An Allison V-1710 with a two-speed supercharger in 1942 (7 Viewers)

[MIflyer]

I have not been able to find the weight of the intercooler/aftercooler systems used with the 2-stage superchargers on the F4F, F6F, or F4U.

Here is some data:

P-61B empty weight: 21,282 LB Used F6F/F4U style R-2800 which gave a top speed of 366 mph at 20,000 ft.

P-61C empty weight: : 24,000 Lb Used turbocharged R-2800, which gave a top speed of 430 mph at 30,000 ft. Of course there could have been other weight increasing features that were not associated with the turbo installation

Small wonder that the USAAF wanted turbos on everything! In terms of absolute performance they were correct.

 

[Shortround6]

The P-61Bs used the -65 which was very similar to the -10s used the F6F.
The P-61Cs used the -73 which was very similar or identical to the -73 engines used in the P-47M.
They also used paddle blade props that were 12' 8" in diameter instead of the 12' 2" props of the P-61Bs.
I have no idea of what they beefed up to handle the potential 2800hp engines instead of the 2000-2200hp engines in the P-61Bs, they did carry as much as 614lbs of water for the mechanical supercharged engines for some missions. The turbo engines had 531lbs total available.
The actual -73 engines were about 150lbs lighter than the -65 engines but the -73 engines were single stage/single speed and weight does not include the turbo.
The -73 engines were about 60lbs heavier than the -59 engines used in the P-47Ds.

 

[Steamed_Banana]

I don't know how we got to P-61, but I think at some point they took off the turrets, and that must have increased speed substantially (probably range too) but I've never seen numbers on that.

 

[Howard Gibson]

Here is some data:

P-61B empty weight: 21,282 LB Used F6F/F4U style R-2800 which gave a top speed of 366 mph at 20,000 ft.

P-61C empty weight: : 24,000 Lb Used turbocharged R-2800, which gave a top speed of 430 mph at 30,000 ft. Of course there could have been other weight increasing features that were not associated with the turbo installation

Small wonder that the USAAF wanted turbos on everything! In terms of absolute performance they were correct.

Be careful. Note the altitude at which the P-61 is doing 430mph. The turbocharger takes your aircraft up to an altitude with thinner air. Most fast aircraft of WWII did it at 25,000ft plus. The book Mosquito, by C. Martin Sharp and Michael J.E. Bowyer has a speed/altitude chart showing Mosquitos Mark_35, 33, and VI. The two-stage Merlin powered Mark_35 did 425mph at 30,500ft. The single-stage Merlin powered 33 and VI did 387mph and 378mph respectively at around 13000ft. Below 10,000ft, the single-stage Mosquitos were faster than the two-stage Mosquito. This explains why the Mark_VI stayed in production throughout the war.

 

[ggiumarra]

It's funny, but I have been pondering this subject (the original question about a single stage/two speed supercharge for the Allison in 1942) for at least a year now and finally got around to asking an acknowledged expert in the field (via a DM on a social media site) about this about a month ago but, unfortunately, either because I failed in both my messages to him to make myself clear or some other reason all I got back was a very broad explanation about superchargers generally and a promise that he would reach out to William Marshall and get back to me with his answer (I never heard anything back on that), which was ironic because it was Marshall's (and coauthor Ford's) book on the P-51B that had really got me seriously thinking about it to begin with (although I believe the idea had occurred to me previously). As it turns out I got much more useful information on the subject when I finally came across this thread a couple of days ago.

Surprisingly, unless I missed it, no one here has noted that on p. 165-6 of P-51B Mustang: North American Aviation's Bastard Stepchild that Saved the 8th Air Force, (the Marshall and Ford book I just referred to) it recounts an exchange between Allison Chairman O. E. Hunt and NAA's President Dutch Kindelberger in March of 1941 in which Allison offers NAA a two-stage/two-speed Allison engine - apparently a design it's already working on, or at least needing a potential customer so it can justify working on it - while NAA requests a single stage/two speed supercharged solution (due to the very significant and therefore unwanted design changes the two-stage/two-speed would entail). In frustration at Allison's refusal to pursue the less technically challenging solution, Kindelberger fires off a message to the British Purchasing Commission for information on the Merlin engine and the following month they receive an 18-page technical document from RR with details of the Merlin XX (which most of you reading this know, has a single-stage/two-speed s/c and was also the basis of the Packard Merlin that went into the P-40F and L). So there you have, from what I can tell, the first initiative to get a Merlin, albeit a less advanced one than it eventually had, into the P-51 and it was in the spring of 1941, and some info highly relevant to the original question, I think.

Before I go any further I should mention that I have been doing research and writing a study on problems with RAF and AAF fighter doctrine and production policy during WWII through the prism of the Mustang. The first part takes on the myth that the Allison Mustang represented little better than a stepping-stone to the Merlin Mustang. In short the three reasons the original Mustang would have been so very useful, particularly in 1942: range, range and range. Sure the original P-51 was a overall a better performer than the P-40 or P-39 but even if it had been somewhat inferior to both its decidedly superior range was a compelling reason for the AAF to acquire and employ them (think the war vs Japan just about anywhere) and for the RAF to use them properly, especially when it came to convoy protection (think a little bit Murmansk and a lot Malta, though in the latter case there is a lot more to the story than "they should have used their Mustang I's" and the idea would be to supplement, not replace the Spitfires there), instead of effectively burying them in the Army Cooperation Command. I should add that the range capability also applied to the fundamental factor of deploying them to begin with. One of the revelations (to me at least) from Marshall and Ford's book was that the Mustang I came equipped with optional internal auxiliary fuel tanks that could increase its ferry range to over 1,700 miles, meaning it could fly straight to Malta from southern England, to Murmansk from the Shetland Islands, or, from Hawaii, to Midway or virtually anyplace on the way to Australia without drop tanks (the South Pacific Air Route, which started operation in Jan 1942 was max 1200 miles each leg west of Hawaii). In 1942 just getting fighters where they were needed was a major problem.

