Influence of base modifications on in-flight base drag in the presence of jet exhaust for Mach numbers from 0.7 to 1.5

The use of external modifications in the base region to reduce the base drag of a blunt-base body in the presence of jet engine exhaust was investigated in flight. Base pressure data were obtained for the following configurations: (1) blunt base; (2) blunt base modified with splitter plate; and (3) blunt base modified with two variations of a vented cavity. Reynolds number based on the length of the aircraft ranged from 1.2 to 3.1 x 10 to the 8th. Mach number M ranges were 0.71 less than or = M less than or = 0.95 and 1.10 less than or = M less than or = 1.51. The data were analyzed using the blunt base for a reference, or baseline condition. For 1.10 less than or = M less than or = 1.51, the reduction in base drag coefficient provided by the vented cavity configuration ranged from 0.07 to 0.05. These increments in base drag coefficient at M = 1.31 and 1.51 result in base drag reductions of 27 and 24 percent, respectively, when compared to the blunt base drag. For M less than 1, the drag increment between the blunt base and the modification is not significant.