admire it. As we chatted the P-51D Crazy Horse taxied by. "That's not a RRRoolllsss RRRoooycee." he said. I said, "What do you mean it's not a Rolls Royce? it's a P-51D. Its a Packard Rolls Royce Merlin V-1650."

He replied "Well, it's toooo smooooth to be a RRRoolllsss RRRoooycee."

I told him that I heard that the RR Merlins were smoother running than the Packards. He said he heard that the Packards were smoother than the Rolls Royces. Turned out he rebuilt Rolls Royce motorcars as a hobby so he may well have known what he was talking about.

Of course many of the Merlins flying today have what are known as "transport heads" which were built postwar for the Canadian Merlin powered copy of the DC-4. They were designed to be smoother running and longer lasting and are much sought after by warbird operators. 

When Allison built the TF-41 version of the RR Spey engine for the A-7D and the USAF started overhauling it that had some big problems. Once I was sent to Myrtle Beach AFB with the orders to get the A-7D's there flying again - all were grounded for an bleed air duct problem. I got them all flying - all that had engines, which was only about half of the 80 that were based there. I later was told that RR tended to stack up part assemblies and match drill them to get closer tolerences, and Allison had copied that, so dismantling engines and then trying to put them all back together without keeping track of which part went with which engine was asking for trouble. 

As for Allison parts in the Merlins, that is the rods, which are more solid than the Merlin rods and almost exactly the same dimensions, except I think in the bearing area.

I understand that Merlins had far, far, more individual parts than did the V-1710.

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## Lighthunmust (Jun 3, 2011)

MIflyer said:


> The Merlin built by RR tended to be assembled using the "Master craftsman" approach, where components such as pistons were closely matched. A teacher I had in college flew P-51's in WWII and he said his personal airplane had a RR Merlin rather than a Packard one and that it made a big difference.
> 
> Or so he said anyway. One day I had flown my Ercoupe into Kissimmee, Florida and a man visiting from Scotland came over to admire it. As we chatted the P-51D Crazy Horse taxied by. "That's not a RRRoolllsss RRRoooycee." he said. I said, "What do you mean it's not a Rolls Royce? it's a P-51D. Its a Packard Rolls Royce Merlin V-1650."
> 
> ...




I always hope to be educated more than educating when participating in these discussions. Posts like the above are why I enjoy being a member of this forum. Great Post MIflyer!


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## Readie (Jun 3, 2011)

Lighthunmust said:


> I always hope to be educated more than educating when participating in these discussions. Posts like the above are why I enjoy being a member of this forum. Great Post MIflyer!




Me too. Well said.

Allison V-1710 Engine - USA

I'm sure I have read somewhere that Allison used US automotive techniques to build their engines rather than the master craftsman approach of RR.
So, in theory, the Allison should have been available by the 1000 and built to an acceptable standard. Given that wartime aircraft were not built to last...
Tools for the job etc.

Art Afons used Allisons to power in Green Monster land speed record car as well.
Green Monster Number 2 was painted by Arfons' mother to resemble the World War II Curtiss P-40 Flying Tigers fighter airplane, with an open mouth showing large teeth. The top speed of the car was estimated at 270 miles per hour (435 km/h), and it could reach 140 miles per hour (225 km/h) in nine to ten seconds from a standing start. Running on passenger car tires, the car required four wheels on the rear drive axle to withstand the power. At the first World Series of Drag Racing at Lawrenceville, Illinois, it clocked the highest top speed at 132.35 miles per hour, and eventually a world record of 145.16 mph.
The later cars had various paint schemes where green was not necessarily the dominant color. The six-wheeled Green Monster Number 6 became the first dragster to break 150 miles per hour in the quarter mile. Green Monster Number 11, Art Arfons' favorite, hit 191 miles per hour to beat Don Garlits.
Arfons used an Allison V1710 V12 airplane engine in several of the Green Monsters. The Allison V12 powered the P-40 as well as many other aircraft including the P-51A, P-39 Aircobra, P-38 Lighting, P-63 and others.

*Shortround*, Is this true? I'm blowed if I can find the source to confirm the US car engine line build technique.

Cheers
John


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## Shortround6 (Jun 3, 2011)

But the British wound up using car building techniques to build the Merlin. When Ford of England took up the task of running the shadow factory at Trafford Park they had to redo the drawings and tolerances.

This is from Wiki but agrees with most other sources;

"Having an abandoned factory in Trafford Park, Ford of Britain was approached about the possibility of converting it into an aircraft engine production unit by Herbert Austin, who was in charge of the shadow factory plan. Building work on a new factory was started in May 1940 on a 118-acre (48 ha) site, while Ford engineers went on a fact finding mission to Derby. Their chief engineer commented to Sir Stanley Hooker that the tolerances used were far too wide for them, and so the 20,000 drawings would need to be redrawn to Ford tolerance levels, which took over a year.[65] Ford's factory was built with two distinct sections to minimise potential bomb damage, it was completed in May 1941 and bombed in the same month. At first, the factory had difficulty in attracting suitable labour, and large numbers of women, youths and untrained men had to be taken on. Despite this, the first Merlin engine came off the production line one month later[66] and it was building the engine at a rate of 200 per week by 1943, at which point the joint factories were producing 18,000 Merlins per year.[27] Ford’s investment in machinery and the redesign resulted in the 10,000 man-hours needed to produce a Merlin dropping to 2,727 in three years, while unit cost fell from £6,540 in June 1941 to £1,180 by the war’s end. In his autobiography Not much of an Engineer, Sir Stanley Hooker states: "... once the great Ford factory at Manchester started production, Merlins came out like shelling peas. The percentage of engines rejected by the Air Ministry was zero. Not one engine of the 30,400 produced was rejected ...".[67] "

I do have copy of Sir Stanley Hookers autobiography and this is essentially in agreement with what that says. R-R could take parts built to the drawings with wider tolerances and either hand select or hand fit them into tight tolerance assemblies using skilled labor. Ford was used to making parts to tighter tolerances and then using semi-skilled labor to assemble units using completely interchangeable parts. The end result (finished engine) may not be that much different.

One of the men from Ford said (basically) they could not make tens of thousands of cars per year at cheap prices without completely interchangeable parts that required no hand fitting. 

That may be the basic "automotive technique" but with a bit tighter tolerances and inspection. "Vees for Victory" claims 20% of the Allison work force were inspectors and gives numbers for the number of operations needed to make a Cadillac car engine connecting road and an Allison rod (Cadillac sub-contracted crankshafts, rods, camshafts and other parts for Allison). It was considerably more for the Aircraft rod. 
Both engines were subject to upgrades in material and construction techniques as production continued. Allison started shotpeening the crankshaft at some point after starting production and by some point in 1942 was nitriding the crankshaft. Thses later crankshafts were much longer lived than the early ones. Bearing materials may have changed. Merlins introduced Crankshafts that feed oil from both ends and other detail improvements. Late war engines could last 2-3 times longer between overhauls than early war engines inspite of increased power output. 

Merlins definitely had a better supercharger set up once Hooker started working on them and so had better high altitude performance but I don't think either engine had much of an advantage over the other otherwise, including quality of build. And quality of build changed during the war for both engines so if one was ahead for a few months it might swap back again later. 

I don't believe I have said anything bad about the Merlin. I just don't think, supercharger aside, the Allison was inferior to the Merlin to nay large degree and certainly not for many of the reasons bandied about on the internet.

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## Readie (Jun 3, 2011)

Thank you Shortround, Interchangeability of parts is one of the phrases I recall from the article as well. a move away from craftsmanship to a more real world approach and true mass production.
I know that you weren't criticising the Merlin, it did have a very shaky start in the 1930's ! and like everything else it was not perfect.
The supercharger design gave it the edge and all I was trying to say that in wartime that 'edge' was all that mattered.
The Allison was a good motor handicapped by the US militaries misunderstandings.
Moral? Leave it to the engineers !!
Best wishes
John


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## MIflyer (Jun 3, 2011)

Speaking of tolerances, I would guess that almost everyone has heard of the story of the Flying Tigers’ engines, but in case y’all have not, here it is.

The British agreed to allow China to have 100 Tomahawk IIA’s to equip the American Volunteer Group and get the later D’s and E’s in exchange. 

But even back then it was common for governments to buy airplanes and engines separately. The British refused to give up 100 V-1710 C series engines to install in the fighters. They probably thought that they would use them as spares for the ones they already had, or to go in their Lightning I fighters. 

Allison stepped up to the challenge of equipping the Chinese fighters, and did so magnificently. The company had plenty of 1710 parts that were manufactured and were found to be non-compliant. They got a team of top engineers and experienced technicians and hand built 100 engines, using the out-of-spec parts, carefully selecting and fitting each one. They added shims or bushings as required, and I would imagine also doing additional machining as required as required.

The Flying Tigers got those special built engines, and each one had virtually been built up like a race car engine (note: after all, we are talking people working in Indianapolis here), or “blueprinted.” 

And those engines built of rejected parts developed more power and used less gasoline than any stock C series V-1710. The Tigers said they could notice it too; their airplanes were noticeably faster than the P-40’s they had been flying in the USAAF. One even said he saw them hit 375 mph in level flight.

So we slipped a ringer in on the Japanese; very experienced pilots of the caliber of Boyington, Howard, and Hill, flying hot rod airplanes. So solly, sons of Nippon!

And I am glad y’all found the info I provided interesting. 

I would also like thank Shortround for the info he provided. I have all kinds of reference books but I had not thought about the superchargers of the V-1710 and Merlin being different sized.

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## Milosh (Jun 4, 2011)

For a description of the V-1710, History of the Allison Engine--Part 2


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## WJPearce (Jun 4, 2011)

Allison down low....

I have really enjoyed this thread and I appreciate all the well thought out responses. 

I am currently reading "The Building of the P-51 Mustang" by O'Leary and it has some interesting information on Allison vs Merlin at low altitude. Please note I am not saying one is better than the other or anything like that, I am just passing along some information that I found interesting.

There is a report written by Charles F Born, Brigadier General, CSC, Asst. Chief of Staff, A-3 and dated 26 August 1943 on "British Army Cooperation Tactical Employment of the Mustang I (P-51)"

This report states the Allison is preferred for their missions (low level daylight intrusion raid "Rhubarbs") because the Allison will cruise at a fuel efficient 1100 RPM while the Merlin is very rough under 1600 RPM.

It also states that the British have operated the Allison at 72 inches for as much as 20 minutes without damage, the Allison is averaging 1500 hours between bearing failures compared to 500-600 for the Merlin, and that the Allison will drag the airplane home even with a bearing ruined.

The report basically states the Allison powered P-51A is better low level fighter-intruder and the Allison is a big part of "why".

That report seems to agree with the "smoother running" and "more durable" comments on this thread.

Also in the book is picture of a F-6A (photo recon P-51A) that was used on D-Day even though Merlin Mustangs were available, supposedly because of its low level performance.

I love both engines. They are just different with each having its own strengths and weaknesses. I do feel that the Allison got a raw deal. Many people act as if the Mustang single-handedly won the war and that the P-51 was garbage until the Merlin was installed. Therefore the Allison must be a bad engine. Not true of course.

Again, thanks to all. Great thread.

WJP

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## Juha (Jun 5, 2011)

Hello,
one can find Charles F Born's report from Mike Williams' site, URL:
E-GEH-16


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## Trilisser (Jun 5, 2011)

It is quite clear from tests relating to the maximum range tests of both the Spitfire and the Merlin Mustang that the highish minimum cruising rpm limit of the Merlin (1600 -1800 rpm) substantially reduced maximum range at the most economical airspeed as especially the Spitfire required very low boost (well below 0 boost) at 1800 rpm to achieve that IAS and thus an inefficient low boost/high rpm (relatively speaking) combination was used. I received data from David Birch of RRHT on the issue and what modifications were required in the Merlin to allow running down to about 1200 rpm but unfortunately I lost the details when my HD crashed.


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## Trilisser (Jun 5, 2011)

Juha, check your e-mail!!!


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## wuzak (Jun 5, 2011)

I think that the difference between the RR Merlin and the Allison V-1710 is partly due to the different circumstances of the manufacturers and their countries. 

RR, and the other British engine manufacturers, were heavily funded by the government in the 1930s, and the situation in Europe required a certain level of urgency. The Merlin was probably put into service earlier than it should have been, but the RAF needed aircraft, particularly high performance fighters, for a potential war.

Allison, on the other hand, was drip fed funds from the US government, who was very much an isolationist government in the 1930s. Recovering from the depression also reduced funds available for development.

Note that the Continental IV-1430 program started not long after the V-1710, but didn't get into production before the end of the war. Continental were drip fed funds and didn't invest their own money in the program, so progress was slow. It was similar for Allison, in that government money for development was tight, and they were directed as to what to develop.

RR had been active in the Schneider Trophy the last couple of times it ran, and used supercharger boost to achieve the performance. This is also the road they took through the war, particularly on the Merlin. High boost dictated lower compression ratios. Allison initially ran higher compression ratios, which restricted the boost that could be used, and thus horsepower. Later Allison dropped the CR and increased boost for turbocharged and two stage engines.

Also, later in the war Allison tested a V-1710 fitted with a two stage supercharger from a 60-series Merlin, the power and torque curves being almost identical with the Merlin. Basically the power that either could produce was down to the air that could be put through it, and the supercharger was the detrmining factor in that.

Most of the war the Allison suffered for having a single speed supercharger. In fact all single stage engines were single speed. RR went to two speed suerchargers early in the war, and that contunued with the two stage engines. Having a multiple speed drive for the single speed supercharger, or a variable speed drive, would have made the single stage altitude rated (turbocharged engines were sea level rated) engine a more useful and competitive unit.

There were a few areas of design where the Allison could be considered to be superior to the Merlin. But the potential superiority was not realised during the war, Allison's design ability being trumped by Rolls-Royce's development ability and determination, and I think it would be fair to say that the Merlin's legendary status is built on the many roles it played during the war, and its influence on the outcome was arguably greater than any other engine of the period.


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## davparlr (Jun 5, 2011)

Thanks everyone for an amazing technical input.

The Merlin engine certainly needs no defense, it has its war record to do that but Allison seems to be generally considered a second rate brother to the Merlin due to its replacement in the Mustang. This discussion has certainly answered my question and, in my mind, raise my opinion of the Allison. I read somewhere that the US paid royalties for the Packard Merlins and wanted the Allison in the P-82 because of that. What was the cost of these royalties?

I have a slight deviation of this thread, although closely related. It seems that the real hero here, when it comes to the Mustang, was the supercharger. Where did the Packard Merlin supercharger come from, was it built in the US under patent? Who manufactured it? Was it modified in any way. I was under the impression it was different from the British Merlin engines, is that true? What is the story here.


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## wuzak (Jun 5, 2011)

davparlr said:


> It seems that the real hero here, when it comes to the Mustang, was the supercharger. Where did the Packard Merlin supercharger come from, was it built in the US under patent? Who manufactured it? Was it modified in any way. I was under the impression it was different from the British Merlin engines, is that true? What is the story here.



I always assumed that the Packard supercharger was built by Packard under licence from the Rolls-Royce design. Some Packard Merlins used a different supercharger gear system (which was lighter, IIRC) to the standard Rolls Royce system. In any case, the supercharger itself was the same.


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## wuzak (Jun 5, 2011)

davparlr said:


> Thanks everyone for an amazing technical input.
> 
> The Merlin engine certainly needs no defense, it has its war record to do that but Allison seems to be generally considered a second rate brother to the Merlin due to its replacement in the Mustang. This discussion has certainly answered my question and, in my mind, raise my opinion of the Allison. I read somewhere that the US paid royalties for the Packard Merlins and wanted the Allison in the P-82 because of that. What was the cost of these royalties?



I believe that Packard Merlin production stopped at the end of the war, and that was partly to do with royalties. The P-82 got Allisons when the Merlins ran out.


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## renrich (Jun 5, 2011)

"The Merlin was the most successful aircraft engine of the WW2 era." Hmmmmmmmm! All well and good to be nationalistic. I expect that most of us are nationalistic to some degree.
BUT! During the fighter conference in 1944, pilots were asked to vote on which engine inspired the most confidence. 79% voted for the R2800, 17% for the Merlin and 1% for the V1710. Perhaps we should amend the statement to : The Merlin was the most successful inline liquid cooled engine in WW2?


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## tomo pauk (Jun 5, 2011)

The people that voted at 1944 fighter conference were overwhelmingly from USA, and mostly flew planes powered by R-2800. No wonder voting was as it was.


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## Glider (Jun 5, 2011)

Can I ask the background of the pilots? I mention this as I would expect a USN pilot to go for the R2800 and any USAAF that flew aircraft powered by the R2800, and any P51 pilot or RAF pilot to go for the Merlin.

People understandably have faith in what they have experienced and trusted.

I should add that I am not knocking the R2800 or upping the Merlin, both were probably the class act in the radial and inline design


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## Lighthunmust (Jun 5, 2011)

wuzak said:


> Allison, on the other hand, was drip fed funds from the US government, who was very much an isolationist government in the 1930s. Recovering from the depression also reduced funds available for development.
> 
> 
> I you haven't read David Brinkley's "Washington goes to War", I recommend you do. I'm sure other books touch on the same subject, but this one is short and to the point. It really gives the reader an understanding of the small size and small mindedness of the U.S. government in the 1930s.
> ...


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## Readie (Jun 5, 2011)

renrich said:


> "The Merlin was the most successful aircraft engine of the WW2 era." Hmmmmmmmm! All well and good to be nationalistic. I expect that most of us are nationalistic to some degree.
> BUT! During the fighter conference in 1944, pilots were asked to vote on which engine inspired the most confidence. 79% voted for the R2800, 17% for the Merlin and 1% for the V1710. Perhaps we should amend the statement to : The Merlin was the most successful inline liquid cooled engine in WW2?


 
No, with respect, the Merlin was the most successful aero-engine,its not all about being English either.
It powered most of the significant WW2 aircraft and secured our liberty.
I have the utmost respect for the P51 but, the Americans could not produce an engine of sufficient performance in time for when the P51 was needed most.
Cheers
John


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## Readie (Jun 5, 2011)

wuzak said:


> I think that the difference between the RR Merlin and the Allison V-1710 is partly due to the different circumstances of the manufacturers and their countries.
> 
> RR, and the other British engine manufacturers, were heavily funded by the government in the 1930s, and the situation in Europe required a certain level of urgency. The Merlin was probably put into service earlier than it should have been, but the RAF needed aircraft, particularly high performance fighters, for a potential war.
> 
> ...


 
On the money there.
Well said
Cheers
John


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## Milosh (Jun 5, 2011)

Readie said:


> No, with respect, the Merlin was the most successful aero-engine,its not all about being English either.
> It powered most of the significant WW2 aircraft and secured our liberty.
> I have the utmost respect for the P51 but, the Americans could not produce an engine of sufficient performance in time for when the P51 was needed most.
> Cheers
> John


 
I seem to recall a couple of engines from Pratt Whitney. Think they were the R-1830 and R-2800.


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## Shortround6 (Jun 5, 2011)

davparlr said:


> I read somewhere that the US paid royalties for the Packard Merlins and wanted the Allison in the P-82 because of that. What was the cost of these royalties?



The US did pay royalties but I think the amount changed at the end of the war. England being totally strapped for cash. Royalties per engine went up, Allison gets 2 stage supercharger working, (please note we are talking about late 1946/early 1947 here), USAAF doesn't really want to depend on foreign engines (although many jet engines are based of the English ones.


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## Shortround6 (Jun 5, 2011)

Readie said:


> No, with respect, the Merlin was the most successful aero-engine,its not all about being English either.
> It powered most of the significant WW2 aircraft and secured our liberty.
> I have the utmost respect for the P51 but, the Americans could not produce an engine of sufficient performance in time for when the P51 was needed most.
> Cheers
> John


 
With respect, that is certainly debatable. It also a bit about timing.
The P&W R-1830 was produced in more numbers than any other larger aircraft engine and might lay claim to most successful on that basis. It did power a number of significant WW II aircraft and certainly played a large part. It was, however a bit earlier in timing than the Merlin and not capable of the power needed for first rate combat aircraft after 1941-42 except in turbocharged 4 engine installations (B-24).

The R-2800 was a bit later in timing than the Merlin and certainly powered a fair number of "significant WW2 aircraft" unless you think the B-26, Lockheed Ventura, A-26, P-47, F-6F, F4U, were insignificant, this not counting minor types and end of war and post war types. With over 125,000 P&W R-2800s produced it may be below the Merlin in numbers but it did go on to be produced for a number of years after merlin production stopped, but that is only natural considering it's later timing. 
Granted neither P&W engine saved England in the BoB or was there for the early part of the European air war (although the R-1830 did it's bit in the battle of the Atlantic and helped with the Bismark).


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## renrich (Jun 5, 2011)

Glider, there is online a source for a complete report of that 1944 Fighter Conference. The reviews say that it is an excellent book for us WW2 airplane wingnuts. I have ordered it and when received I will try to transmit any relevant info to this forum. In fact you can count on me using that report just as I do Dean's book to back up all my arguments My personal choice of an engine if I was going flying and especially into combat as far as confidence that the engine would get me there and back would have been the R2800. The war would have been tougher to win without either the Merlin or the R2800.


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## Readie (Jun 5, 2011)

Milosh said:


> I seem to recall a couple of engines from Pratt Whitney. Think they were the R-1830 and R-2800.


 
WW2 started in 1939 and British liberty was at its greatest peril in the early years of the war. There is an earlier post about the 1930's need to develop more advanced aircraft in Europe. A lot of development this passed America by as you were simply not involved.

When America joined in WW2 you brought a variety of engines, some good as you name and others not so er,... well developed like the Allison.
That is not to say that the Allison was a bad engine. it wasn't but, for a variety of reasons it did not have the power of the Merlin.
Why else would the P51 have been fitted with them?

The Merlin was one of those designs that had fortuitousness to be available to power our aircraft when we needed them most.
There is only one Merlin and loads of US radials that were as good as each as other and go equally un-remarked on by history.

Cheers
John


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## Readie (Jun 5, 2011)

Shortround6 said:


> With respect, that is certainly debatable. It also a bit about timing.
> The P&W R-1830 was produced in more numbers than any other larger aircraft engine and might lay claim to most successful on that basis. It did power a number of significant WW II aircraft and certainly played a large part. It was, however a bit earlier in timing than the Merlin and not capable of the power needed for first rate combat aircraft after 1941-42 except in turbocharged 4 engine installations (B-24).
> 
> The R-2800 was a bit later in timing than the Merlin and certainly powered a fair number of "significant WW2 aircraft" unless you think the B-26, Lockheed Ventura, A-26, P-47, F-6F, F4U, were insignificant, this not counting minor types and end of war and post war types. With over 125,000 P&W R-2800s produced it may be below the Merlin in numbers but it did go on to be produced for a number of years after merlin production stopped, but that is only natural considering it's later timing.
> Granted neither P&W engine saved England in the BoB or was there for the early part of the European air war (although the R-1830 did it's bit in the battle of the Atlantic and helped with the Bismark).



Shortround, of course its debatable, I express my views as you do.
No one would argue that the R2800 wasn't a splendid aero engine and,as you say, powered a lot of aircraft.
My point about the Merlin is acknowledged by your 'timing' comments. America joined both WW's later and, after a lull, produced the goods that helped win both wars.
The Merlin was sensibly used in preference to the Allison so that 'we' had the P51 that was so desperately needed.
Why not use the best that is available? To my mind that sums up the P51.
The Merlin was used in tanks, bombers, fighters and air-sea rescue craft. A fantastically versatile engine with all the best heritage of British engineering.
Cheers
John


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## Lighthunmust (Jun 5, 2011)

renrich said:


> Glider, there is online a source for a complete report of that 1944 Fighter Conference. The reviews say that it is an excellent book for us WW2 airplane wingnuts. I have ordered it and when received I will try to transmit any relevant info to this forum. In fact you can count on me using that report just as I do Dean's book to back up all my arguments My personal choice of an engine if I was going flying and especially into combat as far as confidence that the engine would get me there and back would have been the R2800. The war would have been tougher to win without either the Merlin or the R2800.



I have the book and it is a must have. Only two complaints. There are too many apples and oranges comparisons with regard to comparably developed versions of the aircraft tested. The book leaves you craving more information. If only the parties involved at the Conference had the aircraft resources available, time available to create more extensive test criteria, and the foresight to know how much all of us Warbird Nuts would wish we had better documentation. I'm sure any thoughts of posterity never crossed their minds of the members of the Conference.

P.S. I agree. If my hide were on the line, I'd want the sound of round in front of me.


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## MIflyer (Jun 5, 2011)

The Merlin was built by Packard under license – and that includes the V-1650-1’s (Merlin 45) which were only single stage supercharged as well as versions fitted to Canadian built Mosquitoes and Lancasters, and the Merlin 60 for the P-51. 

I understand that Packard redesigned the Merlin 60 supercharger gear set (as well as successfully fitting the engine with removable heads, which RR had tried and given up on due to coolant leaks). And Packard had Wright redesign the supercharger impeller for the V-1650. I would expect that all of this was done for produceability rather than for performance.

Interestingly enough, one pilot's manual I have for the P-51 says that the best endurance and presumably lowest fuel consumption is at altitudes above 25,000 ft with the supercharger switch set in the manual "low speed" position. Standard US practice for longest range with the V-1710 and R-2800 in WWII was the exact opposite – low altitude and high boost, which I find a curious difference in technique. 

I recall that the royalties on the Merlin paid by the US was $1,500 per engine, which sounds trivial now.

But also realize that the first Secretary of the Air Force, Stuart Symington, was the former head of GM. When the V-1710 did not work out in the F-82 and NAA had to store the completed airframes at their Downey facility (a former Consolidated Vultee plant) for a few years, NAA did some experiments with the engine to try to fix it. Reportedly, Allison then complained to their management, who called the SECAF, and NAA was told to quit fooling around with the V-1710 because Allison knew more than they did. Of course, by that time Allison was focused on jets and had little interest in fixing the V-1710.

I still contend that the problem with the V-1710 in the F-82 was the lack of liquid Inter/Aftercooler. They tried to offset that with water injection to cool the fuel/air charge going into the engine but that was not good enough. NAA thought the engine needed antibackfire screens, fitted one with them, and said that it helped.

I read that the USAF studied the possibility of fitting P-51's with R-2800's after WWII in order to avoid paying the Merlin royalty. An excellent engine and an excellent airframe, but I think it is good that they never built that monstrosity.

By the way, the RCAF said they hated the Spitfire Mk. XXVI, the version fitted with the bubble canopy, clipped wing tips, and Packard V-1650's. The engines were too unreliable for the low altitude mission they had. 

In case you have not read the Gingrich/Forsecten novel "1945" they decide to take the Merlins off the P-51's and fit them on the grounded F-82's to have airplanes capable of dealing with German jets.


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## fastmongrel (Jun 5, 2011)

MIflyer said:


> I understand that Packard redesigned the Merlin 60 supercharger gear set (as well as successfully fitting the engine with removable heads, which RR had tried and given up on due to coolant leaks). And Packard had Wright redesign the supercharger impeller for the V-1650. I would expect that all of this was done for produceability rather than for performance.



Merlins had one piece blocks and heads at first but later models had seperate heads. Packard didnt do any major redesigning they were licensed to build the engines not develop them. Packard did make changes but for production and supply reasons, the Bendix carb and the Wright supercharger drive coupling which was a better design than the RR one. British production also later used the Wright supercharger drive. The biggest change Packard made was using Pontiac silver lead main bearings which were longer lasting than the original copper lead ones.


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## Hop (Jun 5, 2011)

Packard didn't have to pay any royalties during war time. Rolls Royce wanted royalties post war, but I believe Packard stopped production before any were paid.



> I understand that Packard redesigned the Merlin 60 supercharger gear set (as well as successfully fitting the engine with removable heads, which RR had tried and given up on due to coolant leaks). And Packard had Wright redesign the supercharger impeller for the V-1650. I would expect that all of this was done for produceability rather than for performance.



Most of the changes in design were carried out by Rolls Royce and intended for the new 60 series engines. Packard started production before Rolls Royce began production of the 60 series, so got the improvements first. I don't know specifically about the supercharger impeller, but that's certainly true about the 2 piece cylinder head, something Rolls Royce had been preparing since before the war started.


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## davparlr (Jun 5, 2011)

Glider said:


> Can I ask the background of the pilots? I mention this as I would expect a USN pilot to go for the R2800 and any USAAF that flew aircraft powered by the R2800, and any P51 pilot or RAF pilot to go for the Merlin.
> 
> People understandably have faith in what they have experienced and trusted.


 
There were were quite a few representatives in the program including RAF and subcontractor pilots. I found a list of representatives, but no pilot breakdown. These representatives include RAF, RN, and DeHavilland. There were no representatives from Supermarine or RR, although Packard was there. Typically, pilots did not rate the aircraft they were associated with. For example the Navy rated AF aircraft and vice versa. I do not know how many of the representatives were pilots but 36 rated the P-51D. However, since AF were not necessarily rating the P-51, many more pilots may have been present.


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## Glider (Jun 5, 2011)

renrich said:


> Glider, there is online a source for a complete report of that 1944 Fighter Conference. The reviews say that it is an excellent book for us WW2 airplane wingnuts. I have ordered it and when received I will try to transmit any relevant info to this forum. In fact you can count on me using that report just as I do Dean's book to back up all my arguments My personal choice of an engine if I was going flying and especially into combat as far as confidence that the engine would get me there and back would have been the R2800. The war would have been tougher to win without either the Merlin or the R2800.



With comments like that I have just ordered the book. Now how do I get it in past the wife?

An observation re the Rolls Royce vs Packard Merlin. I had a book on the BOB flight and the Lancaster had at one time three RR engines and a Packard. You could always tell the Packard as it ran at a higher temperature than the RR engines. Still within limits and no problems but just a little higher, which was often commented on by new or visiting pilots who were worried that there might be a problem.


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## Lighthunmust (Jun 5, 2011)

MIflyer said:


> I read that the USAF studied the possibility of fitting P-51's with R-2800's after WWII in order to avoid paying the Merlin royalty. An excellent engine and an excellent airframe, but I think it is good that they never built that monstrosity.


 
In February 2000 I wrote a letter to the editors of Flight Journal concerning their special edition "WWII Fighters". I was writing to disagree with Eric Brown's article "Serial Killers" (yes I know I have some nerve to disagree with a living legend). The disagreement was with the methodology he used for determining that the best fighters of WWII were Spitfire MkXIV, FW-190D, and Mustang MkIV aka P-51D in that order (yes I know I am a pipsqueak who he would consider too insignificant to even acknowledge). I specifically mentioned that the USAF considered use of the R-2800 in Mustangs (this is the part where I am sure I lost them if I ever had them taking me seriously). Flight Journal never wrote me back, however three years later they published an article by Corky Meyer where he picked the R-2800 powered P-47 as the best fighter of WWII. The P-47 was my choice when I wrote the letter in 2000.

I cannot recall where I heard of this study you mention. Do you have any idea where confirmation could be found?


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## renrich (Jun 5, 2011)

I am no aero engineer but I don't see anyway that fitting the R2800 could benefit the P51. The Chrysler V12, hemi aircraft engine would seem a lot better fit.


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## Lighthunmust (Jun 5, 2011)

renrich said:


> I am no aero engineer but I don't see anyway that fitting the R2800 could benefit the P51. The Chrysler V12, hemi aircraft engine would seem a lot better fit.


 
I completely agree. The idea of putting a R-2800 in a Mustang is more an indiction of great respect for the engine than the rationality of the people who ordered the study. If the USAF had more P47s than P-51s in 1950, do you think they would have been deployed to Korea instead of the 51s?


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## Shortround6 (Jun 5, 2011)

renrich said:


> I am no aero engineer but I don't see anyway that fitting the R2800 could benefit the P51. The Chrysler V12, hemi aircraft engine would seem a lot better fit.


 Nope, Not much a fit at all. It was actually a V-16.

For what it is worth see Wiki; Chrysler IV-2220 - Wikipedia, the free encyclopedia

Several feet longer than the Merlin and 700-800lbs heavier (without turbo). Since it was sort of 2 V-8s couped together, Propeller drive came out of the middle of the engine between cylinders 4 and 5 in each bank, shortening it to a V-12 would have been difficult.


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## MIflyer (Jun 5, 2011)

Lighthunmust:

From what I recall it was a letter published in an aviation magazine in the timeframe 1988-1993. I was assigned to the Pentagon then and got a lot of reading done on the Metro going to and from home.

From what I recall the writer said he was on the engineering team that studied putting the R-2800 in the Mustang. No doubt that was spurrd by the Korean War in which the P-51 was one of the few effective ground attack aircraft the USAF had. Not only was the availibility of engines a possible issue but so was the vulnerability of the 51 to ground fire.

I would bet on Air and Space Magazine as the source since at that time it was one of only 2 aviation magazines I subscribed to, the other being the EAA Sport Aviation mag, which would not have been likely to cover that sort of thing. 

Ironically the USAF had just about phased out the perfect airplane for the mission in Korea, the P-47N, by that time. Of course one reason the Mustang was so popular was that they had phased out just about every other prop-driven fighter the USAF had in the area in favor of the P-51 and even they were few in number. I have wondered what it would have been like if they could have recovered some of those P-61's sitting around the islands after the war or the 50 P-38's they scrapped shortly before the North Koreans invaded.


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## Milosh (Jun 5, 2011)

Readie said:


> WW2 started in 1939 and British liberty was at its greatest peril in the early years of the war. There is an earlier post about the 1930's need to develop more advanced aircraft in Europe. A lot of development this passed America by as you were simply not involved.
> 
> When America joined in WW2 you brought a variety of engines, some good as you name and others not so er,... well developed like the Allison.
> That is not to say that the Allison was a bad engine. it wasn't but, for a variety of reasons it did not have the power of the Merlin.
> ...


 
And the Allison could have powered those Spitfires and Hurricanes in GB's hour of peril as it put out similar HP as the single stage Merlins of the day. When fitted with the GE turbocharger, the Allison put out more HP at altitude that the 2 stage/2 speed Merlins.


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## Lighthunmust (Jun 5, 2011)

MIflyer said:


> Lighthunmust:
> 
> From what I recall it was a letter published in an aviation magazine in the timeframe 1988-1993. I was assigned to the Pentagon then and got a lot of reading done on the Metro going to and from home.
> 
> ...



I also subscribed to Air&Space during that time frame. When I finished my assignment at the Puzzle Palace at FGGM, just northeast of the Five-sided Asylum, many of my possessions were "lost" by the moving company. I'll bet your right, it was in a back issue of my "lost" Air&Space collection.

Considering the strong desire of the USAAF and USAF to get rid of all those left over WW2 aircraft, for many reasons including not giving Congress the opportunity to deny funding for shiny new jets, it is amazing they had the Mustangs. Just imagine the difference in combat effectiveness, and lives saved on the ground and in the cockpit, if they had sufficient quantities of P-47s and P-61s. Talk about bad timing for scrapping the P-38s. I was not aware of that incident.


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## Piper106 (Jun 5, 2011)

After having read Dan Whitney's excellent "Vees for Victory", I decided that both side of this arguement are right... and both sides are wrong. Allison engines were every bit as powerful at allitude the comparable Merlin engines, but... 

What has condemed the Allison is that fact that it took their engineering department about two extra years to get their engines to the same level of development. It took Allison until nearly 1943 to get their 9.6:1 ratio high allitude single stage single speed blower into the field, while the comparable Merlin 45 was just a little too late for the Battle of Britian. The two stage mechanical Allisons had the same power at allitude as the Merlin 60 serieds engines but the Spitfire 9 with the Merlin 60 was being issued to the filed in late 1941, while the P-63 with two stage Allison was just starting into production in late 1943. The Allison G6 engines for the P-82 again were comparable in power at allitude to Merlin 100 series engines but again, Allison was about 2 years behind (1947 vs.1945). 

And in battle two years is forever. 

That is all I think I know.

Piper106


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## wuzak (Jun 6, 2011)

Milosh said:


> And the Allison could have powered those Spitfires and Hurricanes in GB's hour of peril as it put out similar HP as the single stage Merlins of the day.


 
Not sure that Allison was ready to produce sufficient quantities of the V-1710 to power Spitfires and Hurricanes before 1940.


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## wuzak (Jun 6, 2011)

Hop said:


> Packard didn't have to pay any royalties during war time. Rolls Royce wanted royalties post war, but I believe Packard stopped production before any were paid.
> 
> 
> 
> Most of the changes in design were carried out by Rolls Royce and intended for the new 60 series engines. Packard started production before Rolls Royce began production of the 60 series, so got the improvements first. I don't know specifically about the supercharger impeller, but that's certainly true about the 2 piece cylinder head, something Rolls Royce had been preparing since before the war started.


 
This is my understanding. The design and testing work for the separate heads, which was to solve the leaking problem, had been completed, but the decision was to delay the introduction to coincide with the introduction of the 60 series engines. The reasoning being that there would be too much disruption to production (once to introduce the separate heads, and another to introduce the two stage Merlin). Packard changed over two two stage engine production earlier than RR, and introduced the separate heads first. Not sure if Packard introduced the separate heads on the single stage engines, though. I have a suspicion that all Packard's Merlins had separate heads.


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## wuzak (Jun 6, 2011)

Milosh said:


> When fitted with the GE turbocharger, the Allison put out more HP at altitude that the 2 stage/2 speed Merlins.


 
That all depends on altitude. Power for the V-1710 with turbo was almost constant up to the turbo's critical altitude, then power fell off rapidly.

Rolls-Royce had experimented with a turbo in the late 1920s (on a Falcon, IIRC, with the turbo in the vee), but didn't get great results. And as a mater of policy R-R didn't use turbos with their engines because of the exhaust thrust effect. As altitude increased the efficiency of the prop reduced and the thrsut from teh exhaust became more significant.


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## wuzak (Jun 6, 2011)

MIflyer said:


> 2. When Allison added an auxillary mechanical supercharger stage to the V-1710 they left out an intercooler or aftercooler. The reason is clear - it is too hard to fit one in a sleek fighter airframe IF you make it an air to air cooler like was used in everything else BUT the Merlin 60 series. Have you seen the intercooler of a B-17? It is large and buried in the wing - not that much of a problem for a big bomber. Have you seen the intercooler for a P-47? It is huge and buried in the fuselage where the 2nd seat of its ancestor was (the P-35 was virtually a 2 seat airplane). That was the clear incredible genius of Sir Stanley Hooker. He solved the problem of getting all that draggy air in and out of the aftercooler by going to a liquid to air cooler. The fact that Allison and no one else did not copy that stunningly obvious idea is simply incredible. Using a liquid cooler would have solved the P-38's intercooler problems, made the 2 stage V-1710 as used in the P-63 and F-82 a more viable powerplant, and would have been useful in otehr engine installations as well, for everything from the P-61 to the B-28 to the Republic Rainbow.




The first V-1710s with two stage compressors had an aftercooler, which loked very similar to teh one atop the Merlin 60 series. However, using that meant redesigning the engine supercharger intake and carburettor, or moving the carb to the auxiliary stage. By not having the aftercooler Allison was able to use a common engine stage supercharger and carb for all their variants - single stage, two stage, and turbocharged.

The loss of the aftercooler meant that ADI was required.

btw two stage Merlins had intercooling and aftercooling. The aftercooler is obvious in pictures, while intercooling was achieved by cooling passages around the supercharger casing. Maybe not super effective, but still there.


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## wuzak (Jun 6, 2011)

Lighthunmust said:


> I seem to recall that the Allison was superior to the Merlin in North Africa due to less maintenance issues from the environmental conditions. I am going to check Bodie, but I think they did a study on using Merlins in the P-38 that surprisingly indicated a significant weight gain and no increase or possibly a decrease in overall performance. Have either of you read anything about these issues.



Lockheed did a few studies on the Merlin in the P-38. Usually the performance was similar or superior to the Allison version.

Merlin XX in P-38:

```
Merlin XX    V-1710-F2 (-27/29)
                                        Reprt 2036           YP-38
Takeoff BHP                              1280/3000       1150/3000
Critical Altitude Military bhp                1170            1150 
Critical Altitude, feet                      21000           25000
Critical Altitiude max speed, mph              431             405
P-38 weight, pounds                          14500           14348
Sea level rate of climb, ft/min               3160
Sea level max speed, mph                       354
High speed cruise, bhp/rpm                875/2650       1000/2600
High Speed cruise mph/Alt ft             393/20000          /25000
High Speed cruise fuel use lb/bhp/hr         0.485
Range at high speed cruise, miles/gal         2.78             310*
Service Ceiling, feet                        38100           38000
Engine, with turbo  ducts, pounds            1430            1590
Normal range, miles                            640             650
Normal fuel capacity, gallons                  230             210
```


Merlin 61 in P-38

```
V-1710-F17 (-89/91)           Merlin 61
                                    Military   Normal       Military   Normal
Altitude for max speed, ft             27000    25000          27300    30200
Maximum speed, mph                       418      395            423      403
Sea level                                360      326            343      326
5000ft                                   365      342            365      345
10000ft                                  382      358            386      364
15000ft                                  396      374            406      381
20000ft                                  408      386            406      395
25000ft                                  416      395            414      388
30000ft                                  414      383            419      402
Absolute ceiling, feet                 42300    38500          42300    41200
Service Ceiling, feet                  41600    37800          41600    40400
Climb in 5 minutes, feet               17800                   17800
Climb to 20000ft, minutes                6.2                     5.9
Climb to 25000ft, minutes                8.7                     8.4
Climb to 30000ft, minutes               12.2                    11.8
Distance to takeoff 
of 50ft obstacle, feet                  1640                    1770
```


A later study with an "advanced Merlin"

```
Standard  Advanced   Advanced      
                                       P-38J   Allison    Allison        Merlin
War Emrgency Power, bhp                 1600      1725       2000(wet)     2000
WER engine, rpm                         3000      3200       3400           n/a
Engine?propellor gear ratio           2.00:1    2.36:1     2.36:1        2.36:1
Propellor diameter, feet                11.5      11.5       12.5          12.5
Turbosupercharger, GE Type              B-33      B-39       B-38       Jet Exh
Fuel grade                               130       140        140       Special
Propellor activity factor               89.3      89.3        110           110
Propellor weight increase, lbs             0         0         51            51
Per engine weight increase, lbs            0         0         45           n/a
P-38 operational weight, lbs           16200     16200      17250         16500
Increase in maximum speed, mph             0        12         16            38
Increase in maximum climb, fpm             0       490        850          1300
Impact om manoueverability %               0        0?         -5            -1
Maximum sea level speed, mph             356       364        382           398
Maximm speed @ 30000ft, mph              436       448        452           468
Maximum climb in 5 minutes, feet       18700     21600      23000         25600
Timb to climb to 30000ft, minutes        8.7       7.2        6.2           6.2
Absolute ceiling, feet                 43900     43900      43700         43900
```

These are from Dan Whitney, Vees for Victory.

