Static aeroelasticity: a formal analysis using assumed modes.
Abstract:ESDU 97032 gives a formal analysis of the equilibrium behaviour of a flexible aeroplane of classical configuration in trim or in a quasi-steady pull-out manoeuvre. The aeroplane has a swept wing and tailplane, both flexible in bending and torsion about straight flexural axes, a rigid fuselage, and wing-mounted rigid nacelles. Two structural configurations are considered: with the wing and tailplane ribs normal to the swept flexural axis and with them aligned to the freestream direction. The bending and twist distributions of the wing and tailplane are assumed to be the sum of a set of individual modes, each mode consisting of an amplitude multiplied by its spanwise shape. The mode shapes used are an orthogonal set that satisfy the boundary conditions for a uniform elastic beam built-in at its root, taken here to be normal to the swept flexural axis. Expressions for overall static stability, given by the elevator trim margin, for static stability at constant speed, given by the elevator manoeuvre trim margin, and for aeroelastic static stability, are provided. The coefficients are given of the set of simultaneous equations that determine the unknown variables (incidence, elevator deflection, and wing and tailplane bending and twist deformations) in terms of speed and normal acceleration for the configuration with ribs normal to the relevant flexural axis.
|Data Item ESDU 97032