The second part of my study deals with...well, I'll leave that for later.

Just to quickly comment on a few things I have seen in this thread:

1. Kindelberger wrote Arnold just days after Pearl Harbor offering to triple Mustang production rate within weeks if the AAF gave him the orders (indicating they were currently operating on a single shift). And, no, the "they ran out of budget for more fighters" story doesn't holds up well IMO, but I'll also leave that for later.

2. An earlier post links to a wartime document regarding the Mustang ("war-memo" E-GEH-16) dated 26 August 1943, on the subject of running the Allison at higher manifold pressures, but the original document was dated 20 June 1943 (TNA AIR 23/7323) and also expounds upon "exceptionally low R.P.M." capabilities of the Allison vs the Merlin (which gave the Mustang I extra range), the Allison's reliability (bearing life 2.5 times the Spitfire, for instance) and also the relative performance of the Mustang I against current GAF SE fighters, based on combat experience ("can run way from anything the Germans have" and also out turn either of the German SE fighter types - though, of course, not out climb them),

3. I believe that someone mentioned the Allison Mustangs being used in the recce role. An RAF document from early 1944 (AIR 37/636) holds that an a/c in this role "must be the fastest aircraft in the sky at their operational altitudes (fighter reconnaissance 5000-12000 ft)" and continues that the most timely, accurate and comprehensive results only come when the recce pilot has confidence he is flying the fastest aircraft. Here we see a crucial capability for fighters where high-altitude performance is completely irrelevant. And once again, we see the outstanding performance of the original Mustang: even though it is a type that first came off the assembly line almost two and a half years previously, testing summarized in the report shows the Mustang I still faster at 5,000 ft. than all British types evaluated, the Typhoon, Spitfire IX LF and Spitfire XIV; the only a/c to best it (and by a considerable margin) was the Allison engined Mustang II. Really the document was of the tenor "what are we going to do when we run out of Mustang I's and II's?" For that reason alone the Allison Mustangs ought to have been kept in production, or, at least, the Mustang II/P-51A given a longer production run (only 340 produced out of an original contract for 2,000). Why is it Ok to produce both Allison and Merlin P-40's, but not P-51's?

4.

To your earlier question about the Allison two speed/two stage engine introduced much earlier into the Mustang line, it was impossible to replace the Merlin type integral two speed/two stage supercharger engine design because the Allison auxiliary supercharger design was too long, altered forward CG too much and required a major redesign of the airframe to move the wing forward.

But the original question was specifically NOT about a two speed/two stage engine, but rather a single stage/two speed one. The original question assumes, as was the case, that the two-stage/two-speed solution was technically far more difficult to implement but was wondering, as I was, how practicable a single-stage/two-speed upgrade to the the Allison would be. Really the s/c type on the Allison is only a minor side issue for me, but it's still interesting and hoping drgondog can shed some light on that now that (hopefully) it's clear what the question really is.

Sorry, this ran on longer than intended, though I am sure I still left myself open to a lot of "yes, but" replies that I am not going to take the time to rebut in advance.

 

[ggiumarra]

I could not get an image of an RAF doc to upload that shows relative performance of various Mustang variants (I at various manifold pressures, incl. "overboost", II, P-51B) as well as the 109F and 190, but I will keep trying.

 

[ggiumarra]

--
Success! Hopefully of some interest (AIR 23/7323)

 

[MiTasol]

I tend to work with TIFF files and they will never upload so check what format the file is. Been caught with this many times so this is one possible scenario as there is often no error message..

 

[MiTasol]

It is 55 years since I saw the inside of the back end of the crankcase on an Allison and my memory is far from perfect. GregP will probably tell me I am wrong but my memory is that there are two or three shafts that extend out of the accessory housing and enter bearings mounted in the crankcase.

This may be one of the reasons that Allison did not appear to want to design a two speed single stage engine. IF that two speed engine required an additional shaft entering the crankcase, or, even more so, required moving one of the existing shafts, that would require the redesign of one or both the crankcase halves and the addition of certain manufacturing tools and factory floor space. The older tools must be kept to support the existing engines. That in turn would remove the interchangeability of parts between models which Allison were very proud of. Even the change from E to F engines involved a very small number of parts and was very simple in a good workshop. Many E and later parts were even usable on the early A through D engines. Unlike with Merlin's, and probably all the other V-12 engines, it is possible to use most parts off later Allison E & later engines on earlier E & later engines. Likewise the only differences between the left and right hand Allison's was one internal gear, two ancillaries and the wiring of the ignition harness. On most, if not all, Merlin's this required the design and manufacture of a different crankcase and/or reduction gear as well as other less drastic changes. One part fits all is far cheaper and more efficient to produce and support than one part fits only a small subset of engines.

