could the Allison engine have done what the Rolls Royce Merlin did?

[GregP]

Some posted info is not consistent with my experience.

The early impellers were 8.25 inch, later they went to 9.5 inch, and in the G-6 and later engines they were 10.25 inch impellers. The impellers were NOT too small. The US government required Allison to use the turbosuperchagers (called turbochargers today) as the high-altitude boost system. As such, the normal supercharger impeller was supposed to handle things up to about 15,000 feet, which it did even in the 8.25 inch form.

When the War Materiel Board deleted the turbochargers from the P-39 engines to save them for the bombers (due to small US reserves of Tungsten), the high-altitude boost system required by the US government was lost and the P-39 had to make due with only the small supercharger that was supposed to have a separate high-altitude boost system. They left the turbos in the P-38 and, after the fuel and intake manifold issues were corrected, it performed just fine up to service ceiling except for a very poor cockpit heater, which left the pilots quite cold. It's tough to get hot air all the way from the engine boom to the cockpit when the OAT is well below zero degrees! Electric heaters later cured that issue. If they had turbocharged the P-40, it would have performed MUCH differently. All they had to do was add a foot or two to the fuselage and it would have fit in just fine, according to several former engineers from Curtiss who have given talks at the Planes of Fame.

I make no claims, I am just repeating what I heard here. Don't ask me for the plans ...

Allison asked the government at least twice if not three times if they should develop a 2-stage supercharger for the V-1710 and the answer was no. When you are a small engine company and your primary customer declines to pay for a development, it doesn't get developed. Pure and simple. If the government had allowed the development to proceed, it could have been in service relatively quickly.

I do not claim the Allison-developed 2-stage integral supercharger would have been as good as those of Sir Stanley Hooker, but when you aren't funded to at least try, you don't get it at all. Some boost beats the crap out of NO boost. Also, it is true that if you don't occasionally ask the impossible from your people, you damned for sure won't get it. If the USAAF wanted a 2-stage supercharger, they should have funded it and simply didn't.

The angle between the accessory case and the intake is not acute and the interface is rather smooth. I should know since I worked helping overhaul them for Joe Yancey for almost 2 years and have been inside E, F, and G engines many times for both disassembly and buildup including the accessory case interface. The E and F are exactly the same except for the nose case. The E is for remote installations and connects to a driveshaft and the F has a propeller on the shaft. The G is a different animal with different parts and has a prop on the shaft, too. The displacement is the same. The crankshaft is the same 12-counterweight crank, but the G-series rods are much stronger, the intake is different, the nosecase is different, and the supercharger and accessory case are different with a bigger carburetor.

There is NOTHING inherently wrong in the Allison design and a 2-stage supercharger would have helped a lot. But someone had to pay for development if it was to be done, and the US government elected not to be that party. Allison couldn't afford it on their own. So the government got what they asked for. Plain and simple.

The rotating main engine parts of all Allisons, including the 6-counterweight crankshafts, were all designed for 4,000 rpm but the nose case wasn't. The approved rpm was 3,000 for almost all Allisons until the 12-counterweight crankshafts came out, at which time the approved rpm was raised to 3,200. The pilot had a "blip switch" and each blip would increase or decrease by 200 rpm. If you were in a dogfight and needed extra power, blip-blip and it was there. The crew chief might not like it, but you could DO it.

The approved MAP might have been 57 inches depending on model, but we have talked with a LOT of WWII pilots who said they sometimes used 3,400 rpm and 70 – 75 inches when they needed it. One was retired General Davey Allison (no relation) who demonstrated the P-40 to Claire Chenault. He said that he regularly used 70 inches in demos and never had an issue doing so. He was renowned for "getting the most from a P-40." Of course, he didn't have to work on his engines … and his crew chiefs might have hated his guts and probably did … I don't know for sure.

Joe has engines out there with 1,300+ hours on them and are still running fine with normal maintenance after 15+ years. I don't know of any Merlins doing the same and don't really expect it either since that is a long time for a high-strung WWII V-12.

I think the Merlin is a great engine. The Allison is somewhat maligned for no good reason. It did what it was designed and specified to do. The fact that the government didn't want to fund a 2-stage supercharger was a mistake. Allison did the next best thing and designed an auxiliary-stage supercharger that could be connected to the standard Allison (with a modified accessory case) to make a defacto 2-stage, although the aux stage was hydraulically driven and thus did not have a dogtooth altitude performance chart ... it was smooth. It was MUCH cheaper to design that than an entire new accessory case. The modified acdessory case had a hole drilled in it for the shaft to connect and a seal to be oil tight.

