# V-1710 supercharger development potential



## gjs238 (Feb 17, 2015)

The V-1710 supposedly was designed with a General Motors philosophy to build-in production and installation versatility with a "modular" design to facilitate mass production and provide multiple installation options.

However, did the fundamental design limit development of the integral supercharger - did the design limit or prevent a multi-speed supercharger and/or an integral 2-stage supercharger?

Ironically, the RR Merlin, perhaps not designed with the mass production philosophy and modularity of the V-1710, turned out to have much greater supercharger development potential, with multi-speed and multi-stage versions being developed.

Was the V-1710 basic supercharger design flawed in this regard?


From Wikipedia:
_The engine design benefited from the General Motors philosophy to build-in production and installation versatility. The engine was constructed around a basic power section from which different installation requirements could be met by fitting the appropriate accessories section at the rear and an appropriate power output drive at the front._

_The front of the engine could have one of a number of different output drives. The drive might be a "long-nose" or close coupled propeller reduction gear, an extension drive to a remote gearbox, or a gearbox that could drive two wing-mounted propellers from a fuselage-mounted engine._

_The engine could be set up for right-hand or left-hand rotation, and could be used with a "tractor" or "pusher" propeller. Another feature of the V-1710 design was its ability to turn the output shaft clockwise or counter-clockwise by assembling the engine with the crankshaft turned end-for-end, by installing an idler gear in the drive train to the supercharger, camshafts, and accessories, installing a starter turning the proper direction, and re-arranging the ignition wiring on the right side to accommodate a changed firing order. No change to the oil and Glycol circuits was needed._

_This approach allowed easy changes of the supercharger(s) and supercharger drive-gear ratio. That gave different critical altitude (the maximum altitude at which the engine could produce full power) ratings ranging from 8,000 to 26,000 feet (2,400 to 7,900 m)._


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## Shortround6 (Feb 17, 2015)

We have been over this a number of times in old threads. 

In the late 1930s everybody's superchargers were pretty crappy compared to what was to come in just a few years. In the Mid 1930s GE, designer and builders of the turbos were _ALSO_ supplying supercharger designs _and parts_ to both Wright and P&W. Allison, at times, actually subcontracted parts (like impellers) to/for GE which sold them to Wright and P&W. With 87 octane (or lower) fuel the engines couldn't use much boost and the faults of the superchargers were masked because of this. This was also the reason for the interest in the turbo. The turbo was_ not_ supposed to increase manifold pressure but to "fool" the engine into "believing" it was a sea level. Exhaust back pressure and intake to the carburetor/engine supercharger were supposed to be at or near sea level values and the intercooler was _supposed_ to limit air intake temperatures to 100 degrees F, thus allowing sea level (or close to it) power at high altitudes.

The better fuels (and better engine materials) allowed more boost to be used and showed that the existing supercharger designs weren't that good. They took more power to compress the air and heated it more than theory said they should. This was more noticeable at the higher pressure levels. Wright and P&W started their own supercharger design depts. 
The Allison supercharger as used on the long nose engines wasn't that far behind the supercharger used on the early Merlins. The engine was actually a bit under rated due to other problems besides the supercharger. The engine was 'rated' at 1090hp at 13,200ft compared to the Melrin's 1030hp at 16,250ft. The Allison should have been good for about 970-980hp at 16,250ft. The supercharger was capable of holding 42in (about 6lbs boost) to about 12,000ft (no RAM).
Rolls Royce got Hooker and the supercharger 'game' was never the same. 

Much later (end of war/post war) Allison's got larger diameter superchargers and some experimental engines got two speed gearboxes/clutches. There may have been nothing to prevent such equipment from being fitted earlier except the lack of engineering capacity. Initial concepts for such engines started in 1942 and some of the parts (12 counter weight crankshaft and stronger crankcase and cylinder blocks) were incorporated into engines that did see service during the war.


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## tomo pauk (Feb 17, 2015)

gjs238 said:


> ...
> However, did the fundamental design limit development of the integral supercharger - did the design limit or prevent a multi-speed supercharger and/or an integral 2-stage supercharger?



There was V-1710-131 (military nomenclature; Allison nomenclature V-1710-G3), prototype series of 8 engines with an 'integral' 2-speed supercharger, S/C ratios of 7.48:1 and 9.60:1. Take off power 1600 HP @ 3200 rpm, military rating in high gear 1220 HP @ 3000 rpm @ 15500 ft. The previous G2-R/L (right/left turning) was also projected as a two speed engine, intended for civil aircraft, none produced. The G series are late-war/post-war development, though.
The V-1710 with integral 2-stage S/C was also attempted, apparently in early 1944. After a convoluted work, the two-stage S/C and intercooler from V-1650-3 were mated with V-1710, the resulting power was in the ballpark with V-1650-3. Per Vee's for victory, pg. 333.



> Ironically, the RR Merlin, perhaps not designed with the mass production philosophy and modularity of the V-1710, turned out to have much greater supercharger development potential, with multi-speed and multi-stage versions being developed


.

IMO, the whole modularity thing from the V-1710 was rather a waste. No bombers ever flew in combat with it, that is discounting fighters their derivatives being bombed up. Once there was a need for the Merlin to be built in more modern factories, it was duly modified for that and result was the great quantity of modern engines available when it mattered the most. I don't agree that Merlin have had 'much greater supercharger development potential', more about that just under.



> Was the V-1710 basic supercharger design flawed in this regard?



The integral supercharger of the V-1710 have had one main disadvantage vs. Merlin - it was too small. Merlin was at 10.25 in of impeller diameter, the DB-601E was at 260mm (just a bit over 10in), the V-1710 was at 9.50 in. The Merlin 46 and 47 received yet a bigger S/C, 10.85 in, the full throttle height was at 22000 ft (4000ft greater than at Merlin 45). That was unmatched for a single stage supercharged engine until DB installed a 290mm S/C from DB-603A on the DB-605A thus creating the DB 605AS. The DB-603A was also to receive yet bigger S/C, resulting in the DB-603E with greater power at altitude (sometimes the DB-603AA and DB-603AS are mentioned as having big superchargers).
For how much the size of S/C mattered, we can compare the pictures of the RR Buzzard and RR 'R' (racing) engines - much greater S/C was installed in the R engine.

Another shortcoming - the elbow, feeding mixture from carb to S/C, have had the throat area of just 24.4 sq in. The carburetor throat area shrunk down from 41.3 sq in to 24.4 sq in. Smaller throat area = more losses = less power. 
For comparison, the carburetor of the Packard Merlin V-1650-1 was at 38.3 sq in, the two stage V-1650-7 used one with 46.4 sq in of throat area. As early as February 1938, the USAF have had a report noting that 'Merlin II has a very much enlarged induction system to handle the large quantity of low density air...' and recommending that V-1710 would need to have similar induction system.

A question will emerge - why such a small S/C and restricted inlet elbow? Much has to do with USAF's fixation with turbos. The Airacuda, XP-37, XP-38, XP-39 - those were the 1st fighters intended to have V-1710, and turbo was to be there to do much of compression, so the engine will 'believe' that is still on sea level while being at 20-25000 ft. Such engines have had even smaller carb, with 24.4 sq in of throat area, and was followed by the similarly dimensioned inlet elbow. Once the turbo was gone, the engine had to do with smalish S/C.

I'd say that auxiliary supercharger, as historically, was only viable alternative, the timing being much more of an issue than any other.



> From Wikipedia:
> ....
> _This approach allowed easy changes of the supercharger(s) and supercharger drive-gear ratio. That gave different critical altitude (the maximum altitude at which the engine could produce full power) ratings ranging from 8,000 to 26,000 feet (2,400 to 7,900 m)._


[/QUOTE]

The higher altitudes were domain of 2-stage versions.


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## stan reid (Feb 17, 2015)

I remember these engines with their "stock" superchargers used during the 1960s in the Arfons Bros. (and others) dragsters and Land Speed Record cars. They were also used in the Gold Cup boats (I believe with turbochargers in at least one example) but the Rolls-Royce engines proved more successful there. To my knowledge, RR engines weren't used in any dragsters probably because of limited availability here in the U.S. when drag racing was just getting started. Rolls-Royce engines were used in some LSR cars prewar. To this day, Allison engine machines often show in tractor pulls.


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## Shortround6 (Feb 17, 2015)

The problem with trying to use post war sea level racing use as a comparison tool is that it ignores the altitude problem. 

The long nose "C" series engines, according to factory charts, could pull 62in of manifold pressure (15lbs boost) and make 1700hp at sea level at 3000rpm. The later engines got even better superchargers (although nothing compared to a two stage) and could do a bit better.
the race boats and certainly the dragsters may not have held the engines to 3000rpm either. Increasing engine speed by even 100 rpm increased supercharger impeller speed by 710-960 rpm depending on supercharger gears fitted. 
Much different trade offs were made between power, rpm, over-haul life (or times between engine blow-ups, which is different) in the gound or sea level racers and with aircraft.


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## gjs238 (Feb 17, 2015)

Thanks guys, great replies!
I wasn't thinking so much about the history and attributes, but the mechanical engineering aspect of making the V-1710 supercharger multi-speed or 2-stage.

It seems that either this was much more difficult or impossible to do on the V-1710 than with the RR Merlin, or Allison did not have sufficient resources to do the job.


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## tomo pauk (Feb 17, 2015)

The 2-stage V-1710 were also multi-speed - the auxiliary stage was powered via hydraulic coupling (the engine stage S/C was still 1-speed, ie. fixed gear ratio). Only the 1st few experimental 2-stage engines were outfitted with 2-speed gearbox, again only for auxiliary stage.

Compared with Rolls-Royce, Allison was probably provided with less resources pre-war; most of resources went to engines Army was 'co-designing' with Lycoming and Continental, that went nowhere. The experience of RR in designing and building V-12 engines was greatest in the world, both for military aircraft and racers - while we can say that Allison also have had experience in racing engines, those were for car racing, and don't stand a comparison with RR.
It is my understanding that UK Air Ministry and/or RAF have great confidence in RR to come out with a great engine, and were willing to pay the company for advances. The US Army have had much more strict relations with (at least) Allison, even negotiating that Allison will forget the almost a million US$ if they want a permission to export their engines abroad.
A good part of work strain in Allison went to different V-1710 configurations (turbo, non-turbo, pusher, with extension shaft, double V-1710 with it's iterations; bomber aircraft being intended airframe for many of the versions, that also got nowhere) that further stretched thin Allison design staff. The internal spur reduction gear was a weak spot of the engine, that needing a replacement with external spur red. gear.


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## Shortround6 (Feb 17, 2015)

gjs238 said:


> Thanks guys, great replies!
> I wasn't thinking so much about the history and attributes, but the mechanical engineering aspect of making the V-1710 supercharger multi-speed or 2-stage.
> 
> It seems that either this was much more difficult or impossible to do on the V-1710 than with the RR Merlin, or Allison did not have sufficient resources to do the job.



There may have been a physical aspect. The original rear accessories gear case was too narrow to fit the thicker gear needed to handle the desired 9.60 gear ratio. if the desired air flow was 10,000lbs per minute the 8.80 gear needed about 210hp while the 9.60 gear needed 250hp to drive it. If there wasn't room for a thicker gear was there room for a two speed drive mechanism? 
And what needed to be changed? Some Merlin factories built single speed engines for quite some time while at least one of the factories building two speed engines changed to two stage (with two speeds) fairly quickly. 
_IF_ the engine side of the gear casing is cast into the crankcase block and just a cover is put on do you need to to change the crankcase molds at the casting facility? Do you just need a thicker "cover" and by the way the "cover" may very well be the engine side of the supercharger casing. 

Not great but. 







The gear train at the rear ran not only the supercharger but the vacuum pumps, hydraulic pumps, coolant pumps, oil pumps, etc. most came in separate shafts/gears. But major changes to the rear of the engine might have meant a lot of fooling around. Adding an auxiliary supercharger spaced away from the main engine may have meant more of the original accessories section could be kept. 

More good pictures/drawings. Allison V-1710 Construction and Installation Details

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## stan reid (Feb 17, 2015)

Sorry to go off topic for a minute but does anyone know why these engines weren't dohc? Was it cost or that the increase in power didn't significantly make up for the extra weight or, being bulkier, the loss in aerodynamics?


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## gjs238 (Feb 17, 2015)

Greg P around?


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## Shortround6 (Feb 17, 2015)

You use dohc when you think that a sohc won't control the valves well enough. IE, the valves can/will 'float' at the rpm desired. If the springs can close the valves against the inertia of the valve weight, cam follower/rocker arm in a quick enough fashion the dohc are not needed. Late model Allisons did use much stronger springs than early ones but that had more to do with the much higher intake manifold pressure pressure blowing the intake valves open early (or delaying closing) than trying to turn more rpm.


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## gjs238 (Feb 17, 2015)

RE: DOHC 
How fast were these engines turning compared to today's DOHC automobile/motorcycle engines?


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## stan reid (Feb 17, 2015)

Thanks! Yes, I can see that at the lower rpm anything you might gain from dohc (less reciprocating weight would probably be about it) likely wasn't of any real significance.


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## Shortround6 (Feb 17, 2015)

The Allison and Merlin topped out at 3,000rpm, while making power, they were allowed a certain amount of overreving while diving but the throttle had to be part closed (like over half) But they used some really big valves compared to car engines. 

Springs had to handle weight times the sq of the speed, Lift wasn't that bad .533in (?). I can't find the diameter at the moment.


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## GregP (Feb 17, 2015)

First it didn't need dual overhead camshafts since it had 4 valves per cylinder and they were all actuated by a single camshaft that did not have wear problems. The valve rockers are roller units and it works quite well.

About the supercharger, it is a modular design and larger single-stage impellers were tried. But the design was specified by the US Army originally and it was specified as a single supercharger stage for the low to mid-altitude boost and a turbosupercharger (the name at the time for a turbocharger as it is called today) as the high-altitude boost system. Then they withheld the turbos from all the fighters but the P-38. It had some issues at the start, but they were worked out within about 6 months here in the U.S.A. ... it took about another three months to work them out in Europe because we didn't know how much different European fuel was from US fuel. When we found out, they could then replicate the problem on the test stand and they figured it out.

So the turbo was deleted from the P-39 and was never offered to Don Berlin for the P-40.

With the modular design it was certainly possible to develop a 2-stage or even more stages of supercharging, and Allison offered this option to their primary customer, the US Army Air Corps on at least 2 or 3 occasions and was told no thanks each time. Allison ws a relatively small company and when your major customer does not want to fund a development, it doesn't get funded by anybody ... and it didn't.

Eventually Allison DID develop and auxiliary stage that was flown in the P-63, but it wasn't quite the same as an integral 2-stage similar to the Merlin unit developed by Sir Stanley Hooker. The USAAC / USAAF got exactly what they ordered. The V-1710 has enourmous potential for development, but the arrival of jet engines coupled with the rather obvious end of WWII coming down the pike spelled the end for big piston development, and Allison put their design staff to working on jet engines and merely finished out the wartime production contracts for the V-1710 as they saw the handwriting on the wall, just like everyone else did, too.

Today the Allison is a very relaible and long-lasting warbird engine, but it has a limited number of airframes it is suitable for. It flies in the P-38, P-39, P-40, P-63, several kit-built Spitfires that look WONDERFUL and offer 95% of the performance of a real Spitifre for MUCH less cost, some Yak-3's and Yak-9's, and there is one left-turning Allison V-1710, the ONLY left-turining unit that is not in a P-38, flying in Paul Allen's Ilyushin Il-2. There are many in boats and the Allison wins almost all of the European tractor pulls in its class that happend to include Merlins.

There are few airstrips in Europe, relatively, but they have LOTS of fields, so tractor pulls are popular.

If the V-1710 is built correctly, it is a very good engine. If not built correctly, it ... like any other decent engine that is not to spec, has problems. The best way to build one correctly is to FOLLOW THE BOOK to the letter. There are about 4 shops left that overhaul Allisons in the U.S.A.

In retrospect, it would have been a wise thing to fit a Merlin supercharger stage to an Allison at LEAST for testing, but I don't know if they did. There is no evidence they did ... but there is also no evidence they didn't, so the only people who really know have probably passed away. With no evidence of it, I am left thinking the integral 2-stage unit was never built, if it ever existed and, if it DID exist, it was probably never completed and run.

In the end, the Merlin was and is a great engine if ever there was one, and the Merlin-powered planes did the high-altitude work, except for the P-38, and the Allison-powered planes did a lot of the low to medium-altitude work.

Things might have been different ... but they weren't. The same basic turbocharger helps boost the P-47 along at high-altitude, so we KNOW it is a decent unit. The supercharger is ALSO a decent unit, but not up to the standard of Hooker's superchargers on the 2-stage Merlin. Those babies are works of art. In fact, the impeller of an early Whittle jet engine is essentially a large Merlin inpeller design.


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## gjs238 (Feb 17, 2015)

Is the V-1710 arrangement so different from the Merlin that it precludes a Merlin-like setup? (assuming one had the time and $)
For example, the DB 601/603/605 supercharger arrangements were physically much different than the RR Merlin or V-1710.

Never mind 2-stage, the V-1710 never made it to 2-speed.


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## kool kitty89 (Feb 17, 2015)

Shortround6 said:


> There may have been a physical aspect. The original rear accessories gear case was too narrow to fit the thicker gear needed to handle the desired 9.60 gear ratio. if the desired air flow was 10,000lbs per minute the 8.80 gear needed about 210hp while the 9.60 gear needed 250hp to drive it. If there wasn't room for a thicker gear was there room for a two speed drive mechanism?


Is that why it took so long for 9.6:1 supercharger V-1710s to enter production? I've been wondering about that, but considered it was related to other issues like charge heating issues with earlier variations of the supercharger or simply lack of demand/interest.

As it was, the 9.6:1 ratio engines were only slightly weaker at altitude than the likes of the Merlin 45 or 20 series (or V-1650-1) and even that discrepancy was probably due mostly to the excellent Hooker-based supercharger designs rather than inadequecies on Allison's part. (ie a larger supercharger might not have helped much ... just a universally more /efficient/ one -ie better boost with less charge heating for given power consumption) 

Not sure if going higher than 9.6:1 would have hit other mechanical limits ... again, but charge heating involved would have certainly limited max boost. (depending on fuel type and possibilities of ADI/water injection -I assume a water injection system would have been much simpler and less costly to engineer than a 2-stage supercharger configuration ... then again, WI would have been a godsend to early model P-38s with intercooler issues yet nothing was forthcoming there ... )





GregP said:


> With the modular design it was certainly possible to develop a 2-stage or even more stages of supercharging, and Allison offered this option to their primary customer, the US Army Air Corps on at least 2 or 3 occasions and was told no thanks each time. Allison ws a relatively small company and when your major customer does not want to fund a development, it doesn't get funded by anybody ... and it didn't.


I wonder if sending such proposals to individual aircraft manufactuers might have been another option for securing funding ... or at least swaing the Army for its need. Then again, I'm not sure how that sort of action would mesh with military bureaucracy at the time, or if it could have caused friction between Allison and the Army.

Were Pratt and Whitney's 2-stage supercharger developments funded in-house or NAVY supported? I seem to recall the auxiliary superchargers used on the R-1830 and R-2800 were somewhat similar in configruation to the sort eventually employed on the V-1710 (hydraulically clutched and running independently from the integral single-speed supercharger stage, including lacking any sort of intercooling -until late model R-2800s- though water injection was offered fairly early on for the 2-stage 2800s). 

The 2-stage R-1830s were in production around the time of the Battle of Brittain even ... though the altitude range those engines manage weren't really spectacular compared to single-stage engines tuned well for high-alt. (I think some 2-speed R-1820s even came close ... and German designs certainly did well with mostly single-stage superchargers; still, I suppose the point here is P&W's design philosophy could have fit very well with Allison's ... P&W just got the engineering funding much much earlier)
Good thing for the Wildcat too given the F4F was a dog without that engine.


Aside from that, the V-1710 itself had some nice advantages over the Merlin in terms of production cost/volume, maintanence, and ability to run lean at significantly lower RPM (and specific fuel consumption). Especially for that latter reason. (the latter advantage alone might have been enough to make even the intercooler-less 2-stage Allison's more attractive on the likes of the P-51 than the Merlin 60 series ... had they been in volume production by early 1943, and available for testing some 6 months prior to that)


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## GregP (Feb 18, 2015)

Well gjs238, 

Your assertion above is not quite correct. The Allison DID make it to 2-speed.

The XV-1710-131 was similar to the V-1710-97 except it was fitted with a 2-speed (7.485 : 1 and 9.60 : 1), single stage supercharger and had a different comprression ratio (6.5 : 1). 

This engine flew in the XC-114 and the YC-116. It didn't make it intoa US fighter, but it flew.

It also isn't much known, so probably almost everyone else thought so, too.

It also made it to 2-stage with the auxiliary stage. It wasn't an integral 2-stage, but was 2-stage.

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## tomo pauk (Feb 18, 2015)

If I may (just love to talk about engines, in hope that sometimes it makes sense)



kool kitty89 said:


> ...
> 
> As it was, the 9.6:1 ratio engines were only slightly weaker at altitude than the likes of the Merlin 45 or 20 series (or V-1650-1) and even that discrepancy was probably due mostly to the excellent Hooker-based supercharger designs rather than inadequecies on Allison's part. (ie a larger supercharger might not have helped much ... just a universally more /efficient/ one -ie better boost with less charge heating for given power consumption)



The difference was not that small - 4000 ft (for power of 1125 HP); by 1944 it was 3000 ft, but by then Merlin 45 was yesterday's news. Size of supercharger was an important thing, if greater power at altitude is wanted, as seen when Merlin 46 or 47 were compared with Merlin 45 or 50, plus a host of DB engines that got bigger S/C.



> Not sure if going higher than 9.6:1 would have hit other mechanical limits ... again, but charge heating involved would have certainly limited max boost. (depending on fuel type and possibilities of ADI/water injection -I assume a water injection system would have been much simpler and less costly to engineer than a 2-stage supercharger configuration ... then again, WI would have been a godsend to early model P-38s with intercooler issues yet nothing was forthcoming there ... )



Considering what the ww2 USA funded and get working, adding the auxiliary S/C to the V-1710 looks like crumbs. What was needed was a timely go-ahead signal by USAF, followed by some funding.

