Design and Testing of Flexible Aircraft Structures

Methods for structural design, control, and testing of flexible aircraft structures are considered. Focus is on nonconventional aircraft configurations and control concepts. The interaction between analysis and testing is a central topic and all studies include validation testing and comparison between computational and experimental results. The first part of the thesis is concerned with the design and testing of an aeroelastic wind-tunnel model representing a Blended Wing Body (BWB) aircraft. The investigations show that a somewhat simplified wind-tunnel model design concept is useful and efficient for the type of investigations considered. Also, the studies indicate that well established numerical tools are capable of predicting the aeroelastic behavior of the BWB aircraft with reasonable accuracy. Accurate prediction of the control surface aerodynamics is however found to be difficult. A new aerodynamic boundary element method for aeroelastic timedomain simulations and its experimental validation are presented. The properties of the method are compared to traditional methods as well as to experimental results. The study indicates that the method is capable of efficient and accurate aeroelastic simulations. Next, a method for tailoring a structure with respect to its aeroelastic behavior is presented. The method is based on numerical optimization techniques and developed for efficient design of aeroelastic wind-tunnel models with prescribed static and dynamic aeroelastic properties. Experimental validation shows that the design method is useful in practice and that it provides a more efficient handling of the dynamic aeroelastic properties compared to previous methods. Finally, the use of multiple control surfaces and aeroelastic effects for efficient roll maneuvering is considered. The idea is to design a controller that takes advantage of the elasticity of the structure for performance benefits. By use of optimization methods in combination with a fairly simple control system, good maneuvering performance is obtained with minimal control effort. Validation testing using a flexible wind-tunnel model and a real-time control system shows that the control strategy is successful in practice. Design and Testing of Flexible Aircraft Structures 5