Well AH's Tempest and Typhoon performance is a bit of a mystery to me. There are no offical reports from A.& A.E.E. to the Air Ministry or the Ministry of Aircraft Production showing that kind of performance.
The A.& A.E.E. reports detail what was accepted as the "offical" performance of a tested airplane.
However...
AH's curves for both Tempest and Typhoon "look" like Tempest and Typhoon curves.
Here's my best guess:
Pyro found some numbers from the manufacturer. These are "kinda" close:
Typhoon IB with a Sabre IIA: 412mph at 19,000 ft.
Tempest V with a Sabre IIB: 426mph at 18,500 ft.
Either that or AH doesn't use war time performance tests but rather "engineers" their airplane performance.
Maybe wells is right, as he said A.& A.E.E tested P5212 and got 410 at 20k. Doesn't match up with AH's Typhoon curve though. dunno <shrug>
Niklas, you're right about one thing tho, that Position Error Correcton is on the high side from what I'm used to seeing. The Tempest also had similar position error corrections: At sea level T.A.S. 376, I.A.S. 398, P.E.C. -23.9
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Tempest Performance TestingSpitfire Performance Testing