Development of an Inlet for a Tilt Nacelle Subsonic V/STOL Aircraft

Abstract

A fixed geometry inlet capable of efficient operation to very high angles-of-attack has been developed by the Grumman Aerospace Corporation for a tilt nacelle subsonic V/STOL airplane. The inlet, sized to fit a 5.5-in. (13.97 cm) diameter fan, has been extensively tested and demonstrated very high pressure recoveries and low distortions at higher angles-of-attack than any of the published inlet data to date, including an inlet with the very high contraction ratio of 1.78 on the windward lip. This inlet capability has been achieved by judicious selection of the inlet design parameters affecting flow separation. The substantial angle-of-attack capability of the inlet provides the opportunity for trading off some of the margin at low speed to reduce nacelle maximum diameter, hence weight, and to increase the estimated drag divergence Mach number of 0.75 to higher than Mach 0.80. Tests with lower lip contraction ratio show that this may be possible and investigations exploring this possibility are now in progress at NASA/Lewis.