An Allison V-1710 with a two-speed supercharger in 1942 (1 Viewer)

[ggiumarra]

I wonder why the P-51A had such a relatively poor combat history. Not terrible, mind you, but the fact that they were routinely coming out on the losing end of engagements with Ki-43s over China, Burma and India indicates that there was some kind of problem there.

So I don't pretend to be so well informed by this that I would defend my position vociferously, but from what I understand the P-51A pilots in CBI were largely inexperienced and used poor tactics. One story I am familiar with (hopefully it's even true) is the commander of one squadron of P-51A's getting shot down in his first mission there and when the Japanese pilot was later shot down himself, captured and interrogated he expressed puzzlement over why his victim had not just dived away instead of getting into a turning battle which he wasn't going to win. The tactics a P-51 would have to use vs those Japanese fighters are essentially the same as for the P-40 - it has pretty much the same advantages, it's just those advantages are bigger. If you play to your opponent's strengths, however, the outcome is not going to be good, regardless of your own strengths in other areas.

 

[ggiumarra]

The Allison Mustang did not fit the RAF idea of air superiority fighter in 1941/42 but did offer an excellent low level reconnaissance platform that was survivable in contested airspace. Similarly the Allison Mustang did not fit with the USAAF turbo supercharged fighter and heavy bomber ideas.

Exactly, and that is exactly what I am calling into question. In both cases there was a disconnect between the sort of air war the RAF and AAF wanted to fight and the one that was really being fought in which high-altitude performance was not that important or even superfluous. I am not saying it is never important, just not as important as other attributes, the most important of which, especially in 1942 and at least through much of 1943, was range (as long as you were above a certain minimum in fighter performance otherwise). You needed range in the Pacific and you needed range in the Med. when most all of your fighter missions are happening at medium to low altitude. Those were the places where the real war was going on at that time, a war that didn't fit well with the concepts of the leadership of either the RAF or AAF. I said the single stage/two-speed Allison in 1942 was only a side interest of mine because my point is that the original Mustangs, unmodified in any way, if used properly in 1942 could have made a major difference.

But even later in the war you have situations like in Italy where the RAF commander there is fine with giving up his allocation new Mustang III's (P-51B's) to the AAF (this was maybe in July or August 1944 when the AAF was losing more Mustangs than planned so they appealed to the RAF for higher allocations of Merlin Mustangs) because all his missions are low altitude and he recognizes his new Mustang's performance characteristics are better served as a high-altitude bomber escort. In reality, that RAF commander would have been better off with Allison Mustangs to begin with since they had better at the altitudes his planes were operating at.

One thing you are missing in your timeline (much of which is about the Merlin Mustang so kind of irrelevant - though I am glad you included those tidbits anyways since there were several things in there I didn't know so am glad to expand my knowledge regarding that) is that the British were trying to convince the Americans in 1942 to build more Mustangs in plac of Kittyhawks, but backed down when they got push back (their main goal at the time was to get more Packard Merlins for their own use).

According to one book I have NAA was setting up to produce Allison and Merlin Mustangs at the same time before the first of the latter came off the assembly line. I suspect (but do not have conclusive evidence) the reduction in the P-51A order was less about making room for the Merlin Mustang as it was yet another hurdle the AAF threw up to prevent it from taking business away from its favorite contractor Curtiss (with the idea that they'd find a way to throw sand in the gears once again with the Merlin P-51). If that sounds a little much I would just point out that perhaps the most important finding of the famous Truman Commission dealt with what looked like favoritism towards Curtiss at the expense of NAA, specifically with respect to the P-40 and the P-51 (one interesting factoid I found in that report - and here I'm guilty of perhaps getting off topic - was that in the middle years of WWII at least - Curtiss-Wright was the second biggest US contractor in dollar terms after GM). It didn't actually charge corruption (after all Truman was of the same political party as the current administration), but it sure reads that way between the lines.

 

[Shortround6]

A lot of authors (and congressmen) ae very quick to point fingers/blame when they have no concept of the lead times needed to bring engines, planes, tanks, ships to large production levels.
Not saying there weren't mistakes made or some corruption going on.

Packard was given a contract for 9000 Merlin XX engines (or close equivalent) in Sept 1940. Terms called for a delivery rate of 800 engines a month. 1/3 of the engines were to go to the US and other 2/3rds to the British (or to Canada, Britian could allocate their share to where every they wanted)
It took about 1 full year to get the first 4 production engines built (Sept 1941). Packard built 26 engines in Dec 1941 but increased rapidly after that. It still took until July 1942 to hit the 800 engine a month goal.
Now where the "extra" single stage/ two speed Merlins supposed to come from in 1942?
And where were they supposed to go?
The US only "owned" two Allison powered Muatang Is and then they owned the A-36s. They had stolen the P-51/Mustang IA's (with 20mm cannon) from the British. This was why the British got 50 Mustang IIs in repayment for the 57 P-51s.
Yes Merlin XX powered P-51 aircraft would have been a very nice aircraft. But if you put the US allocation for Merlins into a P-51 airframe and then stick Allisons into the P40F&Ls how much better is your air force as a whole? Hundreds more P-40Ks instead of Fs?
North American was doing well but they only built around 100 A-36s/P-51s a month until April/May of 1943.
Curtiss was building almost 4 times as many P-40s per month in 1942.
Was Curtiss "profiteering"? Maybe, but they were building almost as may P-40s as Lockheed, Bell, and Republic together built fighters in 1942. Things changed later.
It was not easy to turn a 'factory' off. Hundreds if not over a thousand subcontractors. Transportation allocations (rail cars or trucks trips per week or month), raw materials ordered months if not a year in advance. Changing a factory over could be done, it might also mean hundreds of planes or engines not made while the changeover was being done.

