Wind tunnel measurements of the auto-rotation characteristics of Lanchester’s “aerial tourbillion” are presented in the form of tip speed plotted against wind speed. Three configurations were tested, a 10.94 inch diameter model with and without a cowling, and a 7.50 inch diameter model without a cowling. All showed a minimum wind speed for auto-rotation, dependent on friction at the shaft. At each wind speed above this value, there were two equilibrium rotational speeds, an unstable one, giving the required initial rpm for auto-rotation, and a higher stable one, the auto-rotation speed, which with increasing wind speed rapidly approached proportionality to the wind speed.
Fairly good agreement with an approximate blade element theory was demonstrated, the best agreement being obtained with the measurements on the model with cowling.