A twin-engine, low-wing transport model, with a supercritical wing of aspect ratio 10.8 designed for a cruise Mach number of 0.77 and a lift coefficient of 0.55, was tested in the Langley 16-Foot Transonic Tunnel. The purpose of this test was to compare the wing-nacelle interference effects of flowthrough nacelles simulating superfan engines (very high bypass ratio (BPR ss 18) turbofan engines) with the wing-nacelle interference effects of currenttechnology turbofan engines (BPR ss 6). Forces and moments on the complete model were measured with a strain-gage balance, and extensive external static-pressure measurements (383 orifice locations) were made on the wing, nacelles, and pylons of the model. Data were taken at Mach numbers from 0.50 to 0.80 and at model angles of attack from 4ffi to 8ffi. Test results indicate that flow-through nacelles with a very high bypass ratio can be installed on a lowwing transport model with a lower installation drag penalty than for a conventional turbofan nacelle at a design cruise Mach number of 0.77 and lift coefficient of 0.55.