The principle of minimum potential energy is used in conjunction with the Rayleigh-Ritz method to derive the flutter equation for flat, rectangular, orthotropic panels in terms of orthogonal assumed modes and uncoupled generalized coordinates. Orthotropic stiffness components and midplane stresses are assumed to be independent of the panel coordinates, and airloads are represented by a quasi-steady supersonic aerodynamic expression, valid for M > 2 1/2 . Viscous structural damping is also included. The applicable panel boundary conditions for the flutter equation are 1) simply supported on all four edges, 2) clamped on two parallel edges and simply supported on two parallel edges, and 3) clamped on all four edges. An alternate flutter equation is presented in terms of normal coordinates. Stability boundaries are computed, and curves are presented for example isotropic and orthotropic panels. An assessment of the effect of stiffness coupling for clamped isotropic panels shows that previous theoretical solutions are in considerable error for high panel length-to-width ratios and high midplane tensile stresses. Stability boundaries presented herein for orthotropic panels illustrate the effect of panel boundary conditions and angle of orthotropicity. Convergence studies were conducted for both isotropic and orthotropic panels, and resulting difficulties are identified.

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