Propulsion Characteristics Affecting the Aerodynamic Performance of an Externally Blown Flap Transport Model

Abstract

Two wind-tunnel investigations were conducted at Langley Research Center to determine the effect of dif- ferent wake characteristics on the performance of two separate externally blown flap transport configurations. In both cases, the thrust removed lift coefficient could be directly related to the proportion of momentum cap- tured by the flap system. In another investigation of an externally blown flap transport configuration, tufts were used to measure the upwash angles ahead of the wing. Using the thrust-removed lift coefficient, a simple vortex- lattice method provided a good approximation of these angles away from the nacelle inlets. Nomenclature = total area of jet wake which impinges flap m2 = incremental area of jet wake which impinges flap m2 = total area of jet wake at flap m2 = local wing chord m = lift coefficient, lift/^s1 = thrust removed lift coefficient = thrust coefficient, thrust/qs = engine-exhaust-flap impingement parameter = free-stream dynamic pressure N/m2 = incremental portion of jet which impinges flap, N/m2 = jet dynamic pressure at flap location, N/m2 = upper-half radius of nacelle, m = wing area, m2 = static thrust, N = vertical distance, m = angle of attack, degrees = nominal flap deflection angle, degrees =jet exhaust deflection (measured from body axis), tan;1 (normal force/axial force), degrees = inflow angle, with respect to model horizontal axis, degrees = static thrust recovery efficiency, ((normal force)2 + (axial force)2 ) 1/2/T = upflbw angle, with respect to freestream degrees = bypass ratio = externally blown flap The present paper describes the results of a relatively simple analysis based on an engine exhaust flap area impingement parameter, which is a function of the distribution of dynamic pressure impingement on the flap, the area of the flap im- pingement, the total area of the engine exhaust, and the thrust. Isolated engine wake surveys were conducted to define this parameter for one of the EBF models for which aerodynamic performance data were available.2 A uniform dynamic pressure profile was assumed to determine this parameter for the other EBF model correlation with aerodynamic performance data. n A high-lift system, such as an EBF, induces large upflow angles in front of the wing in the region of the nacelle inlets. These flowfields must be defined in order that the nacelles be properly designed to minimize flow distortion at the engine face. This paper also presents the results of an investigation to measure the flow angle near the engine inlets of a represen- tative EBF model. The vortex-lattice method14 was used to calculate these upflow angles, to determine if they could be predicted.