An example is the P&W Kansas City plant. A batch of grinders were 'borrowed' to send to England to help Napier with their sleeve valve problems, Rushed over on the Queen Mary.
Some accounts claim this delayed P&W about 6 weeks getting the KC plant into production. The Real problem was that it took about 6 months to go from 9 engines a month to 300 engines a month. You add up the monthly production, and they might have been around 300 engines further ahead at the end of 6 months if they had gotten the Grinders when they were supposed to have gotten them.

The US had a large problem with lead time. Brand new aircraft sitting on the factory runways were weeks if not 2-3 months from getting into action in NA or the South Pacific.

 

[tomo pauk]

Yes Merlin XX powered P-51 aircraft would have been a very nice aircraft. But if you put the US allocation for Merlins into a P-51 airframe and then stick Allisons into the P40F&Ls how much better is your air force as a whole? Hundreds more P-40Ks instead of Fs?

As always, this gets my vote: V-1650-1 in the Mustang, and do with the extra V-1710s what ever you want, including making more of the P-40Ks

 

[Steamed_Banana]

So I don't pretend to be so well informed by this that I would defend my position vociferously, but from what I understand the P-51A pilots in CBI were largely inexperienced and used poor tactics. One story I am familiar with (hopefully it's even true) is the commander of one squadron of P-51A's getting shot down in his first mission there and when the Japanese pilot was later shot down himself, captured and interrogated he expressed puzzlement over why his victim had not just dived away instead of getting into a turning battle which he wasn't going to win. The tactics a P-51 would have to use vs those Japanese fighters are essentially the same as for the P-40 - it has pretty much the same advantages, it's just those advantages are bigger. If you play to your opponent's strengths, however, the outcome is not going to be good, regardless of your own strengths in other areas.

Apparently not in the rather key area of rolling. P-40s had one of the best roll rates above 200 mph of any Allied fighters, in fact one of the best of any fighters of the war. This is very well documented.

The early Mustangs apparently had a problem with a poor roll rate. This is also documented though it took me a while to find hard numbers on it. The later Mustangs, starting with the Mustang III, had superlative high-speed roll rate.

Roll rate, it turns out, is pretty important when it comes to evading attack.

I suspect this issue with the early Mustangs may have had something to do with the issue. There were combats where some of the P-51A units appeared to use poor tactics, in fact I think I recall the one you are referring to where the commander was killed, but some P-51A were being used by very experienced units like 23rd Fighter Group which definitely knew the ideal tactics to contend with Japanese aircraft.

 

[ColFord]

ggiumarra

Get yourself a copy of Matt Willis book, Mustang - the Untold Story, from Key Publishing UK, another good primer on the early Allison Mustangs and their use.

You'll have to wait for Bill Marshall's second book that follows on from P-51B Bastard Stepchild that Saved the 8th Air Force for more of the story.

Yes, the RAF wanted more Allison engine Mustangs, right up until the end of the war, but given production had moved over to the Merlin engine versions, that was not going to happen. The focus then moved to what they could do to keep the Allison engine Mustangs they had in service and operational as long as possible, until such time as a 'reasonable' 'interim' replacement came along for the requirement. They had enough issues getting spare parts and spare Allison V-1710 engines from the US, it was the trade off between only getting 50 P-51A/Mustang II to replace the the 58 P-51 Mustang/Mustang IA they didn't get and being able to put pressure on insisting on spares to keep the Mustang I and IA in service longer than originally envisaged. Options to utilise Merlin engine Mustangs - most likely Mustang IIIs with Merlins modified for better performance at lower altitudes as a potential successor to the Allison engine Mustangs, didn't proceed, largely due to the higher priority for the Merlin Mustangs for the 'pure' fighter role and also certain aspects of the Merlin's operation and performance at lower altitudes weren't favourable.

Why NAA didn't keep both an Allison engine Mustang and the Merln engine Mustang in production, alongside each other is relatively simple - production tooling. The first of the Merlin engine P-51B used a significantly high percentage of components that were exactly the same as in the earlier Allison engine versions, particularly in the wing structures, fuselage, tail section, then all the ancillaries in things like the hydraulic system, electical system, undercarriage, cockpit, etc. A review of the NAA parts catalogue for the P-51B/C shows a very high percentage of assemblies and components carrying the NA-73, NA-83, NA-91, NA-97 and NA-99 prefixes of the earlier Allison engine Mustangs. To keep both in production would have required setting up a whole new production line and and a complete new set of tooling, plus put extra pressures on the sub-assemby and component manufacturers to meet the significantly increased demand to keep both lines open and growing. Moving the focus solely to the newer Merlin engine Mustang simplified things, even with the new line being built at Dallas. The NA-99 P-51A contract had a 'switch' clause built in, that allowed production of the P-51A to be terminated short of the total contract number, with the balance of the order to be switched to the impending Merlin engine Mustang then being developed.

RAF had the same issue in considering the floated request for Mustang airframes to be built and provided without engines, being given Merlins in the UK. They were to be built up to the forward firewall, no cowlings, no engine bearers, no props. That then begged the question where do the Merlins and props for these come from? What other type misses out on the Merlins? (Spitfires? Mosquitoes? Lancasters? Maybe Hurricanes but they are still needed elsewhere...?) Who designs and makes the required cowlings? Where do the technical resources come from in the UK to do all the required works? Then you end up with a 'non-standard' type, with all that entails in terms of support and operation. It may have been a useful 'interim' type, but then you are left with a relatively small number that potentially chew up a higher amount of support resources than a 'pure' factory built and supported version.

There were changes to the rigging and arrangements for the ailerons between the Allison engine Mustangs and the Merlin engine Mustangs, which improved the roll rate on the Merlin engine versions. The Merlin ones for a start had a larger 'throw', allowing more roll authority and deflection to increase the rate of roll. They also had a revised design and different 'sealing' between the wing trailing edge and the aileron for greater effectiveness. Roll rate is not everything in evading attack. Evading attack is a complete set of operational methodology and tactics to fly to the strengths of your particular aircraft type and avoiding the strengths of your opponents aircraft and tactics. That is both to enemy aircraft threats and ground based threats eg AA & radar.

