In this study, the feasibility of using representative box wing adaptive structures for static aeroelastic control is examined. A deformable typical section is uti lized to derive the optimal and suboptimal relations for induced strain actuated adaptive wings, and the relations developed are used to design representative adaptive lifting sur faces which are assessed in trade studies. The optimal relations developed showed that op timal adaptive airfoil designs are possible for some realistic configurations, and effective sub-optimal designs can be achieved for others. In addition, the important parameters associated with inducing curvature and twist, thereby altering the lifting forces on the air foil, are determined. The most important of which were found to be the airfoil thickness ratio, the actuation strain produced by the induced strain actuators, and the relative stiff ness ratio of the actuator to the wing skin for both camber and twist control. The stiffness coupling parameter and the wing aspect ratio were also found to be important for twist control. The potential benefits of using adaptive airfoils for aeroelastic control, rather than conventional articulated control surfaces, is demonstrated in trade studies. It was found that greater control authority along with a lower weight penalty is achievable using adap tive aeroelastic structures for a variety of wing designs. Thus, strain actuated adaptive wings may be used rather than conventional lifting surfaces to increase performance while reducing weight, decreasing loads in critical areas, improving the radar cross section, and maximizing the lift-to-drag ratio for many flight conditions.
A typical section analysis is employed to provide an understanding of the fundamental mechanisms and limitations involved in performing aeroelastic control. The effects of both articulated aerodynamic control surfaces and induced strain actuators are included in the model as forces and moments acting at the elastic axis of the typical section. The ability of these actuators to effect aeroelastic control is examined for each actuator individually as well as in various combinations. The control options available are examined for single input-single output and mu1 tiple inpu t-mu1 tiple output classical and optimal control laws. A state cost versus control cost analysis is performed to assess the effectiveness of optimal linear quadratic regulator control laws for different actuators and actuator combinations. The cost comparisons show that strain actuation is an effective means of achieving aeroelastic control and a viable alternative to articulated control surface methods. In addition, the advantages of using multiple actuators to avoid limitations associated with single actuator systems is demonstrated.
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