Acceleration comparisons

[FC99]

Originally Posted by gaunt1

Im not good at maths at all, so how is that working? Acceleration is proportional to excess power, or exponential?
Im asking this because something is fishy with the acceleration of some aircraft, primarily the La-5FN. Compared to La-5F, it has ~12% more powerful engine, slightly lower weight, and about the same drag. But acceleration is far-far better. So either the La-5F is porked, or the La-5FN is an UFO in this regard. I suspect the latter. Because if we take the factors above into account, I think it should have only about 15-20% better acceleration, for example 270 to 500 should take about 44-48 seconds, not 36.

Ps=(VT-VD)/W [m/s]
VT(La5FN) > VT(La5F)  -  more powerful engine -> more thrust
DT(La5FN) < DT(La5F)  -  cleaner airframe -> less drag
W(La5FN) < W(La5F)    -  La5FN is lighter 


Ps=dEh/dt
Eh=h+V^2/2g [m]   - Energy height

From that you can calculate acceleration.

All of the above combine = big difference in performance
When you know specific excess power, you can calculate climb and acceleration performance. Or you can go backward and measure acceleration(Like horseback is doing) and calculate Ps and rate of climb from it.