Germans went ahead with DB 605AM (ie. 'plain' 605A with water-alcohol injection). Above 6 km, it was making maybe 50 PS more than 605A? Contrary to that, the worse 2-stage V-1710 beats the best 1-stage V-1710 'F' by 7000 ft, when both engines were making 1125 HP.
The greater rated altitude, the more sense it makes using the ADI, IMO. The P-47 and F4U/F6F benefitted immensely by ADI, so did the DB 605ASM. Agreed that ADI would be a great thing for the P-38s, not just early types. It would make much more sense on a 2-stage V-1710, than on 1-stage, benefits were felt up to 28000 ft with late war trial engines.



> I wonder if sending such proposals to individual aircraft manufactuers might have been another option for securing funding ... or at least swaing the Army for its need. Then again, I'm not sure how that sort of action would mesh with military bureaucracy at the time, or if it could have caused friction between Allison and the Army.
> 
> Were Pratt and Whitney's 2-stage supercharger developments funded in-house or NAVY supported? I seem to recall the auxiliary superchargers used on the R-1830 and R-2800 were somewhat similar in configruation to the sort eventually employed on the V-1710 (hydraulically clutched and running independently from the integral single-speed supercharger stage, including lacking any sort of intercooling -until late model R-2800s- though water injection was offered fairly early on for the 2-stage 2800s).



The USN funded the P&W 2-stage development in a significant amount, both the R-1830 and R-2800 versions. The USAF did not considered the 2-stage R-2800 until the P-61 was discussed. Maybe having a Navy-backed engine was was not looked favorably by Army?
The 2-stage R-2800 did not featured hydraulic coupling like the V-1710, it was 'simple' mechanically clutch with off/1st-speed/2nd-speed possibility. The intercooler was incorporated from the get-go in the 2-stage R-1830 and R-2800, the XF4-U flew with it in May 1940. Water injection was offered later than that, 1942-43.




> Aside from that, the V-1710 itself had some nice advantages over the Merlin in terms of production cost/volume, maintanence, and ability to run lean at significantly lower RPM (and specific fuel consumption). Especially for that latter reason. (the latter advantage alone might have been enough to make even the intercooler-less 2-stage Allison's more attractive on the likes of the P-51 than the Merlin 60 series ... had they been in volume production by early 1943, and available for testing some 6 months prior to that)



The 2-stage V-1710 in a P-51 would be much a better investment than to go with P-63. Not quite as performer at high altitudes as Merlin Mustang until maybe second half of 1944, but still a very useful aircraft for PTO and MTO.
Granted, timing was the key issue.


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## Shortround6 (Feb 18, 2015)

kool kitty89 said:


> Is that why it took so long for 9.6:1 supercharger V-1710s to enter production? I've been wondering about that, but considered it was related to other issues like charge heating issues with earlier variations of the supercharger or simply lack of demand/interest.



It's the primary reason but a lot depends on the actual time line. The Allison _engine_ company/division during the 30s was a very small company and Allison actually had three sub divisions/sections. How much they overlapped I don't know but Allison was a major maker of hard shell bearings and supplied many other companies. This was the major money maker. They also made gear drives and other precision engineering equipment. In the late 20s ALL Packard aircraft engines that used reduction gears used Allison supplied gear sets. They also supplied the gear sets and shafting for many of the US Navy's Airships in 30s. 
As for the V-12 Allison engine part of the business, by the end of 1937 Allison had delivered 16 engines since 1932. 7 of them in 1937. 1938 would see deliveries rise to 14 for the year and 1939 would see 48 (?) delivered. 1940 saw 1178? (accounts/tables differ). 1941 saw over 6400 engines delivered. Allison had offered/suggested a two stage supercharger to the Army in 1938. How solid that offer was I have no idea ( actual drawings/calculations or just a vague suggestions to test interest?) Obviously Allison was pretty busy just getting actual mass production going in 1939/40. in 1937 they had 322 employees (and made just under 1/2 million bearings) and by the end of 1940 they had 4303. Obviously just getting into mass production took a lot of effort. 

As it was, the 9.6:1 ratio engines were only slightly weaker at altitude than the likes of the Merlin 45 or 20 series (or V-1650-1) and even that discrepancy was probably due mostly to the excellent Hooker-based supercharger designs rather than inadequecies on Allison's part. (ie a larger supercharger might not have helped much ... just a universally more /efficient/ one -ie better boost with less charge heating for given power consumption) 



> Not sure if going higher than 9.6:1 would have hit other mechanical limits ... again, but charge heating involved would have certainly limited max boost. (depending on fuel type and possibilities of ADI/water injection -I assume a water injection system would have been much simpler and less costly to engineer than a 2-stage supercharger configuration ... then again, WI would have been a godsend to early model P-38s with intercooler issues yet nothing was forthcoming there ... )



you can only spin an impeller so fast, yes pushing them harder does increase the charge heating but at some point (depending on diameter and rpm) the tips on the impeller go supersonic and set up shock waves inside the supercharger and efficiency really goes to pot in a hurry. Water injection does nothing for this. At the start of the war nobody was getting more than about 2.8 compression ratio out of a single stage compressor. By the _end_ of the war they were getting about 4.0 The Merlin 61 got about 5.3-5.4. Single stage was never going to match a two stage _if_ the two stage was any good. 




> I wonder if sending such proposals to individual aircraft manufactuers might have been another option for securing funding ... or at least swaing the Army for its need. Then again, I'm not sure how that sort of action would mesh with military bureaucracy at the time, or if it could have caused friction between Allison and the Army.



Market forces varied. There wasn't much demand for civil high altitude aircraft, even the Boeing 307 airliner with pressurized fuselage (and using B-17 wings, under carriage and tail parts) use either single speed or two speed superchargers no turbos. 
Engines for military aircraft were purchased by the government and shipped to the aircraft factories for installation. Yes, some aircraft manufacturers could propose new aircraft (or new models) based off proposed engine modifications (and did, part of the reason for the "high" altitude Allison to begin with, high altitude being the ones with 8.77 or 8.80 gears compared to the 6.48 or 7.10 gears in the early turbo engines).



> Were Pratt and Whitney's 2-stage supercharger developments funded in-house or NAVY supported? I seem to recall the auxiliary superchargers used on the R-1830 and R-2800 were somewhat similar in configruation to the sort eventually employed on the V-1710 (hydraulically clutched and running independently from the integral single-speed supercharger stage, including lacking any sort of intercooling -until late model R-2800s- though water injection was offered fairly early on for the 2-stage 2800s).



I believe the P W engines were privately funded although the Navy may have expressed interest. Patents date from 1938 and two aircraft with two stage P&W R-1830s took part in the 1939 Army fighter trials that lead to the selection of the P-40. P W had only been designing their own superchargers for couple of years and these early two stage set ups _apparently_ weren't very good. There _may_ have been cooling issues with the engines too. 
ALL P&W two stage superchargers used inter-coolers. This was part of the problem, the two stage powered planes were slower (due to weight and drag) than the same airframe with a single stage engine _until_ they got above 15,000ft or so. But for some reason the early R-1830 two stage engines didn't make a lot of power up high so the performance advantage up high wasn't all that great. 

The engine used in the two trial planes was good for 1200hp at take-off at 2700rpm, there was _no_ military rating (common on pre war US engines) and "normal" rating ( actually max continuous) was 1050 at 4,000ft ( second stage not in use) 1050hp at 11,000ft and 1050hp at 17,500ft _all_ at 2550rpm. Just a little later P&W was able to offer a single stage, single speed engine (a one off) for the P-36B that gave 1100hp for take off at 2700 rpm and also gave 950hp at 14,3000ft at 2700rpm. 



> The 2-stage R-1830s were in production around the time of the Battle of Brittain even ... though the altitude range those engines manage weren't really spectacular compared to single-stage engines tuned well for high-alt. (I think some 2-speed R-1820s even came close ... and German designs certainly did well with mostly single-stage superchargers; still, I suppose the point here is P&W's design philosophy could have fit very well with Allison's ... P&W just got the engineering funding much much earlier)Good thing for the Wildcat too given the F4F was a dog without that engine.



Germans did well because the big engines required less boost 1.3 Ata is only about 4.5lbs boost and 1.42 ATA is only about 6.2lbs boost (or about 42.6in) the 109 was also rather smaller (less drag) and over 1000lbs lighter than F4F. 

The two stage in F4F was good for 1000hp at 19,000ft at 2550rpm ( P&W never seems to have given it a military rating at 27000rpm) I don't know if this was a limitation due to cylinder cooling or due to heating of intake charge in spite of intercoolers or a propeller problem (governor didn't work right) or what. I would note however that the auxiliary supercharger was probably taking several hundred HP to drive so the cooling load on the cylinder fins in the thinner air at 19,000ft _may_ have been part of the problem.

There is a pilots manual on the F4F on this site, go to the American manuals index; http://www.ww2aircraft.net/forum/other-mechanical-systems-tech-/manual-index-american-36322.html

And while they don't really explain the limits are rather clearly spelled out.


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## Balljoint (Feb 18, 2015)

kool kitty89 said:


> I wonder if sending such proposals to individual aircraft manufactuers might have been another option for securing funding ... or at least swaing the Army for its need. Then again, I'm not sure how that sort of action would mesh with military bureaucracy at the time, or if it could have caused friction between Allison and the Army.
> 
> Were Pratt and Whitney's 2-stage supercharger developments funded in-house or NAVY supported? I seem to recall the auxiliary superchargers used on the R-1830 and R-2800 were somewhat similar in configruation to the sort eventually employed on the V-1710 (hydraulically clutched and running independently from the integral single-speed supercharger stage, including lacking any sort of intercooling -until late model R-2800s- though water injection was offered fairly early on for the 2-stage 2800s).



Bell and Curtiss lobbied against boosted engines for the P-39 and P-40. They didn’t have room to accommodate them.

Wright engines at least got critical turbocharger development from NACA. Charged with a similar project for the Allison they pleaded an unworkable engine design. 

Perhaps recognition of the need for a high-altitude, long-range escort came too late and was too critical to take a chance on the Allison with the Merlin in hand (pretty much).


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## Shortround6 (Feb 18, 2015)

A lot depends on timing. 

the "high-altitude, long-range escort" simple wasn't a realistic option in 1938-39 and part of 1940. The existing engine and fuel combinations wouldn't work. 

US fuel at the time was 100/100 or actually ranged from 100/98 to 100/103-4 depending on batch. British Fuel was 100/115-120 in 1940. The US speced a 100/125 fuel and a number of engines were rated/tested on it but the time 1942 came along the US and British had standardized on a 100/130 specification ( the _first_ of several different 100/130 fuel specifications).
The TWO stage Merlin's stuffed in the first Merlin Mustangs were capable of using about 30% higher cylinder pressures than _any_ American engine in 1939 regardless of supercharger type just due to the difference in fuel. This allowed for a 20-25% higher power output for an equivalent power plant weight. 

please see some of the documents posted in: http://www.ww2aircraft.net/forum/aviation/structure-weight-data-drag-analysis-42716.html

A Mustang ,clean, used 36.4% of it's all up weight for it's powerplant (this does not include the fuel and oil tanks)

A Tomahawk used 29.1% of it's 7650lb weight for it's powerplant, another 2.0% for it's fuel tanks. (this sounds like unprotected tanks) 16.4% went for crew, fuel an oil. 

By the time you get to 1943 and find out that unescorted bomber "idea" was a really bad idea it is too late to design an escort fighter from scratch ( or you get things like the Fisher P-75). The Merlin Mustang was being worked on and ordered well before the disastrous raids that convinced teh American High Command that they needed escorts.


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## tomo pauk (Feb 18, 2015)

This might shed some light re. USN financing P&W to get a workable 2-stage engine to work:


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## tomo pauk (Feb 18, 2015)

Balljoint said:


> Bell and Curtiss lobbied against boosted engines for the P-39 and P-40. They didn’t have room to accommodate them.



The XP-39E, a redesign of the P-39, flew 1st time in April 1942 with a two stage V-1710. The two stage V-1710 was installed in several XP-40Q aircraft, resulting in a good aircraft when Allies have had great aircraft already.



> Wright engines at least got critical turbocharger development from NACA. Charged with a similar project for the Allison they pleaded an unworkable engine design.



Not sure towards where is pointed the last sentence. The turboed V-1710 worked okay, despite some issues, even passed the tests for 2000 HP on 150 grade fuel. The work on turbo V-1710 was stalled after early 1944, so it never got to 3200 rpm and water injection.



> Perhaps recognition of the need for a high-altitude, long-range escort came too late and was too critical to take a chance on the Allison with the Merlin in hand (pretty much).



There is no doubt that it was easier to retrofit the 2-stage engine in an existing airframe than to do than to install a turbo it's accesories. BTW, the P-38 did the hi-alt LR escort, despite not being ideal in that, main shortcoming probably being low numbers available in 1943.


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## GregP (Feb 18, 2015)

We may be fogetting that the Allison production runs were wholy owned by the US government. If the order is for 2500 V-1710-89/91, then that is what you must deliver by contract, not improved engines. This was not a production by a private company for public consumption or competitive sale ... it was production by item number for a government contract. Any improvements would be at company expense, and their profit was always rather marginal as a result of close government oversight.

When they delivered the very sad Lightnings to the British, the fact that both engines turned the same way and the turbochargers were left out was by contract, too. Allison had nothing to do with the deletion of the turbos. It was a feature of the contract with Lockheed.

Allison was fairly trapped since there were no potential customers for the V-1710 OTHER than the US Government, except by government permission. The engine was not available for private sales since there was a war on and the government dictated the sale of their own engine design.

Rolls Royce developed the Merlin on Private funds and accepted government contracts, but Rolls Royce owned the design. As a result, if they developed improved engines, they were free to offer them to the government or whomever else they wanted to. I'll grant that if they had sold some out-of-country during the war, the British governement would had the right of refusal, but such refusal would be if the customer was a hostile foreign power or the sales would impact British deliveries, not a result of the UK owning the engine design.

In the case of the V-1710, it was developed at government request, on a government contract, as an airship engine, and the design was thus wholy government owned. Anything designed at government request on government funds is owned by the government. Any private sales would go through the US Government for solicitation as well as for approval.

Had allison been a larger company, they might have done the development themselves and would not have been in the same situation. A company like Ford, had enough money to do developments on it's own and suibmit them for government consideration. Small companies were mostly not able to be really inventive on their own, and depended on development money for the interested party. If the party happened to be a non-government entity, then the design was owned by the entity paying for the design and development. Grumman might have helped fund things that went into its aircraft, and they might have technically needed government permission to sell Wildcats to, say, the British, but the design was owned by Grumman. So all the "government permission" really was amounted to saying the government did not consider the British to be a hostile foreign power to be denied permission for a sale. 

It was not quite the same thing for Allison as all Allison owned was the factory and production equipment, along with some patents on aircraft bearing design and valve design. The US Government in fact MADE Allison share their bearing patents with Rolls Royce for use on the Merlin. Allison bearings lasted MUCH longer than Roll Royce bearings did ... and there was a war on in which Eruope was at stake. Allison did not share their bearing design willingly, but they were in a bind. Refusal would amount to plant closure since they were told future Allison V-1710 production was in the balance.

You will note that Rolls Royce did not share their 2-stage supercharger design with Allison, despite there being a war on. Personally, I think that would have been a fair trade, bearings for superchargers, but Allsion was not in a position to demand terms and the 2-stage supercharger was developed after the bearing design information exchange. Allison was not forced to share valve design data and didn't.


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## tomo pauk (Feb 18, 2015)

GregP said:


> ...
> It was not quite the same thing for Allison as all Allison owned was the factory and production equipment, along with some patents on aircraft bearing design and valve design. *The US Government in fact MADE Allison share their bearing patents with Rolls Royce for use on the Merlin. Allison bearings lasted MUCH longer than Roll Royce bearings did ... and there was a war on in which Eruope was at stake.* Allison did not share their bearing design willingly, but they were in a bind. Refusal would amount to plant closure since they were told future Allison V-1710 production was in the balance.




Re. bolded part - Rolls Royce acquired from Allison a license for steel backed sleeve bearings, much before the ww2 broke out, ie. they paid the money, not that Allison gave them for free. See pg. 19 of Vee's for victory. US Army can be accused for this or that mistake, but not for making Allison give out their patented thing.



> You will note that Rolls Royce did not share their 2-stage supercharger design with Allison, despite there being a war on. Personally, I think that would have been a fair trade, bearings for superchargers, but Allsion was not in a position to demand terms and the 2-stage supercharger was developed after the bearing design information exchange. Allison was not forced to share valve design data and didn't.



Was the request to RR ever forwarded, if it was ever actually made? When? That 'conspiration theory' takes for granted that it was so easy to slap the Merlin's supercharger in the V-1710 and go your merry way. The theory also neglects that the V-1710 was tested with Merlin's 2-stage supercharger.
Why the US Army, or whomever, did not say: Hey, Pratt Whitney, either you will share the 2-stage supercharger design with Allison, or will be facing consequences?


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## Shortround6 (Feb 18, 2015)

tomo pauk said:


> The XP-39E, a redesign of the P-39, flew 1st time in April 1942 with a two stage V-1710. The two stage V-1710 was installed in several XP-40Q aircraft, resulting in a good aircraft when Allies have had great aircraft already.


The XP-39E was more of a prototype for the XP-63 than related to the rest of the P-39 family. It had 1ft 10in more wing span, 23 sq ft more wing area and a fuselage 1.75 ft longer. it also picked up around 1200-1300lbs of weight _empty_ so something else was going on besides adding the 2nd stage on the supercharger. 
Sometimes engine swaps are easy, and sometimes they are very hard.


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## GregP (Feb 18, 2015)

Tomo, Allison acq`uired the bearing design by US Government insistence. Of course they for paid. But tyhey would never have given the license if not for government insistence.

And that's why I said the trade of supercharger for bearings never happened ... precisely because the bearing license was mandaded well before the 2-stage supercharger was operational ... so it wasn't "on the table," so to speak, at the time. You don't seriously think a US company would license a technology that was making their bearings the only game in town ... unless they HAD to, do you? 

If you do, you don't understand US business.


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## Shortround6 (Feb 18, 2015)

P W also had some bearing technology during WW II. A lead silver alloy on steel backings, they gave the technology away to other US companies. But then P W also only charged a dollar an engine for licence fees and sometimes didn't even collect that.


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## wuzak (Feb 18, 2015)

GregP said:


> Tomo, Allison acq`uired the bearing design by US Government insistence. Of course they for paid. But tyhey would never have given the license if not for government insistence.
> 
> And that's why I said the trade of supercharger for bearings never happened ... precisely because the bearing license was mandaded well before the 2-stage supercharger was operational ... so it wasn't "on the table," so to speak, at the time. You don't seriously think a US company would license a technology that was making their bearings the only game in town ... unless they HAD to, do you?
> 
> If you do, you don't understand US business.



IIRC Rolls-Royce attempted to build the shell type bearings that Allison used, but couldn't get the materials to bond correctly. They then got the licence from Allison. This was in the late 1920s/early 1930s. Probably about the time the Rolls-Royce R was extruding bearings, requiring a change to a master and slave rod arrangement (1931). I have little doubt that the Merlin used shell type bearings from the beginning.

Licencing their product would have made sense for Allison. It meant they didn't have to expand their facilities to make the extra bearings. For each bearing Rolls-Royce made Allison got paid - with no expenditure of their own.

Other US companies licensed products too. Wright licensed products to Russia and Germany, maybe Japan too. So it wasn't unheard of.


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## wuzak (Feb 18, 2015)

GregP said:


> You will note that Rolls Royce did not share their 2-stage supercharger design with Allison, despite there being a war on. Personally, I think that would have been a fair trade, bearings for superchargers, but Allsion was not in a position to demand terms and the 2-stage supercharger was developed after the bearing design information exchange. Allison was not forced to share valve design data and didn't.



They also didn't share it with Napiers or Bristol.

I'm sure that Hooker was published on the design of superchargers at the time, so that info was out there.

I also doubt that Allison requested the 2 stage technology. Though, as Tomo noted, Allison did test a two stage supercharger from a Merlin on the V-1710, though it was late in the war.


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## wuzak (Feb 18, 2015)

stan reid said:


> Sorry to go off topic for a minute but does anyone know why these engines weren't dohc? Was it cost or that the increase in power didn't significantly make up for the extra weight or, being bulkier, the loss in aerodynamics?



It was for compactness.

The Allison V-1710 in cross section





The cam on the Allison was underneath the rockers.

On the Merlin the cam was above, but the central location reduced the frontal area by a small amount.
http://upload.wikimedia.org/wikipedia/commons/1/1e/MerlinHead.JPG


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## wuzak (Feb 18, 2015)

GregP said:


> So the turbo was deleted from the P-39 and was never offered to Don Berlin for the P-40.



The turbo was deleted from the P-39 because it was unreliable and the installation appalling.

Don Berlin designed the XP-37 and YP-37, which were turbo V-1710 powered versions of the P-36. The reliability of the turbos was, again, poor and the installation didn't make for a practical combat aircraft (rearward cockpit location). 

The P-40 was designed specifically to _not_ use a turbo. It may have even been Don Berlin himself who begged for the turbo to be dropped an an altitude rated (rather than sea level rated) V-1710 to be developed.




GregP said:


> Then they withheld the turbos from all the fighters but the P-38. It had some issues at the start, but they were worked out within about 6 months here in the U.S.A. ... it took about another three months to work them out in Europe because we didn't know how much different European fuel was from US fuel. When we found out, they could then replicate the problem on the test stand and they figured it out.



The "European fuel" furphy again?

There were turbocharger issues long before the "fuel issues". This was not directly related to the engine, but was due to issues with the turbos themselves. At high altitudes teh wastegate controls would freeze, causing the turbo to overspeed and explode. This required GE to redesign the wastegate controls as well. This issue was certainly around in 1942, and probably persisted into 1943.

The "fuel issue" was in late 1943, Allison searching for a solution before the engines came into contact with "European fuel".


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## GregP (Feb 18, 2015)

The installation may HAVE been heavy, problematic, and appaling, but it was deleted because the War Marriel baords disapproved all turbochargers for US fighters except for the P-38 and P-47. They were saved for the heavy bombers because it was anticipated that Europe would require bombing from high altitude, and turbocharger production was low relative to aircraft and engine production. The P-63 used a 2-stage Allison with the Aux-stage blower.

