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-hatching is shown to decrease with increasing pressure for camphor. The ablation pattern of melting-vaporizing 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.
NomenclatureA -ablation age = Ci = rolling-moment coefficient = rolling moment /qSd d = model base diameter M = Mach number p = pressure q -dynamic pressure, -g-pV 2 S = model base area T = temperature t = time W = thickness of material ablated away a =» angle of attack 5 -boundary-layer thickness 6 = cone half angle X = ablation surface pattern length (Fig. 8) = ablation surface pattern half angle o> = spin rate Subscripts co = freestream conditions e = boundary-layer edge L = local o = initial r = recovery conditions T = total or stagnation conditions w = wall conditions