High aspect-ratio flying wing configurations designed for high altitude, long endurance missions are characterized by high flexibility, leading to significant static aeroelastic deformation in flight, and coupling between aeroelasticity and flight dynamics. As a result of this coupling, an integrated model of the aeroelasticity and flight dynamics has to be used to accurately model the dynamics of the flexible flying wing. Such an integrated model of the flight dynamics and the aeroelasticity developed by Patil and Hodges is reviewed in this dissertation and is used for studying the unique flight dynamics of high aspect-ratio flexible flying wings. It was found that a rigid body configuration that accounted for the static aeroelastic deformation at trim captured the predominant flight dynamic characteristics shown by the flexible flying wing. Moreover, this rigid body configuration was found to predict the onset of dynamic instability in the flight dynamics seen in the integrated model. Using the concept of the mean axis, a six degree-of-freedom reduced order model of the flight dynamics is constructed that minimizes the coupling between rigid body modes and structural dynamics while accounting for the nonlinear static aeroelastic deformation of the flying wing. Multi-step nonlinear dynamic inversion applied to this reduced order model is coupled with a nonlinear guidance law to design a flight controller for path following. The controls computed by this flight controller are used as inputs to a time-marching simulation of the integrated model of aeroelasticity and flight dynamics. Simulation results presented in this dissertation show that the controller is able to successfully follow both straight line and curved ground paths while maintaining the desired altitude. The controller is also shown to be able to handle an abrupt change in payload mass while path-following. Finally, the equations of motion of the integrated model were non-dimensionalized to identify aeroelastic parameters for optimization and design of high aspect-ratio flying wings. / Ph. D.

A set of techniques is developed that allows the incorporation of flight dynamics metrics as an additional discipline in a high-fidelity aerodynamic optimization. Specifically, techniques for including static stability constraints and handling qualities constraints in a high-fidelity aerodynamic optimization are demonstrated. These constraints are developed from stability derivative information calculated using high-fidelity computational fluid dynamics (CFD). Two techniques are explored for computing the stability derivatives from CFD. One technique uses an automatic differentiation adjoint technique (ADjoint) to efficiently and accurately compute a full set of static and dynamic stability derivatives from a single steady solution. The other technique uses a linear regression method to compute the stability derivatives from a quasi-unsteady time-spectral CFD solution, allowing for the computation of static, dynamic and transient stability derivatives. Based on the characteristics of the two methods, the time-spectral technique is selected for further development, incorporated into an optimization framework, and used to conduct stability-constrained aerodynamic optimization. This stability-constrained optimization framework is then used to conduct an optimization study of a flying wing configuration. This study shows that stability constraints have a significant impact on the optimal design of flying wings and that, while static stability constraints can often be satisfied by modifying the airfoil profiles of the wing, dynamic stability constraints can require a significant change in the planform of the aircraft in order for the constraints to be satisfied.

A set of techniques is developed that allows the incorporation of flight dynamics metrics as an additional discipline in a high-fidelity aerodynamic optimization. Specifically, techniques for including static stability constraints and handling qualities constraints in a high-fidelity aerodynamic optimization are demonstrated. These constraints are developed from stability derivative information calculated using high-fidelity computational fluid dynamics (CFD). Two techniques are explored for computing the stability derivatives from CFD. One technique uses an automatic differentiation adjoint technique (ADjoint) to efficiently and accurately compute a full set of static and dynamic stability derivatives from a single steady solution. The other technique uses a linear regression method to compute the stability derivatives from a quasi-unsteady time-spectral CFD solution, allowing for the computation of static, dynamic and transient stability derivatives. Based on the characteristics of the two methods, the time-spectral technique is selected for further development, incorporated into an optimization framework, and used to conduct stability-constrained aerodynamic optimization. This stability-constrained optimization framework is then used to conduct an optimization study of a flying wing configuration. This study shows that stability constraints have a significant impact on the optimal design of flying wings and that, while static stability constraints can often be satisfied by modifying the airfoil profiles of the wing, dynamic stability constraints can require a significant change in the planform of the aircraft in order for the constraints to be satisfied.

No description available.