 

[Engineman]

It's funny, but I have been pondering this subject (the original question about a single stage/two speed supercharge for the Allison in 1942) for at least a year now and finally got around to asking an acknowledged expert in the field (via a DM on a social media site) about this about a month ago but, unfortunately, either because I failed in both my messages to him to make myself clear or some other reason all I got back was a very broad explanation about superchargers generally and a promise that he would reach out to William Marshall and get back to me with his answer (I never heard anything back on that), which was ironic because it was Marshall's (and coauthor Ford's) book on the P-51B that had really got me seriously thinking about it to begin with (although I believe the idea had occurred to me previously). As it turns out I got much more useful information on the subject when I finally came across this thread a couple of days ago.

Surprisingly, unless I missed it, no one here has noted that on p. 165-6 of P-51B Mustang: North American Aviation's Bastard Stepchild that Saved the 8th Air Force, (the Marshall and Ford book I just referred to) it recounts an exchange between Allison Chairman O. E. Hunt and NAA's President Dutch Kindelberger in March of 1941 in which Allison offers NAA a two-stage/two-speed Allison engine - apparently a design it's already working on, or at least needing a potential customer so it can justify working on it - while NAA requests a single stage/two speed supercharged solution (due to the very significant and therefore unwanted design changes the two-stage/two-speed would entail). In frustration at Allison's refusal to pursue the less technically challenging solution, Kindelberger fires off a message to the British Purchasing Commission for information on the Merlin engine and the following month they receive an 18-page technical document from RR with details of the Merlin XX (which most of you reading this know, has a single-stage/two-speed s/c and was also the basis of the Packard Merlin that went into the P-40F and L). So there you have, from what I can tell, the first initiative to get a Merlin, albeit a less advanced one than it eventually had, into the P-51 and it was in the spring of 1941, and some info highly relevant to the original question, I think.

Before I go any further I should mention that I have been doing research and writing a study on problems with RAF and AAF fighter doctrine and production policy during WWII through the prism of the Mustang. The first part takes on the myth that the Allison Mustang represented little better than a stepping-stone to the Merlin Mustang. In short the three reasons the original Mustang would have been so very useful, particularly in 1942: range, range and range. Sure the original P-51 was a overall a better performer than the P-40 or P-39 but even if it had been somewhat inferior to both its decidedly superior range was a compelling reason for the AAF to acquire and employ them (think the war vs Japan just about anywhere) and for the RAF to use them properly, especially when it came to convoy protection (think a little bit Murmansk and a lot Malta, though in the latter case there is a lot more to the story than "they should have used their Mustang I's" and the idea would be to supplement, not replace the Spitfires there), instead of effectively burying them in the Army Cooperation Command. I should add that the range capability also applied to the fundamental factor of deploying them to begin with. One of the revelations (to me at least) from Marshall and Ford's book was that the Mustang I came equipped with optional internal auxiliary fuel tanks that could increase its ferry range to over 1,700 miles, meaning it could fly straight to Malta from southern England, to Murmansk from the Shetland Islands, or, from Hawaii, to Midway or virtually anyplace on the way to Australia without drop tanks (the South Pacific Air Route, which started operation in Jan 1942 was max 1200 miles each leg west of Hawaii). In 1942 just getting fighters where they were needed was a major problem.

The second part of my study deals with...well, I'll leave that for later.

Just to quickly comment on a few things I have seen in this thread:

1. Kindelberger wrote Arnold just days after Pearl Harbor offering to triple Mustang production rate within weeks if the AAF gave him the orders (indicating they were currently operating on a single shift). And, no, the "they ran out of budget for more fighters" story doesn't holds up well IMO, but I'll also leave that for later.

2. An earlier post links to a wartime document regarding the Mustang ("war-memo" E-GEH-16) dated 26 August 1943, on the subject of running the Allison at higher manifold pressures, but the original document was dated 20 June 1943 (TNA AIR 23/7323) and also expounds upon "exceptionally low R.P.M." capabilities of the Allison vs the Merlin (which gave the Mustang I extra range), the Allison's reliability (bearing life 2.5 times the Spitfire, for instance) and also the relative performance of the Mustang I against current GAF SE fighters, based on combat experience ("can run way from anything the Germans have" and also out turn either of the German SE fighter types - though, of course, not out climb them),

3. I believe that someone mentioned the Allison Mustangs being used in the recce role. An RAF document from early 1944 (AIR 37/636) holds that an a/c in this role "must be the fastest aircraft in the sky at their operational altitudes (fighter reconnaissance 5000-12000 ft)" and continues that the most timely, accurate and comprehensive results only come when the recce pilot has confidence he is flying the fastest aircraft. Here we see a crucial capability for fighters where high-altitude performance is completely irrelevant. And once again, we see the outstanding performance of the original Mustang: even though it is a type that first came off the assembly line almost two and a half years previously, testing summarized in the report shows the Mustang I still faster at 5,000 ft. than all British types evaluated, the Typhoon, Spitfire IX LF and Spitfire XIV; the only a/c to best it (and by a considerable margin) was the Allison engined Mustang II. Really the document was of the tenor "what are we going to do when we run out of Mustang I's and II's?" For that reason alone the Allison Mustangs ought to have been kept in production, or, at least, the Mustang II/P-51A given a longer production run (only 340 produced out of an original contract for 2,000). Why is it Ok to produce both Allison and Merlin P-40's, but not P-51's?

