Worst Case Gust Prediction of Highly Flexible Wings

In this work, the effect of aircraft flexibility on 1g and gust loads is investigated. A commercial aircraft with high aspect ratio wings (HARW) is generated as a baseline case using an in-house sizing tool, with variants of the aircraft created with a reduced stiffness via changes in skin thicknesses, including the associated mass reduction. These aircraft variants are modelled using an aeroelastic code based on an intrinsic beam theory in order to understand the effects of large, geometrically nonlinear deformations on the loads due to level flight and atmospheric turbulence in the form of "1-minus-cosine" gusts. The full, nonlinear results are compared to the same results obtained from the linear system and the linearised system to determine the limits of linear analyses on gust loads predictions. It was seen that reducing the wing stiffness on the baseline aircraft reduced 1g loads due to mass reduction, and also reduced the certain loads envelopes such as root torque and root bending moment by around 17% and 41%, respectively, compared to the baseline. Linear analyses consistently over-predicted these loads as well as the critical gust length, even for the stiffest cases, but severely under-predicted axial and fore-aft loads. However, the large deformations at 1g trim did not cause any round-the-clock gusts to become more critical than a purely vertical gust.