Performance of a stepped airfoil at low reynolds numbers

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Conference Proceeding
Proceedings of the 19th Australasian Fluid Mechanics Conference, AFMC 2014, 2014
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Small Unmanned Aerial Vehicles (UAVs) are becoming more viable replacements for manned flights on dangerous, tedious and expensive missions. Small UAVs provide a complex aerodynamic problem. Compared to manned aircraft, their small size and relatively slower flight speeds, combined with the turbulent nature of the air flow close to the ground, increases the likelihood of the aircraft stalling. As a result the development of new and innovative means of generating lift, which are less susceptible to stalling, would be extremely beneficial to small UAV design. One potential solution is the series of stepped airfoils designed by Kline and Fogleman (KFm). These airfoils, popular with some Radio Control (RC) model pilots, are claimed to be stall resistant. Stall resistance is a desirable property for aircraft operating close to maximum lift, or maximum angle of attack, as would be expected of a small UAV carrying sensory and communication equipment. This work aims to determine the validity of these claims by testing a Rolf Girsberger (RG) -15 airfoil section with a KFm-2 step in a low-turbulence, closed-loop wind tunnel. The tests have been conducted at 4 Reynolds numbers between Re 28 000 and Re 100 000, which we believe are the expected operating conditions of a small UAV. A load cell test rig has been used to determine the maximum angle of attack before the airfoil stalls as well as the efficiency of the airfoil. An unmodified RG-15 airfoil has also been tested as a control. The addition of the KFm-2 step was found to have no useful aerodynamic benefits. The standard RG-15 section would be more suitable for use as a small UAV wing section.
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