4.


But the original question was specifically NOT about a two speed/two stage engine, but rather a single stage/two speed one. The original question assumes, as was the case, that the two-stage/two-speed solution was technically far more difficult to implement but was wondering, as I was, how practicable a single-stage/two-speed upgrade to the the Allison would be. Really the s/c type on the Allison is only a minor side issue for me, but it's still interesting and hoping drgondog can shed some light on that now that (hopefully) it's clear what the question really is.

Sorry, this ran on longer than intended, though I am sure I still left myself open to a lot of "yes, but" replies that I am not going to take the time to rebut in advance.

Hi,
If you have not already consulted it, you should obtain the RRHT Historical book "ROLLS-ROYCE and the MUSTANG" by the late David Birch. This book sets out much of the story from the RR and British side.
According to Hooker, the development of the 2-Stage Merlin was initiated by RR in 1940 when RR were asked to consider Turbocharging the Merlin for the high altitude pressurised Wellington VI bomber development. Hooker wrote that although the turbocharging prospect had positive aspects, the Merlin was optimised for the ejector exhaust operation and Hooker realised that a redesign to 2-stage supercharging using the large Vulture supercharger rotor as the first stage was possible. This design process led to the first development 2-stage Merlins being built in 1941.

Eng

 

[drgondog]

It's funny, but I have been pondering this subject (the original question about a single stage/two speed supercharge for the Allison in 1942) for at least a year now and finally got around to asking an acknowledged expert in the field (via a DM on a social media site) about this about a month ago but, unfortunately, either because I failed in both my messages to him to make myself clear or some other reason all I got back was a very broad explanation about superchargers generally and a promise that he would reach out to William Marshall and get back to me with his answer (I never heard anything back on that), which was ironic because it was Marshall's (and coauthor Ford's) book on the P-51B that had really got me seriously thinking about it to begin with (although I believe the idea had occurred to me previously). As it turns out I got much more useful information on the subject when I finally came across this thread a couple of days ago.

Surprisingly, unless I missed it, no one here has noted that on p. 165-6 of P-51B Mustang: North American Aviation's Bastard Stepchild that Saved the 8th Air Force, (the Marshall and Ford book I just referred to) it recounts an exchange between Allison Chairman O. E. Hunt and NAA's President Dutch Kindelberger in March of 1941 in which Allison offers NAA a two-stage/two-speed Allison engine - apparently a design it's already working on, or at least needing a potential customer so it can justify working on it - while NAA requests a single stage/two speed supercharged solution (due to the very significant and therefore unwanted design changes the two-stage/two-speed would entail). In frustration at Allison's refusal to pursue the less technically challenging solution, Kindelberger fires off a message to the British Purchasing Commission for information on the Merlin engine and the following month they receive an 18-page technical document from RR with details of the Merlin XX (which most of you reading this know, has a single-stage/two-speed s/c and was also the basis of the Packard Merlin that went into the P-40F and L). So there you have, from what I can tell, the first initiative to get a Merlin, albeit a less advanced one than it eventually had, into the P-51 and it was in the spring of 1941, and some info highly relevant to the original question, I think.

Before I go any further I should mention that I have been doing research and writing a study on problems with RAF and AAF fighter doctrine and production policy during WWII through the prism of the Mustang. The first part takes on the myth that the Allison Mustang represented little better than a stepping-stone to the Merlin Mustang. In short the three reasons the original Mustang would have been so very useful, particularly in 1942: range, range and range. Sure the original P-51 was a overall a better performer than the P-40 or P-39 but even if it had been somewhat inferior to both its decidedly superior range was a compelling reason for the AAF to acquire and employ them (think the war vs Japan just about anywhere) and for the RAF to use them properly, especially when it came to convoy protection (think a little bit Murmansk and a lot Malta, though in the latter case there is a lot more to the story than "they should have used their Mustang I's" and the idea would be to supplement, not replace the Spitfires there), instead of effectively burying them in the Army Cooperation Command. I should add that the range capability also applied to the fundamental factor of deploying them to begin with. One of the revelations (to me at least) from Marshall and Ford's book was that the Mustang I came equipped with optional internal auxiliary fuel tanks that could increase its ferry range to over 1,700 miles, meaning it could fly straight to Malta from southern England, to Murmansk from the Shetland Islands, or, from Hawaii, to Midway or virtually anyplace on the way to Australia without drop tanks (the South Pacific Air Route, which started operation in Jan 1942 was max 1200 miles each leg west of Hawaii). In 1942 just getting fighters where they were needed was a major problem.

The second part of my study deals with...well, I'll leave that for later.

Just to quickly comment on a few things I have seen in this thread:

1. Kindelberger wrote Arnold just days after Pearl Harbor offering to triple Mustang production rate within weeks if the AAF gave him the orders (indicating they were currently operating on a single shift). And, no, the "they ran out of budget for more fighters" story doesn't holds up well IMO, but I'll also leave that for later.