Don Berlin WANTED a turbocharger for the P-40, but it was denied, and he designed the P-40 without one,

There are STILL rumors he was allowed to build ONE turbocharged P-40, and I have heard his son say it, but I have no proof of its existence, so it remains a rumor.

As for the doible overhead cam, ther is no need at all for one if you are already operating 4 valves per cylinder from a single overhead cam. The guys using DOHC couldn't figure out a way to use SOHC, or they WOULD have. SOHC is cheaper and more reliable. I can't say which has the better potential, but SOHC works VERY well in the V-1710.


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## wuzak (Feb 19, 2015)

GregP said:


> The installation may HAVE been heavy, problematic, and appaling, but it was deleted because the War Marriel baords disapproved all turbochargers for US fighters except for the P-38 and P-47. They were saved for the heavy bombers because it was anticipated that Europe would require bombing from high altitude, and turbocharger production was low relative to aircraft and engine production. The P-63 used a 2-stage Allison with the Aux-stage blower.



The P-39 lost its turbo after aerodynamic tests by NACA.

The P-63 was a larger aircraft and came several years later.




GregP said:


> Don Berlin NEVER WANTED a turbocharger for the P-40, but it was denied, and he designed the P-40 without one,



There, fixed that for you.

I can't be certain, as I am away from my references, but it was either Don Berlin or the War Material board that asked for a P-36 with V-1710 and no turbo.

Don Berlin had experience with turbos with the XP-37 and YP-37. That experience wasn't at all good. So why would he want one for the P-40?

In any case, no matter who started the process, the P-40 was specified to be a P-36 airframe with altitude rated V-1710 _without_ turbo. 




GregP said:


> There are STILL rumors he was allowed to build ONE turbocharged P-40, and I have heard his son say it, but I have no proof of its existence, so it remains a rumor.



Mainly we hear these rumours from you Greg.

Curtiss built the P-60A with a V-1710 and turbo. It was deemed a fire hazard, so they had to do the installation again. Not sure that a P-40 with turbo years earlier would have been any good anyway.




GregP said:


> As for the double overhead cam, there is no need at all for one if you are already operating 4 valves per cylinder from a single overhead cam. The guys using DOHC couldn't figure out a way to use SOHC, or they WOULD have. SOHC is cheaper and more reliable. I can't say which has the better potential, but SOHC works VERY well in the V-1710.



I don't know if SOHC is more reliable, but it certainly was more compact, at least in the case of the V-1710.


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## kool kitty89 (Feb 19, 2015)

GregP said:


> Don Berlin WANTED a turbocharger for the P-40, but it was denied, and he designed the P-40 without one,
> 
> There are STILL rumors he was allowed to build ONE turbocharged P-40, and I have heard his son say it, but I have no proof of its existence, so it remains a rumor.


With all the trouble the XP-37 had, I wonder how a turbocharged P-40 could have fared better. (maybe more mature turbocharger development paralleling the progress made on the P-38? ... or an earlier adoption of a liquid intercooler?)


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## GregP (Feb 19, 2015)

Well Wayne,

I'll have to say we disagree on several points.

I said he wanted a turbo because of a presentation given by his son at one of our monthly events. You can take it up with him ... I couldn't care less myself, but I WILL put the info out there for someone interested enough to pursue. I'm not.

Same presentation fuels the rumor about the one turbo P-40 he was supposedly allowed to build. As I plainly stated, I have no proof it was ever built. If so, I would like to see the test data and some pictures ... at LEAST one.

EVERYONE in here knows the P-39 wind tunnel test was bad. We beat it to death some time back. That was not why it was deleted from *production* ... it was deleted by virtue of being denied to the program by the War Materiel Board. Had the units been available, the installation could have been made to work, even if it was heavy and not optimum for the airframe. The point would have been to get to higher altitude with fighter performance remaining, not to be optimum. 

EVERYONE in here knows the P-63 was a later, bigger plane. Your point is what? I didn't say it was concurrent. I also didn't tell you who won the Miss America pageant that year. How is the fact that is was a larger aircraft and later relevant to the fact that it used a 2-stage Allison? I don't see it ... but I'm sure you'll tell me.

I think they should have bought some P-63s for combat, but history has already recorded what happened. The Soviets loved them.


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## wuzak (Feb 19, 2015)

Regarding the P-40 and turbo:



> Don Berlin, Chief Designerat Curtiss for the P-36 and P-37 aircraft, was frustrated by the continuing problems with the turbosupercharged Curtiss XP-37 [Models 75I ND 80i] and the lack of potential for the P-36. Given the urgency of the upcoming 1938 Pursuit Competition , he obtained from Allison an estimate for cost and performance of an "altitude" rated V-1710 for use in a P-36 derivative.



_Vees for Victory_, p.93.

It seems that Allison had other enquiries for "altitude" rated V-1710s, 

Regarding the P-63, you were talking about the turbocharger being taken away from the P-39 and then you dropped in a reference to the P-63, which I thought was irrelevent to the point you were trying to make.


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## GregP (Feb 19, 2015)

The turbo was supposed to give the P-39 good altitude performance, but was deleted by hook or by crook or the War materiel Board or whomever. The very similar but larger and later P-63 dispensed with the turbo and got good high altitude pserormance from the 2-stage Allison.

I thought that was relevant ... maybe not.

But the basic design as developed in the best P-63s would have given any other WWII psiton fighter a good run for the money. Perhaps not a jet ... but, then again, none of pistons could either, despite shooting them down in decent quantities. Most of the jet kills were ambush, landing pattern, or some jet malfunction rather than "catching" the jet when he was aware and up to speed an in combat mode.


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## kool kitty89 (Feb 19, 2015)

GregP said:


> The turbo was supposed to give the P-39 good altitude eprformance, but was deleted by hook or by crook or the War materiel Board or whomever. The very similar but larger and later P-63 dispensed with the turbo and got good high altitude pserormance from the 2-stage Allison.
> 
> I thought that was relevant ... maybe not.


The P-63 seems more like a case of just being a more advanced airframe overall. It doesn't seem that unrealistic that the engines used in the P-63 series could have been fitted to variants of the P-39 itself. (though maybe some complications due to added length or change in CoG)

But the P-63 design progressed well and just made more sense as a more all-around capable design ... opposed to say Spitfire or Me-109 development forcing more and more powerful/advanced engines into developments of the same basic airframe. (and the P-39 was probably the closest thing the US ever had to a Spitfire/Me-109 class fighter ... albeit the P-63 also succeeded where the Me-209/309 and Spiteful failed in terms of timely development of a genuinely superior aircraft)



> But the basic design as developed in the best P-63s would have given any other WWII psiton fighter a good run for the money. Perhaps not a jet ... but, then again, none of pistons could either, despite shooting them down in decent quantities. Most of the jet kills were ambush, landing pattern, or some jet malfunction rather than "catching" the jet when he was aware and up to speed an in combat mode.


Good enough to be a reasonable substitute for the Mustang had NA not developed that machine on their own, especially if the merlin engined P-63 project had gone though. (Mustang production started sooner and the USAAF didn't put in massive orders for the P-63, so it's hard to say how well they'd have coped with ramping up production compared to what NA managed historically)

US pilots might have continued to complain about the 37 mm cannon, but it doesn't seem unreasonable that 20 mm alternative mountings could have been substituted, or even just another .50 cal.


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## Shortround6 (Feb 19, 2015)

kool kitty89 said:


> The P-63 seems more like a case of just being a more advanced airframe overall. It doesn't seem that unrealistic that the engines used in the P-63 series could have been fitted to variants of the P-39 itself. (though maybe some complications due to added length or change in CoG).



only if the _variant_ was 1.5 to 2 ft longer. P-63 also changed wing location. 



> Good enough to be a reasonable substitute for the Mustang had NA not developed that machine on their own, especially if the merlin engined P-63 project had gone though. (Mustang production started sooner and the USAAF didn't put in massive orders for the P-63, so it's hard to say how well they'd have coped with ramping up production compared to what NA managed historically)



P-63 still had miserable fuel capacity. 126-128US gallons internal. 



> US pilots might have continued to complain about the 37 mm cannon, but it doesn't seem unreasonable that 20 mm alternative mountings could have been substituted, or even just another .50 cal.



Dropping to a .50 through the prop and the P-39/P-63 loose their reason for being. A 5 machine gun fighter brings what to the table vs the existing 4 and 6 gun fighters?


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## GregP (Feb 19, 2015)

Ho Kool Kitty,

The P-63 as a very good airplane that came along when a few other very good airplanes were in large quantity production.

From your earlier post, the XP-37 DID have troubles and so did the XP-39, but finding solutions to the turbo problem was in sight. Had to be since it WAS successful in the P-38 ... eventually, and also in the P-47 from the start. Had the turbo been allowed to be developed on the P-39 as it was for the P-38, they could have worked out an installation. It would have added weight, but would have also given better high altitude performance.

The powers that be at the time weren't all that convinced that high altitude performance was needed in a fighter, but somehow WERE convinced that high altitude performance WAS needed in a 4-engine bomber. I don't get it, but they reserved the turbos for the bombers ... mostly. It was what it was.

When the mixture and European fuel issue got worked out the V-1710 gave very good performance at altitude in the P-38. Had they pursued the turbocharger in the P-39 and P-40, the war record would certainly have changed ... and they HAD THE TIME to DO it if they only did it. They didn't and the Merlin became the high-altitude engine of choice because of their shortshightedness.

You can make a lot of the same claims for the Edsel automobile ... wrong thing at the wrong time. It could be said of the P-63, too. It looked like a P-39 and there was automatic predisposal to cancel it despite the flight performance. If you improve things, change their looks if the original was a flop.

Think Me 210 / Me 410. The 210 was a killer and the 410 was a good plane that never caught on. VERY similar to the P-39 / P-63 pair of designs.

Then again, the P-51 WAS in quantity production and so was the P-47, both successes if ever there were any for the USA. The F8F had NO chance as a USAAF plane so, despite the potential, it was only looked at by the Navy. The F6F was a great fighter by ANY standards, but was not as good as the P-63 and was ALSO never looked at by the USAAF. The P-63 was a case of too little, too late ... just like the German late-war aircraft (and OTHER weapons) were.

They were advances, but were overshadowed by the hot-shot performers of the current production runs. In the case of the P-63, it really COULD have helped a LOT, but was not needed in the actual event. Uneeded equipment doesn't get much priority, even if it is very good ... MOST of the time. It depends on the reliability of the in-service equipment at the time. In the case of the P-51. it was and IS reliable. Ergo, the P-63 was redundant and no massive retraining was needed for the "new" fighter that no pilot wanted to be assigned to ...

Altogether a self-fulfilling outcome.


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## tomo pauk (Feb 19, 2015)

I don't think that P-63 was that great an aircraft, nor that it was all-around a more capable dsign than Bf-109, let alone Spitfire or Spiteful. The P-63A, in 3 tests available succeeds to beat 400 mph mark in just one (nevermind the projected Bell's performance charts). The Bf 109 was close to 400 mph mark in 1941, beating it in winter or 1941/42, ie. 2 years before the P-63 managed the same. The late war Bf-109 were offering 420-440, or even 450 mph with 2-stage DB 605L
Spitifre was able to average 400 mph in second half of 1942, and got better every year. The Griffon Spitfire was available one year before the P-63E, an aircraft that might equal what Merlin Mustang brought to the table in autumn of 1943 (talking about production dates). The P-63 has either ~70% of fuel as Merlin Mustang, or less than 50%, while the late war Spitfires have had also means to almost double the internal fuel. What P-63 has over 109 or Spit is roll rate, and that's it.

Greg,



> The F6F was a great fighter by ANY standards, but was not as good as the P-63 and was ALSO never looked at by the USAAF.



If I get this right - the P-63 was one step better than great? What standards are applied in this categorization?



> Think Me 210 / Me 410. The 210 was a killer and the 410 was a good plane that never caught on. VERY similar to the P-39 / P-63 pair of designs.



Hate to go further off-topic - but why involve two German aircraft that were not that good? The Me-210 is a killer? Probably against it's early crews.



> Ergo, the P-63 was redundant and no massive retraining was needed for the "new" fighter that no pilot wanted to be assigned to



Not just that P-63 did not bring anything new to the table, but it was inferior to the stuff mass produced in 5 American factories (discounting US Navy fighters); it was almost six US factories, had the Curtiss didn't botched their production of P-47s.



> The installation may HAVE been heavy, problematic, and appaling, but it was deleted because the War Marriel baords disapproved all turbochargers for US fighters except for the P-38 and P-47. They were saved for the heavy bombers because it was anticipated that Europe would require bombing from high altitude, and turbocharger production was low relative to aircraft and engine production.



About twice of turbochargers can be obtained from each P-38 than from each (X)P-39s. So either someone in the Material Division (or wherever) didn't do their math properly, or they judged that P-38 represented a bird in a hand, while the turboed P-39 represented a bird in the bushes. I'm inclined to the later. 
The unarmed XP-39 have had Cd0 of 0.0329, a truly horrendous value for a monoplane with retractable U/C.



> Tomo, Allison acq`uired the bearing design by US Government insistence. Of course they for paid. But tyhey would never have given the license if not for government insistence.



Allison? Think you mean that RR acquired license. Nobody in 1920s/1930s was giving away licenses, let alone to foreign companies. In case you don't have a source that backs up that US government somehow twisted the Allison's arm about this, it goes under 'myths' category.



> And that's why I said the trade of supercharger for bearings never happened ... precisely because the bearing license was mandaded well before the 2-stage supercharger was operational ... so it wasn't "on the table," so to speak, at the time. You don't seriously think a US company would license a technology that was making their bearings the only game in town ... unless they HAD to, do you?



Then why bringing it up?



> If you do, you don't understand US business.



I don't understand many things. 
Yet, I do understand this: if I'm to be taken seriously when talking about anything, it is a good practice to back up my talk with sources.

A tidbit on the proposed XP-40H, from Vee's for victory, pg. 184:
_The Curtiss P-40H was to have been an Allison powered and turbosupercharged version of the P-40E. At conference at Wright Field on June 10, 1941 Mr. Don Berlin of Curtiss received authority to begin such a project and the Material Division immediately shipped one GE Type B-2 turbosupercharger to Curtiss at Buffalo, New York. By that October the decision has been made to not turbosupercharge the P-40, but instead incorporate the feature into the coming Curtiss P-60. The turbo was to be installed behind pilot in the XP-60._

The excerpt is sourced.
So the Curtiss almost got to build the turbo P-40. But not in March 1938 (when Curtiss submitted the P-36 derivative featuring the V-1710 engine), but more than 3 years after that.


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## Shortround6 (Feb 19, 2015)

I would note that decision to drop the turbo from the P-39 was made in 1939.
The War Production Board did not come into existence until Jan 1942 and it's predecessor, the Supply Prioritys and Allocation Board, didn't come into existence until Aug, 1941 and boards/agencies which made up that organization didn't exist or were not even authorized until the summer of 1940.

I would also note that B-17s were being ordered in such low quantities in 1939 and 1940 that Boeing subcontracted and built several hundred A-20s. First B-24s with Turbos aren't built until Nov/Dec of 1941.

Somebody had one check of crystal ball if they took turbos away from P-39s in 1939 to save them for bombers. Army didn't suggest using turbo on B-24s until the summer of 1940, 10-11 months _after_ the Army had ordered 80 P-39Cs.

This is looking like another Furphy.


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## gjs238 (Feb 19, 2015)

GregP said:


> Well gjs238,
> 
> Your assertion above is not quite correct. The Allison DID make it to 2-speed.
> 
> ...



Nice - would love to see prints for the 2-speed engines.


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## GregP (Feb 19, 2015)

Hi Tomo,

The F6F was a great fighter for the Pacific Theater of Operations. It could outclimb a Zero and hit hard enough to do damage when it did so. It wouldn't turn with a Zero but could stay in there for about 3/4 of a turn, enough to get off a shot. The acceleration was MUCH better than a Zero. It was the right package at the right time. The P-63 climbed better, was faster (cruised significantly faster), and hit harder ... ergo my statement.

About the P-39 and the turbo, Ben Kelsey was a huge advocate of the turbocharger. He was in the UK in 1939 when Larry Bell proposed to the USAAC and NACA to produce a variant of the P-39 without the turbo. They agreed and the prototype, which was a ton lighter than a production bird was built and verified the perforamcne gains predicted. Kelsey was NOT a happy camper and when the armor and armament and ammunition, etc. was added, the production plane suffered in performance relative to the prototype. But ... production got started.

Meanwhile, President Roosevelt created the The Office of Production Management and the Supply Priorities and Allocation Board in Jan 1941. They had exactly the same function as the 1-year later War Production Board (official title) and they determined where the turbochargers went. In one if their earliest decisions, they allocated turbochargers to only ONE front-line US fighter, the P-38. Had the P-39 been using a turbo at the time, it would have been removed anyway.

In later years, Ben Kelsey lamented not being present when Larry Bell made his sales pitch becuase he felt like the P-39 turbo issues could have been worked out. He said that because they started production without the turbo did not mean it could not have been added back in at any time. All it would take is the turbos and some development work at Bell. They never got the turbos again, even for the P-63, so they went to the auxiliary stage supercharder on the Allison.

Another often-repeated rumor about the P-39 was that it would tumble end-over-end. In fact, NACA and Bell and the USAAC tested P-39 models both in wind tunnels and in 86 test flights and were never able to get them to tumble. Then, in the 1970's in an attempt to see the real truth, an informal study of the spinning characteristics of the P-39 was done. It might never have been done except they found the original spin test model in storage and decided to test it. 

When balanced at full ammunition load, it spun normally and would not tumble. When balanced at a no-ammunition load, it tumbled rather often and easily while spinning.

Just goes to show that if testing is not done at the CG envelope extremes, then you really don't KNOW what a palne will do at the extremes of the envelope when pushed hard.

Having spoken with several people associated with WWII aircraft development and procurement over the years, including Ben Kelsey (he visited Purdue University when I was in the aeronautical engineering department and we had a round table with him, our professor, and 20 students), I have concluded that had both the P-38 and P-39 been equipped with turbos, one or the other would have been directed to stop using them. Bell was a small-time outfit compared with Lockheed, and I have great difficulty believing the P-38 would have been the one so ordered. In fact, Kelsey said they could never get the turbos back even when the combat operformance of the P-39 shouted out the need for them. The War Production Board just said no.

Kelsey liked the P-39, but he also liked the P-38. I don't know which one would have been ultimately better, but I suspect that, if for no other reason, the range would have dictated staying with the P-38. According to Ben and to Pete Law (Skunk Works), the turbos were considered difficult items to make enough of, and were rather jealously apportioned out when they were in "short" supply. Remember, a B-17 or B-24 took four each, so a couple hundred turbos would only produce 50 bombers. That made then even MORE hard to get.

The P-38 was a case of throwing all the eggs in one basket, so to speak. It did not turn out badly as the P-38 was the mount of our top two aces for the entire war.

Now, I suppose it is possible I have concluded incorrectly. I feel that a LOT of modern looks at the past come to very incorrect conclusions because modern people have no concept of the attitudes and feelings of the people in charge at the time. Modern young people look at the world in a wholely different way than some who grew up and was about 18 - 25 years old when war broke out does. Some things that modern people feel should have been done would NEVER have even been considered and the person(s) proposing them would have been ejected from the neetings.

I choose to believe Ben Kelsey and Pete Law and the guys who were around and who grew up at the time and who KNOW why things were done the way they were done. Logic has nothing to do with some decisions that were made. They were made for very specific reasons that were never laid down in meeting minutes.

I have debated the P-63 in here before and do not propose to replicate that in here. Suffice to say I think it could have been a real asset anywhere it was deployed. If you think otherwise, you are free to do so without comment from me. We all know what happened in the end, and what-ifs are unwinnable by either side of an argument.


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## Balljoint (Feb 19, 2015)

Greg, I pretty much agree. I view the P-39 and P-40 as very successful designs in that, save for the late-recognized need for high altitude, long range escorts, most combat was at lower altitudes, the Desert Air Force, The Cactus Air Force (P-400 CAS), AVG, Soviets etc., all low altitude conflicts served well by these aircraft. In time their weakness in the vertical may have been exploited. But these aircraft held their own during some of the more critical times.

The high altitude Alison P-51 was, to me, a galling missed opportunity. But, given the history during the 1930s and early 1940s, understandable.


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## tomo pauk (Feb 19, 2015)

Greg, thanks for that overview. At any rate, the historic P-39 went in the mass production to fulfill a current need, that being bulking up the numbers of 1st line USAF fighters (even though the European designs moved the goal post in the meantime), along with P-40 and P-38.
Re. deleting turos from aircraft: the brass have had no objections for the production of P-43 and slightly improved P-43A, Republic also started designing the XP-44 that got replaced by P-47B. The brass shortly authorized the XP-40H, the P-60A almost got into production, Curtiss get to produce the P-47 under license instead of (X)P-53 and (X)P-60, the Evansville factory for the P-47s was to be built - all for the turboed fighters. So you'd excuse me that I don't believe that P-39 lost turbo because someone thought there would not be enough of those, while I also don't believe that someone would've started deleting turbos from fighters other than P-38 in 1941.


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## gjs238 (Feb 19, 2015)

GregP said:


> I have debated the P-63 in here before and do not propose to replicate that in here. Suffice to say I think it could have been a real asset anywhere it was deployed. If you think otherwise, you are free to do so without comment from me. We all know what happened in the end, and what-ifs are unwinnable by either side of an argument.



Or would one just be better off with more P-51's?

Reactions: Like Like:
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## gjs238 (Feb 19, 2015)

GregP said:


> Hi Tomo,
> 
> The F6F was a great fighter for the Pacific Theater of Operations. It could outclimb a Zero and hit hard enough to do damage when it did so. It wouldn't turn with a Zero but could stay in there for about 3/4 of a turn, enough to get off a shot. The acceleration was MUCH better than a Zero. It was the right package at the right time. The P-63 climbed better, was faster (cruised significantly faster), and hit harder ... ergo my statement.
> 
> ...



How does the P-47 with it's turbo fit in here?


