Effects of Surface Flats on the Performance of a Remotely Piloted Aircraft

Abstract

T HE characterization of the aerodynamic performance of airfoils has been the subject of focused study since the 1910s. An implicitly assumed requirement is that the model fidelity (experimental or computational) is such that it is an exact rendering of the proposed full-scale flight article. In many instances, however, the actual wing profile may not be representative of its design. Generally, this becomes a greater issue as the size and dimensions of the vehicle reduce. With the proliferation of small-scale unmanned aerial vehicles, such concerns have increased in relevance. Wing geometry deviationsmay be due to damage, poor assembly, or simplified structure and design. This is commonly seen in radio-controlled (R/C) aircraft. Weight and cost considerations result in aircraft composed largely of balsa and plywood with aMonoKote skin covering. Generally, the wing skin is not supported between the ribs or the leadingand trailing-edge spars. This naturally results in flats when the skin is attached and stressed. As a result, the airfoil design and that actually implemented on the aircraft may be significantly different. Although wing/airfoil contour issues or alterations due to effects such as battle damage [1,2] have been investigated, little information appears available on a systematic study of contour effects thatmay result fromR/C modeling techniques. Consequently, a low-speed wind-tunnel investigation has been undertaken to quantify the effect of surface flats on the behavior of a Clark-Y airfoil. Data presented include surface pressure, wake survey, integral lift and drag coefficients, and surface flow visualization.