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Hover Performance Correlation for Full‐Scale and Model‐Scale Coaxial Rotors

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The hover performance data of full‐scale and model‐scale coaxial rotors have been compared with CAMRAD II predictions having a free vortex wake analysis. Performance correlations of a coaxial rotor were made with a variation of key parameters including the rotor spacing and height. To understand aerodynamic behavior of the U.S. Army Aeroflightdynamics Directorate (AFDD) coaxial rotor operating over a range of Reynolds numbers from 36,000 to 180,000, the Reynolds number scaling effect was explored using an airfoil design code, MSES. It was found that the coaxial rotor spacing effect on hover performance was minimal for the rotor spacing larger than 20% of the rotor diameter. The measured performance data showed that more thrust was lost from the lower rotor of a coaxial than the upper rotor due to a larger rotor‐to‐rotor wake interference effect, and the lower rotor kept only an 81% of the single rotor OGE (out‐of‐ground effect) thrust whereas the upper rotor maintained a 90%. The lower rotor IGE (in‐ground effect) thrust increased quickly by 26% as the rotor approached to the ground from the position of an 80% of the rotor diameter to 10%, and the corresponding IGE power increased by 17%. These thrust and power characteristics were well predicted. Overall, the performance prediction for the coaxial rotor was satisfactory when compared with the measured data.

Document Type: Research Article


Affiliations: Aeroflightdynamics Directorate (AMRDEC), U.S. Army Research, Development and Engineering Command, Ames Research Center, Moffett Field, CA

Publication date: 2009-07-01

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  • The Journal of the American Helicopter Society is the world's only scientific journal dedicated to vertical flight technology. It is a peer-reviewed technical journal published quarterly by AHS International and presents innovative papers covering the state-of-the-art in all disciplines of rotorcraft design, research and development. (Please note that AHS members receive significant discounts on articles and subscriptions.)

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