In that he also says that a two stage Allison version was proposed, but no performance figures were shown.

Notice that at some altitdes the turbocharged Allison has an advantage because of its more even power delivery with altitude, but at others is less.


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## Readie (Jun 6, 2011)

Milosh said:


> And the Allison could have powered those Spitfires and Hurricanes in GB's hour of peril as it put out similar HP as the single stage Merlins of the day. When fitted with the GE turbocharger, the Allison put out more HP at altitude that the 2 stage/2 speed Merlins.


 
But, it wasn't and it didn't.
The Merlin steals the thunder and the worthy Allison is the also ran.
Cheers
John


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## Milosh (Jun 6, 2011)

wuzak said:


> Not sure that Allison was ready to produce sufficient quantities of the V-1710 to power Spitfires and Hurricanes before 1940.


 
It is not about if there was enough Allisons but about that the HP produced. I am sure the Soviets would have preferred Allisons in the Spitfires and Hurricanes they received.


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## Glider (Jun 6, 2011)

Piper106 said:


> After having read Dan Whitney's excellent "Vees for Victory", I decided that both side of this arguement are right... and both sides are wrong. Allison engines were every bit as powerful at allitude the comparable Merlin engines, but...
> 
> What has condemed the Allison is that fact that it took their engineering department about two extra years to get their engines to the same level of development. It took Allison until nearly 1943 to get their 9.6:1 ratio high allitude single stage single speed blower into the field, while the comparable Merlin 45 was just a little too late for the Battle of Britian. The two stage mechanical Allisons had the same power at allitude as the Merlin 60 serieds engines but the Spitfire 9 with the Merlin 60 was being issued to the filed in late 1941, while the P-63 with two stage Allison was just starting into production in late 1943. The Allison G6 engines for the P-82 again were comparable in power at allitude to Merlin 100 series engines but again, Allison was about 2 years behind (1947 vs.1945).
> 
> ...


 
That fits my understanding as well, nicely put


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## wuzak (Jun 6, 2011)

Milosh said:


> It is not about if there was enough Allisons but about that the HP produced. I am sure the Soviets would have preferred Allisons in the Spitfires and Hurricanes they received.


 
Why?

They just wanted as many aircraft that they could lay their hands on.


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## Readie (Jun 6, 2011)

Milosh said:


> It is not about if there was enough Allisons but about that the HP produced. I am sure the Soviets would have preferred Allisons in the Spitfires and Hurricanes they received.


 
Why would anyone prefer am Allison to a Merlin?
Unless you mean that it was either a Spitfire / Hurricane with an Allison or no Spitfire/Hurricane at all.
Cheers
John


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## Readie (Jun 6, 2011)

Piper106 said:


> What has condemed the Allison is that fact that it took their engineering department about two extra years to get their engines to the same level of development. It took Allison until nearly 1943 to get their 9.6:1 ratio high allitude single stage single speed blower into the field
> And in battle two years is forever.
> Piper106


 

If we English had only the Allison I would be speaking German.
The Merlin is more than just another aero engine it represents our identity.
Cheers
John


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## renrich (Jun 6, 2011)

SR, thanks for the correction and the link. I had forgotten the details on the Chrysler engine. I did not realise that Merlins powered the RN ships which were the major factor in keeping the Germans from definitely planning to invade England, along with the fact that Hitler never seriously planned on that invasion. The BOB was a very good effort on the part of the RAF but it is a myth that the Germans were kept from invading by "losing" the BOB. Even without the Merlin, I expect the British would have soldiered on and been a big part of the winning coalition.


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## buffnut453 (Jun 6, 2011)

The invasion was a bluff but Hitler absolutely wanted Britain out of the war and losing the BoB would have resulted in precisely that. Without the Merlin engine in 1940, Fighter Command would have lost the air superiority battle over southeast England to leave London completely exposed. Under those circumstances, it is entirely conceivable that the factions who wanted to sue for peace with Germany (and there were many in high places who wanted to do just that - Lord Halifax and his side-kick R A Butler were 2 of the more influential) would have removed Churchill and the world would be a very different place today.


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## Milosh (Jun 6, 2011)

Readie said:


> If we English had only the Allison I would be speaking German.
> The Merlin is more than just another aero engine it represents our identity.
> Cheers
> John



In 1940, the Allison performed just as well the Merlin. *If* the Allison had powered the Spitfires and Hurricanes in 1940, they would have performed just as well as the Merlin powered a/c.

Wuzak, Merlins in Soviet use had very bad serviceability, while the Allisons did not. 

The P-40 was powered by both engines and there wasn't much, if any difference, in the performance with either engine.


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## buffnut453 (Jun 6, 2011)

So why were the Allison-powered Mustangs relegated to Army Cooperation tasks? Answer - because the Allison lacked altitude performance which was vital for 1940 because it didn't have the 2-stage supercharger as discussed previously in the thread. 

Bear in mind that you can't just drop in an engine in June of 1940 and expect it to work. The Merlin had been available since 1938 in sufficient numbers to support re-equipment of fighter command. What was the Allison's performance in 1938? Also, there's the challenge of securing export for the Allison in 1939 and enabling licence-building of the engine in the UK. 

The Allison was a good engine but in no way was it ready for the combat environment of the BoB.


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## Lighthunmust (Jun 6, 2011)

Milosh said:


> I
> Wuzak, Merlins in Soviet use had very bad serviceability, while the Allisons did not. .


 

Which should increase the importance of the Allison in the minds of everyone when you factor in that the Russians did most of the dying and killing during WW2. It appears that the Allison was the superior engine whenever maintenance operations were conducted under adverse conditions not found at a fighter base in Britain and where high attitude combat is rare.


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## buffnut453 (Jun 6, 2011)

Undoubtedly so, but Hitler didn't attack the USSR until after he'd lost the BoB. The fact remains that having Britain as an adversary to the west diverted resources that were badly-needed for the Eastern Front. With Britain a non-combatant, there would have been no campaign in the Western Desert. What impact would Rommel and his forces have had on the Eastern Front? Again, the Allison was an excellent engine but it wasn't ready for the combat environment of the BoB.


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## Lighthunmust (Jun 6, 2011)

buffnut453 said:


> Undoubtedly so, but Hitler didn't attack the USSR until after he'd lost the BoB. The fact remains that having Britain as an adversary to the west diverted resources that were badly-needed for the Eastern Front. With Britain a non-combatant, there would have been no campaign in the Western Desert. What impact would Rommel and his forces have had on the Eastern Front? Again, the Allison was an excellent engine but it wasn't ready for the combat environment of the BoB.



No doubt the Merlin was in the right place at the right time. The BoB definitely affected Barbarosa, the extent of which is not agreed upon from what I have read. I was speaking of the importance of the Allison during the entire war. The campaign in North Africa also bolstered the reputation of Allison serviceability being better than the Merlin in adverse conditions.


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## buffnut453 (Jun 6, 2011)

Lighthunmust said:


> No doubt the Merlin was in the right place at the right time. The BoB definitely affected Barbarosa, the extent of which is not agreed upon from what I have read. I was speaking of the importance of the Allison during the entire war. The campaign in North Africa also bolstered the reputation of Allison serviceability being better than the Merlin in adverse conditions.



Fair enough. Incidentally, is there definitive evidence of Allison serviceability being better than the Merlin in the Western Desert or is it simply that the P-40 was more associated with that campaign due to the publicity given to 112 Sqn's sharkmouthed aircraft?


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## Readie (Jun 6, 2011)

renrich said:


> SR, thanks for the correction and the link. I had forgotten the details on the Chrysler engine. I did not realise that Merlins powered the RN ships which were the major factor in keeping the Germans from definitely planning to invade England, along with the fact that Hitler never seriously planned on that invasion. The BOB was a very good effort on the part of the RAF but it is a myth that the Germans were kept from invading by "losing" the BOB. Even without the Merlin, I expect the British would have soldiered on and been a big part of the winning coalition.[/QUOTE
> 
> The BoB kept the Germans at bay.
> From your comment about it being a 'good effort' I honestly think that its difficult for Americans to really understand the threat of invasion and attack on their country. Hitler wanted to beat us before the Commonwealth and our allies could arrive. The thought of losing the BoB was unthinkable and is one of the pivotal points in our modern history.
> ...


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## Shortround6 (Jun 6, 2011)

While Merlins were used in some coastal craft the majority of fast craft were powered by either Hall-Scotts (many of the Fairmile Launches) or Packard Marine engines which were NOT Merlins but a 2500cu in engine derived from a late 1920s aircraft engines.


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## gjs238 (Jun 6, 2011)

Milosh said:


> And the Allison could have powered those Spitfires and Hurricanes in GB's hour of peril as it put out similar HP as the single stage Merlins of the day. When fitted with the GE turbocharger, the Allison put out more HP at altitude that the 2 stage/2 speed Merlins.


 Which is why in other threads I keep pondering how to effectively accomplish this in a single-engined fighter. A forward cockpit rear engine/rear turbo layout seems a good way to accomplish this with minimal ducting.


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## Milosh (Jun 6, 2011)

buffnut453 said:


> So why were the Allison-powered Mustangs relegated to Army Cooperation tasks? Answer - because the Allison lacked altitude performance which was vital for 1940 because it didn't have the 2-stage supercharger as discussed previously in the thread.



I didn't know Mustangs were available during the BoB.

What Merlins had a 2 stage supercharger in 1940?

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## buffnut453 (Jun 6, 2011)

Mustangs weren't available in the BoB, they came after...which is precisely my point. The Allison engine fitted to the Mustang MkIs lacked the altitude performance to enable the aircraft to be used in the fighter role so they were consigned to army co-op instead. If the early Mustangs couldn't hack the altitudes at which Fighter Command expected to operate, how would fitting an earlier version of the same engine to a Hurricane or a Spitfire in 1940 have improved things for the RAF in the BoB?


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## Readie (Jun 6, 2011)

buffnut453 said:


> Fair enough. Incidentally, is there definitive evidence of Allison serviceability being better than the Merlin in the Western Desert or is it simply that the P-40 was more associated with that campaign due to the publicity given to 112 Sqn's sharkmouthed aircraft?



The DAF (Desert Air force)

The air defence of the UK always received priority, so the DAF was generally equipped with older aircraft types. Initially equipped with obsolete types like the Gloster Gladiator biplane fighter and the Bristol Blenheim light bomber, the DAF made a good showing against the equally obsolete Italian Air Force. After the direct threat to Great Britain receded, newer types were assigned to the DAF, such as the Hawker Hurricane and Douglas Boston medium bomber in 1941.
US built P-40 Tomahawk/Kittyhawk also went to the DAF as it was unsuited to European operations which were generally fought at much higher altitudes and against more formidable opposition. The P-40 was used initially as an air superiority fighter but it was also adapted (and found to be ideally suited) to ground attack missions.
The DAF always outnumbered its Axis opponents and concentrated on long-range interdiction and direct tactical Eighth Army support. Unfortunately these tactics meant that the faster Messerschmitt Bf 109s of Jagdgeschwader 27 usually had the advantage of height and surprise over the low-level, slow-flying DAF fighters and losses were correspondingly heavy.
In 1942, the DAF reorganized its tactics and upgraded its inventory. Spitfires were eventually assigned in the air superiority role, becoming operational in August 1942, which allowed the DAF to finally turn the tide.
The DAF adapted the Luftwaffe concept of tactical air support and Army co-operation by using fighter-bombers controlled via radio by "Forward Air Controllers"; trained air force observers attached to forward Army units.
The DAF improved the concept by introducing "cab ranks" of fighter-bombers in the air waiting to be called in to attack specific tactical targets. In this way the DAF provided vital and decisive air support to the Eighth Army until the end of the war, fighting through Egypt, Libya, Tunisia, Sicily and mainland Italy. The tactical concepts which had proven so successful in the latter part of the North African campaign were subsequently adopted with even greater success during the Invasion of Europe in 1944.

The tropicalization of the Hurricane and the performance degradation from tropical filters notwithstanding, the Hurricane would still be slower than any model of P40. Hence the preferance for P40 and Spitfire MkV for fighter vs fighter roles in North Africa. Hurricanes were still used in fighter/bomber and ground attack roles though, right up to the end of the desert campaign. 

Horses for courses.
Cheers
John


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## Readie (Jun 6, 2011)

buffnut453 said:


> Mustangs weren't available in the BoB, they came after...which is precisely my point. The Allison engine fitted to the Mustang MkIs lacked the altitude performance to enable the aircraft to be used in the fighter role so they were consigned to army co-op instead. If the early Mustangs couldn't hack the altitudes at which Fighter Command expected to operate, how would fitting an earlier version of the same engine to a Hurricane or a Spitfire in 1940 have improved things for the RAF in the BoB?


 
Buffnut, it wouldn't.
No one in their right mind would fit an Allison over the Merlin.
Cheers
John


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## Readie (Jun 6, 2011)

Shortround6 said:


> While Merlins were used in some coastal craft the majority of fast craft were powered by either Hall-Scotts (many of the Fairmile Launches) or Packard Marine engines which were NOT Merlins but a 2500cu in engine derived from a late 1920s aircraft engines.



Shortround, This is interesting. I lifted the thread from British W11 wood boats.

12-10-2003, 04:36 AM
The MTBs and MGBs had three Packard Merlins, went at very silly speeds, and were inclined to catch fire and blow up, due to the difficulty of keeping that much gasoline without leaks whilst doing 41 knots, even before the Germans took a hand in things. They also had what were apparently quite lamentable electic servo-pneumatic and servo-mechanical control systems. The larger Fairmile Motor Launches (ML's) which were 112ft LOA had two gasoline engines and made about 20 knots.

For much of WW2 they were involved in fighting with German E-Boats which laid mines in the swept channels followed by coastal convoys and would also attack merchant ships with torpedoes and gunnery. 

A very small number were built with Paxman high speed diesel engines for the spcial task of bringing ball bearings, which Britain could not make in the required quantities or to the right specifications, I am not sure which, from Sweden.

The Merlin engined types did not have the range. Unfortunately the Paxmans were not wonderfully reliable, and quite a number of the blockade runners were caught in the open as sitting ducks, with engine failure, so some Mosquito bombers were modified for the task instead. 

My late father, who was in the RNVR, shared the common opinion of all who had to do with the MTBs MGBs and MLs that the German E-boat was a very much better boat - diesels and hydraulics. He was with the group that overran the German base at Catania during the invasion of Sicily and found, intact, what appeared to be a complete set of drawings for the E-boat, which he sent off to the Admiralty with much satisfaction; he used to say that the "thank you" letter caught up with him sometime after VJ day, by which time he was in Burma.
Hwyl
12-10-2003, 05:05 AM
Andrew,I did not realise that there are two types of Merlin engines. Are the Packard and Rolls Royce engines completely different?
Andrew Craig-Bennett
12-10-2003, 05:31 AM
No; same engine. R-R design, V12, 27 litre, water cooled, aero engine. A Packard Merlin is a Rolls-Royce Merlin engine, built by Packard in the USA. Packards did modify the design a little, in the direction of simplicity and ease of mass production, but the differences are small.

Well before WW2, it was obvious that the Merlin engine was the best British aero-engine; the Spitfire and Hurricane were designed around it "off the drawing board", and it was also obvious that, as a key element of the war effort, the RR factory that built it was a prime target for bombing.

"Shadow" factories were set up within Britain, and in the USA Packards also contracted to build Merlin engines. They built an awful lot of them - the Packard Merlin powered the P51 and in its marine version it powered British high speed light craft. Packards had started to build the engine for US-built Spitfires; later it was adopted for the P-51. 

The mass production of the Merlin was a notable part of the war effort; RR are not, never have been, mass production engineers, and the Merlin was descended from very specialised engines built in small numbers. The original design for the Merlin was a private venture by RR; not in response to any government tender, so all development work was privately funded. 

RR did two things with their engine; they developed a quality control programme to achieve very high reliability (basically, they took engines off the production line at random, ran them at full power until they broke, then found out which bit had broken and made it stronger!) and they worked out how to mass produce it whilst keeping it reliable.

I think that rather more than 160,000 Merlins were built; only a few hundred were the marinised version. I don't think any marinised ones survive, although a handful of MLs and MTBs do.

Cheers
John


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## Lighthunmust (Jun 6, 2011)

The importance of the Battle of Britain is hard to overstate. The main reason for that importance is not because it saved Britain or influenced Barbarosa. The influence on an isolationist America containing a significant population of ethnic Germans, Irish, etc., who previously had no affinity for Britain was probably the most important aspect of the BoB. Allisons probably would have gotten the job done, but Readie is right. No one in Britain in their right mind would have installed anything but the well understood Merlin in a Hurricane or Spitfire at that time.


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## Readie (Jun 6, 2011)

Lighthunmust said:


> The importance of the Battle of Britain is hard to overstate. The main reason for that importance is not because it saved Britain or influenced Barbarosa. The influence on an isolationist America containing a significant population of ethnic Germans, Irish, etc., who previously had no affinity for Britain was probably the most important aspect of the BoB. Allisons probably would have gotten the job done, but Readie is right. No one in Britain in their right mind would have installed anything but the well understood Merlin in a Hurricane or Spitfire at that time.


 
I agree with a lot of your post, the BoB was vital to us as it was the first defeat for Nazi Germany and we repelled the attacks on our island or, were seen to repel the Germans if you are cynical.
A propaganda gift for Churchill whose rallying cries are well documented. In the context of 1940 any 'win' however slim was vital to the British will to fight and in those terms the BoB was a total victory.
It has entered our culture and 'the few' are revered along with their aircraft and engines.
Britain and America were culturally closer in those days than we are now and, understandably, there was still a reluctance for America to get drawn into another European war. But, you did in the end. I wonder if there was a third European conflict whether you would now?
Cheers
John


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## MIflyer (Jun 6, 2011)

wuzak said:


> The first V-1710s with two stage compressors had an aftercooler, which loked very similar to teh one atop the Merlin 60 series. However, using that meant redesigning the engine supercharger intake and carburettor, or moving the carb to the auxiliary stage. By not having the aftercooler Allison was able to use a common engine stage supercharger and carb for all their variants - single stage, two stage, and turbocharged.
> 
> The loss of the aftercooler meant that ADI was required.
> 
> btw two stage Merlins had intercooling and aftercooling. The aftercooler is obvious in pictures, while intercooling was achieved by cooling passages around the supercharger casing. Maybe not super effective, but still there.



Which is just the point I have been making.

1. By not producing a 2 speed (that is single speed impeller speed not a two stage) supercharger, Allison limited the performance of the V-1710 in everything that did not use a turbo, P-39, P-40, P-51. Take a look at the performance graphs in America's Hundred Thousand. With two speeds you had a step in the performance where the first speed topped out and the 2nd, higher one kicked in. With nothing more than a 2 speed supercharger the Mustang Mk.1 would have topped 400 mph and been good for more than medium and low altitude. The P-40 and P-39 would have been better as well. They would not have been as good as with a 2 stage Merlin but better than they were. 

2. By not redesigning the two-stage V-1710 engine to take a liquid cooled aftercooler they hurt the performance of the P-63, and especially the F-82. And by not developing a two stage two speed supercharger to directly bolt on the V-1701 and replace the single speed unit that eliminated their ability to compete with the Merlin 61 series. 

By taking an "automotive viewpoint" with ease of production being the priority so to be able to use the same accessory case and same basic supercharger design for all V-1710 engines Allison needlessly reduced the value of their products. Given the separate rear case of the V-1710 (as opposed to the Merlin's single case) they could have done this easily without changing the design of the rest of the engine.

Note that they followed the single stage, single speed approach with the V-3420, which was supposed to use a turbo to boost the engine as well.

Government is partially to blame as well. An engineer at NACA was given the job of figuring out how to improve the V-1710 and took the attitude that "it's hopeless, given how bad this engine is." From the perspective of 70 years later we might be Monday morning quarterbacks but it looks pretty clear what needed to be done, and saying "it's hopeless" sure was not the answer. Almost the first technical report that NACA issued, in the immediate post-WWI timeframe, was on the positive effects of supercharging on aircraft engine performance, but in 1942 they said "it's hopeless."


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## Shortround6 (Jun 6, 2011)

Readie said:


> Shortround, This is interesting. I lifted the thread from British W11 wood boats.
> 
> Cheers
> John



Interesting but in rather direct conflict with the information in "British and Dominion Warships of WW II" by H.T. Lenton J.J. Colledge and in "Selected Papers on British Warship Design in World War II" Naval Institute Press, Chapter 5 Coastal Force Design by W J Holt.

For some pictures of the Packard try here: Packard V12 Marine Engine

It appears that very few R.N. craft had Merlins during WW II. RAF crash tenders may be different. British were importing and using Issota Fraschini engines in boats built before Italy joined the war in 1940. Fairmile As, Bs and Cs used Hall Scotts, the D boats used the big Packards.


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## Shortround6 (Jun 6, 2011)

MIflyer said:


> Which is just the point I have been making.
> 
> 1. By not producing a 2 speed (that is single speed impeller speed not a two stage) supercharger, Allison limited the performance of the V-1710 in everything that did not use a turbo, P-39, P-40, P-51. Take a look at the performance graphs in America's Hundred Thousand. With two speeds you had a step in the performance where the first speed topped out and the 2nd, higher one kicked in. With nothing more than a 2 speed supercharger the Mustang Mk.1 would have topped 400 mph and been good for more than medium and low altitude. The P-40 and P-39 would have been better as well. They would not have been as good as with a 2 stage Merlin but better than they were.



The two speed drive would NOT have helped the Allison. The 8.80 gear set in the -39 engine was as high as they could go with out redesigning the the drive. THE existing gears would not handle the power when they tried 9.60 gears. For the 9.60 gear performance just look at any Allison with a take-off power of 1200hp and 1125-1150hp at 15,000-15,500ft. That was as good as it was going to get for the Alison. A lower gear, like the 7.48 was needed to get 1325hp for take off. With a 2 speed box you could use 6.44 gears for take-off and very low level flying which would give around 1415hp for take-off but had no extra capacity or a WER rating while keeping the 1150hp at 15,000ft. Going muc above the 9.60 gears would have just sent the impeller tips past supersonic and not gotten any better altitude performance.


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## Readie (Jun 6, 2011)

Shortround6 said:


> Interesting but in rather direct conflict with the information in "British and Dominion Warships of WW II" by H.T. Lenton J.J. Colledge and in "Selected Papers on British Warship Design in World War II" Naval Institute Press, Chapter 5 Coastal Force Design by W J Holt.
> 
> For some pictures of the Packard try here: Packard V12 Marine Engine
> 
> It appears that very few R.N. craft had Merlins during WW II. RAF crash tenders may be different. British were importing and using Issota Fraschini engines in boats built before Italy joined the war in 1940. Fairmile As, Bs and Cs used Hall Scotts, the D boats used the big Packards.



History PT Boats

I have learnt something this evening. Thanks Shortround.
I think it may be the sound of the Packard that has confused people?
Cheers
John


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## Readie (Jun 6, 2011)

Shortround6 said:


> ...sent the impeller tips past supersonic and not gotten any better altitude performance.



True, every supercharger has its design limitation.I have a supercharger on my car and I can only increase its speed (17% decrease in pulley size) by a certain percentage before it overheats and the power curve falls.
Superchargers offer a great deal of boost,but they also take power to turn whereas a turbo is 'free' power with the exhaust gases.
Cheers
John


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## Lighthunmust (Jun 6, 2011)

buffnut453 said:


> Fair enough. Incidentally, is there definitive evidence of Allison serviceability being better than the Merlin in the Western Desert or is it simply that the P-40 was more associated with that campaign due to the publicity given to 112 Sqn's sharkmouthed aircraft?


 
Off the top of my head I can't point you in the right direction for definitive evidence. But as discussed here and other threads, it is common belief. I know I heard about this issue long before anyone other than DARPA was on the net. If I come across something in my books I will PM you.


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## renrich (Jun 6, 2011)

The BOB was indeed the first time that the German war machine was checked and was important from a morale point of view. It would have even been a greater morale booster if the Germans had actually launched an invasion and a good part of the Wehrmacht had been drowned in the English Channel. However, "The truth is says Fuller, with the possible exception of Goering, the LW commander, nobody believed in Operation Sea Lion. Certainly the German Admirals did not, nor the generals, nor Hitler himself who, according to General Blumentritt, in July told Runstedt privately that he did not intend to carry out Sea Lion." Page 449, "The Decisive Battles of the Western World" JFC Fuller.

The first directive for invasion of England was issued in mid-July under the code name, Sea Lion. All preparations were to be completed by the middle of August. The air preparation was to take one week. Absolutely ridiculous! Apparently even Hitler realised how absurd the plans were. It seems to me that Hitler may have felt at some point that an arrangement with Britain could be made where Germany ruled the continent and the British could go on about their business as usual with their trade and Empire.

The BOB was a momentous event for Britain and perhaps even Joe Kennedy, Ambassador to Great Britain for the US, was shaken in his belief that England could not hold out.


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## fastmongrel (Jun 6, 2011)

Readie said:


> True, every supercharger has its design limitation.I have a supercharger on my car and I can only increase its speed (17% decrease in pulley size) by a certain percentage before it overheats and the power curve falls.
> Superchargers offer a great deal of boost,but they also take power to turn whereas a turbo is 'free' power with the exhaust gases.
> Cheers
> John



No such thing as *free* power

Much higher boost pressure is needed in a turbo for the same bhp due to pressurized air being much hotter, due to conduction from white hot exhaust manifold.

Much more complex management needed in a turbo, to control fueling and ignition due rise of boost pressure compared to a gear driven blower.

Higher pressures and temperatures encouraging detonation, turbo can be a big engine destroyer.

More intercooling needed to cool inlet air.

Much higher incidence of fire due to white hot turbo and manifold.

Compromised exhaust manifold and system function due to restriction of turbo and waste gate not letting the gas flow freely.

Waste gates are fickle things that can jam leading to your cylinder heads coming off with a bang.

Not able to use exhaust jet nozzles worth hundreds of horsepower to the non turbo engine.

Higher cost and with early installations higher weight and greater bulk.

Greater sensitivity to detonation due to unstable octane blends.

The list of exhaust driven blower cons is at least as long as that of a gear driven blower.

The reason you cant get much increase in power in your supercharger by increasing speed is because inlet wont let the air flow you cant just spin it faster. Your cramming too much air in and we all know what happens when you compress air too fast *HEAT*


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## Piper106 (Jun 6, 2011)

I think the Lancaster (and the follow-on development, the Lincoln) was handicapped by being Merlin powered. 

Four turbo charged Allisons (basically the whole engine package from a P-38J/L) would have been more effective. More allitude capability compared to the Merlin 20 series in the Lancaster (equal to the Merlin 85 engines in the Lincoln) to help get above the flak and fighters. The stronger Allison power section could handle more power longer than the Merlin (good for the long climb to allitude) with less maintenance. Most importantly, the turbocharged Allison burned less fuel than a Merlin for the same horsepower, so more bombs for the same takeoff weight. 

Griffon power in the Shackleton (another Lancaster follow-on) was also less than ideal. Allison had a turbocompound V-1710 running in their test cell. A single stage single speed version of a gas sipping Allison turbocompound would have been a better match to the Shackleton than the Griffon. (Note, this assumes that Napier misfires with their diesel work. They already had data and blueprints for the Jumo 205 diesel, a Deltic version of a Jumo 205 would have been could have been winner for long range patrol aircraft. Even the 'simplified' second version of the Nomad was wayyyyy too complicated. As with the Sabre, Napier reached too far). 

I'm going to stand back after I send this post, just in case a vein in Readie's forehead bursts... 

Piper106


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## Lighthunmust (Jun 6, 2011)

Piper106 said:


> I think the Lancaster (and the follow-on development, the Lincoln) was handicapped by being Merlin powered.
> 
> Four turbo charged Allisons (basically the whole engine package from a P-38J/L) would have been more effective. More allitude capability compared to the Merlin 20 series in the Lancaster (equal to the Merlin 85 engines in the Lincoln) to help get above the flak and fighters. The stronger Allison power section could handle more power longer than the Merlin (good for the long climb to allitude) with less maintenance. Most importantly, the turbocharged Allison burned less fuel than a Merlin for the same horsepower, so more bombs for the same takeoff weight.
> 
> ...


 

The Lancaster from the BoB squadron will be arriving over your house sometime tonight to give you Readies response.


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## Milosh (Jun 6, 2011)

Lighthunmust said:


> The Lancaster from the BoB squadron will be arriving over your house sometime tonight to give you Readies response.


 
No it will be the Canadian Lancaster.


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## renrich (Jun 6, 2011)

Actually, the Lancaster would have probably been a much better and more survivable bomber with four R2800s powering it.


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## Lighthunmust (Jun 6, 2011)

renrich said:


> Actually, the Lancaster would have probably been a much better and more survivable bomber with four R2800s powering it.


 
But it wouldn't be as pretty.

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## MIflyer (Jun 6, 2011)

Okay then I guess it is settled.

Almost every supercharged engine built in WWII was made in a two-speed single stage supercharged version. But we could not do that with the V-1710 to give a performance peak at 5000 ft as was done with the V-1710-87 of the A-36A, and also at 20,000 ft as was done with the V-1710-81 of the P-51A. admittedly those two engines used different supercharger impellers but a happy medium must have been impossible. 

Every other engine could do that if you made a two speed version, but not the V-1710.

That clears it up. Thanks everybody.

I am just glad I did not know these kinds of facts when I was working as an engineer on aircraft pressurization and pneumatics.


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## Lighthunmust (Jun 6, 2011)

MIflyer said:


> Okay then I guess it is settled.
> 
> Almost every supercharged engine built in WWII was made in a two-speed single stage supercharged version. But we could not do that with the V-1710 to give a performance peak at 5000 ft as was done with the V-1710-87 of the A-36A, and also at 20,000 ft as was done with the V-1710-81 of the P-51A. admittedly those two engines used different supercharger impellers but a happy medium must have been impossible.
> 
> ...


 
Please don't leave the discussion. I only know a little about the engine you are discussing, but find it very interesting. I now know I have been foolish to have not purchased some of the engine books I've seen. I am ordering Vees for Victory today. I seem to recall another book being available about WW2 aircraft engines that I will purchase. MIflyer and anyone else, do you have any engine book recommendations that are not for an engineer but for a layman.


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## Shortround6 (Jun 6, 2011)

MIflyer said:


> Okay then I guess it is settled.
> 
> Almost every supercharged engine built in WWII was made in a two-speed single stage supercharged version. But we could not do that with the V-1710 to give a performance peak at 5000 ft as was done with the V-1710-87 of the A-36A, and also at 20,000 ft as was done with the V-1710-81 of the P-51A. admittedly those two engines used different supercharger impellers but a happy medium must have been impossible.
> 
> ...


 
OK I will bite, Just what other 2 speed engines had second power peak at 20,000ft? 
2 Speed only, not 2 stage. 

BTW, most sources give a power peak at 15,500ft for the V-1710-81.

Engine chart on page 271 Of "Vees for Victory" gives 950 hp at 20,000ft at 3000rpm and about 37in manifold pressure.


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## Shortround6 (Jun 6, 2011)

Lighthunmust said:


> MIflyer and anyone else, do you have any engine book recommendations that are not for an engineer but for a layman.



Graham White's book "Allied Aircraft engines of World War II" gives a nice over view of the allied side. 

"Major Piston Aero Engines of World War II" by Victor Bingham is a real mixed bag. Lots of information, pictures and drawings but numerous mis-prints and mistakes make it hard to rely on. 
You don't have to be an expert when the book disagrees with itself or displacement figures don't agree with given bore and strokes. 

Bill Gunsten's "Development of Piston Aero Engines" does help explain some of the "engineering' stuff for laymen.


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## Lighthunmust (Jun 7, 2011)

Shortround6 said:


> Graham White's book "Allied Aircraft engines of World War II" gives a nice over view of the allied side.
> 
> "Major Piston Aero Engines of World War II" by Victor Bingham is a real mixed bag. Lots of information, pictures and drawings but numerous mis-prints and mistakes make it hard to rely on.
> You don't have to be an expert when the book disagrees with itself or displacement figures don't agree with given bore and strokes.
> ...


 
Thanks Shortround6. I was just looking at what is available on Amazon.


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## Readie (Jun 7, 2011)

Piper106 said:


> I think the Lancaster (and the follow-on development, the Lincoln) was handicapped by being Merlin powered.
> 
> Four turbo charged Allisons (basically the whole engine package from a P-38J/L) would have been more effective. More allitude capability compared to the Merlin 20 series in the Lancaster (equal to the Merlin 85 engines in the Lincoln) to help get above the flak and fighters. The stronger Allison power section could handle more power longer than the Merlin (good for the long climb to allitude) with less maintenance. Most importantly, the turbocharged Allison burned less fuel than a Merlin for the same horsepower, so more bombs for the same takeoff weight.
> 
> ...


 
Very good...I had to smile.
Cheers
John


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## Readie (Jun 7, 2011)

fastmongrel said:


> No such thing as *free* power
> 
> Much higher boost pressure is needed in a turbo for the same bhp due to pressurized air being much hotter, due to conduction from white hot exhaust manifold.
> 
> ...



My Eaton supercharger can produce more power than standard by spinning faster but, at a cost of a shorter life. The extra power also comes with bigger injectors,bigger intercooler ( a guy in Eastern Europe makes a cracker) bigger valves / different timing, porting and a free flowing exhaust ( pref with no cat) and a remap. All of which must be declared to the insurance company of course...
I would expect an increase from 163 to 210-225 bhp. However, dyno's and superchargers dont mix so its hard to measure exactly.
I used the word 'free' on purpose as the supercharger does take a lot of power to turn whereas a turbo uses exhaust gases which are produced anyway.
My car's supercharger gives its a lot of poke and torque,poor emissions and mpg. The turbo version is more powerfull, gives better mpg and costs less to tax.
But...its souless.
Cheers
John


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## Shortround6 (Jun 7, 2011)

fastmongrel said:


> No such thing as *free* power



True


fastmongrel said:


> Much higher boost pressure is needed in a turbo for the same bhp due to pressurized air being much hotter, due to conduction from white hot exhaust manifold.



Are we talking about cars or aircraft. Most aircraft Kept the intake ducts separated form the exhaust ducts by space and shielding. In most cases the turbine (hot) section was exposed to the slipstream. Only real point of conduction was through the shaft connecting the turbine and the bearing assembly. 


fastmongrel said:


> Much more complex management needed in a turbo, to control fueling and ignition due rise of boost pressure compared to a gear driven blower.



Again, cars or aircraft? American aircraft used a two stage system that was designed , at least at the start, to give a constant pressure to the carburetor up to the rated altitude of the turbo. No change in fuel feed or ignition due to turbo. 


fastmongrel said:


> Higher pressures and temperatures encouraging detonation, turbo can be a big engine destroyer.



True but since every large aircraft engine was supercharged to some degree or other it makes little difference if the if the higher pressures and temperatures are coming from a gear drive blower or a turbo.


fastmongrel said:


> More intercooling needed to cool inlet air.



I would really like to see some proof of this. Since there were only 3 production engines that used both turbo and mechanical drive superchargers as first stages in a two stage system. You also have to take out the variables. Like the relative efficiency of the compressors you are comparing. If compressor "A" is operating at 65% efficiency and compressor "B" is at 70% then compressor "A" will heat the intake air more regardless of how it is driven.


fastmongrel said:


> Much higher incidence of fire due to white hot turbo and manifold.



DO you have any statistics? 


fastmongrel said:


> Compromised exhaust manifold and system function due to restriction of turbo and waste gate not letting the gas flow freely.



A bit firmer ground here. GM figured at 20,000ft about an 8% loss in power due to Back pressure compared to an engine with open exhaust. Back pressure at 20,000ft being much loser than sea level due to out side air being half the density/pressure. GM may have been putting a bit of a spin on things because few turbo installations actually ran at as low a back pressure as an open exhaust even at sea level with waste gate wide open. 


fastmongrel said:


> Waste gates are fickle things that can jam leading to your cylinder heads coming off with a bang.



A more likely scenario is the turbo coming apart with a bang as the stuck waste gate causes the turbine to over speed. P-38s and some bombers didn't have "scatter shields" around the part of the turbo that faced the crew for nothing. 


fastmongrel said:


> Not able to use exhaust jet nozzles worth hundreds of horsepower to the non turbo engine.



This is a big variable. It works better the higher you go (less back pressure) so it sort of paralleled the turbo, it works better the faster you go so it doesn't work as well for climb as it does for speed. Nozzles have to optimized for one speed/altitude condition or they are a compromise everywhere ( ok, maybe only a few percent) 
They work best on V-12s. Short exhausts give best pressure/highest exhaust gas velocity. trying for short stacks on a radial can give you the cowl of a B-25. IS the extra thrust worth the extra drag? 
Turbos do help a bit with high altitude cruise, Jet exhaust stacks may help but between the slower speed hurting their efficiency and the much lower mass of the exhaust the jet thrust vs prop hp ratio changes dramatically. 


fastmongrel said:


> Higher cost and with early installations higher weight and greater bulk.



Quite true


fastmongrel said:


> Greater sensitivity to detonation due to unstable octane blends.



given that both American two stage systems didn't introduce the fuel until after the 1 st stage and the intercooler I am not sure how this is a factor. P-38s were often limited by their intercoolers. Intake temperature was to be held to 100 degrees F at the intake of the carburetor. The "unstable octane blends" didn't have a clue as to what happened to the air before it arrived at the carburetor. As long as it is the same pressure and temperature the inlet of the carburetor the fuel will act the same.


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## gjs238 (Jun 7, 2011)

What were the supercharger arrangements of the Continental I-1430 and Ford GAA?
Would they have accommodated a 2-speed arrangement, unlike the V-1710?


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## Readie (Jun 7, 2011)

Neatly sums it up 


_View: https://www.youtube.com/watch?v=hjz8pAGRvsg_

Goering remarked 'if the English had fitted Allisons's instead of Merlin's to their Spitfires we would have won...'


_View: https://www.youtube.com/watch?v=Svx6tg5Ofc8_

'Captain to bomb aimer.... we have a little present for those Allison boys in Scottsdale and Montrose ...'


_View: https://www.youtube.com/watch?v=FojsG1oSOv4_

A sound and sight to stir the blood of any true Englishman.

Enjoy

Cheers
John

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## Shortround6 (Jun 7, 2011)

gjs238 said:


> What were the supercharger arrangements of the Continental I-1430 and Ford GAA?
> Would they have accommodated a 2-speed arrangement, unlike the V-1710?


 The Continental was intended to be used with a turbo charger and had a single speed supercharger drive to the engine supercharger in most versions (there were at least 13 different versions) there were one or two two speed versions and a 2 speed two stage version but many of these models never made it into an airframe for flight testing. 
I don't believe the Ford engine ever made it out of the test cells to be installed in a test mule aircraft so it's actual configuration is also pretty open ended.


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## Readie (Jun 7, 2011)

Shortround6 said:


> The Continental was intended to be used with a turbo charger and had a single speed supercharger drive to the engine supercharger in most versions (there were at least 13 different versions) there were one or two two speed versions and a 2 speed two stage version but many of these models never made it into an airframe for flight testing.
> I don't believe the Ford engine ever made it out of the test cells to be installed in a test mule aircraft so it's actual configuration is also pretty open ended.


 
Shortround, do you know if 'turbo lag' was a factor with these turbo charged engines? I know that early car turbo engines were very prone to lag and I wondered if this technology was in its infancy the same issue would spoil performance or fly ( drive) ability.
Superchargers are pretty much instant, but would any turbo lag be negated by a 27 litre engine exhaust volume? 
Cheers
John


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## Shortround6 (Jun 7, 2011)

Readie said:


> Shortround, do you know if 'turbo lag' was a factor with these turbo charged engines? I know that early car turbo engines were very prone to lag and I wondered if this technology was in its infancy the same issue would spoil performance or fly ( drive) ability.
> Superchargers are pretty much instant, but would any turbo lag be negated by a 27 litre engine exhaust volume?
> Cheers
> John



Remember that there were NO single stage turbo charged aircraft engines in WW II. ALL Planes that used a turbo back then (unlike private planes in the 60's and newer) had the turbo feeding an engine driven supercharger. Yes it can take time for one of those old turbos to spool up but it took time for the engine to speed up too. Think of the propeller as a 300-500lb flywheel. A constant speed propeller was also like a variable speed transmission. the more power you feed it the more pitch (resistance) it put on the blades. 
Then there is flying technique, proper cruise with a P-38 called for low engine rpm but several lbs of boost. The turbo should have been partially wound up to begin with. That was part of the Problem with P-38s in Europe. Some local "expert" had told the pilots in England they would get better throttle response if they cruised at higher rpm and low boost. This was against the advice of both Allison and Lockheed. Not only was the turbo idling but the low pressure meant that the intake charge was too cool and proper fuel vaporization was a problem among other things.


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## Readie (Jun 7, 2011)

Shortround6 said:


> Remember that there were NO single stage turbo charged aircraft engines in WW II. ALL Planes that used a turbo back then (unlike private planes in the 60's and newer) had the turbo feeding an engine driven supercharger. Yes it can take time for one of those old turbos to spool up but it took time for the engine to speed up too. Think of the propeller as a 300-500lb flywheel. A constant speed propeller was also like a variable speed transmission. the more power you feed it the more pitch (resistance) it put on the blades.
> Then there is flying technique, proper cruise with a P-38 called for low engine rpm but several lbs of boost. The turbo should have been partially wound up to begin with. That was part of the Problem with P-38s in Europe. Some local "expert" had told the pilots in England they would get better throttle response if they cruised at higher rpm and low boost. This was against the advice of both Allison and Lockheed. Not only was the turbo idling but the low pressure meant that the intake charge was too cool and proper fuel vaporization was a problem among other things.


 
Thanks,I hadn't considered the propeller.

I found this as well about ejector exhausts.
Merlin 55 ejector exhaust detail, Spitfire LF.VB, EP120
The Merlin consumed an enormous volume of air at full power (equivalent to the volume of a single-decker bus per minute), and with the exhaust gases exiting at 1,300 mph (2,100 km/h) it was realised that useful thrust could be gained simply by angling the gases backwards instead of venting sideways.
During tests, 70 pounds-force (310 N; 32 kgf) thrust at 300 miles per hour , or roughly 70 horsepower was obtained which increased the level maximum speed of the Spitfire by 10 mph to 360 mph The first versions of the ejector exhausts featured round outlets, while subsequent versions of the system used "fishtail" style outlets which marginally increased thrust.

