Lateral dynamics of flight on a great circle.

The lateral stability of a hypersonic vehicle representative of a space shuttle or hypersonic transport is calculated at two lift coefficients at speeds up to parabolic. Linearized equations of motion are used and Newtonian Impact Theory is utilized for stability derivative estimation. The damping in the natural modes is very small or negative, the dominant motion being an extension of the conventional Dutch Roll mode. The mode is unstable for high subcircular speeds. Coupling of the roll-convergence and spiral modes occurs at about 40% of circular speed and after decoupling, some instability exists at supercircular speeds. A new undamped mode describing lateral position variation's found exactly. The results are not very sensitive to CL and approximations to the modes are discussed and compared with the numerical solutions.