A morphing aircraft can be defined as an aircraft that changes configuration to maximize its performance at radically different flight conditions. These configuration changes can take place in any part of the aircraft, e.g. fuselage, wing, engine, and tail. Wing morphing is naturally the most important aspect of aircraft morphing as it dictates the aircraft performance in a given flight condition, and has been of interest to the aircraft designers since the beginning of the flight, progressing from the design of control surfaces to the variable-sweep wing. Recent research efforts (mainly under DARPA and NASA sponsorships) however, are focusing on even more dramatic configuration changes such as 200% change in aspect ratio, 50% change in wing area, 5o change in wing twist, and 20o change in wing sweep to lay the ground work for truly multi-mission aircraft. Such wing geometry and configuration changes, while extremely challenging, can be conceptually achieved in a variety of ways - folding, hiding, telescoping, expanding, and contracting a wing, coupling and decoupling multiple wing segments, etc. These concepts can be classified under a few 'independent' categories and sub-categories so as to permit a systematic evaluation of benefits and challenges. This paper presents: 1) a review of prior work leading to current R&D efforts, 2) classification of morphing designs, and 3) a summary of technical challenges encountered in designing a morphing aircraft.
Gossamer or inflatable structures have been a subject of renewed interest for space applications because of their lightweight, on-orbit deployability, and minimal stowage volume. For these structures to be effective, their vibration must be controlled while maintaining the low weight and the foldability criteria. Piezoelectric materials have become strong candidates for actuator and sensor applications in the active vibration control of such structures due to their lightweight, conformability to the host structure, and distributed nature. In this study, vibration suppression of an inflated toroidal structure using piezoelectric actuators and sensors has been attempted. First, following the Sanders' shell theory, the governing equations of motion of a shell under pressure in the presence of piezoelectric patches have been presented, and the actuator/sensor equations are obtained. A sliding mode controller and a sliding mode observer are designed to suppress the vibration of the inflated toroidal structure using Macro-Fiber Composite (MFC) actuators and Polyvinylidene Fluoride (PVDF) sensors. The numerical simulations show that the piezoelectric actuators and sensors are suitable for vibration suppression of an inflatable structure. The robustness properties of the controller and observer against the parameter uncertainty and disturbances are also studied.
Inflatable structures have been a subject of renewed interest in recent years for space applications. Actuators and sensors made of piezoelectric materials are recently being considered for the vibration and shapes control of such structures. This study is directed towards developing actuator and sensor models of piezoelectric films attached to an inflatable structure, which can be modeled as a shell under pressure. The derivations are made using the definitions of strain energy and kinetic energy. We use Sanders' shell theory to model the vibration of shell and derive the constitutive equations for combinations of shell and piezoelectric patches in unimorph and bimorph configurations. Equations of motion for the shell vibrating in the presence of actuators have been obtained. The inertia terms in the equations of motion are modified in order to account for the mass of the actuators. The generalized forces due to piezoelectric actuators are found. Finally, a sensor equation is provided.
One of the limitations of a piezoelectric material is the amount of force it can exert. Hence, it is important to optimize the locations and sizes of the actuators so that the required control effort is minimum. Similarly, to obtain good signal to noise ratio, sensors should be chosen to provide maximum output for the vibration in the modes of interest. These problems become more critical as the number of actuators and sensors increases. In this study, we find optimum places and sizes of actuators/sensors on an inflated toroidal shell using genetic algorithm. Using the expressions for the generalized forces and sensor voltages developed previously, modal forces and modal sensing constants are determined. To obtain a cumulative performance measure of all the controlled modes, controllability and observability indices are used. Using these performance indices, optimal locations and sizes of the actuators and sensors are determined so that the actuators require minimum energy and the sensors provides maximum output energy. Finally, using an optimal control, the vibration suppression of the inflated torus using these actuators and sensors has been demonstrated.