Quote:
Originally Posted by Crumpp
Your theory is not based on facts. It would be a fundamental error to toss aside convention of n = ~.85 for it.
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The test air speed is below 0.4Mach or 0.2 mach . Of course, 0.4 Mach is just a cruise speed, at medium-low speed, 3-blade CSP could get constant propeller efficiency within envelop.
4-blade propeller efficiency drops from 90% to 85% while 3-blade remaining constant 81%.....
If you test propeller with slow air speed and small propeller rpm, a 4-blade propeller could maintain constant efficiency up to 3.6 advance ratio.
It is the high Mach number decrease propeller efficiency. No air compressibility, no significant effociency drop.
Btw, in late WWII, almost 100% allied aircrafts equipped with 4-blade propeller.