Hovering Measurements for Twin-Rotor Configurations with and Without Overlap

Results of an investigation in the Langley full-scale tunnel of the hovering performance of large-scale twin-rotor-helicopter models are presented. Measurements of thrust, torque, and rotor flapping are given for overlapped (approximately 76 percent of blade radius) and nonoverlapped configurations and for two different rotor solidities. The measured performance is compared with single-rotor measurements and with available rotor theory. These tests show that the hovering performance of a single rotor and of two rotors without overlap or vertical offset are the same and hence may be calculated by single-rotor theory. These tests in conjunction with results of previous coaxial-rotor tests show that the performance of highly overlapped rotors can be reasonably predicted by available rotor theory.