WarpDriveProps.com 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 multi-blade 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 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

* Prop Diameter. In inches.

* Engine Rpm. ( Max )

* Engine Gear. Example. 2,58:1 set 2.58, with no gear use 1.

= Prop Tip Speed in Mph.

* Outside Temp. in Celsius ( Normal is 20 Celsius. )

= The Speed of sound in Mph. Calculated using outside temp.

= Prop Tip Speed in Mach. Maximum performance between 0.8-0.92 Mach.

A propeller does not work well just under and over Mach speed.
Just under Mach (0.92+) the propeller will vibrate, makes excessive noise and will have poor efficiency .

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Theoretical Speed Calculator

Only calculated.

* = INPUTS

* Prop Pitch. Measured in inches at 75% of the prop disk radius. Convert degrees pitch to inches of pitch.

* Engine Rpm. (In cruise or test)

* Engine Gear Ratio. (If direct drive put 1)

* Aircraft drag. 85 to 75%. If the aircraft is very aerodynamically clean use 0.85 . Default id 75% (0.75)

= Speed in Km.

= Speed in Mph.

= Speed in Knot.

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