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## wuzak (Feb 19, 2015)

tomo pauk said:


> A tidbit on the proposed XP-40H, from Vee's for victory, pg. 184:
> _The Curtiss P-40H was to have been an Allison powered and turbosupercharged version of the P-40E. At conference at Wright Field on June 10, 1941 Mr. Don Berlin of Curtiss received authority to begin such a project and the Material Division immediately shipped one GE Type B-2 turbosupercharger to Curtiss at Buffalo, New York. By that October the decision has been made to not turbosupercharge the P-40, but instead incorporate the feature into the coming Curtiss P-60. The turbo was to be installed behind pilot in the XP-60._
> 
> The excerpt is sourced.
> So the Curtiss almost got to build the turbo P-40. But not in March 1938 (when Curtiss submitted the P-36 derivative featuring the V-1710 engine), but more than 3 years after that.



Thanks for that Tomo.

I forgot (or didn't know) about that specific proposed variant.

It doesn't change the fact that the P-40 was not intended to use a turbo from the start.


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## tomo pauk (Feb 19, 2015)

> It doesn't change the fact that the P-40 was not intended to use a turbo from the start.



Indeed - 3 years of difference between XP-40 and XP-40H proposals.


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## GregP (Feb 19, 2015)

Hi guuys,

The P-47 and P-38 were the high altitude fighters we produced with turbochargers. As it turned out, the P-47 was excellent at high altitude and better than most at low altitude, but was at a disadvantage at mid-altitudes. The P-51's was made into a winner almost be accident. It slipped under the radar because it was designed to a British request. When the Brits got some allison-powered units, they decided they were rather good ... at elast better than other American fighters, but lacked an altitue capability. The Brits then proceeded with the Mustang X while the foks at North American proceeded with the P-51B/C. Either one could have been a winner.

Had the P-51 had to go through the War Production Board's review, I do not pretend to know if it would have made it or not, but we know it survived and thrived. Many decisions weree made to give much-needed work to specific areas of the country. There were aircraft plants on the east coast, midwest, and west coast, and they ALL got some work in the end, even Brewster ... who arguably shouldn't have.

And gjs, we could have used more P-51's instead of P-63's. In the end, that's exactly what we got. It worked out fine. I like the P-63, but would not change hsitory just to have some built for the U.S.A. ... it was an almost-made-it that didn't make it in US service. But it DID get produced for Lend-Lease to the Soviet Union, so at least SOME got into the fray somehow. According the Soviets, they acquitted themselves well and were liked by their pilots. I suspect one of the features they liked best was a good cockpit heater! ... and maybe a few creature comforts not usually seen on Soviet fighters.

Ah well, at least there are a few flyable planes about, and we have one locally at Palm Springs that flies in our airshow every year.

Tomo, I won't try to convince you of anything in US WWII politics. Since it is decades old news, it doesn't much matter anyway. Heck, the Falklands conflict is old news. WWII is interesting only because it interests ME. I don't see many young people out there helping to restore the old planes ... it is mostly guys 55 and older. When we're gone, I doubt seriously if many of the flying WWII planes today will continue to fly all that much longer as the skills needed to sustain them die off with us and the ability to fabricate spare parts goes away, too.


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## gjs238 (Feb 19, 2015)

GregP said:


> I don't see many young people out there helping to restore the old planes ... it is mostly guys 55 and older. When we're gone, I doubt seriously if many of the flying WWII planes today will continue to fly all that much longer as the skills needed to sustain them die off with us and the ability to fabricate spare parts goes away, too.



The youngsters will just 3D print everything


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## GregP (Feb 19, 2015)

I hope that turns out to be TRUE!


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## kool kitty89 (Feb 19, 2015)

Shortround6 said:


> P-63 still had miserable fuel capacity. 126-128US gallons internal.


This really is an odd issue and more puzzling since most of the range figures on internal fuel seem relatively high for such a limited fuel capacity. (more so given the range is signigicantly longer than the P-39 in spite of being larger and heavier ... and limited range/fuel capacity was one of the biggest shortcomings of the P-39, so failing to address that seems particularly strange)

But beyond that, the P-63 had larger area wings and a thicker airfoil than the P-51, yet carried less fuel AND was unable to mount guns inside the wings? The radiators took up some of the space and wheel placement may not have been as efficient as the P-51, but that still seems really limited. (more so since the P-39 itself carried nearly as much fuel in its wing cells)




> Dropping to a .50 through the prop and the P-39/P-63 loose their reason for being. A 5 machine gun fighter brings what to the table vs the existing 4 and 6 gun fighters?


Centerline armament (and considerably higher RoF than the synchronized guns), same as the P-38s that were field modified to 5 .50s. (still a 20 mm would make the most sense so long as it had an in-flight cocking mechanism to clear stoppages like the P-38 -given the problems with the US Hispanos )

And regardless, for pilots that found the 37 mm gun more or less useless in fighter vs fighter combat, an added .50 would have still been better. (a conversion like that on the P-39 would have been more problematic given the CoG issues there with the stall/spin made much worse as the nose was lightened ... unless ballast was fitted)






GregP said:


> From your earlier post, the XP-37 DID have troubles and so did the XP-39, but finding solutions to the turbo problem was in sight. Had to be since it WAS successful in the P-38 ... eventually, and also in the P-47 from the start. Had the turbo been allowed to be developed on the P-39 as it was for the P-38, they could have worked out an installation. It would have added weight, but would have also given better high altitude performance.


The poor cockpit placement on the XP-37 also would have had to been dealt with. (maybe possible to move the turbo to the rear like the P-60/P-47/P-43, but managing that while keeping fuel tankage decent seems like it may have been a mess)

And on that note, the P-43 should be on the list of USAAF fighters allowed to have turbos. (on top of numerous prototype projects, including Grumman's XP-50)



> You can make a lot of the same claims for the Edsel automobile ... wrong thing at the wrong time. It could be said of the P-63, too. It looked like a P-39 and there was automatic predisposal to cancel it despite the flight performance. If you improve things, change their looks if the original was a flop.


The P-39 being that looked-down upon still confuses me somewhat. Aside from the unpleasant stall/spin characteristics, the P-39 seemed to be in a similar class as the early (single stage) Spitfire or 109 and significantly better performing than the P-40, let alone Hurricane. (shorter range than the P-40 but longer than the Spit or 109 -aside from the stripped-down P-39N with reduced internal fuel)

For that matter, it had better overall low/mid alt performance than the contemporary early model P-38 or P-47 (especially with over-boosting taken into account), albeit limited range was even more dramatically obvious there, though (still not as bad as the 109/Spit/Hurricane -or most Soviet fighters).

It should have made a better fighter-bomber than the spit/109, though weaker than the P-40 in that role. (or A-36 ... hurrcane had shorter range but larger wings to cope with varied bomb/rocket loads, same for the Typhoon) 



> Then again, the P-51 WAS in quantity production and so was the P-47, both successes if ever there were any for the USA. The F8F had NO chance as a USAAF plane so, despite the potential, it was only looked at by the Navy. The F6F was a great fighter by ANY standards, but was not as good as the P-63 and was ALSO never looked at by the USAAF. The P-63 was a case of too little, too late ... just like the German late-war aircraft (and OTHER weapons) were.


The F4U would have been most interesting to the USAAF of anything USN/USMC specific. (let alone with it having more trouble fitting as a carrier capable fighter)

But on the P-63, with the Mustang already in the picture, it was the all-around better aircraft for nearly any purpose. (P-63 might have had an edge in bomber interception with that 37 mm ... but the US really didn't need a plane in that role at the time) If it came down to engine vs airframe allocation, puting those 2-stage Allisons into P-51s would almost certainly have been the wiser move.


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## GregP (Feb 19, 2015)

The P-43 was a stop-gap at BEST and was a very small production run that was tried to see how the systems would perform in the real field. 

The USAAC considered the P-43 and its variants obsolete from the start and used them only for training purposes. In fall 1942, all surviving USAAF (transitioned from USAAC in June 1941) P-43s were redesignated RP-43 indicating they were unfit for combat. Most of the aircraft that were not sent to China were modified for photo-reconnaissance duties and used for training. Eight P-43s were loaned to the Royal Australian Air Force in 1942 and served with No. 1 Photo Reconnaissance Unit, based at Coomlie, Northern Territory. The RAAF flew many long range, high-altitude photo reconnaissance missions before the six survivors were returned to the USAAF in 1943.

With only 272 built, the P-43 was a sort of non-event ... we made 10 - 15 thousand front line fighters and the 272 P-43 were not first-line aircraft when they rolled off the lines.


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## tomo pauk (Feb 20, 2015)

The reason why the P-63 have had more range than P-39 was the ability to carry 3 drop tanks, rather than just one on P-39. Great for ferrying, not so much for combat on long ranges, where the internal fuel capacity is a major factor. The P-63 did not carried any fuel in front of the main spar, there was enough space to almost double up the internal fuel capacity. 
As for armament, I'd propose deleting gun pods, while chaning the 37mm for belt-fed 20mm. Should give more chances vs. fighters, while giving some speed due to lack of gun pods.


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## kool kitty89 (Feb 20, 2015)

tomo pauk said:


> The reason why the P-63 have had more range than P-39 was the ability to carry 3 drop tanks, rather than just one on P-39. Great for ferrying, not so much for combat on long ranges, where the internal fuel capacity is a major factor.


I was actually speaking more for the normal/clean ranges being compared, but I suppose I might also be seeing apples and oranges figures (ie good/ideal cruising for the P-63 vs more average/faster/low alt cruising for P-39). I knoe the ferry range figures are MUCH longer for the P-63, but I'm thinking more in terms of 600-700 miles vs 950 miles. Though on second look, that 950 mile figure is specifically for the P-63D. Not sure if that model had expanded internal tankage compared to others.

That and the figures I'm seeing for the P-39 are mostly for mid-speed cruise, nothing minimal/long range optimized, granted, few things actually point out range using optimimal/minimal cruise. (some tactical planning charts do, but I've only seen those for a handful of aircraft) This is somewhat significant given the V-1710 had particularly good qualities for low RPM very lean cruising. 




> The P-63 did not carried any fuel in front of the main spar, there was enough space to almost double up the internal fuel capacity. [.quote]
> Interesting so, had the requirement been pressed to Bell for extending long-range capability, the existing airframe should have been fairly straighforward to adapt for this purpose? (given the Russian operations, the limited fuel capacity wouldn't have been much of a concern)
> 
> 
> ...


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## tomo pauk (Feb 20, 2015)

kool kitty89 said:


> I was actually speaking more for the normal/clean ranges being compared, but I suppose I might also be seeing apples and oranges figures (ie good/ideal cruising for the P-63 vs more average/faster/low alt cruising for P-39). I knoe the ferry range figures are MUCH longer for the P-63, but I'm thinking more in terms of 600-700 miles vs 950 miles. Though on second look, that 950 mile figure is specifically for the P-63D. Not sure if that model had expanded internal tankage compared to others.



The one-off P-63D was indeed provided by increased fuel tankage vs. the rest of P-63 line, even vs. P-63E that would be coming after it. 'America's hundred thousand' states 168 gals of fuel, vs. 126-128 for -A, -C and -D. 
A curiosity on the P-63 was that a 64 US gal tank (self-sealing, slipper flush fitting), was a posibility on belly rack; ie. an extra fuel that was to be carried in combat. Not sure how big was the performance penalty, though. During e war the P-47 was also tested with a similar tank of 75 gals. 



> Interesting so, had the requirement been pressed to Bell for extending long-range capability, the existing airframe should have been fairly straighforward to adapt for this purpose? (given the Russian operations, the limited fuel capacity wouldn't have been much of a concern)



My understanding is that P-63 was envisioned as an aircraft that would be able to outclimb the Fw-190 and Zero, or at least there is a line in the 'Vee's' about that. Small (for non-European measuring sticks) fuel tankage should contribute to that, the P-63 was a good climber. However in late 1943, when the P-63 entered production, the long range was a requirement for the USAF fighters, not the great RoC. For Bell to install greater fuel tanks would mean further delays to the production, since it would mean different ribs.
The Soviets needed range. They went ahead with Yak-9D and -9DD, that provided increase in fuel tankage, at the cost of performance. The appeal of foreign fighters, among other features, was that they were able to mount drop tanks, a feature seldom seen on Soviet-made fighters.



> Agree. My comments on the .50 were mostly as an interim/stop-gap option for cases where the 37 mm was unattractive and 20 mm was not functioning properly. (without the ability to re-**** M2 Hispano cannons, they were generally too unreliable to service -the Navy got away with that by using excessive amounts of librication wax and grease on the amunition ... not fool proof, but enough to alleviate some of the issues with chamber size and firing pin position -most stoppages were due to lightly struck primers)



The Hispano worked okay aboard the P-38 - rigid fuselage mount benefits a bit? The ability to re-c0ck the Hispano would be a safety feture, of course.



> The single-stage V-1710 did compare rather favorably with the Merlin 45/50 series on the whole.



I will politely disagree with that. At 20000 ft, the better V-1710 (ie. 9.60:1 S/C gear) it with give around 950 HP, vs. ~1130HP of Merlin 45. It will enter production some 15-18 months later than Merlin 45. It will compare favorably under 10000 ft, though, not a great thing in a fighter aircraft.
What the V-1710 will have against early Merlin 45 might be the better carb (pressure injection vs. float-type) and use of 6-per-side exhaust stacks rather than 3-per-side; those are engine add-ons, though. The Merlins also received better carbs not long after the 9.60:1 V-1710s were introduced.


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## kool kitty89 (Feb 20, 2015)

tomo pauk said:


> My understanding is that P-63 was envisioned as an aircraft that would be able to outclimb the Fw-190 and Zero, or at least there is a line in the 'Vee's' about that. Small (for non-European measuring sticks) fuel tankage should contribute to that, the P-63 was a good climber. However in late 1943, when the P-63 entered production, the long range was a requirement for the USAF fighters, not the great RoC. For Bell to install greater fuel tanks would mean further delays to the production, since it would mean different ribs.


Right redesign a 'wet' wing to expand fuel. Shame they didn't catch on during the early prototype phase and put emphasis on that area. (especially in a modular fashion like the P39's fuel cells allowed) The P-59 had that problem too ... LOTS Of wing space for fuel, but only a moderate amount used. (granted a bit moot given it didn't develop into a useful combat ... or even recon aircraft)

The F2A actually comes to mind too for having the opposite problem. The poor thing started out with an exceptional fuel load for its size, but the designers seemed to put even more emphasis on fuel load over keeping weight down and climb performance up to the point of crippling it and exacerbating the build quality/manufacturing problems. (from 160 gallons on the F2A-1 to 240 gallons on the F2A-2/3 ... double the Wildcat's internal fuel load in spite of being a smaller, lighter built plane)




> The Hispano worked okay aboard the P-38 - rigid fuselage mount benefits a bit? The ability to re-c0ck the Hispano would be a safety feture, of course.


The pilot ability to re-**** the cannon in-flight was a big part of this, most/all wing mounted variants didn't feature that until electrical cocking with the post-war M3. (electrical priming probably would have resolved many of the issues too ... not sure why that wasn't persued as the British did for their post-war Hispanos)




> I will politely disagree with that. At 20000 ft, the better V-1710 (ie. 9.60:1 S/C gear) it with give around 950 HP, vs. ~1130HP of Merlin 45. It will enter production some 15-18 months later than Merlin 45. It will compare favorably under 10000 ft, though, not a great thing in a fighter aircraft.
> What the V-1710 will have against early Merlin 45 might be the better carb (pressure injection vs. float-type) and use of 6-per-side exhaust stacks rather than 3-per-side; those are engine add-ons, though. The Merlins also received better carbs not long after the 9.60:1 V-1710s were introduced.


The cropped Merlin 50 series vs the 8.8 supercharged Allisons was a bit more favorable and available earlier (though official boost limit restrictions may have been raised later than on the Merlin). 

We've already been over the unfortunate delay in higher alt supercharger speeds on the V-1710 though. 9.6:1 would have been VERY useful earlier on and having that along with the 8.8 blower to choose from would have made the situation much closer to the Merlin 45/50 series. (in terms of installing one or the other based on low/mid alt performance needs)

Aside from that the V-1710 had more economical cruise ability than the merlin and I think was a bit lighter and had a slightly smaller frontal area. (I know the single-stage Allison was lighter than the Merlin 20 series, not sure about the weight savings on the 45)

For that matter, I don't recall reading much of anything on overboosting V-1650-1 powered P-40s or Hurricane Mk.IIs. (low blower should have been fairly close to the low-alt Merlin 50 and high blower pretty much identical to the 45)


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## Von Frag (Feb 20, 2015)

tomo pauk said:


> This might shed some light re. USN financing P&W to get a workable 2-stage engine to work:



I would like to know more about this P-40/R1830 test mule that could climb like that and hit 389 mph at 22,000 ft. Certainly it was stripped of armor and all uneccessary equipment. Why not use a P-36 airframe? It was designed for the 1830 from the start. Could they not fit the 2 stage SC onto it? Are there any photos or surviving test results?


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## tomo pauk (Feb 21, 2015)

The P-40 with R-1830 is mentioned, for example, here, scroll down a bit. Picture has it as unarmed.



kool kitty89 said:


> ...
> The cropped Merlin 50 series vs the 8.8 supercharged Allisons was a bit more favorable and available earlier (though official boost limit restrictions may have been raised later than on the Merlin).



The Merlins with cropped impeller (9.50 in, or same as V-1710) were indeed comparable with V-1710 that has 8.80:1 S/C gearing. Not all those V-1710 were created equal, though. The engines with 'regular' crankcase (prior early 1942) were good for ~1500 HP at 4500 ft on WER, once the reinforced crankcase was introduced the allowed boost was upped and power went to ~1590 HP at 2500 ft, WER. Those more powerful engines were contemporary with 'cropped' Merlins.
OTOH, the 'cropped' Merlin was maybe the 3rd category between available 1-stage Merlins, after 2-speed models and regular 45/46/47/50 marks.



> We've already been over the unfortunate delay in higher alt supercharger speeds on the V-1710 though. 9.6:1 would have been VERY useful earlier on and having that along with the 8.8 blower to choose from would have made the situation much closer to the Merlin 45/50 series. (in terms of installing one or the other based on low/mid alt performance needs)



Indeed it was unfortunate. The 9.60:1 S/C on V-1710 means a P-40 that can do almost 380 mph, P-39 of circa 390, the P-51 above 400 mph.



> Aside from that the V-1710 had more economical cruise ability than the merlin and I think was a bit lighter and had a slightly smaller frontal area. (I know the single-stage Allison was lighter than the Merlin 20 series, not sure about the weight savings on the 45)



'Vee's' list the Merlin 50M at 1385 lbs, and V-1710-39 at 1310 lbs.The same engine will have frontal area of 5.19 sq ft, the 2-speed Merlin is at 5.85; the 1-speed?
Smaller frontal area is good if the advantage can be taken of. If cockpit is wide enough for a pilot to comfortable sit in it and man the aircraft, going 'thinner than that is not going to yield any practical advantage. The lower consumption should pay off.



> For that matter, I don't recall reading much of anything on overboosting V-1650-1 powered P-40s or Hurricane Mk.IIs. (low blower should have been fairly close to the low-alt Merlin 50 and high blower pretty much identical to the 45)



Not sure about V-1650-1. The Merlins in Hurricane II were overboosted up to +16 psi as war went on, here. The later 1-stage Merlins were using up to +18 psi.


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## kool kitty89 (Feb 21, 2015)

Von Frag said:


> I would like to know more about this P-40/R1830 test mule that could climb like that and hit 389 mph at 22,000 ft. Certainly it was stripped of armor and all uneccessary equipment. Why not use a P-36 airframe? It was designed for the 1830 from the start. Could they not fit the 2 stage SC onto it? Are there any photos or surviving test results?


Mating the 2-stage R-1830 to the XP-42 style close-cowled fan-cooled installation (the final, satisfactory one similar to the Fw-190's, Tempest II, and XP-47J's) is something I've wondered about since first reading about the XP-42. Only real problem I can see is competition with the F4F for engines ... which already had shortages.

Hmm, though AS a navy fighter in place of the F4F entirely, yes that would seem like a much more capable aircraft but possibly have the issues of higher landing speeds due to wing loading. 

The F2A with the same engine would have been interesting too but ... Brewster's mismanagement crippled the existing models as it was. (plus the R-1820-40 had relatively good altitude performance too, so the gain might not have been that dramatic)


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## Shortround6 (Feb 21, 2015)

Trouble with the R-1830 powered P-40 as Flown by P&W as a _test mule_ was that it didn't set those performance figures _until_ late supper/early fall of 1942. Nice achievement but a bit late to make a practical fighter. It took about 6 months to go from First flights of Merlin Mustang prototypes to start of production and in fact P-51Bs were ordered several weeks before prototypes flew (in either England or US).

They were still fooling around with cowls on the XP-42 at _least_ until Dec of 1941 ( the plane was used for other research work later in the war) and maybe later. 

The engine shortage for F4Fs was in 1941, it seems to have been resolved by early or summer of 1942. 

Weight savings between Single speed Merlin and the Allison are too small to worry about. You could sometimes get a bigger change in weight by changing propellers. The engines rejected different amounts of heat to the coolant and oil systems and needed slightly different radiator/s and oil coolers. Dry weight doesn't include the starter system and that can change things also (not to mention generators, P-39s were pretty much an all electric airplane, electric propeller and may need bigger generator than a Plane using a hydraulic propeller. ) 



> Right redesign a 'wet' wing to expand fuel. Shame they didn't catch on during the early prototype phase and put emphasis on that area. (especially in a modular fashion like the P39's fuel cells allowed) The P-59 had that problem too ... LOTS Of wing space for fuel, but only a moderate amount used. (granted a bit moot given it didn't develop into a useful combat ... or even recon aircraft)
> 
> The F2A actually comes to mind too for having the opposite problem. The poor thing started out with an exceptional fuel load for its size, but the designers seemed to put even more emphasis on fuel load over keeping weight down and climb performance up to the point of crippling it and exacerbating the build quality/manufacturing problems. (from 160 gallons on the F2A-1 to 240 gallons on the F2A-2/3 ... double the Wildcat's internal fuel load in spite of being a smaller, lighter built plane)



Integral tanks or "wet wings" had been a common feature (or at least not uncommon) in 1939/40 but quickly went away with the demand for self sealing tanks/fuel storage. You can't have both. P-43 tried and leaked fuel even without combat damage. 

