Prop tip speed and throttle RPM range design question

As I understand it the tip speed should not exceed .8 Mach 1.

Should that be the throttle limit, or should the limit be higher?

These are the figures for an online calculator:


  • 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, make excessive noise and will have poor efficiency .

Heh… we could add an ambient temp monitor and an altimeter, and adjust automatically! :wink: