Survey of Blunt Body Dynamic Stability in Supersonic Flow <s> E. Shoulder Geometry <s> An experimental program has been conducted in ballistics ranges to investigate the aerodynamic characteristics of three candidate NASA configurations for a Mars probe/lander: a blunted 60° half-angle cone, a spherical segment, and a blunted tension shell. The drag, staticand dynamic-stability coefficients were determined in air for Mach numbers from 0.6 to 13. At supersonic and hypersonic Mach numbers, the drag coefficients corrected to zero angle of attack were slightly higher for the spherical-segment configuration than for the other two shapes. All three configurations were statically stable. The dynamic-stability coefficients for the 60° half-angle cone and spherical-segment configurations were stabilizing in the supersonic and hypersonic region. Destabilizing dynamic-stability coefficients were measured for all three configurations in the transonic region. <s> BIB001 </s> Survey of Blunt Body Dynamic Stability in Supersonic Flow <s> E. Shoulder Geometry <s> Analytical studies indicate that rolling blunt entry vehicles are susceptible to angle-ofattack divergence in the terminal regime. To investigate this problem, an experimental program was conducted where models were spun up and dropped inside the 500-ft-high Vehicle Assembly Building at Cape Kennedy. The angle-of-attack motion was recorded photographically, and from these data the dynamic stability coefficient was determined. The data confirm the results of the analytic studies and suggest that the dynamic stability coefficient increases, in a favorable way, as the roll rate increases. <s> BIB002
Low subsonic drop tests by Jaffe BIB002 indicated a slight decrement in stability performance for sphere cone bodies having rounded shoulders (shoulder radius 5% of maximum diameter) compared to that of a sharp configuration. Transonic studies by Krumins BIB001 and Sammonds  noted no noticeable difference for near identical forebody configurations and shoulder radii. Fletcher's  results for flat faced, expanding 10 o conical sections in subsonic flow noted significant improvement in stability performance when the corners were rounded to 10% of the maximum diameter. However, this effect was not present when he tested identical models at a Mach number of 2.91  . Also, when contracting conical sections were examined for the same effect, it was found that rounding the corner to 15% also improved subsonic stability, although to a lesser extent than the expanding configuration. Having a sharp shoulder provides a discontinuity that provides a fixed separation point for the flow as it accelerates over the body. Schlieren images of Fletcher's M=2.91 test shown in Fig. 21 demonstrate this effect. The flow features downstream of the bow shock are more defined for the sharp cornered body relative to those for the body with the rounded shoulder. Taking this into consideration, it is possible that the environment behind the sharp body would experience less temporal variation and thus less pressure variation on the aftbody to induce instabilities. This hypothesis would coincide with Jaffe's results. Conversely, if the recompression shock were strengthened due to the pressure of a steadier flow field, the recirculation region behind the body may actually see stronger pressure fluctuations through the interaction between the recompression shock and the base flow. This mechanism was proposed by Teramoto  . Given the previous discussion, we see that conflicting conclusions could be drawn regarding effect of corner radius on the dynamic response, depending on the interpretation of the resulting flow structure.