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Propeller Tip Speed Calculator
Determine Propeller RPM Redline
Would you like 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. 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.
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 rapidly
degrade the performance of your propeller.
The tip speed of the multiblade fans used for air cushion pressure and
thrust is limited to about 460 FPS or 314 MPH !
USE THIS CALCULATOR AT YOUR OWN RISK
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 well 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).
To determine how fast your propeller can theoretically push or pull you through the air at
a given rpm and pitch, multiply your propeller's pitch in inches (usually measured at 75
percent of the prop disk radius) times the RPM. Then multiply that figure times .000947
which gives you your speed in miles per hour. Then multiply this figure by .85 if your
aircraft is reasonably aerodynamically clean or by .80 or .75 if your aircraft is somewhat
"draggy". This last operation compensates for propeller slippage and some
aircraft drag. The end result should be a reasonably accurate estimate of your aircraft's
airspeed potential. Use this process to help determine the amount of propeller pitch you
need for your particular aircraft. Use the Theoretical Speed Calculator below.

Propeller Tip Speed Calculator
Compensation for outside temp in Celsius. Speed in Mph.
* = REQUIRED INPUTS
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Theoretical Speed Calculator
(Only calculated)
* = INPUTS
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