In fact that is part of the F2A story. Original 160 gallons was held in two tanks made up of the mains spars in the wing as front and back walls, wing skinning as top and bottom and solid ribs as tank ends. Trouble was trying to put self sealing liners in such a structure and/or repairing combat damage. Extra fuselage tank and wing leading edge tanks replaced one of the wing tanks normal capacity ( other tank was kept in use to _simplify(?)_ fuel piping system, the reserve taps and overflow piping being connected to it. The other tank was _sealed_ and could only be unsealed with the authorization of the squadron commander. poor climb was NOT the result of trying to carry 240 gallons of fuel. BTW the early F4Fs with unprotected tanks held the same 160 gallons as the early F2As.


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## tomo pauk (Feb 21, 2015)

Problem with that P-40 with 2-stage R-1830 is that speed figures are without any military stuff on board. Once the guns, ammo, armor, military radio navigation systems are installed, much of the claimed speed will be lost. It is unlike that a resulting battle-worthy fighter will be faster than P-40F (Packard Merlin V-1650-1), that one was good for 360+ mph just above 20000 ft. Good for Asia/Pacific, bad for ETO MTO of 1941 and further.


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## Shortround6 (Feb 21, 2015)

kool kitty89 said:


> Hmm, though AS a navy fighter in place of the F4F entirely, yes that would seem like a much more capable aircraft but possibly have the issues of higher landing speeds due to wing loading.
> 
> The F2A with the same engine would have been interesting too but ... Brewster's mismanagement crippled the existing models as it was. (plus the R-1820-40 had relatively good altitude performance too, so the gain might not have been that dramatic)



A P-36 as a Navy fighter instead of the F4F has a _lot_ of problems. Stall speed is part of it. Another part is is the vertical impact speed at which the plane hits the deck. Higher on average than land planes. Early P-36s had problems with wing wrinkling/bending as it was. slamming them onto decks with arrestor landings was not going to turn out good. 

Everybody wants to keep the P-36 weight as built but fails to realize that Curtiss ( and Brewster) _Management_ did NOT add weight for the fun of it. 
A Hawk 75 had a wing that weighed about 840lbs. I don't know what the weight of a P-36 wing was ( and you have the before and after modification weights). The 5th P-40 built had a wing that weighed 1003lbs (provision for but not including a single .30 cal in each wing), later P-40s had wings that weighed around 1120-1130lbs. How much was the change in structure due to the six .50 cal guns and how much was to beef up the wing so the plane was *still* stressed for an ultimate 12G load factor at over 8000lbs vs the the under 5700lbs of a Hawk 75 I don't know. The sales brochure for the Hawk 75 says the Cyclone powered Hawk was stressed for 12 Gs while the Twin Wasp powered model was stressed for 11.5Gs (it weighed 230lbs more). 
However there is a line right below that states "The Airplane can be furnished at standard load factors at an increase in weight and price". 
The Hawk 75 with Cyclone engine had a powerplant weight of 1985lbs. early P-40 had a power plant weight of about 2100lbs. 
Hawk 75 had one .50 cal with 200 rounds and one .30 cal with 600 rounds. 

Brewster was sort of in the same boat. First planes built were _designed_ to have one .50 and one. 30. the wing guns were added in. The Early Planes also used not only and single speed supercharger but the engine did not use a reduction gear. Prop turned the same speed as engine crankshaft. Later Buffaloes not only got an engine with a reduction gear but got engines with more cooling fins and with steel crankcases instead of aluminium and other changes. They also got bigger, heavier props to handle the extra power. The Buffaloes wing went up by 172lbs. Landing gear got heavier, the better engine/powerplant went up by 547lbs. There is some dispute about the amount of ammo for the wing guns, .50 cal ammo weighs about 30lbs per hundred. changing from 200rpg to 400rpg for just the two wing guns is an increase of 120lbs. Changing the Fuselage guns from 200rpg to 500rpgs is another 180lbs.


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## kool kitty89 (Feb 21, 2015)

Shortround6 said:


> Integral tanks or "wet wings" had been a common feature (or at least not uncommon) in 1939/40 but quickly went away with the demand for self sealing tanks/fuel storage. You can't have both. P-43 tried and leaked fuel even without combat damage.


I meant more wing fuel cells ... the 'wet wing' term seems to get used loosely at times. (the P-47N is described as such)



> In fact that is part of the F2A story. Original 160 gallons was held in two tanks made up of the mains spars in the wing as front and back walls, wing skinning as top and bottom and solid ribs as tank ends. Trouble was trying to put self sealing liners in such a structure and/or repairing combat damage. Extra fuselage tank and wing leading edge tanks replaced one of the wing tanks normal capacity ( other tank was kept in use to _simplify(?)_ fuel piping system, the reserve taps and overflow piping being connected to it. The other tank was _sealed_ and could only be unsealed with the authorization of the squadron commander. poor climb was NOT the result of trying to carry 240 gallons of fuel. BTW the early F4Fs with unprotected tanks held the same 160 gallons as the early F2As.


I was under the impression the F2A-2 had no self sealing and 240 gallons internal capacity while some of the export models and F2A-3 got additional/redesigned self-sealing tanks.

The F2A-3 was heavier still overall, but the F2A-2 has seen a major weight increase as well but seemed to focus more on long range than compromising to keep weight down. (that or integral modifications to the airframe wouldn't actually save much/any weight compared to simply limiting fuel and ammunition load)



Shortround6 said:


> Brewster was sort of in the same boat. First planes built were _designed_ to have one .50 and one. 30. the wing guns were added in. The Early Planes also used not only and single speed supercharger but the engine did not use a reduction gear. Prop turned the same speed as engine crankshaft. Later Buffaloes not only got an engine with a reduction gear but got engines with more cooling fins and with steel crankcases instead of aluminium and other changes. They also got bigger, heavier props to handle the extra power. The Buffaloes wing went up by 172lbs. Landing gear got heavier, the better engine/powerplant went up by 547lbs. There is some dispute about the amount of ammo for the wing guns, .50 cal ammo weighs about 30lbs per hundred. changing from 200rpg to 400rpg for just the two wing guns is an increase of 120lbs. Changing the Fuselage guns from 200rpg to 500rpgs is another 180lbs.


Even with all that, the F2A-3 seemed to perform favortably compared to the similarly powered F4F and F4F-4 and had trade-offs with the F4F-3. (longer range vs poorer altitude performance vs weak bombload -the F4F certainly made for a better fighter-bomber)

Manufacturing volume and maintanence/reliability issues seem to be the real disadvantages compared to the F4F.


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## Shortround6 (Feb 22, 2015)

kool kitty89 said:


> I was under the impression the F2A-2 had no self sealing and 240 gallons internal capacity while some of the export models and F2A-3 got additional/redesigned self-sealing tanks.



The F2A-2 had no self sealing and 160 gallons internal capacity. Some of the export models got rudimentary self-sealing tanks, Like treated leather coverings of the existing standard tanks. F2A-3 got the additional tanks which were self sealing. 



> The F2A-3 was heavier still overall, but the F2A-2 has seen a major weight increase as well but seemed to focus more on long range than compromising to keep weight down. (that or integral modifications to the airframe wouldn't actually save much/any weight compared to simply limiting fuel and ammunition load)



F2A-2 saw no increase in range over the F2A-1, what it saw was a change in engine which resulted in a 360lb increase in both empty and _normal_ gross weight. However the Early F2A-2 was NOT combat capable as defined by US standards in the summer of 1941. The US Navy was also playing games with different load-outs ( 2 gun fighter, 4 gun over load fighter, 2 gun bomber, 4 gun overload bomber and zero gun ferry condition) which _might_ have masked the real situation. Also masking the situation was some of the load/weight charts are for 660lbs of fuel (110gal) and not even the full 1080lbs (160 gal) capacity. 

Not much to choose in bombload until the FM-2 shows up. F4F-3 adn F4F-4 usually rated for a pair of 100lb bombs. 

Trying to back a little more on topic, what hurt the American fighters as much as "a less than the best supercharger design" was that they were *heavy!!*. 

A MK V Spit was just under 6500lbs. A P-40C without drop tank went 7500lbs, A P-40E without tank went about 8300lbs and a P-39D-2 without tank could go 7700lbs. 
A MK IX Spit was just under 7500lbs. 

Changing the supercharger and picking up 100-150hp at altitude might not be enough to even things out. Close the gap somewhat certainly.


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## kool kitty89 (Feb 23, 2015)

Shortround6 said:


> The F2A-2 had no self sealing and 160 gallons internal capacity. Some of the export models got rudimentary self-sealing tanks, Like treated leather coverings of the existing standard tanks. F2A-3 got the additional tanks which were self sealing.


Thanks for the correction, I forget where I first saw the 240 gallon figure, I was thinking it was on Joe Baugher's page (which, granted, isn't always accurate either), but looking again, it's only the F2A-3 that he lists at 240 gallon maximum capacity. (which, as you mentioned, wouldn't have been a normal loadout at all)

Baugher's page also shows a moderate increase in range for the F2A-2 over the F2A-1, but that might not be comparing similar loadouts, or could be a consequence of the R-1820-40's fuel economy. (I recall mention to that model having particularly efficient cruise capabilities)




> Not much to choose in bombload until the FM-2 shows up. F4F-3 adn F4F-4 usually rated for a pair of 100lb bombs.


Thanks again. Both the F2A-3 and F4F-3/4 had the 2x 100 lb bombload, and the F2A was never fitted for drop-tanks.



> Trying to back a little more on topic, what hurt the American fighters as much as "a less than the best supercharger design" was that they were *heavy!!*.
> 
> A MK V Spit was just under 6500lbs. A P-40C without drop tank went 7500lbs, A P-40E without tank went about 8300lbs and a P-39D-2 without tank could go 7700lbs.


Yep, heavier, sometimes heavier armmed, and usually longer range aircraft. P-39 was the closest to its European counterparts, but still usually heavier aside from some stripped-down configruations. (but the same would apply to the P-40N and some field modifications made on earlier models)


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## tomo pauk (Feb 23, 2015)

A bit on topic.
The 2-stage V-1710, like the V-1710-121 (military designation; F28R Alison designation - R denoting the rotation to the right) being test flown in early 1944 were comparable with V-1650-7 in altitude power. The military power was about 1100 HP at 25000 ft for both engines; the V-1650-3 was still a better hi-alt powerplant than either. For WER the F28R used water-methanol to help out (like almost all V-1710, it didn't have an inter-cooler ) managing 1750 HP at 9500 ft; 1500 HP at 15000 ft. When over-revved to 3200 rpm (that being one of rare thing where V-1710 excelled over Merlin, but it is questionable whether service engines ever used it legally), the WER went to 1680 HP at 17000 ft, and 1190 HP at 25000 ft. All values for the F28R are for climb, ie. with minimum ram available.
For comparison sake - V-1650-3 was good for 1300 HP at 26400 ft, so not that much better. Quirk being that V-1650-3 was available about a year earlier, the British 2-stage Merlin 61 about 2 years earlier.
The F28R is one of rare things where the 'Vee's for victory' got it wrong, claiming that power of 1700 HP on 3200 rpm was available at *2*6000 ft, or about 10000 ft higher than it is documented in this pdf. That power at altitude was maybe 'reachable' with late war big engines with 2-stage S/C and inter-cooler, like R-2800-18, RR Griffon or Jumo 213E.


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## wuzak (Feb 23, 2015)

Maybe the V-1650-9 would be the US Merlin contemporary of the two stage V-1710?

Certainly the V-1650-3 was a high altitude version, but it was an earlier one, like the Merlin 63, without the strengthening that came with the later engines.

The V-1650-7 was the US equivalent of the Merlin 66 - a "low altitude" version.


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## GregP (Feb 24, 2015)

Let's see ... low altitude Merlin 66 equivalent for the P-51D?

Best speed was 437 mph at 25,000 feet and service ceiling was 41,900 feet.

I don't think "low altitude" applies here.

Could be wrong ...


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## Edgar Brooks (Feb 24, 2015)

The L.F. designation, on the IX, was due to the supercharger, of the Merlin 66, going over to high gear at 14,000', instead of the "normal" 21,000' of the other 60-series Merlins.


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## wuzak (Feb 24, 2015)

GregP said:


> Let's see ... low altitude Merlin 66 equivalent for the P-51D?
> 
> Best speed was 437 mph at 25,000 feet and service ceiling was 41,900 feet.
> 
> ...





Edgar Brooks said:


> The L.F. designation, on the IX, was due to the supercharger, of the Merlin 66, going over to high gear at 14,000', instead of the "normal" 21,000' of the other 60-series Merlins.



As Edgar said.

Comaprison between the V-1650-7 and V-1650-9, as posted elsewhere.


Alt (ft)V-1650-7 MAPV-1650-7 hpV-1650-9 MAPV-1650-9 hp067178067150348006717301546500066.517206715481000056.314706715901380012896716221500047.2123215641600067158015151900067150013692000065.214556713202500055.512256713402670011576713473000046.4102559.412093500037.785549.410124000029.870040.6830

As you can see, the V-1650-7 loses MAP from a relatively low altitude, then is back to 67inHg MAP from 16,000ft. The difference between the 14,000ft Edgar stipulated and the 16,000ft here may be due to the ram effect.

The FTH for the V-1650-7 appears to be 19,000ft.


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## kool kitty89 (Feb 24, 2015)

tomo pauk said:


> When over-revved to 3200 rpm (that being one of rare thing where V-1710 excelled over Merlin, but it is questionable whether service engines ever used it legally)


With over and unferreving changing supercharger speed, you'd need to account for added charge heating at higher RPM even if the engine itself could handle the strain perfectly well. Though that does bring up another aspect I'd forgotten to consider. Maybe it would be too fiddly to manage in service, but wouldn't rev-limiting also allow higher maximum boost at low alt on engines limited by charge heating? 




> The F28R is one of rare things where the 'Vee's for victory' got it wrong, claiming that power of 1700 HP on 3200 rpm was available at *2*6000 ft, or about 10000 ft higher than it is documented in this pdf. That power at altitude was maybe 'reachable' with late war big engines with 2-stage S/C and inter-cooler, like R-2800-18, RR Griffon or Jumo 213E.


1700 HP at 25,000 ft sounds more like a turbocharged V-1710.


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## tomo pauk (Feb 24, 2015)

> Maybe it would be too fiddly to manage in service, but wouldn't rev-limiting also allow higher maximum boost at low alt on engines limited by charge heating?



The 3200 rpm rating was allowed only when water injection was used, since indeed it would heat the charge too much. We might recall that DB 601A and 601N were allowed for over-revving only above critical height, probably to avoid overheating the charge.



wuzak said:


> Maybe the V-1650-9 would be the US Merlin contemporary of the two stage V-1710?



I don't have accurate data about when the V-1650-9 went into production, so it's a bit hard to compare it with a 2-stage V-1710. 
However, sticking with production engines - the P-51H was 1st delivered in February 1945, so we can compare it with the engine from the P-63C, that fighter 1st delivered in December 1944. The V-1710 in question would then be the E21 (Allison designation; V-1710-117 military designation). It was good for 1100 HP at 25000 ft, military rating. Still less than V-1650-7 and V-1650-3, and much less than -9, that one making 1200 HP at 30000 ft on military rating.

The P-63E, 1st delivered in May 1945, finally managed to equal the V-1650-3 and -7 (those being old news by then), with 1100 HP at 28000 ft with V-1710-109 (E22; main distinction vs. the E21 being relocation of the carburetor between compressor stages, while allowed for 3200 rpm for WER). The V-1650-9 can use water injection, that makes above 1400 HP at 30000 ft, and above 1800 HP at 20000 ft. Vs. that, the E22 can use 3200 rpm and water injection, but still makes only 1340 HP at 27500 ft with ram - that would amount to ~23500 ft without ram, and won't cut it vs. the V-1650-9.


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## tomo pauk (Feb 24, 2015)

As seen above, the Allison was managing for the 2-stage V-1710 to come out with ever better 'altitude power', so the supercharger development potential was there, even if it was running late vs. 2-stage Merlin or R-2800. The main obstacles for earlier development of 2-stage V-1710 was probably in the US Army fixation with turbos as means for hi-alt power, followed with quite a bit of resources poured in the hi-per engines the Army was trying to 'co-develop' with Continental and Lycoming. 
Some of the things might get the finger pointed on the Allison, too - lack of inter-cooler on the production 2-stage engines; that, coupled with deletion of backfire screens that meant the engines used on the P-82E were in problems when greater boost was to be used. 
Installing of the carburetor in the location between the S/C stages necessitated the use of 'speed density' fuel pump in the place of the carb if inter-cooler is to be used, as it was the case for the rare V-1710 F32R. That fuel pump needed more development, and the F32R was limited to only 54 in Hg during flying tests. In light of that, we don't know whether the XP-51J, the Mustang with the F32R, actually ever managed the claimed 491 mph. The max power was to be 1700 HP @ 3200 rpm at 20700 ft ('WER wet') or 1200 HP @ 3000 rpm at 30000 ft (military power). 
Gruenhagen notes: _The water injection system was not used on the XP-51J due to calibration problem with the speed density unit._; he lists the take off power 1500 HP @ 3200 rpm on 58 in Hg.


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## GregP (Feb 25, 2015)

Hi Tomo,

3200 rpm was allowed only when equipped with a 12-counterweight crankshaft from the first G-series onward. None of the 6-counterweight engines were ever allowed 3200 rpm. At Reno, we've seen 3600 rpm on a stock warbird in the Bronze class for a couple of laps at the end and that was at the limit of the Curtiss Electric prop.

In tractors today in Europe, they are running them a 4800 rpm without damage ... but it's only for short tractor-pull runs. Nothing like a flight. Tractors rarely pull for more than 15 - 20 seconds. Still, that much overspeed without damage is indicative of VERY good primary balance coupled with strong rods and cranks. Some of them are not even runiing G-series rods!


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## tomo pauk (Feb 25, 2015)

The V-1710-121 was run on 3200 rpm already in early 1944, I'll re-post the link to the XP-40 testing: pdf.


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## GregP (Feb 25, 2015)

Nothing with a service ceiling of 41,000+ feet was really a low-alitude engine in WWII. Perhaps with respect to a later development, but was it a low-altitude engine with respect to earlier developments?

In the development scheme of things, the -7 was after the -1 and -3. It was supposed to be better, and I'd expect a -9 to be better than a -7, too, assuming the new dash isn't / wasn't a special-purpose engine, such as a sped record one-off or other special project. That's what I meant anyway.

When the -7 came out, it wasn't a low-altitude engine. You might consider it so when compared against the -9 but remember the -9 was not an engine that saw combat in WWII as the P-51H didn't see combat in WWII. It barely made the war, but wasn't a factor in combat at all.

I was thinking of WWII comparisons and will grant it seems to be "low-altitude" compared with the -9 of post-war fame.


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## wuzak (Feb 26, 2015)

GregP said:


> Nothing with a service ceiling of 41,000+ feet was really a low-alitude engine in WWII. Perhaps with respect to a later development, but was it a low-altitude engine with respect to earlier developments?



The -7 had lower Full Throttle Height/Critical Altitude in both Full Supercharge (FS) and Medium Supercharge (MS) gears (HI and LO in US parlance).



GregP said:


> In the development scheme of things, the -7 was after the -1 and -3. It was supposed to be better, and I'd expect a -9 to be better than a -7, too, assuming the new dash isn't / wasn't a special-purpose engine, such as a sped record one-off or other special project. That's what I meant anyway.



The -1 was a single stage 20-series Merlin. 

The -3 was equivalent to a Merlin 63. 

The -7 was equivalent to a Merlin 66.

The -9 was equivalent to a 100-series Merlin (not sure whjich one exactly - I will have to check).

The -3 and -9 had the same supercharger gear rations, while the -7 had different ratios.

The 66 was strengthened compared to the -3, and the -9 was further strengthened. The -9 also featured further refinements, such as end-to-end lubrication of the crankshaft, compared with the earlier engines.



GregP said:


> When the -7 came out, it wasn't a low-altitude engine. You might consider it so when compared against the -9 but remember the -9 was not an engine that saw combat in WWII as the P-51H didn't see combat in WWII. It barely made the war, but wasn't a factor in combat at all.



It was a low altitude engine compared to the Merlin 70 series engines, which did see service in Spitfires and Mosquitoes.

Spitfire IXs were fitted, initially, with Merlin 61s or Merlin 63s. Around 1943/1944 they started putting in Merlin 66s and Merlin 70s. The Merlin 66 versions were named LF.IX, the Merlin 70 versions named the HF.IX. 

The LF.IX had better low altitude performance and climb rates than the HF.IX, which took over the performance advantage at mid altitudes and held it at high altitudes.

I believe that the Mustang received the V-1650-7 was to bolster its low altitude performance, particularly climb.

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## GregP (Feb 26, 2015)

Wayne, 

The USA didn't USE UK-built Merlins (in US-built aircraft anyway) and you specifically said a -7 and -9. or so I thought. Those were specific-use engines for the most part.

I made an assumption here that you were talking Packard Merlins in WWII. If you weren't, OK ... I understand. I thought this was a WWII forum and the US and UK-built Merlins weren't interchangeable in a LOT of respects. Today they are not considered interchangeable ... at least by the 20 or so owners I know. Some of them have Rolls Royce Merlins and some have V-1650-X, and ALL like what they have ... but they don't interchange parts very without rework of said parts. That's from the owners, not me. I know ALlisons pretty well but have only helped a bit on Merlins. More lack of opportunity than anything. The owners that HAVE issues with them tend to send them to Mike Nixon instead of trying to work it our with local guys.

If you are opening it up to ALL Merlins, then go for it. I'd stop at WWII since this is a WWII forum, but they STILL make parts for Merlins today if you want to get technical about it. They race every year at Reno and can stomp the crap out of any WWII or slightly post-war stock Merlins ... for about 8 laps or so anyway ... at about 5,000 feet. Nobody knows their higher altitude characteristics.

I was assuming a sort of logical limit but, hey, go for it. 

When you compare P-51's, you don't usually hold up the P-51D or H to a P-51A and say how far the design progressed. But you CAN if you lean that way.

About the 3200 rpm, you are right, they DID make four V-1710-121 (F-26R) engines that could be operated at 3200 rpm. They needed some test mules for the G-series rods. Forgot about those 4 engines. The original engine in the XP-40Q-2 was a -101 and only was run to 3,000 rpm. It was later when the engine was changed to the -121 that they tried that rpm. Helped a bit ... but not much.

