Effects of Flow Separation on Shuttle Longitudinal Dynamics and Aeroelastic Stability

The longitudinal dynamic and aeroelastic stability characteristics of various shuttle configurations have been investigated at transonic speeds. Wing flow separation dominates the orbiter dynamic stability in a manner that indicates a potential aeroelastic problem for the first torsional mode of the orbiter wing. Throughout the transonic speed range, flow separations of various types are shown to dominate both dynamic and aeroelastic stability of the launch configuration, causing limit cycle oscillations of certain symmetric elastic modes. The limit cycle oscillations threaten the structural integrity in two ways: 1) by outright overstressing of the structure due to large modal deflection, and 2) by fatigue due to the continued flexing of the structure. Fatigue is a more significant consideration for the reusable (100 flights) shuttle than it has been for previous space boosters, especially in view of the coexisting problem of thermocycling.