The same principle would apply to other in line engines and may be even radials?
Cheers
John


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## davparlr (Jun 7, 2011)

Readie said:


> The same principle would apply to other in line engines and may be even radials?
> Cheers
> John


 Not much of a trade off for the P-47. The turbo supercharger on the P-47D-25 allowed the engine to generate an incredible 2300 hp all the way up to 33k. Of course, even more incredible was the P-47M/N, which generated 2800 hp up to 33k, and 2600 hp up to 35k, over twice the power of the high altitude, non turbo charged Ta-152H and 800 hp more than the dual engined Do-335A-1. Loss of exhaust thrust was insignificant compared to power gained.


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## Lighthunmust (Jun 7, 2011)

davparlr said:


> Not much of a trade off for the P-47. The turbo supercharger on the P-47D-25 allowed the engine to generate an incredible 2300 hp all the way up to 33k. Of course, even more incredible was the P-47M/N, which generated 2800 hp up to 33k, and 2600 hp up to 35k, over twice the power of the high altitude, non turbo charged Ta-152H and 800 hp more than the dual engined Do-335A-1. Loss of exhaust thrust was insignificant compared to power gained.



Until I saw one at the Yanks Museum in Chino,CA the P-47M seemed like a mythological beast. Seeing your location davparir I am guessing you have seen it. If not, make time, you will enjoy Yanks.


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## gjs238 (Jun 7, 2011)

So, we've learned a great deal about the limitations of the Allison design.
And about the flexibility of the RR design and the genius of Sir Stanley Hooker.

What about DB superchargers?
I know about the fluid coupling w/barometrically controlled speed.
Were the earlier designs fixed-speed?
Did the design lend itself to two stages?
How did high altitude performance compare to RR and US turbo designs?


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## Shortround6 (Jun 7, 2011)

As far as I can find out the first 601s used a single speed drive, there may have been a 2 speed drive on an other early model. German superchargers were no better and no worse than anybody else's in 1938-40. Since the German engines needed less boost than the Merlin or Allison the same performance supercharger could supply the required pressure at a somewhat higher altitude. Once they went to higher boost (anything much over 1.42 Ata) they were running into the same problems as the allies. However by that time better performing superchargers were coming into use. 

By "performance" I mean the pressure ratio and efficiency. A supercharger that can achieve the same pressure ratio with better efficiency not only uses less power to drive, it heats the intake charge less and allows slightly higher boost before detonation, the cooler charge is also denser at the same pressure and offers more power from that aspect. Super charger design tended to move in fits and starts on both sides. 

The Germans certainly knew of the advantages of two stage supercharging having used it on at least two different Grand Prix cars in the Late 30s. Granted they were roots superchargers but the basic principle of slitting the work over two superchargers instead of one still applied. Two stage superchargers actually took less power than a single supercharger for the same boost and heated the intake charge less. Obviously using two added weight, bulk and cost even before you hit boost levels that required inter cooling.


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## wuzak (Jun 7, 2011)

Shortround6 said:


> As far as I can find out the first 601s used a single speed drive, there may have been a 2 speed drive on an other early model. German superchargers were no better and no worse than anybody else's in 1938-40. Since the German engines needed less boost than the Merlin or Allison the same performance supercharger could supply the required pressure at a somewhat higher altitude. Once they went to higher boost (anything much over 1.42 Ata) they were running into the same problems as the allies. However by that time better performing superchargers were coming into use.



The DB series engines used a variable speed drive for their supercharger. Basically a fluid coupling altered the speed of the impeller depending on the altitude reached. 




Shortround6 said:


> The Germans certainly knew of the advantages of two stage supercharging having used it on at least two different Grand Prix cars in the Late 30s. Granted they were roots superchargers but the basic principle of slitting the work over two superchargers instead of one still applied. Two stage superchargers actually took less power than a single supercharger for the same boost and heated the intake charge less. Obviously using two added weight, bulk and cost even before you hit boost levels that required inter cooling.


 
The Mercedes-Benz W154 used the M154 engine with two superchargers in 1938. The superchargers were of the same size, and worked in parallel, not series. For 1939 the W154 ran the M163 version of the 3l V12, which had a two stage supercharging system. One blower was smaller in size than the other.

Alfa Romeo designed the 158 for Voiturette racing in the late 1930s. I believe it had a single supercharger. Post war the 158s dominated GP racing, and were developed into the 159 with two stage supercharging.

Britain's response to the Alfa was the BRM Type 15, which was powered by a 1.5l V16 with two stage supercharging by Rolls-Royce. The supercharger was a mini Merlin 60-series style supercharger, with both stage impellers mounted on a common shaft. R-R suggested some things that would help with engine response, as centrifugal compressors work at high rpm and don't make boost low down. BRM ignored or couldn't afford R-R's suggestions.


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## wuzak (Jun 7, 2011)

davparlr said:


> Not much of a trade off for the P-47. The turbo supercharger on the P-47D-25 allowed the engine to generate an incredible 2300 hp all the way up to 33k. Of course, even more incredible was the P-47M/N, which generated 2800 hp up to 33k, and 2600 hp up to 35k, over twice the power of the high altitude, non turbo charged Ta-152H and 800 hp more than the dual engined Do-335A-1. Loss of exhaust thrust was insignificant compared to power gained.



Power is one thing, but how much power is translated into forward motion is another.

At such altitudes the performance of the prop falls off, unless the prop is designed for such altitudes. And if the prop is designed for high altitudes it will be less effective down low.

Take, for instance, the Mosquito. For the high altitude types, like the XVI, "paddle blade" props were used. For Sea Mosquitoes, where performance at sea level was paramount for getting off carrier decks, "needle blade" props were used.

The later M/N Thuderbolts repositioned the supercharger such that some exhaust thrust was still available. The residual thrust on turbo installations such as on the Lightning was essentially lost. The XP-67 had the turbo with its shaft axis parallel to the engine crankshaft, with the exhaust and bypass exhaust (through the wastegate) exiting through the rear of the nacelles.


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## wuzak (Jun 7, 2011)

Shortround6 said:


> The Continental was intended to be used with a turbo charger and had a single speed supercharger drive to the engine supercharger in most versions (there were at least 13 different versions) there were one or two two speed versions and a 2 speed two stage version but many of these models never made it into an airframe for flight testing.
> I don't believe the Ford engine ever made it out of the test cells to be installed in a test mule aircraft so it's actual configuration is also pretty open ended.


 
There was only one type of IV-1430 engine cleared for test flight, and it flew in both the XP-49 and XP-67. Both used a single stage, sea level rated engine with turbosupercharger. It was rated at around 1350hp, and 1600hp WEP, but in flight tests it is unlikley to have made much more than 1000hp, hence the disappointing (and near identical) performance of both the XP-49 and XP-67.

It is interesting to note that the IV-1430 had more hours on single cylinder development than the whole Merlin testing program until production started! The IV-1430 program started around the same time as the V-1710 and Merlin. 

The IV-1430 had several variants of supercharger proposed, as well as two speed gearboxes for propellor drives. But this was wasted effort while the core engine was not running and nowhere near production.

Late in the war an IV-1430 was tested to 2300hp, apparently. But by then the program was being wound down.


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## davparlr (Jun 7, 2011)

wuzak said:


> Power is one thing, but how much power is translated into forward motion is another.
> 
> At such altitudes the performance of the prop falls off, unless the prop is designed for such altitudes. And if the prop is designed for high altitudes it will be less effective down low.


 Apparently the P-47M was quite able to convert the massive horsepower into forward motion. At 35k, the much cleaner Ta-152H was capable of 459 mph, the P-47M, 475 mph. In fact the P-47M was faster than the Ta-152H all the way up until the nitrous kicked in.


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## davparlr (Jun 7, 2011)

Lighthunmust said:


> Until I saw one at the Yanks Museum in Chino,CA the P-47M seemed like a mythological beast. Seeing your location davparir I am guessing you have seen it. If not, make time, you will enjoy Yanks.


 
I have been there. Their airshow in May is something to behold. Watching an F6F chase a Zero around the field, and a F-86 and a Mig-15 play catch-me-if-you-can is absolutely stunning.

Reactions: Like Like:
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## wuzak (Jun 7, 2011)

Piper106 said:


> I think the Lancaster (and the follow-on development, the Lincoln) was handicapped by being Merlin powered.
> 
> Four turbo charged Allisons (basically the whole engine package from a P-38J/L) would have been more effective. More allitude capability compared to the Merlin 20 series in the Lancaster (equal to the Merlin 85 engines in the Lincoln) to help get above the flak and fighters. The stronger Allison power section could handle more power longer than the Merlin (good for the long climb to allitude) with less maintenance. Most importantly, the turbocharged Allison burned less fuel than a Merlin for the same horsepower, so more bombs for the same takeoff weight.



If Bomber Command wanted better altitude performance from the Lancaster then surely they would have put 60- or 70-series engines into pace, a much simpler exercise than converting to the Allisons.

FWIW a B-17E (IIRC) was converted from Wright R-1820 power to Allison V-1710 power by Lockheed Vega, who were one of the factories producing the B-17. This was the XB-38. It had better performance than the standard version, but was deemed too much work to stop the production lines and change over. The engine installation owed much to that of the P-38, though the turbo remained in the standard B-17 location (bottom of nacelles). the coolant radiators were located in the leading edge between the engines.




Piper106 said:


> Griffon power in the Shackleton (another Lancaster follow-on) was also less than ideal. Allison had a turbocompound V-1710 running in their test cell. A single stage single speed version of a gas sipping Allison turbocompound would have been a better match to the Shackleton than the Griffon. (Note, this assumes that Napier misfires with their diesel work. They already had data and blueprints for the Jumo 205 diesel, a Deltic version of a Jumo 205 would have been could have been winner for long range patrol aircraft. Even the 'simplified' second version of the Nomad was wayyyyy too complicated. As with the Sabre, Napier reached too far).



Allison was unwilling to invest in the TC V-1710 without orders. The TC needed a better turbine - an air-cooled turbine was required as the exhaust was too hot for the standard GE turbine used for the prototypes (the turbine was from a C-series turbo - which is used for R-2800 applications, rather than a B-series turbo usually coupled to a V-1710). Additionally, Allison wanted to concentrate on jet power.

Napiers were building Jumo Diesels under licence before WW2, IIRC. The Deltic version would have been too heavy and been to draggy for an aircraft installation.

In any case, the Shackleton was post war, and as Britain was very cash strapped they could not afford to buy American engines, and preferred to use and develop engines from their own country. 

As the Shackleton was designed as an ASW aircraft, altitude performance was not necessary, and its range and endurance was more than sufficient for the task.

I'd also add that a better alternative would have been the turboprop engines that began appearing after the war.


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## fastmongrel (Jun 8, 2011)

wuzak said:


> As the Shackleton was designed as an ASW aircraft, altitude performance was not necessary, and its range and endurance was more than sufficient for the task.
> 
> I'd also add that a better alternative would have been the turboprop engines that began appearing after the war.



There was a proposal to fit RR Dart turboprops on the Shackleton but as usual the proposal was dropped because "it is going out of service soon it would be a waste of money". This was in the early 60s the Shack was still rattling along nearly 30 years later

My Brother in law flew many hours on Shacks as a Warrant officer electronics specialist and he says one Shack MR3 flew with a Rolls Royce Dart turboprop on an inside engine position to test the installation. The Dart was plumbed into the Viper turbojet booster engines fuel tank.

He reckons his hearing is permanently damaged by the racket inside a Shack and he was heartily glad when they transferred to the warm, draught free, quiet and vibration free Nimrod.


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## gjs238 (Jun 8, 2011)

wuzak said:


> FWIW a B-17E (IIRC) was converted from Wright R-1820 power to Allison V-1710 power by Lockheed Vega, who were one of the factories producing the B-17. This was the XB-38. It had better performance than the standard version, but was deemed too much work to stop the production lines and change over. The engine installation owed much to that of the P-38, though the turbo remained in the standard B-17 location (bottom of nacelles). the coolant radiators were located in the leading edge between the engines.



I wonder how this would have held up to German attacks, compared to the air cooled engines.


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## Lighthunmust (Jun 8, 2011)

gjs238 said:


> I wonder how this would have held up to German attacks, compared to the air cooled engines.


 
It would have been a huge mistake. No additional performance would have balanced the increased mechanical vulnerability.


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## wuzak (Jun 9, 2011)

Lighthunmust said:


> It would have been a huge mistake. No additional performance would have balanced the increased mechanical vulnerability.


 
Note that the USAAC had considered in-line liquid cooled engines essential for bombers because they could give more power for a certain capacity.

Not sure how much more vulnerable a B-17 would have been with the Allisons. The performance gain would have been totally lost by the tactics of mutual defensive fire, as this meant that the B-17s could rarely perform as well as it was able.

The B-29 could have had reduced "mechanical vulnerability" had they adopted the V-3420 installation of the XB-39 - some 30mph faster, more takeoff power, and proven and reliable engines (V-3420 was basically two V-1710s). The XB-39 used an engine installation, first trialed on the XP-19, which was specifically designed to bolt up to the same bulkhead as the R-3350. All cooling requirements were handled within the power egg.


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## johnbr (Jun 9, 2011)

Me I would have gone with the saber on the B-29


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## Lighthunmust (Jun 9, 2011)

wuzak said:


> Note that the USAAC had considered in-line liquid cooled engines essential for bombers because they could give more power for a certain capacity.
> 
> Not sure how much more vulnerable a B-17 would have been with the Allisons. The performance gain would have been totally lost by the tactics of mutual defensive fire, as this meant that the B-17s could rarely perform as well as it was able.
> 
> The B-29 could have had reduced "mechanical vulnerability" had they adopted the V-3420 installation of the XB-39 - some 30mph faster, more takeoff power, and proven and reliable engines (V-3420 was basically two V-1710s). The XB-39 used an engine installation, first trialed on the XP-19, which was specifically designed to bolt up to the same bulkhead as the R-3350. All cooling requirements were handled within the power egg.



When did they consider liquid cooled engines essential? Who in USAAC/USAAF thought they were essential? I am well aware of various studies and trials, but do not recall hearing anything on the essential need for liquid cooling. 

How much more vulnerable? As much as billions of coolant system piercing pieces of flak can create. Liquid cooled engines may have made a stronger case for the use of more HMG instead of more cannon on Luftwaffe fighters. More bullets to pierce versus less shells to burst. 

The only thing wrong with the mechanical vulnerability of the B-29 power plant aside from the engine cowling was that its first name wasn’t P&W and its last name 2800.


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## Shortround6 (Jun 9, 2011)

It was in the 30s that liquid cooling was considered essential. Part to it was theory. They hadn't really done much for trials. Aircooling wasn't developed as much as it was just a few years later. This liquid went along with the "hyper" cylinder or engine and we know how that turned out. 

The P&W R-2800, fine as it was, may not have been able to power a B-29. There is not only take-off power and Military power but Cruising powers to consider. The R-3350 may have had a max cruise power using auto-lean settings of several hundred horsepower more than the R-2800. Considering that these max auto lean settings produced power down around 1200hp an extra couple of hundred HP is actually quite a percentage change.


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## Readie (Jun 9, 2011)

I must admit that I had always thought that liquid cooling was preferable for internal combustions engines as it provided a more stable temperature and therefore allowed the engine to develop more power and reliability.

In all combustion engines, a great percentage of the heat generated (around 44%) escapes through the exhaust, not through either a liquid cooling system nor through the metal fins of an air-cooled engine (12%). About 8% of the heat energy finds its way into the oil, which although primarily meant for lubrication, also plays a role in heat dissipation via a cooler
Most liquid-cooled engines use a mixture of water and chemicals such as antifreeze and rust inhibitors. The industry term for the antifreeze mixture is engine coolant. Some antifreezes use no water at all, instead using a liquid with different properties, such as propylene glycol or a combination of propylene glycol and ethylene glycol. Most "air-cooled" engines use some liquid oil cooling, to maintain acceptable temperatures for both critical engine parts and the oil itself. Most "liquid-cooled" engines use some air cooling, with the intake stroke of air cooling the combustion chamber. 

Comparing air and water, air has vastly lower heat capacity per gram and per volume (4000) and less than a tenth the conductivity, but also much lower viscosity (about 200 times lower: 17.4 × 10−6 Pa·s for air vs 8.94 × 10−4 Pa·s for water). Continuing the calculation from two paragraphs above, air cooling needs ten times of the surface area, therefore the fins, and air needs 2000 times the flow velocity and thus a recirculating air fan needs ten times the power of a recirculating water pump. Moving heat from the cylinder to a large surface area for air cooling can present problems such as difficulties manufacturing the shapes needed for good heat transfer and the space needed for free flow of a large volume of air. Water boils at about the same temperature desired for engine cooling. This has the advantage that it absorbs a great deal of energy with very little rise in temperature (called heat of vaporization), which is good for keeping things cool, especially for passing one stream of coolant over several hot objects and achieving uniform temperature. In contrast, passing air over several hot objects in series warms the air at each step, so the first may be over-cooled and the last under-cooled. However, once water boils, it is an insulator, leading to a sudden loss of cooling where steam bubbles form (for more, see heat transfer). Unfortunately, steam may return to water as it mixes with other coolant, so an engine temperature gauge can indicate an acceptable temperature even though local temperatures are high enough that damage is being done.
An engine needs different temperatures. The inlet including the compressor of a turbo and in the inlet trumpets and the inlet valves need to be as cold as possible. A countercurrent heat exchange with forced cooling air does the job. The cylinder-walls should not heat up the air before compression, but also not cool down the gas at the combustion. A compromise is a wall temperature of 90°C. The viscosity of the oil is optimized for just this temperature. Any cooling of the exhaust and the turbine of the turbocharger reduces the amount of power available to the turbine, so the exhaust system is often insulated between engine and turbocharger to keep the exhaust gases as hot as possible.

The temperature of the cooling air may range from well below freezing to 50°C. The cooling system is designed to vary cooling so the engine is neither too hot nor too cold. Cooling system regulation includes adjustable baffles in the air flow (sometimes called 'shutters' and commonly run by a pneumatic 'shutterstat); a fan which operates either independently of the engine, such as an electric fan, or which has an adjustable clutch; a thermostatic valve or just 'thermostat' that can block the coolant flow when too cool. In addition, the motor, coolant, and heat exchanger have some heat capacity which smooths out temperature increase in short sprints. Some engine controls shut down an engine or limit it to half throttle if it overheats. Modern electronic engine controls adjust cooling based on throttle to anticipate a temperature rise, and limit engine power output to compensate for finite cooling.
Finally, other concerns may dominate cooling system design. As example, air is a relatively poor coolant, but air cooling systems are simple, and failure rates typically rise as the square of the number of failure points. Also, cooling capacity is reduced only slightly by small air coolant leaks. Where reliability is of utmost importance, as in aircraft, it may be a good trade-off to give up efficiency, durability (interval between engine rebuilds), and quietness in order to achieve slightly higher reliability — the consequences of a broken airplane engine are so severe, even a slight increase in reliability is worth giving up other good properties to achieve it.

Cheers
John


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## gjs238 (Jun 9, 2011)

Right from Wikipedia


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## Readie (Jun 9, 2011)

gjs238 said:


> Right from Wikipedia



Yes, I couldn't find a more succinct source. Other than a degree in Physics !
Cheers
John


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## Lighthunmust (Jun 9, 2011)

Shortround6 said:


> It was in the 30s that liquid cooling was considered essential. Part to it was theory. They hadn't really done much for trials. Aircooling wasn't developed as much as it was just a few years later. This liquid went along with the "hyper" cylinder or engine and we know how that turned out.
> 
> The P&W R-2800, fine as it was, may not have been able to power a B-29. There is not only take-off power and Military power but Cruising powers to consider. The R-3350 may have had a max cruise power using auto-lean settings of several hundred horsepower more than the R-2800. Considering that these max auto lean settings produced power down around 1200hp an extra couple of hundred HP is actually quite a percentage change.



As you frequently are, I think you are correct about the R2800 being marginal. I admit I have a bias toward P&W over Wright.
It is my understanding that the primary problem with the R-3350s on the B-29 was insufficient cooling due to cowl design. The result being failures and fires. The fires burning through the wing in less than a minute with catastrophic wing failure occurring.


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## Readie (Jun 9, 2011)

Lighthunmust said:


> As you frequently are, I think you are correct about the R2800 being marginal. I admit I have a bias toward P&W over Wright.
> It is my understanding that the primary problem with the R-3350s on the B-29 was insufficient cooling due to cowl design. The result being failures and fires. The fires burning through the wing in less than a minute with catastrophic wing failure occurring.



I copied this from Wiki for interest and my learning...

By 1943 the ultimate development of the new bomber program, the B-29, was flying. However the engines remained temperamental, and showed an alarming tendency of the rear cylinders to overheat, partially due to minimal clearance between the cylinder baffles and the cowl. A number of changes were introduced into the aircraft production line in order to provide more cooling at low speeds, and the planes were rushed to operate in the Pacific in 1944. This proved unwise, as the early B-29 tactics of maximum weights combined with high temperature airfields produced overheating problems that were not completely solved, and the engines had a tendency to swallow their own valves. Because of a high magnesium content in the crankcase alloy, the resulting engine fires were often so intense the main spar could burn through in seconds, resulting in catastrophic wing failure.
Early versions of the R-3350 were equipped with carburetors, though it was the poorly designed elbow, or entrance to the supercharger that led to serious problems with inconsistent fuel/air distribution. Near the end of World War II, in late 1944, the system was changed to use direct injection where fuel was injected directly into the combustion chamber. This change improved engine reliability immediately. After the war the engine was redesigned, and became a favorite for large aircraft of all designs, most notably the Lockheed Constellation and Douglas DC-7.

Got there in the end
Cheers
John


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## Lighthunmust (Jun 9, 2011)

gjs238 said:


> Right from Wikipedia


 


Readie said:


> Yes, I couldn't find a more succinct source. Other than a degree in Physics !
> Cheers
> John



What search terms are you using on wikipedia?

I don't doubt your veracity, considering all the individuals in positions of power within the USAAC during the 1930's with certitude on so many ideas that the events of 1939-45 quickly showed to be very wrong. 

If the "Brass" was fixated on liquid cool performance it is the same thing narrow vision that resulted in the battlecruiser. I'm sure you know how unsuccessful those faster, similarly armed, but more vulnerable, battlecruisers fared when facing slightly slower, similarly armed, but less vulnerable battleships. The idea that they were enamored with inlines is especially interesting considering that radials were used on every major design after 1935. Perhaps this is more due to availability than desire, but thank goodness it happened.

When I first posted the issue of mechanical reliability I was also implying mechanical reliability under fire. B-17s and B-24s with liquid cooled engines would have resulted in many more loses from enemy fire.


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## Readie (Jun 9, 2011)

Lighthunmust said:


> What search terms are you using on wikipedia?
> 
> I don't doubt your veracity, considering all the individuals in positions of power within the USAAC during the 1930's with certitude on so many ideas that the events of 1939-45 quickly showed to be very wrong.
> 
> If the "Brass" was fixated on liquid cool performance it is the same thing narrow vision that resulted in the battlecruiser. I'm sure you know how unsuccessful those faster, similarly armed, but more vulnerable, battlecruisers fared when facing slightly slower, similarly armed, but less vulnerable battleships. The idea that they were enamored with inlines is especially interesting considering that radials were used on every major design after 1935. Perhaps this is more due to availability than desire, but thank goodness it happened.



I just put my question /thoughts etc onto google and see what comes up. Or, I read my books...

The RN made some howlers with HMS Hoods armour. Its 3 knot advantage was no match for her 1918 designed armour. Central magazines was another blind alley.
Mind you, all of this is said with the benefit of hindsight.

I couldn't agree more that we were lucky to have the stalwarts we had in WW2. Liquid or Air cooled are two approaches to achieve the same thing. The ultimate piston engined aircraft. I have favoured liquid for the reasons I rather clumsily tried to show in an earlier post but, I fully accept that the last double radials had their measure in power / weight .

The USA radials and Bristol Centaurus are superb.

Cheers
John


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## Shortround6 (Jun 9, 2011)

Lighthunmust said:


> I don't doubt your veracity, considering all the individuals in positions of power within the USAAC during the 1930's with certitude on so many ideas that the events of 1939-45 quickly showed to be very wrong.
> 
> If the "Brass" was fixated on liquid cool performance it is the same thing narrow vision that resulted in the battlecruiser. I'm sure you know how unsuccessful those faster, similarly armed, but more vulnerable, battlecruisers fared when facing slightly slower, similarly armed, but less vulnerable battleships. The idea that they were enamored with inlines is especially interesting considering that radials were used on every major design after 1935. Perhaps this is more due to availability than desire, but thank goodness it happened.



Not really a good analogy. Battlecruisers were quite successful when used for what they were designed for, fighting armoured cruisers. They were not intended to be fast battleships no matter what the press releases said. 

The decade between 1930 and 1940 was one of tremendous development in aircraft engines and fuel. Any boob can supercharge the crap out of an engine and get a lot of power for a few seconds. The trick is getting th engine to last for several minutes at such power, and even more important, getting the engine to go several hundred hours between overhauls. The big enemy of high performance engines is heat. the cooler you can get an engine to run the more boost you can use for more power. Many engine designers of the time started by designing a cylinder to get the most power they could from it and then laid out the engine/multiplied the cylinder to get the desired power for the complete engine. Liquid cooled cylinders could make more power for the same size as aircooled engines could. part of this was just the levels of technology of the time ( which actually changed almost by the year). A high powered aircooled engine needs cooling fins, lots of them and big ones. In a lot of cases the depth of fin and the spacing was beyond the state of the art in casting technology so fins had to be machined. As casting, forging, machining technologies improved more and deeper fins could be put on cylinders (and heads) to allow for better cooling and more power. A few figures from P &W will show the trend. The 1927 wasp cylinder was 149 cu in and good for about 45hp with a total fin area of 1200 sq in. By 1932 the 131 cu in twin wasp cylinder was good for about 67hp and had 1500 sq in of finning. By 1940 the R-2800 cylinder of 155cu in had 3100 sq in of finning for its roughly 100hp per cylinder and the "C" seies cylinder of 1945 had 4300 sq in of finning for it's 125 hp per cylinder. Sq in of fin per HP varied from 26 on the wasp to 34 on the "C" series R-2800. 
Wright engines showed similar massive increasing in finning ending with the famous sheet metal fins rolled and caulked into machined grooves. The Bristol Hercules went through at least 4 different cylinder head designs with increased finning as it's power went up. 
Without these manufacturing break through's in casting, forging and machining the aircooled engine could have hit dead ends. At times during the 30s the future of the aircooled engine's ability to compete with the liquied cooled engine didn't look good. The air cooled makers managed to keep pulling tricks out of their bag but betting on what would happen 3-5 years down the road was never a sure thing.


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## davparlr (Jun 9, 2011)

Shortround6 said:


> The P&W R-2800, fine as it was, may not have been able to power a B-29. There is not only take-off power and Military power but Cruising powers to consider. The R-3350 may have had a max cruise power using auto-lean settings of several hundred horsepower more than the R-2800. Considering that these max auto lean settings produced power down around 1200hp an extra couple of hundred HP is actually quite a percentage change.


Spitfireperformance has good data on the R-2800 under P-47M performance however I could only find rudimentary info on the 3350. What I found was that the 3350 max continuous power at 28k was 2050 hp, the R-2800 in the P-47M had a max continuous power of 1650 hp there, and at most altitudes up to 33k. Now, I think the 3350 was supercharged, not turbocharged, if so, power might drop off quicker than for the turbocharged 2800, which did not drop off.


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## wuzak (Jun 9, 2011)

The R-3350s in the B-29 were turbocharged. The V-3420s in the XB-19, being tested as a backup for the R-3350s, were also turbocharged, but used an experimental turbocharger - for installation in teh XB-39 the turbochargers were deleted. The XB-44 was the first B-29 to be fitted with R-4360s, but were not turbocharged. The XB-50 used turbocharged R-4360s.


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## wuzak (Jun 9, 2011)

Lighthunmust said:


> When did they consider liquid cooled engines essential? Who in USAAC/USAAF thought they were essential? I am well aware of various studies and trials, but do not recall hearing anything on the essential need for liquid cooling.
> 
> How much more vulnerable? As much as billions of coolant system piercing pieces of flak can create. Liquid cooled engines may have made a stronger case for the use of more HMG instead of more cannon on Luftwaffe fighters. More bullets to pierce versus less shells to burst.
> 
> The only thing wrong with the mechanical vulnerability of the B-29 power plant aside from the engine cowling was that its first name wasn’t P&W and its last name 2800.


 
In the early '30s it was considered that an air-cooled engine of the power required for future bombers would be impractical for aircraft use.

Armour plate could have been used to protect vulnerable systems if need be.


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## Lighthunmust (Jun 9, 2011)

Shortround6 said:


> Not really a good analogy. Battlecruisers were quite successful when used for what they were designed for, fighting armoured cruisers. They were not intended to be fast battleships no matter what the press releases said.
> 
> Without these manufacturing break through's in casting, forging and machining the aircooled engine could have hit dead ends. At times during the 30s the future of the aircooled engine's ability to compete with the liquied cooled engine didn't look good. The air cooled makers managed to keep pulling tricks out of their bag but betting on what would happen 3-5 years down the road was never a sure thing.



Even though I have yet to receive and read those engine books we corresponded about, I think you are overstating your case and underestimating mine.

I think the battlecruiser analogy it is far better than you are giving it credit.

What was the fate of most Battlecruisers? A record of failure and obsolescence more than success. Why? Because of an over emphasis of one aspect of warship design due to the influence of Jackie Fisher’s fantasy. A fantasy that you will always hold the advantage in any combat engagement due to your weapons, speed, and tactics. Fisher forgot the combat rule that you are a target more often than a shooter, and you are only dead once. If you make something that looks like a battleship eventually both sides are eventually going to treat it as a battleship. If you make something that looks like a tank both sides are going to treat it as a tank. The analogy fits the inline versus radial issue just fine with regard to sacrificing protection for performance. Engines protect the crew from crashing to the ground. Using an engine type with marginally more performance when the stakes are life and death for the crew and the nation is wrongheaded thinking. The hope that the expected inline performance would balance against the advantages of radials is a mistake as much as the 1930’s thinking that bombers would run away from or shoot down attacking swarms of fighters. Claire Chennault understood this in the 1930’s.

Regarding the supposed preference for inlines:

From the Curtiss A-12 entry in Wikipedia:

The A-12 entered service in 1932 and remained in service until 1942.
Engine - "1× Wright R-1820 "Cyclone" 9-cylinder air-cooled radial engine, 690 hp (515 kW)"

“The most obvious difference between the A-12 and the A-8 is the air-cooled, radial engine in the A-12, which replaced the A-8's inline, water-cooled engine. This was a response to the USAAC's move toward a preference for radial engines, especially in attack aircraft. The rationale behind this preference is that the radial engine has a lower profile, making it less vulnerable to ground fire, and a simpler cooling mechanism, which is also less prone to groundfire, as well as overall maintenance problems.”

From “American Combat Planes” - Ray Wagner:
“The second example (of the YB-9) was flown November 13, 1931, with Curtiss V-1570-29 Conquerors, the last inline engines to be used on an Army bomber for over 11 years”





wuzak said:


> In the early '30s it was considered that an air-cooled engine of the power required for future bombers would be impractical for aircraft use.
> 
> Armour plate could have been used to protect vulnerable systems if need be.




Pages 195-231 of Wagner’s ACP covering the years 1931-1945 are filled with over a dozen bombers having radial engines. The only exceptions are the experimental one-off XB-38 and the experimental two-off XB42. If the gentlemen running USAAC in the 1930’s preferred inlines; they did little to implement that preference.

I have requested the search terms that Readie and gjs238 used to find reference to an inline preference by the gentlemen running the USAAC in the 1930’s. I would really like to see the article. Perhaps the three engine books I just ordered, partly due to Shortround6’s, recommendation may contain the reference to preference. Damn right that rhyme is intended!  For now I think the gentlemen of the USAAC might have preferred blondes (inlines), but certainly married brunettes (radials). Inlines are fine if you're flying within you're own lines, use a Radial to avoid foreign burial. All rhymes double damn intended!

Not enough armor plate could be used without unacceptable lose of performance. If it could have been practical we would have a great many less HE-111 crash sites in England.

Guys help me out. Show me the light by making a better case for your opinions. As always: Thanks for the education.


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## Shortround6 (Jun 10, 2011)

Lighthunmust said:


> , I think you are overstating your case and underestimating mine.
> 
> The analogy fits the inline versus radial issue just fine with regard to sacrificing protection for performance. Engines protect the crew from crashing to the ground. Using a engine type with marginally more performance when the stakes are life and death for the crew and the nation is wrongheaded thinking. The hope that the expected inline performance would balance against the advantages of radials is a mistake as much as the 1930’s thinking that bombers would run away from or shoot down attacking swarms of fighters.



You have to understand the thinking of the time rather than apply 70-80 years worth of hind sight. At times they were not looking for marginally more performance but rather substantial jumps in performance. In some cases they over reached and in other cases technology moved faster than expected. 


Lighthunmust said:


> Regarding the supposed preference for inlines:
> 
> From the Curtiss A-12 entry in Wikipedia:
> 
> ...



Well, this shows a little bias right here. Lets yank out a 1926-27 water cooled v-12 and stick in an up to date 1932 radial engine with 15% more power and then tell ourselves how clever we are. OK, a bit of an exaggeration but the V-1570 Conqueror had pretty much reached the end of the line before the 20s were out. It was finished off with merger of Curtiss and Wright in July of 1929. Curtiss-Wright didn't care which engine they sold so no more development was put into the Conquerer. 


Lighthunmust said:


> From “American Combat Planes” - Ray Wagner:
> “The second example (of the YB-9) was flown November 13, 1931, with Curtiss V-1570-29 Conquerors, the last inline engines to be used on an Army bomber for over 11 years”
> 
> Pages 195-231 of Wagner’s ACP covering the years 1931-1945 are filled with over a dozen bombers having radial engines. The only exceptions are the experimental one-off XB-38 and the experimental two-off XB42. If the gentlemen running USAAC in the 1930’s for inlines; they did little to implement that preference.



I would note that just about every one of those bombers used pretty much versions of standard commercial engines until at least 1939-40. The USAAC spent darn little money on R&D of radial engines. They were feeding Allison, Continental and Lycoming for Liquid cooled projects. Continental was little more than a parts supplier for the army at times. They simply made parts and ran test to army designs and specifications for the hyper engine project. Both the Continental and Lycoming started out as flat 12s that could be buried in the wing for better streamlining by eliminating the the engine nacelle. Try that with an air cooled radial without a very fancy gear box. This idea got over taken by technology, as the 30s went on airfoils and wing structure changed and fat wings went away. Unless you had a really big bomber (B-15/B-19) the wing wasn't going to be thick enough to hide even a flat 12. 
The Army was also trying for high altitude flight with the turbo charger. They were afraid the much thinner air at altitude wouldn't properly cool the air cooled engines. 
Then there is keeping up with the "Jones's". With France, Germany and Great Britain all using liquid cooled engines for large numbers of their warplanes it would take a might confident man to ignore liquid cooling in the 30s. 


Lighthunmust said:


> Not enough armor plate could be used without unacceptable lose of performance. If it could have been practical we would have a great many less HE-111 crash sites in England.



Nobody was armoring much of anything in airplane in the 30s. 

You might also want to consider that the liquid cooled early P-40 had 22% less drag than the radial powered P-36, confirmed by flight tests. That is total drag not engine drag. Look at the A-8 and A-12 again. The liquid cooled A-8 was slightly heavier and yet was 6mph faster despite the A-12s radial having 15% more power. The Conquerer had a higher service ceiling despite having NO supercharger, none, nada, zip, zilch. Of course this is wike and ceilings might not be correct.


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## Lighthunmust (Jun 10, 2011)

Shortround6 said:


> You have to understand the thinking of the time rather than apply 70-80 years worth of hind sight. At times they were not looking for marginally more performance but rather substantial jumps in performance. In some cases they over reached and in other cases technology moved faster than expected.
> 
> 
> Well, this shows a little bias right here. Lets yank out a 1926-27 water cooled v-12 and stick in an up to date 1932 radial engine with 15% more power and then tell ourselves how clever we are. OK, a bit of an exaggeration but the V-1570 Conqueror had pretty much reached the end of the line before the 20s were out. It was finished off with merger of Curtiss and Wright in July of 1929. Curtiss-Wright didn't care which engine they sold so no more development was put into the Conquerer.
> ...


 
I think I have some understanding of the thinking in the 1930s only because it has not changed much as far as the American military is concerned. I think you may be right about throwing money at inlines. The longer we debate, the more I am remembering things read years ago. I do think their real preference was for power. The kept finding that in radials with the benefit of also desired dependability under adverse conditions. Really, they were worried about cooling at altitude? Had none of them seen what Mallory was wearing to climb Everest? Had none of them ever been 10,000 feet above sea level? No doubt they were envious of the those so sophisticated europeans and their flashy seaplane air-racers and slick monoplane fighters powered by inlines. With commercial aviation providing the funding for radials, why not throw money at glamourous inlines? It is not so much my use of hindsight as their narrow mindedness, petty resistance to anything upsetting the status quo, and shortsightedness that was the problem. That and Army and Navy brass determined to limit the autonomy of the USAAC.

I agree about armor not being on their minds. The minimal engine power available would alone preclude much thought of adding additional weight. After all Bomber pilots wouldn't be caught and if by luck a fighter showed up it would be promptly dispatched by a socket mounted .30cal.

Obviously someone thought the A-12's marginal decrease in performance was worth the gain in dependability. The best way to measure performance is with reproducibility. Coming back from the mission to fly another mission was the best measure of the performance of an engine.


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## Shortround6 (Jun 10, 2011)

It is not "military" thinking I was referring to, but the thinking of many people in the aeronautics industry. The 'debate' over liquid cooling vs air cooling had been going on since before WW I. As technology ebbed and flowed, First one side would have an advantage and then the other. 


the problem with cooling at high altitude is not the temperature, which is obviously lower but the density. At 33,000ft the air is one third the density of sea level. The engine is cooled by XXX pounds of air per minute flowing through the fins or radiator. While you can supercharger the engine to get the power what do you do to "supercharge" the cooling system?

I really do have to question this part of your post.

"No doubt they were envious of the those so sophisticated europeans and their flashy seaplane air-racers and slick monoplane fighters powered by inlines. With commercial aviation providing the funding for radials, why not throw money at glamourous inlines? It is not so much my use of hindsight as their narrow mindedness, petty resistance to anything upsetting the status quo, and shortsightedness that was the problem. That and Army and Navy brass determined to limit the autonomy of the USAAC."

There is really no way to debate that kind of thinking and there is no need to try to 'goad' people into giving you information.

I think I will check out of this discussion for a while.


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## billswagger (Jun 10, 2011)

The Allison attached to the P-51 was said to have performed better.
Maybe i'm stating the obvious, but the air frame will effect performance more so than the engine. 
I think the Allison gets its reputation of lower performance at higher altitude because it was never designed to be operated at the heights the military required of it. 
This point was probably made earlier in the thread, but the P-40 was a lower to mid altitude fighter and the Allison performed quite well when compared to other liquid cooled V-engines. The poor altitude performance reputation probably comes from the lack of performance the P-40 experienced, but that may also be due to weight, wing loading, drag....etc.
For example, a contemporary 109 Db601 puts out around 1000hp at 17000ft, and less than 900hp above 20,000ft. 
The 109 is lighter and requires less power to gain similar performance. 
Similarly, with the Spitfire, but i don't have figures for the Merlin, only that it had a better FTH. 
When compared at lower heights, the Merlin and Allison were nearly the same.
The Merlin was a good engine, but i've also read that the Allison was much more durable from an RPM standpoint. 
I refer to racing boats of the 1950-1960s era that used both surplus engines of ww2, and the Allisons were said to be better suited for the RPMs required for boat racing and both types of engines achieving similar outputs.


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## wuzak (Jun 10, 2011)

billswagger said:


> The Allison attached to the P-51 was said to have performed better.
> Maybe i'm stating the obvious, but the air frame will effect performance more so than the engine.
> I think the Allison gets its reputation of lower performance at higher altitude because it was never designed to be operated at the heights the military required of it.
> This point was probably made earlier in the thread, but the P-40 was a lower to mid altitude fighter and the Allison performed quite well when compared to other liquid cooled V-engines. The poor altitude performance reputation probably comes from the lack of performance the P-40 experienced, but that may also be due to weight, wing loading, drag....etc.
> ...


 
The Allison attached to the P-51 performed better at low altitude because its installation was slightly less draggy, and at low altitude the engine performance was similar or better than the Merlin, because the Merlin was a high altitude version. A low altitude version would have fared better at low altitudes. 

The Allison's main problem, when not coupled to a turbocharger, was that it had a single speed supercharger. Later they developed the two stage supercharger with variable speed auxiliary stage, but single stage engines remained single speed. That could have been rectified if so desired, but it wasn't to be the case.


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## gjs238 (Jun 10, 2011)

wuzak said:


> That could have been rectified if so desired, but it wasn't to be the case.



It seems the Allison design left less room for "rectification" that other designs.


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## Lighthunmust (Jun 10, 2011)

Shortround6 said:


> I really do have to question this part of your post.
> 
> "No doubt they were envious of the those so sophisticated europeans and their flashy seaplane air-racers and slick monoplane fighters powered by inlines. With commercial aviation providing the funding for radials, why not throw money at glamourous inlines? It is not so much my use of hindsight as their narrow mindedness, petty resistance to anything upsetting the status quo, and shortsightedness that was the problem. That and Army and Navy brass determined to limit the autonomy of the USAAC."
> 
> ...



Did you think I was referring to you or members of this forum with this comment?
The narrow mindedness etc.,etc, was referring to members of the USAAC hierarchy. I was not attempting to goad anyone, apparently it came off that way and I apologize for my lack of clarity. I do however think a discussion of the impact on aircraft technical development by pre-war attitudes and politics of the USAAC, and Army and Navy leadership would be interesting.


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## buffnut453 (Jun 10, 2011)

wuzak said:


> The Allison attached to the P-51 performed better at low altitude because its installation was slightly less draggy, and at low altitude the engine performance was similar or better than the Merlin, because the Merlin was a high altitude version. A low altitude version would have fared better at low altitudes.
> 
> The Allison's main problem, when not coupled to a turbocharger, was that it had a single speed supercharger. Later they developed the two stage supercharger with variable speed auxiliary stage, but single stage engines remained single speed. That could have been rectified if so desired, but it wasn't to be the case.



Wen the Mustang MkI entered service, none of the other RAF fighters had two-stage superchargers but the Allison still lacked altitude performance, hence the Mustang was assigned to army co-op tasks.


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## gjs238 (Jun 10, 2011)

buffnut453 said:


> Wen the Mustang MkI entered service, none of the other RAF fighters had two-stage superchargers but the Allison still lacked altitude performance, hence the Mustang was assigned to army co-op tasks.


