Propeller simulation

CSP=contant speed propeller, within the speed envelope, the efficiency of CSP is roughly constant, but how about high speed diving such as 0.7-0.8 Mach?

The efficiency of propellers goes down as speed increases. At very high speeds nearing the speed of sound, the propeller acts more like a large solid disk creating drag more than it does a thrust producing device. This is the main reason Jets became ascendant as propellers could not practically increase in speed any further.

The efficiency of propellers goes down as speed increases. At very high speeds nearing the speed of sound, the propeller acts more like a large solid disk creating drag more than it does a thrust producing device. This is the main reason Jets became ascendant as propellers could not practically increase in speed any further.

Sorry for my delay reply, starkey. The issue is not simple at all, on the contrary, the propeller efficency (IAS approching 0.8mach)is one of the most misteries in WWII. The propeller efficiency is positive even at 1.0 mach so the propeller is always draging the plane never stopping the plane with WWII plane max dive speed.

We all know the tip of propeller velocity is much bigger than plane IAS/TAS for the high speed rotation(2700-3000rpm usually). On the runway, even P47 is stopped(zero speed) but with max engine axis rotate(2700rpm), the propeller tip terminal speed is near sonic!

First of all, 3-blade and 4-blade configuration differ in efficiency. In WWII, soviet and german always 3-blade while allied late plane equipped with 4-blade. Some research said that conventional 3-blade is almost as good as 4-blade WITHIN speed evolope.This is confirmed with conventional Airfoils, such as Clark-Y for USA, RAF16 for Britain and Göttingen for German. But the USA NACA new airfoil is another story, 4-blade NACA airfoil outperforms 3-blade NACA at 0.4mach. What about difference even IAS is near 0.8 mach where the CSP(constant speed propeller) could NOT maitain regular efficiency (ie 80%)and drops a lot to merely 40%? 50%?)

Mt=propeller terminal speed, is usually bigger than 1.0mach when P47 flys with 2520-2700rpm. If you decrease rpm from 2700 to 2520, the propeller efficiency goes up a little for less air compressibility.

We can see even with J=2.8= V/nd, ie 900km/h, propeller is still higher than 50% which means half engine output (1000hp) is draging the plane forwards.

My interpretation is that, in a 1v1 low altitude dogfight, an experienced RAF pilot flied new 18lbs boost SpifireIX, was beaten by a American rookie pilot in a P47C by the tactic named "dive extension/pitch back" before mid-April 1943 when 56th Fighter Group had never met Luftwaffe.

http://forum.1cpublishing.eu/showthread.php?t=33730&page=3