2. An earlier post links to a wartime document regarding the Mustang ("war-memo" E-GEH-16) dated 26 August 1943, on the subject of running the Allison at higher manifold pressures, but the original document was dated 20 June 1943 (TNA AIR 23/7323) and also expounds upon "exceptionally low R.P.M." capabilities of the Allison vs the Merlin (which gave the Mustang I extra range), the Allison's reliability (bearing life 2.5 times the Spitfire, for instance) and also the relative performance of the Mustang I against current GAF SE fighters, based on combat experience ("can run way from anything the Germans have" and also out turn either of the German SE fighter types - though, of course, not out climb them),

3. I believe that someone mentioned the Allison Mustangs being used in the recce role. An RAF document from early 1944 (AIR 37/636) holds that an a/c in this role "must be the fastest aircraft in the sky at their operational altitudes (fighter reconnaissance 5000-12000 ft)" and continues that the most timely, accurate and comprehensive results only come when the recce pilot has confidence he is flying the fastest aircraft. Here we see a crucial capability for fighters where high-altitude performance is completely irrelevant. And once again, we see the outstanding performance of the original Mustang: even though it is a type that first came off the assembly line almost two and a half years previously, testing summarized in the report shows the Mustang I still faster at 5,000 ft. than all British types evaluated, the Typhoon, Spitfire IX LF and Spitfire XIV; the only a/c to best it (and by a considerable margin) was the Allison engined Mustang II. Really the document was of the tenor "what are we going to do when we run out of Mustang I's and II's?" For that reason alone the Allison Mustangs ought to have been kept in production, or, at least, the Mustang II/P-51A given a longer production run (only 340 produced out of an original contract for 2,000). Why is it Ok to produce both Allison and Merlin P-40's, but not P-51's?

4.


But the original question was specifically NOT about a two speed/two stage engine, but rather a single stage/two speed one. The original question assumes, as was the case, that the two-stage/two-speed solution was technically far more difficult to implement but was wondering, as I was, how practicable a single-stage/two-speed upgrade to the the Allison would be. Really the s/c type on the Allison is only a minor side issue for me, but it's still interesting and hoping drgondog can shed some light on that now that (hopefully) it's clear what the question really is.

Sorry, this ran on longer than intended, though I am sure I still left myself open to a lot of "yes, but" replies that I am not going to take the time to rebut in advance.

Thoughtful post. There were a lot of moving parts behind the Arnold/Kindelberger/Echols/Allison/R-R dialogues between May 1941 and May 1942. Some that come to mind include;

1. A very strained relationship between NAA and Allison that traced back to Allison's cavalier attitude about not meeting the contactual delivery date for the V-1710-39 of early September 1940 for the X-73, resulting in dialogue between BPC/War Ministry support to draw one from AAC inventory and deliver 1 October. To add to the strain, the V-1710-39 that was delivered did not conform to Allison design documents, resulting in mandatory changes to the engine bay to enable installation and run-up testing which further delayed flight testing for nearly a month. Last Allison was 'unapologetic' in the view of NAA.

The stated desire for the two speed/single stage approach by NAA was based minimizing airframe changes with zero associated commitment by Mat.Cmd. (Echols) to buy a new version when they were in the process of evaluating the Mustang I. Further complicating the design discussions were the underlying attitude that Allison was a poor partner that could not meet commitments and had a very poor field service/support team based on NAA experience to date. The comment by Kindelberger/Atwood that they would prefer the 'simpler solution' was to set the stage to go outside from the family and pick a perceived more reliable Merlin XX for the upgrade. The proposed Allison Allison V-1710-47 which was first installed and delivered in the XP-63 May 43 was far too long to install forward of the NA-73/83/91 airframe and would impose an unacceptable forward CG, requiring a major re-design of the aft frame to accommodate moving the wing forward as well as changes to the horizontal stabilizer location to accommodate the wing movement's impact to static margins.

The desire to incorporate the Merlin in the Mustang was stimulated by the evaluation and approval of better quality and performance and a knowledge that the Merlin 60 discussions were in process between Packard and R-R. That said, perhaps unbeknownst to Kindelberger and Atwood was the simple fact that the combined political sway Curtiss still had with Echols, and Echols refusal to buy the P-51 for the AAF guaranteed that NAA would not receive a priority to compete for V-1650-1 engines, nor woul they be allocated a share of the British allocations for Canada built airframes for RAF. In any case the question is moot as GMC quashed the project.

Allison was motivated to secure orders to replenish existing P-39 and P-40 markets with a new airframe ordered by Mat.Cmd, and were somewhat successful at teaming up with Bell for the V-1710-47 2 speed/single stage with Auxiliary supercharger delivered in XP-63. IIRC the P-40Q may have been supplied with a version of that engine. Somebody else can add/subtract from that memory.

IIRC the Echols sponsored XP-46 did consume the rest of FY41/42 Fighter budget, but HQ-Plans Division in late 1942 was increasingly frustrated by Echols R&D management for both pursuit and attack aircraft in late 1941. NAA had insight which in turn led to investing in the NA-97 preliminary design beginning in October 1941. Coincidentally Eaker was tasked to command 8th BC at the end of the year and while leaving the 20th PG he visited NAA, flew the Mustang and was very impressed with it relative to P-40 and P-39 - and so stated to Arnold and Spaatz stimulating a visit in January 1942.