The RAF was well aware of the long range potential of the Allison engine Mustangs once they got the first ones in the UK in late 1941. The early ACC units to receive them quickly did the calculations and figured out that the potential radius of operations was significantly more purely on built in internal fuel than what was possible using other types: eg Hurricane, Spitfire, fitted with external tanks to extend their range. The Allison engine Mustang fortuitously had a range of attributes that well suited it to the ACC and low level tactical reconnaissance role, more so than most of the alternatives proposed at various times up until VE-Day. Add to that the modifications the RAF developed to improve their performance below 8,000-10,000ft, that met a niche requirement excellently. The fact that it was also called upon to perform roles outside those normally associated with the 'pure' ACC roles, such as long rang escort to low level bombers of RAF 2 Group; long range 'Instep' patrols into the Bay of Biscay supporting Coastal Command operations; the standing low level interceptor patrols off the English coast protecting against Luftwaffe hit and run raiders and low level minelaying aircraft; plus providing escort to RN naval light forces (MTBs and MGBs) operating beyond the range of other RAF fighters of the time tells a little of the overall picture. There were things the RAF's Allison engine Mustangs could do in the later stages of the war in the ETO, that no other comparable types in RAF service could do, particularly in the low level fighter reconnaissance role. Their ability to carry internally a growing range of oblique and vertical reconnaissance cameras with varying length focal lenses, and operate in contested airspace, able to defend themselves, all added to their value.

Internal RAF politics also come into play - suggest if you get the opportunity have a look at the series of books written by Greg Baughen about the RAF's wartime policy deliberations and the politics at play: Fighter Command, Bomber Command, Trenchardian doctrines, etc. He covers the Air Staff's aversion to being tied to close air support over their view of how an air war should be conducted very well - lots of references and quotes from Air Staff minutes.

Important thing to consider, the initial allocations of the Merlin engine Mustangs for both the RAF and to the USAAF in the ETO, were to RAF units as a part of 2TAF to be used as a part of the support to ground forces in the invasion of Europe in a long range interdiction/bombing role; and to USAAF 9th TAC AF units to support the US Army for the invasion. They were initially viewed as CAS aircraft, but the need for the long range, high altitude bomber escort brought about a rapid change in tasking and allocation.

 

[ggiumarra]

Apparently not in the rather key area of rolling. P-40s had one of the best roll rates above 200 mph of any Allied fighters, in fact one of the best of any fighters of the war. This is very well documented.

The chart you sent confirms what I was just figuring out about the Mustang I, so thank you. On the one hand RAF tests of the Mustang I at Boscomb Down in mid-1942 showed its roll rate as "much faster than on any present-day fighter tested at this Establishment" (AVIA 18/732), and in tests vs a captured Fw 190 around the same time the Mustang I performed much closer to it in roll than either the Spitfire V or IX, but other sources I've seen state that the Mustang I had a poor roll rate. What your chart shows is what I suspected - it varies quite a bit depending on speed. At low speed it is showing not too good at all, whereas over about 380 mph it surpasses even the Mustang III (the Boscomb Down tests seemed to have been at high speed). Only the Mustang I and III are depicted over 400 mph, I'm guessing because above that speed the stick forces on the other a/c become excessive. What I'm seeing is the P-40 (it is strange they show a Tomahawk and not a Kittyhawk this late in the war, however) does indeed have a great roll rate over 200 mph and at 275 it is truly in a class of its own, but it drops off rapidly from there and at just over 300 the Mustang III passes it up as does the Mustang I over about 315 (though the P-40 still is showing very good roll up to 400 and perhaps the Kittyhawk was better than the Tomahawk in this regard). This corresponds closely to accounts I've read of P-40 pilots saying the P-40 required a strong arm at high speeds.

I know it is just one metric (though, as you say, a very important one), but it really graphically (pun intended) illustrates the concept that you've got to know the relative strengths of your a/c. When considering roll the Hamp wants to fight very slow (duh), the P-40 somewhat faster, and the P-51 faster yet (which speed may have been hard to maintain when maneuvering in level flight).

Too bad the Ki-43 is not depicted, but if it's anything like the Hamp then we may have found an explanation as to the poor showing of the P-51A. If their pilots had been taught the details of the speeds the P-40 had a significant advantage over their Japanese opponents they may have tried to roll with them in speed ranges in which the P-40 could best them but the P-51 could not. By the time those that had survived may have figured it out (which may have taken longer than if they were approaching things with a "clean slate") they had moved on to the P-51B. Just a theory, however.

In any event, thanks for the info.

 

[ggiumarra]

...suggest if you get the opportunity have a look at the series of books written by Greg Baughen about the RAF's wartime policy deliberations and the politics at play: Fighter Command, Bomber Command, Trenchardian doctrines, etc. He covers the Air Staff's aversion to being tied to close air support over their view of how an air war should be conducted very well - lots of references and quotes from Air Staff minutes.

Oh, lord. I was going to go to bed and get some sleep before I replied again, but you went and mentioned Greg. Yeah, I know Greg fairly well and even try to get together with him whenever I'm in London (when I go the the National Archives at Kew). You could say I am very much influenced by his works, though I have to say I originally made the effort to meet him when I first discovered that he quite independently came to some of the same conclusions that I had, although his scholarship was definitely much more in depth than mine when it came to the RAF (I suppose now, however, in a few very specific areas I've dug in a little deeper and my research generally spans many subject areas of WWII history beyond military aviation). At times I write things in my study that I feel quite satisfied with and then on further reflection I think to myself "isn't this just derivative of what Greg has already written?" and then wonder if I'm just wasting my time! Ha! I do hope I can add something to what he has already contributed, but he is sure to get my first draft with the request "make sure I don't fail to give you credit where I failed to properly do so!" and I won't show it to anyone else before he replies back!

