Thanks Aleatorylamp,
The evolution of the P-40 series is actually quite interesting though not necessarily a happy one.
We are certainly getting near the end of the P-40 line. I have already started work on dimension checks for the P-40N.
When I am done there, I will likely take a little break and then go back to the ancestor of the series: The P-36 / Hawk 75.
Consider how this story evolved:
A fairly good 1930's design, The P-36 / Hawk 75, makes a nice transition from Biplane fighters to Monoplane and retains the flying qualities of the Biplane with performance of contemporary (for 1935) monoplanes.
A couple years later, the US Army sees the developments in Europe with inline engines and wants the improved performance.
Curtiss responds by fitting the Allison V-1710 to the Hawk 75 an eventually gets to the Hawk 81.
The level speed is improved but everything else suffers: Climb Rate, Maneuverability and Handling are all noticeably worse with the Hawk 81 which is actually a fairly competitive design but for Altitude performance which can be blamed entirely on the engine.
A few years later, Curtiss does a major redesign to fit the new Allison F series engines and arrives at the P-40D/E (Hawk 87) series.
Firepower and Protection are better but engine power is actually very nearly the same and performance actually doesn't change much.
If anything, climb rate is worse because of the increased weight.
One of the major changes in the Allison engine was in the reduction gearing (which raised the thrust line). The new gearing could handle output that the old gearing could not. Some folks figured out that the Allison could actually take much more boost than was claimed.
They managed to get an engine rated at 1150 HP to put out around 1550 to 1600 HP.
With the beginning of Merlin engine production at Packard in the United States, some of the engines which were intended for Bombers were installed in the P-40E series which resulted in the P-40F. Altitude performance was considerably improved.
About this time, the extra engine torque was causing directional controllability problems which were addressed by first adding a fillet to the fin and afterwards with a longer tail section which remained with all subsequent P-40s.
The P-40 was always a relatively heavy aircraft for its power and Curtiss tried to address this issue in a very interesting manner.
With the P-40L model, Curtiss reduced weight by decreasing the ammunition load and removing one internal fuel tank (the Forward tank).
Some other parts were also replaced with lighter and more poorly made pieces. The decreased operational capabilities and increased maintenance issues caused many of the changes to be reversed in the field. Thus these changes were ineffective.
The demand for Merlin engines was greater than the production capacity so the P-40 was forced to revert back to the Allison.
By this time, the P-40 was considered to be suited for use as a fighter-bomber or for places where the opposition was not very modern.
It was sent to China, Burma, India, to Australia and New Zealand, to the Mediterranean, and as an export aircraft to the Soviet Union.
An Allison engine with an improved supercharger also entered production at this time which is the main distinction between the P-40M being built now and the earlier P-40K. This also might explain why the P-40M never served operationally with US forces though Australia, New Zealand and the Soviets used them.
The "improved" supercharger gave better altitude performance but had much less capability at low altitudes.
My intention here was to use South East Asia Command insignia as carried by the RAF (not RAAF or RNZAF) but I don't know for sure that the RAF ever used the P-40M operationally either.
Just to complete this story:
The P-40N was a more successful attempt to produce a lightened version. The earliest version (P-30N-1) was visually the same as the P-40M other than having only two instead of three guns per wing. The changes which distinguish this model were all in internal equipment.
The next P-40Ns had the cut down rear fuselage that we typically associate with this model.
The P-40N was the fastest and possibly the best performing of the production models but even then, production was terminated at the end of 1944. By the end of the war, it was no longer serving as a front-line fighter in any of the major services.
- Ivan.
