Hi Wells,
Originally posted by wells:
They couldn't go any faster, because I was using only about 35" in those tests. 
I am just testing out induced drag as throwing in excess thrust at the same time would add too many variables. But since the FM is now very close to calculations for induced drag, you could take your max thrust predictions and see how the thrust model works out to calculations?
Hmm, were you setting up a constant speed cruise before the test so that you knew for sure that the thrust and drag were balanced before starting the 4g turn? That's a good thought, and it may well have come quite close to isolating the induced drag, it would also explain your altitude loss figures in the flight tests. Unfortunately it wouldn't reveal anything worthwhile about the actual rate of energy loss when turning with the benefit of full power. Other than the interesting observation that when the same calculations, using the same data, but factoring in thrust and parasite drag are done, the ranking (at least for the few aircraft I checked) comes out the same. Which might make it a useful shortcut method of comparison.
However, all of those calculations depend on the values chosen for the Oswald Efficiency factor. It looks as though you have calculated those values from wing geometry as a function of wing Aspect and Taper. However, Oswald's efficiency factor is a function of Aspect, Taper, Sweep, Mach, Camber and Twist. If I calculate new values including leading edge sweep and mach no, as well as aspect ratio and taper ratio, only ignoring camber and twist and then redo the calculations, the ranking comes out as:
1 P38
2 F4U
3 P51
4 P47
In which the F4U beats the P51 (they were quite close in your tests also). Perhaps it would be worth re-testing the F4U and P51? If so, it would probably be easier and more reliable to time how long it takes to decelerate from one speed to another in level turn tests at constant g. That way you also account for the previously ignored drag components and thrust.
The previous result simply demonstrates that the outcome is sensitive to changes in Oswald values. In any case, calculating the Oswald efficiency factor from wing geometry is problematic. The values obtained are generally only valid for low AoA work because the calculations require that the flow remains fully attached, whereas in practice that is rarely the case. Generally such methods produce optimistic results, particularly since we are interested in performance close to the edge of the envelope. Just curious
Where did you obtain your Oswald values? Did you know that it is possible to discover exactly what values are being used by AH? I haven't done it myself yet because I've been otherwise absorbed
Anyway, an interesting thread!
Badboy
[This message has been edited by Badboy (edited 09-20-2000).]
