Electronic control of frequency converter sets for testing aircraft models

THE TESTING of airplane scale models in wind tunnels has brought about a demand for variable frequency a-c power for controlling the speed of power model motors used to drive the propellers of the plane models. To obtain aerodynamic data on the plane model which are equivalent to the expected performance of the actual plane, it is necessary to drive the model propellers at speeds greatly in excess of propeller speeds of the actual plane. During tests in the wind tunnel, it must be possible to control propeller speed and to measure accurately the speed as well as power input into the propeller.