Novel aircraft configurations are being proposed to meet the demanding environmental goals of the future of aviation. The proposed configurations range from wings with an increased aspect ratio to completely novel designs, such as joined-wing configurations. These configurations show increased aerodynamic efficiency, resulting in overall reduced fuel consumption. These benefits come at a cost of added structural complexity—longer wings require a more careful design of their internal structure, are heavier, and are subject to larger deflections—and unpredictable aeroelastic effects during flight—joined-wing aircraft are prone to buckling of the aft wing and tail boom.
On the one hand, characterizing these novel aircraft configurations in terms of their aeroelastic behavior is of extreme importance if they are to be used in future commercial aircraft designs. Due to the significant cost and risk associated with the testing of full-scale aircraft, reduced-scale flexible unmanned air vehicle (UAV) models are an attractive alternative that can be used to understand the aeroelastic behavior of these designs during flight. On the other hand, current aeroelastic computational codes are relatively new, and their ability to accurately predict the aeroelastic performance of full-scale aircraft requires extensive validation. There is a need for experimental data sets demonstrating in-flight aircraft elastic behavior for tuning such models.
Flexible UAV demonstrators have been developed for the study of active flutter suppression systems, to validate flight dynamics models, identify structural vibration modes and validate design methodologies. However, few studies have focused on developing reduced-scale models to investigate the nonlinear behavior of joined-wing aircraft. Previous work has demonstrated the airworthiness of scaled joined-wing demonstrators through the successful flight of geometrically-scaled remotely piloted vehicles, but the assessment of geometric nonlinearities in flight is yet to be determined.
The main objective of this work was to characterize the aeroelastic behavior of novel aircraft models through the design and testing of flexible linear and nonlinear reduced-scale UAV demonstrators and to explore the development of medium-fidelity tools for the dynamic aeroelastic analysis of such models. To this end, reduced-scale flexible high aspect ratio wing (HARW) and joined-wing aircraft configurations were designed, manufactured, tested, and characterized numerically through aerodynamic, structural, and aeroelastic studies, and experimentally through flight testing. A unified medium-fidelity aeroelastic framework based on an accelerated unsteady panel method and a flexible multibody dynamics formulation based on absolute coordinates was developed and used to investigate the unsteady aerodynamics of the two aircraft models.
This work illustrates the feasibility of using flexible reduced-scale flight test demonstrators as cost-effective platforms for testing the aeroelastic response of HARW aircraft configurations. It also reinforces the importance of accounting for geometric nonlinearities in the aeroelastic analysis of joined-wing configurations. The developed framework also expands the application range of flexible multibody dynamics based on absolute coordinates in time-domain simulations of large elastic deformations coupled with rigid body motion that arise in next-generation aircraft.