 
"none of the other RAF fighters had two-stage superchargers"
But then wouldn't those fighters also lack altitude performance?
Or was it that they had two speed blowers?
Or perhaps the single-stage single-speed blowers were optomized for a higher altitude?
Or perhaps the single-stage single-speed blowers were better designed?


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## Readie (Jun 10, 2011)

The Pratt Whitney R-2060 Yellow Jacket was a liquid-cooled aircraft engine project developed for the United States Army in the early 1930s.The engine had five banks of four in-line cylinders, and displaced 2,060 cubic inches. Designed to produce 1,000 hp, the engine produced 1,116 hp on its final run after 35 hours of testing. The engine was cancelled in favor of continuing development of Pratt Whitney's air-cooled R-1830 Twin Wasp radial engine. (source wiki)

Another dalliance with liquid cooling by the Americans. I must confess I had never heard of the 'yellow jacket'

Cheers
John


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## Readie (Jun 10, 2011)

Piston Engines

This is interesting. The US Navy recognised the weight advantage of the radial for its own carrier borne aircraft.

1930 - 1939 Military Aircraft

A long list here. Showing the use of inline and radials by designers.
I'm not making any particular point, just posting the link for general interest. There are some obscure aircraft listed !!
Cheers
John


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## davparlr (Jun 10, 2011)

The discussion on liquid cooled inline engines verses air cooled radials took me back to my childhood growing up in Pensacola. I remember one of the innumerable airshows put on by the Blue Angels that I attended that they had a demonstration of a P-51 and an F8F. It was one of those hot, humid summer days Pensacola is so famous for. The P-51 flew first. It took off and flew a few demo runs and then came around and landed. The announcer, obviously a Naval aviator, said that the P-51, due to its liquid cooled engine had overheated and had to land. Next came the F8F. It took off and flew a few demo runs and then came around an landed. The announcer said that the F8F had overheated.


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## Shortround6 (Jun 10, 2011)

gjs238 said:


> "none of the other RAF fighters had two-stage superchargers"
> But then wouldn't those fighters also lack altitude performance?
> Or was it that they had two speed blowers?
> Or perhaps the single-stage single-speed blowers were optomized for a higher altitude?
> Or perhaps the single-stage single-speed blowers were better designed?


 
It is a little bit of everything, it is also the fact that the Allison powered planes were heavier than the Spitfire, Hurricane, Bf 109, etc. An Allison powered Mustang can tip the scales at over 8000lbs with only 630lb of internal fuel (105 US gals?) so even if you had shoved a Merlin 45 into it it would have been a bit lacking in high altitude performance compared to a MK V Spitfire being about 1400lbs heavier (about 20%). Merlin 45 was single speed. It was also good for 1185hp for take off.

engine..........take-off .........military power/low gear......WEP/Low...........Militay power/high.... WEP high
Allison-39........1150..............1150/11,700ft..................1490/4,300ft.......------..............-------
Allison-81........1200..............1125/15,500ft..................1410/9,500ft.......------..............------
Merlin 45.........1185..............1210/18,250ft..................1515/11,000ft.....------..............------
Merlin XX.........1280..............1260/12,250ft.................1485/6,000ft......1175/21,000ft......1490/12,500ft

Merlin XX and 45 used the same supercharger.


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## gjs238 (Jun 10, 2011)

Readie said:


> The Pratt Whitney R-2060 Yellow Jacket was a liquid-cooled aircraft engine project developed for the United States Army in the early 1930s.The engine had five banks of four in-line cylinders, and displaced 2,060 cubic inches. Designed to produce 1,000 hp, the engine produced 1,116 hp on its final run after 35 hours of testing. The engine was cancelled in favor of continuing development of Pratt Whitney's air-cooled R-1830 Twin Wasp radial engine. (source wiki)
> 
> Another dalliance with liquid cooling by the Americans. I must confess I had never heard of the 'yellow jacket'
> 
> ...



That's neat. Why must a water cooled engine be an in-line? Radial water cooled is cool.


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## davparlr (Jun 10, 2011)

Then the roughly 400 hp advantage of the 3350 would probably continued as altitude went up. The additional 1600 hp per plane would be like having an additional engine.


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## davparlr (Jun 10, 2011)

Lighthunmust said:


> is a mistake as much as the 1930’s thinking that bombers would run away from or shoot down attacking swarms of fighters. Claire Chennault understood this in the 1930’s.


 
I don't think the idea was as much of a mistake as was the understanding of the rate of advancement that was occurring at the time. When the B-17 was conceived, the proposed fighters at the time was not significantly faster than the bomber and defensive system would be more effective. However by the time the bomber was deployed, technology in fighters had significantly improved and implemented much faster than bomber advancements could. The concept of speed as an superior advantage for a bomber has never been disproved nor abandoned, starting with the amazing Mosquito. In the 50s, the Mig 15 had a devil of a time, and as far as I know never succeeded, trying to catch a B-47s, as they buzzed Russian airfields. This is would have also been true with the Mig 21 trying the catch the equally fast B-58, and the tri-sonic B-70 was killed by advancements in anti-aircraft missiles, not by a fighter threat.


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## Messy1 (Jun 10, 2011)

I have been following this thread closely. Learned a lot. Thanks to all contributors!


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## tomo pauk (Jun 10, 2011)

Well put, Messy1


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## Lighthunmust (Jun 10, 2011)

davparlr said:


> I don't think the idea was as much of a mistake as was the understanding of the rate of advancement that was occurring at the time. When the B-17 was conceived, the proposed fighters at the time was not significantly faster than the bomber and defensive system would be more effective. However by the time the bomber was deployed, technology in fighters had significantly improved and implemented much faster than bomber advancements could. The concept of speed as an superior advantage for a bomber has never been disproved nor abandoned, starting with the amazing Mosquito. In the 50s, the Mig 15 had a devil of a time, and as far as I know never succeeded, trying to catch a B-47s, as they buzzed Russian airfields. This is would have also been true with the Mig 21 trying the catch the equally fast B-58, and the tri-sonic B-70 was killed by advancements in anti-aircraft missiles, not by a fighter threat.


 
The mistake is the same one made for millennia: failure to realize that every weapon creates a counter-weapon or countermeasure, the technology your are using on your weapon may be adapted for a counter-weapon or countermeasure. I agree with you on the comprehension of the rate of technological advance, but like the principles of Sun-Tzu from 2500 years ago, these basic principles never change. Just the failure to consider a vast use of the many methods of detection available without the benefit of radar should have been a factor for bomber design and doctrine. I don’t think they really considered it and how it would enable a defender to have fighters up and waiting. Even without Radar I think the BoB would have ended the same way with only more time and bloodshed added. Obviously I have the benefit of hindsight, but the lack of foresight and respect for the ingenuity of opponents to develop countermeasures was in my opinion rife within the U.S. military and political sphere in the 1930s and continues today. By the way, I am ex-Army and ex-NSA analyst so I am not a hater of the U.S. Military.

I absolutely agree with you about the advantages of speed. The heavy defensive gun armament on bombers being on the losing side of history. Speed, Deception, and Stealth being the future. No doubt that Geoffrey de Havilland had better foresight than many planners of his day. There was a thread in 2005 about the Mosquito versus the B-17 that addressed this issue. Ultimately you fight with what you’ve got rather than what you might have had. Speed is not everything and not of unlimited availability. Many Mosquitos were shot down by fighter aircraft. 

A RB-47 flying out of Alaska was scouting out the Kamchatka Peninsula on 17 April 1955, when it was bounced by Soviet MiG-15s in international airspace. The RB-47 and its crew disappeared. - wikipedia

I seem to recall from my reading about NSA, other RB-47s were lost to subsonic MiG-17s.

B-68s had limited endurance even at high altitude when using enough speed to out race a MiG 21. Even if the SAM were never invented it would have been in trouble facing the density of MiG defenders over hundreds of miles.

The same is true of the B-70. The problem is just more difficult for the defender, but not insurmountable for a nation structured as the USSR was. A dense defense of MiG-25s would have been created. I think the B-70 system would have been eventually killed by a fighter threat. I think there is a reason besides treaty and satellites why deep over flights of the USSR with SR-71s didn’t happen. Detection technology was advancing about as fast as aviation technology. Not just radar, but detection using a wide spectrum of the EM band. Sometimes the most up to date technology is not the answer. If I recall correctly the Serbs shot down a F-117 using an old radar system that probably nobody designing the F-117 expected to encounter.

Much appreciation for davapir for creating this thread and the great posts the participants are making. I should have “Vees for Victory” and the other two engine books I ordered by next week. Your posts are only making my eager anticipation grow.

Reactions: Like Like:
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## Readie (Jun 10, 2011)

Popular Science - Google Books

I found this on line.
Cheers
John


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## Lighthunmust (Jun 10, 2011)

Readie said:


> Popular Science - Google Books
> 
> I found this on line.
> Cheers
> John


 

Bravo! I have been bookmarking these sites you are posting. Oh how I wish that most of my pre-1993 book and magazine collection had not been "lost" by the movers. I had a bunch of National Geographics from the 30s-60's that had articles like this one. Thank you John.


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## Readie (Jun 10, 2011)

Lighthunmust said:


> Bravo! I have been bookmarking these sites you are posting. Oh how I wish that most of my pre-1993 book and magazine collection had not been "lost" by the movers. I had a bunch of National Geographics from the 30s-60's that had articles like this one. Thank you John.




Thanks Steve, like you my collection of old mags and encyclopaedic materials that covered article like my post as all long gone. I search ebay daily trying to rebild it but, its a tall order.
Cheers
John


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## Messy1 (Jun 10, 2011)

Readie said:


> Popular Science - Google Books
> 
> I found this on line.
> Cheers
> John


 
Great link. Excellent article. Thanks for sharing Is there a way to print those articles off?


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## davparlr (Jun 10, 2011)

Lighthunmust said:


> > Many Mosquitos were shot down by fighter aircraft.
> 
> 
> Sill, the Mosquito was an effective high speed bomber depending on speed only.
> ...


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## Lighthunmust (Jun 10, 2011)

davparlr said:


> Lighthunmust said:
> 
> 
> > > Sill, the Mosquito was an effective high speed bomber depending on speed only.
> ...


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## wuzak (Jun 10, 2011)

Readie said:


> Popular Science - Google Books
> 
> I found this on line.
> Cheers
> John


 
Interesting that the article shows an engine being turbocharged with two small turbines, one for each bank, driving a central double sided impeller.

Kinda like this picture from Flight Global of a turbocharged Merlin.

http://www.flightglobal.com/airspac...olls-royce-merlin-xx-supercharger-cutaway.jpg

Note that this doesn't have an engine stage mechanical supercharger. The air intake is pointed towards the rear, but could easily be pointed upwards for a top intake (like Allisons) or downwards for a bottom intake (like Merlins). The impeller and housing could be positioned so as to feed the eye of an engine stage supercharger, if so desired.

The intercooler (technically it is actually an aftercooler) is a liquid to air intercooler - an air to air intercooler would be larger.

But it does show that a turbocharged V12 aero engine could possibly have been turbocharged and used in a single engine fighter, without going to teh size and bulk of a P-47. Or it could have bene used in a multi engined aircraft like the Lancaster and Mosquito.


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## wuzak (Jun 10, 2011)

Lighthunmust said:


> P.S. How are you guys breaking up posts to create multiple quote balloons? I obviously haven't figured it out.


 
They would be using this




icon, then using Reply to Thread.


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## Lighthunmust (Jun 10, 2011)

Thank you for the reply wuzak.


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## wuzak (Jun 10, 2011)

Lighthunmust said:


> Thank you for the reply wuzak.


 
Your welcome. Unfortunately the icon didn't come up. But it is the quote mark with a + on the bottom right.


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## Readie (Jun 11, 2011)

wuzak said:


> Interesting that the article shows an engine being turbocharged with two small turbines, one for each bank, driving a central double sided impeller.
> 
> Kinda like this picture from Flight Global of a turbocharged Merlin.
> 
> ...


 
Interesting, Thanks for posting that Wuzak. A Turbo Merlin eh? ummmmm.
I used to live in Ulverstone, Tas when I was a boy. Do you know that area?
Cheers
John


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## Readie (Jun 11, 2011)

Messy1 said:


> Great link. Excellent article. Thanks for sharing Is there a way to print those articles off?



I can get the 'print' icon up. If that doesn't work for you try to save the doc and then print it...
Usually its hard to print these items off as they want you to buy them lol.
Cheers
John


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## wuzak (Jun 11, 2011)

Readie said:


> Interesting, Thanks for posting that Wuzak. A Turbo Merlin eh? ummmmm.
> I used to live in Ulverstone, Tas when I was a boy. Do you know that area?
> Cheers
> John



Yes, not that I have spent much time there.


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## Readie (Jun 11, 2011)

wuzak said:


> Yes, not that I have spent much time there.



We left for Melbourne in 1964 so I can only recall parts. Google Earth is a great tool for visiting old haunts.The part where we lived doesn't seem to have changed much, I can still spot the cattle grid at the end of the drive !
Cheers
John


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## billswagger (Jun 11, 2011)

gjs238 said:


> It seems the Allison design left less room for "rectification" that other designs.


 
I also wonder what political agendas were being served at a time when most Allison engined aircraft were being shipped away on lend lease programs.
Even though they might be allies, why would the US ship similarly capable or better aircraft to foreign countries? 
The idea of arming an ally with equally capable aircraft as your own might not be seen as a wise military decision considering isolationism had most countries looking out for themselves at the time the war was going on.
In some ways, the Allisons lack of development may have been because the aircraft were deemed hand me downs going to outside countries.
It may have been purposefully neutered.
There are other examples of front line fighters using limited technology as to not lose trade secrets when enemies capture aircraft. 
Why would Allison (General Electric) care, they still make a grip on the gov't contract selling the engines. 
The other reason, Packard had begun building better engines in the US and so much of the production was shifting toward their use instead of the Allison. 
Allison just filled the gap until other factories ramped up. 
IMO, they could've done much better. 
Why they didn't seems to have been a political strategy.


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## Lighthunmust (Jun 11, 2011)

wuzak said:


> Interesting that the article shows an engine being turbocharged with two small turbines, one for each bank, driving a central double sided impeller.
> 
> Kinda like this picture from Flight Global of a turbocharged Merlin.
> 
> ...



If I recall correctly a book or article I read years ago stated that the Merlin due to it's design was difficult to turbocharge. What do you know about this? Is it true? Did any aircraft use turbocharged Merlins?


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## Shortround6 (Jun 11, 2011)

billswagger said:


> I also wonder what political agendas were being served at a time when most Allison engined aircraft were being shipped away on lend lease programs.
> Even though they might be allies, why would the US ship similarly capable or better aircraft to foreign countries?
> The idea of arming an ally with equally capable aircraft as your own might not be seen as a wise military decision considering isolationism had most countries looking out for themselves at the time the war was going on.
> In some ways, the Allisons lack of development may have been because the aircraft were deemed hand me downs going to outside countries.
> ...



Or, it could be just as you said. Allison was so busy trying to get production going in 1940-41 they didn't have much effort to spare in developing the engine (specifically supercharger).

Allison went from 530 employees in 1938 to 786 in 1939 to 4,303 in 1940 to 9,673 in 1941 to 14,323 in 1942. 

Engines delivered went from 13/14 (one was a V3420) in 1938 to 48 in 1939 to 1153 in 1940 (342 to the AAC) to 6,433 in 1941 to 15,319 in 1942. 

At this point, Allison was behind the curve and trying to catch up. A number of projects had been on the back burner and slipping. 

Please remember that Allison, Wright and P&W and each only started to design their own superchargers in 1936-38. There was no background of experience to fall back on.


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## wuzak (Jun 11, 2011)

Lighthunmust said:


> If I recall correctly a book or article I read years ago stated that the Merlin due to it's design was difficult to turbocharge. What do you know about this? Is it true? Did any aircraft use turbocharged Merlins?


 
Not sure that anybody actually tried.

Rolls-Royce had experimented with turbochargers, but had also determined that the exhaust thrust was significant, and they preferred to use the exhaust thrust. Th effect became more significant the faster the plane flew and the higher the altitude.


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## wuzak (Jun 11, 2011)

billswagger said:


> The other reason, Packard had begun building better engines in the US and so much of the production was shifting toward their use instead of the Allison.



Packard began building Merlins because Rolls-Royce needed help with production to supply the British industry. Initially there was no plan to use Merlins for US aircraft. Most Packard Merlins ended up in British aircraft.




billswagger said:


> Why would Allison (General Electric) care, they still make a grip on the gov't contract selling the engines.



Allison was owned by General Motors, not General Electric.


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## Estefan (Sep 29, 2012)

Does somebody know what was the weight of GE supercharger supplied compressed air for Allison engine?


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## renegate326 (Nov 16, 2013)

Readie said:


> It was an inferior design to the Merlin. That's why the P51 received Britain's finest aero engine.
> Cheers
> John



You Brits are really funny in inventing fantasies instead of sticking to facts..


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## renegate326 (Nov 16, 2013)

And today its owned by R-R what a fate?


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## renegate326 (Nov 16, 2013)

Göring has never said something like this..On the contarary R-R engines in Battle of Britain were prone to fail easily due to carburrator stall..ME-109 had fuel injection, and had to just climb to escape from a Spitfire. The Spitfire could only compete with the ME 109 after the introduction of 100 octane fuel from America. The Spitfire wasn´t particularly better. The 109´s biggest enemy was it´s lack of range when flying to England. Luftwaffe pilots worried more about lack of fuel than Spitfires as they had no more than 12 minutes in British airspace a huge disadvantage. I met a former Luftwaffe pilot many many years ago,he said that ME-109 would have beaten Spitfires easily had the war had taken place on a neutral airspace !


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## renegate326 (Nov 16, 2013)

Readie said:


> If we English had only the Allison I would be speaking German.
> The Merlin is more than just another aero engine it represents our identity.
> Cheers
> John



ME-109 had fuel injection, and had to just climb to escape from a spitfire. The spitfire could only compete with the ME 109 after the introduction of 100octane fuel from America and Browning machine guns made in the US The Spitfire wasn´t particularly better , the R-R Merlin engines were extremely unreliable during Battle of Britain and were prone to failure due to carburator stall . The 109´s biggest enemy was it´s lack of range when flying to England. The pilots worried more about lack of fuel than spitfires as they had only 12 minutes time in english airspace ! 
I met a 90 years old German Luftwaffe pilot many years ago who said that ME 109 would have beaten Spitfires easily had the war had taken place in a neutral airspace under equal conditions. Merlin didnt save Britain in WW2,it was German's decision to postpone the invasion in order to allocate more resources for the USSR invasion..Had they put pressure another week or so, RAF would throw the towel ,luckily Germans were not aware of this !


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## Wurger (Nov 16, 2013)

renegate326 said:


> You Brits are really funny in inventing fantasies instead of sticking to facts..



OK.. let's stick to the facts... talking obout Messerschmitt 109 the correct name is Bf 109 but not ME-109.


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## vinnye (Nov 16, 2013)

If I remember correctly, the problem that the merlin had was with negative g loading on the carb. So that would mean going inverted for example. I do not recall the carb having any problem when climbing?


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## Milosh (Nov 16, 2013)

> The spitfire could only compete with the ME 109 after the introduction of 100octane fuel from America....... etal



Oh dear, someone who doesn't know the facts.


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## wuzak (Nov 16, 2013)

renegate326 said:


> The spitfire could only compete with the ME 109 after the introduction of 100octane fuel from America and Browning machine guns made in the US



Spitfires used US made Brownings in the BoB?

AFAIK, they only had US made Brownings on some (most?) XIVs, some IX/XVIs. And then only two per plane - as a backup weapon. The primary weapon being the 0mm Hispano MK II cannon (Mk V in the 20-series Spitfires).




renegate326 said:


> the R-R Merlin engines were extremely unreliable during Battle of Britain and were prone to failure due to carburator stall



The engine would cut out under negative G because of fuel starvation. That means they couldn't just push over into a dive.

But cutting out becuae of fuel starvation is a different thing to unreliability. Not sure, but I would think the engine would restart once the fuel supply was restored.




renegate326 said:


> I met a 90 years old German Luftwaffe pilot many years ago who said that ME 109 would have beaten Spitfires easily had the war had taken place in a neutral airspace under equal conditions. Merlin didnt save Britain in WW2,it was German's decision to postpone the invasion in order to allocate more resources for the USSR invasion..Had they put pressure another week or so, RAF would throw the towel ,luckily Germans were not aware of this !



Luftwaffe weren't fighting the entire RAF in the BoB.


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## Milosh (Nov 16, 2013)

wuzak said:


> Luftwaffe weren't fighting the entire RAF in the BoB.



Not only that but the Germans couldn't replace the a/c they lost while the British did.


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## Denniss (Nov 16, 2013)

The loss of highly experienced flying crew was even more fatal.


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## wuzak (Nov 16, 2013)

Denniss said:


> The loss of highly experienced flying crew was even more fatal.



And it was twofold for the Germans in the BoB.

If the pilot was shot down and survived, and was able to bail out, he would end up in England and captured.


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## Glider (Nov 16, 2013)

renegate326 said:


> Göring has never said something like this..On the contarary R-R engines in Battle of Britain were prone to fail easily due to carburrator stall..ME-109 had fuel injection, and had to just climb to escape from a Spitfire. The Spitfire could only compete with the ME 109 after the introduction of 100 octane fuel from America. The Spitfire wasn´t particularly better. The 109´s biggest enemy was it´s lack of range when flying to England. Luftwaffe pilots worried more about lack of fuel than Spitfires as they had no more than 12 minutes in British airspace a huge disadvantage. I met a former Luftwaffe pilot many many years ago,he said that ME-109 would have beaten Spitfires easily had the war had taken place on a neutral airspace !



Climbing wasn't the problem with the Merlin, negative 'G' was in a push over, until it was sorted out. No one has ever claimed that the Spit I was better than the 109E both were very well matched with different advantages and disadvantages. As for the 100 octane it certainly helped but wasn't the be all and end all, the CSP was equally advantageous. 



> It was German's decision to postpone the invasion in order to allocate more resources for the USSR invasion. Had they put pressure another week or so, RAF would throw the towel ,luckily Germans were not aware of this


If you really think this is the case I suggest you read any one of the hundreds of books on the BOB and you might learn something.

In brief the Luftwaffe totally failed in their bid to dominate the skies, they were out of ideas, planes and most importantly pilots.

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## GregP (Nov 16, 2013)

I’ve been reading this thread with some interest. As some of you may know, I worked in a shop specializing in Allison overhauls for a year and a half. Let’s look at a real-life comparison of 2-stage engines.

1942: Brits were flying the Spitfire IX was flying with a Merlin 61 with 1,560 HP in low gear and 1,370 HP in high gear. The P-63 was flying an Allison V-1710-93. 1,825 HP max and 1,180 HP mil. Advantage Allison at max power and Merlin at mil power.

1943: The Brits were flying the Spitfire XIV with a Merlin 266 with 1,705 HP max and 1,580 HP mil. The P-63 was flying with an Allison V-1710-117 making 1,800 HP max and 1,100 mil. Same advantage to each. The P-51B/C was flying a Merlin V-1650-3 at 1,600 HP max and 1,330 mil.

1944. The P-51D/K were flying a V-1650-7 at 1,720 HP max and 1,505 mil. The P-51J was flying an Allison V-1710-119 at 1,900 HO max and 1,200 Hp mil. Same advantage to each.

Late war: The P-51H was flying with a V-1650-9 at 1,830 HP max at sea level and 1,400 mil at 13,750 feet. The P-82 was flying with an Allison V-1710-143 at 2,250 Hp max at sea level and 1,700 HP at 21,000 feet, ands 1,250 Hp mil at 32,7010 feet.

From the real-life numbers, the 2-stage engines seem pretty comparable with the advantage going to Allison at high power and mostly the Merlin at mil power, but switching to the Allison both places late in the war.

I would fly behind either anytime, and really have no real preference except I am MUCH more familiar with the Allison, having worked on overhauling them for some time. Nothing against the Merlin. It was and remains a fine engine, whether of British or US manufacture. I have NO data that show the American or British versions had significantly different times between overhaul from one another. 

So was and IS the Allison a very good engine.

Both were 250 - 450 hour engines between overhauls during the war. Today, Allisons last longer if operated by the book, but both give good service for the money. Neither owner would be dissatisfied, but the Allison owner would spend less money. Neither are high-altitude engines today and neither ever get to max power since the gasoline they use today isn't of the 120+ octane variety.

Both very good powerplants and the Merlin certainly earned it's laurels in WWII as a first-class engine. In my view, the Allison also earned a good reputation, being employed in generally lower performance airframes and the government never funded an integral 2-stage supercharger, so teh aux-stage unit was a cobbled-together stopgap. In the field, however, the Allison held a tune better and was tougher. Altogeter a pretty even exchange with the Merlin being the engine that got most of the glory.

Bravo Rolls-Royce and thanks to Allison. We needed you both.


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## Milosh (Nov 16, 2013)

> 1942: Brits were flying the Spitfire IX was flying with a Merlin 61 with 1,560 HP in low gear and 1,370 HP in high gear. The P-63 was flying an Allison V-1710-93. 1,825 HP max and 1,180 HP mil. Advantage Allison at max power and Merlin at mil power.
> 
> 1943: The Brits were flying the Spitfire XIV with a Merlin 266 with 1,705 HP max and 1,580 HP mil. The P-63 was flying with an Allison V-1710-117 making 1,800 HP max and 1,100 mil. Same advantage to each.
> The P-51B/C was flying a Merlin V-1650-3 at 1,600 HP max and 1,330 mil.
> ...



Not at 20,000ft+ Greg. V-1650s using 150 octane were just over 2000hp.

Spitfire XIV used a R-R Griffon engine not a PM 266 which powered late war production Spitfires, ie the Mk XVI


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## GregP (Nov 17, 2013)

Yup it WAS the XVI, not the XIV ... typo, thanks!

The dash numbers I quoted are close ... the Merlin 266 made 1,720 HP, not 1705 ... my fault.

Yes there were a few Merlin over 2,000 hp, not the dash numbers I quoted.

The entire point is the two engines were quite comparable in both single and two-stage variants. The US government declined an integral 2-stage Allison development at least twice and the two-speed part also needed funding, but Allison was funded to produce the engine dash numbers specified in the contracts, not for new developments. No funding equals no new devlopments in small firms, and Allison WAS a small firm. They exhausted their internal funding the development of the V-1710 to start with and were scrambling to ramp up for production. They made it with little to spare. New machining equipment was and is expensive.

The USAAC specified the turbo for mhigh altitudes, not Allison. Left to their own devices, I don't know which boost type they would have gone with, but the funds for it were apparently not there at the time. No funding equals no new product development, even today.


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## Shortround6 (Nov 17, 2013)

> I’ve been reading this thread with some interest. As some of you may know, I worked in a shop specializing in Allison overhauls for a year and a half. Let’s look at a real-life comparison of 2-stage engines.



OK, Lets do that.



> 1942: Brits were flying the Spitfire IX was flying with a Merlin 61 with 1,560 HP in low gear and 1,370 HP in high gear. The P-63 was flying an Allison V-1710-93. 1,825 HP max and 1,180 HP mil. Advantage Allison at max power and Merlin at mil power.



"XP-63A flew for the first time on April 26, 1943" that is with the Allison V-1710-93 First flight of an XP-63 with an Allison V-1710-47 was December 7, 1942. 




> Late war: The P-51H was flying with a V-1650-9 at 1,830 HP max at sea level and 1,400 mil at 13,750 feet. The P-82 was flying with an Allison V-1710-143 at 2,250 Hp max at sea level and 1,700 HP at 21,000 feet, ands 1,250 Hp mil at 32,7010 feet.



Late war? late indeed, first flight of an Allison powered P-82 was February 17, 1947. "At the time of V-J Day, 555 P-51Hs had rolled off the Inglewood production lines."

The Allison does get short shrift many times that it in no way deserves. The Allison company, it's engineers and workers ( and GM) deserve much more credit for it's development and manufacture than is usually given them.


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## Hop (Nov 17, 2013)

> Merlin didnt save Britain in WW2,it was German's decision to postpone the invasion in order to allocate more resources for the USSR invasion..Had they put pressure another week or so, RAF would throw the towel ,luckily Germans were not aware of this !



At no point were the RAF a week away from defeat. On the morning of the 7 September, hours before the Luftwaffe switched the bulk of their attack to London, the heads of Fighter Command held a meeting to discuss their strategy to hold out for the next few months. There was no talk of imminent collapse.

It was the Luftwaffe who faced defeat, although they didn't know it. The Luftwaffe began their main campaign on 13 August. Serviceable, operational aircraft on that date:

Jagdgeschwader (single engined fighters) - 853
Zerstörergeschwader (twin engined fighters) - 189
Kampfgeschwader (bombers) - 1,008
Sturzkampfgeschwader (dive bombers) - 286

RAF Spitfires and Hurricanes - 579
Blenheims, Gladiators and Defiants - 99

On 7 September the Luftwaffe switched to attacks on London. Strength on that date:

Jagdgeschwader (single engined fighters) - 658
Zerstörergeschwader (twin engined fighters) - 112
Kampfgeschwader (bombers) - 798
Sturzkampfgeschwader (dive bombers) - 133

RAF Spitfires and Hurricanes - 621
Blenheims, Gladiators and Defiants - 73

As you can see, in the 4 weeks the Luftwaffe concentrated attacks on the RAF, Luftwaffe strength fell, RAF strength increased slightly.

At no point were the Luftwaffe "winning". The Luftwaffe were incapable of carrying on the battle in the way they fought in August and early September, which is one of the main reasons they switched to attacks on London.

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## DerAdlerIstGelandet (Nov 17, 2013)

renegate326 said:


> You Brits are really funny in inventing fantasies instead of sticking to facts..



And what are you French known for?


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## GregP (Nov 17, 2013)

OK Shortround, let’s look at it.

The Bell XP-63’s, S/N’s 41-19511 and 41-19512, first flew on 7 Dec 1942 with the V-1740-47 engine fitted with an auxiliary supercharger. I’ll grant it didn’t last that long, suffering a gear up landing in late Jan 1943 … but it did make very good power at high altitude. When you are talking about the October delivery of the P-63 you are talking about service delivery, not when it was flying. Getting planes into service usually took the USA some 9 - 12 months after planes were flying here in the States. The auxiliary-stage (2-stage) Allisons made good power up high. I wish they had incorporated an integral 2-stage supercharger, but that was not to be.
The multi-speed part was achieved in the aux stage with a variable hydraulic speed coupling, but the integral supercharger in the engine accessory case never got multi-speed capability.

The XP-82 did fly in June 1945, but it flew with Merlin engines. Since the British were increasing the license fees for the Merlin, that wasn’t something that ever going to last and it didn’t. The Allison engine F-82 flew 17 Feb 1947, but 1948 was when they reached operational service. Might have been much sooner, but wartime priority and pressure was greatly reduced on VJ day.

Allison development was effectively halted in late 1945 except for the P-82 engines (-143 / -145) and Allison largely concentrated on jet engines from then forward.

In the end, the Allison did have some issues and the government wasn’t seemingly all that willing to have them worked out because they didn’t fund a lot of things that would have improved performance and possibly speeded development. I have seen that in other products the US procured as well. Take a good look at the F-111 project and you see another case of government meddling that resulted in many problems.

I like both the Merlin and the Allison today and only wish they could be maintained in running condition longer than will probably prove possible. Parts sources are getting very scarce. It would be nice to see one or both of these engines reproduced or modified with fuel injection and modern ignition technology. Maybe then we’d see the reliability potential of both designs.

One quote from Don Wright, a F-82 field service representative states, “It was an electrician’s nightmare, and it wasn’t the fact that the engines wouldn’t lift the airplane off or fly it. Rather you could never keep it in commission. All of the systems in there were all of the latest electronic advancements from the labs. This was done in a period when the labs at Wright Field put all these requirements into this airplane. It was just a mess all of the time, we had water injection for takeoff, we had WER, and we had a speed density pump instead of a carburetor. Really though the problem with the airplane was to get it to stay in commission. I don’t know the percent of time the engines caused it to be out of commission, but it always seemed to be due to the electronics.”

Note Don Wright was a North American Field Service Representative, not an Allison representative. I’d like to find those data myself, just out of curiosity, but it is unlikely at this late date and it is what it is.


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## tomo pauk (Nov 17, 2013)

The 1st trials of the Merlin 61 in a Spitfire were conducted in Jan 6th 1942, ie. almost a full year before the XP-63 flew. The V-1710-47 (or E-9, used on the XP-63) were not cleared for the WER, military power was 1100 HP at 21000 ft, 1325 HP for TO. Merlin 61 was not just earlier in the fray, it was making better power.
The next 2-stage V-1710 in use, the E-11* (V-1710-93) was used on XP-63A (as SR6 stated, 1st flew in late April 1943) and P-63A, was good for 1150 HP at 22400 ft, 1325 for TO. The WER power (dry) was how much, 1200 HP at 20000 ft, under 1500 HP at SL? Again, the Merlin 61 of 1942 vintage beats it, the newer Merlins (66 and 70, flight tested in November 1942, in use from summer of 1943, also the 63) further move the goal post. The 1st production P-63A was delivered at October 1943, the 1st production (not prototype!) P-51B is flown on May 5th 1943. The introduction of water injection to the P-63 will boost the power, but that will be felt between SL (1800 HP+ there) and ~22000 ft, or about the same as 'low level' Merlin 66 (1,710 HP @ 8,500 ft and 1,520 HP @ 21,000 ft; thanks, Mike).

Where the plane with 2 stage V-1710 in the same time looses and captures some ground is that it lacks the intercooler - less drag, but also less power. Above 20000 ft, and availability-wise, the 2-stage Merlin held the upper hand at least until VJ day.

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## fastmongrel (Nov 17, 2013)

RAF Army Co-operation squadrons absolutely loved there Alison engined Mustangs I II and kept them running till the spares ran out. Apparently there wasnt much that could stick with the Allison Mustang at low level even in 45 when the airframes must have been getting quite tired.

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## GregP (Nov 17, 2013)

Hi Tomo,

The Merlin had the high-altitude upper hand when the Allison was run at 60" MAP while the Merlin went higher. I'll give you that one. The Merlin 66 was cleared at the time for +18.00 psi, which was 66+ inches of Mercury.

I'd really love to get ratings at equal boost and altitudes!

We KNOW from interviews that US pilots may times flew Allisons at 75 inches of boost ... and later variants were cleared for 90 inches, but the official ratings during most of the war were at 57 inches. That is what is normally in print at the time.

There are WAY too many comparisons where the indigenous engine is allowed to run higher boost while the engine being compared was limited to some arbitrary number. In my view, if you want a real comparison, run them at the same boost, but that's just my opinion.

In any case, both engines served with distinction.


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## tomo pauk (Nov 17, 2013)

> GregP said:
> 
> 
> > Hi Tomo,
> ...


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## GregP (Nov 17, 2013)

I've never heard anything bad about the DB 601/3/5 engines except that there are so few left around ... except that many Luftwaffe pilots witnessed post war the ease with they could started with an electric starter, and wished fervently they had those in WWII in their Messerschmitts. Instead, they got by with the mechanics doing the hand-crank ineretia starting task. On cold mornings this could be a real chore! At least I have heard that from former Luftwaffe mechanics.

I have no data on the times between overhauls for Axis engines, but I suspect they were somehwat shorter early in the war due mainly to being operated from farmer's fields more often than Merlins and Allison were for a large part of the early war. The off-airport operation was probably about equal in the late 1943 through 1944 time frame and was probably more for the Allied engines than the German engines in 1945 as the Allies advanced and the Germans returned to home airfields. This is pure conjecture on my part, but few WWII fighters ran an air filter and fields could be quite dusty as planes took off. 

Dust SHOULD mean lower TBO times when operating without an air filter.


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## EKB (Dec 5, 2015)

I know this is an old thread but I just found it while searching for something else. 




> What was the Allison's performance in 1938? Also, there's the challenge of securing export for the Allison in 1939 and enabling licence-building of the engine in the UK.




A horsepower graph for the V-1710-33 (C15), dated 5th December 1939, reads:

1,690 b.h.p. at Sea Level (61.0”Hg)
1,480 b.h.p. at 4,000 feet (54.0”Hg)
1,310 b.h.p. at 8,000 feet (48.0”Hg)
1,100 b.h.p. at 12,500 feet (40.0”Hg)
1,000 b.h.p. at 15,500 feet (36.0”Hg)
840 b.h.p. at 20,500 feet (30.0”Hg)
700 b.h.p. at 25,000 feet (24.1”Hg). 

All brake horsepower readings at 3,000 r.p.m. Supercharger gear 8.77:1.

The pre-war Air Corps restriction was 40.0”Hg. That was soon dispensed with in the combat zones. P-40 pilots of 3rd Squadron/AVG had the engines set-up to run at 58.0”Hg (1,600 b.h.p.) and this was within a few months of the Pearl Harbor attack. Some pilots asked the crew chiefs if they could get 62.0”Hg, which meant overspeeding the engine to about 3,200 r.p.m. 

The source is *Vees For Victory! : The Story of the Allison V-1710 engine 1929-1928.* by Daniel Whitney, p.124.





> the Allison lacked altitude performance which was vital for 1940 because it didn't have the 2-stage supercharger as discussed previously in the thread.




You exaggerate the differences between Rolls Royce and Allison.

The Merlin III (standard Spitfire engine in 1940) was rated for medium altitude and produced only 500 b.h.p. at 30,000 feet. The Merlin 45 (standard Spitfire engine from 1941-1943) developed about 700 b.h.p. at 30,000 feet. That information is found on the engine horsepower graph published by the Rolls Royce Heritage Trust.

A USAAF horsepower graph for P-51 serial 41-37320 shows the Allison V-1710-39 engine produced 500 b.h.p. at 32,000 feet (8.80:1 supercharger gear). The horsepower graph for P-40N serial 42-9987 says that the V-1710-81 engine produced 700 b.h.p. at 30,000 feet, due to a higher gear ratio of 9.60:1. 

The Merlin III had a low supercharger gear ratio of 8.58:1, which makes it obvious that high altitude power was not a major priority until after the Battle of Britain. 

Single-stage Merlin engines that followed had a higher gear ratio of 9.089:1. Some had a larger diameter rotor for high flying and others had a smaller “cropped” rotor for increased low level power. There is more about this in *The Merlin in Perspective - the combat years* by Alec Harvey-Bailey.

Two-stage supercharged Merlin engines were not available in 1940, so I don’t understand why you penalize Allison for not having what Rolls Royce itself could not provide. Let’s not forget that the U.K. and British industry were on war footing in 1939, while Allison and its suppliers worked within a peacetime economy until 1942. 





> If the early Mustangs couldn't hack the altitudes at which Fighter Command expected to operate, how would fitting an earlier version of the same engine to a Hurricane or a Spitfire in 1940 have improved things for the RAF in the BoB




Do not confuse engine power with loaded weight of airplanes. A P-51 fitted with a Merlin III would not climb higher or faster than it did with the V-1710-39. A P-51A fitted with a Merlin 45 would not climb higher or faster than it did with the V-1710-81. 

A more direct way of comparison would be: add 2,000 lbs. of ballast to the Spitfire Mk I (to match normal combat weight of a Mustang Mk I or Kittyhawk Mk I) and then pit them against each other in climbing trials. 





> So why were the Allison-powered Mustangs relegated to Army Cooperation tasks?




Why were so many Spitfires relegated to Army Cooperation tasks? 

In January 1944, 18 of 23 Spitfire IX squadrons on English bases were assigned to 2nd Tactical Air Force. The British home islands still contained 27 squadrons equipped with the Spitfire V, with more overseas, even though this type had been obsolete for two years.

By June 1944, most of the Spitfire IXs had the Merlin 66 and most of the Seafires had a Merlin 32 or Merlin 55M. Those engines were not geared for high altitude performance. 





> The Allison was a good engine but in no way was it ready for the combat environment of the BoB.




A Spitfire with the Allison engine would probably out-climb the Merlin III version to 20,000 feet. The Merlin engines cut out in negative-g combat; while the Allison and Daimler Benz engines did not. The V-1710 would have been more than sufficient during the Battle of Britain. But only if we nose dive into a fantasy world where it was politically acceptable for the 1930s British government to develop the Hurricane and Spitfire with foreign made aero engines.


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## EKB (Dec 5, 2015)

> If we English had only the Allison I would be speaking German. The Merlin is more than just another aero engine it represents our identity. It powered most of the significant WW2 aircraft and secured our liberty. The Merlin was used in tanks, bombers, fighters and air-sea rescue craft. A fantastically versatile engine with all the best heritage of British engineering.




Except that French engineering devised the two-speed supercharger drive. Rights to copy the Farman design were bought and paid for by Rolls Royce and that is what raised the Merlin engine from mediocrity. 

Without the French Connection, the Merlin 20, 60, 70, 80 and 100 series would not exist. The Packard V-1650 series (which in turn copied the basic design of the Merlin 20, 60 and 100 series) would not exist.





> The supercharger design gave it the edge and all I was trying to say that in wartime that 'edge' was all that mattered. The Allison was a good motor handicapped by the US militaries misunderstandings.
> 
> Moral? Leave it to the engineers !!




_Vive la France!_





> WW2 started in 1939 and British liberty was at its greatest peril in the early years of the war. There is an earlier post about the 1930's need to develop more advanced aircraft in Europe. A lot of development this passed America by as you were simply not involved.




Allison played to its audience in the same manner as Rolls Royce. The U.S. Army Air Corps wanted turbo boost for high-altitude flying, e.g. P-38, P-47, B-17, B-24 and B-29. For the P-38 the USAAF preferred low gear ratios on the internal supercharger because that made the Allison engine more efficient and powerful at low altitude. 





> I must admit that I had always thought that liquid cooling was preferable for internal combustions engines as it provided a more stable temperature and therefore allowed the engine to develop more power and reliability.
> 
> No, with respect, the Merlin was the most successful aero-engine, its not all about being English either.




The true acid test for aero engines is the civilian market, where the main goals are safety, dependability and profit. Liquid-cooled engines like the Merlin, Griffon and Sabre were not successful commercially. 

Moreover a Lancaster or Stirling bomber with four turbo-supercharged R-2800 engines would easily out-lift, out-climb, and out-pace those with Merlins or Hercules II engines.





> Why would anyone prefer am Allison to a Merlin?




Because they wanted to go very fast below 15,000 feet. In July 1942 sixteen Mustangs of No. 2 Squadron flew a sweep into the Ruhr. This was the first time that Allied single-engine fighters (armed with guns, that is) violated German airspace and all planes returned. 

Had they preferred to do this job with Spitfires, it would have been a one way ticket.


