Design and experimental results for a high-altitude, long-endurance airfoil

Currently, there is interest in the development of high-altitude, long-endurance vehicles for a number of missions including communications relaying, weather monitoring, and provision of targeting information for cruise missiles. The preliminary design of such aircraft is complicated, however, by the lack of suitable airfoils. This is due to the fact that such vehicles, unlike those for which the majority of airfoils have been developed in the past, operate at fairly high lift coefficients and at relatively low Reynolds numbers. Thus, to provide realistic airfoil performance information for preliminary design efforts, an airfoil has been designed for an aircraft with missions similar to those noted. The airfoil is unflapped and has a thickness of 15% chord. The design Reynolds number range is 7 × 10⁵ to 2 × 10⁶. Low drag is predicted for lift coefficients ranging from 0.4, which corresponds to a high-speed dash, to 1.5, the maximum endurance condition. Further, the airfoil is designed specifically such that the maximum lift coefficient is unaffected by surface contamination. Consequently, takeoff and landing in rain or with insect residue on the wings should present no special difficulties. The airfoil has been tested in the NASA Langley Low-Turbulence Pressure Tunnel and, with the exception of the maximum lift coefficient prediction, the results generally confirm the theoretical predictions.