Experimental Studies of Ablation Surface Patterns and Resulting Roll Torques

Because of the interest in differential ablation patterns and their implications for the roll characteristics of small hypervelocity vehicles, conical models covered with various lowtemperature ablative materials were tested in a hypersonic wind tunnel. A unique feature of these tests was the direct measurement of roll torques during the actual ablation process. These tests were conducted at Mach 6 on sharp-nosed models, mostly subliming camphor and special Korotherm. The scale of cross-hatchin g is shown to decrease with increasing pressure for camphor. The ablation pattern of melting-vapor izing naphthalene is similar to that of subliming camphor. The cross-hatched pattern of subliming Korotherm in the wind tunnel is found to be similar to that of silica phenolic in flight. Some rolling moment coefficient data are presented.