I stand corrected there.

It was only the G-series for production planes ... but they DID do it in the very pretty but short-lived the rebuilt XP-40Q-2 in 1944, about the time the G-series was being tested and turned into a shippable engine.

I think the big pistons would have dome some amazing things power-wise had development continued instead of dying in 1945 - 1946. I can see Allisons and Merlins (as well as some others) getting another 300 - 500 HP with continued development, and I think a LOT of it would have come from RPM increases and improved boost systems. The Merlin would have needed new rods and pistons, but they were not out of reach, certainly, and it was a very smotth-running and reliable engine in most of its forms. A winner for sure.


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## wuzak (Feb 26, 2015)

GregP said:


> Wayne,
> 
> The USA didn't USE UK-built Merlins (in US-built aircraft anyway) and you specifically said a -7 and -9. or so I thought. Those were specific-use engines for the most part.
> 
> I made an assumption here that you were talking Packard Merlins in WWII. If you weren't, OK ... I understand. I thought this was a WWII forum and the US and UK-built Merlins weren't interchangeable in a LOT of respects. Today they are not considered interchangeable ... at least by the 20 or so owners I know. Some of them have Rolls Royce Merlins and some have V-1650-X, and ALL like what they have ... but they don't interchange parts very without rework of said parts.



Packard Merlins were almost entirely interchangeable with British built Merlins. There were a few items that differed, such as the supercharger drive gear train (on 2 stage engines) and the output shaft for US use and the carby IIRC.

Remember that the bulk of Merlins produced by Packard went to thr UK. They were used in the Lancaster, Spitfire and Mosquito. The Spitfire XVI was a Spitfire IX with a Packard built Merlin - the Merlin 266. Merlin 225s were supplied by Packard for Mosquito production (Canadian production mainly?). Merlin 224s and 228s were for Lancasters.

British bound Packard Merlins had SBAC standard output shafts, American bound Merlins had SAE standard shafts.

The screws, nuts and bolts used on Packard Merlins were BA (the small ones, on the supercharger housing for example) and Whitworth (standard or fine).

Each Packard model was equivalent to a Rolls-Royce model, or family of models. Except the experimental version with the fluid coupling drive for the supercharger. They used the same ratings as were used for Rolls-Royce. These ratings are denoted by RM.XSM - this means Rolls-Royce (R), Merlin (M), rating number (X), supercharger specification (S = supercharged = fully supercharged, M = medium supercharged, L = low supercharged). 

The Merlin 66 was rated RM.10SM. The V-1650-7 was rated RM.10SM.

The V-1650-3 was the Packard equivalent of the Merlin 63. The supercharger used gear ratios of 6:39:1 (MS/Lo) and 8.095:1 (FS/Hi).

The V-1650-7 was the Packard equivelent of the Merlin 66. The supercharger used gear ratios of 5.8:1 (MS/Lo) and 7.34:1(MS/Hi) .

The V-1650-9 was rated RM.16SM (or was it 14SM?), as were the Merlin 113 and 114.. The supercharger used gear ratios of 6:39:1 (MS/Lo) and 8.095:1 (FS/Hi).

So, the V-1650-7 ran the supercharger slower than either the -3 or -9, which means that the pressure ratio is lower. The lower speed means that the supercharger uses less power to drive, but runs out of capacity at a lower altitude. That is why it is called a "low altitude" engine.

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## GregP (Feb 26, 2015)

If you like to believe they were interchangeable, go ahead; no argument here. From the owners I know, it isn't the case. It could ALSO be that these late-day Merlins have been modified over the years so they are not very interchangeable, but ... maybe they started out that way. Could be so.

The old crew chiefs say no, but that could be just wanting to run US engines in US planes. If they never installed a British Merlin, maybe they just don't know. Also could be. I have NOT gotten into Merlins the way I have Allisons.

One of the few things I can say for SURE about the Merlin is that when Joe Yancey got the Dago Red engine, he had to do custom machining to get the supplied spare parts to fit within specified tolerances. We didn't know if the parts were Packard or RR ... we ujsed what was supplied. You can make of that whatever you want. Without guessing, I KNOW the Merlin 224 was a basically stock Packard-built Merlin 24. Ditto the other 220-series post-war engines.

Some owners of the -3s and -7s say it isn't so (intercahngeability). I don't know all that many ... maybe 8 or so. I am not an owner but will usually believe an owner over a book, especially when I ride with him in the plane and note he is flying it EXACTLY to book numbers and is getting book speeds exactly as expected ± a few knots at the book manifold pressure and rpm.

I'd bet Rod Lewis and Tom Friedkin own both US and British Merlins at the same time. They should know but I only see them at airshow time.

So no argument here other than there are some guys with pretty good credentials who say otherwise. They certainly could be wrong. 

I know one guy who had a crank made, but I don't know the specs and would not care to guess whether it was made stock or not. Runs good, but we haven't discussed specs at all.

Most of the -7s I see these days have transport heads on them (... not stock for a -7), modern mags coupled with the stock Merlin carbs, stock superchargers, gearing and accessories, but some are running different reduction gears from different model Merlins or even custom reduction gears for the racers.

The most stock V-1650-7 I have seen in years is at the Museum now and has transport heads with almost everything else as stock as possible ... except for more modern mags and a modern new spark plug wiring harness. I can get pics Saturday and also of a single-stage, 2-speed Merlin 224 ... but the pics likely won't tell you anything you didn't probably already know. 

All the other -7s I've seen in the last 5 - 6 years won't tell you much about -7s because they aren't stock in several areas ... depends on parts available. So this really COULD be a case of modern -3 and -7 engines simply not having the parts to BE interchangeable. I can't say and don;t wish to guess. I know we are running out of Merlin parts and they are flying parts now they'd have thrown away 25 years ago.

We fly two -7 engines at this time and Ken Wagner flies a Rolls Royce Merlin ... but I have never looked at the data plate for the exact engine model (the cowling has always been on it ... except when they pulled the engine and sent it to Mike Nixon). I will ask next time I see Ken. His plane is Lady Alice and is as bone-stock as it can be except for the panel, which has some modern consessions. BEAUTIFUL P-51.

Here is Ken's P-5D:







and here is Dr. Ken Wagner, as happy as every other time I've ever seen him:






If I flew a P-51D, I'd probably be happy all the time, too!

Cheers.

Update:

Hey Wayne,

Found some info that says the Merin 266 was a Packard-built Merlin 66 and the V-1650-7 was similar to a Merlin 66, but modified for the P-51D. The Mods are not specified in the only place I found these data.

Know anything about the differences between a Merlin 266 and V-1650-7? Or was it simply renamed and they were the same engine otherwise? I know they went to American accessories, such as vacuum pumps, etc. Know of any OTHER modifications?

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## wuzak (Feb 27, 2015)

Merlin 266 had SBAC (Society of British Aircraft Constructors) output shaft splines.
V-1650-7 had SAE (Society of Automotive Enginners) output shaft splines.

These pictures show the differences.
http://upload.wikimedia.org/wikipedia/commons/e/e5/RR_Merlin_labeled.jpg
http://usautoindustryworldwartwo.com/images/Normandy/allison-v-1710-107w-1.jpg

I think, but am not certain, that they used different carburettors. Other than that, I cannot think of any major changes.

US built 2 stage engines had a different drive system for the supercharger (epicyclic) than did British built Merlins (Farman).


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## GregP (Feb 27, 2015)

I knew the Merlin 66 was used in LF Spits, but never considered the V-1650-7 to be a low-altitude engine since it typically fought in Europe at 20 - 30+ thousand feet. Would be nice to find out for sure, but I see te V-1650-3 was similar to a Merlin 63 high-altitude version. 

Why the hell would they go from a high-altitude to a lower-altitude engine for a fighter supposed to escort bombers?

Makes no sense to me, but I don't really have the time right now to look at it.

Cheers.


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## wuzak (Feb 27, 2015)

Climb and mid-altitude (c. 20,000ft) performance. I'm sure that is the reason.


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## wuzak (Feb 27, 2015)

GregP said:


> If you like to believe they were interchangeable, go ahead; no argument here. From the owners I know, it isn't the case. It could ALSO be that these late-day Merlins have been modified over the years so they are not very interchangeable, but ... maybe they started out that way. Could be so.



When I say interchangeable, I mean between equivalent series. There will be some components in a V-1650-3 that can't or shouldn't be used in a V-1650-7 or -9, simply because the part has been strengthened and may be bigger and thus will not fit on the earlier engine.

btw, the 220-series Merlins were not post war - they were very definitely war era engines, serving in Mosquitoes and Lancasters.

The "transport" Merlins were the 600 and 700-series. 

The V-1650-9 is a 100 series engine, so most parts should be a direct swap for those in a Merlin 130/131 (from a Hornet). But with end-to-end lubrication teh crankshaft would be unsuitable for early marks, and -3 and -7 crankshafts wouldn't work in a -9 becuase the bearings would not be properly lubricated, if at all.


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## tomo pauk (Feb 27, 2015)

Re. 'low' vs. 'hi' Merlins - when compared with other similar engines, the Merlin is almost always a high altitude engine. However, once we compare one 2-stage Merlin with another 2-stage Merlin, we will always call the one with rated height of ~20000 ft a low-alt version, the one with rated height of ~25000 will be called mid-alt version, the one with rated height of ~30000 ft would be the hi-alt version.
Hope it makes sense 

The Merlin 226 (Packard production) was used on the Spitfire Mk.16?


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## Edgar Brooks (Feb 27, 2015)

tomo pauk said:


> The Merlin 226 (Packard production) was used on the Spitfire Mk.16?


No, it was the 266, which actually started life as the Packard-built 69, but became surplus to requirements due to them no longer being needed on the Canadian-built Mosquito. First conversions were done here, then taken over by Packard, and, because the mods essentially produced an engine identical to the Merlin 66, it was given the number 266.


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## tomo pauk (Feb 27, 2015)

Ah, I see - not 226, but 266. Thanks.


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## GregP (Feb 27, 2015)

Hi Wayne,

I DO belive they were very equivalent and, yes, I was talking about interchangeable. Maybe we're saying essentially the same thing.

Again, I donlt condsider anything thath has a service ceiling of over 41,000 feet to be low altitude ... but maybe it starts losing speed versus the other engines at ... say ... 26,000 feet on up. I was talking baout the PLANE it was used in.

I'll ask tomorrow if the guys at Planes of Fame think the -7 was a "US-modified" Merlin 66. Perhaps it really was and, if so, they'll likely know the exact differences since they have operated virtually all Merlin marks over the years.

I'm leaning toward believing you are right, but will ask and report back, probably Sunday ... assuming the Hintons are there. Maybe not since our F-86F was just flown east for a show yesterday ... Steve usually flies it with the Horsemen. If not, I'll STILL get pics of the -7 and 224 ... assuming the -7 hasn't been installed this weel, that is.

Best regards, - Greg


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## Edgar Brooks (Feb 28, 2015)

According to Rolls-Royce the -7 was the same as the -3, but with different supercharger gear ratios (5.80 7.35 against 6.39 8.095.)
Both were the equivalent of the Merlin 61.
Years ago, I read, but was never able to verify, that Packard used larger, and fewer, bolts to attach the supercharger to the crankcase, which wouldn't have helped interchangeability, never mind the different intercooler header tank layout.

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## GregP (Mar 1, 2015)

A Merlin -61 makes WAY more sense to me for a V-1650-7 since the P-51D, it's primary mount, usually operated at 20,000 to 35,000 feet, at least in Europe.


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## tomo pauk (Mar 2, 2015)

Lumsden notes the V-1650-3 as equivalent of Merlin 63, the V-1650-7 as 'similar' to the Merlin 65, 66, 68, 69. FWIW.


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## stan reid (Mar 11, 2015)

stan reid said:


> Sorry to go off topic for a minute but does anyone know why these engines weren't dohc? Was it cost or that the increase in power didn't significantly make up for the extra weight or, being bulkier, the loss in aerodynamics?



I see that the Napier Lion was dohc.


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## GregP (Mar 11, 2015)

Both the Allison and the Merlin were 4-valve per cylinder SOHC and didn't need to be DOHC. The SOHC design was and IS quite good in both engines. Nothing wrong with either DOHC or SOHC as long as it does the job equally as well as the other would, and these DID.


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## Shortround6 (Mar 11, 2015)

A lot of things change over time. Valve springs are one of them. They look simple but changes in alloys, heat treatment, and finishing techniques (shot peening/bead blasting) and other things mean that the rpm limits of different types of valve trains change enormously over the years. Push rod engines with cam/s in the block now routinely operate at speeds that DOHC only reached in racing applications in WW I or the 1920s. And they last hundreds of thousands of cycles longer. If an engine in the late 1920s managed to go 500 hrs without breaking a valve spring the Maker took out full page ads in magazines celebrating/advertising the event. As valve springs got better the need for complicated valve mechanisms that kept reciprocating (as opposed to rotating) valve train parts as few and as light as possible. 




Not even a rocker arm or cam follower. It doesn't get much simpler for the valve spring. 
The gears and shafts needed to operate 6 cams for a 12 cylinder engine are another story.
As valve springs got better they could simplify the cam drives at the expense of using cam followers or rocker arms.

Please note that after a change of designers and over 10 years Napiers next engine used long pushrods. 
napier rapier | 1935 | 0548 | Flight Archive





despite running at 3900rpm at full throttle. 
Granted it was only a 539 cu in engine and had small cylinders and valves. 16 cylinders to do what a Lycoming IGSO-540 will to today ( or would do in the 1960s)

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## BiffF15 (Mar 11, 2015)

Shortround,
Why were there 6 cams vice 4 (2 per bank) in a V-12?
Cheers,
Biff


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## Shortround6 (Mar 11, 2015)

The Lion was a W-12, not a V-12.

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## GregP (Mar 11, 2015)

Good points Shortround. 

Joe Yancey has shelves of Allison valve springs and some have "collapsed" over time. Most are as good as the day they were made. We tested each spring before installing it in an overhauled engine. Today, valve springs are one of the things you CAN have made new, if necessary. 

Somehow, nobody seems to want to make Allison or Merlin sodium-filled Stellite valves or valve seats with Stellite for warbirds, despite the Kennametal Stellite Company, inventor of Stellite, still being in business. The Allison doesn't need the valve seats, but the Merlins have a valve seat that screws in and breaks off at the "proper torque" value ... at least according to Rolls-Royce. I have seen them loosen in use but, to be fair, only in one Merlin that I know of. The seat cannot losen in the Allison as it an integral part of the head.

Heck, if you want to cut new seats in an Allison, you have to search out the old, long-nose valve grinders. They don't make them anymore, though you CAN still get stones.

Both engines' installed populations, including the "runners" that start but are not in a plane, car, or boat, could use an influx of new valves. Several could use new camshaft and not a few new crankshafts. I think there are enough Allison cylinder liners around for years yet, but the Merlin crowd could use some of them ,too. As long as we're asking for parts, main bearings and cam bearings would be appreciated, too.

Let's face it, the life spans of the existing warbirds would take a huge jump if someone restarted production of the Merlin and the Allison, even if on a limited basis.


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## drgondog (Mar 12, 2015)

GregP said:


> A Merlin -61 makes WAY more sense to me for a V-1650-7 since the P-51D, it's primary mount, usually operated at 20,000 to 35,000 feet, at least in Europe.



The -7 was used in the P-51B/C as well as the D/K, and deployed because it had slightly better power in the middle altitudes through a lower FTH, while the -3 was significantly better above 26000 feet.

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## Milosh (Mar 12, 2015)

Greg,
With the introduction of the P-51C-5-NT onto the Dallas production line and the P-51B-15-NA in the Inglewood production line, the Packard V-1560-7 engine was adopted as standard.

P-51B
42-106739/106978 North American P-51B-15-NA
43-24752/24901 North American P-51B-15-NA
390 a/c

P-51C
Of the 1750 built all but 350 42-102979/103328 North American P-51C-1-NT used the -7 engine.

1950 used the -3 engine
1790 used the -7 engine


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## Shortround6 (Mar 12, 2015)

They may have switched to a more "medium" altitude engine because the anticipated _shift_ to higher altitudes did not occur or occurred after the the engine switch was made. 
Fw-190s with radial engines never got very good at much over 20,000ft. The Germans took a while to get the big supercharger DB605s in service. While some 109s did have GM-1 it was certainly not all 109s used for bomber interception. 

The -7 offered about 100-110 more HP for take-off than the -3 at the same boost and may have helped with the bigger fuel load?


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## drgondog (Mar 12, 2015)

SR - I would expect that the extra TO Power (1490 vs 1380) of the -7 over both the -3 and the -9 would have been nice to have


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## GregP (Mar 13, 2015)

I still think the V-1710 had good potential for development as a 2-stage engine, but it was never funded by the USA.

Anyone else have an opinion about it?


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## gjs238 (Mar 13, 2015)

Greg - Not sure if you've seen or worked on any RR, DB or Junkers engines to make an informed comparison, but I would love for someone to be able to say, "The way the V-1710 was mechanically configured, there is no way a Merlin 2-stage supercharger configuration could have been installed on a V-1710 without major redesign."

I'm wondering if the modular approach Allison took with the V-1710 design precluded a RR 2-stage supercharger layout.

An extreme example would be the DB engines with their sideways mounted superchargers, radically different from a RR or Allison setup.


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## tomo pauk (Mar 13, 2015)

GregP said:


> I still think the V-1710 had good potential for development as a 2-stage engine, but it was never funded by the USA.
> 
> Anyone else have an opinion about it?



I agree that there was a good potential for the V-1710 with 2-stage supercharger. 
It was funded by the USA, otherwise it is very much possible that there would not be any to power the P-63; support funding for that was a bit late, esp. when we look at USN material support for 2-stage engines of P&W (even Wright produced a handful of 2-stage R-2600s!).


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## GregP (Mar 13, 2015)

The aux stage was not exactly what I had in mind.

I was talking about a 2-stage, integral supercharger, similar to the Merlin. Had one been developed, I'm sure it could have been debugged and put into service. Of course, that's an assumption on my part and probably qualifies as a "what if," but they worked out the rest of the bugs, so I am extrapolating.

It is also possible they could have simply made up and adapter plate and molted in teh Merlin S/C unit. Again, that never happened, either.

Good thing the merlin was there and developed as the war went along. The Griffon never DID replace the merlin in service, good though it was.


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## kool kitty89 (Mar 13, 2015)

gjs238 said:


> Greg - Not sure if you've seen or worked on any RR, DB or Junkers engines to make an informed comparison, but I would love for someone to be able to say, "The way the V-1710 was mechanically configured, there is no way a Merlin 2-stage supercharger configuration could have been installed on a V-1710 without major redesign."
> 
> I'm wondering if the modular approach Allison took with the V-1710 design precluded a RR 2-stage supercharger layout.
> 
> An extreme example would be the DB engines with their sideways mounted superchargers, radically different from a RR or Allison setup.


I've actually been meaning to pose the possibility of Allison mounting an auxiliary supercharger in a DB/Jumo style side position, particularly given the (potentially) shorter length and better ram intake position in a P-39/63 configruation. (might have made the modifications to the XP-39E less dramatic too)

The aspect of the RR 2-stage approach that the V-1710 couldn't follow was a single shaft 2-stage design. Any added supercharger stages would be more or less used like a turbocharger, independently driven from the single-speed integral supercharger. This is fairly similar to the approach Pratt and Whitney took for their 2-stage designs, Allison just didn't have the funding or resources (internal or external) of P&W to carry out that development early on, and even most later developments were more primitive than what the superchargers on the R-2800 had developed into. (lack of intercooling was a big issue ... adapting a liquid intercooler arangement akin to the P-38J/L's -or Merlin's- would have made a world of difference)


That aside, the other limiting factor was supercharger design. Allison's own designs may have been reasonable enough, but paled in comparison to Rolls Royce's. Size/space constraints for the integral mounting point may have been a limiting factor too, but the roughly equivalent 9.5" diameter impeller used on the 'cropped' Merlin 50 series still performed significantly better than the Allison's at similar speed (the higher displacement of the engine made up for some of the difference -higher power at lower boost). With Merlin quality supercharger design, the single-stage Allison might have reasonably matched the Merlin 45 or 47 or even exceeded them a bit. 

Stanley Hooker quality compressor design applied to GE's turbos might have had some significant improvements too. (including lower intercooling requirements for given boost pressure)


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## GregP (Mar 13, 2015)

There is NOTHING whatsoever that precludes the Allison block from using a 2-stage case exactly like the Merlin. I have seen them side by side, without superchargers and there isn't a lot of difference. The only penalty I can see is a small bit of added length, and the Merlin unit has that, too. Of course, it would also need an intercooler similar to the Merlin, whether in the same place or not is an issue for debate. On the V-1710-119, it WAS in the same place.

The auxiliary drive on most later Allison WAS a hydraulic coupling. It just wasn't mounted sideways.

I submit the Allison V-1710-119 was a match for the Merlin in all categories, but was overtaken by the jet engine. Had development continued, for some reason, it would have given good service. But, jets were the new darlings of the military and essentially killed the big piston engines. Too bad, but at least a few still exist today.

The fact that the V-1710 "caught up" to the Merlin in it's -119 guise in no way detracts from the brilliance of the Merlin. It just means Allison also developed a good engine that had equivalent performance. Unfortunately, it never made the war and only flew in a few experimental aircraft. It was a case of "too late" for thw war effort, but "too late" beats the crap out of "never."

Most of the planes I love had Merlins or radials, but I DO love the P-38. Nothing else like it in the sky when the sky is full of WWII aircraft. That could change if someone restores a Fokker G-1, a P-61, or perhaps a Savoia-Marchetti SM.92, or a few others. I keep wainting for the Twin Mustang restoration to result in a flying aircraft.

That would be nice to see at an airshow, huh?

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## wuzak (Mar 13, 2015)

I think there was no technical reason why Allison could not have built a two stage supercharger like the Rolls-Royce designs. 

Why they didn't is probably more to do with the philosophy of Allison, particularly with regards to modularity and the ease of manufacture.

