When P51 dives to 4500 m=15000ft altitude, and reaches 640km/h=400 mph IAS, that is 1.25*640=800 km/h=222m/s TAS, the mach number is equal to 222/322=0.69. That's fuselage speed.
However, the speed of tip of airscrew is far more 0.69 mach.
4-blade hamilton airscrew,10.5 feet diametre, the reduction ratio of airscrew rotating to engine is 0.477. 3000rpm engine, 1431rpm=23.85r/s airscrew, the rotating speed of tip is：3.14*10.5*0.303*23.85=238m/s
So the combination speed is: (238^2+222^2)^0.5=325 m/s.
Unfotunatly, sonic speed at 4500m altitude is 322m/s, that is to say, the tip of airscew is 1 mach. There is no mach number "concept" in il2's model at all, how can I believe that il2 simulates 1 Mach aerodynamics very well?
Quote:
http://en.wikipedia.org/wiki/Indicated_airspeed
In aneroid instruments the indicated airspeed drops-off with increasing altitude as air density decreases. This leads to an apparent falling-off of airspeed at higher altitudes. For this and other reasons never exceed speeds (abbreviated VNE) are often given at several differing altitudes in some aircraft's operating manuals, the VNE IAS figure falling as height is increased, as shown in the sample table below.
Diving below mph IAS
30,000*ft 370
25,000*ft 410
20,000*ft 450
15,000*ft 490
10,000*ft 540
Ref: Pilot's Notes for Tempest V Sabre IIA Engine - Air Ministry A.P.2458C-PN
|
Tempest could dive to 450 mph IAS below 20000ft, aha, tempest's big rotol 14-ft airscrew, 3800rpm, 450mph IAS, the tip of rotol must be supersonic, so is P51's hamilton, thus the efficiency curves of their airscrews play an important role when they dive to high speed.
Why tempest outdives p51? For more efficiency airscew @ supersonic? Maybe. For much more heavier fuselage? Probably.
All in all, il2's model is lack of supersonic simulation, that's why we couldn't experience what tempest/p51 should be. That's why tempest couldn't outdive dora easily in game.