They SHOULD have been funded to develop a 2-satge integral unit ... but weren't. Ah well. Today nobody uses the Allison OR the Merlin high-altitude capabilities since that would be IFR. All warbird pilots want to play figher pilot, so they stay VFR on days of severe clear and dogfight when they get the chance at low altitudes where the difference between the Allison and the Merin is almost nothing. Both camps are usually happy with their engines today ... until they have to pay for an overhaul. Then the Allison guys are happier since the cost is about half of that for a Merlin.

 

[wuzak]

The early impellers were 8.25 inch, later they went to 9.5 inch, and in the G-6 and later engines they were 10.25 inch impellers. The impellers were NOT too small. The US government required Allison to use the turbosuperchagers (called turbochargers today) as the high-altitude boost system. As such, the normal supercharger impeller was supposed to handle things up to about 15,000 feet, which it did even in the 8.25 inch form.

In the turbocharged systems the turbo compensated for altitude, and that's all it did. And the integral supercharger was there to boost the intake charge above atmospheric (sea level) pressure. Which they did.

In engines without turbocharger the supercharger was to do both. It did this by being spun faster (different gearing). Unfortunately this meant that the engine couldn't take the boost the supercharger was capable of delivering at lower altitudes, so the intake had to be throttled to prevent overboosting.

 

[R Pope]

The Allison is a much smoother running engine, all right, in the same way that a stock small block Chevy runs smoother than a blown Hemi in a dragster. The Merlin gets more power out of less displacement, so it is a bit rough around the edges, especially when starting up.
One feature of the Allison is the relative simplicity of its construction. Less parts, and 'way less bolts! A Merlin has buckets full of little bolts all over the place, with multi-piece castings instead of one big one where possible. Also the Allison is lighter.

 

[Aozora]

Greg, you might be interested in this which details the restoration to flight of the P-40N-1 42-104730, RAAF serial A29-448: The Whole Nine Yards. The Story of an Anzac P-40 by John King: Reed Books Pty P. Back - AbeBooks.co.uk

Some interesting comments on the V-1710 and the V-1710 v Merlin:

And performance figures:

 

[drgondog]

P-51B was 7 in deeper top to bottom than a a P-51A, in part to fit the Merlin and the intercooler/larger radiator and larger duct.

.

Yes, but more for improving the aerodynamic transition from XP-51B (the P-51A airframe) cowling to wing - and hence the radiator/intercooler ducting boundary layer characteristics. Remember the 'hump' transition from lower engine cowl to wing on the XP-51A and the Mark X?

 

[dobbie]

I really don't think the Allison was developed to its full potential. It produced more power down low than a lot of other liquid cooled engines and the A model Mustang down low was one of the fastest fighters on the deck in its time frame. That tells me they got a lot right with both the airframe and the engine. And as several people have pointed out, the Allison lasted a lot longer between overhauls, was lighter, and its modular construction paid off in its adaptability. Due to its construction, if the powers that be wanted a 2 speed 2 stage supercharger, I have to think that its development time would have been shorter.

 

[Milosh]

Wasn't the Allison considered a 'sea level' engine? I read that someplace.

 

[bob44]

Here is an interesting report on the P51 with the Allison. One of the few times that puts the Allison above the Merlin.
E-GEH-16

 

[tomo pauk]

Hello, dobbie,

I really don't think the Allison was developed to its full potential. It produced more power down low than a lot of other liquid cooled engines and the A model Mustang down low was one of the fastest fighters on the deck in its time frame.

+1 on that.

We all know that from late 1943 on, the turboed V-1710 was making 1600 HP on 130 PN fuel, 3000 rpm. It was tested, eventually successfully, with 150 PN fuel (75 in Hg, 3000 rpm = 2000 HP); the lousy plumbing notwithstanding. Allison was also equipping their engines with water injection from late 1943 on; the engines were capable to make 3200 RPM on WER (5 min rating), later, with new crankshaft, 3200 rpm was available with military rating (15 min duration) - it would be interesting to see a turbo V-1710 with such improvements,

 

[tomo pauk]

Wasn't the Allison considered a 'sea level' engine? I read that someplace.

'Sea level rating' engines were the engines with turbo. Ie. 'the engine was rated for 1200 HP from sea level up to 25000 ft of altitude'.
The 'altitude rated' engines were the ones with mechanical supercharger. Ie. 'the engine was rated for 1200 HP at 15000 ft of altitude'.

