Introduction

Aircraft propellers produce gyroscopic torques. In model aircraft these torques can be more important than they are in larger aircraft, primarily because most model aircraft use propellers directly driven by the shaft at high angular speed.

To estimate these torques one must know the rate at which the aircraft is rotating in pitch or yaw, engine speed, and the moment of inertia of the propeller. Accurate devices are available to measure engine speed so that engine speed is well known, no moment of inertia data seems to have ever appeared in the model aircraft literature.

This note describes a the results of accurate measurement of the weight (or more properly, mass)size and moment of inertia of a number of propellers. From this data an approximate estimate of the moment of inertia for any propeller can be made.

The use of these data in estimating torques and the relation of torque to aircraft rotation is shown. In particular the large oscillations in gyro torque for one and two blade propellers is described.

There are other torques generated by propellers from aerodynamic forces and other forces other than thrust, so this information covers only a part of the complete picture in regard to the forces and moments generated by installed propellers.