Force and Deformation Measurement on Low Aspect Ratio Membrane Airfoils

This paper investigates the effects of pre-strain and cell aspect ratio on free trailing edge, aspect ratio two, membrane wings at low Reynolds number (Re ~ 50,000). At these conditions, the membrane visually vibrates. Of particular interest is the comparison of the membrane wing aerodynamic performance to rigid models fabricated in the shape of the time-averaged membrane deformation. Three pre-strain levels, 1%, 2% and 4%, were applied to flat membranous wings with one, two and three cells. Force and deformation measurements were performed in a low speed wind tunnel. From digital image correlation results, the rigid, time-averaged deformation wings were fabricated using three-dimensional printing. The aerodynamic loads for the printed wings were acquired at the same test conditions as membranous wings to extract the dynamic and static benefits of flexibility. In general, the membrane wings outperformed the printed wings at both pre-stall and stall conditions. Nomenclature AR = Aspect ratio AOA or  = Angle of attack b' = Membrane cell span c = Length of chord c' = Membrane cell chord CL = Lift coefficient CL,α = Lift curve slope CD = Drag coefficient CD,o = Minimum drag coefficient CM = Pitching moment coefficient f = Frequency L/D = Lift-to-drag ratio q = Dynamic pressure Re = Reynolds number t = Membrane thickness  = Dimensionless aeroelastic parameter 1 Graduate Research Assistant, AIAA Student Member 2 Undergraduate Research Assistant 3 Associate Professor, AIAA Associate Fellow 4 Graduate Research Assistant, AIAA Student Member 5 Associate Professor, AIAA Associate Fellow 6 Professor, AIAA Member 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 07 10 January 2013, Grapevine (Dallas/Ft. Worth Region), Texas AIAA 2013-0682 Copyright © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. 2 American Institute of Aeronautics and Astronautics