Get yourself a copy of Matt Willis book, Mustang - the Untold Story, from Key Publishing UK, another good primer on the early Allison Mustangs and their use.

Got it a couple of years ago. It's definitely a good book, but doesn't deal much with the areas I'm addressing in my study, which are closer to Greg's in some ways, I suppose.

You'll have to wait for Bill Marshall's second book that follows on from P-51B Bastard Stepchild that Saved the 8th Air Force for more of the story.

Can't wait. Any details as to what it covers over and above "Bastard" and when we might expect it?

You wrote too much else for me to respond to at this late hour, but I would say though it was all very interesting, a lot of it is only tangentially related to what I'm saying and some of the rest I'm not sure I entirely agree with.

 

[drgondog]

Yes, the P-51A, which, despite what even many aviation historians think, was not the original version of the Mustang, but the first major variant that began production a year and a half later. The original Mustang was designated by the AAF as just the P-51 (no letter suffix) which can be confusing because we all refer to various US warplane types generically (regardless of variant) without a letter suffix. The P-51B was known in RAF service as the Mustang III and the P-51D, the Mustang IV, btw.

Beyond that, when you consider that it was not until the C version of the P-47 (technically the C-3, I think) and the F version of the P-38 that those warplanes were deemed ready for front line service, it really is a testament to the engineering and production prowess of NAA that even before the Mustang's A version it was a very capable and generally reliable a/c.

Slight correction - the AAF "P-51" was the NA-91 P-51-NA and later the P-51-2-NA in recce version, forerunner of F-6 series. The RAF designation was Mustang IA. The NA-73s 41-038 and 41-039 were "XP-51" delivered in August and December 1941. The NA-99 P-51A was Mustang II in RAF service.

 

[ThomasP]

re

. . . (after all Truman was of the same political party as the current administration) . . .

??

Not trying to start a political argument, but Truman was a Democrat while Trump is a Republican.

 

[ggiumarra]

re

??

Not trying to start a political argument, but Truman was a Democrat while Trump is a Republican.

I wasn't talking about Trump but FDR. Perhaps if I'd written "the then current administration" I could have been more clear but I guess I thought from the context it couldn't mean anything else.

 

[drgondog]

Apparently not in the rather key area of rolling. P-40s had one of the best roll rates above 200 mph of any Allied fighters, in fact one of the best of any fighters of the war. This is very well documented.

A better description is that its peak roll rate is

The early Mustangs apparently had a problem with a poor roll rate. This is also documented though it took me a while to find hard numbers on it. The later Mustangs, starting with the Mustang III, had superlative high-speed roll rate.

I'll dig up the XP-51 roll rate, pre aileron modification mid-1942 but the P-40 shows peak roll at 275 and crossing over the P-51B a approximately 300mph. That said the P-40 out rolled the P-51A significantly through 320mph. It also out rolled the A6m above 200mph.

Roll rate, it turns out, is pretty important when it comes to evading attack.

I suspect this issue with the early Mustangs may have had something to do with the issue. There were combats where some of the P-51A units appeared to use poor tactics, in fact I think I recall the one you are referring to where the commander was killed, but some P-51A were being used by very experienced units like 23rd Fighter Group which definitely knew the ideal tactics to contend with Japanese aircraft.

View attachment 873684

I agree that the tactics for combat vs IJA fighters for the P-51A and A-36 in CBI were poor.

 

[Steamed_Banana]

The two-stage Merlin was developed in 1940 to support high altitude Vickers Wellingtons. When the British ran into problems with fighters, the two-stage Merlin was available and debugged. In the case of the Mustang, the two-stage Merlin was an opportunity. When would Allison move a reliable two-stage V1710 into production?

The whole point of the thread is when could Allison have designed and moved a single stage, two speed V-1710 (roughly equivalent to Merlin XX) into production, and could it have been done by early 1943. I think two-stage ala Merlin 60 or R2800 etc. would inevitably happen later.

 

[drgondog]

Can't wait. Any details as to what it covers over and above "Bastard" and when we might expect it?

I is in editing now at P&S. Their POV is that it will be released in July.

It is a four part book.
The first segment is a detailed examination of the history of developing the long-range-escort-fighter from just pre-AWPD-1 in which the 'escort fighter' is described as a long range, fast, agile multi engine escort with crew served weapons. Through 1943, the parallel development of the history of droppable tanks, the Fighter Aircraft Range Extension Program and the politics/false starts (YB-40/XP-75) combined with increasing high losses of 8th AF - all leading to:
Failure of Republic to deliver long range escort capable P-47 until mid-1944. Why?
Relentless pressure by AAF to increase internal fuel on P-38, P-47 and P-51B.
Political forces which stripped the P-38 from 8th AF inventory to support Torch. Why and who
The failure of AAF (and Germany and RAF) to deliver a single engine long range escort. Why and extensive range discussions?
Discussion and rebuttal of 'bomber mafia conspiracy'.

The second segment is a discussion of the influences that led to the parallel development of the P-51D and XP-51F.
Early pressures for bubble canopy and heavier armament for the P-51D.
Kindelberger pitch to Arnold to build a better fighter than the Spitfire IX. Why the weight study between XP-51B and Spitfire IX?
Why the first P-51D was not accepted in production with 55-gal fuselage tank. What influence did the AAF decision to order all production Mustangs delivered after Jan 1, 1944 have on the Lightweight P-51F?