Allison V-1710 in P-38 was a sea level rated ones, the altitude rated engines were in P-39/40/51.

 

[Shortround6]

Wasn't the Allison considered a 'sea level' engine? I read that someplace.

"Sea Level" has to do with the level of supercharging. It has nothing to do with the rest of the engine.

Lets consider the Merlin III compared to the Merlin VIII, Pretty much the same engine, Coffman starter aside, EXCEPT the VIII used a 6.313 supercharger gear instead of the 8.588 gear of the III.

What this did was lower the the FTL of 1030 hp at 16,250 ft and 6 1/4 lbs boost down to 1060 hp at 7500 ft at 4lbs boost. A serious problem for a plane that needed to fight at high altitude.

What it did FOR the airplane was change the take-off rating from 880 hp at 3000 rpm and 6 1/4lb boost to to 1080 hp at 3000 rpm at 5 3/4lb boost.

The Allison could be changed from sea level engine to an "altitude rated" engine by changing the supercharger drive gears.

The problems with a single speed drive (and a single stage) are.

1. IF your supercharger can only supply a pressure ratio of 2.8 to 1 and you need 44in of pressure to make rated power then you are limited to an altitude of about 17,000ft by simple mathematics. Engines are a bit more complicated.

2. The faster you spin the supercharger (higher gear) the more power it takes ALL THE TIME and the more it heats the intake charge. The hotter the charge the less dense and the less power you make even at the same pressure.
To keep from over boosting the engine at sea level you have to close the throttle down but the supercharger is still taking almost the same power to drive and heating the air a large amount. This is the 200hp difference in the two Merlin engines.

SO you can either have power up high (if 15-17,000ft is high) or down low but not both. Or you can pick a compromise gear ratio with peak power at 9-12,000ft and get some of the take-off power back.

This also explains two speed superchargers but they do little for power at 15,000ft and above for an engine that was already using a high gear ratio.

Merlin X two speed engine used an 8.75 high gear and got 1010 hp at 17,750 ft using the same supercharger/inlet and carburetor as the Merlin III, 20 less hp 1500ft higher.


The "sea level" Allisons used a lower gear ratio than the 8.80 in the altitude rated engines. The First production P-38 engines used 6.44 gears and engines in later P-38s using 7.48 and 8.10 gears.
Later altitude rated Allisons got 9.60 gears.

Please remember that 1940/41 American 100 octane fuel was NOT the later 100/130 fuel and both boost and inlet temperatures had to be lower than later engines and also remember that the Allisons went through a number of modifications to beef up or strengthen various parts, there were four different crankshafts for example, all dimensionally interchangeable but able to handle different stress levels.

 

[Hop]

The Whole Nine Yards. The Story of an Anzac P-40 by John King: Reed Books Pty P. Back - AbeBooks.co.uk

In the last paragraph on page 141 the book claims the cost of the Packard V-1650 included a $6,000 royalty payment to Rolls Royce. This is wrong, there were no royalty payments made during the war. Rolls Royce were interested in charging royalties post-war, but Packard ended production.

 

[GregP]

Thanks for the lead on the book, Aozora. I appreciate it.

 

[fastmongrel]

Yes the Allison could have done everything the Merlin could with the advantages and disadvantages you will get with 2 different engines. Only problem it couldnt have done it in 1940 because no way is HM Government going to buy engines from the US pre war so you need to re engineer the Allison to British standards and build a factory just as Packard did for the Merlin. Go look at how long that took during wartime and consider that peacetime its probably going to take twice as long. So probably at the lastest in 1934 someone in the Air Ministry is going to have to persuade the Treasury to spend millions on a license for an experimental engine pretty much owned by another nations air force.

Yeah like that is going to go smoothly and quickly.

 

[Aozora]

In the last paragraph on page 141 the book claims the cost of the Packard V-1650 included a $6,000 royalty payment to Rolls Royce. This is wrong, there were no royalty payments made during the war. Rolls Royce were interested in charging royalties post-war, but Packard ended production.

Yes, I was wondering about that statement as well; the source used is Vees For Victory!: The Story of the Allison V-1710 Aircraft Engine 1929-1948 (Schiffer Military History)

Thanks for the lead on the book, Aozora. I appreciate it.

No sweat - if you want I can keep an eye open and find a copy because it doesn't seem to be an easy book to find on the net.

