Experiments on an inlet-airfoil designed for heat exchangers of a high altitude RPA

Abstract

This paper first reviews a design method for an efficient inlet-airfoil to be used on the cooling installations of high altitude environmental research aircraft. The design method addresses the primary design requirement for subsonic endurance at high altitude. The flight conditions present an aerodynamically unfavorable combination of low chord Reynolds number (below 500,000) and high subsonic Mach number (up to 0.5). At these flight conditions the inlet-airfoil must meet the heat exchanger cooling flow requirements while maintaining the aerodynamic performance of the airfoil. The design method is closely coupled with not only the aircraft performance requirements but also the characteristic flow physics of low Reynolds number flows. Using a current concept aircraft as a baseline, the method has been used to develop an example design. Next, this paper presents details of the design, construction and geometric validation of a wind tunnel model. Results of wind tunnel testing will be reviewed, which show excellent agreement with computational predictions, using the MSES code. Tests were executed in the ODU 3 by 4 foot low-speed wind tunnel, using specially built endplates. Model lift and pitching moments were estimated from surface pressure distribution; drag by an adaptation of the Betz method.