The third segment is devoted to detailed design changes, including introduction of future 7075 alloys to reduce weight.
Detailed segments for P-51F, G, early NA-117 H, and J developments. Specific features and testing issues.
Explanation of peak performance, particularly in P-51F when the 1650-9 was installed.
How politics arising at Mat.Cmd. delayed purchase decision for request in Oct 1943, combined with internal fuel required by AAF, killed P-51F from ever serving in AAF.

leading to:
The final lightweight, the NA-126 P-51H

The Appendices presents:
Detailed range tables AAF FAREP, Table for Actual Ranges attained for combat victory credits by fuel load and a/c type vs AAF tables.
Maps FAREP vs Actual.
Technical Section including drag comparison, model variation weight and balances, NAA range calcs for both ferry and combat radius, Engine horsepower, Total Victory credits by theater and quarter (ETO only)

 

[Steamed_Banana]

So I don't pretend to be so well informed by this that I would defend my position vociferously, but from what I understand the P-51A pilots in CBI were largely inexperienced and used poor tactics. One story I am familiar with (hopefully it's even true) is the commander of one squadron of P-51A's getting shot down in his first mission there and when the Japanese pilot was later shot down himself, captured and interrogated he expressed puzzlement over why his victim had not just dived away instead of getting into a turning battle which he wasn't going to win. The tactics a P-51 would have to use vs those Japanese fighters are essentially the same as for the P-40 - it has pretty much the same advantages, it's just those advantages are bigger. If you play to your opponent's strengths, however, the outcome is not going to be good, regardless of your own strengths in other areas.

I should have spelled this out a little more clearly, but I'll do so now.

At the same time as the P-51A was first being deployed in Theater in late 1943, there were already three US fighter groups flying P-40, plus some Chinese units. The P-40 was the main US type in Theater, while the main British type was the Hurricane.

Notably 23rd FG (from the original AVG) in China and Burma since 1942, 51st FG in China, Burma and then India (often split with some squadrons going back and forth) also since 1942, and later the 80th FG operating out of India from Sept 1943.

All three of these units mostly used P-40s through some time in 1944, though 23rd FG also got some P-51As as early as fall 1943. 23rd FG transitioned to P-51B/C in mid 1944.
51st FG used P-40s until late 1944 and into 1945, when they transitioned to P-51B/C/D
80th FG used P-40s until late 1944 when they transitioned to P-47s

All three of these units had a quite successful combat record against the JAAF, in fact they were by the most successful Allied fighter units in Theater, and arguably the only types which consistently held their own (and a bit more) against the Ki-43-II until the arrival of the Merlin-engined Mustangs and the Spitfire Mk VIIIs.

So if the P-51A has the same advantages, I would have to wonder why the combat record of the aircraft type in Theater was so much worse. The same is actually true to some extent in the MTO with the A-36, though the P-51A was not really used as a fighter there. P-51A and A-36 together so far as I know only had one ace during the war. The 23rd FG alone had 32.

Clearly there was something different about the deployment of the two types. And there was such a huge difference with the Merlin-engined types that it's hard to credit higher altitude performance alone, IMO.

 

[Steamed_Banana]

The chart you sent confirms what I was just figuring out about the Mustang I, so thank you. On the one hand RAF tests of the Mustang I at Boscomb Down in mid-1942 showed its roll rate as "much faster than on any present-day fighter tested at this Establishment" (AVIA 18/732), and in tests vs a captured Fw 190 around the same time the Mustang I performed much closer to it in roll than either the Spitfire V or IX, but other sources I've seen state that the Mustang I had a poor roll rate. What your chart shows is what I suspected - it varies quite a bit depending on speed. At low speed it is showing not too good at all, whereas over about 380 mph it surpasses even the Mustang III (the Boscomb Down tests seemed to have been at high speed). Only the Mustang I and III are depicted over 400 mph, I'm guessing because above that speed the stick forces on the other a/c become excessive. What I'm seeing is the P-40 (it is strange they show a Tomahawk and not a Kittyhawk this late in the war, however) does indeed have a great roll rate over 200 mph and at 275 it is truly in a class of its own, but it drops off rapidly from there and at just over 300 the Mustang III passes it up as does the Mustang I over about 315 (though the P-40 still is showing very good roll up to 400 and perhaps the Kittyhawk was better than the Tomahawk in this regard). This corresponds closely to accounts I've read of P-40 pilots saying the P-40 required a strong arm at high speeds.

I know it is just one metric (though, as you say, a very important one), but it really graphically (pun intended) illustrates the concept that you've got to know the relative strengths of your a/c. When considering roll the Hamp wants to fight very slow (duh), the P-40 somewhat faster, and the P-51 faster yet (which speed may have been hard to maintain when maneuvering in level flight).

Too bad the Ki-43 is not depicted, but if it's anything like the Hamp then we may have found an explanation as to the poor showing of the P-51A. If their pilots had been taught the details of the speeds the P-40 had a significant advantage over their Japanese opponents they may have tried to roll with them in speed ranges in which the P-40 could best them but the P-51 could not. By the time those that had survived may have figured it out (which may have taken longer than if they were approaching things with a "clean slate") they had moved on to the P-51B. Just a theory, however.

In any event, thanks for the info.

This is another roll rate chart with more aircraft types shown, the famous NACA 868

(keep in mind that these numbers vary based on altitude, loading of fuel and possible extra guns or ammunition etc.)

This shows roll rate for the P-40F (at 50 lbs stick force), peaking at 95 degrees per second between 250 mph -295 mph, with the XP-51 (eg Mustang I) starting at 50 degrees and slowly improving to 80 at 330 mph. Here too the roll rate from P-40 and Mustang I seems to converge around 380 mph, but that is extremely fast for fighter combat. The P-51B by contrast still starts low around 60 but reaches 90 degrees per second at 260 mph and peaks at 95 degrees at 300-325, which is excellent high-speed roll.

Note that the original Spitfire has a good roll at low speed (105 degrees at 200 mph), but a rather poor roll rate at higher speeds, dropping to 75 degrees at 300 mph; but the 'improved' Spitfire with clipped wings and metal ailerons, has a phenomenal roll rate peaking at 150 degrees at 200 mph and still at 95 degrees at 350 mph. This were all changes made to cope with the Fw 190, which rolled like it was on ball-bearings (as you can see on the chart) but is surpassed by the P-51B at 360 mph. A very important detail.

