The Mustang MkI had an Allison engine because of two key reasons. Firstly, the British Purchasing Commission sent to the USA in 1938 was vastly inexperienced in modern fighter design, their main priority being to buy just about anything available. Secondly, when the BPC's engineers sat down with John Attwood of NAA to flesh out the Mustang spec between January and April 1940, no-one in that team (or, indeed probably anyone) had realised how important altitude performance was going to become in the ETO by the end of the Battle of Britain. If they had of, they would never have ordered any of the available American designs. Instead, they were operating with the little data available from fighting in Poland, which had involved lots of low-level action, and didn't have any reason to suspect the Allison would make the Mustang as altitude-crippled as the P-40. After all, the BPC had originally asked NAA to build P-40s, it was NAA whom insisted they could build something better. So, no, the British did not want a low altitude fighter, it's just all the Americans could offer.
Wildcat during the Battle of Britain
- Thread starter pinehilljoe
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GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
Going to have to do better than that 
Why? The only engines available in numbers in the USA in 1940 were the Allison, the Wright Cyclone and the Pratt & Whitney Twin Wasp. The latter two were draggy radials already reaching their design limits, which meant the choice was really down to the Allison. Even if the US government had approved exporting the turbocharger tech required to make the Allison work at altitude, the XP-37 showed the problems of trying to squeeze that much ducting into a small(ish) fighter. There was no point in building just airframes in the USA and then shipping engines from the UK because every Merlin was needed already for production in the UK. The only fighter in production in the USA with the Allison was the P-40, so that was the yardstick.Going to have to do better than that
The RAF could have had a winner if the P-39 had been built with the turbo, but it was crippled by NACA, who were totally centered on level speed over every other consideration. The Mustang MkI was better than the P-40, and was at least used in the ETO as a recce and ground-attack fighter, but it took the RR Merlin and British intervention to make it into the P-51B.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
The P-39 had a considerable amount of issues, there is no way it was going to be on the level of the P-40 (which served on ALL fronts from the start of the war to the finish) or the Mustang/P-51/A-36.
No amount of most postulating or Google/wiki searches will change historical fact.
My Great Uncle, who flew P-36s, transitioned into the P-39 and stated that "your life was not worth a plugged nickel in that bastard" (he went on to the P-38, btw) and while the P-39/P-400 had some success in the PTO, it was not a fighter that would have held up well in the ETO (not Eastern Front, where combat occurred at low to medium altitudes).
In regards to the P-40, it held it's own in the CBI, PTO, MTO, Aleutians and Eastern Front.
So while it might not have been ideal for northern European operations, it held it's own across the rest of the world...
No amount of most postulating or Google/wiki searches will change historical fact.
My Great Uncle, who flew P-36s, transitioned into the P-39 and stated that "your life was not worth a plugged nickel in that bastard" (he went on to the P-38, btw) and while the P-39/P-400 had some success in the PTO, it was not a fighter that would have held up well in the ETO (not Eastern Front, where combat occurred at low to medium altitudes).
In regards to the P-40, it held it's own in the CBI, PTO, MTO, Aleutians and Eastern Front.
So while it might not have been ideal for northern European operations, it held it's own across the rest of the world...
Shortround6
Major General
The P-40 was heavier than the other fighters you list. That affected the ceiling. Do not confuse cause and effect.Strange, then, that the service ceiling of the P-40C was lower than the Hurricane, Dewotaine 520, and ME109, given that you insist the Allison was at no disadvantage to the inline engines powering those other fighters.
The XP-40 came out of the failed XP-37 of 1937, which was the turbocharged Allison in a much-modified P-36 airframe. The XP-40 was a much simpler modification, but came with the Allison V-1710-19 pegged to a rated altitude of 11,000 feet. The P-40/B/C's V-1710-33 had a rated altitude of 12,800ft, lower than the Dewotaine 520's Hispano-Suiza 12Y-49 (rated altitude 17,224ft) and the Bf109E's DB601A (14,800ft). Sorry, but the high-altitude pursuit policy of the USAAC was turbocharged, fullstop. Everything else was meant for the low-level role.
Ratings for the V-1710-33 seem to be a bit scattered but include 1090hp at 13,200ft and 1040hp at 14,300ft.
There was some disagreement between Allison and the army over these ratings as the army wanted the Higher HP rating.
Which Db 601A? The A-0, the A-1 or the Aa?
we are also discussing what an airplane was 'designed" to do. The D. 520 was on it's 4th version of the Hispano engine when it got to the -49 version. most of the production models were built with the-45 engine which had a critical altitude of 4200 meters (and 920hp at that altitude) earlier prototypes had the -31 engine with a critical altitude of 3250 meters.
Both the P-40 and the P-39 were built with the highest altitude engines the Army could get at the time, while they waited for the trubo charger to become an item that could be used in squadron service. The Army did want the turbo, they just couldn't have it in 1939-40. rather than wait for any new fighters they bought the best altitude engine they could get.
Sorry, that is the way it was. Both planes were substitutes until the army could get what it wanted, that does not mean they were 'meant' for the low altitude role.
fastmongrel
1st Sergeant
Pre war what was considered high altitude, I am going to guess anything above 15,000 feet.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
You'll find that on average, pre-war ceilings ranged in the mid-20,000 foot range.
The B-18 (cutting edge for it's time) had a ceiling of 24,000 feet, the SM.79 was 24,500 feet, He111 was 21,500 feet and the Hampton and Wellington were 19,000 feet and 18,000 feet respectively.
With the introduction of better engines, more reliable oxygen systems and eventually, pressurized cabins, the altitudes increased considerably.
Admiral Beez
Captain
Circling back to the beginning. Put the Wildcat of 1942 into the BoB and you have something useful.
What's the point? The store is all sold out of time machines. I checked. "It is unknown when or if this item will be in stock again."
Admiral Beez
Captain
I know, but the whole premise of this thread needs a time machine.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
Again, Grumman G-36A (French F4Fs) were diverted from France to Britain and were assigned to 804 Naval Air Squadron based at Skaebrae in October 1940.
Even though 804 RNAS operated under RAF Fighter Command, they didn't see combat until December, downing two Ju88s off Scape Flow.
The Mustang was bought to be better than the P-40 and it was. It was still in use at the end of the war and its performance at low level was still impressive. That 21 miles of water raises the level of combat, once D-Day established a beach head things moved down, neither the Typhoon nor Tempest were optimised for high altitude, because they didn't need to be.
Shortround6
Major General
Put the Spitfire VC of 1942 into the BoB and you have something very useful, I will leave out the Spitfire IX
Shortround6
Major General
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
It was my understanding that the French Purchasing commission requested the Wright GR-1820-G205A, which had a single-stage, 2-speed supercharger, that was rated 1250hp.
The British Martlet (G-36B) had the P&W R-1830-S3C4--G (rated at 1,200hp.)
Why not a few P-47s as top cover too?Put the Spitfire VC of 1942 into the BoB and you have something very useful, I will leave out the Spitfire IX
Or a staffel of Me262s?
I think we have "time machine creep" here.
Why settle for halfway measures?
