EVALUATION OF STABILITY TRENDS THROUGH STATIC TESTING IN TACTICAL MOTORS

This paper describes static testing of full-scale tactical solid rocket motors with pulsing to study stability characteristics to varying pulse amplitudes. Four tests were conducted in motors having identical casing and finocyl grain geometries using reduced smoke composite propellant. Spherical polytetrafluoroethylene balls (ejecta) with diameters of 15, 20, 25, and 30 mm were employed to achieve pulse amplitudes of 0.5% of motor pressure and higher. Each motor was pulsed twice at 65% and 80% of burn times. The observations from these tests have been brought out in this paper. The pulse caused a small DC pressure shift in the pressure even when the motor is stable to the pulse amplitude imposed. The margin of stability was -36 s<sup>-1</sup> for a pulse amplitude of 1% (20-mm ball) of the motor pressure. The motor could be pulsed into nonlinear instability with a pulse amplitude of 1.6% (25-mm ball) and, as expected, with a pulse amplitude of 3.65% (30-mm ball). The DC pressure shift and peak-to-peak amplitude of limit cycle oscillations are almost the same in both cases, indicating that these are independent of the pulse amplitude beyond the critical value of pulse amplitude. The impressed pulse has no additional effect on the motor pressure once the motor is experiencing limit cycles with a DC shift.