The stats here for the A6M are probably incorrect here, incidentally.. But I have another one with more accurate numbers.

The importance of this big chart is that it gives you a ballpark idea of what a competitive roll rate is, and that is around 70- 80 degrees per second here by the mid war. You can also see that early-war aircraft had very good roll at low speed, while later war aircraft (F6F, P-47) tended to have reasonably good roll rates at higher speeds.

The issue regarding 'strong hand' is actually a 'strong leg', in the P-40, with rudder forces increasing as speed goes up, but this became a factor at over 400 mph and specifically in dives, and could be trimmed out. This was still considered a nuisance by a lot of pilots, but it was advantageous over other types with no rudder trim (like Bf 109). The rudder forces were eased by the later run of the P-40F and K by lengthening the fuselage.

This chart...

Shows roll for an early P-40, a P-36, and early Spitfire and Hurricane, using 30 lbs of force. Note the P-40 peaks here at 110 degres at 280 mph.

This chart, from an Australian test, shows roll rates for a 'Hap', (left, and distinguishing between rolling left and right), a Tomahawk, and a Spitfire (Spit Vc) with metal ailerons).

It's a little hard to read but you can see that the Hap (A6M3) peaks at close to 100 degrees at about 175 mph, then swiftly drops off, to 45-60 at 250 mph and 40-45 at 300 mph; the Spitfire peaks at about 160 mph, and more slowly tapers off to ~50 at 300 mph, and the Tomahawk peaks once again (at 85 degrees) around 280 mph and then falls off to 60 by 350 mph.

Some other roll data that i was able to find (not yet any charts though), peak roll rates:
(take these with a grain of salt as i was unable to confirm them with primary sources)

Ki-43-I and II 130-140 degrees per second (below 250 knots)
F4U-1 85-90 degrees per second (or ~100 degrees per second, maybe depending on altitude)
Fiat G.50 and MC 200 both around 100 degrees per second
Spitfire IX about 100 degrees per second
Spitfire VIII close to 150 degrees per second
P-38L (boosted ailerons) 90 degrees per second
Ki-61 60-70 degrees per second
P-38F 50 degrees per second

 

[Shortround6]

The whole point of the thread is when could Allison have designed and moved a single stage, two speed V-1710 (roughly equivalent to Merlin XX) into production, and could it have been done by early 1943. I think two-stage ala Merlin 60 or R2800 etc. would inevitably happen later.

There are several things going on here. In no particular order.

Timing, it took RR about 6-8 different Merlins to get to the 2 speed Merlin X engine. About 4-5 years.

Tooling. Several of the RR factories built both single speed and two speed engines. Some factories only built one type. On the flip side. P&W built two stage engines before they built a 2 speed engine. Wright was building 2 speed engines about 2 years before P&W. Wright had also figured out how to offer conversion kits for some existing engines.
An awful lot depends on the exact design of the parent engine and the design of the supercharger drive/s. Also remember that US design practice was to increase take-off power with a low gear, not to improve altitude performance. US military was late getting into the game and the US engine makers (P&W and Wright) were building airliner engines. Fighter engines were a sideline until 1939/40 and bomber engines were the 3rd place market...........except................the Army was trying to get turbo chargers on anything they viewed as "high altitude".
This meant there was little financial incentive to build high altitude military engines until 1940 or later.

Allison tooling up/production problems. Allison production by year. sources vary.
1937 = 7
1938 = 12
1939 = 48
1940 = 1153*
1941 = 6433
1942 = 15,319
1943 = 20,350

* about 900 in the last 4 months.
1937 engines were good for 1000HP?
Late 1943 P-38 engines were good for 1600hp WEP?

Allison engineers tried "a bridge too far"? Skipped the two-speed supercharger and jumped to the two-stage supercharger for a much better potential increase in ceiling.
Then they totally flubbed in initial design work on the two stage. They didn't seem to understand how air flow worked (they were not the only ones).

Allison (and GM) did a lot things right but as can be seen by the 1937-39 numbers they were not an engine factory. They were an experimental/prototype shop that did, with the help of GM, expand into a major production complex and built better (higher powered and longer lasting) engines.
I keep asking, without getting any real answers, were was Allison supposed to got to for answers/Guidance in supercharger design in the United States?
P&W and Wright superchargers in 1939-42 were not very good even if two speed.

 

[Steamed_Banana]

There are several things going on here. In no particular order.

Timing, it took RR about 6-8 different Merlins to get to the 2 speed Merlin X engine. About 4-5 years.

Sure but both the Merlin and domestic P&W etc. types were potentially available to Allison in 1941-42. So we aren't necessarily talking about designing from scratch so much as adapting something.

Tooling. Several of the RR factories built both single speed and two speed engines. Some factories only built one type. On the flip side. P&W built two stage engines before they built a 2 speed engine. Wright was building 2 speed engines about 2 years before P&W. Wright had also figured out how to offer conversion kits for some existing engines.
An awful lot depends on the exact design of the parent engine and the design of the supercharger drive/s. Also remember that US design practice was to increase take-off power with a low gear, not to improve altitude performance. US military was late getting into the game and the US engine makers (P&W and Wright) were building airliner engines. Fighter engines were a sideline until 1939/40 and bomber engines were the 3rd place market...........except................the Army was trying to get turbo chargers on anything they viewed as "high altitude".
This meant there was little financial incentive to build high altitude military engines until 1940 or later.

Allison tooling up/production problems. Allison production by year. sources vary.
1937 = 7
1938 = 12
1939 = 48
1940 = 1153*
1941 = 6433
1942 = 15,319
1943 = 20,350

* about 900 in the last 4 months.
1937 engines were good for 1000HP?
Late 1943 P-38 engines were good for 1600hp WEP?

