Note that ClarkY 4,6 blade test was carried in a low speed wind tunnel, only 110mph, only 550rpm. So there is no air compressibility in the test, 4-blade propeller could maintain 80% efficiency up to 3.6 advance ratio.
I have no direct proof of 4-blade NACA16 efficiency at high Mach number. I just suspect that 3-blade 3.3m propeller lose efficiency much more than a 4-blade Naca16 around 0.65-0.75 Mach----above level speed envelope, within dive limit.
Last edited by BlackBerry; 07-04-2012 at 10:42 PM.
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