seanychen
Posts: 2914
Joined: 7/20/2002
From: Canton,
MI, USA
Status: offline
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Remember, a propeller has a non-constant angle-of-attack of the airfoil section when you go from root to tip. I was searching on the web for lift vs AOA experimental data, and someone found that 5 degrees to 25 degrees gives the optimal lift-over-drag ratio for a typical airfoil. So while increasing propeller pitch can increase lift toward the tip, the section toward the root will approach stall and generate very little lift; hence the lift generated by the entire prop is not too much different.
After a little calculation, I estimated that if diameter is 3~4 times the pitch, then most of the prop section will be in the optimal lift range. So props like 12.25x3.75, 16x4, 18x6, 24x8, 30x10 fall in that range.
Also remember that stall angle is dependent on velocity. A high pitch root prop section may stall at 6000 rpm, but at 10000 rpm it may be lifting.
All in all, it's not possible yet to precisely predict static thrust of a given prop via calculation, because there are too many unknow variables. The best method with today's technology is through experimental data and provide some sort of correlation plot for other users.
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E_Total = M*G*H + 1/2 M*V^2
When H=0, all of airplane's velocity becomes crash energy!
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Printable Version
All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Tachometer Readings >> Propeller Thrust Calculator 
Propeller Thrust Calculator - 
Real vs. T-HP - 
(used APC airfoil) 