The combined frustration of failed delivery to expectations by Echols, combined with politically stimulated desire to meet/exceed CAS capability of Luftwaffe, combined with perhaps vague desire by Arnold to keep the NAA Mustang line open for contingency led to the A-36 discussions - but IMO the real influence was Arnold's briefing by Winant/Hitchcock and the Air Staff of RAF on the proposed Merlin conversion effort in May when he and Adm Tower were in London. Winant urged Arnold and Asst Secy War Lovett to sponsor both the Mustang and the Merlin Mustang parallel project at NAA.

The XP-78/51B and A-36 and P-51A contract convertible to P-51B efforts all converged in April through June, 1942 despite Mat.Cmd. resistance - which was crushed by Gen Fairchild in Military Requirements and supported by Arnold. Perhaps notable is that the XP-75 discussions were on-going between Echols and GMC/Fisher. Notable is that Priority A-1 was given to NAA for the first two V-1650-3 in June, cutting off potential Curtiss allocations for the time being.

Allison appealed to GMC to once again intervene and NAA team walked through the 'reasons for', not the least being the Military Requirements sponsorship for the P-51B to replace the P-39/40 and A-36 as the 'battlefield superiority fighter for the future - ensuring orders for NAA airframes above and beyond British interests. In early 1943 the AAF was evaluating the Mark 10 and receiving high marks from Air Service Command as potential high altitude escort fighter to compliment the P-38.

As to the question of Arnold's involvement in the Mustang story. The timeline shows that Arnold's involvement in directing priority toward NAA in both the A-36 and the XP-78/P-51B projects were important. Curiously he does not take credit for the P-51B but it is implicit in his works that Bob Lovett had Great influence on many AAF procurement decisions and both Lovett and Winant were on record advising Arnold how important the Merlin conversion, if successful, would be as a long range high performance fighter. The allocation of Priority 1 for the XP-78 project followed Lovett's letter of June 11 to Arnold, so stating his perceived importance .Lovett, according to Arnold was also the sponsor for AAF development of a superior CAS combined with battlefield air superiority capability leading to acceptance of the A-36.

He states that 'it was our fault that we didn't buy it earlier', but equally clear that contracts for A-36, P-51A, P-51B-1, P-51C-1 and XP-78/P-51B were all executed before his alleged discussions with Roosevelt - theoretically stimulated by Hitchcock's memo of October 1942.

 

[Engineman]

Hi,
If you have not already consulted it, you should obtain the RRHT Historical book "ROLLS-ROYCE and the MUSTANG" by the late David Birch. This book sets out much of the story from the RR and British side.
According to Hooker, the development of the 2-Stage Merlin was initiated by RR in 1940 when RR were asked to consider Turbocharging the Merlin for the high altitude pressurised Wellington VI bomber development. Hooker wrote that although the turbocharging prospect had positive aspects, the Merlin was optimised for the ejector exhaust operation and Hooker realised that a redesign to 2-stage supercharging using the large Vulture supercharger rotor as the first stage was possible. This design process led to the first development 2-stage Merlins being built in 1941.

Eng

It is also possible to note, that the early 2-Stage Merlin developments were one-piece cylinder block engines, designed originally for a FTH of 30,000' and were not suitable for very high Boost, but were aimed at about 1000hp @30.000'. However, I think it is interesting to consider how much the desire to improve the Spitfire performance led pressure for RR to push forward with the Merlin 2-piece block and the later High Boost performance improvements. I would expect that the combined pressure of Spitfire IX and Merlin Mustang requirements
led to the full development and great performance of the 25lb Boost late 2-Stage Merlin.

Eng

 

[ThomasP]

re

. . . even though it is a type that first came off the assembly line almost two and a half years previously, testing summarized in the report shows the Mustang I still faster at 5,000 ft. than all British types evaluated, the Typhoon, Spitfire IX LF and Spitfire XIV; the only a/c to best it (and by a considerable margin) was the Allison engined Mustang II. Really the document was of the tenor "what are we going to do when we run out of Mustang I's and II's?" For that reason alone the Allison Mustangs ought to have been kept in production, or, at least, the Mustang II/P-51A given a longer production run (only 340 produced out of an original contract for 2,000). Why is it Ok to produce both Allison and Merlin P-40's, but not P-51's?

Was there an Allison engined Mustang II?

FWIW

re a 2-speed Allison

There was no (obvious to me) industrial/engineering based problem with developing a 1-stage/2-speed supercharger for the Allison. The only question is how efficient the SC would be based on Allison's knowledge at the time and what they had to work with in terms of money, materiel, and time. So would it be worth it in terms of money, time and material - both directly in the engine redesign & manufacture, and/or the needed redesign of airframes to accommodate the new engine?

In 1940(?) US Materiel Command had already noted that the Allison SC was significantly less efficient that RR's, and memos were exchanged within the various government agencies concerned that no further major investment in development of the Allison engine should be made by the Government.

The Merlin XX/V-1650-1 was fitted to the production P-40F/L, and to a P-51 prototype by RR in the UK (I think?), plus couple of prototypes of other US airframes (sorry, I do not remember which ones at the moment). In the prototypes of the P-40 and P-51 both, it was done without much trouble, though some redesign of the forward fuselage was required. IMO this proves there was no 'significant' problem doing so.

