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

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Steady two-dimensional compressible turbulent boundary-layer flow past a slightly wavy wall is studied both analytically and experimentally in the Mach number range 0.8 ^ M e ^ 1.8 at unit Reynolds numbers on the order of 10 6 per inch. The measured and predicted wall pressure distributions are in good agreement and indicate that the nonuniform flow in the boundary layer can produce essentially a subsonic type of wall pressure signature (p max in valleys) in the presence of moderately supersonic inviscid flows. An interesting cusping of the pressure is also observed in the transonic regime. Measurements of the wall temperature perturbations are also made; the results agree with theory in showing a strong correlation between 7^a x and P max .

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