To do a 2 stage design like Rolls-Royce would require a complete new supercharger design. In the case of Allison's two stage design, the engine stage supercharger remained the same, while the Auxiliary stage supercharger was, essentially, a bolt on module. The core of the two stage engines with the carbuerretor attached to the engine stage supercharger, instead of the auxiliary stage, were identical, or near enough to, the equivalent turbocharged version.


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## kool kitty89 (Mar 13, 2015)

GregP said:


> There is NOTHING whatsoever that precludes the Allison block from using a 2-stage case exactly like the Merlin. I have seen them side by side, without superchargers and there isn't a lot of difference. The only penalty I can see is a small bit of added length, and the Merlin unit has that, too. Of course, it would also need an intercooler similar to the Merlin, whether in the same place or not is an issue for debate. On the V-1710-119, it WAS in the same place.


There seemed to be some difficulty in making the integral supercharger variable speed (there's some references to 2-speed single stage models, but I haven't seen more specifics on how that was configured -or even it it was some oddity like having the integral stage removed entirely and running only an 'auxiliary' stage).

Using 2 stages geared at a fixed speed similar to the existing engines (without intercooling or water injection) doesn't seem like it'd solve much aside from perhaps providing boost/altitude performance beyond the structural limits of the single integral stage. (still suffering from practical limits of power consumption and charge heating along with fixed FTH -aside from using engine RPM to vary supercharger RPM) You'd also need strong enough gearing to allow for the load -the main limit that delayed the 9.6:1 supercharger speed)

I suppose if they did manage to configure something like that AND manage better efficiency than what happened with existing single stage impellers, it might have been worthwhile. (ie if, for whatever reason, the specific engineering limits on Allison's compressor designs favored such a configuration -in terms of power absorbed and heat generated during compression- compared to what RR -or German engines, and some American radials- managed with single-stages, then it would have been worthwhile)
Obviously, including some form of intercooling between those stages (or adding water injection) would change the game.



> The auxiliary drive on most later Allison WAS a hydraulic coupling. It just wasn't mounted sideways.


Yes, which is why that configruation came to mind, particularly given Bell was the only one to actually use 2-stage Allisons during the war it seems like tailoring them to those machines would make sense. (I was imagining the supercharger intake positioned somewhere along the lines of the intercooler scoop of the XP-39 -though smaller ... maybe still a bulged faring if the side-mounted impeller housing extended too far beyond the engine perimeter)




> I submit the Allison V-1710-119 was a match for the Merlin in all categories, but was overtaken by the jet engine. Had development continued, for some reason, it would have given good service. But, jets were the new darlings of the military and essentially killed the big piston engines. Too bad, but at least a few still exist today.


It still would have been very significant for the P-82s that had so much service trouble with the more primitive 2-stage Allisons they adopted for mass production.

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## gjs238 (Mar 13, 2015)

2 speed V-1710 is another worthwhile point.
I believe that was a major advantage of the V-1650 powered P-40F and P-40L.


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## GregP (Mar 13, 2015)

You know, I have spoken with a few former pilots and crew chiefs and have been told the Allison was awful by a few; have been told the pilots weren't operating them properly by a few, and have been told the maintenance was pretty much ignored by still others ... since jets were the darlings they were trying to "kill off" the last remaining pistons.

I am at the point where I do not belive any of them. It appears there were issues, but it is VERY hard to get down to what caused them, the Allison, lack of training in operating procedures, bad maintenance, or whatever.

When I worked for Joe Yancey, he built a G-6 and it is still running fine. Of course, it is being run by someone who is a private owner and is operating it as Joe told him to, and he doesn't ask for WER EVER. much less "frequently."

Tough to know what they were experiencing 50 - 65 years ago.

I'll allow there were issues, but am really not sure what the actual issues were.

In the Merlin world, I have seen one owner have metal in the oil at 25 hours. When it was fixed, he now has 850 hours on it and is running strong. So ... the Allison is not the only engine with some rather anomalous issues that crop up every once in awhile. The Merlin in the museum's 'Spam Can" P-51D has 900 hours on it and purrs sweetly every time it starts. Last time it needed service, they just changed the rings! Go figure.


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## gjs238 (Mar 14, 2015)

GregP said:


> You know, I have spoken with a few former pilots and crew chiefs and have been told the Allison was awful by a few; have been told the pilots weren't operating them properly by a few, and have been told the maintenance was pretty much ignored by still others ... since jets were the darlings they were trying to "kill off" the last remaining pistons.
> 
> *I am at the point where I do not belive any of them.* It appears there were issues, but it is VERY hard to get down to what caused them, the Allison, lack of training in operating procedures, bad maintenance, or whatever.
> 
> ...



I think this relates to what drgondog was trying to explain earlier.


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## tomo pauk (Mar 14, 2015)

gjs238 said:


> 2 speed V-1710 is another worthwhile point.
> I believe that was a major advantage of the V-1650 powered P-40F and P-40L.



Nope. The major advantage of the V-1650-1 was that it featured a bigger supercharger, with a less restricted inlet elbow (the 'item' connecting carburetor and impeller). That was worth 3000-4000 ft of rated height, or a difference of ~200 HP vs. a V-1710 with 9.60:1 S/C gearing at 20000 ft.
More supercharger speeds means the engine is more flexible. It won't give altitude capability just because it is a 2-speed engine - compare Merlin 45 (1-speed S/C) vs. Merlin XX (2-speed S/C).

added: 2-speed V-1710 would make it interesting for bomber applications, though


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## tomo pauk (Mar 14, 2015)

GregP said:


> The aux stage was not exactly what I had in mind.
> 
> I was talking about a 2-stage, integral supercharger, similar to the Merlin. Had one been developed, I'm sure it could have been debugged and put into service. Of course, that's an assumption on my part and probably qualifies as a "what if," but they worked out the rest of the bugs, so I am extrapolating.
> 
> ...



There was a V-1710 with Merlin 2-stage supercharger inter-cooler. It took a while, and wrecked some S/C in the process, but the end result was a power vs. altitude same as 2-stage Merlin.

I don't get it why the V-1710 with aux S/C is such a boogaboo.


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## kool kitty89 (Mar 14, 2015)

gjs238 said:


> 2 speed V-1710 is another worthwhile point.
> I believe that was a major advantage of the V-1650 powered P-40F and P-40L.


Partially yes, but partially just the altitude rating combined with a more efficient supercharger design (and a sheer larger supercharger). Had Packard been producing single speed Merlin 45s rather than XXs, the disparity in altitude performance would have been similar but the merlin would have lost a bit more power down low (and a bit of weight).

The 9.6:1 supercharger V-1710s got a lot closer to Merlin 45 performance levels, but still a few thousand feet lower FTH. It's hard to say how much might have improved with larger impellers and/or diffusor casings allowed ... and the same things limiting those also limited the 2-speed gearing configuration I believe. The integral supercharger on the V-1710 didn't leave space to allow variable speed gearing or larger supercharger and initially even limited maximum single speed gear ratios. (the 8.8:1 speed was in part limited by the gearing they could manage to fit and how much strain it could take)

Actual performance and efficiency (in terms of pressure for given power consumption and charge heating at a given RPM) of the integral supercharger didn't seem to change much or at all from the V-1710s of 1940 and those of 1944. (changes in screens, filters, and ram inlet, duct and manifold design had more affect on things)

Changes on the single-stage merlins were far more dramatic (same for the single stage german engines) That includes performance for the smaller 9.5" impeller blower used on the low altitude merlin 50 series. (compared to the 8.8 blower Allison it still had a significantly higher FTH and similar power -depending particular WER ratings compared ... Allison always made more power at less boost, but also always at lower critical altitudes)


And again, I am curious as to whether examples listed (by USAAF documentation) to be single stage but variable speed (and often larger than 9.5" for the impeller) might have been engines with the integral stage deleted entirely and a single external hydraulically coupled supercharger stage was used exclusively.






GregP said:


> I am at the point where I do not belive any of them. It appears there were issues, but it is VERY hard to get down to what caused them, the Allison, lack of training in operating procedures, bad maintenance, or whatever.


Seems more likely an 'all of the above' situation, perhaps hard to nail down what issues were most critical or even if any one set of problems was consistently critical.

Also hard to tell what issues might have been specific to the P-82 itself given A. there were no merlin powered variants in service to directly compare records to, and B. there were no single engined Mustangs fielding similar V-1710 powerplants to compare either.


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## tomo pauk (Mar 14, 2015)

The V-1710-143/145 (right/left turning) lacked 2 things the Merlin had: backfire screens and inter-cooler(s). The backfire screens were ceased to be installed in the V-1710s once the 'Madam Queen' intake manifold was introduced in winter of 1943/44; lack of the backfire screens 'earned' 1000-1500 ft of rated height in the war-time engines. That really backfired back (pun intended) once the greater manifold pressures were 'demanded' from the 2-stage V-1710 - there was no inter-cooler to cool the charge, and, once the detonation happened in one cylinder it was able to quickly spread in the intake manifold, due the lack of the backfire screens. 
It seems that max manifold pressure was limited to 60 in Hg, at least it is so claimed by Edgar Schmued. 60 in Hg means measly power for a 27L engine post-war.


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## gjs238 (Mar 14, 2015)

kool kitty89 said:


> The 9.6:1 supercharger V-1710s got a lot closer to Merlin 45 performance levels, but still a few thousand feet lower FTH. It's hard to say how much might have improved with larger impellers and/or diffusor casings allowed ... *and the same things limiting those also limited the 2-speed gearing configuration I believe. The integral supercharger on the V-1710 didn't leave space to allow variable speed gearing or larger supercharger and initially even limited maximum single speed gear ratios. (the 8.8:1 speed was in part limited by the gearing they could manage to fit and how much strain it could take)*



Excellent (or rather, Aha!) this is what I was looking for.
I suspected that there were inherent design limitations in the V-1710 that impeded growth.


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## gjs238 (Mar 14, 2015)

kool kitty89 said:


> The aspect of the RR 2-stage approach that the V-1710 couldn't follow was a single shaft 2-stage design. Any added supercharger stages would be more or less used like a turbocharger, independently driven from the single-speed integral supercharger. *This is fairly similar to the approach Pratt and Whitney took for their 2-stage designs,* Allison just didn't have the funding or resources (internal or external) of P&W to carry out that development early on, and even most later developments were more primitive than what the superchargers on the R-2800 had developed into. (lack of intercooling was a big issue ... adapting a liquid intercooler arangement akin to the P-38J/L's -or Merlin's- would have made a world of difference)
> 
> 
> That aside, the other limiting factor was supercharger design. Allison's own designs may have been reasonable enough, but paled in comparison to Rolls Royce's. Size/space constraints for the integral mounting point may have been a limiting factor too, but the roughly equivalent 9.5" diameter impeller used on the 'cropped' Merlin 50 series still performed significantly better than the Allison's at similar speed (the higher displacement of the engine made up for some of the difference -higher power at lower boost). With Merlin quality supercharger design, the single-stage Allison might have reasonably matched the Merlin 45 or 47 or even exceeded them a bit.



Didn't P&W call them the "sidewinder"?


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## Piper106 (Mar 14, 2015)

Couple of items to stir the pot.
1. In the fall of 1942 Allison proposed the F-24R engine which would have used "a newly designed integral two-stage supercharger". Dan Whitney "Vees for Victory" page 272. Asked if there were any further details over at AEHS, and unfortunity nothing more seems to have survived. I assume that this would have been something like the merlin 60 engines, but cannot prove it. 
2. I seem to recall the problem with the historic Allison two stage engines was that the auxillary supercharger made the engine too long to fit into the Mustang B/C/D/K series airframe without serious center of gravity issue. In the P-51 F/G/H/J series the firewall was relocated further back, and the Allison two stage engine could be installed (as it was on the P-51J).
3. Backfire screens are a 'Band-Aid' fix on the real problem, that the mixture to that cylinder is too lean, and the combustion is way late (lean mixtures burn more slowly then a proper air/gas mixture) with the mixture stll burning when the intake valve reopens. I seem to recall reading that the problem with the V-1710-143/145 engine was that the speed density injection system ran the engine too lean causing backfires. Whether than was lack of development of the speed density injector (or as I believe) poor maintenance/incorrect replacement parts, has never been conclusively proved, nor may it ever be conclusively proved.


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## Piper106 (Mar 14, 2015)

Everyone gets on Allison's case for not having a intercooler on their two stage mechanical supercharged engines. 

Well... on the Merlin 620 series commercial engines (with an intercooler) on North Atlantic flights, the mixture got so cold during cruise that the engines had trouble. (I assume fuel components condensing out, leading to problems very similar to those seen with the P-38 during WW2). Rolls Royce had to modify the engines to heat the intake charge for cruising conditions. While we like to talk about engines running hard pulling war emergency power, I think in reality even fighters spend most of there time at low cruise power. It could be argued that water injection for the few minutes when WEP is needed might be equal to hauling around an intercooler all the time for the few minutes it is needed.

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## Shortround6 (Mar 14, 2015)

> Didn't P&W call them the "sidewinder"?


Yes and no.

ALL P W 2 stage engines (at least production ones) used a single speed supercharger on the engine and a two speed drive *plus* neutral for the auxiliary supercharger. Take-off and low altitude was done with the Auxiliary supercharger in neutral, then as power fell off the supercharger was engaged in low gear and finally high gear was selected. 

The "sidewinder" engine was ONLY used in the F4U-5 and used *three* impellers. TWO mounted sideways (Like a DB engine) with one on each side _but_ operating in parallel. Both always ran at the same speed as each other and had the same neutral/low/high speed set up as the other P W engines. They feed the engine supercharger which was one speed.

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## kool kitty89 (Mar 14, 2015)

gjs238 said:


> Excellent (or rather, Aha!) this is what I was looking for.
> I suspected that there were inherent design limitations in the V-1710 that impeded growth.


Some of the details I summarized there, I hadn't actually seened confirmed until earlier in this very thread ... that said, actually looking at the physical supercharger installations on the merlin and V-1710 ... even comparing the single-stage single speed ones, I'm not sure the Allison engineers could have done much better even with the likes of Hooker's expertise. (the integral supercharger mounting is really cramped and doesn't make for much flexibility in terms of optimized diffusor arrangements, let alone increased impeller size)

The 8.8 and (especially) 9.6 supercharged engines were already limited pretty much to non-turbo installations (turbos were mated with lower blower ratio engines), so universal installation in that regard isn't much of a bonus (unless you're manufacturing nearly identical airframes with and without turbochargers) so the main issue would be standardized volume production ... IF keeping the supercharger/accessories section of the engine even streamlined manufacturing that much. (early V-1710s made some other significant changes like the reduction gearing on the long-nosed C vs short nosed F series)

And given all the trouble that seemed to go into auxiliary supercharger development, I'm not sure simply focusing on producting models that deleted the integal supercharger+carb intake placement entirely in favor of an arrangement that allowed a wider variety of superchargers would have been more practical. (from an engineering time + manufacturing time standpoint)

Pratt Whitney expanded development of BOTH their single-stage (single and 2-speed) superchargers as well as developing auxiliary systems and facilitating turbocharger arrangements ... Wright seems to have focused more specifically on single stage (fixed and 2-speed -maybe some 3-speed) with provisions for turbo installations (though the R-2600 seemed to have trouble).
It's hard to say what would have been the most effective for a smaller firm like Allison ... but most other manufactuers focused on single stage superchargers exclusively until they hit a wall and needed 2-stage (where single stages would have been unreasonably large). That was the situation in England, Germany, and Japan, including implementations of 3-speed single stage superchargers in some cases. (and sometimes single stages + aftercoolers)




Piper106 said:


> 2. I seem to recall the problem with the historic Allison two stage engines was that the auxillary supercharger made the engine too long to fit into the Mustang B/C/D/K series airframe without serious center of gravity issue. In the P-51 F/G/H/J series the firewall was relocated further back, and the Allison two stage engine could be installed (as it was on the P-51J).


Same for the P-39 forcing the more extensive redesign of the XP-39E (and P-63). Which again makes me wonder why a side-mounted arrangement wasn't attempted in able to keep the engine length closer, if even at the expense of some drag. (depending on the exact mounting position of the supercharger)



> 3. Backfire screens are a 'Band-Aid' fix on the real problem, that the mixture to that cylinder is too lean, and the combustion is way late (lean mixtures burn more slowly then a proper air/gas mixture) with the mixture stll burning when the intake valve reopens. I seem to recall reading that the problem with the V-1710-143/145 engine was that the speed density injection system ran the engine too lean causing backfires. Whether than was lack of development of the speed density injector (or as I believe) poor maintenance/incorrect replacement parts, has never been conclusively proved, nor may it ever be conclusively proved.


Backfires related to detonation would be pre-ignition and burning too quickly ... so a bit different /if/ detonation issues were even related to the backfiring ones. (it's possible detonation issues were a separate problem and backfire problems were limited to lean cruise conditions)

Granted, had Allison switched to a direct-injection arrangement for post-war developments that would have changed a number of issues too, backfiring and detonation included, but that's another topic. (just comes to mind with the R-3350 switching to that)




Piper106 said:


> Well... on the Merlin 620 series commercial engines (with an intercooler) on North Atlantic flights, the mixture got so cold during cruise that the engines had trouble. (I assume fuel components condensing out, leading to problems very similar to those seen with the P-38 during WW2). Rolls Royce had to modify the engines to heat the intake charge for cruising conditions. While we like to talk about engines running hard pulling war emergency power, I think in reality even fighters spend most of there time at low cruise power. It could be argued that water injection for the few minutes when WEP is needed might be equal to hauling around an intercooler all the time for the few minutes it is needed.


That also sounds like a problem with ability to regulate airflow to the intercooler ... the same problem can happen with oil and collant radiators (overcooling situations). Radiator duct/flap designs are a big part of this. (along with simply using larger radiator area than needed or operating in colder environments than intended)

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## GregP (Mar 14, 2015)

Hi gjs 238,

Yeah, I get the feeling that if Bill and I could sit and talk, we'd agree on a lot of things. Tough to have realistic conversations on a forum when it gets into argument so easily. It's less easy to misunderstand each other face to face.

I don't think there was anything especially wrong with the Allison and aux stage, but it was too long and heavy for what it was. Still, it could have been made to play well in an airframe had the time been spent to DO it. The P-63 wasn't bad at all ... we just didn't buy many, probably because of the superficial resemblance to the P-39. The Soviets liked them well enough.

Hi koolkitty,

Not sure if the situation was all of them or a combination of one or two. The Allison G-series I have seen run great and are reliable. That sort if flies in the face of what gets said in many places, but it is a fact from the ones I've seen in service today. I'd really like to know.

Heck, I hadn't heard the term "kinner time bomb" in 20 years until Harrison Ford went down, and now it's in the news again. Fickle people. They don't remember the years of good service, they remember the first failure. It's like the restaurant business ... only as good as the last meal.

Couple of weeks ago I said I'd get pics of the V-1650-7 and Merlin 224 we have at the museum. I got them and will try to post tomorrow when I have time to mess with it. Unrelated to THIS thread, but you can at least see the case differences between a single-stage and a 2-stage Merlin. I'll title the post "Single and Two-Stage Merlin pics."


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## wuzak (Mar 15, 2015)

Interestingly the V-3420 used a 10.0" diameter supercharger impeller for single stage models. Only 1/2" larger than the V-1710, despite being twice the capacity.


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## GregP (Mar 15, 2015)

Hi Wayne,

Though Joe has two V-3420's, he hasn't gotten around to getting one running yet. Something about selling Allison and making money versus spending money to get a show engine running keeps getting in the way.

I have not invested the time yet to look at the altitude performance of the V-3420 but, if it didn't have a turbo ... I don't see how it could be a high-altitude engine. The standard V-1710 wasn't without a turbo.


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## kool kitty89 (Mar 15, 2015)

GregP said:


> I don't think there was anything especially wrong with the Allison and aux stage, but it was too long and heavy for what it was. Still, it could have been made to play well in an airframe had the time been spent to DO it. The P-63 wasn't bad at all ... we just didn't buy many, probably because of the superficial resemblance to the P-39. The Soviets liked them well enough.


Unfortunate delays to development, initial targets for more of an interceptor and medium-range fighter (and thus not exploiting added wing space for fuel) and said delays putting it too far back to make it worthwhile delying things further for a redesigned wing. (more or less making an american counterpart to the Spitfire/109 ... or maybe Tempest/190 -kind of somewhere in between all those in terms of speed, power, range, armament, and sheer weight/size)

Rather than trying to correct the P-39's major flaws of altitude performance and range. (along with easier maintinence -which the P-63 did aim address)

That and canceling the less ambitious XP-39E outright. (which didn't suffer quite the same delays in testing as the XP-63, so might have made it into service early enough to actually be attractive to the USAAF)

Sticking so heavily with the 37 mm cannon was odd too, using a 20 mm on more than just the P-400 and a limited number of early P-39s and then no more limited its usefulness.




GregP said:


> I have not invested the time yet to look at the altitude performance of the V-3420 but, if it didn't have a turbo ... I don't see how it could be a high-altitude engine. The standard V-1710 wasn't without a turbo.


The integral stage on the V-3420 seems a fairly similar installation to the 1710's, though the 2-stage mounting on the 3420 seems a fair bit more compact given the size/capacity. At a glance, the bell housing for the integral stage appears proportionally larger for just a 1/2" gain in impeller size, so possibly more space used for the diffusor.

http://www.michaelp.org/photos/fantasy_of_flight/allison_v-3420_engine_2.jpg

http://svsm.org/albums/Allison-V-3420/P1340676.jpg

http://svsm.org/albums/Allison-V-3420/P1340677.jpg

http://gallery.oldholden.com/d/95762-1/Allison+V-3420+_amp_+drive.JPG




Huh, and the supercharger placement (and housing) in the F series V-1710 chaged more than I'd assumed compared to the older C15 series. Plane Talking - HyperScale's Aircraft Scale Model Discussion Forum: Allison V-1710 photos?

Whatever the changes, it didn't seem to make the supercharger on the -39 (F3R) any better performing than the -33 (C15). Take-off and Mil power were higher, but at similar boost (or overboosting) they had virtually identical power and identical critical altitudes.

A shame they didn't take advantage of that redesign to work in provisions for more variable configuration of the integral supercharger stage. (including aerodynamics of the carb intake and supercharger ducting)


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## Shortround6 (Mar 15, 2015)

XP-39E was longer because it was designed to to fit that war winning wonder engine, the army designed and Continental built, the V/O/IV-1430. 

