A base drag reduction experiment on the X-33 linear aerospike SR-71 experiment (LASRE) flight program

Drag reduction tests were conducted on the LASRE/X-33 flight experiment. The LASRE experiment is aflight test of a roughly 20-percent scale model of anX-33 forebody with a single aerospike engine at the rear.The experiment apparatus is mounted on top of anSR-71 aircraft. This paper suggests a method forreducing base drag by adding surface roughness alongthe forebody. Calculations show a potential for basedrag reductions of 8 to 14 percent. Flight resultscorroborate the base drag reduction, with actualreductions of 15 percent in the high-subsonic flightregime. An unexpected result of this experiment is thatdrag benefits were shown to persist well into thesupersonic flight regime. Flight results show no overallnet drag reduction. Applied surface roughness causesforebody pressures to rise and offset base dragreductions. Apparently the grit displaced streamlinesoutward, causing forebody compression. Results of theLASRE drag experiments are inconclusive and morework is needed. Clearly, however, the forebody gritapplication works as a viable drag reduction tool.