Quote:
Originally Posted by looksharp
also... are you switching to rich mixture at sea level ????
i can get 290 mph out of the spit 2a at sea level with boost cut off enabled and rich mixture just as it should be
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No I don't think it was this way, the engine is rated with its full boost of 6,25 psi, going over that should give you an extra margin on top of the normal performance.
That's what I have understood from the sources I could cross.
Also if you note that the military power was only to be used for short time, I don't think it was the meaning to level the aircraft and apply more than its rated power in order to determine its maximum speed. You have to take into account that it was leveling up for a relatively long time before a stable reading could be obtained, say between 5 and 10 minutes most probably.
If you find informations supporting that it shall have its performance with the boost cutout open and applying the full available boost, I think it'd be worth to share.
In my opinion, we should have the right performance without use of bost cutout, up to my understanding. Octane grade 100 was probably also not available in 1938 for the Mk I prototype. The prototype itself fit with a wooden fixed pitch propeller reached 349 mph TAS at 17'000 ft.
I'll try to get more accurate datas from one of the big books I have related to Spitfire, a very good and complete one indeed. Those are interesting lecture.
Edit
I find no information supporting that the max speed of Mk I & II were measured with more than the rated power at 6 psi of boost.
Apparently the Mk I had 1030 bhp at altitude (either 16,250 or 17,000 ft ?) and Mk II 1150 bhp at 14'500 ft, source "The story of the spitfire" book.