Try different temperatures then you will see just how much the speed of sound can vary.

REMEMBER, .88 to .92 mach is a redline. This is NOT the most efficient tip speed range for your propeller to operate.

If you want the quietest and most efficient thrust propeller system, select a prop configuration (and reduction drive ratio) that will keep the tip speed for your cruise rpm at or below 700 feet per second or 475 mph. Above this speed "compressibility" of the air in front of the prop leading edge begins to occur which begins to degrade the performance of your propeller.

The tip speed of the multi-blade fans used for air cushion pressure and thrust is limited to about 460 FPS or 314 MPH !

Over .92 mach the airflow begins to detach from the propeller which decreases efficiency and dramatically increases noise. To improve performance and public relations you should consider reducing RPM so your tip speed will be below 0.92 mach.

To convert MPH to feet per second multiply by 1.4667. To convert feet per second to MPH multiply by 0.681818. If you have a propeller speed reduction unit (PSRU) divide your gear ratio (i.e. 2.58) into the maximum engine RPM (i.e. 6800 rpm) to determine your propeller RPM (i.e. 2636 propeller RPM).

USE THIS CALCULATOR AT YOUR OWN RISK

Propeller and Fan Tip Speed Calculator

*Compensation for outside temp in Celsius. Speed in Mph. *

** = REQUIRED INPUTS
*