Effect of elastic case on stability of radial modes in solid propellant rockets

The coupling of the combustion process and the mechanical vibrations of a solid propellant rocket may result in acoustic instability if a mechanical disturbance is amplified by energy release in the combustion zone. Acoustic stability depends on the balance of energy sources and energy sinks. Energy dissipations in the gas and the viscoelastic solid propellant binder are taken into account. The instantaneous frequencies of the structural system are determined from the undamped system. In this paper the influence of relative thickness of the elastic case on acoustic stability of the lowest radial mode is discussed. It is found that in the early part of the burning process a thicker case makes a more stable motor. Near burnout, however, the motor becomes more stable for a thinner case.