Experimental and Numerical Study of a Model Coaxial Rotor

The hover performance of a small scale tilt rotor (similar to the XV-15) was measured in both single and coaxial configurations, in and out of ground effect and with various separation distances between the rotors. The performance of the single rotor, when in ground effect, strongly depends on the degree to which it is loaded. When configured as a coaxial rotor, with matching RPM and torque settings, the separation distance between the rotors appears to have little effect. However, proximity to the ground greatly affects the performance of each individual rotor as well as collectively. An analytical model based on a generic blade-element theory with experimentally calibrated velocities is presented. Calculations made with the rotors at various separation distances were in good agreement with the measured results.