Why still no dive acceleration difference?

[BlackBerry]

Originally Posted by Crumpp

Do the math with the actual numbers, blackberry.

All units in SI. Assume there is no air compressibility during dive, and 80% prop efficiency all along dive.

Fw190A8

m----mass,3500kg
A----dive angle
p----engine output,HP
r----propeller efficeincy=0.8=80%
Vmax ----max level speed at SL, 580km/h=161m/s
d----drag coefficient
g----gravity, 9.8 m/s^2
t---- engine thrust, N


when level flys at Vmax, fw190a8 in equilirium, zero acceleratiom, all forces are balanced.

t=P*r/V=2000*735*0.8/161=7300N

m*g* sin(0)+t=d*Vmax^2

d=t/Vmax^2=7300/161^2=0.2816

when dive in 45 degree, let the new equilirium speed as V:

new engine thrust should be 7300*(161/V)

m*g* sin(45)+t=d*V^2

3500*9.8*0.707+7300*(161/V)=0.2816*V^2

thus

v^3-86115V-4173651=0

Finally, we get V=315.2m/s=1134.7km/h.
And BMW801 still produce thrust as 7300*(161/315.2)=3729N=380kgf>10% aircraft weight


P47D

m----mass,6000kg
A----dive angle
p----engine output,HP
r----propeller efficeincy=0.8=80%
Vmax ----max level speed at SL 550km/h=153m/s
d----drag coefficient
g----gravity, 9.8 m/s^2
t---- engine thrust, N



when level flys at Vmax, P47D in equilirium, zero acceleratiom, all forces are balanced.

t=P*r/V=2000*735*0.8/153=7686N

m*g* sin(0)+t=d*Vmax^2

d=t/Vmax^2=7686/153^2=0.3283>0.2816

Obviuosly ,P47d has more air drag coefficenct due to bigger wing area.


when dive in 45 degree, let the new equilirium speed as V:

new engine thrust should be 7686*(153/V)

m*g* sin(45)+t=d*V^2

6000*9.8*0.707+7686*(153/V)=0.3283*V^2

v^3-126628V-3581962=0

Finally, we get V=369.2m/s=1329.1km/h>1134.7km/h.
And R2800 still produce thrust as 7686*(153/369.2)=3187N=325kgf>5% aircraft weight

Obviuosly, 6-ton p47d gets more benifit than 3.5-ton fw190A8 in a 45 degree dive.

IMO, P47D has two advantage over fw190a8 in a steep dive.

1) more weight, more benifit. This is proved by calculations above. I believe the il2 FM could handle this kind of calculation very well.
2) higher propeller efficiency at high speed(>Vmax) dive.I suspect the il2 FM could NOT handle this kind of calculation very well.

I suggest that we try to reproduce the P47D vs Fw190G in a 65 degree dive from 10000ft altitude in il2 4.11m, at initial dive stage, let fw190G go ahead, pull away rapidly. This can be achieved by decreasing P47 throttle. And then we can check whether the p47D(with full throttle) could overtake fw190G in the end of dive, ie, at 3000ft altitude with much greater speed.

If not, I prefer that il2 FM has undermodelled 4-blade aircrafts/overmodelled 3-blade dive acceleration for many years. That's totally ridiculous for allied aircrafts such as p47, p51, tempest, spitfire,f4u, etc.