Performance Measurements of a 1/6-Scale Model of the 1907 Cornu Rotor

Abstract

Measurements of the performance of an approximate 1/6-scale Cornu 1907 rotor system are discussed. The rotor was tested in hover, both in and out of ground effect, over a range of rotational speeds and collective blade pitch angles. The measurements showed that the rotor had low aerodynamic efficiency, with a maximum attainable figure of merit of only about 0.35 for out of ground effect operating conditions. An analysis of the measurements showed that the performance of this rotor is dominated by relatively high induced losses, with an average induced power factor of over two, mainly because of the use of low-aspect-ratio blades. Extrapolation of the performance polar back to zero thrust with the aid of modified momentum theory suggests that the average profile drag coefficient for the blade sections was of the order of 0.1. However, even with the benefits of a proper airfoil section of lower drag, it is shown that without also using a blade design of higher aspect ratio, the figure of merit of the Cornu rotor design could not be improved much above 0.4. The measured results confirm previous modeling assumptions used for the aerodynamic and performance analysis of the Cornu rotor design and conclusions drawn regarding the unfeasibility of successful free flights of the Cornu helicopter.