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Propeller Tip Speed Calculator

To determine your Propeller RPM Redline, to know how fast your propeller tips are traveling ?

Enter some different combinations of prop diameter and RPM setting below to find out.

Note: Ambient temperature is needed to determine the speed of sound for a particular day, as the speed of sound varies according to air temperature. Try different temperatures then you will see just how much the speed of sound can vary.

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.

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. 3500 rpm) to determine your propeller RPM (i.e. 1'356 propeller RPM).

This is also a reference for Static Thrust Calculations.



Propeller Tip Speed Calculator


Prop Diameter:

Engine Rpm:  (Maximum rev's)
Engine Gear:  Example. If 2.58:1, set to 2.58, with no gears use 1.
Prop Speed:  RPM
 Prop Tip Speed:  Mph    Fps  (MPH to feet per second, multiply by 1.4667)
Outside Temp:  in Celsius ( Normal is 20 Celsius. )
Speed of Sound:  Mph. Calculated using Outside Temperature entered in Celsius.
Prop Tip Speed:  Mach. Best performance between 0.80~0.92 Mach.

Propeller Tip Speed Calculator, Compensation for outside temp in Celsius.

Remember: A propeller does not work well just under or over Mach speed.

At or above Mach (0.92+) the propeller will vibrate, make excessive noise and will have poor efficiency.


Theoretical Speed Calculator


Prop Pitch:  inches at 75% of the prop disk radius (40/28 =28). Convert degrees pitch to inches of pitch.
Engine Rpm:  (In cruise or test)
Engine Gear Ratio:  (If direct drive put 1)
Aircraft drag:  If the aircraft is very aerodynamically use 0.85, Default =40% (0.40) for PPG.
Speed in Km:
Speed in Mph:
Speed in Knot:


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