High Altitude Long Endurance (HALE) configurations have gained much popularity in the recent past. Although, HALE aircraft enable efficient and environmental-friendly flying, they necessitate a large Aspect-Ratio wing. These slender structures are prone to large, non-linear deformations which further increase the unsteady nature of aerodynamic flow that can detrimentally impact the structure. In the light of this trend towards an efficient aviation industry of tomorrow, Airbus Innovations UK has ventured into the development of a folding wing tip concept whose benefits are two-fold. First, is the ability to increase span during flight, thereby reducing the induced drag. The folding capability also ensures entry gate requirements at airports. Secondly, the folding mechanism presents load alleviation capabilities with appropriate hinge setup. Alleviation of loads on lifting surfaces directly translates to reduction of the Wing Root Bending Moment (WRBM), which means a reduction of weight. Thus, a further improvement in efficiency of flight. In this work, a nonlinear aeroelastic solver is developed. The proposed partitioned framework couples the industry standard commercial software package MSC Nastran, a structural solver to the Unsteady Vortex Lattice Method (UVLM), an aerodynamic solver. The UVLM module developed, exhibits both static and dynamic capabilities. Three wake models are incorporated. Horse-shoe wake is employed for static simulations and convective wake procedures are available for transient dynamic simulations. The independent modular solvers are coupled using Radial Basis Functions (RBFs) and Nearest Neighbour (NN) approaches. This framework enables the solver to capture the combined effects of structural nonlinearities and unsteady flows. The proposed solver is then verified and validated for two different test cases: NASA CRM Wing and Pazy Wing. Experimental validation is carried out using existing results from related work. The solver is then used to evaluate the “AlbatrossOne”, a hinged wingtips concept by Airbus Innovations UK. Both static and dynamic responses are analysed for load alleviation capabilities.

Recent decades have seen the range of applications for aircraft expand to niches like weather monitoring, reconnaissance and satellite launch (Air Launch to Orbit, ALO). The requirements for such roles necessitate unconventional features like twin fuselages (in case of ALO mother ships) and very high aspect ratio wings (for long endurance missions). For conventional aircraft, aside from improving safety, the driving factors for new designs have always been increased efficiency and performance. The prevalent approach has been to reduce weight and induced drag by using higher aspect ratio wings. Consequently, newer designs are lighter, more flexible and closer the failure limit. Therefore, the interaction between flight loads and the airframe, i.e.\ aeroelasticity has become important for a safe design. High aspect ratio wings undergo large magnitude, low-strain deformations. An accurate understanding of their aeroelastic behaviour requires nonlinear analysis methods. This thesis implements a reliable nonlinear aeroelastic analysis method in NASTRAN. The aeroelastic analysis modules in commercial finite-element analysis software are aerodynamically and structurally linear. At the same time, such software often has advanced nonlinear structural analysis capabilities. This thesis modifies and combines two approaches mentioned in literature. NASTRAN's aeroelastic module is used to obtain rigid aerodynamic loads and its nonlinear structural module to obtain structural deformations. For a given angle of attack, altitude and airspeed a wing is analysed iteratively until the rigid air loads and structural deformations for successive iterations converge. The nonlinear structural module is used to obtain pre-stressed structural modes for this converged condition. These modes are then used in flutter analysis. An idealised HARW with arbitrary properties is analysed using this method and using TU Delft's in-house aeroelastic optimisation software: Proteus. Static aeroelastic deformations and flutter analysis results are compared for validation. Following this, the results of the linear and nonlinear aeroelastic analysis are compared. It is shown that linear analysis over-predicts the deformation in flexible wings and that the inclusion of pre-stress changes the damping of critical flutter modes; thereby changing the flutter point for the wing. For the test case analysed in this thesis, the inclusion of geometric nonlinearity and follower force effects resulted in large changes in the flutter speed with change in the angle of attack. In this way, the thesis successfully implements a nonlinear aeroelastic analysis method which can be used to improve aircraft designs during the preliminary stage.