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. This calculator can be very useful when trying to determine the ideal propeller speed reduction ratio. You may want your propeller to reach its redline (.88 to .92 mach) at the same time your engine reaches its maximum rpm limit, its redline. To calculate this ratio, divide the maximum prop rpm, as you have determined by using this prop tip speed calculator, into the maximum engine rpm. |
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| 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). 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 theoretical airspeed. Use this process to help determine the amount of propeller pitch you need for your particular aircraft. This calculator is provided courtesy of P. Ponk Aviation. Visit their website at www.pponk.com. USE
THIS CALCULATOR AT YOUR OWN RISK |