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The installation of advanced (M = 0.8) turboprop propulsion systems on transport aircraft represents a challenging task to design engineers. The installation aerodynamics of wing-mounted, single-rotation (SR), tractor turboprop systems have been extensively investigated by NASA Ames using a large powered semi-span wind tunnel model. Two configurations have been studied: a straight under-the-wing (UTW) nacelle and a contoured over-the-wing (OTW) configuration. The installation characteristics of these two configurations are presented in terms of installed drag, wing pressure distributions, and surface oil flows. Through the use of wing leading-edge modifications, the installed drag of the UTW nacelle was reduced to less than isolated nacelle drag at the cruise condition of M = 0.8 with a wing CL of 0.5. At this condition, the favorable interference is attributed to the recovery of a portion of the swirl in the slipstream generated by the single rotation propeller.

An initial wind-tunnel test was conducted to investigate the aerodynamic interactions between a propeller slipstream and a supercritical wing at transonic Mach numbers. The primary independent variables examined included Mach number, wing lift coefficient, and slipstream Mach number and swirl. The interference effects were found to be weak functions of free-stream Mach number, wing lift coefficient, and slipstream Mach number; swirl was found to have a significant effect. At a free-stream Mach number of 0.8 and a lift coefficient of 0.5, incremental drag results for 7° of swirl (upwash inboard) and a slipstream Mach number of 0.87 indicate a penalty equivalent to a 0.024 loss in propeller efficiency. However, at 11° the drag increment was favorable and was equivalent to a 0.032 increase in propeller efficiency. Wing pressure data indicated the effects of the slipstream were essentially restricted to that section washed by the slipstream.

The paper provides an overview of the renewed interest in turboprop propulsion systems for future commercial transport designs. The potential operating cost advantage of advanced turboprop designs is shown relative to advanced turbofan designs. Critical technology items for the aerodynamic installation of turboprop propulsion systems are presented, along with experimental results addressing the main technology issue for wing-mounted turboprop installations. Nacelle installation effects are presented for overwing and underwing nacelles. The drag reduction for nacelle contouring is also shown. Wing/nacelle/power data are presented for the baseline wing geometry and for a wing modified to reduce the propeller power effects.