 

[tomo pauk]

Hello, Fastmongrel,
To be fair, the introducing questions were:

Was there any intrinsic design feature that precluded Allison engines from powering single engine fighters over Germany at 25000 feet, of was it all just a case of the American engine being hobbled by the thinking of the time - that high altitude fighters weren't required?

We all know that Allied fighters, flying over Germany at 25000 ft, were the thing of winter 1943/44 and later, not the thing of BoB vintage. I'd answer in this way: no, there was no any intrinsic feature that precluded Allison engines from powering single engine fighters over Germany at 25000 feet.
The second part of the question is covered by Shortrund6 in exemplary fashion.

The V-1710, being produced in UK on the other hand, does not make any sense, I agree with you. About the only US engine worth producing in the UK was the R-2800, IMO, and even that one would hardly influenced the ww2.

 

[GregP]

Please keep an eye open for it. I will, too.

 

[tomo pauk]

Some posted info is not consistent with my experience.

The early impellers were 8.25 inch, later they went to 9.5 inch, and in the G-6 and later engines they were 10.25 inch impellers. The impellers were NOT too small. The US government required Allison to use the turbosuperchagers (called turbochargers today) as the high-altitude boost system. As such, the normal supercharger impeller was supposed to handle things up to about 15,000 feet, which it did even in the 8.25 inch form.

Neither the 8.25 in impeler (used in 2, yes, two, prototype GV-1710 engines) nor the 10.25 in impeller have nothing to do with ww2 warfare. Compared to Merlin's impeller (10.25 in, non-cropped), they were smaller, and the intake system have had far smaller inlet area, 'stealing' 2 in Hg of manifold pressure. That was noted by USAF brass Allison, where it was concluded that the rework of the inlet system of the single-stage V-1710 will demand 2-3 year work.
per 'Vee's for victory'

When the War Materiel Board deleted the turbochargers from the P-39 engines to save them for the bombers (due to small US reserves of Tungsten), the high-altitude boost system required by the US government was lost and the P-39 had to make due with only the small supercharger that was supposed to have a separate high-altitude boost system. They left the turbos in the P-38 and, after the fuel and intake manifold issues were corrected, it performed just fine up to service ceiling except for a very poor cockpit heater, which left the pilots quite cold. It's tough to get hot air all the way from the engine boom to the cockpit when the OAT is well below zero degrees! Electric heaters later cured that issue. If they had turbocharged the P-40, it would have performed MUCH differently. All they had to do was add a foot or two to the fuselage and it would have fit in just fine, according to several former engineers from Curtiss who have given talks at the Planes of Fame.

I make no claims, I am just repeating what I heard here. Don't ask me for the plans ...

I know there are some claims, but they don't add up. If War Materiel board wanted more turbos, they can save 2 on each unbuilt P-38, instead of 1 on each unbuilt P-39 (need 4 for B-17). The 'small US reserves of tungsten' would be the hanger talk, yes? How come the P-39 now ended up with small supercharger, since you deemed even the 8.25 in to be not to small (P-39 have had 9.50 inch one)? WHat would be the "a separate high-altitude boost system" for the P-39???
As for the P-38s heating system 'analysis', you cannot be really serious about that? The engine compartment was at about the same location as at another twin engined planes, and there was no talk about frozen pilots in Mosquitoes, Dinahs, Beufighters, Bf-110, Me-410, let alone at B-17/24, where their huge crew compartments received enough heating to keep 10-fold crew ready able. I'd say someone messed up the stuff in P-38 - Lockheed?
The tubo P-40 has it's own thread, hopefully this thread will be free from that hanger talk 'top of the pops'.

Allison asked the government at least twice if not three times if they should develop a 2-stage supercharger for the V-1710 and the answer was no. When you are a small engine company and your primary customer declines to pay for a development, it doesn't get developed. Pure and simple. If the government had allowed the development to proceed, it could have been in service relatively quickly.

+1 on this.

I do not claim the Allison-developed 2-stage integral supercharger would have been as good as those of Sir Stanley Hooker, but when you aren't funded to at least try, you don't get it at all. Some boost beats the crap out of NO boost. Also, it is true that if you don't occasionally ask the impossible from your people, you damned for sure won't get it. If the USAAF wanted a 2-stage supercharger, they should have funded it and simply didn't.

They could went with auxiliary-stage earlier, provided it was funded.

