Keywords: Wall corrections, Rotor Performance, Wind tunnel test, Flight test
Abstract: Accurate measurements of rotorcraft performance as measured in a wind tunnel are strongly influenced by the test section configuration, whether it be closed or open jet. The influence of wind tunnel walls on the induced velocity of lifting bodies has been studied by many researchers over the years. Methods have been developed to adjust the angle-of-attack and dynamic pressure for fixed wing aircraft in a wind tunnel to approximate free flight conditions. These methods have largely been adopted by the rotorcraft community with very little testing to verify the applicability of these methods to helicopter rotors and flight test measurements. Recent tests conducted by the Deutsche Forschungsanstalt für Luft- und Raumfahrt e.V. (DLR) in the Duits-Nederlandse Wind Tunnel (DNW) have provided data suitable for the evaluation of these methods. A 40% scale model Bo105 rotor was tested in five different wind tunnel test sections: 1) 6x6m closed, 2) 8x6m closed, 3) 8x6m open slots, 4) 9.5x9.5m closed, and 5) the 8x6m open jet. These data along with full-scale data from a NASA Ames 40- by 80-Foot Wind Tunnel test and a DLR flight test program provide a means to evaluate wind tunnel wall correction methods specifically for helicopter rotors. Good correlation of rotor power over a range of advance ratios for these three data sets has been shown using wall correction methods after accounting for trim deficiencies between the data sets.
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