Nonlinear Folding Wing Tips for Gust Loads Alleviation

Within the scope of sustainable aviation, increasing the operational efficiency and diminishing pollutant emission is a key requirement for future transonic transport aircraft development. In an aerodynamic context, dynamic folding wing tips (FWT) show to possess great potential in the context of future aircraft design. On the one hand the folding wing tip enables higher wing spans, meanwhile meeting airport gate and runway limitations. Additionally, the FWT concept offers the capability for load alleviation under gust, also maintaining optimal efficiency in cruise flight condition. In this work, the implementation of a nonlinear folding wing tip on a transonic transport aircraft wing is numerically investigated. Unsteady Reynolds Averaged Navier-Stokes simulations are conducted in cruise flight condition at an altitude of h = 35 000 ft, an angle of attack (AoA) of [angle of attack] = 1° and a free-stream Mach number Ma[freestream/ ambient conditions] = 0.78. In the early design phase, the wing and the FWT segment are considered as rigid bodies, modelling a rotation of the FWT segment around the hinge line. Possible interactions between wing, nacelle and fuselage are neglected. Therefore only the wing and FWT segment are considered. The gust is characterised by a 1-cosine gust defined by certification specifications CS25. A sensitivity analysis evaluates the effect of the hinge angle [flare angle] = 45. on the lift coefficient, the root bending moment as well as the pressure distribution at the wing surface. The effects are compared to the baseline configuration, fold angle [fold angle] = 0. Under gust load, the non-linear fold yields to a maximum reduction of the AoA at the FWT to [Delta angle of attack] = -4.03. Thus, the wing root bending moment (WRBM) diminishes by [delta] CwRBM = 10.0%, concurrently the lift coefficient alleviates only by [delta]CL = 4.24%. Further, flow field analysis verifies the load alleviation on the FWT segment. A potential oblige shock can be identified at the transition between the wing and the non-linear FWT segment.