Engines for propeller-driven aircraft are limited in their maximum rotational speed by the fact that the tip speed of the propeller must not approach the speed of sound in air (mach i). taking 6 ft as a typical diameter for a propeller of a light airplane and 1100 fils as the speed of sound, find the upper limit on the rpm (revolutions per minute) of the propeller shaft.

1750 rev/min

Explanation:

We know that the linear speed and rotational speed are related by:

   v = ω R   so the max rotational speed is

  ω = v / R = 1100 ft/s   / 6 ft   =  183.3 radians/sec

You are asked to convert this to rev/min:

  183.3 rad/s * ( 1 rev / 2π rad )* ( 60 sec / 1 min) = 1750 rev/min

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