The experimental and theoretical aerodynamic characteristics of aerofoil sections suitable for remotely piloted vehicles

Abstract

Using the design requirements of Remotely Piloted Vehicles (RPV's), selected for wind tunnel testing over the Reynolds number range 3 x 105 to 1 x 106. The first aerofoil, NACA 643-418, showed a degradation of performance in terms of lift-to-drag ratio as the Reynolds number was reduced. There was also a laminar separation bubble of notable extent on both the upper and lower surfaces at most incidences throughout the Reynolds number range. The second aerofoil, Göttingen 797, had good performance in terms of lift-to-drag ratio and maximum lift coefficient, even at the lowest Reynolds number. This was attributed to the flat bottom of the aerofoil, which allowed the formation of extensive laminar flow on the lower surface without the formation of a laminar separation bubble. The third aerofoil, Wortmann FX63-137, generally exhibited the best aerodynamic performance in terms of maximum values of both lift-to-drag ratio and lift coefficient, throughout the Reynolds number range considered. Four alternative lower surface geometries for this aerofoil were also tested. The modifications reduced the maximum values of both the lift coefficient and lift-to- drag ratio of the original aerofoil throughout the Reynolds number range, but generally improved the lift-to-drag ratios at low values of lift coefficient. The notable exception was the modification which resulted in a flat bottomed section. This had maximum values of lift-to-drag ratio which were within a few percent of those of the original aerofoil throughout the Reynolds number range. Wind tunnel results were used to evaluate low-speed aerofoil analysis computer programs written by Eppler and Somers (13) and Van Ingen (18). The results were disappointing. However, using the same wind tunnel results it was noted that computer programs using semi-inverse viscous methods show great promise.