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Post-test sidewall insulation measnrements obtained from static firings of the Titan 34D and Tj.tan IV solid rocket motors (SRMs) revealed twc regions of thin insulation approximately 180" apart in each segment. Since the insulation ablatjon rate should not be dependent on angular positi.on, the added ablation was believed to be the result of an increase in the time the insulation was exposed to hot propellant gas, probably caused by the propellant burning in an asymmetric manner. To quantify the extent of the asymmetric burning, the insulation ablated depth data was reduced to give the increase in propellant burn rate required to cause the observed marks. A statistical analysis was then performed on the burn rate increase data so that the safety o f the vehicles could be judged from an insulation standpoint. v

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Experiments involving either sublimation or evaporation at the base surface of a cylindrical cavity were performed respectively using naphthalene and water as the transferred vapor. The cavity was mounted in the lower wall of a flat rectangular duct through which turbulent air was passed. Supplementary experiments were also carried out using a cavity with a constricted opening (i.e., a Helmholtz resonator). The base surface mass transfer did not decrease monotonically with increasing cavity depth. Rather, there were two local maxima, respectively at about 0.06D and 0.5D (D = cavity diameter). Of these, the first is due to the reattachment of the shear layer on the cavity base. For the second, both fluid-elastic and fluid-resonant oscillations were ruled out as causes on the basis of definitive experimental data, leaving fluid-dynamic oscillations as a possible cause. The base surface Sherwood number was well correlated by power-law dependences on the Reynolds and Schmidt numbers. Fluid flow experiments encompassing oil-lampblack flow visualization, helium bubble flow visualization, and spectral analysis of the pressure field at the cavity base were also carried out.