The angle between the accessory case and the intake is not acute and the interface is rather smooth. I should know since I worked helping overhaul them for Joe Yancey for almost 2 years and have been inside E, F, and G engines many times for both disassembly and buildup including the accessory case interface. The E and F are exactly the same except for the nose case. The E is for remote installations and connects to a driveshaft and the F has a propeller on the shaft. The G is a different animal with different parts and has a prop on the shaft, too. The displacement is the same. The crankshaft is the same 12-counterweight crank, but the G-series rods are much stronger, the intake is different, the nosecase is different, and the supercharger and accessory case are different with a bigger carburetor.

The G was not the ww2 engine, no matter how good it was to be (or not?), it's out of the thread's scope.

There is NOTHING inherently wrong in the Allison design and a 2-stage supercharger would have helped a lot. But someone had to pay for development if it was to be done, and the US government elected not to be that party. Allison couldn't afford it on their own. So the government got what they asked for. Plain and simple.

Agreed

The rotating main engine parts of all Allisons, including the 6-counterweight crankshafts, were all designed for 4,000 rpm but the nose case wasn't. The approved rpm was 3,000 for almost all Allisons until the 12-counterweight crankshafts came out, at which time the approved rpm was raised to 3,200. The pilot had a "blip switch" and each blip would increase or decrease by 200 rpm. If you were in a dogfight and needed extra power, blip-blip and it was there. The crew chief might not like it, but you could DO it.

Nice tid-bit. What planes were equipped with those?

The approved MAP might have been 57 inches depending on model, but we have talked with a LOT of WWII pilots who said they sometimes used 3,400 rpm and 70 – 75 inches when they needed it. One was retired General Davey Allison (no relation) who demonstrated the P-40 to Claire Chenault. He said that he regularly used 70 inches in demos and never had an issue doing so. He was renowned for "getting the most from a P-40." Of course, he didn't have to work on his engines … and his crew chiefs might have hated his guts and probably did … I don't know for sure.

I'm sure many pilots pushed their engines and got away with that. However, we don't hear much about the pilots that were pushing the engine and didn't got away with that (all rights reserved, SR6).

 

[Milosh]

"Sea Level" has to do with the level of supercharging. It has nothing to do with the rest of the engine.

Iirc what the definition of a 'sea level' engine was the Allison could only maintain its rated takeoff power at sea level with the power decreasing as altitude was gained. Thus a 'sea level' engine. An 'altitude engine' was an engine that could maintain its takeoff power to altitude.

Maybe the person who made the statement was talking out his rear end.

 

[GregP]

Boy Tomo, you do ask a lot of questions.

The separate high-atitude boost system for the P-39 was a turbocharger that was ordered removed. It left few choices for Allison other than to change the supercharger gearing and try to make due with what was designed as the low-altitude boost system for the V-1710. That has been covered in earlier posts above.

If I had left out the 8.25 and 10.25 inch impeller, you would have mentioned it, too, wouldn't you? But I didn't claim any impeller got into combat, so what is your point? I said they were all used and they were. Allisons ran these three impellers during the design's evolution. During early design, it was assumed the turbo would be available, When that proved not to be the case, they had to take as expedient action as they could to compensate for a major engine change that was unexpected. I doubt anybody who had developed their design WITH the turbo could have done much better in as short a time when the turbo was suddenly and unexpectedly taken away. On the other hand, Rolls-Royce DID have Sir Stanley Hooker, though even HE might have a hard time if a turbo was suddenly removed from one of his designs. It might require serious redesign. Don't know, it didn't happen.

The title of the thread doesn't specify WWII, it asks whether the Allison could have done what the Merlin did. Both engines were in use before, during, and after WWII. The Planes of Fame still uses both today. The G-series engines ran in 1942 but, yes, the P-82 was a post-war product, much as the de Havilland Hornet was, too, even though it used engines that were developed and ran in WWII, too. If you want to confine it to WWII, then the P-82 is surely not included.

The blip switch was the swtich used to set the rpm of the constant-speed propeller. I know the P-40E and N have it but would only be guessing about the rpm control of the rest since I have never asked about it when I am in one of the cockpits. I was making the assumption that rpm control was fairly standardized, but that might be wrong. All have SOME type of rpm control that is easily used if more rpm is desired.

Last point, very much agree. If someone blew up their Allison or Merlin (or radial, or DB, Jumo, or Homare, etc.), they'd likely not tell anbody if they managed to get back home before the war ended. Likey as not it would get reported as an "engine faiure." Honesty has never been one of humankind's top 10 traits, has it?