P-40 Tiger Shark in RAF...

[mosquitoman]

Why wasn't the Allison as good as the Merlin at high altitudes?
I've always heard this but I don't know why

[cheddar cheese]

I think it was because of the Merlins two-stage supercharger.

Originally Posted by mosquitoman

Why wasn't the Allison as good as the Merlin at high altitudes?
I've always heard this but I don't know why

It was, as long as it had a two stage supercharger or a turbo-supercharger. The problem with most Allison engined planes earlier on in the War (P-39, P-40, P-51A) was that they had only a single stage supercharger. The P-38 is the exception, and it had good high-altitude performance from even the earlier models (though the pilot would freeze his butt off), because it included both a single stage supercharger plus a turbocharger acting as the second stage.

The P-39 was originally designed to have two stage supercharging or turbo-supercharging (I cannot recall which), but the idiots at the US ordinance commitee (Congress) thought they were also skilled at aircraft design and felt the scoops would hurt the aerodynamic lines of the plane and dictated they should be removed. This was rectified in the later P-63, which had good high alt performance.

=S=

Lunatic

[mosquitoman]

Thanks for that, I always wondered why they changed to a Merlin in the Mustang

Originally Posted by mosquitoman

Thanks for that, I always wondered why they changed to a Merlin in the Mustang

Because when the British specified the P-51 it was to be in the same class as the P-40, which meant only a single-stage supercharger (as also found on early Spitfires). Thus it was much easier to adapt the Merlin 65 engine, with it's internal supercharger stage, into the P-51 to have two stages of supercharging. If this had been done using the Allison, the plane would have had to have been more significantly modified to incorporate a 2nd external supercharger stage.

On the otherhand, the P-51 probably would have gotten a turbo-supercharger if it had not gone to the Merlin. it would probably have had to be located behind the engine, and the fuselage lengthened accordingly.

=S=

Lunatic

[GT]

Update.

[Bushranger]

In North Africa, 1941, flying Tomahawk Mk2's or P-40C's.

P-40 is my favourite but most underrated plane in WW2 IMHO. It did it's just bloody well with bugger all training