Effects of nacelle position and shape on performance of subsonic cruise aircraft

The reduction of installed-propulsion-system drag by installing circular and D-shaped-cross-section nacelles in an underwing-aft position is investigated experimentally in the NASA-Langley 16-foot transonic wind tunnel. Measurements were made at Mach 0.70 to 0.85, -2.5 to 4.1-deg angle of attack, and 3.4 to 4.0 million/ft Reynolds numbers using the NASA USB full-span transonic transport model; and results were compared with those for the wing-body and underwing-forward/pylon-mounted-nacelle (UTW) configurations. While all nacelle configurations are found to have interference drag, which can probably be reduced by eliminating supersonic flows, both aft configurations are shown to reduce drag relative to UTW and increase lift coefficients. The aft D-nacelle had the lowest drag, 6.8 percent of airplane drag lower than UTW at Mach 8.0 and lift coefficient 0.45. Wing pressure distributions and the effects of deflectors are discussed.