Stability testing of full-scale tactical motors

The U.S. Naval Air Warfare Center has participated in a program to develop an improved understanding of linear and nonlinear combustion instability in solid propellant rocket motors. One goal of this program was to develop a systematic database of motor and stability data. This paper describes the linear aspects of the motor firings and analysis. The motors that were used had diameters of 127 mm and were 1.7 m long. The majority were loaded with an 88% solids reduced-smoke ammonium perchlorate propellant with a nominal burning rate of 6.1 mm/s at 6.9 MPa. In addition, motors have been fired that contain 1% 8-mu m aluminum oxide, 90-mu m aluminum oxide, and 3-mu m zirconium carbide as stability additives in place of 1% ammonium perchlorate. Motor pressures ranged from 3.45 to 10.34 MPa and various grain geometries were tested. Pressure-coupled combustion response measurements were made at the nominal motor operating pressures, Motor performance and stability calculations were made using the Air Force Solid Performance Program and the Standard Stability Prediction Program for the motor configurations that were fired. The stability predictions were compared to the data obtained from the motor firings. The results indicate that it is possible to theoretically predict linear motor stability for the class of motors discussed in this paper. It was also learned that higher-pressure motors tend to be less stable and that stability additives are very effective in controlling pulsed instabilities.