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. Some of the effects that affect control line model aircraft are: (1) In Speed and Racing; flown anti-clockwise a strong nose up moment. (2) In Aerobatics and Combat;  a nose-out moment in inside loops and nose-in moment in outside loops.

In all control line models with either one or two blades this torque goes from zero to two times the average and back twide per revolution, introducing a significant vibration. Three blade propellers eliminate this vibration.

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. It also has a litte windows JavaScript program to calculate the magnitude of the gyro torque averaged over one revolution. It uses "modeler units" and is the last page of this section.

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 the propeller generates not only thrust but side forces as well. This information covers only a part of the complete picture in regard to the forces and moments generated by installed propellers.