They used the two stage Allison when the Army/Continental failed to be ready on time.


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## kool kitty89 (Mar 15, 2015)

Shortround6 said:


> XP-39E was longer because it was designed to to fit that war winning wonder engine, the army designed and Continental built, the V/O/IV-1430.
> 
> They used the two stage Allison when the Army/Continental failed to be ready on time.


Which also happened to need a longer engine compartment and couldn't be fitted to existing P-39 airframes. (otherwise the XP-39E itself might have stayed engineless and a more straightforward conversion of the P-39 to a 2-stage V-1710 may have taken place)


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## Koopernic (Mar 15, 2015)

wuzak said:


> I think there was no technical reason why Allison could not have built a two stage supercharger like the Rolls-Royce designs.
> 
> Why they didn't is probably more to do with the philosophy of Allison, particularly with regards to modularity and the ease of manufacture.
> 
> To do a 2 stage design like Rolls-Royce would require a complete new supercharger design. In the case of Allison's two stage design, the engine stage supercharger remained the same, while the Auxiliary stage supercharger was, essentially, a bolt on module. The core of the two stage engines with the carbuerretor attached to the engine stage supercharger, instead of the auxiliary stage, were identical, or near enough to, the equivalent turbocharged version.



From memory the Two stage Merlins impellers came from the vulture and peregrine both of which achieved production but were abandoned.


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## wuzak (Mar 15, 2015)

Koopernic said:


> From memory the Two stage Merlins impellers came from the vulture and peregrine both of which achieved production but were abandoned.



No, that is incorrect.

The first stage for early two stage Merlins was 11.5" compared to the 12.0" of the Vulture (per RRHT). Later versions were 12.0". The second stage was 10.1", compared to 10.25" for single stage Merlins.


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## Shortround6 (Mar 15, 2015)

I believe the story may have it's roots in the fact that they used a Vulture impeller in the first test rig. It was handy, it was *about* the right size (desired airflow) and gave them something to go on. I haven't read anything about using a Peregrine impeller though. I would guess it was too small. You have to deal with both pressure and volume.


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## GregP (Mar 15, 2015)

Everyone we spoke with at Joe Yancey's said they were running them at 75 inches in late production models. By "everyone" I mean former pilots, since usually only owners, former pilots, and former crew chiefs came by the shop when we were breaking in newly-overhauled Allisons. Joe usually had anywhere from zero to 4 visitor during engine runs, and we usually ran them for anywhere from 2 - 6 hours on the test stand before the rings seated sifficiently for Joe to be happy with it going flying. 

The backfire screens are effective only at startup if you aren't well trained on how to start the engine. Once it is running, the backfire screens are useless and cost intake manifold flow. Unless you are a ham-handed idiot, nobody backfires an engine after it is running, assuming the carburetor isn't WAY out of tune. If it is that far out, you have no business trying to run it. Carbs typically last 5 years before needding overhaul, but they NEED it after 5 years.

If anyone wants a pic, I have an Allison backfire sceen in pristine condition. It isn't needed once you can start the engine and really isn't needed once it is running, but it makes for a nice piece of engine bit in your display case.


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## BiffF15 (Mar 15, 2015)

GregP,

Just post it!

Cheers,
Biff

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## wuzak (Mar 15, 2015)

Shortround6 said:


> I believe the story may have it's roots in the fact that they used a Vulture impeller in the first test rig. It was handy, it was *about* the right size (desired airflow) and gave them something to go on. I haven't read anything about using a Peregrine impeller though. I would guess it was too small. You have to deal with both pressure and volume.



The second stage in the original test rig may have been the standard Merlin impeller.


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## GregP (Mar 15, 2015)

Hi Biff,

OK. Here are some allison parts. If you look at the rods, the one with the cut in the middle is a fork rod. The rod in the middle is a blade rod.:







Here is a closeup of the Allison Backfire Screen. It goes into the intake manifold where it bolts onto the cylinder head, but is not needed at all once you can start an Allison. If you get to WER power, you will be in auto-rich anyway ... or you will be walking home.:







Here are some early and late model wrist pins. The one with the thin end is early and experienced some cracks in service, so they eliminated the champfer and just went with cylindrical wrist pins:






Here are some valves. Naturally the larger valve is intake and the smaller valve is exhaust. The valve stems are Sodium filled and the material is Stellite:






And, finally, here are a couple of heavily modified pistons. These come out of one of Guy Lombardo's Championship-winning hydroplanes. He had the bottom rim cut off and modified the remaining bottom slot to be the new bottom ring. Unsurprisingly, these "slapped" at idle and had lower lifespans. The holes in the sides were for lightening and they don't really work. Stock pistons really work better than these!:






All for now.

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## BiffF15 (Mar 15, 2015)

Greg,
Thanks for posting! What is the reason for the fork and blade rod set up? Does the Allisin have cylinders that are directly across from each other?
Cheers,
Biff


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## gjs238 (Mar 15, 2015)

BiffF15 said:


> Greg,
> Thanks for posting! What is the reason for the fork and blade rod set up? Does the Allisin have cylinders that are directly across from each other?
> Cheers,
> Biff



From Wikipedia:
https://en.wikipedia.org/wiki/Connecting_rod

_*Compound rods*

Many-cylinder multi-bank engines such as a V12 layout have little space available for many connecting rod journals on a limited length of crankshaft. This is a difficult compromise to solve and its consequence has often led to engines being regarded as failures (Sunbeam Arab, Rolls-Royce Vulture).
The simplest solution, almost universal in road car engines, is to use simple rods where cylinders from both banks share a journal. This requires the rod bearings to be narrower, increasing bearing load and the risk of failure in a high-performance engine. This also means the opposing cylinders are not exactly in line with each other.
In certain engine types, master/slave rods are used rather than the simple type shown in the picture above. The master rod carries one or more ring pins to which are bolted the much smaller big ends of slave rods on other cylinders. Certain designs of V engines use a master/slave rod for each pair of opposite cylinders. A drawback of this is that the stroke of the subsidiary rod is slightly shorter than the master, which increases vibration in a vee engine, catastrophically so for the Sunbeam Arab.

Radial engines typically have a master rod for one cylinder and multiple slave rods for all the other cylinders in the same bank.

The usual solution for high-performance aero-engines is a "forked" connecting rod. One rod is split in two at the big end and the other is thinned to fit into this fork. The journal is still shared between cylinders. The Rolls-Royce Merlin used this "fork-and-blade" style. A common arrangement for forked rods is for the fork rod to have a single wide bearing sleeve that spans the whole width of the rod, including the central gap. The blade rod then runs, not directly on the crankpin, but on the outside of this sleeve. The two rods do not rotate relative to each other, merely oscillate back and forth, so this bearing is relatively lightly loaded and runs as a much lower surface speed. However the bearing movement also becomes reciprocating rather than continuously rotating, which is a more difficult problem for lubrication.
A likely candidate for an extreme example of compound articulated rod design could be the complex German 24-cylinder Junkers Jumo 222 aviation engine, meant to have — unlike an X-engine layout with 24 cylinders, possessing six cylinders per bank — only four cylinders per bank, and six banks of cylinders, all liquid-cooled with five "slave" rods pinned to one master rod, for each "layer" of cylinders in its design. After building nearly 300 test examples in several different displacements, the Junkers firm's complex Jumo 222 engine turned out to be a production failure for the more advanced combat aircraft of the Third Reich's Luftwaffe which required aviation powerplants of over 1,500 kW (2,000 PS) output apiece._

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## wuzak (Mar 15, 2015)

BiffF15 said:


> Greg,
> Thanks for posting! What is the reason for the fork and blade rod set up? Does the Allisin have cylinders that are directly across from each other?
> Cheers,
> Biff



Fork and blade was common for WW2 era "in-lines". All th emajor engines had them - DB 6, Merlin, Allison, Jumo 211, 213, Sabre.

The reason is to save some length, as the banks do not need to be staggered.

There may also have been some bending moment considerations for the crank pin.

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## GregP (Mar 15, 2015)

They work very well and are easy to balance. Joe typically gets his pistons within .5 - 1.0 grams of each other. He does the same for rods and wrist pins, but the wrist pins are MUCH closer in weight ... on the order of .05 grams. You don't balance valves ... you make them have perfect edges and ensure perfect seats, and that is their contribution to power ... perfect sealing.

Joe has helped develop some racing cams for the Allison .. .for the tractor crowd, but uses stock cams for aero engines, as required by the Allison overhaul books. He is the only person I know of who actually has and uses an Allison factory crankshaft bearing sizing gauge. When you torque the mains to spec, you MUST be able to tunr the gauge by hand. If you can't, it's too tight. He checks initial sizing with plastigage and rarely has to hone bearings after inital preparation. You might expect that after years of overhauliing nothing but ALlisons.


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## kool kitty89 (Mar 16, 2015)

Shortround6 said:


> I believe the story may have it's roots in the fact that they used a Vulture impeller in the first test rig. It was handy, it was *about* the right size (desired airflow) and gave them something to go on. I haven't read anything about using a Peregrine impeller though. I would guess it was too small. You have to deal with both pressure and volume.


Given both the vulture and peregrine used pre-Hooker supercharger designs, using one (or both) would have made sense for convenience of preliminary testing, but I'd think all the production merlins from the XX onward used Hooker based designs. (be it the impeller, diffusor, manifold, or other ducting)


I also hadn't realized the Napier Sabre used a double-sided supercharger impeller akin to Whittle's turbojet designs. That's an interesting way to go about things.

http://4.bp.blogspot.com/-T4uySZSSv0g/TqG3YrIFitI/AAAAAAAAAj4/IqOZAPTxsO0/s1600/napier_sabre.jpg




GregP said:


> Everyone we spoke with at Joe Yancey's said they were running them at 75 inches in late production models. By "everyone" I mean former pilots, since usually only owners, former pilots, and former crew chiefs came by the shop when we were breaking in newly-overhauled Allisons. Joe usually had anywhere from zero to 4 visitor during engine runs, and we usually ran them for anywhere from 2 - 6 hours on the test stand before the rings seated sifficiently for Joe to be happy with it going flying.


Late model P-38s seemed to handle 75" (2000 HP WEP) fairly well, were those comments regarding P-82 experience, P-38, or both?


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## wuzak (Mar 16, 2015)

kool kitty89 said:


> I also hadn't realized the Napier Sabre used a double-sided supercharger impeller akin to Whittle's turbojet designs. That's an interesting way to go about things.



Yes, until it was replaced by a single sided impeller in the Sabre V.

The Rolls-Royce R also had a double sided impeller.







Cutaway from Lyndon Jones.


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## Shortround6 (Mar 16, 2015)

The Merlin XX and 45 used the same impeller and diffuser as earlier Merlins, they just changed the intake elbow and front cover. Just is actually not a good word as the intake elbow and front cover and carb mount were all a one piece casting which made it rather hard to do experiments. If you wanted to change anything you needed a new and complicated casting.


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## tomo pauk (Mar 16, 2015)

wuzak said:


> Interestingly the V-3420 used a 10.0" diameter supercharger impeller for single stage models. Only 1/2" larger than the V-1710, despite being twice the capacity.



The big US engines used fairly small superchargers/impellers. The R-2600 and R-2800 were mostly at 11 in diameter, the C series of the R-2800 went to 11,5 in. Engine stage S/C of the R-2800-21 (used on many of P-47s) was only 10.5 in. Contrary to that, Hercules and BMW 801 used a 13 in impeller, though some Hercules versions used the 12 in impeller (result was a bit better low alt performance). The R-3350 started at 12 in, later versions were at 13 in.

Aux stage was at 12.18 in for the V-3420, and 13 in for the R-2800.


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## Shortround6 (Mar 16, 2015)

Impeller diameter helps tell you the tip speed and may have something to do with pressure. Impeller _thickness_ is not mentioned and that may have something to do with the total mass airflow. Large diameter shallow impeller vs smaller diameter but thicker impeller? 
An R-2800 is going to need around 45-48% more pounds of air per minute than an Allison at the same pressure?


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## gjs238 (Mar 16, 2015)

And what about impeller speed?


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## GregP (Mar 16, 2015)

Most of the comments we heard were regarding the P-38J and L. Joe only spoke to about 2 - 3 people who had anythning to do with the P-82 while I was there, and none of them mentioned MAP specifically. They also didn't say anything bad about the engines except to say they had not experienced any of the issues they had heard about from other guys. That's not a very big cross section, so I usually don't make much of it one way or the other. 

When Joe built up a G-6, he ran it at 65" on the test stand and it ran just fine. We had to stop there because it was pulling the test stand (A Ford F-350) across the pavement backwards and was threatening to pull the front tires off the ground. Joe mounts the Allion so the prop hangs off the back of the bed and he uses a 55-gallon drum of coolant for the radiator. Usually we limit test runs to about 30 - 40 minutes or so each out of nothing else but getting tired of standing 10 feet from a howling Allison in the propwash.


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## tomo pauk (Mar 16, 2015)

gjs238 said:


> And what about impeller speed?



I reckon it you mean 'tip speed'? Most of designers seem to want to stay at tip speed that is equal or just a bit lower than speed of sound. Going faster than speed of sound 'kills' impeller efficiency (impeller sucks too much of engine power for the pressure ratio achieved), going too slow means that S/C is not used as much as possible. Higher impeller speeds will consume more power than lower impeller speeds, hence the 2-speed or infinite-number-of-speeds supercharger gearing.
The V-1650-1 have had impeller tip speed of 1273 fps* (maximum) in high gear (9.49:1 S/C gearing), the V-1710 with 8.80:1 gearing was at 1094 fps, the V-1710 with 9.60:1 was at 1194 fps. The later V-1710 have usually had 2500 ft greater rated height, the rated powers being usually 1125 HP @ 14500 ft for the 9.60:1 S/C versions, and 1150 HP @ 12000 ft for the 8.80:1 S/C versions.
The cost was that 'higher' V-1710s have had less power down low than 'lower' types.

Merlin II/III were at 1151 fps (10.25 in impeller - same as with Merlin XX/45/V-1650-1, geared 8.58:1, when crankshaft speed is 3000 rpm).

* yep, faster than speed of sound, 1,127 fps


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## Shortround6 (Mar 16, 2015)

Speed of sound _inside_ the supercharger may be different. Depends on the speed of sound in the higher pressure/higher temperature air. 

http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html

speed of sound in 100C/212F air is 1287.4fps.


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## kool kitty89 (Mar 17, 2015)

Shortround6 said:


> Speed of sound _inside_ the supercharger may be different. Depends on the speed of sound in the higher pressure/higher temperature air.
> 
> Speed of Sound
> 
> speed of sound in 100C/212F air is 1287.4fps.


Yep, though I'd thought it was mainly temperature and not pressure (or density) that affected speed of sound. (humidity is a factor too though, but that's actually changing the chemical composition of the air -more water in it)

This would also be one point to using aftercooling over intercooling (air stays hot until after the final stage), though also a point to using a larger diameter impeller for the first stage and/or runnin the final stage slower. (intercooler cooling air between stages means lower local speed of sound for the 2nd stage -or 3rd if there's one)


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## gjs238 (Apr 4, 2015)

The DB and Junkers superchargers appear to be "external" to the engine and driven from the engine accessory gearbox.
If so, that seems to offer greater modularity and ease of making changes (or indeed, mounting multiple superchargers) as opposed to the Allison, which appears to be, to a large extent, part of the engine structure itself.


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## kool kitty89 (Apr 4, 2015)

gjs238 said:


> The DB and Junkers superchargers appear to be "external" to the engine and driven from the engine accessory gearbox.
> If so, that seems to offer greater modularity and ease of making changes (or indeed, mounting multiple superchargers) as opposed to the Allison, which appears to be, to a large extent, part of the engine structure itself.


Allison's (and Pratt and Whitney's) auxiliary superchargers were configured more like those of Jumo and DB designs, also driven via hydraulic fluid coupling (akin to a torque converter on automatic transmissions) facilitating the modular arrangement.

This is the same reason I brought up the potential for side-mounting the Aux stage on the V-1710 and reducing the length. (potentially allowing it to fit in existing designs more easily)

Not only were the auxiliary stage superchargers late to the scene, but they added so much length to the engine that it made mounting impossible in the P-39 without heavy modification, while it added enough nose length to cause problems with center of gravity on the P-51 (possibly P-40 as well)


German engines also used direct fuel injection, not carburetors (or manifold fuel injection as in 'pressure carburetors' ) so it somewhat simplified supercharger arrangements as well. (the merlin and allison have carburetors injecting fuel into the supercharger intake or between the aux -or turbo- and integral stages)



Though it's also worth noting that, in spite of the supercharger arrangement, the german manufacturers were also rather late in introducing larger/more powerful superchargers (be it 2-stage like the Jumo 213 or large single stage as with the DB 605AS).

I'm not sure on the exact reasons for this on the German end of things, but for Allison it was more of a funding and overall engineering resource limits problem. They were a relatively small company compared to other major aero engine manufacturers and if the US government wasn't forthcoming with funding, they'd be very hard pressed to invest in independent developments. (the Army was uninterested in auxiliary supercharger development during the critical early period, leaving over a year in development lag time compared to the likes of Pratt and Whitney and Rolls Royce)

The Army did manage to push a ton of funding for a variety of other projects, including their Contenental Hyper engine pet project ... which the V-1710 itself eventually overtook in spite of less focused interest.

I wonder if Allison could have gained some funding from the Navy if they'd offered alternative water cooled variants early on (glycol safety issues being one of the major concerns of the USN -radiator vulnerability was a concern too, but overcoming the glycol issue might have been enough to at least make it worth investing in).


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## GregP (Apr 5, 2015)

It doesn't look more "modular" to me. It just looks mounted 90° to the crankshaft. The Allison takes a special 5-sided accessory case, but yoiu have to mount the carb / supercharger / accessories somewhere. All you'd have to do is make a matching accessory case, and people have done so. The guys on the European tratcor-pull circuit run twin turbocharged Allisons with fuel injection, so we KNOW it can be done.

In the case of the Jumo above, if you want to change the S/C, you need another one engineered to fit. Same with an auxilliary ALlison accessory case ... just a bit smaller.

I'd like to see that Jumo running!


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## kool kitty89 (Apr 5, 2015)

Oh, perhaps worth noting is that Jumo 211 is also mounted upside down.


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## Shortround6 (Apr 5, 2015)

The better to see the fuel injection pump &#128512;

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## tomo pauk (Apr 19, 2015)

The early example of V-1710 - the F11R, with a 2-speed S/C was the prototype featuring a 'mixed-flow' supercharger designed by TEC company, of Mr. Birmann. The S/C measured 10.25 in in diameter and was geared 8.80:1 in high speed, and made same power at 16000 ft as the other engines with same gearing at 12000 ft. It was also slightly better at altitude than V-1710s with 9.60:1 S/C gearing, but those went into production, not the F11R, that made more sense for bomber aircraft due to higher TO power.
Too bad the F11R's S/C was not geared 6.93:1 and 9.60:1, the power would've been at least on par with Merlin 20s, and much better more flexible than other 1-stage V-1710s. 

(open the pic separately for high resolution; disregard the supposed aircraft)


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## GregP (Apr 19, 2015)

I think it is too bad that Allison never developed an integral 2-stage, multi-speed supercharger. But, we can't change what happened and they didn't ever develop it. They did make the Auxulliary-stage unit but it was heavy in comparions to an integral unit and too long for other than specialized uses.

They are quite interesting to see in person though, and are not difficult to overhaul, being VERY similar to a nosecase overhaul.


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## kool kitty89 (Apr 19, 2015)

tomo pauk said:


> The early example of V-1710 - the F11R, with a 2-speed S/C was the prototype featuring a 'mixed-flow' supercharger designed by TEC company, of Mr. Birmann. The S/C measured 10.25 in in diameter and was geared 8.80:1 in high speed, and made same power at 16000 ft as the other engines with same gearing at 12000 ft. It was also slightly better at altitude than V-1710s with 9.60:1 S/C gearing, but those went into production, not the F11R, that made more sense for bomber aircraft due to higher TO power.
> Too bad the F11R's S/C was not geared 6.93:1 and 9.60:1, the power would've been at least on par with Merlin 20s, and much better more flexible than other 1-stage V-1710s.


With the tip speeds of the 9.6:1 9.5" impeller already pushing supersonic speeds (depending on temperature), the 10.25" impeller at 8.8:1 would be getting pretty close as well. 9.6:1 would be too high, but perhaps very slightly higher (say 8.9:1) would be possible without major losses in efficiency, but 8.8:1 really is already pretty close to the limits.

That said, assuming the figures are accurate, that engine would at least have been better than the single speed single stage models, and apparently without an increase in length (so closer to adapt to existing airframes, unlike the aux stage models). The low gear would certainly help with take-off performance and WEP at low level


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## tomo pauk (Apr 20, 2015)

The Merlin 20 series was turning a 10.25 in impeller at 9.49 times of crankshaft rotation speed. Max tip speed was 1273 fpm. The V-1710 with 10.25 in impeller and 9.60:1 ratio will mean tip speed by a bit over 1%, so were at under 1290 fpm. Not much of a problem, in light of what Merlin 20s accomplished at it's tip speeds?
With a rated height (in 2nd gear) being at 18500-19000 ft (for 1120 HP?), installing a water-injection system should be worth an effort?
In F, E and G series V-1710, the 8.8:1 gearing means that drive wheel has 56 teeth, and driven wheel has 15 teeth; the 9.60:1 means 56 vs. 14 teeth. In case yet another redesign of S/C drive-train is not undertaken, an 'in-between' gear ratio cannot be installed.

added: the Merlin 46 and 47 featured the impeller of 10.85 in diameter. Gearing was 9.06:1. That will mean tip speed of some 1287 fpm. Rated height was at 22000 ft, where the engine produced 1100 HP, boost +9 psig was there. Provisional chart.
Being a single speed engine tailored for high altitudes (being a 1-stage engine), the power was not that great at medium and, especially, at low heights.


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## tomo pauk (Apr 20, 2015)

The engine with a 2-speed S/C having a 10.25 in impeller and 9.60:1 gearing (in 2nd gear) was intended to power cargo aircraft. 3200 rpm was allowed for take off, compression ratio was 6.50:1. 
The serially produced G6 have had CR of 6:1, along with bigger engine-stage S/C impeller. 

(open separately for hi-res)


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