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## thedab (Dec 5, 2015)

EKB said:


> Except that French engineering devised the two-speed supercharger drive. Rights to copy the Farman design were bought and paid for by Rolls Royce and that is what raised the Merlin engine from mediocrity.
> 
> Without the French Connection, the Merlin 20, 60, 70, 80 and 100 series would not exist. The Packard V-1650 series (which in turn copied the basic design of the Merlin 20, 60 and 100 series)
> 
> except thats for a two-speed and not for a two-stage


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## Capt. Vick (Dec 5, 2015)

It was named after a girl?

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## tomo pauk (Dec 5, 2015)

Since were unlikely to hear much from Readie for the time being:



EKB said:


> ...
> A horsepower graph for the V-1710-33 (C15), dated 5th December 1939, reads:
> <snip>
> All brake horsepower readings at 3,000 r.p.m. Supercharger gear 8.77:1.
> ...



The book states at pg. 119 that V-1710 C15 engines were downrated in good deal of 1941 in the USAF service to 2770 rpm max, thus making only 950 HP at 8000 ft, military power. The so-called modernized V-1710 C15s were outfitted with stronger crankcase and bearings. 
Compared with the unauthorized overboosting, and thus risky for both pilots and aircraft, the Merlin III have had authorised boosting to +12 psi (54.3 in Hg) already in 1939 (1938?) and +16 psi (62.5in Hg!) for Sea Hurricane, mid 1941, respective powers of 1300 and 1440 HP. The Allison and USAF were plenty late with WER ratings, took them until mid 1942 to come out with that officially.
The Merlin III still beats the C15 in altitude power, albeit not by much.




> The Merlin III (standard Spitfire engine in 1940) was rated for medium altitude and produced only 500 b.h.p. at 30,000 feet. The Merlin 45 (standard Spitfire engine from 1941-1943) developed about 700 b.h.p. at 30,000 feet. That information is found on the engine horsepower graph published by the Rolls Royce Heritage Trust.
> 
> A USAAF horsepower graph for P-51 serial 41-37320 shows the Allison V-1710-39 engine produced 500 b.h.p. at 32,000 feet (8.80:1 supercharger gear). The horsepower graph for P-40N serial 42-9987 says that the V-1710-81 engine produced 700 b.h.p. at 30,000 feet, due to a higher gear ratio of 9.60:1.



Horsepower at 20000 ft:
-Merlin III: 890; in service in 1937
-V-1710-33 (C15): 860; in service in 1940 (similar for -33, or F3R engine)
-Merlin XX: 1060 HP; in service in mid 1940
-Merlin 45: 1120; in service in winter of 1940/41
-V-1710-81 (F20R): 950; in production from mid 1942

Bared the aplication of magic dust, there is no way that V-1710 will beat the Merlin in altitude power.

Where the V-1710 might come ahed is the injection carb vs. float carb used in early Merlins, not just for allowing a quick negative G maneuver, but for being less restricting for airflow.



> The Merlin III had a low supercharger gear ratio of 8.58:1, which makes it obvious that high altitude power was not a major priority until after the Battle of Britain.
> Single-stage Merlin engines that followed had a higher gear ratio of 9.089:1. Some had a larger diameter rotor for high flying and others had a smaller “cropped” rotor for increased low level power. There is more about this in *The Merlin in Perspective - the combat years* by Alec Harvey-Bailey.



Merlin III was a single speed supercharged engine, the gear ratio employed is 'high', rather than 'low'; if there was a high altitude engine in 1937-40 that was the Merlin III. The early merlin variant with 'low' supercager gearing was the VIII, used on Fulmar. 
The gearing does not tells the whole story - Merlin III, VIII, XX and 45 employed the supercharger with impeller of 10.25 in diameter, vs. most of the V-1710s with 9.5 in (as with the 'cropped' Merlins). Coupled with the size of whole intake section that was far bigger in Merlin, the better altitude performance should not came as a surprise. 
Merlin 46 and 47 were with 10.85 in impeller, no wonder they were making 1100 HP at 22000 ft (but with less power down low). 



> Do not confuse engine power with loaded weight of airplanes. A P-51 fitted with a Merlin III would not climb higher or faster than it did with the V-1710-39. A P-51A fitted with a Merlin 45 would not climb higher or faster than it did with the V-1710-81.



The P-51 with Merlins would've been better in speed and climb at altitude than with V-1710s. The Merlin XX and 45 were in volume production before the V-1710-39, and it the -39 can't compete with either Merlin. An 1/4 of power surplus matters. 
The -81 is two years too late, it just managed to best the the pre-war Merlin III, it still has 10% less power than the XX or 45. 



> By June 1944, most of the Spitfire IXs had the Merlin 66 and most of the Seafires had a Merlin 32 or Merlin 55M. Those engines were not geared for high altitude performance.


 
The Merlin 66 was better in altitude work than BMW 801D or DB 601A. If one does not want the 66, the 63 and 70 series are available in 1943, unlike the two-stage V-1710 with similar power.


> A Spitfire with the Allison engine would probably out-climb the Merlin III version to 20,000 feet. The Merlin engines cut out in negative-g combat; while the Allison and Daimler Benz engines did not. The V-1710 would have been more than sufficient during the Battle of Britain. But only if we nose dive into a fantasy world where it was politically acceptable for the 1930s British government to develop the Hurricane and Spitfire with foreign made aero engines.



The Merlin was a workable engine 3 years before the V-1710. Waiting for the V-1710 will do to the RAF same as if we delete the Chain Home, or worse.
The situation in the USA was that both R-2800 and license produced Merlin were wanted, in case the V-1710 ends up as a flop.




> Because they wanted to go very fast below 15,000 feet. In July 1942 sixteen Mustangs of No. 2 Squadron flew a sweep into the Ruhr. This was the first time that Allied single-engine fighters (armed with guns, that is) violated German airspace and all planes returned.
> Had they preferred to do this job with Spitfires, it would have been a one way ticket.



What you've said has everything to do with Mustang, not with V-1710 supposedly being better than Merlin.

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## gjs238 (Dec 5, 2015)

Capt. Vick said:


> It was named after a girl?



Grumman named it's machines after women as well: F4F, F6F


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## fastmongrel (Dec 5, 2015)

EKB said:


> The true acid test for aero engines is the civilian market, where the main goals are safety, dependability and profit. Liquid-cooled engines like the Merlin, Griffon and Sabre were not successful commercially.
> 
> Moreover a Lancaster or Stirling bomber with four turbo-supercharged R-2800 engines would easily out-lift, out-climb, and out-pace those with Merlins or Hercules II engines.
> 
> .



Acid test ???? what on earth does a post war Passenger plane have to do with building fighter engines. How many post war transport planes used V1710s.

As for a Lanc with Turb R2800s being a better performer. Well of course it would be an R2800 has 70% greater swept volume than a Merlin and has a Turbo. Good luck getting a production R2800 turbo version much before 1943.


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## tomo pauk (Dec 5, 2015)

tomo pauk said:


> ...
> Bared the aplication of magic dust, there is no way that V-1710 will beat the Merlin in altitude power.
> ...



That works for listed engines, of course.

The 2-speed drive was licensed from Farman indeed, and it was applied in Merlin X before shooting started. The 1st production V-1710 with more than one S/C speed was available in second half of 1943, ie. some 4 years later.


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## EKB (Dec 5, 2015)

tomo pauk said:


> Since were unlikely to hear much from Readie for the time being:
> 
> 
> 
> ...




The United States was not at war until the last three weeks of 1941, so the "not by much" comment is hardly a good way to frame the real or imagined advantages of the Merlin engine.

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## tomo pauk (Dec 6, 2015)

Please, don't get me wrong - having the V-1710 in production and in service was a major boost to the Allied cause in ww2. The V-1710 was in combat before the USA entere the war, so a comparison with Merlin (or other engine in the time frame) is a valid one IMO. And in that comparison the V-1710 comes out as second best. Further, the USA have had in production, in winter of 1941/42, better engines than the V-1710.


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## fastmongrel (Dec 6, 2015)

EKB said:


> The United States was not at war until the last three weeks of 1941, so the "not by much" comment is hardly a good way to frame the real or imagined advantages of the Merlin engine.



Comparing a MkIII Merlin to a V1710-C15 you must take into account that the MkIII had gone into service in 1937 and was being replaced in service by the MkXII and MkXX Merlins around the turn of 1940/41. I cant find when the III went out of production but it must have been roughly the same time the Spit I and Hurri I went out of production in late 1940. Using 100 Octane, continuous +12 psi boost in the XII and continuous +14psi boost in the XX they were both producing in the region of 1,400 hp at full throttle height. In Jan 1941 the 40 series engines came along and they could run +16 psi boost and were producing 1500hp at FTH.

None of this is to denigrate the superb Allison the RAF Tactical Squadrons loved there Allison engined Mustang MkIs and kept them going till spares ran out in 1945 when the airframes must have been worn out. The fact is the non Turbo Allison was always behind the curve when compared to the Daimler Benz and Rolls Royce engines when it came to altitude performance. This wasnt Allisons fault they built what the customer and owner of the engine the USAAC wanted. 

If the USAAC had wanted a mechanically supercharged V1710 with the same or better performance at high altitudes than the RR Merlin or DB 601/605 I am sure they could have built it.

The DB 601/5 series and RR Merlin series ran neck and neck from 1935 to 1945 never able to get the better of each other the non turbo Allison was second all the way there might only have been a length in it but it was still paying place odds nearly all the time.


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## tomo pauk (Dec 6, 2015)

fastmongrel said:


> ...
> If the USAAC had wanted a mechanically supercharged V1710 with the same or better performance at high altitudes than the RR Merlin or DB 601/605 I am sure they could have built it.



Very true. The Alllison company was proposing the 2-stage supercharged V-1710 already in 1938, the USAAC was not interested.



> The DB 601/5 series and RR Merlin series ran neck and neck from 1935 to 1945 never able to get the better of each other the non turbo Allison was second all the way there might only have been a length in it but it was still paying place odds nearly all the time.



The DB 601 and Merlin indeed went neck and neck. The DB 605, on the other hand, developed considerably less power than the 2-stage supercharged Merlin of the same era for some 2 years, catching up in mid 1944 with DB 605ASM.
The 2-stage V-1710 catched up with DB 605A by mid 1944. (*no, second half of 1943*)
With that said, too bad there was no in-service single engined fighter made in USA with turboed V-1710.


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## gjs238 (Dec 6, 2015)

fastmongrel said:


> the RAF Tactical Squadrons loved there Allison engined Mustang MkIs and kept them going till spares ran out in 1945 when the airframes must have been worn out.



The Allison engined Mustang MkIs must have blown away the similarly powered P-40's.
And V-1650-1 powered Mustang MkIs also would have blown away the similarly powered P-40F's and P-40L's.
Gotta wonder (dream) if Allison engined Mustang MkIs could have/should have replaced P-40's and P-40 production ended sooner.

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## fastmongrel (Dec 6, 2015)

gjs238 said:


> The Allison engined Mustang MkIs must have blown away the similarly powered P-40's.
> And V-1650-1 powered Mustang MkIs also would have blown away the similarly powered P-40F's and P-40L's.
> Gotta wonder (dream) if Allison engined Mustang MkIs could have/should have replaced P-40's and P-40 production ended sooner.



Hi gjs it was the Mustang MkIII with the V1650 motor. 

I have read that the Tactical boys ran their Allisons all day at sea level on 130 octane and +18 pounds of boost and the engines took it and came back for more. There was talk of trying the Allison engined MkIs on 150 octane and as much as +25 pounds of boost and sending them on Diver operations against V1s but by that time they were considered too old for it to be worthwhile modifying the engine. They were also reckoned to have less vibration than a Merlin though someone once told me that was the Supercharger drive not the engine. Dont know enough about that to say yes or no personally.

I have found vibration and noise to be more a factor of engine mounting and auxillaries like water pumps, alternators, fuel pumps and blowers than engine design. For example at work we have two 4 cylinder diesel engined cars virtually the same capacity and power but the Ford ticks over like a swiss watch and the Vauxhall (actually an Isuzu engine) ticks over like a piston is about to make a break for freedom. The Ford has a short auxillary belt that runs the Alternator and the Air con pump. The Isuzu has an auxillary belt half a mile long that runs the Alernator, Water pump, Air con pump, and the power steering pump.


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## tomo pauk (Dec 6, 2015)

gjs238 said:


> The Allison engined Mustang MkIs must have blown away the similarly powered P-40's.
> And V-1650-1 powered Mustang MkIs also would have blown away the similarly powered P-40F's and P-40L's.
> *Gotta wonder (dream) if Allison engined Mustang MkIs could have/should have replaced P-40's and P-40 production ended sooner.*



A definite 'yes', the V-1650-1 in Mustang would've made for an excellent aircraft for 1942/43.


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## EKB (Dec 6, 2015)

tomo pauk said:


> The V-1710 was in combat before the USA entere the war, so a comparison with Merlin (or other engine in the time frame) is a valid one IMO.




On pg.332, Dan Whitney quoted USAAF statistics which shows that the Packard Merlin finished dead last in reliability, with the shortest engine life and highest maintenance hours between overhauls as compared to the Allison V-1710 and Pratt Whitney R-2800.





tomo pauk said:


> And in that comparison the V-1710 comes out as second best.




Do you have numbers to validate this, or are you just floating the idea?





tomo pauk said:


> The so-called modernized V-1710 C15s were outfitted with stronger crankcase and bearings. Compared with the unauthorized overboosting, and thus risky for both pilots and aircraft, the Merlin III have had authorised boosting to +12 psi (54.3 in Hg) already in 1939 (1938?) and +16 psi (62.5in Hg!) for Sea Hurricane, mid 1941, respective powers of 1300 and 1440 HP. The Allison and USAF were plenty late with WER ratings, took them until mid 1942 to come out with that officially.




Comparing peacetime restrictions with wartime restrictions offers no proof that Rolls Royce Merlins were less troublesome.

Single piece Merlin cylinder blocks cracked and leaked from high boost pressures and so did two piece engine blocks intended to correct that problem. Wartime experience also showed weaknesses in connecting rods, main bearings, pistons, valves, lubrication points, supercharger drives, magneto gears, and of course carburettors. 

Failures of the supercharger clutch and friction plates gave ongoing problems that continued into the Griffon series. In 1946, all deck-landings of the Seafire Mk XV were prohibited until Rolls Royce re-designed the supercharger unit.

High dust conditions caused the failure of many Rolls Royce engines. Ginger Neil of No. 249 Squadron said that he went through five engines in eight weeks on Malta, even though the Merlins were “almost brand new”.





tomo pauk said:


> TThe -81 is two years too late, it just managed to best the the pre-war Merlin III, it still has 10% less power than the XX or 45.




My sources show that at 30,000 feet, the output of all three engines is approximately 700 b.h.p. More importantly, Allison could not build the V-1710-81 until the customer asked for it. Buyers dictate requirements to the engine maker, not the other way round as your reply suggests.





tomo pauk said:


> Merlin III was a single speed supercharged engine, the gear ratio employed is 'high', rather than 'low';




Alec Harvey-Bailey worked at Rolls Royce and his definition (p.14) does not agree with yours …

_“ The Merlin came to the forefront in the air fighting during the Dunkirk period and subsequently during the Battle of Britain. The engines which carried the brunt of the fighting were basic single stage supercharged types, notably the Mk II and III although some Merlin XIIs in Spitfire IIs with *higher geared superchargers*.”_


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## tomo pauk (Dec 6, 2015)

EKB said:


> On pg.332, Dan Whitney quoted USAAF statistics which shows that the Packard Merlin finished dead last in reliability, with the shortest engine life and highest maintenance hours between overhauls as compared to the Allison V-1710 and Pratt Whitney R-2800.



No problems with that, there was no perfect engines.



> Do you have numbers to validate this, or are you just floating the idea?



I've provided the sources for my nubers that everybody can check out and call me fishy if it's not true.



> Comparing peacetime ratings and wartime ratings offers no proof that Rolls Royce Merlins were less troublesome.
> 
> Single piece Merlin cylinder blocks cracked and leaked from high boost pressures and so did two piece engine blocks intended to correct that problem. Wartime experience also showed weaknesses in connecting rods, main bearings, pistons, valves, lubrication points, supercharger drives, magneto gears, and of course carburettors.



As above - no engine was perfect. The V-1710 received new crankshaft (several times), new reduction gear, new piston rings, new intake manifold (again several times), supercharger drives, carburetors, all in the trying to improve both reliabilty and power. 
BTW, the Merlin III was rated for +12 lbs boost (1300 HP) before the war.



> Failures of the supercharger clutch and friction plates gave ongoing problems that continued into the Griffon series. In 1946, all deck-landings of the Seafire Mk XV were prohibited until Rolls Royce re-designed the supercharger unit.



Should we now compare the Griffon with V-1710?



> High dust conditions caused the death of many Rolls Royce engines. Ginger Neil of No. 249 Squadron said that he went through five engines in eight weeks on Malta, even though the Merlins were “almost brand new”.



Without dust filters. every engine will fail in dusty conditions.



> My sources show that at 30,000 feet, the output of all three engines is approximately 700 b.h.p. More importantly, Allison could not build the V-1710-81 until the customer asked for it. Buyers dictate requirements to the engine maker, not the other way round as your reply suggests.



The V-1710-81, Merlin xx and 45 will still give more at 30000 ft. Thing being that -81 is two years late vs. the Merlin XX and year and a half vs. Merlin 45.
The Allison'sr 1st attempt for increased supercharger gearing (on F14R engine) was unsucessful, per pg. 272 of the Vee's. The F20R (V-1710-81) received wider (hence stronger) drive gears, thus solving the problem. 
My reply didn't suggest that Allison was incapable of coming out with a better performing engine, the US Army squandered plenty of money on the 'hi-per' engines instead funding the V-1710. Power of the V-1710 grew with each year. The thing is that it was a year and a half (give or take few months) behind the Merlin's altitude power levels, when we talk about single- and two-stage engines.



> Alec Harvey-Bailey worked at Rolls Royce and his definition (p.14) does not agree with yours …
> 
> _“ The Merlin came to the forefront in the air fighting during the Dunkirk period and subsequently during the Battle of Britain. The engines which carried the brunt of the fighting were basic single stage supercharged types, notably the Mk II and III although some Merlin XIIs in Spitfire IIs with *higher geared superchargers*.”_



I think that you have misunderstood what Mr. Haryey-Bailey said. The Merlin III was 'geared' at 8.58:1, the XII and 45 were at 9.089:1, less that 5% difference. Both were 'high' geared (same as the V-1710 was 'high' geared whether it employed 8.77:1, 8.8:1 or 9.6:1). Having a gearing that is less than 5% 'faster' does not mean that other gearing is suddenly 'low'. Stating gearing without taking into account the supercharger diamenter is pointless.
For 'low' geared superchargers, please look at Merlin VIII (on Fulmar) and V-1710-87 (F21R, on A-36).

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## Aozora (Dec 7, 2015)

EKB said:


> On pg.332, Dan Whitney quoted USAAF statistics which shows that the Packard Merlin finished dead last in reliability, with the shortest engine life and highest maintenance hours between overhauls as compared to the Allison V-1710 and Pratt Whitney R-2800.



And yet thousands of Packard Merlins were used on P-51B/C/D/K's, Mosquitoes and Lancasters that all flew thousands of long range operations totaling hundreds of thousands of hours. The fact is all three engines were reliable enough for the purpose for which they were built - namely wartime service, often under extremely adverse conditions.



EKB said:


> Single piece Merlin cylinder blocks cracked and leaked from high boost pressures and so did two piece engine blocks intended to correct that problem. Wartime experience also showed weaknesses in connecting rods, main bearings, pistons, valves, lubrication points, supercharger drives, magneto gears, and of course carburettors.



While EKB later quotes from Alec Harvey-Bailey's _The Merlin in Perspective: The Wartime Years_, EKB failed to quote from Harvey-Bailey when H-B explained how Rolls-Royce's continual testing and development overcame the problems that he describes (eg: pages 57, 58 66):



> _Inlet Valves_
> A number of failures occurred in early operations....The tulip failures were cured by stiffening the rim of the valve....The inlet valve clearence was reduced to .010...Sufficient judgement was not given to this decision....Numerous failures occurred due to incorrect clearances....Valves would also occasionally fail from frettage fatigue at the collet location. Phosphor bronze collets were introduced and proved effective...
> 
> _Exhaust Valves_
> The standard valves were made in KE 965 with sodium cooled stems and gave little trouble at military lives but a few casualties were occurring at 420 hrs. Various seating combinations were tried, but in wartime, Brightray on the valve seat and Stellite on the seat in the head gave as good results as any.



I suggest that EKB read and digest the entirety of Harvey-Bailey's book, especially pages 31 to 71, *before* he makes sweeping generalizations about the supposed ongoing "weaknesses in connecting rods, main bearings, pistons, valves, lubrication points, supercharger drives, magneto gears, and of course carburettors." The implication that the Merlin suffered from a large number of ongoing design problems and constant component failure is grossly wrong.



EKB said:


> Failures of the supercharger clutch and friction plates gave ongoing problems that continued into the Griffon series.



Evidence for this would be great.


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## GregP (Dec 7, 2015)

You all know I worked in an Allison overhaul shop for a few years. I love the Allison. We liked to joke that you could fly an Allison farther than you can ship a Merlin.

But the fact remains that the Merlin was and IS a very good engine. Yes, Merlin rods are weaker than Allison rods ... but they don't give up the ghost until somewhat over 2,600 HP, which is more than the engine produced in normal WWII military trim. There are a number of things I don't particularly like about the Merlin, but I'd own either own if I could, and I would expected to get 750 - 1000 hours of use out it before overhaul in civilian service. At the Planes of Fame, we just changed a Merlin in one our P-51D models, and it had a very long and trouble-free lifespan during that time. Yes, you DO have to tighten the head bolts every 25 hours and so forth, but there are normal regular maintenance requirements for any large aviation piston engine.

So despite being a lover of Allisons, I have to say the Merlin earned it's stripes and then some, and richly deserves it's place as one of the great aero engines of all time. Rolls Royce didn't design a perfect engine and neither did Allison, but Rolls also didn't miss by all that much.

The Merlin DID have a shorter overhaul life than the Allison. But overhaul was NOT when the engine broke or wore out. It was when the military decided to swap it for a fresh engine and send the "run out" engine in for an overhaul while it was still in good overhaulable shape. These days, all owners want their pet Allison or Merlin to get 750 - 1000 hours before overhaul, and they mostly DO, assuming a good overhaul. I know many people who are flying Merlins right now with 400 - 700 hours on them and they are running just fine.

If only we had an ongoing parts supply!

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## EKB (Dec 7, 2015)

Aozora said:


> EKB said:
> 
> 
> > Failures of the supercharger clutch and friction plates gave ongoing problems that continued into the Griffon series.
> ...





Commander Mike Crosley, DSC:

_“ The second lethal shortcoming of the Seafire XV was a supercharger fault. The self-change mechanism from one blower speed to the higher speed was similar in action to the automatic clutch and gearbox of a car. When changing blower speeds on the climb, the blower speed of about 15,000 rpm had to be speeded up to 20,000 rpm in a matter of seconds. If the clutch gripped too tightly it would strip the gears. If it gripped too loosely it would burn out. In both failures the engine would lose its supercharger and it would stop, catch fire, misfire or overheat. The only method of avoiding such failures was the engage the gear manually at reduced rpm. This was not always possible, neither did it always work, for there were several fatal engine failures.”_


R. M. Crosley. *They Gave Me a Seafire.* Airlife Books, 1986 (See Appendix 11). 




Aozora said:


> The implication that the Merlin suffered from a large number of ongoing design problems and constant component failure is grossly wrong.





I did not write that. If you have statistics regarding component failures (to back up your opinions) then by all means post it.






Aozora said:


> And yet thousands of Packard Merlins were used on P-51B/C/D/K's, Mosquitoes and Lancasters that all flew thousands of long range operations totaling hundreds of thousands of hours. The fact is all three engines were reliable enough for the purpose for which they were built - namely wartime service, often under extremely adverse conditions.





Please refer to attached chart for engine life and maintenance hour averages for Packard Merlin (V-1650) and other U.S. engines ...


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## tomo pauk (Dec 7, 2015)

Methinks it is realy too bad we don't have the 'master thread' about the V-1710. 
Even if it involves comparisons with other ww2 engines

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## fastmongrel (Dec 7, 2015)

Its a pity the Merlin V1650 was so rubbish. Just think over 150,000 lumps of junk were built over about 12 years and those idiots didnt know they were doing it wrong.

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## rochie (Dec 7, 2015)

fastmongrel said:


> Its a pity the Merlin V1650 was so rubbish. Just think over 150,000 lumps of junk were built over about 12 years and those idiots didnt know they were doing it wrong.



Especially as they put them in that pile of shite, one trick pony the spitfire !


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## Airframes (Dec 7, 2015)

There was a problem with both the Rolls Royce, and Packard Merlin. One didn't have 'Made in the USA' (or Germany!) stamped on it, and the other one did !!

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## Aozora (Dec 7, 2015)

EKB said:


> Commander Mike Crosley, DSC:
> 
> _“ The second lethal shortcoming of the Seafire XV was a supercharger fault. The self-change mechanism from one blower speed to the higher speed was similar in action to the automatic clutch and gearbox of a car. When changing blower speeds on the climb, the blower speed of about 15,000 rpm had to be speeded up to 20,000 rpm in a matter of seconds. If the clutch gripped too tightly it would strip the gears. If it gripped too loosely it would burn out. In both failures the engine would lose its supercharger and it would stop, catch fire, misfire or overheat. The only method of avoiding such failures was the engage the gear manually at reduced rpm. This was not always possible, neither did it always work, for there were several fatal engine failures.”_
> 
> ...



And how does this prove that the Merlin suffered from



> Failures of the supercharger clutch and friction plates...that continued into the Griffon series?





EKB said:


> I did not write that. If you have statistics regarding component failures (to back up your opinions) then by all meanspost it.



So, why did EKB write this:



EKB said:


> Single piece Merlin cylinder blocks cracked and leaked from high boost pressures and so did two piece engine blocks intended to correct that problem. Wartime experience also showed weaknesses in connecting rods, main bearings, pistons, valves, lubrication points, supercharger drives, magneto gears, and of course carburettors.



if not to imply that the Merlin continually suffered from these problems? Otherwise what was the point of writing it?

Considering that the Merlin was being continually developed from a 1,000 hp engine to one able to produce 2,000 hp, it's no wonder that problems would emerge; it's the fact that the problems were solved that's important.




EKB said:


> Please refer to attached chart for engine life and maintenance hour averages for Packard Merlin (V-1650) and other U.S. engines ...



Yes...and?


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## BiffF15 (Dec 7, 2015)

Airframes said:


> There was a problem with both the Rolls Royce, and Packard Merlin. One didn't have 'Made in the USA' (or Germany!) stamped on it, and the other one did !!



So few words that say so much...


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## thedab (Dec 7, 2015)

got it wrong


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## EKB (Dec 7, 2015)

Aozora said:


> And how does this prove that the Merlin suffered from So, why did EKB write this:
> 
> 
> 
> ...




From your latest reply, it’s obvious that you have no idea how many engines suffered “component failures”. Despite your lack of knowing the numbers, you continue to raise and argue that point, for reasons that only you can answer.

If you are so sure of your convictions, maybe you can explain why Rolls Royce would switch to two piece engine block if there were no serious problems with the single piece engine block.

If troubles with the supercharger mechanisms were (supposedly) fixed and perfected with the Merlin, maybe you can give us your take on why these issues lingered with the Griffon engine - and this after World War II ended.


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## FLYBOYJ (Dec 7, 2015)

EKB said:


> Please refer to attached chart for engine life and maintenance hour averages for Packard Merlin (V-1650) and other U.S. engines ...



I've been reading this with some amusement, but for the record I don't have a dog in this fight but I will say you need to show all the charts indicated in your post and keep in mind that this is a CONUS chart and at face value doesn't represent combat conditions. It should also be compared with the number of airframes those engines are "attached" to and the hours those airframes are flown as a fleet.

My 2 cents - the stock market looks good!

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## Aozora (Dec 7, 2015)

EKB said:


> From your latest reply, it’s obvious that you have no idea how many engines suffered “component failures”. Despite your lack of knowing the numbers, you continue to raise and argue that point, for reasons that only you can answer.



 EKB raised the whole "Merlin is so-o-o unreliable vs the Allison" schtick; it's up to EKB to support his own convictions with more than just meaningless, bald statements. In the meantime I suggest EKB read Harvey-Bailey carefully to find out for himself how Rolls-Royce resolved various component failures.



EKB said:


> If you are so sure of your convictions, maybe you can explain why Rolls Royce would switch to two piece engine block if there were no serious problems with the single piece engine block.



I suggest EKB read Harvey-Bailey, pages 55-56 to find out.




EKB said:


> If troubles with the supercharger mechanisms were (supposedly) fixed and perfected with the Merlin, maybe you can give us your take on why these issues lingered with the Griffon engine - and this after World War II ended.



I suggest EKB read Harvey-Bailey, pages 40-45 to find out. The isolated troubles of the Griffon on some Seafires have nothing to do with the Allison V-1710.


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## GregP (Dec 7, 2015)

Just for completeness, here are the data from Table 115 for the Statistical Journal of the USAAF:






These are, as Joe said above, all Continental USA numbers and are somewhat unrelated to engines being operated on the front lines. I'd expect front-line engines to be overhauled either slightly sooner or about the same time since any Merlin or Allison that was running at overhaul hours was running pretty decently. If the engine was being operated on, say, Malta, where Coral dust was so prevalent, it wouldn't make TBO and would be overhaul based on condition rather than overhaul hours.

The Merlins were great engines for high-altitude, long-range flying,and the Allison was developed into one, but wasn't quite there when it was needed. Right when Allison started building the G-series engine and they really made decent power, they started cancelling pistons for jets, and Allison never did get the G-series engines as reliable as earlier Allisons were. For my money a -100 series E-series or F-series engine was the best Allison for the money.

As for the Merlin, it was there, could do the job well if not superbly, was reliable in service, and usually lasted some 35 - 50 mission before needing to be swapped out. That isn't all that bad. Many Merlins were found to be "in spec" when received for overhaul, and the "overhaul" consisted mostly of new bearings, perhaps a valve or two, cleanup of parts, and possibly new supercharger impellers, with possibly a gear or two, depending on inspection. Rods were probably changed on the second or third overhaul regardless of condition. I seriously doubt they wore out many cams or crankshafts. They are stout units. Typical of British engines, they gave some serious attention to ignition systems at overhaul.

But in service, the Merlins were as reliable as any aero engine of the day, and moreso than some.

I can say this. I've worked 8 Planes of Fame airshows. We usually have 30 - 35 WWII aircraft there with a mixed bag of Allisons, Merlins, Wrights, Prats, and a smattering of others. The planes fly for 3 days with about 50 - 65 sorties per day. That's 1200 - 1400 sorties in my airshow years there. We've had maybe 5 - 6 mission aborts in that time with one being a flat tire, one being hydraulic-related (A Corsair could get the wings to come down), and 2 of the aborts were radials. That leaves 1 or 2 aborts for the V-12s, and, as I recall, a P-51D had a run-down battery on one, and the other was a Curtiss-Electric prop on a P-40E that needed brushes.

In my book, that ain't bad considering we have probably about half Merlins there in a typical year.

Above, I'm calling an "abort" a plane that is scheduled to take off and the pilot goes out to it to fly the show and then discovers something wrong. There were a few others that never tried to fly because something was discovered before the scheduled flight. Most of those are not engine-related.

We did have one B-17 have an emergency in flight when he hit a BIG bird. The damage was a hole in the leading edge inboard of the #1 engine, and was not engine-related. He landed safely and flew home on schedule. Who knew a bird had that much blood or that many feathers?

By the way. The Merlin was done in typical British craftsman fashion and the Allison was optimized for production. Consequently the Allison has about 7,000 parts including nuts and bolts and the Merlin has about 11,000 parts. A significant amount of the Merlin labor is dealing with another 2,000+ fasteners, many with pal-nuts! The actual overhaul labor is very similar, but taking a Merlin apart and putting one back together again means handling probably 5,000 more fasteners than for an Allison (apart and back together, both tasks). These are aircraft nuts and don't "spin" off by hand. You use a wrench all the way (no, not a ratchet wrench!), and that takes awhile.

For clarity, it is not really 2,500 more fasteners, it is 2,500 more parts. A fastener was a bolt, a washer, a nut and pal nut or a bolt, a washer, a lock washer, and a nut ... depending on application. Sometimes there were two washers. Then there is the safety wire and/or cotter pins to consider. None are hard to work with, but all take time to place and tighten to spec.

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## EKB (Dec 7, 2015)

FLYBOYJ said:


> I've been reading this with some amusement, but for the record I don't have a dog in this fight but I will say you need to show all the charts indicated in your post




I have a copy of the original source, but which charts are you talking about?


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## tomo pauk (Dec 8, 2015)

The power chart for the V-1710-39, taken from the manual for the Mustang I/Ia (link). My addition is the red rectangle, representing 1200 HP at 18000 ft for the Merlin 45.

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## FLYBOYJ (Dec 8, 2015)

EKB said:


> I have a copy of the original source, but which charts are you talking about?


 See post 257


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## fastmongrel (Dec 8, 2015)

GregP said:


> Malta, where Coral dust was so prevalent, it wouldn't make TBO and would be overhaul based on condition rather than overhaul hours.



I dont know if there are any Coral Reefs on Malta anymore but the Island is made from a fairly soft but incredibly gritty Corraline Limestone with layers of Greensand which is an even grittier soft Sandstone containing lots of mineralised marine life. Both types of dust plus any liquid turns it into something resembling Valve Lapping in compound. 

So yes its Coral dust just 55 million year old Coral dust


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## GregP (Dec 8, 2015)

I took that from WWII operation accounts. Almost all mention dust and several mention coral dust. Whether it is sand or coral, it seems to eat engines for breakfast. I known they had coral dust in the Pacific as I've experienced it myself.

What they really needed in the Pacific were air filters, at least for takeoff, landing and ground operations. Don't believe they ever got them.


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## GregP (Dec 8, 2015)

I took that from WWII operation accounts. Almost all mention dust and several mention coral dust. Whether it is sand or coral, it seems to eat engines for breakfast. I known they had coral dust in the Pacific as I've experienced it myself.

What they really needed in the Pacific were air filters, at least for takeoff, landing and ground operations. Don't believe they ever got them.


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## fastmongrel (Dec 8, 2015)

The Bf109F seemed to have a very good filter that had a flap to divert air when taking off and landing but let the air flow freely when in the air. The early RAF Vokes filter robbed power and speed some Hurricane MkIs in the Med struggled to top 300mph with the Vokes.


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## Aozora (Dec 8, 2015)

I don't think the Mustang I P-51 had dust filters, but they were fitted to the P-51A's carburettor air intake, and the A-36's.
(from the _Manual of Instructions for the P-51A Mustang Fighter Airplane (Contract AC-30479, NAA, August 1 1943)_

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## tomo pauk (Dec 8, 2015)

Very interesting  Are those manuals available for download?


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## Aozora (Dec 8, 2015)

tomo pauk said:


> Very interesting  Are those manuals available for download?



Yep; via membership of Avialogs: Aviation E-Library and more: it's a great resource.

The carby air intake for the A-36 had a different system to that of the P-51A 

(_Erection and Maintenance Instructions for A-36A Airplane _(15 November 1943; revised 25 October 1944)

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## EKB (Dec 10, 2015)

Aozora said:


> EKB raised the whole "Merlin is so-o-o unreliable vs the Allison" schtick;




You need to show us when Mustangs with the Allison engine suffered this many problems:


_“ Operational Diary—1944 [4th Fighter Group] 

*25 February 1944*—The ground crews had their hands full trying to get about 50 Mustangs [P-51B] ready for combat. Before morning all of the kites had been painted in QP, WB, VF livery in anticipation of the first Mustang show the next day.

*26 February 1944*—Weather scrubbed the 4th’s Mustang debut but at least there was time for familiarization …

*27 February 1944*—At 1315 a Rolls-Royce tech representative held a briefing on the P-51. Don Blakeslee held a discussion on flying problems with the Mustang which had been disappointingly numerous. A plague of mechanical gremlins diminished the pilots’ enthusiasm for the new fighter. Jim Goodson, Willard Millikan and George Carpenter had bounced the new paddle-bladed P-47s of the 56th and frustratedly reported that these Thunderbolts were a match for the Mustang upstairs and downstairs. This added to the air of uncertainty.

*28 February 1944*—Maj. Clark led the first Mustang mission, a Free Lance under Type 6 control with two 75-gallon drop tanks under the wings of each kite … Both 334 and 336 got 12 aircraft up while 335 put up 11, but there were several aborts due to mechanical problems …

*29 February 1944*—The P-51’s ugly side reared its head—Mills prop began throwing oil and his wing tanks would not feed; Biel’s cooling system and RT went out Beil's cooling system and R/T went out; Rafalovich could not get enough manifold pressure and his R/T also quit. France, Chatterley and Smith could not catch up with the Group. All six were forced to abort the mission. After everyone got back a bunch of disgruntled pilots went to the briefing room at 1645 to hear a 354th Group pilot talk about mechanical failures with the Merlin engine.

*4 March 1944*—During combat several pilots were hampered by windscreen frost and jammed guns. At 18,000 feet and 550 mph indicated, Ward’s canopy, wing and tail came off, hitting Megura’s kite … Paul Ellington had engine problems and bailed out over the Dutch Coast … Bob Richards was killed when he went in near Framlingham returning from the show. Blakeslee returned fuming, his guns wouldn’t fire at all._

[John Godfrey later said that Richards crashed due to motor trouble].

_*7 March 1944*—New spark plugs were put in the kites to see if this might improve the engine problems.

*8 March 1944*—In spite of claims of 16 destroyed, rough engines and unservicable drop tanks were the order of the day.

*13-15 March 1944*—In spite of the successes against the Germans, the P-51s were mechanical nightmares and they were grounded. Rough engines, props throwing oil, glycol leaks and auxiliary tank feed problems were causing aborts on every mission. These two days all the wing bolts were replaced and engine mount bolts were magnafluxed, but these precautions weren’t effective. On the 17th Burtonwood manufactured new motor mount bolts but even these turned out to be unsatisfactory and by April North American had to rush 250 sets VIII FC. 
Table II prop kits for the Mustang arrived in February and March stripped and useless, so propellers continued to be in short supply until July. V-1650 engines were also in short supply through March and April. All this added up to low mission strengths for quite a while. Many times a squadron was able to get but 10 airplanes up for a mission. To get 20 up was a minor miracle … 
The gloom over losses due to engine problems was hard to dispel. At least five pilots went down during March due to glycol and engine failures, possibly more since several losses are noted due to unknown causes. The gunnery and electrical systems also failed with regularity, resulting in lost kills. And the installation of the 65-gallon upright tank behind the pilots’ seat without baffle plates to prevent violent shifts in the center of gravity was considered a nightmare by several pilots.
Blakeslee’s crew chief, Harry East Jr. never could get the right bank of the Chief Cook’s Merlin to quit smoking and missing. Col. Don kept the kite because it was fitted with a better-vision Malcolm hood. 43-6437 was not replaced until the hydraulic line was perforated, much to East’s relief.”._


See p.40-45
Garry Fry Ethell. *Escort To Berlin: The 4th Fighter Group in World II*. Arco, 1980.






Aozora said:


> it's up to EKB to support his own convictions with more than just meaningless, bald statements.





Show us evidence that P-51s with the Packard Merlin engine were more reliable than P-51s with the Allison engine. Surely you can do better than fling accusations like cream pies.







Aozora said:


> I suggest EKB read Harvey-Bailey, pages 40-45 to find out. The isolated troubles of the Griffon on some Seafires have nothing to do with the Allison V-1710.




If you didn’t want to read bad news about the Griffon engine, then you shouldn’t ask direct questions about the Griffon engine. I can't protect you from the truth. A brief overview of the Merlin engine written by a former Rolls Royce employee (Harvey-Bailey) was not intended to be a completely catalogued timeline of problems. It's a summary and nothing more.


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## fastmongrel (Dec 10, 2015)

A large number of the problems you list were not with the V1650 engine (Its not a Merlin) but with the plane and ancillaries. These were new planes to the unit the ground boys were inexperienced on the new type. Go look at any Unit history covering the period after the changeover between types and you will find the same thing. Go look at any unit logs when the unit had used the new P51 in combat for 6 months and compare.

This thread was about someone asking genuine questions about why the Allison didnt seem to get the fame that other engine types got. You are simply trying to knock down an engine because of its fame and mythology, what people say and think now has no bearing on 70 years ago. 

The Merlin/V1650 engines might have had more problems than a V1710 but ask yourself this question would you want to take on the Luftwaffe in their backyard at 30,000ft in a P51 B,C,D or K powered by a 1943 V1710 with a 2 speed 1 stage non Turbo blower or a V1650 with 2 speed intercooled 2 stage blower. You cant say "ahh but the V1710**** series ran on the stand in 1945 for 10 million hours and gave 3,000hp at 50,000ft and had freakin laser beams on the cam boxes" its between a V1650-3 or its May 1943 Allison equivalent.

Oh and by the way yes the Merlin/V1650 is my favourite engine of all time but I am not blind to its many flaws and unsuitability for passenger air use. I dont have a 2nd favourite but a group of engines which I regard as exceptional but just not Merlin/V1650s and in that group of 6 is the V1710.


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## tomo pauk (Dec 10, 2015)

The introduction of the Merlin Mustang was a new thing for the 8th AF, with Packard just begining the production of 2-stage V1650s in Spring 1943. As a new outift, it will come with more or less a number of issues. That was true for P-47 (P-47B was unfit for war, the engine problems persisted until mid-1943 with P-47C and D, again engine problems with M), F4U (both engine and airframe, not just for carrier service), P-38 (host of the problems with engines' installation, most notably in the P-38J, insufficient heating prior spring of 1944 when installation of second generator allowed for a redesign of the cockpit heating sytem). P-40 in 1941 with restricted engine power.
Basically everytime the design, either airframe or engine or both, was pushing forwar it encountered issues, some designs (and the design staff) being better in overcoming the issues than another. The fact still stand that Merlin Mustang ranged far and wide against German and other Axis targets, with the unprecedented range and performance - just what and when was needed, even if we account the P-38 history. This, added to the wordwide use of the Merlin will still mean plenty for anyone.

If we talk post-war pistons, let's recall that V-1710 powered P-82 were never as reliable nor as performing as V-1650 powered P-82s.


