Abstract:

Acoustic measurements were made on the bottom surface of the 86% scale large-scale propulsion model (LSPM) of an advanced short takeoff and vertical landing (ASTOVL) airplane. The measurements were ob-tained during fixed hover heights where the lower wing surface varied from 5 ft (airplane's wheels on the ground) through 36 ft above the ground for a wide range of propulsion thrust mixes and airplane control surface configurations. The complete propulsion system provided four exhausts through an integrated unit consisting of an aft located main jet engine, which powered a forward located shaft driven lift fan and was completed with two main engine bleed high-pressure bypass roll jets (in the wings). Flush surface measurements were made at 12 locations on the bottom surfaces and time correlated with the operating propulsion parameters. An empirical acoustic model was made through analyses of the geometry and the data, and was used to predict contours on the bottom of the aircraft. [This work was performed by Lockheed Martin Skunk Works at the NASA-Ames Research Center.]