The Application of Circulation Control Aerodynamics to a Helicopter Rotor Model

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Abstract
A Higher Harmonic Circulation Control rotor model, based on several years of two‐dimensional research in the field of circulation control airfoils, was designed, built and tested at the Naval Ship Research and Development Center. Unique features of the model included blades with elliptical shaped circulation control airfoils, and a simple cyclic control mechanism based on blade pressure variation rather than blade pitch variation. The model proved that trimmed flight could be achieved without any moving parts other than the rotating blades. It further demonstrated that the high lift capability and efficiency of circulation control airfoils could be extended into the three‐dimensional regime. Aerodynamic trends displayed by the model have been coupled with two‐dimensional results to improve the theoretical programs used to predict model performance. Variables such as slot height‐to‐chord ratios, slot height‐to‐trailing edge radius ratio, Reynolds number and Mach number have been identified as factors which significantly affect the performance of circulation control airfoils. These effects have therefore been incorporated into the programs. Good agreement between theory and model results have led to a second generation rotor design.

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