The work presented in this paper describes the modelling of a low-order aeroelastic solver, built with the aim of analysing the dynamics of very flexible wing aircraft, with a focus on the coupling between the flight dynamics and the structural dynamics. The model implements a geometrically exact, low-order nonlinear beam solver based on beam shape functions coupled with Vortex Lattice Method (VLM), specifically adapted to account for large deformations. The static solution calculated by implementing the VLM was compared with the one calculated using strip theory as aerodynamic solver, showing good agreement in magnitude, but different load distribution. The aeroelastic solver was then used to analyse the dynamics of a flexible aircraft constrained to a circular trajectory with free pitch (resembling the motion on a Pendulum Rig) and on a spherical motion with free pitch and yaw (resembling the motion on the University of Bristol 5-DOF Manoeuvre Rig), for two different values of pitch stiffness and three different flexible wings (5% deflection, 10% deflection and 15% deflection with respect to the wing semispan). The results show that when the stiffness is high, it suppresses any interaction between the flight dynamics and the structural dynamics. Therefore there is no impact of the wing flexibility on the aircraft motion. On the other hand, when lowering the value of the pitch stiffness, the interaction between the wing dynamics and the pitch dynamics become evident. However, the impact of the wing flexibility was found to be always negligible on the yaw dynamics.
High aspect ratio wings have been a major topic for research due to their capability to improve the aerodynamic efficiency of modern aircraft. Many numerical studies have shown their flexibility causing nonlinearity through geometric effects and their impact on internal loads and dynamics, such as reduced flutter speed and coupling with the aircraft body causing body freedom flutter. Experimental work is present in the literature for validation of cantilever wing models but only a few have implemented wind tunnel testing on dynamically-mounted full-span aircraft models. The work presented here develops a rigid-flexible coupled numerical model for a wind tunnel test platform known as the 5-degree-of-freedom manoeuvre rig. This model is used for the simulation of a full-span flexible model aircraft constrained by the rig for the investigation of the coupling between rigid body and flexible modes together with geometric nonlinear effects. The modeling of the wing flexibility is based on a reduced order geometrically exact structural method linked with a vortex lattice aerodynamic model. The aircraft fuselage and empennage, and the manoeuvre rig, are modelled as rigid bodies. The findings of the study will aid future experimental wind tunnel explorations.
Spoilers are secondary control surfaces mainly used for roll control, load alleviation and as airbrakes. However, when considering very flexible wings, spoilers could also play a primary role in controlling the aircraft's attitude as an ideal alternative or complement to ailerons since they are distributed over the wingspan and, therefore, potentially less affected by the wing deformation. However, due to its nonlinear nature, spoilers aerodynamics can only be accurately simulated through high-fidelity software, such as CFD. The work presented in this paper aims to provide a novel method to model spoiler aerodynamics in a low-fidelity Unsteady Vortex Lattice framework by proposing an approach able to predict the impact of multiple spoilers on the wing lift distribution. The approach is verified through data acquired in a series of wind tunnel tests on a rigid wing equipped with servo-controlled spoilers carried out in the University of Bristol Low Turbulence Wind Tunnel. Load cell measurements and PIV data are shown for comparison. Numerical predictions show good agreement with the experimental data proving the low-fidelity UVLM aerodynamic solver's ability to successfully model the nonlinear flow field behind the extended spoiler.
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