We know that mid 1942 V-1710 were already cleared for WEP rating amounting to 1570 hp

Allison engineers tried "a bridge too far"? Skipped the two-speed supercharger and jumped to the two-stage supercharger for a much better potential increase in ceiling.
Then they totally flubbed in initial design work on the two stage. They didn't seem to understand how air flow worked (they were not the only ones).

This was indeed the problem.

Allison (and GM) did a lot things right but as can be seen by the 1937-39 numbers they were not an engine factory. They were an experimental/prototype shop that did, with the help of GM, expand into a major production complex and built better (higher powered and longer lasting) engines.

That's a good way to put it.

I keep asking, without getting any real answers, were was Allison supposed to got to for answers/Guidance in supercharger design in the United States?
P&W and Wright superchargers in 1939-42 were not very good even if two speed.

Well, I think it's clear that for this to work, it would have to be more of a matter of Allison adapting an existing design for a two speed supercharger rather than inventing their own from scratch, so to speak.

From posts in this thread it seems that the Merlin XX supercharger was actually considered for the Allison, which seems obvious, and the P&W were also obviously available. We have some licensing issues for RR and possibly Farman, and / or to P&W or Wright and / or GE. And we know that the US had a preference for turbo as the solution to all of this, which they did in fact ultimately succeed at, at least in part, with the P-47 and P-38. This is the reason that this never happened is partly related to this preference.

But it does look like it was possible. Production capacity in time to matter may have been somewhat limited initially, but I suspect more (and maybe a bit improved?) P-40F/L types, some two speed P-51A+, and P-39 with two speed supercharger may have continued to be useful to varying degrees to the end of the war. A few P-38s with reliable two speed superchargers instead of the turbos might have been a very helpful stop gap for Pacific / CBI / MTO.

And A-36 with strengthened wings and a two speed supercharger seems like a winner to me too.

One question I'd have is how bad was the two speed P&W supercharger and what would a V-1710 with that supercharger look like performance wise.

 

[Geoffrey Sinclair]

On fighter altitude performance.

Exactly, and that is exactly what I am calling into question. In both cases there was a disconnect between the sort of air war the RAF and AAF wanted to fight and the one that was really being fought in which high-altitude performance was not that important or even superfluous. I am not saying it is never important, just not as important as other attributes, the most important of which, especially in 1942 and at least through much of 1943, was range (as long as you were above a certain minimum in fighter performance otherwise). You needed range in the Pacific and you needed range in the Med. when most all of your fighter missions are happening at medium to low altitude.

It is a basic rule when air forces fight each other altitude goes up, if the army and/or navy are involved altitude tends to go down.

In early 1941 the RAF was expecting Battle of Britain the repeat and since almost no one expected the USSR to survive into 1942 Barbarossa simply delayed that by a year. As a result it held all Spitfire fighter versions in Britain to enable Fighter Command to go from 40 Hurricane and 19 Spitfire squadrons to 12 Hurricane and 58 Spitfire during 1941, with the Hurricanes in theory earmarked for Typhoon. It was also having to deal with the Luftwaffe fighters maintaining a performance edge over the Spitfire for much of 1941 to mid 1942.

Malta needed fast climbing fighters. The Western Desert operations needed a reason to force the Luftwaffe to fight, instead the Luftwaffe fighters evolved the tactic of using their altitude performance advantage to fight in the vertical, picking off mostly allied fighters, since going for escorted bombers meant ending up below the escort. The RAF in Egypt really needed something like a wing of Spitfires to help counter the tactic. The range of the Bf109 and Ju87 meant the Luftwaffe was in range of the Hurricane and P-40.

End 1942 and the Luftwaffe was facing a need to fight in the west (viable high altitude bomber force) and south (allied ground operations) by which stage there were 772 Mustangs built with production switched to the A-36. Britain had imported 666 of them.

In 1943 the allies moved to largely deciding when, were and how high the air fighting would take place. The Luftwaffe in the south was defeated in mid 1943, withdrew and never returned in numbers thanks to the pressure from the west. Even the 15th Air force was finding few hostile fighters, in July 1944 its aircraft claimed 732 enemy aircraft shot down, in August 267, the air force claimed another 355 shoot downs September 1944 to May 1945 inclusive.

The allies expected major air battles as part of Operation Overlord, which did happen, what was not put into the plans was a major defeat of the Luftwaffe fighter arm before the invasion causing it to lose quality even as numbers remained, plus the Luftwaffe losing much of its remaining operational bomber force in the Baby Blitz.

9th Air Force ETO report, "The averages of 663 tactical aircraft and the small overage in combat crews were quickly reduced when extensive operations were started. Combat losses immediately wiped out the excess fighter and reconnaissance aircraft, and insufficient replacements created a critical shortage which existed until V-E Day despite the fact that some groups were converted to aircraft models which had a larger replacement flow."

There were not enough Mustangs in the world for a lot of the time in 1944 despite the type being largely shielded from combat until 1944.

The obvious way to obtain more Mustangs is to replace the order for Curtiss P-47G to P-51, then converting the P-40 line, Curtiss started P-47G production in September 1942, peaked at 55 in November 1943, final production in March 1944, with 354 built, from a contract dated 31 January 1942, P-40 production ended in November 1944.

But even later in the war you have situations like in Italy where the RAF commander there is fine with giving up his allocation new Mustang III's (P-51B's) to the AAF (this was maybe in July or August 1944 when the AAF was losing more Mustangs than planned so they appealed to the RAF for higher allocations of Merlin Mustangs) because all his missions are low altitude and he recognizes his new Mustang's performance characteristics are better served as a high-altitude bomber escort. In reality, that RAF commander would have been better off with Allison Mustangs to begin with since they had better at the altitudes his planes were operating at.