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## gjs238 (Dec 10, 2015)

tomo pauk said:


> The introduction of the Merlin Mustang was a new thing for the 8th AF, with Packard just begining the production of 2-stage V1650s in Spring 1943. As a new outift, it will come with more or less a number of issues. That was true for P-47 (P-47B was unfit for war, the engine problems persisted until mid-1943 with P-47C and D, again engine problems with M), F4U (both engine and airframe, not just for carrier service), P-38 (host of the problems with engines' installation, most notably in the P-38J, insufficient heating prior spring of 1944 when installation of second generator allowed for a redesign of the cockpit heating sytem). P-40 in 1941 with restricted engine power.
> Basically everytime the design, either airframe or engine or both, was pushing forwar it encountered issues, some designs (and the design staff) being better in overcoming the issues than another. The fact still stand that Merlin Mustang ranged far and wide against German and other Axis targets, with the unprecedented range and performance - just what and when was needed, even if we account the P-38 history. This, added to the wordwide use of the Merlin will still mean plenty for anyone.
> 
> If we talk post-war pistons, let's recall that V-1710 powered P-82 were never as reliable nor as performing as V-1650 powered P-82s.



For a moment I thought I had been reading the F-35 thread

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## tomo pauk (Dec 10, 2015)

Way off-topic, and way too wrong - the 15-20 years of the JSF/F-35 development that was supposed to use off shelf things to speed up the design has nothing to do with US succeses like the P-51, 47 or 38. Just think what Kelly Johnson's team would've done with SR-71 in 15-20 years.

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## FLYBOYJ (Dec 10, 2015)

EKB said:


> You need to show us when Mustangs with the Allison engine suffered this many problems:



To make an accurate comparison you need to show us when that many Allison Mustangs were being fielded under the same conditions. I would guess they would have had the same issues.

These squadron reports and tid-bits should not be used to accurately determine MC rates, they could be misleading. The real determination of aircraft reliability considers the number of aircraft assigned to a squadron, minus those grounded for routine maintenance. At that point a fly order is formulated and it is factored against ground and air aborts, that gives you your true MC rates.

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## Aozora (Dec 10, 2015)

Some more Allison info, describing the differences between "F" series engines (from the _Allison Handbook of Operation and Maintenance for Allison V-1710 "F" Type Engines_ 1 April 1943):


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## EKB (Dec 11, 2015)

FLYBOYJ said:


> To make an accurate comparison you need to show us when that many Allison Mustangs were being fielded under the same conditions.





To begin with the Mustang was not a new type of airplane in March 1944. Wright Field tested the first production model P-51B one year earlier and issued a report in May 1943, by which time the RAF already had fifteen squadrons of Mustang Is in the U.K. Missions to Germany started in July 1942. 






FLYBOYJ said:


> I would guess they would have had the same issues.





The two-stage Packards used by 4th FG in March 1944 were similar to the Merlin 61. Some of the problems with this engine did not apply to the Mustang I or Mustang II.



_*September 1942* —“ I did very little operational combat flying during September. I did do a couple of high altitude interception attempts, one on the Ju 86 which came over at high altitude, as always. On this attempt I had trouble with the second-stage blower [Merlin 61], and when I finally reached 34,000 feet, I had much surge in the engine. Most of my time was spent testing our new Spit 9. We seemed to have a lot of trouble with the radio transmissions on them, and a lot of trouble with the cannons. Nevertheless, we were all looking forward to flying them operationally, because they were a vast improvement over our Spit 5’s.” _

Richard Alexander
133 (Eagle) Squadron


_*6 September 1942* —“ Spike Miley was having trouble with his power [Merlin 61] and was lagging behind. An FW 190 was stalking him, so I broke formation and went back to help him. As I turned left to be in the sun so the Hun would have less chance of seeing me. He didn’t see me and I came around and hit him good. Pieces started flying off his plane and he turned right, going down in a steep turn. I was sure he was finished and I caught up with Spike and we were able to rejoin the squadron. About then all hell broke loose as fifteen FW-190s hit us. Two of the Fortresses were shot down and we lost two planes, Doorly and Gudmundsen.” 

*7 September 1942* —“ We were about twenty-five miles inside the Dutch coast when my engine [Merlin 61] began to surge and run very rough and only make about 50 percent power. I began to lag behind and soon lost sight of the squadron. Our controller in England heard me calling to the squadron for help and said they had six enemy fighters plotted on their scope between me and the coast. They were just milling around, waiting for me, since my squadron was already well west of them in mid-Channel. I was now alone and on my own. ” _

Leroy Gover
133 (Eagle) Squadron


R. L. Alexander. *They Called Me Dixie*. Robinson Typographics, 1988 (p.102). 
P. D. Caine. *Spitfires, Thunderbolts and Warm Beer*. Brassey's, 1995 (p.105-106).





FLYBOYJ said:


> The real determination of aircraft reliability considers the number of aircraft assigned to a squadron, minus those grounded for routine maintenance.




Obviously true. But too many people have fallen back on nostalgia or compact technical histories of engines and airplanes and that is always misleading.


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## EKB (Dec 11, 2015)

fastmongrel said:


> A large number of the problems you list were not with the V1650 engine (Its not a Merlin) but with the plane and ancillaries. These were new planes to the unit the ground boys were inexperienced on the new type. Go look at any Unit history covering the period after the changeover between types and you will find the same thing. Go look at any unit logs when the unit had used the new P51 in combat for 6 months and compare.
> 
> This thread was about someone asking genuine questions about why the Allison didnt seem to get the fame that other engine types got. You are simply trying to knock down an engine because of its fame and mythology, what people say and think now has no bearing on 70 years ago.
> 
> ...





Is it better to play favorites or sort out what really happened? Germany had more critical problems than the Allies thanks to shortage of heat-resistant materials. In 1945 the Daimler-Benz engines put in the Me 109 averaged about 10 hours between changes, per General Steinhoff. Sometimes the engine technicians had to unpack and test several DB 605s before they found one that started up and ran acceptably.


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## tomo pauk (Dec 11, 2015)

The Germans were in far better situation in 1941-43 (and no, they did not need such great heat resistant materials in their non-turbo engines), yet they have these issues, ranging from big to still significiant:
-BMW 801C and D, mid 1941 to oct 1942
-Jumo 222
-Db 606
-Db 603A, whole of 1943
-DB 605A, 'the engine that killed Marseille', from mid 1942-late 1943
-DB 601N - 1 minute emergency rating??
-Jumo 211N - managed to kill half of Ta 154 that crashed

They would've traded the 'reliability' of their engines with relibility of Merlin every day, and twice on sunday.


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## GregP (Dec 11, 2015)

They built about 168,000 Merlins from all suppliers and it is inevitable some would malfunction. It IS a machine. They were built at Derby (RR), Crewe (RR) Glasgow (not sure, but I think it was a British government factory and not RR), Manchester (Ford of Britain), and by Packard in Detroit, Michigan, U.S.A..

You are making a mountain out of a molehill here, EKB. The history is written. Merlins proved to be the best engine of the European war of the liquid-cooled V-12 variety. You might as well accept it or you're trying to rewite history all by yourself. That usually doesn't generate a large numbers of supporters.

Did the Merlin have some issues? Of course, especially with continuous development happening. ALL wartime-developed engines had these issues, some less than others. Allison didn't have quite an many issues, but they weren't getting bombed, either. The Allison was some 2 years or so behind the Merlin development since we weren't on the edge of war. It was strong and robust down low but fell off about the mid-teens in altitude unless turbocharged. I think we mostly all know the issues with Allisons as this has been discussed at length in here. They were worked out, but it took time.

Meanwhile the ETO proved to be largely a high-altitude theater, probably due to European weather making many flying days into IFR conditions. When IFR, it is usually best to be higher than the mountains, so they ALL went up high except on clearer days or if it was unavoidable for some reason. The supercharger of the Merlin 2-stage units is what made the engine work so well up high. Sir Stanley Hooker helped that unit a LOT.

The Merlin DID have some issues. A P-51 (or Spitfire, etc.) would shudder and vibrate when the supercharger switched to high gear and the pilots simply throttled back and anticipated it. There was no fanfare when it shifted down to low range ... the manifold pressure just dropped. But all in all, it was a VERY good unit and outperformed the DB 601/3/5 despite being of considerably less displacement. The DB was a good engine, too, but also had wartime development issues, some of which were never completely solved.

Almost all of the Merlin's chief faults WERE completely solved. It still had some quirks, but has a solid reputation even 75 years later among people who still operate it. That lone says quite a lot.

At the Planes of Fame, we just changed one out with a long, reliable run as history. It lasted a LONG time, but I am not at liberty to post the hours. The numbers are private. Suffice to say it lasted MUCH longer than any wartime Merlin and ran very well for all that time, with few problems. I know maybe six - eight people who have had and are having that experience right now. Few problems in current service, a LONG time after it was built. The only DBs I know of that run do so only infrequently. The Merlins and Allisons fly quite regularly. We have one local here with a beautiful, very-late P-51 and he flies it almost every weekend ... with no trouble. He isn't the only local Merlin to fly very frequently, either.

You might be barking a lot about nothing much. Everyone who operated Merlins liked them in operation. They took a lot a hours to overhaul when that event came around, but active operations were good.

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## fastmongrel (Dec 11, 2015)

OK EKB I will play by your rules. The Merlin/V1650 was so unreliable why was the USAAF so stupid it used every engine it could get its hands on and even went so far as to build a new production line at Continental to make more V1650 engine's. Please explain why the USAAF wasted so much money and why they should have used a different engine. Please explain how using the Merlin/V1650 prolonged the war.


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## pbehn (Dec 11, 2015)

Many of the merlins problems as far as being taken apart number of fasteners etc probably stem from it being designed for RAF fighters. I doubt Rolls thought they were going to make more than a few thousand at most. A production of 168,000 units would seem like fantasy in the days when it was designed and production lines thought of. It should have been replaced by the vulture and Sabre but in effect outlived them both.


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## fastmongrel (Dec 11, 2015)

GregP said:


> They built about 168,000 Merlins from all suppliers and it is inevitable some would malfunction. It IS a machine. They were built at Derby (RR), Crewe (RR) Glasgow (not sure, but I think it was a British government factory and not RR), Manchester (Ford of Britain), and by Packard in Detroit, Michigan, U.S.A..



Continental started producing V1650s as well but were too late and the contracts were cancelled, as far as I have read they produced between 6 and 55 engines.


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## wuzak (Dec 11, 2015)

fastmongrel said:


> Continental started producing V1650s as well but were too late and the contracts were cancelled, as far as I have read they produced between 6 and 55 engines.



Obviously it was far better for them, in the middle of the war, to continue with the development of a motor they started in 1932 and had only yielded a handful of flight-worthy units.


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## FLYBOYJ (Dec 11, 2015)

EKB said:


> Obviously true. But too many people have fallen back on nostalgia or compact technical histories of engines and airplanes and that is always misleading.



Isn't that what you're doing here?!? You're arguing about Merlin reliability vs the Allison but not providing actual MC rates in comparative numbers and just posting quotes from combat reports that document individual situations.

I think Greg's post above says it all.

This old thread discusses aircraft reliability, I don't know if the links are still intact.

http://ww2aircraft.net/forum/aviation/reliability-ww2-fighters-10837-3.html

P-51 Maintenance...

Mustang! - Documents

I'll try to find some old sources that shows 8 AF aircraft abort rates and maintenance issues and IIRC there was nothing really glaring (with the exception of some P-38 squadrons - two engines mean 2x the maintenance) when you factored in aircraft numbers against hours flown.


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## EKB (Dec 11, 2015)

GregP said:


> They built about 168,000 Merlins from all suppliers and it is inevitable some would malfunction. It IS a machine. They were built at Derby (RR), Crewe (RR) Glasgow (not sure, but I think it was a British government factory and not RR), Manchester (Ford of Britain), and by Packard in Detroit, Michigan, U.S.A..
> 
> You are making a mountain out of a molehill here, EKB. The history is written. Merlins proved to be the best engine of the European war of the liquid-cooled V-12 variety. You might as well accept it or you're trying to rewite history all by yourself. That usually doesn't generate a large numbers of supporters.
> 
> ...




Well I didn't write that Merlin engines never worked as advertised. It that were true, very little would have been accomplished. 

All top of the line aero engines had technical flaws—it's a matter of degree. If some people don't want to read about those problems that's fine with me.

The trend for Allied fighters in the ETO gradually moved to chiefly low altitude flying. The expansion of tactical air forces, anti-shipping operations, low level German raiders, and buzz bombs saw to that. By 1944 most of the high altitude fighting was done by heavy bomber escorts, but even they were assigned to strafing airfields, trains and other ground targets.


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## EKB (Dec 11, 2015)

FLYBOYJ said:


> Isn't that what you're doing here?!? You're arguing about Merlin reliability vs the Allison but not providing actual MC rates in comparative numbers and just posting quotes from combat reports that document individual situations.
> 
> I think Greg's post above says it all.
> 
> ...




I have some data on abort rates for the month of March 1945:

The 428th Fighter-Bomber Squadron was equipped with the Lockheed P-38J and P-38L, based at Florennes. The squadron recorded 662 sorties with eight aborts. The 1.2% abort rate in March was a record low for the 428th; their overall wartime rate for early returns was about 4%. Average time aloft per mission was about 2 hours and 25 minutes.

The 359th Fighter Squadron was equipped with the North American P-51D, based at Martlesham Heath. The squadron flew 404 sorties with 22 aborts. Average time aloft per mission was about 4 hours and 40 minutes.

The 365th Fighter Group was equipped with the Republic P-47D, based at Florennes and Aachen. The three squadrons amassed a total of 1,876 sorties with eight aborts. The average time aloft per mission was about 1 hour and 55 minutes.


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## FLYBOYJ (Dec 11, 2015)

Since the initial charts comparing overhaul times was based on CONUS operations, I have two documents side by side comparing the noted overhaul hours against individual aircraft flying hours.







http://www.afhso.af.mil/shared/media/document/AFD-110331-045.pdf

If we were able to break out any Packard powered P-40s being operated in the US, this could give somewhat of a comparison. The V-1650 was over 100 man hours more to overhaul but I think you'll see there were more flight hours being put on them.


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## FLYBOYJ (Dec 11, 2015)

EKB said:


> I have some data on abort rates for the month of March 1945:
> 
> The 428th Fighter-Bomber Squadron was equipped with the Lockheed P-38J and P-38L, based at Florennes. The squadron recorded 662 sorties with eight aborts. The 1.2% abort rate in March was a record low for the 428th; their overall wartime rate for early returns was about 4%. Average time aloft per mission was about 2 hours and 25 minutes.
> 
> ...



Abort rate vs sortie flown factoring in flight hours will paint a good comparison.


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## fastmongrel (Dec 11, 2015)

I see the R1820 had the lowest maintenance hours. Therefore the R1820 was the best engine in WWII, is that how it works


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## FLYBOYJ (Dec 11, 2015)

fastmongrel said:


> I see the R1820 had the lowest maintenance hours. Therefore the R1820 was the best engine in WWII, is that how it works


As well as a two legged table!


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## rochie (Dec 11, 2015)

For gods sake no one tell him the Sabre was a british engine as well, he'll have a field day on it serviceability rates


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## Airframes (Dec 11, 2015)

I had heard that _all_ of the _perceived_ problems with the various models of Merlin engine were very simply rectified - by fastening a plate onto the engine block, and rocker covers, which was stamped "Rollz und Royze"................

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## fastmongrel (Dec 11, 2015)

rochie said:


> For gods sake no one tell him the Sabre was a british engine as well, he'll have a field day on it serviceability rates



What!!! you mean the Saber wasnt the most reliable simple engine ever built. Why did no one tell me


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## rochie (Dec 11, 2015)

fastmongrel said:


> What!!! you mean the Saber wasnt the most reliable simple engine ever built. Why did no one tell me



Dude you have to read all the way to the bottom of the memo's


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## GregP (Dec 11, 2015)

Hey EKB,

It's OK to discuss the Merlin's faults or the faults of any engine or aircraft or even pilot. Many people in here will be glad to talk with you in here about faults that were uncovered. That isn't a problem. The Merlin was great engine that had a few issues that were more or less worked out. Let's just not call it a bad engine because they had to fix a few issues along the way. No piston aero engine of the time was without faults when it went from initial power levels to double in about 4 years.

Some issues were never fixed. One of the faults that vexes me is that Rolls Royce for some reason injects oil onto the reduction gears as they are moving in to mesh with each other. That is a mechanical no-no. Oil is incompressible. It adds a lot of completely unnecessary stress. The correct procedure is what the Allison did. They inject oil onto the gears as they come part from meshing and the oil has a chance to spread out and have excess throw off as it rotates around and remeshes. As a result, there were very occasional Merlin prop shaft failures. Not a lot, but some. The answer these days is to make a longer tube and run it around to the other side of the gear. Some do at overhaul; some don't.

I really don't like the way the valve seats are installed. You screw them in and tighten until the stem breaks off. Then you adjust the grind of the valve to match after you grind the valve seat. It adds time, but in service, it works fine. The hit comes at overhaul.

The center cam clamp is a tough nut to make. The rods are weak for hopped up engines, but are fine for stock power levels. You have to torque the cylinders every 25 hours (never on an Allison). But once you factor these things in, it starts and runs well, and lasts a good length of time between expensive overhauls.

Today, flying warbirds, the Allison is MUCH cheaper to operate and most warbird owners never get to 25,000+ feet since hardly anyone wants to waste expensive Merlin time flying IFR. They also mostly fly old fighters in severe clear weather. There is NO reason to risk an old fighter or a life in IFR weather today. If you need to get home that badly, take the airlines.

In cruise you can get an Allison down to some 39 - 42 gallons per hour (US gallons). The Merlins will get down to some 55 gph, and you CAN lean them further, but you run the risk of being too lean. So the Allison will cruise some 10 gph less, but that's not much of a savings if you fly a warbird with either engine in it, so most operators fly then at about a gallon a minute at cruise regardless of potential leaning capability. No risk of damage that way. If you're worried about a 10 gph difference, you can't afford to fly a warbird.

Most Merlins these days are seeing some 600 - 800 hours at overhaul time; some a bit longer. For Allisons, I know a few people flying then with 1,100 hours on them and going strong. But maybe these guys are just cheap. If I could afford either engine, I'd probably think about overhaul at about 700 - 800 hours whether it was running well or not. Props get overhauled every 5 years at a non-inconsiderable cost. Carburetors need it ever 5 years, too ... assuming they get flown enough. If they sit too long, the carb will require overhaul sooner.

A typical overhaul on a P-51 Hamilton Standard prop is about $100,000 USD. A typical carburetor overhaul for an Allison is about $5,000 USD. So yes, they are expensive to operate and overhaul but, what military aircraft isn't?

Notwithstanding all of the above, the Merlin is a great engine.

Wanna' talk warbird costs nobody ever sees? Try buying main gear tires for a Lockheed P-38! Try some $100,000 USD per set! Nobody makes them so, when they are needed, some tire manufacturer has to tool up and make a special run of 20 or so tires! That adds a LOT of non-recurring cost! And you get about 40 ladings on them on pavement. That means you are using up $2,500 in tire wear every single time you touch down! Any P-38 operator would love to fly from a grass strip!

Try finding wing slat bearings for a F-86! Some $5,000 per set and they used to be $20 per bearing!

The list is endless. Most people would cringe over the cost of a set of wheel pants for a Stearman Speedwing biplane, never mind the cost of other more mundane items. Nobody ever said flying surplus military airplanes was a cheap undertaking. At least, nobody since the 1960s anyway, when you could get a P-51 for $5,000, probably with a spare engine and a full tank of gas.

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## Milosh (Dec 11, 2015)

EKB said:


> I have some data on abort rates for the month of March 1945:
> 
> The 428th Fighter-Bomber Squadron was equipped with the Lockheed P-38J and P-38L, based at Florennes. The squadron recorded 662 sorties with eight aborts. The 1.2% abort rate in March was a record low for the 428th; their overall wartime rate for early returns was about 4%. Average time aloft per mission was about 2 hours and 25 minutes.
> 
> ...



The reason for these aborts are ........?

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## Aozora (Dec 12, 2015)

EKB said:


> The two-stage Packards used by 4th FG in March 1944 were similar to the Merlin 61. Some of the problems with this engine did not apply to the Mustang I or Mustang II.



Actually, the Merlin 61 was a limited production engine that was quickly superseded by the Merlin 63/63A with reinforced refined components that allowed, for example, increased boost pressures (+18 lbs). The Merlin 66 was improved over the 63/63A. Because R-R Packard continually exchanged information, it was Packard that introduced the two-piece cylinder block that was adopted by Rolls-Royce. In addition, the two stage V-1650s had different supercharger drives, different water pumps and different intercoolers, etc. (see attachment) 



EKB said:


> _*September 1942* —“ I did very little operational combat flying during September. I did do a couple of high altitude interception attempts, one on the Ju 86 which came over at high altitude, as always. On this attempt I had trouble with the second-stage blower [Merlin 61], and when I finally reached 34,000 feet, I had much surge in the engine. Most of my time was spent testing our new Spit 9. We seemed to have a lot of trouble with the radio transmissions on them, and a lot of trouble with the cannons. Nevertheless, we were all looking forward to flying them operationally, because they were a vast improvement over our Spit 5’s.” _
> 
> Richard Alexander
> 133 (Eagle) Squadron
> ...



All anecdotal. It's very easy to blame the engine, but what did the engineering reports say about what caused the problems? The pilots may say one thing, but what counts is what the engineers back at base had to say. Something as simple as a faulty spark plug lead or foreign matter in oil or a faulty solenoid can cause all sorts of problems with a perfectly sound engine.



EKB said:


> Obviously true. But too many people have fallen back on nostalgia or compact technical histories of engines and airplanes and that is always misleading.



Dismissing Alec Harvey-Bailey's book on the Merlin as unreliable or misleading, because it's supposedly nothing more than "compact technical histories of engines and airplanes" is a cheap shot: Harvey-Bailey knew more about the developmental problems of the Merlin than anyone, and he knew what solutions were adopted. Making up an arbitrary rule that dismisses such a source... 



EKB said:


> The trend for Allied fighters in the ETO gradually moved to chiefly low altitude flying. The expansion of tactical air forces, anti-shipping operations, low level German raiders, and buzz bombs saw to that. By 1944 most of the high altitude fighting was done by heavy bomber escorts, but even they were assigned to strafing airfields, trains and other ground targets.



Which shows that one of the great strengths of the two-stage Merlin was its ability to allow fighters such as the P-51 to operate as a high altitude bomber escort and a medium to low altitude attack aircraft; the Allison didn't quite make the grade in covering the gamut of high to low altitude roles.

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## EKB (Dec 13, 2015)

Milosh said:


> EKB said:
> 
> 
> > I have some data on abort rates for the month of March 1945:
> ...




You'll need to visit the archives for that much detail. The early returns of the 359th Fighter Squadron were not out of line with other P-51 units using the Packard Merlin engine.

From March 1945 through April 1945 the 479th Fighter Group was equipped with the P-51D. During this period the group was based at Wattisham. They dispatched 2,110 sorties with 105 aborts. Average mission time was about 5 hours and 30 minutes.

From March 1944 through April 1944 the 363rd Fighter Group was equipped with the P-51B. During this period the group was based at Rivenhall and Staplehurst. They dispatched 1,677 sorties with 221 aborts. The total number of early returns was 268—but I did not count 47 P-51s that were recalled due to weather, on 18th March 1944. The group was also grounded for a week in the same month. Average mission time was about 3 hours and 40 minutes.

I think this reinforces my earlier post showing that the P-51B was a highly defective airplane in the spring of 1944.


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## fastmongrel (Dec 13, 2015)

So your saying its not the engine thats at fault but the aircraft.


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## EKB (Dec 13, 2015)

fastmongrel said:


> So your saying its not the engine thats at fault but the aircraft.




If that is your belief then prove it.


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## fastmongrel (Dec 13, 2015)

EKB said:


> If that is your belief then prove it.



You started with a diatribe against the engine but now your saying



EKB said:


> I think this reinforces my earlier post showing that the P-51B was a highly defective airplane in the spring of 1944.



Oh and I dont need to prove anything you started this particular horse its up to you to find solid proof that doesnt consist of a few selected quotes that when taken out of context reinforce your beliefs. I know the Merlin/V1650 had faults and I can happily off the top of my head without recourse to google list several dozen but I dont feel the need to knock anything to try and prove my belief that the people at the pointy end of WWII didnt make a mistake.

You are trying to prove a theory so its up to you to provide a proper well laid out set of proofs with a list of sources. I dont need to do anything but react to your claims I have no need to prove my claims because I am claiming nothing.


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## EKB (Dec 13, 2015)

fastmongrel said:


> You started with a diatribe against the engine but now your saying - "I think this reinforces my earlier post showing that the P-51B was a highly defective airplane in the spring of 1944."





I posted the following message three days ago about defects found in the P-51B, many of which were not engine-related, so I have no idea why you now contend that point wasn’t raised earlier:




EKB said:


> You need to show us when Mustangs with the Allison engine suffered this many problems:
> 
> 
> “ Operational Diary—1944 [4th Fighter Group]
> ...




I’m pretty sure that the pilots who turned back early from a mission did not feign those kind of problems because they had a hot date in London.





fastmongrel said:


> what people say and think now has no bearing on 70 years ago.




If only you practiced what you preach.


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## fastmongrel (Dec 13, 2015)

I cannot understand the thread of your argument you seem to have two opposing views. I am out of this discussion now as you seem to be heading towards being personal. 

As the great Jedi Master Yoda said recently. Fun you will have on your own


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## FLYBOYJ (Dec 13, 2015)

EKB said:


> I think this reinforces my earlier post showing that the P-51B was a highly defective airplane in the spring of 1944.



I show 1,578 Allison Powered Mustangs built, 1,987 P-51Bs and 1,750 P-51Cs (Texas razorbacks) built. I believe some of the Allison P-51 production run overlapped P-51B/C production. Although you keep showing individual combat reports, if the P-51B was truly "defective" as you say, don't you think someone at the war department would have stopped Merlin production and reverted back to an all Allison fleet or just cancelled the P-51 Merlin production line all together?

What you're showing IMO was no different than many of the other aircraft entering combat service, especially in the numbers, environment and mission assignments this "new" airframe was expected to perform in, if anything the P-51B performed well despite the examples you're showing. Agree, there were some major issues with the P-51B when it first entered service and there was much improvement needed to get the full potential out of the aircraft, but despite these issues I think history tells us that the marked improvement over the Allison airframe was apparent. I've met several WW2 veterans who flew both versions and even spoke of some of the same issues you're trying to highlight, but in the end they would have chosen a Merlin powered P-51, except for Col. Mike Alba - he would have preferred to stay in the P-38!!!

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## pbehn (Dec 13, 2015)

A defective airplane is defective, not just in the first few weeks it appeared. Things like oil and coolant leaks are production quality control issues not the aircraft design and complaints about the radio have nothing to do with the aircraft. To suggest that the merlin itself was defective in 1944 is a little off the wall, it powered almost all British front line fighter recon. and bomber aircraft up to that time, especially the ones on the longest missions with two or four of them.

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## FLYBOYJ (Dec 13, 2015)

pbehn said:


> Things like oil and coolant leaks are* production quality control issues *not the aircraft design and complaints about the radio have nothing to do with the aircraft.



Many of these aircraft were test flown at the factory, disassembled and then shipped to Europe, reassembled and sent off to squadron so the potential for "quality" issues were great.


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## pbehn (Dec 13, 2015)

FLYBOYJ said:


> Many of these aircraft were test flown at the factory, disassembled and then shipped to Europe, reassembled and sent off to squadron so the potential for "quality" issues were great.



I was going to make a similar point but I dont know how far they were disassembled after their test flight at the factory. Most of the problems highlighted should have been sorted in commissioning checks. I would think that is what was done to solve them, all part of learning how to put a new piece of kit in service.


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## tomo pauk (Dec 13, 2015)

pbehn said:


> ...To suggest that the merlin itself was defective in 1944 is a little off the wall, it powered almost all British front line fighter recon. and bomber aircraft up to that time, especially the ones on *the longest missions with two or four of them*.



Or just with one of them


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## gjs238 (Dec 13, 2015)

I wonder if the V-1650 powered P-40's also had such development issues.


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## GregP (Dec 13, 2015)

The P-40F did not have a lot of issues but, being a single-stage engine, was also not better than the Allison P-40. Some were a few mph faster. Some weren't. As far as I've been able to check, the two airplanes were about equal in performance with the Merlin version deleting the carburetor airscoop, making for marginally better visibility.

Either engine seems to have been about the same. Now had they put in a 2-stage Merlin, then we'd have seen a real jump in P-40 performance. The single-stage planes weren't much given to playing at ETO combat altitudes.


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## GrauGeist (Dec 13, 2015)

I wouldn't spend too much time arguing with this person, as this exact same argument happened here: Reliability of aircraft engines nearly 10 years ago.

With virtually the same figures pulled out of context to support the same circular argument 

I will say that perhaps the single most informative comment in all 9 pages of that particular discussion, was in another member's reply:


> "Anecdotal information is difficult to include and draw reliable conclusions from"

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## tomo pauk (Dec 13, 2015)

gjs238 said:


> I wonder if the V-1650 powered P-40's also had such development issues.



Nope.


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## pbehn (Dec 13, 2015)

tomo pauk said:


> Or just with one of them



Well, I considered including single engined aircraft but then someone would have said they were mainly point interceptors, only a small percentage of Spitfires were long distance recon versions, but by 1944 they had been venturing into Germany with Merlins for a long time.


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## tomo pauk (Dec 13, 2015)

The Fulmar was also managing long missions, combat included, over the water for the start. On a single Merlin engine.


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## pbehn (Dec 13, 2015)

tomo pauk said:


> The Fulmar was also managing long missions, combat included, over the water for the start. On a single Merlin engine.



Yes, that is the sort of comment for no reason whatsoever that I was trying to avoid, valid though your comment is it is it is a distraction, the merlin was originally designed for single engined aircraft, if it had been consistently unreliable it would not have been chosen to power four engined bombers for long distance bombing raids. I am not saying it was better than the Allison in reliability, I am saying it was not an intrinsically unreliable engine in 1944, whatever airframe it was bolted into.


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## pbehn (Dec 13, 2015)

tomo pauk said:


> Nope.



Were the ground crews used to dealing with water cooled engines? Were P51B ground crews used to dealing with water cooled engines? This is how a discussion goes off on a wild tangent.


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## GregP (Dec 13, 2015)

This isn't much of a discussion anymore. It started off asking about the Allison and morphed into a discussion of the Merlin. Go figure.

On topic, there was nothing wrong with the Allison that a change in USAAF requirements would not have cured. The choice of high-altitude boost systems was the USAAC's choice, a turbocharger. Had they hedged and asked for multiple high-altitude boost systems, we might have had a different story. But we didn't.

There is nothing wrong with the Merlin as a service engine. It takes a lot of labor to overhaul it, but in service it runs just fine.

And it doesn't matter a bit what an aero engine was designed for. It matters how it gets used and what the results are. The reputation, good or bad, is earned in the air, not in the design phase. Merlins did everything asked of them and more. Allisons did, too.

If the turbo installation was debugged, it worked fine, If it was an early system, it had a few issues that were addressed and solved; a bit later than the Merlins, but they were solved. A P-38J or L had no real turbo issues other than normal in-service things that happen. They never did let Curtiss put a turbo in the P-40 or Bell complete the turbo in the P-39, so those were low-altitude airplanes.

The engines weren't bad, they performed as advertised at the altitudes expected, and made overhaul as expected. It's just that the enemy wasn't fighting where the P-39s and P-40s were flying all that much.


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## DerAdlerIstGelandet (Dec 13, 2015)

I see EKB is trying to ruffle feathers again...


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## GregP (Dec 14, 2015)

Hey EKB,

You better stop while you're still in good standing. Mission abort rates are not necessarily attributable to the aircraft. If the main abort reasons are systems, then the aircraft is to blame. If the main abort reasons are engines, then the engine is to blame. Also, the abort rates for each engine are a great subject to explore.

Look really hard at bombers. They have multiple engines and can generate very realistic engine failure rates quickly.

Single-engine fighters can do so with some camouflage. Did a Curtiss Electric prop fail due to motor brushes? Or what? Was it a burst oil line? What about an electrical fault?

You have shown abort rates for some P-51s. What about the same data for P-47s or P-39s or P-40's or Spitfires or Hurricanes, etc.?

Use the scientific method and form a hypothesis and attempt to disprove it yourself. If you can, it's wrong. If you can't it MAY be right.

Good luck.

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## GrauGeist (Dec 14, 2015)

Greg, don't forget even a hard landing can knock prestone lines loose or foul other equipment which in turn can cause trouble on the next "go-round" unless the crew spots it before hand.


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## GregP (Dec 14, 2015)

Not forgetting ... I can't elaborate every possibility in a short post, but I get your point.

Mission aborts are generally attributable to some system, be it powerplant, prop, gear, hydraulic, gasoline (as in run out), electrical, or some system failure. It certainly isn't combat if it is an abort.

Could be armament arming issues as well as anything else. If you can't shoot, you'd better RUN.

Some analysis might be indicated.


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## Milosh (Dec 14, 2015)

GrauGeist said:


> I wouldn't spend too much time arguing with this person, as this exact same argument happened here: Reliability of aircraft engines nearly 10 years ago.
> 
> With virtually the same figures pulled out of context to support the same circular argument
> 
> I will say that perhaps the single most informative comment in all 9 pages of that particular discussion, was in another member's reply:



That is some thread with Huck and Kurfurst being major participants.

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## LisaM (Jan 3, 2016)

Not sure what the argument is over, everyone knows that the Allison was a very fine engine, but RR were the masters of supercharging with long accumulated experience and a depth of technical and scientific skills that Allison could not match (nor anyone else for that matter).

But on a different topic I think NA made a mistake with the P-51B, a better approach would have been to develop an interim type (like the Spit V or IX) based on one of the better Mustang X prototypes. It would have got it into service far faster (albeit with lower. but still very good performance), the engineering risks would have been reduced (much based on the tried and tested P-51A). It would have been a useful 'interim type', more than competitive with the 109s or 190s of the era, later superseded with a more developed version (and almost certainly due to the lessons learned in operations, more reliable than the first P-51Bs).

The 'undergunning' alone was astonishing given that the Mustang I had 8 machines guns and the II, 4 x 20mm cannon. There was a real weird element in the USAAF about guns which continued right up to the F-86.

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## tomo pauk (Jan 3, 2016)

The experience of the RR was indeed great, they started designing and producing aircraft engines from the days of ww1, and between the wars they were the prime source of V-12 engines anywhere in the world. Both for military needs and racing. They reckoned early enough that low compression ratio plus a sizable/capable supercharger are the keys for the success of the supercharged aircraft engine. 
The USAF was wrong to turn down the, in 1938 suggested, 2-stage supercharged V-1710, thinking that turbed one will do. Compare that with USN and indeed the RAF tht seized the opportunity with 2-stage engines as early as possible.

We might call the P-51B-K an interim type, the P-51F/G/H/J being wholesale redesigns. Until/unless there is no 2-stage Merlins available, there is no point in an even 'more interim' type. Eg, in July 1943, there were only 173 2-stage V-1650s delivered to the NAA, while there are 534 P-51B airframes completed - lack of 360 engines.
Experiences with Mustang X pointed out that cooling capacity need to be increased, in order to cater with increased cooling loads vs. Allison Mustang. The whole project of Mustang with 2-stage Merlin was a very swift thing IMO. What Allies missed was the Mustang with 1-stage V-1650 that ended in the indifferent P-40F/L, the 1st engines were evailable by the end of 1941. Or even with the P-51A/Mustang II instead of A-36.

The Mustang Ia was with cannons, the II was with 4 HMGs. The 8-gun Mustang sounds nice, but 4 of the guns were .30s, and 2 of the HMGs were slower firing due to being synchronised. USAF/USN probably settled with HMGs beacuse their 20mm cannon was not that a reliable thing, especially in wing installations. Despite trying hard with the 20mm.

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## pbehn (Jan 3, 2016)

LisaM said:


> Not sure what the argument is over, everyone knows that the Allison was a very fine engine, but RR were the masters of supercharging with long accumulated experience and a depth of technical and scientific skills that Allison could not match (nor anyone else for that matter).
> 
> But on a different topic I think NA made a mistake with the P-51B, a better approach would have been to develop an interim type (like the Spit V or IX) based on one of the better Mustang X prototypes. It would have got it into service far faster (albeit with lower. but still very good performance), the engineering risks would have been reduced (much based on the tried and tested P-51A). It would have been a useful 'interim type', more than competitive with the 109s or 190s of the era, later superseded with a more developed version (and almost certainly due to the lessons learned in operations, more reliable than the first P-51Bs).
> 
> The 'undergunning' alone was astonishing given that the Mustang I had 8 machines guns and the II, 4 x 20mm cannon. There was a real weird element in the USAAF about guns which continued right up to the F-86.


The development of he P 51/Mustang was a fortunate comedy of errors, the A36 Apache version was ordered as a dive bomber purely because there was no money for fighters but there was some for bombers. The British were moving from 303MGs to canon so the Mustang/P51 had the pleasure of trying out many combinations.


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## FLYBOYJ (Jan 4, 2016)

LisaM said:


> But on a different topic I think NA made a mistake with the P-51B, a better approach would have been to develop an interim type (like the Spit V or IX) based on one of the better Mustang X prototypes. It would have got it into service far faster (albeit with lower. but still very good performance), the engineering risks would have been reduced (much based on the tried and tested P-51A). It would have been a useful 'interim type', more than competitive with the 109s or 190s of the era, later superseded with a more developed version (and almost certainly due to the lessons learned in operations, more reliable than the first P-51Bs).
> 
> The 'undergunning' alone was astonishing given that the Mustang I had 8 machines guns and the II, 4 x 20mm cannon. There was a real weird element in the USAAF about guns which continued right up to the F-86.



Understand that many times these decisions are not made by the manufacturer but by the customer, including what type of armament will be utilized.


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## XBe02Drvr (Mar 27, 2016)

...or sound as sweet!


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## XBe02Drvr (Mar 27, 2016)

XBe02Drvr said:


> ...or sound as sweet!


Ooops that was in reference to a hypothetical R2800 powered Lancaster/Shackleton several pages back. ("It might've worked, but it wouldn't have been as pretty!")


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## kool kitty89 (Apr 19, 2016)

I was considering adding to this topic: Single stage V-1710: options for improvements?
but this thread's been active a lot more recently and covers most of the same thing (and a lot more).


Addressing that specific topic of single-stage first:

The 7 notable mechanical limitations/problems the early (C series -mostly commonly the V-1710-33 of the P-40B/C/Tomohawk -Curtiss Model 81) were:

1. relatively weak reduction gearing making any stress of overboosting beyond the relatively modest performance limits very destructive to this engine (I believe this is what gained reputations for stripping gears with the AVG's rather abusive use of the engine, possibly some cases in the MTO as well) This was addressed with the E/F and later series engines to the point of often tolerating very heavy out-of-spec abuse. (this might have still been a bottleneck for overrev, but the prop/hub/blade-mounts would likely be a bigger bottleneck)

2. crankshaft strength and to some extent overall finish (I've been digging around for the disucssion that had more specifics on this -particularly the actual changes between the C and E/F series and later models of the E and F prior to the added changes with the G series, but I haven't found it yet). From what I recall, the F series received a smoother finnish than the C series and had strengthening allowing higher power levels. (the well-balanced design of the C series already made for smooth running and ability to overrev -unlike the Merlin and some others- and made such more tempting for pilots to exploit, or attempt to)

3. inability to use the smaller 14-tooth supercharger gear needed for 9.6:1 supercharger operation (8.8 uses a 15-tooth gear) due to structural limits of the existing gear pitch/width requiring a redesign of the mount to allow space for a thicker gear. The required changes would have disrupted production and added costs the Army was unwilling to pay. (this was the main reason for delay in adopting this iirc, there's been more accurate and detailed discussion on it before, and I might have the exact terminology wrong, but I think this is about right)

4. Lack of 2-speed drive. Similar to the gear-tooth issue but requiring even more dramatic redesign of the compact accessory section of the engine, presumably with greater overhead in production changes than most other design problems/fixes. (and wouldn't benefit turbocharged engines) The Army would likely sooner fund an auxiliary supercharger than 2-speed drive given the concerns over efficiency of production.

6. Backfire screens adding drag in the engine manifold and reducing manifold pressure and/or mass flow for any given altitude and supercharger configuration. These were later removed as unnecessary some time after the 9.6:1 supercharger had been introduced. (I think the P-39M is the only fighter to receive a 9.6:1 supercharged engine retaining those screens)

7. Kink/bottleneck in the supercharger intake manifold around the carburetor/throttle body. This was one issue that I don't believe was ever solved and was also mainly limited by the Army's unwillingness to invest in the necessary changes to production. (this problem was noted pre-war, perhaps even prior to any large scale serial production had started but possibly after initial production tooling had been laid out -I'm not sure, but that seems likely given the cost/delay for modifying a non-production design would be so much less as to make that ridiculous, even with a turbocharger-oriented altitude performance program)


The latter issue is rather similar to what the pre-XX series Merlin suffered (in terms of intake chocking the supercharger -noted by Hooker when he began work on improving it) with the exception that Allison's engineers and the USAAF were aware of the problem when RR seemed less so until Hooker inspected the design. So it seems they had the engineering ability to solve (or at least start work on improving) the issue but the Army declined to fund such changes. Solving that issue (like with the Merlin) should have reduced charge heating and increased critical altitude for any given manifold pressure, resulting in higher power levels at any given pressure and higher maximum pressures without suffering detonation. (the latter more important with 9.6 superchargers and possibly Pre-J P-38 given the poor intercooling and any little bit of reduced charge heating in the supercharger still being relevant ... though clearing that kink should make ALL turbo installations less bottlenecked and more efficient)

Lack of aggressive/exhaustive testing combined with relatively conservative ratings in general seemed to plague the V-1710 as far as WEP and take-off ratings went, possibly even maximum continuous power. The E and F series should have been capable of pushing well beyond 3000 (perhaps even 3300-3400) RPM and unauthorized operation at such speeds were noted (let alone post-war tractor pulls and such pushing them far far higher -even without the G-series crankshaft) but no official testing leading to up-rating seems to have been done on this. (reduction gear and prop would be the breaking points for overrev, but without proper testing of those limits, there'd be no reference for even designing around WEP limits and no context for aircraft designers to appropriately test their aircraft and propeller combinations -or note whether different reduction ratios would be needed) The smooth running nature of the engine might have made a 3000 RPM max continuous rating also possible, but specific limits on boost pressure at that rating would also have to be noted separately from military/WEP (or 30-minute limits).

Likewise, tests specific to 100/130 and 100/150 octane fuel should have been completed sooner (or used more incomplete results for operational clearance/expanded operational testing).