Much of Henry Ford's refusal to build Merlins for the British has been attributed to Henry not being willing to make war materiel for foreign countries, but (IMO) this was just an excuse, it was as much NIBUS (Not Invented By Us Syndrome). It is telling that he was prepared to build the Merlin XX until he showed his redesigned version and it was found unacceptable. Part of the real reason was probably greed - building an engine to a foreign design meant that he could not claim the design as his own - he could build it only under license and hence control and royalties would be owed to RR (and/or Farman?). He was also a not-so-closet anti-semite and Nazi sympathizer. (Henry Ford was one of the conspirators named in the 1934-35 Business Plot, during the subsequent Congressional investigation into said plot.) When the US entered WWII major industries were informed (in one way or another) by the US government that their participation was no longer voluntary.

Allison(GM) also suffered from NIBUS. They could have copied the RR designed 1-stage/2-speed SC used on the Merlin XX series, or later the 2-stage/2-speed SC used by the Merlin 60 series, but refused to do so. Instead they pushed their own 2-stage design - which was considerably heavier, more bulky, and less efficient than RR's. In terms of war effort this makes absolutely no sense, unless you are acknowledging that your engine is inferior to the RR designs.

As drgondog mentions above, the USAAF & Materiel Command had decided the Merlin P-51 was to be the 'battlefield superiority fighter' of choice, and after that point in time there was really no point in further development of the V-1710 other than what was already being done - to the point where there was no real reason to develop the 2-stage for the Allison into the post-war period - the current Merlin 2-stage SC was still superior so the only reason left was NIBUS & profits. (Again. IMO, the commonly expressed excuse of having to pay royalties on the Merlin is bogus due the the US being easily able to demand not having to pay license fees in exchange for forgiveness of some of the UK's debt - the % would have been unnoticeable in comparison to the total debt - and/or other trade exchange favors. The UK government would have told RR to suck it up.)

 

[drgondog]

re

Was there an Allison engined Mustang II?

Yes - P-51A = Mustang II

As drgondog mentions above, the USAAF & Materiel Command had decided the Merlin P-51 was to be the 'battlefield superiority fighter' of choice, and after that point in time there was really no point in further development of the V-1710 other than what was already being done - to the point where there was no real reason to develop the 2-stage for the Allison into the post-war period - the current Merlin 2-stage SC was still superior so the only reason left was NIBUS & profits. (Again. IMO, the commonly expressed excuse of having to pay royalties on the Merlin is bogus due the the US being easily able to demand not having to pay license fees in exchange for forgiveness of some of the UK's debt - the % would have been unnoticeable in comparison to the total debt - and/or other trade exchange favors. The UK government would have told RR to suck it up.)

Minor correction. Early 1942 Plans Division and Close Air Support group agreed that a.) a change to battlefield doctrine required fast pursuit type capable of both CAS and battlefield air superiority - Mat.Cmd. was focused on the fat and slow but heavily armed Brewster XA-32 which Military Requirements did NOT want. CAS determined that while the A-36 was just fine as interim solution, that CAS doctrine moved from dive bomber capable to high speed 'slant' bombing - hence the P-51A. That said, decision for P-51A long run was dependent on the P-51B failing to meet expectations. But they hedged the bet by agreeing with NAA to switch the P-51A production to P-51B at AAF request.

 

[ggiumarra]

Was there an Allison engined Mustang II?

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.

 

[ggiumarra]

Since this thread seems to be still active with participants that have detailed knowledge on the subject, forgive me for posting here an appeal to anyone who has a copy of the late 1941 AAF pursuit board report and/or the early 1942 Arnold document where he calls for greater range for fighter a/c. I see both referred to in various works, but me being me, I would very much like to see the full text of those documents.

 

[Steamed_Banana]

--
Success! Hopefully of some interest (AIR 23/7323)

View attachment 873623

The big question for me is given this clearly outstanding performance (this is much faster than i was aware of for the P-51A!) and it's superior range, plus per your comment apparently good turning performance compared to German fighters (do you have any numbers for that, as in turn times?) 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. Especially considering many (though definitely not all) of the pilots flying them for 1st Air Commando Group and 23rd FG were quite experienced. Not sure if the 51st FG ever got any.

The A-36 also had some significant potential I think, though strengthening wings may have been a more substantial change.

I can provide some examples of the operational history over Burma if needed. The crazy thing is that on a couple of occasions Ki-43s seem to have shot down P-51As after long chases. They did the same thing to P-38s!

I have read about an issue with ailerons which seems to be confirmed in this thread (and it was apparently more than just an issue with rigging, some changes to the aileron mounting were done to the P-51B per a comment up-thread.


It's extremely interesting that they did in fact look at using Merlin XX (do we know where this happened precisely?) and possibly even test-fit one on a Mustang and also per ThomasP that

They [Allison] could have copied the RR designed 1-stage/2-speed SC used on the Merlin XX series, or later the 2-stage/2-speed SC used by the Merlin 60 series, but refused to do so.

Do you have a source or anything verifying this? And a date we can peg this to? Because if so it's pretty key to the whole thread. If it boils down to Allison just not wanting to adopt elements of a foreign design that is really something!

 

[Geoffrey Sinclair]

Ford in Britain built its first Merlin in August 1941. The Mustang requirement included pilot and fuel protection from the start, avoiding the need for retrofits, add it was using the relatively proven Allison engine and supercharging.

Why is it Ok to produce both Allison and Merlin P-40's, but not P-51's?