P-51A 1,200 HP available for take off, Merlin P-51 either 1,380 or 1,490 HP, that translates to several hundred feet lower take off runs for the same weight, or more weight for the same take off run. The P-40K had 1,325 HP for take off the P-40M and N 1,200 HP (Francis Dean, America's Hundred Thousand). The P-40 could have wing and under fuselage bomb/fuel tank racks, the P-51 wing only.

the British were trying to convince the Americans in 1942 to build more Mustangs in plac of Kittyhawks, but backed down when they got push back (their main goal at the time was to get more Packard Merlins for their own use).

The British were definitely trying to convince the Americans to build more P-51 for much of 1942, involving Churchill easily shows that, not sure whether there was a consistent line about what to cut back on, they knew the Americans had the final decision.

According to one book I have NAA was setting up to produce Allison and Merlin Mustangs at the same time before the first of the latter came off the assembly line. I suspect (but do not have conclusive evidence) the reduction in the P-51A order was less about making room for the Merlin Mustang as it was yet another hurdle the AAF threw up to prevent it from taking business away from its favorite contractor Curtiss

Curtiss-Wright had been around a long time with many good designs, it had a bank of goodwill as a result, output as a percentage of total, 1940 to 1945 and as a total of 1940 to 1945 production, ignoring licensed production

Aircraft, 22.87, 24.97 25.46, 18.15, 19.64, 18.06, total 20.47
Engines, 22.51, 14.18, 12.31, 7.70, 7.06, 7.38, total 8.90
Propellers, 22.35, 20.89, 25.31, 19.67, 18.71, 20.95, total 20.48

Remembering the 20 July 1942 US/UK agreement for 1,200 Merlin Mustangs built January to October 1943, split half each, with the RAF releasing Packard Merlins from its order to the USAAF.

The USAAF ordered 1,200 Mustang on 24 August 1942 on AC-30479, 400 more on 28 December 1942 on AC-33923 then another 550 as a supplement to AC-30479 on 5 January 1943, the supplement was paid for out of fiscal year 41/42 funds, the rest from 42/43 funds, total 2,150

In build order AC-30479 310 P-51A 43-6003/6312, AC-33932 400 P-51B 43-12093/12492, AC-30479 890 P-51B 43-6313/7202, AC-30479 548 P-51B and 2 P-51D 42-106429/106978. The early Merlin Mustangs were built in reverse serial batch order.

As of end January 1943 the idea was 310 P-51A, 400 P-51B-1 (AC-33923), 400 P-51B-5, 1,190 (150 not yet contracted) P-51D-1, total 2,300 of which 2,150 contracted. First P-51A acceptance March 1943. As of end January 1943 Dallas was meant to produce 400 P-51C then switch to 600 P-51E, with another 350 P-51E not yet contracted for. What versions were planned to be produced often changed.

25 January 1943 was the date of the last big P-40 order, 4,000 aircraft, supplemented by another 1,000 on 14 February 1944 and 220 on 20 June 1944.

perhaps the most important finding of the famous Truman Commission dealt with what looked like favoritism towards Curtiss at the expense of NAA, specifically with respect to the P-40 and the P-51 (one interesting factoid I found in that report - and here I'm guilty of perhaps getting off topic - was that in the middle years of WWII at least - Curtiss-Wright was the second biggest US contractor in dollar terms after GM). It didn't actually charge corruption (after all Truman was of the same political party as the current administration), but it sure reads that way between the lines.

Given the breadth of the Curtiss-Wright group and the head start with P-40 production it is not surprising in 1942/43 it was one of the bigger suppliers. The trouble with going into conspiracies is absence of evidence can be treated as proof of two conspiracies, the original and the cover up. Just about everyone in the US had at least one loved one in the military, it was a strong deterrent to systematic corruption. It seems the main thing not accepted was gasoline rationing, the mafia becoming involved.

Making China/Burma/India a big recipient of Allison P-51 does show the USAAF attitude at the time, given the theatre was the lowest priority.

The Curtiss Wright group received $451,764,000 of public and $33,767,000 of private funds for expansion, North American $79,230,000 public and $5,670,000 private. Douglas $195,287,000 public 15,333,000 private. Pratt & Whitney (United a/c) $176,594,000 public and $36,397,000 private. Packard $93,919,000 public and $313,000 private. Nash Kelvinator $62,583,000 public and $581,000 private. Aircraft were expansive, creating engine plants very expensive. Douglas (aircraft) plus Pratt & Whitney (engines) plus Nash Kelvinator (Propellers) ended up with about as many public funds as Curtiss-Wright.

General Motors $479,078,000 public $25,931,000 private (Allison $101,239,000 and $15,246,000 of this), Ford $225,050,000 public and $10,607,000 private (Willow run cost $94,898,000). Overall the aviation industry received nearly $2,400,000,000 in public funding for expansion.

There is no doubt many aircraft stayed in mass production well after they were no longer front line material or something obviously better was available, the reality of mass production of complex machines combined with the pressure of current operations.

V-1710 production 1940, monthly, 3, 7, 6, 7, 12, 29, 60, 70, 230, 285, 176, 256, total 1,141, for 1 P-38, 13 P-39 and 778 P-40. Wartime production, 1 stage + 2 stage by year, 1940 to 1945, War production Report as well as the CAA report.

1,141 + 0, 6,447 + 0, 14,904 + 1, 20,549 + 514, 17,324 + 2,867, 3,841 + 1,645 total 64,206 + 5,027

 

[tomo pauk]

I keep asking, without getting any real answers, were was Allison supposed to got to for answers/Guidance in supercharger design in the United States?

USA was not cut off from the rest of the world.
People in the aero engine business in the USA knew by 1938 that supercharger on the Merlin was phisically bigger, and accurately pointed out that the altitude performance of the engine will be better because of that. The benefits of 2-speed drives for S/C were known before ww2, ditto for the 2-stage mechanical supercharging.