It seems the British Air Ministry and Rolls Royce were both more aggressive with testing WEP and general engine limits and more willing to push less than exhaustively tested ratings before putting them into practice. (given the more conservative and stringent nature of Aircraft design specifications the USAAC/AAF and USN had already established pre-war, this seems less surprising, and the V-1650-1 somewhat reflects this as well given the apparent lack of WEP clearance compared to the contemporary Merlin XX and 45 series)

Overrev is particularly significant as it would have boosted critical altitude as well, and partially side-stepped the 9.6:1 gear delay. (exceeding 3200 RPM with 9.6:1 gearing would also seem unwise as the impeller tip speed would exceed the speed of sound by a significant margin even taking generous charge-heating into account, and would also exceed any real-world tip-speed examples during war-time use, while 3200~3250 RPM itself would rather closely match the tip speeds employed with the V-1650-1's supercharger in high gear, or the experimental 10.25" diameter 2-speed single stage Allison supercharger at 9.6:1) On that note, an 8.8 supercharger on an engine running at 3300 RPM will result in a speed equivalent to 9.68:1 at 3000 RPM. (so very similar tip-speeds to 9.6:1 engines at normal military power operation)

Overly conservative ratings can be more dangerous in practice due to leaving the real, hard, extreme operating limits of the machines totally vague and questionable, resulting in a rather high incentive for individual experimentation and unauthorized operation in the field with no reference to how dangerous such operation was. (compared to pushing the Merlin beyond WEP specifications, which was much more reliably going to end in failure) The rather dramatic warning of 57" boost limit on the 9.6:1 engines seems to be among the exceptions of extreme limits being posted, but even that is exaggerated in its imperative as experienced showed pushing closer to 60" was still possible without detonation on those engines, and their notice doesn't note this behavior at all. (P-39N flight testing even lists use of 59.8" manifold pressure being used)

OTOH, there may have been cases of Allison recommending/clearing use of certain engine settings, but the USAAF never implementing them. (2000 HP with 75" MAP on 100/150 fuel was cleared for the P-38L's engines, but may not have been officially cleared for P-38 operations ... though obviously would at least have given a nicer guide for unauthorized use operationally)
150 Grade Fuel

Making improvements on the base, single-stage engine is pretty universally important as it extends usefulness to all existing designs using the engine (no serious modifications to address changes in weight or changes in overall dimensions) while equally extending those improvements to engines using turbochargers or external auxiliary superchargers.




Now, to the points beyond the basic single-stage engine:

The big overarching issue here is the Army simply should have supported Allison's R&D far, far better, and put those hyper-engine projects at much lower priority. This includes putting turbocharger+intercooler development on higher priority too, specifically for technology making it more suitable in small, sleek single-engine aircraft.

Turbos have 2 big issues for small fighters (P-39 is a great example in the extreme here), their own size/bulk, and the size/bulk/drag caused by the intercooler. The larger the turbo, the larger the intercooler and resulting ducting, and restricting turbocharger design to relatively large units precludes the possibility of medium-altitude optimized variants with reduced size/weight/intercooling capacity requirements. (say targeting a critical altitude in the 20,000-25,000 ft range) Or even having turbos small enough to allow reasonable use with no intercooling at all, more akin to Allison's non-intercooled auxiliary superchargers.

This issue can be drastically reduced by adopting a liquid intercooler, and Allison could (with enough funding) have tackled this engineering project themselves, optimizing around GE's turbochargers. (this would have been a critical development all around, and really the biggest single achievement for extending the V-1710 beyond single-stage operation) Given the coolant loop would be shared with the engine's own cooling system, this seems a reasonable thing for Allison to invest in developing rather than GE. (and turbocharger relevant, thus more likely to gain Army support/acceptance) If this work had been done early enough, the P-38 could have abandoned its wing intercoolers sooner and gained both power and (potentially) leading-edge fuel tanks in the wings for longer range operations. (granted, still needed cockpit heating, dive flaps and hydraulic -or tab- boosted ailerons to make a really potent escort fighter ... just the boosted ailerons to make a good warm-climate/low alt fighter though)



One possible workaround for the funding difficulties would have been licensing/adapting existing auxiliary supercharger technology from P&W, or at least using it to accelerate Allison's own development (and avoid delays with half-hearted 'cheap' attempts at repurposing the same integral supercharger housing+impeller into an auxiliary stage, among other things Allison tried initially). Particularly the pre-war developments for the R-1830 (which should have fit the mass flow and pressure requirements of the early V-1710 rather well, likely matched with the 7.48:1 integeral stage speed intended for low-alt and turbocharged installations). Work to allow either rear or side-mounted auxiliary stage orientation (or perhaps even under or top-mounted) would improve flexibility of installing such engines on existing designs using single-stage engines. The V-1710 was specifically designed for modular accessories, so having that sort of flexibility really should have come with the territory.


ADI/water injection is useful, but given the research and testing necessary for addressing concerns over corrosion (especially when used in combat -ie relatively recently before landing, not just on take-off) and required bulk/weight of an ADI fluid tank (again, reduced for use on-take-off only) makes this less attractive than intercooler development. I'm not sure if the R-2800 had operating limits for water-injection use to this effect or not, but the relatively early-ear introduction of that mechanism seems like it might have been initially limited for take-off purposes (akin to that on the Bramo 323R-2). For carrier or short airfield use, that added boost on take-off could be critical, especially for long-range or fighter-bomber missions with heavy external loads.


Edit:
Found the discussion on crankshaft variations
Curtiss-Wright: Loss of Don Berlin and downfall


Shortround6 said:


> According to "Vee's for Victory" there were 4 'different' crankshafts used in the Allisons. The first 3 look identical, at least from a distance. I don't work on them so there may be minor visual clues. The first were 'plain' crankshafts which I believe the C-33s got. The next version was shot peened, different surface texture? much improved fatigue life. I don't know when it was introduced. Then they nitrided the crankshafts in addition to the shot peening. This allowed for another major increase in fatigue life.
> 
> Each step allowed for roughly an unlimited life at a stress level that the preceeding step would only tolerate for a very short period of time. Nitriding was introduced in early 1942 and allowed about a 70% increase over the old plain steel (not shot peened) Crankshaft in stress levels for the crankshaft with both cranks operating at a level that they could sustain for an unlimited duration. Also in 1942 the casting method for the engine blocks changed. The new method required about 10% fewer operations to manufacture ( casting was closer to finished dimensions), weighed a bit less and was stronger. There may have been changes in the vibration damping system between the "C"s and the later engines. Or between certain models of the later engines.
> 
> ...

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## Shortround6 (Apr 20, 2016)

Part of the problem with pre-war development was that Allison was basically an engine experimental shop attached to a bearing factory.
At some point in 1938 if I remember right, Allison had 25 people in the "engine" engineering section including the guy/s who ran the blueprint machine. The Army was late in making payments and at one point had requested Allison investigate fuel injection, This was while Allison was working on the basic engine, the remote engine for the P-39, the V-3420 double engine, the pusher engine for the Airacuda (which wound up with a turbo). Allison told them they didn't have the engineering staff and and if they wanted fuel injection pick one of the other projects to drop.
Allison was making a couple of engines a month in 1938. Much of the engineering staff was diverted to designing production tooling when the big contracts came until more staff could be hired (and a new, much larger factory built, which had to be designed  ).
At one point in 1940 or early 1941 ( I forget which) Allison was short over 800 machine tools despite having one of the highest priority ratings that existed. Allison wound up with over 800 sub contractors supplying parts. By this time supply was certainly not the problem of the design staff but in the early years? Who was deciding what was built in house and what was contracted out?

Another big problem is that engines were often not delivered until months or even a year after they had been contracted for. Granted contracts could be amended so that new improvements might be implemented during a production run but sometimes "new" models of engine were being worked on and promised so as to dove tail with with aircraft production a year in the future. The P-40D was ordered with the -39 Allison almost a year before the prototype flew. The Air Corp had ordered 5 "F" series engines in 1939 using FY (fiscal year) 1940 funds for a model test and one each for the XP-46/46A and XP-47/47A. The XP-47s were canceled or morphed into the Thunderbolt (kept a piece of canopy framing?) and the XP-46 didn't fly until Feb 1941. P-40D flying with the extra engines from the XP--47S???

This confusion as to what the army wanted was one reason the Allison was designed the way it was, a central power section with the reduction gears as a separate section and the accessories as a separate section so the maximum use could be made of the production tooling for the different versions the Army was dreaming up. They would sometimes make p-40 engines for 1-2 weeks and then make p-39 engines for a few weeks and then switch back to P-40 engines and so on.

Sometimes money helps and sometimes it is luck. The improved casting technique for the engine blocks had actually been developed by a husband and wife artist team for casting aluminum sculptures. Totally outside the normal foundry industry. How much extra money had to do with finding them I have no idea 

Part of the problem with the turbos was that the basic design may not scale well. And what you are trying to accomplish.

An Allison needs 10,000lbs of air per hour to make 1672 hp in the cylinders which translates to 1285hp to the prop for an engine with 9.60 gears after you take out the friction and power to drive the supercharger. You could get 1415hp from an engine with 6.44 gears but that maxed out the supercharger, it can't supply more than 10,000lb of air with a crank speed of 3000rpm.

You need both mass flow *and* pressure. At 25,000ft the turbo only has to compress the air 2.6 times to get sea level air pressure. At 20,000ft the turbo still has to compress it about 2.2 times (or just under) while flowing the same mass of air. You aren't going to save much of anything trying to design and build a slightly smaller turbo-supercharger.

The need for inter-coolers is can be shown by charts in standard text books of the day. Temperature rise though an auxiliary supercharger (regardless of how driven) to deliver sea level pressure with a compressor of 65% efficiency (and granted some superchargers could get a bit over 70%) was just under 50 degrees at 5000ft, around 90 degrees at 10,000ft, about 125 degrees at 15,000ft, 175 degrees at 20,000ft and 210/215 degrees at 25,000ft according to one chart. Granted the air does get colder as you climb so that at 20,000ft the air going to the cab may be only 100 degrees or so compared to the 59 degrees at sea level for standard conditions.

At under 20,000ft you may not need an inter-cooler but at under 20,000ft you don't need the turbo either.
At 20,000ft the exhaust thrust from a Melrin XX on a Hurricane was worth 126.8hp at 340mph. Mass flow was 151lbs per minute and exhaust gas velocity was 1788fpm from the exhaust nozzles. Running the exhaust through 5-7 feet of pipe and then through a turbine is going to kill a fair amount of the velocity even if you build a trick variable nozzle after the turbo.

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## tomo pauk (Apr 20, 2016)

The V-1710 does not need the extra supercharger gear, for low level (thus becoming a 2-speed supercharged) until/unless USAF wants a bomber powered by such an engine. And then, if USAF wants a bomber powered by V-1710, using the turbo might make a lot of sense, the turbo engines were with low-geared integral supercharger already available.


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## wuzak (Apr 20, 2016)

tomo pauk said:


> The V-1710 does not need the extra supercharger gear, for low level (thus becoming a 2-speed supercharged) until/unless USAF wants a bomber powered by such an engine. And then, if USAF wants a bomber powered by V-1710, using the turbo might make a lot of sense, the turbo engines were with low-geared integral supercharger already available.



A two speed drive for the V-1710 fitted to the P-40 and P-39 may have helped their performance.

Improved altitude performance could be chased, while maintaining low altitude performance at a similar level for not much extra weight (<100lb).

Single speed superchargers are compromises. Gear for high altitude performance, lose out at low altitudes.


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## Shortround6 (Apr 20, 2016)

Two speed superchargers and better fuel over lapped. The first few engines to use 2 speed superchargers were running on 87 or 91 octane fuel depending on country. The fuel limited the amount of boost and therefore the power an engine could develop. If you wanted power at 12-15,000ft you sacrificed power at low altitudes, sometimes a lot of power. The two speed supercharger was a way to get it back given the fuel limits. A Merlin X picked up almost 200hp for take-off over the single speed Merlin III with both running 87 octane fuel. About a 22% increase. 
With 100 octane fuel more boost could be used at low altitude and more power developed which lessened the need the for 2 speed superchargers (although they were still nice to have) Fighters, before they started hanging 1000-2000lbs worth of bombs/drop tanks on them, could usually get by with single speed superchargers for take-off/low altitude. The Allison and Merlin benefiting from the move/s from 87 octane to 100 (or 100/115?) to 100/125 to 100/130 and finally 100/150. 

Had fuel development stagnated or stalled for a long period of time perhaps more effort would have been put into 2 speed superchargers. 
Please note that air cooled engines could not be pushed using higher boost to the extent that the liquid cooled engines could until the war was more than 1/2 over. 

And please note that the long nose Allison running on US 100 octane fuel (100/100) offered just 35 less hp for take-off than a Merlin X running on 87 octane while still offering 1090hp at 13,200ft. Merlin III being good for 60hp less 3,000ft higher. 

The ideal was better fuel, 2 speed supercharger drives and better compressor designs. But often one or two could fill in in for the other/s to some extent.


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## tomo pauk (Apr 21, 2016)

wuzak said:


> A two speed drive for the V-1710 fitted to the P-40 and P-39 may have helped their performance.
> 
> Improved altitude performance could be chased, while maintaining low altitude performance at a similar level for not much extra weight (<100lb).
> 
> Single speed superchargers are compromises. Gear for high altitude performance, lose out at low altitudes.



The P-39 and P-40 have had problems with hi-alt performance. Installing the 2-speed drive with an extra low gear does not help their performance above 12-15 kft. What helped, albeit belatedly, was installation of higher gearing for the, still, 1-speed S/C. We can recall that P-39N was not lacking performance at low level.
Granted, with 2-stage supercharger, more than one S/C speed was necessarry.


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## kool kitty89 (May 5, 2016)

Aftercooling or water injection would have helped single-stage performance at all altitudes, especially for the 9.6:1 supercharger (or overreved 8.8) due to the charge cooling and improved density.

Additionally, I'd failed to consider the possibility of water injection (or for that matter, fuel vapor) increasing the speed of sound further, thus allowing impeller tip-speeds to be well in excess of the speed of sound at ~100*C (or there about) as humidity greatly increases this value. So even at the 9.6:1 ratio, overreving quite a bit might not hit mach 1 tip speeds.


Given the small size of Allison's staff, it's pretty impressive they managed to engineer what they did ... the Army probably should've taken more notice of that talent though. Aside from just diverting more funding to Allison directly, there's possibilities like second sourcing engine production to Continental and/or possibly outsourcing some of the supplemental engineering to Continental (or perhaps Chrysler, but it really seems like Continental got the brunt of the Hyper-Engine funding). Outsourcing to expand testing (especially for maximum WER limits) would have been a big thing to offload from Allison's limited internal staff/engineering resources too.


They did make quite a lot out of the engine in the end, though, even if it never got used as such operationally:
http://www.enginehistory.org/Convention/2009/Presentations/SuperchargingAllison.pdf

That final turbo-compound variant featured multi-port fuel injection and aftercooling (though the 3200 RPM WER limit was still rather conservative, particularly above its critical altitude).

Interesting that they went port-injected rather than direct injected. That's the only WWII era example of multi-port fuel injection I'm aware of. Interesting that both single-port (pressure injection carb) and multi-port fuel injection both made a reappearance with GM in the 1980s when engine computers were coming on the scene. (single-port fuel injection was called TBI -throttle body injection- in GM literature) Strange that port injection wasn't more common for WWII engines though given it offers many of the advantages of direct injection without the high pressure fuel pump requirements. (most of the timing and precise per-cylinder mixture control, though not as precise timing as direct injection it's still close and offers some degree of charge cooling where high pressure direct injection does not)



I suppose a non-structural reason for avoiding super-high RPM ranges was the ideal cruising performance at 1600 RPM making propeller and reduction gear design rather difficult. (to perform efficiently from 1600 to 3400 or perhaps close to 4000 RPM) And it's not like multiple reduction gears would have been a very practical option ... or at least, clutched prop reduction gearing doesn't seem to have been appealing enough to implement during the war. OTOH, Jumo pushed the 213 to 3250 RPM and its optimal cruise speed was proportionally lower to the smaller capacity V-1710, so perhaps 3400 RPM wouldn't have been unreasonable.




On the note of reduction gearing, though, I got to thinking about the transition from the C to F model (long nose to short simplified/stronger spur-gear arrangement) changes and whether it might have been easier or just all around more useful to avoid the integral gearing of the F series and standardize with the E series alone. If a very short extension shaft+remote gear box could be implemented, it would mean using the exact same engines in the P-40/P-38/P-39/P-51, simplifying production while making propeller and reduction gear changes much simpler and even possible as retrofits. Plus it might retain some of the (at least theoretical) cleaner long/tapered nose that the Tomahawk and XP-38 sported (I believe the YP-38 as well). The thrust-line would still be raised compared to the C series though, so the stub-shaft + separate gearbox wouldn't be able to perfectly mimic the P-40B/C installation.


On that note, I'm unsure whether the XP-46 really used an F series engine or not. Some articles mention using the -39, but Joe Baugher's page mention the -39 being planned for installation, but the -29 actually installed (possibly a typo). The -29 was one of the low-altitude (or turbocharger-oriented) engines the YP-38 used, which should be a C series engine with low-altitude 7.48:1 supercharger ratio. The XP-46 really looks like it has the P-40B/C/Tomahaek (H81) nose and propeller profile and carb intake placement. If the V-1710-29 really was used, then the performance testing of that aircraft would be nowhere close to what the -39 could have offered. (granted, actual info on the XP-46's performance is somewhat vague and contradictory from what I've seen and might be using a standard C15/V-1710-33 of the contemporary P-40 for all I know, but the cited 'poorer performance' than the P-40D prototype seems unusual in any case given how much more stripped down the thing was and the lower drag area -smaller wing and radiator area) The V-1710-29 WOULD be rated for 1150 hp take-off/military like the -39, just with much lower rated altitude. (similar to the A-36 vs Mustang I/IA ... except limiting boost pressure on the A-36 and 1150 rather than 1325 HP military -albeit at the same altitude the A-36 could do 1150 hp, but several thousand feet lower than the -39's ~12,000 ft)

I believe the XP-38 used early 'sea level' rated 6.44:1 gear ratio C series engines, while the YP-38 adopted 7.48:1 engines. (I don't think the 6.44:1 ratio was used in any operational aircraft) The -27 and -29 engines appear to have been used on the P-38D and E, with the F being the first model to use F-series engines, ironically enough. (and hence take-off power rising from 1150 to 1325 HP -like the A-36, and parallel to the 8.8:1 counterparts rising from 1040 to 1150 hp take-off/military -prior to later up-rating and WER)



Edit:
Looking at that above-linked article more (and the claims of placing the carb between the aux and integral supercharger stages improving altitude performance) I realized the inlet to the aux stage in the intermediate carburetor configuration has inlet guide vanes that might be acting as swirl throttle if they're not static. This might explain why they delayed implementation of an intermediate carburetor location given the added testing involved and superior performance. Using a conventional throttle plate to restrict air flow between 2 mechanical supercharger stages might also be problematic, so having a wide-open carburetor with the aux supercharger inlet acting as the throttle would make plenty of sense. (the text and drawings don't make it clear whether this is the case, though) A swirl throttle arrangement would also make the hydraulic coupling less necessary given the efficiency and improved low altitude performance of the variable inlet guide vane arrangement. (though it might also help compensate for the hydraulic coupling having only 1 gear, thus having the best of both the features of the Jumo 213 and DB-601/605/603, and also avoiding excessive oil heating at high engine RPM low-boost conditions, though a declutched/neutral position would help with that too, if it has one, thus avoiding the accessory drive end of the fluid coupling's turbine spinning at high speed, doing little work and generating lots of waste heat)


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## wuzak (May 5, 2016)

kool kitty89 said:


> Aftercooling or water injection would have helped single-stage performance at all altitudes, especially for the 9.6:1 supercharger (or overreved 8.8) due to the charge cooling and improved density.
> 
> Additionally, I'd failed to consider the possibility of water injection (or for that matter, fuel vapor) increasing the speed of sound further, thus allowing impeller tip-speeds to be well in excess of the speed of sound at ~100*C (or there about) as humidity greatly increases this value. So even at the 9.6:1 ratio, overreving quite a bit might not hit mach 1 tip speeds.



Aftercooling and ADI allow the engine to develop more boost, so without improvements to the supercharger the extra performance of such systems will tend to be concentrated at lower altitudes.


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## wuzak (May 5, 2016)

kool kitty89 said:


> That final turbo-compound variant featured multi-port fuel injection and aftercooling (though the 3200 RPM WER limit was still rather conservative, particularly above its critical altitude).



Not sure that they did.

The turbo-compound used a standard G-series core engine.

The AAC had Allison investigating injection (not sure if it was port or direct - have to check) for the V-1710 and X-3420 in the mid 1930s.




kool kitty89 said:


> On that note, I'm unsure whether the XP-46 really used an F series engine or not. Some articles mention using the -39, but Joe Baugher's page mention the -39 being planned for installation, but the -29 actually installed (possibly a typo). The -29 was one of the low-altitude (or turbocharger-oriented) engines the YP-38 used, which should be a C series engine with low-altitude 7.48:1 supercharger ratio. The XP-46 really looks like it has the P-40B/C/Tomahaek (H81) nose and propeller profile and carb intake placement. If the V-1710-29 really was used, then the performance testing of that aircraft would be nowhere close to what the -39 could have offered. (granted, actual info on the XP-46's performance is somewhat vague and contradictory from what I've seen and might be using a standard C15/V-1710-33 of the contemporary P-40 for all I know, but the cited 'poorer performance' than the P-40D prototype seems unusual in any case given how much more stripped down the thing was and the lower drag area -smaller wing and radiator area) The V-1710-29 WOULD be rated for 1150 hp take-off/military like the -39, just with much lower rated altitude. (similar to the A-36 vs Mustang I/IA ... except limiting boost pressure on the A-36 and 1150 rather than 1325 HP military -albeit at the same altitude the A-36 could do 1150 hp, but several thousand feet lower than the -39's ~12,000 ft)



The crime of the XP-46 was that the performance improvement, if there was any, was insufficient to warrant disrupting production of the P-40.




kool kitty89 said:


> Looking at that above-linked article more (and the claims of placing the carb between the aux and integral supercharger stages improving altitude performance) I realized the inlet to the aux stage in the intermediate carburetor configuration has inlet guide vanes that might be acting as swirl throttle if they're not static. This might explain why they delayed implementation of an intermediate carburetor location given the added testing involved and superior performance. Using a conventional throttle plate to restrict air flow between 2 mechanical supercharger stages might also be problematic, so having a wide-open carburetor with the aux supercharger inlet acting as the throttle would make plenty of sense. (the text and drawings don't make it clear whether this is the case, though) A swirl throttle arrangement would also make the hydraulic coupling less necessary given the efficiency and improved low altitude performance of the variable inlet guide vane arrangement. (though it might also help compensate for the hydraulic coupling having only 1 gear, thus having the best of both the features of the Jumo 213 and DB-601/605/603, and also avoiding excessive oil heating at high engine RPM low-boost conditions, though a declutched/neutral position would help with that too, if it has one, thus avoiding the accessory drive end of the fluid coupling's turbine spinning at high speed, doing little work and generating lots of waste heat)



I'm not sure how much an improvement using the carburettor between the supercharger stages gave to altitude performance. I suspect it has a lot to do with the intake shape of the carburettor on the auxiliary supercharger.

Practically speaking, using the carburettor between compressor stages allowed the core engine to be, essentially, the same as used in a turbocharged installation. The downside is that charge cooling could only come using ADI, and not an aftercooler.
I believe it also shortened the length of the whole engin without that massive carburettor hanging off the back.


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## tomo pauk (May 6, 2016)

The relocation of carb gained some 2500 ft to the rated altitude. It also allowed for 4000 ft gain in condition of full ram, vs. just 1500 ft in case the carb was at the entrance of the 1st stage. Net result - aircraft's (P-63C) max speed on military power was attained at ~29000 ft, vs. at ~24000 ft for the P-63A. Rate of climb at high altitudes was also improved, along with max speed.


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## GregP (May 6, 2016)

The Turbo-Compound was the V1710-127 or was an E27 in Allison parlance and did not use a G-series core. The G-series started with the V-1710-97, but was not used in the -109. The -127 was essentially the same as a -109 engine except equipped with mechanical feedback exhaust turbine and a different propeller shaft gear ratio.

The prop gear ratio was 2.48 : 1.

No agenda here, just saying ...


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## wuzak (May 7, 2016)

GregP said:


> The Turbo-Compound was the V1710-127 or was an E27 in Allison parlance and did not use a G-series core. The G-series started with the V-1710-97, but was not used in the -109. The -127 was essentially the same as a -109 engine except equipped with mechanical feedback exhaust turbine and a different propeller shaft gear ratio.
> 
> The prop gear ratio was 2.48 : 1.
> 
> No agenda here, just saying ...



Vees for Victory stated that the -E27/-127 was based on components from the -E30/-133, which was the latest development standard at the time.


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## wuzak (May 7, 2016)

tomo pauk said:


> The relocation of carb gained some 2500 ft to the rated altitude. It also allowed for 4000 ft gain in condition of full ram, vs. just 1500 ft in case the carb was at the entrance of the 1st stage. Net result - aircraft's (P-63C) max speed on military power was attained at ~29000 ft, vs. at ~24000 ft for the P-63A. Rate of climb at high altitudes was also improved, along with max speed.



The change improved the altitude performance not because of the carburettor position, but because of the reduction in losses in the air flow for 1st stage to 2nd stage.


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## GregP (May 7, 2016)

The Allison docs say it came from the -109.

If I have to choose between Allison and Vees for Victory, I choose Allison since they made the engines. In the end it doesn't matter since it never flew, even if it was interesting.

I think the V-1710 still had development potential, as we have gone over before, but the jet engine put that on hold forever. At least the Allisons Joe is delivering these days have -100 series internals and almost perfect balance. I'm sure that all helps a lot more than anything else.

Cheers.


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## kool kitty89 (May 8, 2016)

wuzak said:


> Practically speaking, using the carburettor between compressor stages allowed the core engine to be, essentially, the same as used in a turbocharged installation. The downside is that charge cooling could only come using ADI, and not an aftercooler.
> I believe it also shortened the length of the whole engin without that massive carburettor hanging off the back.


The common core engine arrangement is why I'd have thought they'd have gone with that configuration from the start, using the aux stage literally in place of a turbocharger (sans intercooler ... though, technically, an intercooler could have been installed as well, just as with a turbo).

I don't see why that arrangement would preclude use of an aftercooler, though. Use of a standard modular core engine would preclude it, yes, but the inter-supercharger carburetor placement seems perfectly compatible with aftercooling. (an intercooler in series with the aux stage and carb intake would be more compatible with the modular add-on arrangement though and technically COULD be of liquid cooled type and not air to air, and would probably be best located at the carb intake, minimizing bulk and length of glycol plumbing to only slightly more than the aftercooler arrangement does)

Mimicking the behavior of a turbocharger really seems like the best/most foolproof direction Allison could have taken and is probably why they discarded the fixed gear ratios in favor of a fluid coupling relatively early on. (even a single-speed fluid coupling would allow pretty useful performance, particularly with a full-neutral setting avoiding excessive oil/fluid heating at low altitudes) I wonder if examining the impeller size and RPM range of GE's turbos would have accelerated development more than building off Allison's own superchargers alone (or potentially outsourcing to Wright or P&W)

I know GE's supercharger designs were quite lacking in the 1920s and early 30s (leading to P&W and Wright investing in developing their own) but the added competition led GE improving their own hardware quite a bit from what I understand. (and even if the compressor design was inferior to what Allison was already working with, the mass flow, diameter, and operational RPM range would be useful for testing -including avoiding stall conditions between the two stages)

For that matter, running an auxiliary supercharger of identical construction to the integral stage, but driven totally independently (off some sort of supplemental powerplant or perhaps even electric motor) could have been used for initial trials and rather quickly written off that sort of pairing as unworkable, or established what range of operating conditions it was workable within and whether those were worthwhile. (without wasting time actually developing the 2nd stage's mechanical or fluid coupling mechanism)




wuzak said:


> The change improved the altitude performance not because of the carburettor position, but because of the reduction in losses in the air flow for 1st stage to 2nd stage.


This is counter-intuitive given the intermediate carb installation requires a longer duct with more twists and turns leading from the aux stage to the carb than is the case for the aux stage directly into the engine stage.

Reduction in intake losses from the carb-less aux stage intake manifold seems to be the big gain here, possibly in addition to charge cooling between the two stages being more efficient than at the intake of the aux stage.


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## IdahoRenegade (May 21, 2016)

Was there ever any development with a air/water intercooler in the turbo/Allison installation? It seems like it would have greatly simplified the ductwork, since you can simply install a fairly small air/water heat exchanger in the intake plumbing between the turbo/supercharger, rather than ducting that large volume of air to a big chin-mount core-type air/air heat exchanger (or wing leading edge duct), then back half the length of the boom. Much easier to route a couple small water lines. Not only would the plumbing be much simpler but the frictional losses in the intake ducting would be less, and pressure drop across the HE should have been lower. In addition the 2nd water/air cooler (to "dump" the heat from the water) could have been smaller, less drag inducing and easier to package. Correct me if I'm wrong, but weren't the 2-stage Merlins intercooled this way?


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## wuzak (May 21, 2016)

Some of the two stage Allisons had a Merlin style aftercooler.


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## Shortround6 (May 21, 2016)

The two stage Merlins were actually "after-cooled". The terms get confused at times. Especially when used in reference to cars. 
An inter-cooler is used to cool the intake charge *between *supercharger stages. An after-cooler is used to cool the charge *after *all supercharging is done. Some engines have used both. 

The air to air setup vs the air to liquid (water alone may not work at high altitudes without anti-freeze) is hard to evaluate based on generalities. The US _may_ have felt/believed that the air to air system was more resistant to battle damage. A few 8-13mm holes in the duct work (or even in the matrix, US system of matrix between supercharger stages meant there was only compressed air in the system, no fuel)) while reducing the performance will not lead to total failure of the system in a few minutes time. A liquid cooled system that is holed may reach a point where it is no longer providing _any _cooling. That may balance against the harder job of keeping large ducts air tight even during normal flying vrs keeping the liquid lines tight, a much easier job. The air to air system only has a few doors or flaps as moving parts vs adding a pump for the liquid cooled system which may still require a door or flap to control airflow through the remote (non-engine) heat exchanger. 
Pressure drop across the intercooler is dependent on the relative airflows, the size and design of the matrix and to some extent the changes in duct size leading to and from the matrix. 
Size of the Matrix (heat exchanger) is also dependent on the amount of cooling desired, and thus the airflows needed. I believe, but could very well be wrong, the the Merlin system was supposed to remove 40% of the heat _added _by the superchargers (both stages). The American turbo system intercoolers were measured in a totally different way (although performance of the matrix/heat exchanger could have been measured exactly the same) in that they were supposed to deliver the required air to the carb mounted on the engine supercharger at no more than 100 degrees Fahrenheit at sea level pressure (or close to it). 
Trying to guess which system was better with so little information is difficult, and we are referring to the systems of the time, not which system is better in 1990 and later race cars, as air flows would be measured in pounds of air per minute not cubic feet as the system/s have to work at altitudes where the air density is 1/3 or less of what it is at sea level. They also have to work at climbing speed which is about 1/2 or less of level speed flight and so gets 1/2 or less of the air flow of full speed level flight. 
Granted neither engine was using anywhere near it's full supercharger capacity at sea level or near it and so didn't need the full amount of charge cooling. 
Both the Melrlin and Allison were developing about the same amount of power in the cylinders. 1650cu in vs 1710 at 3000 rpm and at 60-62in of manifold pressure means aside from the 4% difference in displacement the only other variables are the compression ratio and the actual intake charge density (which is dependent on the intake charge temperature). Pressure is an easy to measure data point but it is not mass airflow (pounds per minute) and it is mass airflow that governs power. 
Large differences in power to the crankshaft are from differences in internal friction, pumps and such *and* how much power was being used to drive the superchargers. 
I would note however that the Merlin system at altitude (over 23-24,000ft) is running air that is already compressed 5-6 times before it hits the cooling matrix and is _very_ hot. The P-38 system is cooling air that is compressed only about 3 times or less.

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## tomo pauk (May 21, 2016)

The XP-51J used one cooling circuit for joint needs of the aftercoolers and the oil system, and another circuit for colling the water-gycol mixture. The joint aftercooler/oil system used heat exchanger to split the cooling further. Heat exchangers were also used on the Jumo 213 line of engines (coolant+oil in A, C and F versions, coolant+oil+aftercooler on E variant). 
D.520 'Ameiloree' (sp?, means 'Improved') also used heat exchanger for oil coooling.

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## IdahoRenegade (May 22, 2016)

As far as susceptibility to battle damage of a air/liquid vs air/air system, I can see advantages and disadvantages to each. The air/liquid system has smaller liquid lines than the ductwork of the air/air system and should have a smaller heat exchanger. Meaning that it should be slightly less likely to take hits. A hit on the ductwork of the air/air system or the HE means that you are losing pressurised air, meaning reduced boost available to the engine. Whereas by eliminating most of the ductwork you reduce that concern, while opening yourself up perhaps more to a loss of inter/aftercooling. Pick your poison I guess.

As far as intercooling vs aftercooling, aftercooling would seem to offer a couple advantages. First you are cooling the intake air after all the compression is done, meaning that you should be able to supply a cooler air mass to the engine. Intercooled air is re-heated in the mechanical supercharger, limiting how cool it will be at the engine. In addition, by providing the 2nd stage of boost before cooling, the air charge is hotter. Heat exchanger efficiency increases with increased deltaT or temperature difference between the two "fluids" (air is a fluid for this purpose). So a given number of BTUs/min can be dissipated with a smaller HE and with a smaller volume of cooling air.


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## wuzak (May 22, 2016)

Intercooling reduces the power required to drive the second stage. A useful thing, as it increases power to the prop.


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## Shortround6 (May 22, 2016)

I would note that neither system, as used in WW II, actually cooled the air down to anywhere near ambient temperatures. The R-R system was supposed to reduce the intake charge temperature by about 40%. I have no figures for a two stage Merlin but a Merlin XX supercharger raised the temperature by 148 degrees centigrade for 9-10lbs of boost. A two stage supercharger would heat the air a bit less if keeping the boost the _same_ but will heat the air more if higher boost is used _or _9-10lbs boost is used at higher altitudes than the MK XX supercharger could provide it. A MK XX Merlin in a Hurricane doing 340mph at 20,000ft including the ram effect was compressing the air about 3.64 times, a Merlin 61 in a Spitfire could compress the ambient air 6.2 times at 33,000ft (including ram) for 9lbs boost or 5.7 times at 27,000ft for 15lbs boost. 
A heat exchanger that lowered the intake temp by 40% would lower the MK XX intake charge by about 60 degrees C. leaving it at 88 degrees higher than the ambient air it took in, leaving out heating in the intake duct (yes a ram air intake does heat the incoming air even if only by 10 degrees or so) and cooling by fuel evaporation. Obviously the Merlin 61 even with the 2 stage supercharger is going to heat the air a whole lot more. 
_IF_ you want a bigger temperature reduction you need a bigger heat exchanger and a higher flow of cooling medium, wither air or liquid. 
However after around a 40-45% reduction you start getting into diminishing returns. For WW II Air to air inter-coolers/heat exchangers a 40% reduction could be had for an air flow equal in mass to the intake charge. a 1.5:1 ratio got around a 53/54 % reduction, a 2:1 ratio got around a 62% reduction while a 3:1 ratio only got a 70% reduction. 
The US system/s (at least the turbo units) tried to get the inlet temperature of the engine supercharger down to 90-100 degrees Fahrenheit under worst case scenario. To do this they had to reduce intake charge temperatures of around 170-180 degrees Fahrenheit (at 25,000ft) down to the under 100 degree limit. This is using ambient air of about -30 degrees Fahrenheit. (rise in temperature due to the turbo compressor was around 220 degrees F. 
I would note that a 50 degree rise in intake temperature carries through the entire engine. That is 50 degrees higher in the intake duct means 50 degrees higher in the intake manifold, it means 50 degrees higher in the combustion chamber and it means 50 degrees higher exhaust gas temperature. 
As has been mentioned the US system did make the the second stage more efficient but at the cost of greater bulk. 
Without more specific information it is very hard (involves too much guess work) to pick which was better. 

AS far as minor battle damage goes (a few small caliber bullets) the effect on the air to air system is going to be minimal. 
At 99 degrees C an 8mm hole is going to flow about 30cu ft a minute at a pressure differential of 30lbs inside and 5lbs outside air pressure or less than 3% of the air flow of an engine making around 1100hp to the prop. That would be a hole in the intake duct not a hole in the cooling air duct.

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## GregP (May 26, 2016)

Why would intercooling reduce the power required to drive the second stage? The air-fuel mixture is not burning in the intercooler, it is only getting cooled. If the after cooler brings the charge to the same temperature before getting injected into the cylinders, then the power produced would be the same.

Now if the aftercooler doesn't quite get the charge cooled down to the same temperature as without the intercooler, then adding an intercooler while retaining the aftercooler would lower the charge temperature and possibly produce slightly more power, but it doesn't change the power required to drive the seconds stage in any way.


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## Shortround6 (May 26, 2016)

It _may _make the 2nd stage more efficient. Better results for the "same" power input. Since the cooler air is denser the supercharger _may_ be able to flow more air at the same impeller rpm and pressure. However due to the denser air it may take more power to turn the impeller so saying the intercooler _reduces _power may not be quite right either. 
You have pressure and volume/mass flow on one side and power required and efficiency on the other and rarely are all four put together.






This compressor map gives us pressure, air flow and efficiency *but *does not give us the power required. It *will* take more power to turn the impeller/s at 35,000rpm and flowing 60lb/min than it will at 35,000rpm and flowing 30lb/min. 

I would also note that the difference in efficiency is pretty much related to excess heating of the intake charge. A supercharger that is 65% efficient is using 65% of the input power to actually compress the air. the other 35% is pretty much turning into _excess_ heat over and above the heat of simple compression. A supercharger doing the same work but running at 72% efficiency requires slightly less power but more importantly heats the intake charge less. With an aircraft supercharger using 100hp or more for the type engine/s we are talking about 5-10 hp more or less to drive the supercharger is almost too small to measure or worry about but 5-10hp turning directly into heating the intake charge to higher temperatures may have more impact on actual power developed due to the difference in density of the intake charge and running closer to the detonation limits.

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## wuzak (May 26, 2016)

GregP said:


> Why would intercooling reduce the power required to drive the second stage? The air-fuel mixture is not burning in the intercooler, it is only getting cooled. If the after cooler brings the charge to the same temperature before getting injected into the cylinders, then the power produced would be the same.
> 
> Now if the aftercooler doesn't quite get the charge cooled down to the same temperature as without the intercooler, then adding an intercooler while retaining the aftercooler would lower the charge temperature and possibly produce slightly more power, but it doesn't change the power required to drive the seconds stage in any way.



These answers might help:
what is the purpose of inter cooler in multistage compressor



> Inter-coolers are provided between successive stages of a multi-stage compressor to remove the heat of compression hence reduces the work of compression (power requirements). The work of compression (power requirements) is reduced by reducing the specific volume through cooling the air. Thus inter-cooling affects the overall efficiency of the machine.


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## GregP (May 28, 2016)

I believe that only if we assume the first compression gets the mixture to a point where it will be excessively hot when compressed the second time. If they used an aftercooler only and it got to the same temperature as the intercooled and aftercooled unit, then I'd doubt it very seriously. Still, it could be.

One logical supposition is that they would not have fitted an intercooler had it not been needed in the first place, so perhaps you are right. It may be that fitting both an intercooler and an aftercooler actually did produce results that justified the extra weight and complexity. I'd latch on to that only if we could see comparative testing that showed it, though. Interesting avenue of investigation that I may take some time to look into later. I can believe it was possible, but would want some proof of same.

Thanks for suggesting it. Don;t have time now due to getting ready to reach new (to me) classes, but will get back to it along the way.

Some of the car turbos are getting intercooled even with only 6 - 8 pounds of boost, so it is easy to believe a lot more boost (+18 or more) on a bigger engine could use it. Some cars are even getting aftercooled, but these are mostly exotics. Not too many for the everyday driver. So far, I haven't noticed one that is both intercooled and aftercooled in cars. Maybe in Formula 1, but I haven't checked that and so don't claim it to be so. I really like the F1 Mercedes turbo that runs the shaft through the engine to be away from the exhaust heat. It removes the necessity for some of the cooling by removing some of the heat from the surrounding environment.


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## Shortround6 (May 28, 2016)

with the cars we are getting back to confusion in terminology. Very few, if any, cars are using two stage supercharging for 6-8lbs boost. 
Many times what is called an inter-cooler on a car is really an after-cooler. Cars also are using much less compression to get 6-8lbs of boost than aircraft unless that car can get 6-8lbs at the top of Pike's peak. 7.5lbs boost at sea level only calls for compressing the air 1 1/2 times at sea level. 7.5 lbs boost at 18,000ft calls for compressing the air 3 times. 
Most cars (single seat race cars excepted) are nowhere near as volume limited as fighter planes and the weight/drag of an inter-cooler/aftercooler is relatively insignificant on street cars or race cars derived from street cars.


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## wuzak (May 28, 2016)

I can't think of any cars that use two stages of compression.

There are many with twin turbos - but that is usually one for a set of cylinders and a second for another set. Less commonly used is a series set up where there are two different sized turbos, one for low speed boost and one for high speed boost, but they don't work as a first and second stage compressor.

Another case is a supercharged and turbocharged car, a few of which exist. These also operate with one (the supercharger) for low speed and the other (turbocharger) for high speed.

The current F1 turbos have only one stage of compression per the rules. They are after-cooled.

Road cars have higher compression ratios than WW2 aircraft and lower boost, generally, but have less exotic fuels to use but better combustion chamber designs.

Also, the Rolls-Royce two stage engines featured water passages around the supercharger housing to achieve a small amount of inter-cooling.

The intercooler helps the power in two ways. It reduces the power required to drive the engine stage supercharger and it lowers the temperature at the outlet of the second stage. 

The aftercooler does the latter, which enables more boost or higher compression to be run and more fuel.


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## DOFpower (Nov 3, 2016)

Maybe BMW's quad turbo diesel.


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## soulezoo (Nov 4, 2016)

Maybe I can help here. I've had a bit of experience in designing and spec'ing twin turbos for the purpose of high output diesels.

Shortround provided a good bit of info already, let's see if I can "compress" this answer.

The twin turbos I work with are sequential in that we have a large (primary) turbo that takes ambient air (this can be described as "high-volume, low pressure turbo) and compresses this air and feeds to smaller (secondary) high pressure turbo that compresses the air once more and feeds the engine.

Most commonly, there is only one Charge Air Cooler (CAC- more commonly described as intercooler, or as above "aftercooler"). The CAC is almost always air to air and the goal is to get the compressed air something close to ambient but is usually closer to 70-100*F over ambient.

