GAU-8 Projectile Afterbody Drag Reduction by Boattailing and Base Injection with Heat Addition.
Final rept. Jul 77-May 78,
AIR FORCE FLIGHT DYNAMICS LAB WRIGHT-PATTERSON AFB OH
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An experimental investigation was performed on a GAU-8 mm projectile model in order to determine whether base injection of different gases at a temperature of up to 900 R, which simulates the effects of fumers, would produce a reduction in the afterbody drag. Wind tunnel tests were performed at Mach 3, using different boattail angles and two different gases, air and helium. Pressure data were taken, together with schlieren photographs illustrating the flow field. Results show that afterbody drag reduction of 30 to 40 is obtained by small gas injection. Afterbody boattail angles of 4 to 7 angles additionally reduce the afterbody drag by about 15. Injection of gas heated to 700 R does not further reduce the afterbody drag but increasing the temperature of the injected gas up to 900 R produces an afterbody drag reduction of approximately 15. For the same mass injection rates, helium injection is more efficient than air. Author
- Ammunition and Explosives