Survey of Blunt Body Dynamic Stability in Supersonic Flow <s> Axial and Transverse Sting Effects <s> Available experimental results are reviewed and organized to provide a logical explanation of aerodynamic support interference for dynamic wind-tunnel testing. Configurations involving bulbous bases, mass addition, boundary-layer transition near the base, and hypersonic low-density flows are shown to be particularly sensitive to sting interference effects. Transverse rod support interference occurs at all Mach numbers depending on oscillation amplitude and/or trim angle of attack. The postulated flow model predicts that cylindrical and flared stings can have opposite interference effects in agreement with experimental observations. An analytical method of correcting the wind-tunnel results for dynamic support interference is proposed. <s> BIB001 </s> Survey of Blunt Body Dynamic Stability in Supersonic Flow <s> Axial and Transverse Sting Effects <s> With the retirement of the Space Shuttle, NASA is designing a new spacecraft, called Orion, to fly astronauts to low earth orbit and beyond. Characterization of the dynamic stability of the Orion spacecraft is important for the design of the spacecraft and trajectory construction. Dynamic stability affects the stability and control of the Orion Crew Module during re-entry, especially below Mach = 2.0 and including flight under the drogues. The Launch Abort Vehicle is affected by dynamic stability as well, especially during the re- orientation and heatshield forward segments of the flight. The dynamic stability was assessed using the forced oscillation technique, free-to-oscillate, ballistic range, and sub-scale free-flight tests. All of the test techniques demonstrated that in heatshield-forward flight the Crew Module and Launch Abort Vehicle are dynamically unstable in a significant portion of their flight trajectory. This paper will provide a brief overview of the Orion dynamic aero program and a high-level summary of the dynamic stability characteristics of the Orion spacecraft. <s> BIB002
With knowledge that the near wake and its effects on the aftbody have a significant influence on the dynamic stability characteristics of a vehicle, efforts to reposition the forced oscillation sting to eliminate its contributions to the aftbody pressure field (and thus damping) have been. Dayman et al  suggest use of a transverse sting (crossing through the center of rotation of the vehicle) for Mach numbers greater than 3 or when studying damping at high angles of oscillation because the wake interference is "restricted to the sides of the aft portion of the model, where aerodynamic forces in the pitch plane are probably minor" for the class of models which were investigated. However, they cite earlier work by Dayman  that found significant alteration of the wake geometry for transverse supports as small as 2.5% of the model diameter and caution that dynamic response with a transverse sting is not to be assumed to be perfectly representative of free flight behavior. Reding and Ericsson BIB001 ,  compared the pitch damping of slender, bulbous-based, blunted cones with transverse and axial sting arrangements and found vast differences in the resulting dynamic response at Mach numbers between 1 and 2 ( Fig. 8) . Again, the largest discrepancies arise in the regime where dynamic stability issues are most critical. Their studies suggested that the transverse sting arrangement introduced an undamping effect on the vehicle while the axial sting improved damping. They point to the loads induced by the presence of a sting and their convective time lag in the near wake as the source for the interference for both sting configurations ( Fig. 9 ) BIB001 ,  . Accepting that it will be exceedingly difficult to eliminate the influence of either sting setup, they propose a "quasi-steady" technique to correct for the influence of the stings. This method combines interference loads and communication speeds within the wake (both determined from through measurements taken during static experiments) to ascertain the approximate induced normal loads. This technique assumes a small sting (i.e. neglects effects of the alteration of the wake geometry due to its presence). Using this technique, they site experimental extrapolation to zero sting size as a possible way to totally account for the effects, although getting a sufficiently small sting to ensure a confident extrapolation is difficult without sacrificing the required stiffness. During recent aerodynamic characterization of the Orion Crew Module by Owens et al BIB002 , a trade study on the sting angle for a forced oscillation test was conducted to determine if the sting geometry had a significant impact on the damping results. The damping was measured with the sting in an axial arrangement (0 o ) and with an entry angle of 27.5 The results for the subsonic and transonic Mach numbers are shown in Fig. 10 . It can be seen that the sting setup has a great influence on the resulting dynamic aerodynamic characterstics of the vehicle. As a result of this conclusion, a new transverse sting setup was implemented into the Langley Transonic Dynamics Tunnel (TDT), capable of doing forced oscillation, free oscillation, and static testing without changing the test setup (Fig. 11) . Like Reding and Ericsson BIB001 ,  , it was thought that the transverse sting arrangment would only affect the flow on the aftbody and be less intrusive on the near wake (and therefore dynamic response). The primary intention of the transverse setup was to reduce the angle of attack dependence of the sting effects.