Aerodynamic Effect Of Exhaust Plumes

The effect of rocket exhaust jets or plumes on the aerodynamic characteristics of a missile is usually to decrease the vehicle drag at supersonic missile speeds and to increase it at subsonic speeds. On subsonic vehicles, a supersonic rocket plume acts very much like an ejector and sucks adjacent air into its path. This affects vehicles where the rocket is located on a tapering aft end. The ejector action of the flame accelerates the adjacent air, thereby increasing the skin friction locally and usually reducing the pressure on the vehicle aft body or base plate near the nozzle exit location.

At supersonic speeds there often is a turbulent wake area with a low local pressure at the aft end of projectile. With the action of a rocket plume, the void space is filled with rocket gases and the pressure on the aft portion of the body is increased. This increases the pressure thrust and thus reduces the base drag. Exhaust plume effects are discussed in Chapter 18. In fact, some artillery munitions and short-range rockets can achieve increased range (by 10 to 50%) by adding a small rocket-type gas generator; its plume fills the void at the base of the projectile with reaction gas at a finite pressure, thus increasing the base pressure of the projectile and reducing the base drag.

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Project Management Made Easy

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