Elasto-static and modal modeling on flexible wings carrying multiple external stores

The design of highly flexible aircraftinvolves several critical phenomena which are not considered in traditional aircraft design. Large structural deflections under nominal loads and flight conditions, point out that linear structural models are often inadequate in the accurate flutter prediction. In place of a linear Euler-Bernoulli theory, usually sufficient in the evaluation of natural frequencies of slender structures when deflections are lower than transversal dimensions, a nonlinear analysis is required as there is strong dependency between natural frequencies and beam deflections which could lead to flutter instability at lower flight speeds. The model complexities increase when one or more stores are placed under the wing. In this study numerical and experimental investigations are carried out to better understand the nonlinear behaviour of highly flexible wings with external stores positioned at selected spanwise, chordwise, and flapwise stations, when both geometrical and aerodynamic nonlinearities are not negligible. Good correlation between numerical and experimental investigations was found, showing strong edge and torsion frequencies and associated mode shapes dependency on the initial deformation.