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According to the Stormbirds group, who built six replica Me 262's so accurately that the Messerschmitt factory issued them consecutive serial number plates, the redline airspeed for a production Me 262 in WWII was 540 mph, where the replicas are redlined today. If you go faster than that, you are a test pilot, and they all wish you good luck.
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During 1943 the Allies still had thousands of older type aircraft in service such as the P-40, Hurricane and Spitfire Mk V. The newly introduced P-47B and P-47C were nothing to brag about. Early model Fw-190As compare well to all of those aircraft.
The P-51 starts showing up during early 1944, the same time the improved Fw-190A8 entered service. The P-51D arrived in Europe during the summer of 1944, just a few months before the Fw-190D9 entered service.
I The FW 190's harsh stall is a bit exaggerated: some allied tests on captured FW 190s talk of aileron flutter making the pilot unconscious. A fluttering aileron is not normal on a 190 and signe of bad adjustment of the complicated pushrod linkages. (latter modified). Obviously its going to stall your tips earlier (stalls start at the rear of a wing) and the shaking will disguise your warning.
The real cause of the sharp stall was the two spar wing. The two spars made the wing torsionally stiff and unlikely to be twisted in the opposit direction to the aileron and thereby reduce the roll rate (a big problem for the spitfire with its thin single spar wing). However under heavy G the tip could twist up more than the trailing edge and thereby reduce the 2 degree washout angle. There was a FW report on this. .
The increased performance obtained with 150 Grade Fuel was put to good use by Mustangs, Tempests and Spitfires in intercepting Buzz Bombs launched against Britain beginning mid June. Performance increases at sea level were as follows:
150 Grade Fuel
130 Grade...............................150 Grade
Spitfire IX 335 mph...................358 mph +25 lb
Spitfire XIV 359 mph.................366 mph +21 lb
Tempest V 372 mph..................386 mph +11 lb
Mustang III(V-1650-3) 360 mph..390 mph +25 lb
At the time the FW 190A8 could do 359mph on C3 fuel (about 96/130). The tempest v entered service in April 44 around the same time as the FW-190. So the
Tempest V on 100/130 was 12 mph faster than the FW 190 on a slightly inferior fuel but had inferior high altitude performance. 100/150 fuel however created
a greater gape.
I don't think the FW was outclassed, at least around june.
it would be interesting to know what engine modifications ( if any ..on the merlins, P&Ws, etc) were done for them to run with the higher octane fuel. were the existing valves, etc. able to cope with the higher octanes without burning up too quickly, did engine life suffer or was the merlin so robust to be able to absorb the additional temps and stress like it was made for it... you step up too far the engine will scream like a raped rabbit but could start to throw rods..burn pistons or valves..etc.
It would be interesting to know what the BMW 801D2 radial would have been able to do with 100/150 fuel.