The air coming out of a twin turbo designed as I describe above can compress air and create temps that exceed 600*F! This can often exceed the capabilities for a CAC to properly cool the air. An air to water CAC of much smaller dimension is used after the primary turbo that can often cool the air to below ambient before entering the secondary turbo making for a more efficient air charge and many more pounds/min of air (or often described as more oxygen molecules in the CFM that is moving). The drawbacks to the system is complexity, weight, space and air restriction. The restriction comes in as there is necessary dwell time of the air within the CAC on either end to be able to exchange the heat. The benefit is obvious. High air temps in a gasoline engine is undesirable as this can cause detonation. In any case, thoughtful Charge Air Cooling means that a super/turbocharger can then compress and move a much higher volume of air than otherwise possible due to excessive air temps. The hotter air is, the more it expands and the fewer oxygen molecules are available for combustion for a given air volume.

In my personal truck, (and yes you will read this correctly), my twin turbos have given me up to 100 psi (that's PSI, not inches of mercury), of boost. That is a diesel with special aerospace headstuds to keep the head down under those extreme cylinder pressures.

And that is a 5.9 liter engine that produces 1150 hp and pushes a 7800lb truck to low 11's in the 1/4 mile. That's what boost can do for you!

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## tomo pauk (Nov 4, 2016)

That's impressive, not just from European perspective 
Any pictures you can post, either in this thread or elsewhere?


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## soulezoo (Nov 4, 2016)

Sure. I'll take a couple this weekend and post them.


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## yulzari (Nov 5, 2016)

and of course water injection does an equivalent job by using it's latent heat to soak up the adiabatic heating of a compressed charge by turning the atomised water spray into steam.


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## johnbr (Nov 5, 2016)

Allison engine








TurboCompound V-1710-127


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## Old Wizard (Nov 5, 2016)




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## Balljoint (Nov 8, 2016)

johnbr said:


> Allison engine
> View attachment 356516
> View attachment 356517
> 
> TurboCompound V-1710-127



Great engine. Just lagging a year or two in development. Allison is way down the list in regard to blame or incompetency.

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## soulezoo (Nov 13, 2016)



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## soulezoo (Nov 13, 2016)

The above photo is the one I promised a week ago. The photo shows the top turbo, a Garrett 4094r, well but the larger bottom turbo, a Garrett 4718r, is hidden. The 90* pipe shown goes from the bottom turbo and feeds the top turbo. The two braided steel lines shown in the pipe going from top turbo to the intercooler are the nitrous injection lines. Not shown in the photo but are located on the intake on the other side of the engine are 5 lines for the methanol/water injection.


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## Old Wizard (Nov 13, 2016)




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## fastmongrel (Nov 16, 2016)

Just casting this into the cam boxes would have made the V1710 a winner

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## duplex (Jun 9, 2017)

Balljoint said:


> Great engine. Just lagging a year or two in development. Allison is way down the list in regard to blame or incompetency.


 
It was a great engine in its own right . There is no doubt that had RAF fighters been powered by Allison during BoB ,the result would have been the same .18 RAAF pilots bacame aces with P-40's powered by Allisons .Aside from all these nationalistic feelings , I'm at a loss trying to figure out what decisive role Merlin might have played during BoB , it looked pretty tragic compared to 109's state of the art direct fuel injections, 100 octaine fuel perhaps?

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## tomo pauk (Jun 9, 2017)

<since I'm at work, I'll get some popcorn>


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## Balljoint (Jun 9, 2017)

The problem with the Allison only developed when the Allied bombers started daylight flying at 20,000’+. It was solvable by a two-speed, two-stage Allison or Packard Merlins –a tossup in my view. Of course the situation wasn’t aided by the bomber boys attachment to self defending bombers, or the thought that a fighter with long range fuel capacity couldn’t defend itself, let alone the bombers.
 
They lacked the hindsight that we’re blessed with

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## pbehn (Jun 9, 2017)

duplex said:


> It was a great engine in its own right . There is no doubt that had RAF fighters been powered by Allison during BoB ,the result would have been the same .18 RAAF pilots bacame aces with P-40's powered by Allisons .Aside from all these nationalistic feelings , I'm at a loss trying to figure out what decisive role Merlin might have played during BoB , it looked pretty tragic compared to 109's state of the art direct fuel injections, 100 octaine fuel perhaps?


In 1940 it was a great engine block. It did not have the supercharger of turbo charger to give performance at altitude. If we only had Allison engined aircraft in the BoB then combat would take place above 20,000 ft where the Allison was way down on power. The decisive role of the Merlin was powering the Hurricane and Spitfire which saw off the LW. The Merlin was 27 Litre swept volume while the Db 601 was 34 Litres.


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## tomo pauk (Jun 9, 2017)

duplex said:


> It was a great engine in its own right . There is no doubt that had RAF fighters been powered by Allison during BoB ,the result would have been the same .18 RAAF pilots bacame aces with P-40's powered by Allisons .Aside from all these nationalistic feelings , I'm at a loss trying to figure out what decisive role Merlin might have played during BoB , it looked pretty tragic compared to 109's state of the art direct fuel injections, 100 octaine fuel perhaps?



Pray tell, why would anyone consider the Merlin engine as 'pretty tragic'? Since when the presence of a fuel injection is a determinant of a great ww2 piston engine?
As for the Merlin in the BoB, there was no what might have been, since it actually was - an important piece in the mechanism that dealt the 1st defeat to the Luftwaffe. The Allison of any year was inferior of a Merlin of the same year, 1940 included, it was acknowledged as such by the USA, and entered license production there as a single major foreign piece of equipment by the date.

There was no such thing as '100 octaine fuel'; fuel injection was a feature of an engine, not of an aircraft.

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## XBe02Drvr (Jun 9, 2017)

duplex said:


> There is no doubt that had RAF fighters been powered by Allison during BoB ,the result would have been the same


pbehn speaks truth. The Allison of 1940 couldn't match the Merlin at 20K and above and certainly not the Daimler because it's supercharger was optimized for max power down low, not at altitude. The USAAC decided in the thirties to cast its lot with turbochargers at altitude and superchargers for lower levels, thus American technology for high altitude superchargers lagged a bit behind Europe by the time of BoB.
Turbochargers of the day didn't fit gracefully in P-40 sized aircraft, and even if it had the power at altitude, it wouldn't have had the speed or maneuverability to counter Emil up high. It was a low altitude airframe, heavy, with a draggy high lift airfoil.
Cheers
Wes


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## tomo pauk (Jun 9, 2017)

XBe02Drvr said:


> pbehn speaks truth. The Allison of 1940 couldn't match the Merlin at 20K and above and certainly not the Daimler because it's supercharger was optimized for max power down low, not at altitude. The USAAC decided in the thirties to cast its lot with turbochargers at altitude and superchargers for lower levels, thus American technology for high altitude superchargers lagged a bit behind Europe by the time of BoB.



The engines for high-altitude aircraft (ones also featuring a turbo) also featured another supercharger, thus making a two-stage supercharging in effect. American superchargers' techology was every bit as good as European, whether in 1939, 1941 or 1944, Germany included. Neither Soviets nor Italian came close to the US superchagers. The 1st gear-driven two stage supercharged engine was the US product. 
The V-1710-33 (one of the 1st 'military-grade') Allisons was making more power above 14000 ft than the DB601A of 1940.




> Turbochargers of the day didn't fit gracefully in P-40 sized aircraft, and even if it had the power at altitude, it wouldn't have had the speed or maneuverability to counter Emil up high. It was a low altitude airframe, heavy, with a draggy high lift airfoil.
> Cheers
> Wes



The P-40 was a bigger and heavier A/C than the Bf 109, and it was heavier than the Spitfire or Hurricane. P-40 carried more fuel and (in most cases) armament weight than the Eurpoean fighters. The airfoil choosen was not that draggy - 15% T-t-C ratio at root, same percentage as with Fw 190 or Hellcat. 'Low altitude airframe' it was not, as it can be seen when the 2-stage V-1710 was installed, for the performance equal to the Fw 190D-9. The early P-40 were as fast as the Emil, with more range and better roll rate.
The turbos of the day were same size as in 1942 or 1944, the slender booms of the P-38 accepted them after all.

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## Milosh (Jun 9, 2017)

Didn't almost all RAF fighter squadrons use 100 octane fuel during the BoB?


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## XBe02Drvr (Jun 9, 2017)

Tomo, thanks for the info. Clearly you've researched this more than I.
Couple of questions. Where was the -33 Allison when the BoB came along? I was under the impression that came later. I should have been clearer about superchargers. It wasn't so much inferior technology as choosing to gear it for max power down low at the cost of high altitude performance. The late thirties Army thought of single engine fighter planes as accessories to the ground army, not high altitude dogfighters.
Cheers
Wes


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## GregP (Jun 9, 2017)

The issue with the altitude capability of the Allison was the direct result of Air Corps requirements. They got what they ordered. They also declined to fund the development of a higher-altitude version. Allison's use of the auxiliary, 2nd-stage supercharger was a low-cost development that was not optimum, but could be considered for a bomber's larger nacelles. Had the Air Corps / USAAF decided to make a 2-stage integral engine, Allison could have done it. Not sure about the timeframe, but it wasn't magic ... only unfunded.

The powers that be at the time declined to look at a long-term solution, and the Merlin was a gift horse when there was a need. They COULD have asked Allison to make one with a similar supercharger arrangement. That they didn't says a lot about making due. It says nothing about the ability to do it.

Maybe that's why Allison was given the opportunity to develop early jet engines ... the Air Corps saw the piston in technological decline and turbine in technological rise.

Now, there is NOTHING wrong with a Merlin, carb or not, It's a good engine; even a great one. So was and IS the Allison. It all depended on what you were going to do with it, and how high you were going to be. The Allison could get up into the mid 30s altitude, but ti didn't have fighter performance when it got there on one the way up. That's not a disadvantage if you aren't in a fighter. The Allison-engiend B-17 was faster than the R-1820 version, and cruised a lot faster, too.

In modern ownership, the Allison has a much longer time between overhauls. But that isn't a wartime requirement. All military piston aviation engines were overhauled before they really needed it. If they waited until overhaul was needed, the pilot might decline to fly it. So, the fact that the DB605 was slated for a 100-hour TBO doesn't make it a bad engine. It means that the engines in service were reliable, ran well, and generally had 100 or less hours on them as they sat waiting for a mission. That's all.

To me, the title of the thread has a problem. The Allison didn't have many problems, though it did have a few (4, to be exact) when operated in Europe, at first. All were solved. The Air Corps had a short-sighted view of what they wanted and it turned out that what they wanted in 1929 (when the Allison was developed) was NOT what was required in 1940. The intervening time could have been used to update the low-volume engine, but it wasn't. The time from Pearl Harbor until 1943 could ALSO have been used to develop high-altitude capability, but it wasn't, either.

So, we can thank the British for seeing clearly what was needed and having a genius like Sir Stanley Hooker around to help with the supercharger development. I'd like to have seen something like the Fw 187 with a pair of aux S/C Allisons in it, OR a pair of 2-stage Merlins in it. But ... the planes we DID see were really good ones and I can't complain.

There was no shortage of good aircraft on either the Allied or the Axis side. They were the pinnacle of piston development at any particular time in the war. Naturally, some were better than others.


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## pbehn (Jun 9, 2017)

Milosh said:


> Didn't almost all RAF fighter squadrons use 100 octane fuel during the BoB?


I believe that once the USA agreed to supply it (at a cost) they all did.


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## pbehn (Jun 9, 2017)

tomo pauk said:


> The turbos of the day were same size as in 1942 or 1944, the slender booms of the P-38 accepted them after all.



Very true Tomo but all the turbo and cooling gear are where the pilot with his controls normally are.


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## pbehn (Jun 9, 2017)

tomo pauk said:


> As for the Merlin in the BoB, there was no what might have been, since it actually was - an important piece in the mechanism that dealt the 1st defeat to the Luftwaffe.



A great point, I would add that the RAF did not accept the Mustang as a front line fighter despite its speed range and agility, its poor performance at altitude was the reason and the Allison engine as delivered was the reason. If USA turbo and supercharger technology was as good as the opposition why were US bombers escorted by Merlin engined P-51s?


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## Shortround6 (Jun 9, 2017)

It's a lot more complicated than it appears. Those lousy British British carburetors (and the American ones) helped cool the intake charge by about 25 degrees C over what the fuel injected German engines could due to fuel evaporation in the supercharger. They were also much cheaper and simpler to make, requiring about 1/4 the parts and much, much less precision machining which meant that the machines and operators could be making something else.

If you are going to use a "snapshot in time" like the BoB of under 2 months you had better make sure your facts are right.

The Merlin III could make 6-6.25lbs (roughly 42in or 1.4AtA) of boost in the intake manifold with no ram at 16,250ft. which is better than any other supercharger in squadron use in Aug of 1940 could do. It made 1030hp at that altitude.
The Allison -33 in the long nosed P-40s made 1040hp at 14,300ft using 41in of MAP or 5.5 lbs? British Spitfire or Hurricane would have lost about 2,000 ft of ceiling (service,operational and combat ceilings). That assumes of course that that the British got -33 engines _after _
the first 288 or so. The early engines broke and had to be sent back for a "*re-work*" that included such minor items as a modified crankshaft. Allison fixed the engines at company expense and continued to improve the engine in may ways resulting in an ever improving engine not only in power but in durability and reliability. However d o not confuse mid or late war engines with engines being built in 1940 (or with the electric Curtiss propellers that were slow to change pitch and allowed the engines to overspeed)
The mid 1940 DB 601 engines didn't come close in supercharger performance. The supercharger on the DB601A-1 model was good for about 39in (4.5lbs) at 4000 meters (about 13,200ft). An improved supercharger was brought into service during 1940 that boosted the 1.3 Ata Limit to 4500 meters or 14,850ft.
Of course in Aug/Sept Spitfire IIs began to trickle into service with Merlin XII engines with better altitude perfroamcne than the Merlin III and Sept of 1940 saw a few Hurricane IIs start to show up with the Merlin XX engines which not only had two speeds but the supercharger with Hooker improvements. This supercharger could carry 6lbs boost (42in or 1.4ata) to over 20,000ft. In other words the Fall of 1940 (after the BoB?) Merlin supercharger could match the performance of the DB605A of 1942, or perhaps we should say that it took Daimler Benz until 1942 to match the performance of the Merlin Superchargers of the fall of 1940.

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## Milosh (Jun 9, 2017)

pbehn said:


> I believe that once the USA agreed to supply it (at a cost) they all did.



Went looking and came across this, Use of 100 Octane Fuel in the RAF during BOB

Stocks of 100 Octane
30th September 1939 153,000 tons(b)
27th February 1940 220,000 tons(b)
31st May 1940 294,000 tons(a)
11th July 1940 343,000 tons(b)
31st August 1940 404,000 tons(a)
10th October 1940 424,000 tons(c)
30th November 1940 440,000 tons(a)

There is further data in the quite heated at times discussion mainly due to a well known anti Brit person.

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## Shortround6 (Jun 9, 2017)

We have a number of threads covering these topics, including some on enduring myths of WW II

The US Army didn't get what they asked for in 1939-40-41 for superchargers, they got what was _technically possible. _ 
1. Allison was a small company with only about 25 men in the engineering dept and not all of them were engineers, that number includes the guy/s who ran the blueprint machine. They didn't have the staff to work on multiple supercharger set-ups. 
2. Allison had one of the best superchargers in the world in 1939-40 in terms of the Pressure it would deliver vrs the pressure of the air entering it. Pressure ratio. *NO *American company had a single stage supercharger that was any better.
3. One of Hooker's claims to fame was that he very quickly realized that some of the formulas people had been using to design superchargers for over 20 years were flawed. Doesn't matter how many engineers you have, if you are using flawed formulas/design tools you are going to get flawed results. 
4. Fuel _capable_ of using high manifold pressure was relatively new. Many people didn't realize how bad their superchargers were because 2-4lbs boost (34-38in MAP) was all the fuel would support. 87 octane would support 6lbs boost in some engines (not all).
This was the big reason for the Armies push for turbochargers. By using two stages separated by an intercooler they could use more boost with the same fuel than a single stage supercharger would allow. 

Contrary to legend Britain was NOT saved by the timely arrival of a tanker full of US 100 octane gas. The British had been stockpiling 100 octane fuel since the middle of 1939. 
One also has to be careful in reading as while quite a bit of British fuel came from the _"Americas" _that doesn't necessarily mean it came from America (the United States). There was a large refinery in Trinidad for instance since before WW I that had been progressively enlarged. At some point in 1940 it reached the capacity of 285,000 barrels per DAY. It had reached 9000 barrels a day back in 1919. 

We are also back to the American 100 octane vs British 100 octane thing. American refineries could certainly produce fuel to British specifications but it was far different than USAAC 100 octane fuel. Using USAAC 100 octane with 12lbs boost would have seen blown up Merlin's all over southern England in 1940. This also goes back to the Allison. There was only so much you could do with 100 octane fuel and that is what the American fuel was, 100 octane or PN number lean, not rich and in fact more than one batch actually measure under 100 PN under rich conditions. British 100 octane at the time of the BOB was actually between 115 to 120 PN number when measured later.

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## pbehn (Jun 9, 2017)

Milosh said:


> There is further data in the quite heated at times discussion mainly due to a well known anti Brit person.



I dont know anything about the "anti Brit person" I just seem to remember that to perform at best the RAF needed 100 Octane fuel but didnt have the refining capacity to satisfy demand. Supply of 100 octane fuel became a political issue because of neutrality. Eventually there was an agreement based on "a dollar per barrel" (as I remember it).


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## Milosh (Jun 9, 2017)

Read the thread. The Brits had enough capacity and even increased stocks without American help.


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## Shortround6 (Jun 9, 2017)

I believe there was a refinery (at least one?) in western England that was also producing 100 octane fuel from imported feed stocks. 

Now the British may very well have been working to assure even more supply (or as back up in case of bomb damage?) which is only a prudent thing to do, especially with the U-boat war (what percentage of fuel gets sunk/lost en-route?) But that is a far cry from "American" gas saved England which is where some of these arguments go.

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## pbehn (Jun 9, 2017)

Shortround6 said:


> I believe there was a refinery (at least one?) in western England that was also producing 100 octane fuel from imported feed stocks..



The UK could produce 100 octane, it could also import it. No one knew how much effect German bombing would have on refineries, they seem vulnerable but are not as vulnerable as they seem. I live in Teesside which had a large petrochemical industry, the LW did not make any significant/successful raids on it in the whole war.


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## wuzak (Jun 9, 2017)

GregP said:


> The issue with the altitude capability of the Allison was the direct result of Air Corps requirements. They got what they ordered. They also declined to fund the development of a higher-altitude version. Allison's use of the auxiliary, 2nd-stage supercharger was a low-cost development that was not optimum, but could be considered for a bomber's larger nacelles. Had the Air Corps / USAAF decided to make a 2-stage integral engine, Allison could have done it. Not sure about the timeframe, but it wasn't magic ... only unfunded.



The Merlin of 1940 only had a single stage supercharger but it gave higher altitude performance than the V-1710.

Perhaps because the V-1710 was originally intended to be used with a turbocharger it ended up with a smaller than optimum supercharger, which impacted altitude performance somewhat.


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## GregP (Jun 10, 2017)

Possibly true Wuzak, can't say for sure as I have never seen a real reason why the supercharger wasn't developed when it went from airship to aircraft.

If I had been around at the time and in the position to do anything about it, I'd have at LEAST paid to have the Merlin 2-stage S/C combo fitted to an Allison to see how much difference it made, as I expect it would have. But, they didn't and I really wonder why. Doesn't matter anymore, but would be nice to know. Or they COULD have tried the hydraulic coupling the Bf 109 used. Didn't do THAT, either.

I love the Merlin, for sure. Have to say the same for the Allison. Both are good engines today, but the Merlin would have been the better choice at 17,000 feet and higher during the war by far, unless the Allison were a turbo (P-38) or a 2-stage (P-63). Merlin might have been slightly ahead anyway since Hooker flat KNEW his business. Seems like a child would have seen that when he switched from the airship to the aircraft, mid-teens in altitude would have been eclipsed quickly.

Nothing we can do about it now, though. Things were what they were, and I'm really not too much on "what-ifs."


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## wuzak (Jun 10, 2017)

Allison did test a Merlin 2 stage supercharger on the V-1710 (but not mounted to the engine) and found, unsurprisingly, they got almost exactly the same power numbers as the Merlin.

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## MiTasol (Jun 10, 2017)

Two items

One of the strengths of the Allison (designed long before the Merlin) was that it was (probably) the first modular engine (like all modern military and transport engines).







You could change a C model Allison to an E or F model or an x hand rotation engine to y hand rotation engine with the minimum of effort and you could almost always use late model parts in the early model engine within very simple rules.

Changing from C to E to F model (and with C and F engines changing reduction gear ratio) was merely a gearbox change.

Reduced to the most basic level, converting rotation involved removing the reduction and accessory boxes, splitting the crankcase, rotating the crankshaft end for end, adding/removing one or two gears in the accessory box, rewiring the ignition harness and reassembling.

Fitting a set of high compression type three of four pistons and type two or three piston pins to an earlier low compression engine was a standard option (though fitting type one or two low compression pistons or early pins to a high compression engine was naturally not permitted).

The Merlin did not have any of these abilities.

Stupidly, in my opinion, the USAAC never approved Allison designing a one piece two stage supercharger version of the accessory drive housing for the V-1710 because, almost certainly, this could have been introduced without disrupting the earlier engine production (unlike the Merlin where such a significant change meant a whole new production line, new crankcase etc). The nearest Allison came to a two stage was the ASB engines where the accessory gearbox was changed and the Axillary Stage Blower externally mounted and driven from the new gearbox.

Another outcome of this Allison modular design strength was that the company (and every USAAC/F heavy maintenance shop) could convert engines during overhaul to later, higher powered versions of the same basic engine (or salvage many early engine parts for use in late model engines).

The Brits used a similar process to convert Spitfire Vs to Spitfire IXs but there was no equivalent process for Merlin's because they were not a modular design.

Secondly

In the mid sixties I spent some time in Reno at the Harrah Casinos engine shop where they were using late model Allison E type engines (from P-63's) in racing hyroplanes. These engines were reliably turning out over 5,000bhp on the dyno though some of that power came from the ASB being driven, not by the Allison itself, but by a full race Chrysler hemi developing some 800bhp. The Allison's could make and take the power because they were originally designed to be water cooled so had much more coolant capacity than the Merlin which was designed for Glycol/Prestone from day one.


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## Shortround6 (Jun 10, 2017)

wuzak said:


> The Merlin of 1940 only had a single stage supercharger but it gave higher altitude performance than the V-1710.
> 
> Perhaps because the V-1710 was originally intended to be used with a turbocharger it ended up with a smaller than optimum supercharger, which impacted altitude performance somewhat.



I am constantly amazed that people criticize the Allison for not having 1942/43 altitude performance in 1939/40. Nobody else did.
The Allison had better altitude performance than the R-1830 with a singe stage supercharger, Better than the R-1820 with single stage supercharger and better than the R-2600 A with single stage supercharger, it was better than the 1940 DB 601 or Jumo 211. Or ANY Italian engine and most if not all Japanese 1940 engines. Or any service Russian engine in 1940 (the AM-35 was not in service for most of 1940). No French engine came close. 
Granted it did hit it's limits fairly soon but the same basic supercharger ( a few modifications to inlet and diffuser and new gears) was able to make a bit over 7lbs of boost at 15,500ft while flowing enough air to get 1125hp to the prop. 
P & W was making two stage superchargers for a reason, their single stage wasn't very good and the designs provided by GE to american manufacturers, to be polite, sucked.

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## MiTasol (Jun 10, 2017)

Shortround6 said:


> It's a lot more complicated than it appears. Those lousy British British carburettors (and the American ones) helped cool the intake charge by about 25 degrees C over what the fuel injected German engines could due to fuel evaporation in the supercharger.



_"It's a lot more complicated than it appears." _

*Too true!*

The American carburettors such as the Stromberg PD series were not carburettors in the normal sense of the word but injection carburettors and exempt from the gravity considerations that plagued the Merlin and other British (and pre-ww2 American) engines.

A normal carb depends on the reduction in air pressure through the throat (Bernoulli's theorem) to suck the fuel from the float chamber into the airflow.

The Stromberg PD uses that pressure differential to meter fuel which is injected into the eye of the supercharger where it is mixed not only by the spray pattern of the injection nozzle itself but also by the inherent turbulence and temperature rise of the supercharger. A win win on both the British and German systems.

Unlike Rolls Royce, Allison and other American companies spent considerable time ensuring that the fuel mixture at each cylinder was as nearly exactly the same as possible, relatively easy on single row radials but more difficult on twin rows and much more difficult on the R-4360 and V-12 engines where induction lengths were not exactly identical (and now you know why the Allison has such a weird induction manifold and Merlin such a simple manifold)

As a result the Allison had far superior fuel mixture consistency than the Merlin, though not as good as the injected German engines, but that produces a weight penalty that the Merlin did not suffer.



Allison







Merlin





Which was the better engine? That very much depends on what criteria you use to define better.


Mi

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## GregP (Jun 11, 2017)

Th standard Allison carb isn't bad at all. Neither is the Merlin carb. If they WERE, the engines would not be good to great ones, and both ABSOLUTELY WERE. They weren't fuel injection, but they weren't bad.

Just look at who won the war, and you'll see it plainly.

After the war, piston engines didn't matter much, though Argentina DID make some very good piston aircraft (Nancu comes to mind, used Merlins; 460 mph) in addition to the Soviet Union (Lavochkins and Yaks). Mostly today, the Soviet fighters (Yak-3s) use Allisons.Says something about the relative availability of the two, but they perform quite well relative to the Merlin crowd in peacetime fun flying. Ask anyone who flies one. I have. They don't much fly at 25,000 feet and above ... though they CAN. I'd surely fly one!


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## wuzak (Jun 11, 2017)

GregP said:


> Th standard Allison carb isn't bad at all. Neither is the Merlin carb.



I believe the Allison used an injection type carb from quite early on. It was, in effect, a single point injection system.

The early Merlins and Griffons used an actual carburetor, which had a float chamber, etc.

The Merlins would, therefore, cut out under negative G. The V-1710s, as I understand it, wouldn't.


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## XBe02Drvr (Jun 11, 2017)

wuzak said:


> It was, in effect, a single point injection system.


Commonly known stateside as a "pressure carburetor", the poor man's fuel injection. Good old Bendix.
Cheers,
Wes


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## Shortround6 (Jun 11, 2017)

MiTasol said:


> The Stromberg PD uses that pressure differential to meter fuel which is injected into the eye of the supercharger where it is mixed not only by the spray pattern of the injection nozzle itself but also by the inherent turbulence and temperature rise of the supercharger. * A win win on both the British and German systems.*
> Mi



AN excellent post aside from the bolded part. I believe the British system also got a good mixture due to "inherent turbulence and temperature rise of the supercharger." as the carburetor was before the supercharger.
Unlike the French, the Russian Klimov series and most (all?) Italian inline/V engines where the supercharger blew threw carburetors spaced down the sides of the cylinder banks.








Granted this did free the engine from the threat of carburetor icing. 

Now which is harder to make, one BIG carb or six little ones. Or harder to keep "in tune".


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## Glider (Jun 11, 2017)

pbehn said:


> I dont know anything about the "anti Brit person" I just seem to remember that to perform at best the RAF needed 100 Octane fuel but didnt have the refining capacity to satisfy demand. Supply of 100 octane fuel became a political issue because of neutrality. Eventually there was an agreement based on "a dollar per barrel" (as I remember it).


The UK didn't need to prouce their own 100 octane fuel as supply was considerably in excess of demand during the BOB. One refinery did produce 100 octane for a short time as a back up to ensure that we could if we wanted to but that switched back to normal production after the trial.
Interestngly, the only time I was able to find evidence of a shortage of 100 octane fuel was in May 1944. With the vast amount of fuel being used in the preparation for D Day, the problem was distributing it fast enough to keep up with operational requirements. This did cause some problems.

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## tomo pauk (Jun 11, 2017)

MiTasol said:


> _"It's a lot more complicated than it appears." _
> 
> *Too true!*
> 
> ...



The float-type carburetors, as used on Merlins and the like before 1943/44 were robbing the power at altitude, being too restrictive and necessitating the ice guard. The switch to 'fuel pumps' (pressure carburetors, as noted by Wes) gained rise in the rated altitude and ceilings for the Spitfires: the 8-10 mph speed gain was recorder on the Spitfire Vs. (link)



> Unlike Rolls Royce, Allison and other American companies spent considerable time ensuring that the fuel mixture at each cylinder was as nearly exactly the same as possible, relatively easy on single row radials but more difficult on twin rows and much more difficult on the R-4360 and V-12 engines where induction lengths were not exactly identical (and now you know why the Allison has such a weird induction manifold and Merlin such a simple manifold)
> 
> As a result the Allison had far superior fuel mixture consistency than the Merlin, though not as good as the injected German engines, but that produces a weight penalty that the Merlin did not suffer.



The last paragraph is bashing the Merlin. Allison tried 3 types of intake manifolds before they got it right. 1-stage Merlin with pressure carb also consumed less fuel on usual war-time powers - not a sign of a lousy fuel distribution.




> Which was the better engine? That very much depends on what criteria you use to define better.
> 
> 
> Mi



Merlin was a better engine. 
It's propulsive power at altitude was always better (equled or barely suprpased by turbo V-1710 that comes wih own set of issues), they introduced 2-stage variation almost 2 years earlier, V-1710 never got the 2-speed variant, the 2-stage V-1710 never received intercooler. A most powerful Merlin was an easier retrofit on an existing aircraft than a most powerful V-1710. 

Modularity in factory line does not help a pilot in a combat. BTW - the change from a small , 9.5 in supercharger to the big 10.25 in (as suggested when Americans saw the Merlin) was judged as setting back the V-1710 programe by 2 years in 1938.


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## XBe02Drvr (Jun 11, 2017)

Merlin vs Allison, Ford vs Chevy, Rolls vs Bentley, conservative vs liberal; ENOUGH ALREADY!! THERE IS NO DEFINITIVE ANSWER that will vanquish the opposition to acknowledge defeat! That's the point, isn't it?
Cheers,
Wes


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## tomo pauk (Jun 11, 2017)

Shortround6 said:


> It's a lot more complicated than it appears. Those lousy British British carburetors (and the American ones) helped cool the intake charge by about 25 degrees C over what the fuel injected German engines could due to fuel evaporation in the supercharger. They were also much cheaper and simpler to make, requiring about 1/4 the parts and much, much less precision machining which meant that the machines and operators could be making something else.



American carburetors (at least the ones used on main military engines) were initially better than British types, ie. pressure carbs were better than float-type carbs. The much glossed-over things with using one big carb on a V12 engine of ww2 vintage, vs. other types of fuel distribution was that it necessitated backfire screens (a.k.a. 'flame traps') that were 'stealing' rated height even for non-ram conditons (= static engine). Venturi in the carb, along as the small pipes/tubes act as restrictior. 
Thus, even if the fuel spray is indeed cooling the mixture, two areas where rated altitude is decreased can be hardly cancelled by one area where rated altitude is increased.



MiTasol said:


> Two items
> 
> One of the strengths of the Allison (designed long before the Merlin) was that it was (probably) the first modular engine (like all modern military and transport engines).
> You could change a C model Allison to an E or F model or an x hand rotation engine to y hand rotation engine with the minimum of effort and you could almost always use late model parts in the early model engine within very simple rules.
> ...



Unfortunately, the C series used weaker crankcase and crankshaft than the mid-war F and E series, so the gearbox change is of no help. The impeller gearing was also different and weaker on the C engines than on those F and E series of engines. Earlier pistons were high compression (for 6.65:1) vs. late pistons (that never made it to the war, 6:1 CR). Now that we're at it, let's chage the intake manifold, the early ones were problematic.
In the Merlin, the chagnge from x to y rotating engine was a merely gearbox change.





> Stupidly, in my opinion, the USAAC never approved Allison designing a one piece two stage supercharger version of the accessory drive housing for the V-1710 because, almost certainly, this could have been introduced without disrupting the earlier engine production (unlike the Merlin where such a significant change meant a whole new production line, new crankcase etc). The nearest Allison came to a two stage was the ASB engines where the accessory gearbox was changed and the Axillary Stage Blower externally mounted and driven from the new gearbox.
> 
> Another outcome of this Allison modular design strength was that the company (and every USAAC/F heavy maintenance shop) could convert engines during overhaul to later, higher powered versions of the same basic engine (or salvage many early engine parts for use in late model engines).
> 
> The Brits used a similar process to convert Spitfire Vs to Spitfire IXs but there was no equivalent process for Merlin's because they were not a modular design.



As noted above, installing the parts from early V-1710s is a show stopper. Conversion from one engine to another is not equivalent to the conversion from one aircraft to another.


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## Zipper730 (Jun 11, 2017)

davebender said:


> I think this is the main problem. The U.S. Army Air Corps bet on the wrong horse.


I wouldn't say that, but I think the problem is that they almost exclusively focused on turbochargers over any twin-stage supercahger system


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## Shortround6 (Jun 11, 2017)

tomo pauk said:


> The float-type carburetors, as used on Merlins and the like before 1943/44 were robbing the power at altitude, being too restrictive and necessitating the ice guard. The switch to 'fuel pumps' (pressure carburetors, as noted by Wes) gained rise in the rated altitude and ceilings for the Spitfires: the 8-10 mph speed gain was recorder on the Spitfire Vs. (link)



It may be that the British simply did not build larger carburetors for the later engines? You don't normally use the same carburetor/s on a 1000hp engine that you would use on a 1500hp engine any more than you use the same carburetor on a 40hp motorcycle and a 60hp motorcycle. 
The US used different sized carburetors on single stage and two stage Merlins. There were carb changes on the early Allisons. 




tomo pauk said:


> It's propulsive power at altitude was always better (equled or barely suprpased by turbo V-1710 that comes wih own set of issues), they introduced 2-stage variation almost 2 years earlier, V-1710 never got the 2-speed variant, the 2-stage V-1710 never received intercooler. A most powerful Merlin was an easier retrofit on an existing aircraft than a most powerful V-1710.
> 
> Modularity in factory line does not help a pilot in a combat. BTW - the change from a small , 9.5 in supercharger to the big 10.25 in (as suggested when Americans saw the Merlin) was judged as setting back the V-1710 programe by 2 years in 1938.



The Allison may very well be the better _engine. _Rolls-Royce may well have supplied a better _powerplant. _
Semantics perhaps. but there is little doubt that the Allison block/heads, crankshaft, con-rods etc were better. However only by use in post war racing applications, few wartime Merlins failed due to lack of strength. The Merlin superchargers were always better, but here everybody keeps trying to make it a two horse race. The Allison supercharger wasn't as good but was good for 2nd or 3rd place for most of the war in comparison to *all *the other horses in the race. German, Italian, Japanese, Russian. It took until 1943/44 for P &W and Wright to beat it using single stage superchargers. 

I would also note that for both the US and British the engine makers did NOT make their own carburetors, they bought them from outside suppliers for most of the war. So the engine makers cannot take credit for better fuel systems and can only shoulder the portion of blame for bad ones in regards to not switching to another _available _system. I would also note that many times the engine maker and/or airframe maker was also at the _mercy _of outside suppliers when it came to radiators, oil coolers and intercoolers. The P-63 was _supposed _to have an intercooler. the outside supplier failed miserably.


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## tomo pauk (Jun 11, 2017)

Shortround6 said:


> ...
> The Allison may very well be the better _engine. _Rolls-Royce may well have supplied a better _powerplant.
> _
> Semantics perhaps. but there is little doubt that the Allison block/heads, crankshaft, con-rods etc were better. However only by use in post war racing applications, few wartime Merlins failed due to lack of strength.



The items you're refering to are the part of 'power section' of the engine. As a whole engine, a ww2 piston engine for military application, Merlin was better.



> The Merlin superchargers were always better, but here everybody keeps trying to make it a two horse race. The Allison supercharger wasn't as good but was good for 2nd or 3rd place for most of the war in comparison to *all *the other horses in the race. German, Italian, Japanese, Russian. It took until 1943/44 for P &W and Wright to beat it using single stage superchargers.



Main problem with the supercharger of the V-1710 was it's small size, for a desired airflow and pressure ratio required above 15000 ft, not helped by initial 'slow' gearing. The resricted size of the intake (pre-impeller) also contibuted to the insufficient performance above at high altitudes. That, coupled with small cubic capcity of the V-1710, made te engine lacking vs. main German and British types, until a 2-stage version appeared (by what time the bar was upped considerably by Merlin). Let's recall that 1st useful 2-stage V-1710 produced barely more power above 20000 ft than the Merlin 46 (1-stage supercharger) and a DB 605A.


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## Shortround6 (Jun 11, 2017)

Zipper730 said:


> I wouldn't say that, but I think the problem is that they almost exclusively focused on turbochargers over any twin-stage supercahger system



A certain points in time the turbo simply offered much more. Like in 1939 the turbo was offering sea level power to somewhere between 20 and 25,000ft. 
The P & W two stage R-1830 engine used at the 1939 fighter trials was good for 1200hp at take-off, but only 1050hp at 11,000ft in low gear and 1050hp at 17,500ft in high gear. This was "improved" to 1000hp at 19,000ft in the first F4F wildcats. 

This was the only existing system in actual development with a flyable engine in 1939 and 1940 in the US, P & W didn't get the first two stage running until 1938. 

The turbo also offered a number of theoretical advantages, including the fact that the auxiliary stage was almost totally independent of the engine in regards to rpm/boost. In other words, volume of exhaust gas permitting, you could adjust to turbo unit to give anything from no boost, to all the boost the engine would take, delivered to the mouth of the carburetor and be infinitely variable, no fixed gear ratios and clutches, hydraulic couplings (which had upper and lower limits).
The turbo didn't work as quick and easy as promised but then some of the other supercharger systems had a few problems too. 
Also note that both systems benefited from the improved fuels.


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## Shortround6 (Jun 11, 2017)

The first engines used in the P-38 were developed to run on 92 octane fuel. The advantage of the turbo can be seen in that engines with 6.44 gears to the small supercharger offered a take-off rating of 1150hp using 39.4in ( 4.75lbs?) MAP and would still give 1150hp at 25,000ft using the same 39.4in MAP (this was the goal I don't know how it worked in practice)

Now compared to the C15 engine (running US 100 octane) and making 1040hp the F2 engine as above was _supposed _to be running about 112 degrees F in the intake manifolds with a 70 degree intake while the C15 would be running a mixture temperature of 196 degrees F. 
The F2 engine used 240hp in friction and to drive the supercharger with the small gears, The C15 engine used 290hp for friction and to drive the supercharger with the 8.80 gears. Basically 50 more hp driving the supercharger. The C15 was making 1330 indicated HP vs the F2s 1390 but the difference in cylinder pressure was 205 IMEP vs 214.5 IMEP.
A two stage engine with a mechanical blower is going to need higher cylinder pressures to drive the blower even if the intercooler works as good as the turbo set up. The 2nd stage Allison came up with took over 200 hp to drive to get 10,000lbs of air per hour, this is the amount of air you need to make 1672hp in the cylinders. So subtract say 210hp to drive the 2nd stage and the 290 hp for the friction and the supercharger drive for the C15 engine and you are down to 1172hp, only trouble is what is the IMEP? and what kind of fuel do you need to run at those pressures without suffering from detonation?

The early unsupercharged airship engines ran on either 80, 83, or 87 octane fuel, there are 23 model designations of Allisons running on 91-93 octane fuel, I don't know if all were built or how far they were tested, a number were rebuilt into later models, most never flew.
Point is that the size/type supercharger you design for 87-91 octane fuel is smaller and has less pressure than the one you design for 100/130 fuel and in 1938-39 no one knew that 100/130 existed or could be made.
Please see loss of power at low altitudes for the DB605 with the supercharger from the DB603 engine. Better high altitude perfroamce put less power for take-off and low altitudes 

Now please note that Allison had built 30 engines total from 1930 to the end of 1938 and only built 46 more in 1939, in 1940 they built 1178 engines.


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## wuzak (Jun 11, 2017)

Shortround6 said:


> Now please note that Allison had built 30 engines total from 1930 to the end of 1938 and only built 46 more in 1939, in 1940 they built 1178 engines.



Which is why the following statement is simply not true.



duplex said:


> There is no doubt that had RAF fighters been powered by Allison during BoB ,the result would have been the same


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## wuzak (Jun 11, 2017)

tomo pauk said:


> In the Merlin, the chagnge from x to y rotating engine was a merely gearbox change.



I'm not 100% certain on that.

If the engine was a left hand rotation engine then, yes, it was just a matter of removing the reduction gears and idler and replacing them with the reduction gears from a right hand rotation engine.

But the right hand rotation engine did not have the position for the idler gear shaft.

http://users.skynet.be/BAMRS/dh103/pics/crankcase.jpg


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## Shortround6 (Jun 11, 2017)

Even with a magic wand creating over 1000 engines in 1939 the British fighters would have lost several thousand feet of altitude. 
Spitfire may have survived, much more doubt about the Hurricane. 
And that is assuming perfectly sorted out C15 engines. 

People should NOT confuse the engines/supercharger and the aircraft. Germans got altitude performance from a 3rd tier engine (altitude wise) by using the smallest, lightest fighter of the BoB fighters, not because of a better supercharger.


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## GregP (Jun 12, 2017)

You cannot change a left into a right-hand turn Allison with very little effort. I worked at an Allison shop and we built them.

True, there are very few parts changes, but ... if you have a left turn Allison and need a right turn, it's pretty much a major disassembly.

There is zero to is very little difference in effort to assemble either left or right-hand turn from parts, but to change one to the other is NOT a simple thing. The camshafts must be swapped end for end, there is an idler gear to add in the nosecase AND in the cam train (meaning the accessory housing also comes off ... that's the whole engine!), and you will need a starter that turns the other way. Last, but not least, you need the ignition harness for the other-handed turn. Maybe one or two more, but that's it. Still, to change from one to the other means disassembly of the intake track, and engine down to the crankscase, removal of the nosecase, adding a gear in the nose case, etc.

But assembly is basically the same for either-handed turning if you are building up from parts. I'd decline to do it unless I completed disassembly, stripped, and repainted the engine case, cylinder heads, and valve covers. Might as well LOOK like a fresh engine when you're done ... if you're going to all the trouble anyway!

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## TheMadPenguin (May 22, 2019)

wuzak said:


> Kinda like this picture from Flight Global of a turbocharged Merlin.
> 
> http://www.flightglobal.com/airspac...olls-royce-merlin-xx-supercharger-cutaway.jpg



AirSpace community site is gone? Has anybody a new link to a re-incarnated site?


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## GrauGeist (May 22, 2019)

TheMadPenguin said:


> AirSpace community site is gone? Has anybody a new link to a re-incarnated site?


They have bent to the pressures of Social Media, unfortunately.
Their most active community can be found at facebook here: FlightGlobal


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