There are a number of reasons including people at the time making predictions about the future. The P-40 was the interim USAAF fighter, a P-36 update that could be around in numbers in 1940/41/42, until the P-38 and in particular P-47 could take over. The early fighting in Europe stressed altitude performance, the single stage Merlin was a way to boost the P-40. Curtiss built the P-40F January 1942 to January 1943, the P-40L January to April 1943, first P-47B accepted in December 1941, then 5 in March 1942 then production from May, the Curtiss line opened in September, Evansville in October, first P-51B accepted in April 1943.

P-40 production, 1940 to 1942, 778, 2,246, 4,454, P-51 0, 138, 634. Getting any P-51 in 1941 or 1942 was a bonus and the 2 speed 2 stage Merlin was the obvious upgrade choice. In numerical terms the P-51 was a 1944 fighter and even then considered in short supply. To get Inglewood into B-25 and P-51 production required moving AT-6 to Dallas, to get the factory into mass P-51 production meant moving B-25 production to Kansas City. To get Dallas into mass P-51 production required ending B-24 production aided by the wind down in trainer requirements. For Allison Mustang production to continue into 1943/44 required another production line or taking over an existing line, preferably one using Allison engines at a time the allies considered themselves short of fighters. While the British might be impressed with Allison Mustang low level performance the USAAF tactical reconnaissance unit Mustangs in France in 1944 mostly used Merlin with a few Allison.

320 Mustang I/NA-73, 300 Mustang I/NA-83, 148 P-51/Mustang IA, 500 A-36A, 310 P-51A/Mustang II

When it comes to US single stage Merlin production for the British most ended up in Lancasters, when it comes to placing orders for the engines as of 1940 the RAF was going to use Vulture Manchester, Merlin Halifax and Hercules Stirling, during 1941 Manchester became Merlin Lancaster, during 1943 Merlin Halifax became Hercules Halifax. At several thousand aircraft a year times 4 engines that is a lot of adjustments, cutting planned Stirling production in favour of Lancaster would up Merlin requirements by 700 engines a month for example., throw in the need for more Hurricanes due to the problems with the Sabre Typhoon.

The British Merlin Mustang time line.

10 May 1941, RAF Chief of Staff to Ministry of Aircraft Production, future needs, "With fighters, height is gauged important", the most promising a Spitfire with ceiling exceeding 40,000 feet ,"These ceilings are not an inch too high". During the Battle of Britain and particularly in October heights had gone up, ultimately to Bf109 being reported at around 30,000 feet.

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. Limits on Mustang numbers and requirements for a possible 1943 invasion of France added to the decision to keep the Mustang out of Fighter Command at the time. End February 1943 there were 713 Mustang received, 107 lost, 302 were with Army Co-Operation Command, 1 with Bomber and 7 with Fighter Command, another 78 were being assembled.

October 1941 First Mustang arrives in Britain, 7 more in November, 24 more in December.

24 January 1942, RAF orders 10 Army Co-Operation squadrons equipped with Mustangs.

Rolls Royce performance estimates of Merlin Mustang, April 1942. Air Vice Marshall Wilfrid Freeman becomes very interested and starts briefing key Americans.

(6 June 1942, Winant's cable to Hopkins and Arnold talked Merlin 28 and 61.)

Air Vice Marshall Linnell formally informs the US Merlin Mustangs a good idea, 9 June 1942.

3 RAF Merlin Mustang conversions were ordered on 15 June 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, 20 July 1942.

Air Marshall Richard Williams, RAAF representative in Washington, in a letter dated 20 July 1942 notes "The improved Mustang with Merlin 61 engine will not be in production until 1943." It was part of a section discussing the need for fighters with performance at altitude to counter the Zero. Apparently the local USAAF had asked for P-47 and were being sent P-38 "reported everywhere as being heavy in maintenance."

August 1942 General Echols inspects Merlin Mustang prototypes at Rolls Royce Hucknall.

British order request for 120 engineless Mustang airframes a month for Britain and up to 200 a month for overseas theatres 27 August 1942. RAF talks about an order for 3,000 Merlin Mustangs, half for the RAF.

2 P-51 airframes officially accepted as XP-51B prototypes, August 1942, to await engines.

16 September, Churchill to Roosevelt, "the Fortress and long range fighter are indispensable"

British request for bulk Merlin Mustangs 8 October 1942.

Mustang X first flight 13 October 1942.

Churchill request to Hopkins for Merlin Mustangs 16 October 1942, after 6 Mustang X test flights.

British request for 400 engineless Mustang airframes to be sent and converted to use Merlins. 5 November 1942. Around this time Rolls Royce laid out ideas for a Merlin 28 version given possible Merlin 60 series supply issues.

XP-51B first flight 30 November 1942.

 

[Steamed_Banana]

I am sure it would have been tricky but any single speed Allison engined Mustang could safely be replaced by two speed Allison-engined Mustang, whether for British or US use. It would do anything the single speed version could do, but also much more. Even just a few hundred of these would have been very valuable.

 

[Howard Gibson]

I am sure it would have been tricky but any single speed Allison engined Mustang could safely be replaced by two speed Allison-engined Mustang, whether for British or US use. It would do anything the single speed version could do, but also much more. Even just a few hundred of these would have been very valuable.

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?