Why still no dive acceleration difference?

[BlackBerry]

Originally Posted by MadBlaster

what about windmilling and internal friction /cylinder compression of engine? bmw801 only had 14 cyl. p47 had 18 cyl. so, maybe some inefficiency of 3 blade wide was offset by less internal friction in the 801 and that is why they went with 3 blade wide.

bf109k4 ：3-blade prop
spitfire xiv：4-blade prop even 5-blade

Both are liquid cooling engine.

btw，r2800 and bmw801 share almost same front area.

[MadBlaster]

you miss the point.

What a wide 3 blade may lose in "thrust" vector efficiency from more drag , it may gain in 'weight" vector efficiency when "thrust" vector efficiency is at zero in a dive and high TAS. The wider blade means higher tip speed from ram air verses thinner 3 blade. This means greater torque to overcome internal friction from the engine. The pilot can reduce internal friction by lowering manifold pressure, but not completely. The engine will still tend to over-speed and this is mitigated by lowering rpms/coarsening blade pitch. So, internal friction of the engine is more easily overcome by the weight vector with the wider blade I speculate.

One way to measure the internal friction of the engine. What was the cranking force required to start the 801? What was the cranking force required to start the r-2800? If two engines are identical, it takes more cranking force to start an engine with a 4 blade wider diameter prop attached than a 3 blade smaller diameter. The engines were not identical. The r-2800 had more cylinders than the 801. If you take off the props, I suspect it takes more cranking force to start the r-2800. I suspect the p47 had more internal friction to overcome than the fw190. This would hamper dive acceleration.

[Crumpp]

Why decreased in max. level flght?

Inncrease the area of our lifting surface = more drag

If you know how to do sections, then you know the common expression in propeller blade element theory is Cb for chord length and our local section Drag is expressed as:

~D = 1/2pVb^2CbCD

[Cloyd]

OK Gents,

I've read this thread with fascination, but the details are WAAAAY over my head. Do you have a conclusion, ie, IL2 is way off or it is close enough for a $40 flight sim that is a decade old?

Cloyd

[MadBlaster]

lol, I have no idea.

maybe add some sound effects when the tip speeds go mach.

maybe add some sound effects to p47 turbine spinning up.

I did notice in up3, rc4, there seems to be turbo lag in the dial indicator verses the engine rpm indicator. so somebody was thinking good thoughts. i think it was a mod p47, maybe p47B. felt a little more agile than the others too.

[Crumpp]

bf109k4 ：3-blade prop
spitfire xiv：4-blade prop even 5-blade

Try to find a WWII fighter with cowl guns and a 4 bladed propeller. I cannot think of a single one.

[BlackBerry]

Originally Posted by Cloyd

OK Gents,

I've read this thread with fascination, but the details are WAAAAY over my head. Do you have a conclusion, ie, IL2 is way off or it is close enough for a $40 flight sim that is a decade old?

Cloyd

Read this article and you will know high-speed propeller was a leading edge issue in WWII when people didn't know much about the transonic aerodynamiacs(0.8-1.0 Mach). They even could NOT precisely test the propeller efficiency at high speed in fullscale wind tunnel.

http://aerade.cranfield.ac.uk/ara/19...report-640.pdf

Il2 is a very closed simulation when speed is below 0.8 Mach, but when speed of anything(wing, propeller tip,etc) is beyond 0.8 Mach, not very accurate.

[Cloyd]

Originally Posted by BlackBerry

Read this article and you will know high-speed propeller was a leading edge issue in WWII when people didn't know much about the transonic aerodynamiacs(0.8-1.0 Mach). They even could NOT precisely test the propeller efficiency at high speed in fullscale wind tunnel.

http://aerade.cranfield.ac.uk/ara/19...report-640.pdf

Il2 is a very closed simulation when speed is below 0.8 Mach, but when speed of anything(wing, propeller tip,etc) is beyond 0.8 Mach, not very accurate.

I have been flying this sim for over a decade, and I really only know how to fly two planes well - I-153 and F4F-3. (Yes, I realize that neither of these was available in the initial release.) Is it safe for me to assume that I don't have to worry about the performance of my preferred rides in the 0.8 to 1.0 Mach range?

Cloyd

[AndyJWest]

If you ever go that fast in an I-153, you have a problem. And almost certainly, no wings...