Quote:
The main problems with the P-39 were lack of supercharger which limited its performance over 20,000ft
Another myth perpetuated!
Anyone who has had anything to do with the Allison engine, as fitted to the P-39 and P-40, ie the 'E' and 'F' series engines, will tell you that it has a single stage, single speed supercharger. Even the "long nose" 'C' series engines were supercharged. The problem is that the engine was originally specified and designed to be used with a turbocharger, as in the P-38 Lightning, which would then give you the altitude performance.
Rolls Royce got the jump on the development of the Merlin from the single stage, single speed supercharged engine, to adding the gearbox for the two speed supercharger, to finally adding the second stage compressor and intercooler to produce the 60 series Merlin, because the British needs for performance were far more urgent and government cash was made available.
Allison developed the equivalent to the 60 series Merlin in the 'G' series, which had a two stage intercooled supercharger, driven by a constantly variable ratio hydraulic drive. Unfortunately, this engine was a little too late and it was also longer, making it not economical to redesign and retool the Mustang, which was being ramped up in production.
The P-82 Twin Mustang was designed to use the 'G' series engine (although the XP-82 flew with Merlins - see Tom Reilly's great project!) and flew with great success.
One needs to understand that a lot of progress happened in quite a short period of time.
I recommend reading Dan Whitney's terrific book "Vee's for Victory!" on the development of the Allison and the Rolls Royce Heritage Trust "The Merlin in Perspective".