AN INVESTIGATION OF THE AEROELASTIC TAILORING FOR SMART STRUCTURES CONCEPT
Abstract
This paper describes an on-going research effort demonstrating the concept of variable stiffness tailored aeroelasticity for smart structures. In particular, a wing structure is designed, or tailored aeroelastically, as a force multiplier for control actuation. This variable stiffness concept may be used as a way to employ light¬weight and low power output smart materials in lifting surface structures. A simple, unswept, rectangular wing model is used to explore the feasibility of utilizing the variable stiffness tailored structure as a force multiplier in conjunction with an outboard, trailing edge control surface. This experimental approach involves the design of a simple wing model with adjustable stiffness to lower the control surface reversal dynamic pressure and use the control surface as a "tab" to twist the wing. Analytical and experimental results are presented that indicate that it is possible to tailor the torsional stiffness of a wing such that the reversal speed is significantly reduced from a baseline stiffness configuration. The results of this study show where, for this example, use of the tailored structure as a force multiplier in conjunction with the trailing edge control surface may be beneficial.

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Cindy L. Giese,1 Gregory W. Reich,2 and Mark A. Hopkins2 Wright Laboratory Wright-Patterson Air Force Base, Ohio
Kenneth E. Griffin3 Southwest Research Institute San Antonio, Texas

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I. Introduction
The application of Smart Structures technology offers some intriguing possibilities for high performance aircraft. Examples of applications of smart materials in aircraft structures include structural shape changes, flap deployment, and dynamic structural responses which
Aerospace Engineer Aerospace Engineer, Member AIAA Principal Engineer, Member AIAA
This paper is a declared work of the US Government and is not subject to copyright protection in the United States.
may enhance an aircraft's lift production, reduce its aerodynamic drag and radar observability, and increase its structural health. These particular applications must be examined individually to determine the weight, size, power consumption, and power output requirements of the smart material for the specific intended task.
The Mission Adaptive Wing program in the 1980s was one of the first "smart," conformable wing programs. It examined the idea of smooth shape changes in flight to achieve improved performance for multiple flight conditions without conventional flaps. The program succeeded in demonstrating the benefits of this technology, however, the complexity and weight penalty of the conventional internal actuators prevented widespread implementation of the technology.
An entire body of research on Active Flexible Wing Technology demonstrated advantages of post-reversal aileron control utilizing multiple control surfaces on future aircraft designs. This approach did not require any heavy, complex actuators. The concept of tailored aeroelasticity for smart structures was inspired initially by this work.1,2,3
The research effort presented in this paper was conducted to explore experimentally the concept of aeroelastic tailoring of smart structures as presented by Griffin and Hopkins.4 Their work documented the aeroelastic tailoring of an F-16 composite wing for smart structures materials applications. The wing was tailored to improve its ability to act as a force multiplier by decreasing the aileron reversal dynamic pressure enough to permit the aileron to be used in a post-reversal fashion for transonic maneuvering. The changes in reversal dynamic pressure are a result of adapting the structural stiffness of the primary structure as a function of the aircraft flight condition. The stiffness changes were performed to take advantage of the post-reversal aileron control using an outboard, trailing edge control surface.
This investigation explores the feasibility of the concept defined in Reference 4 using a simple, unswept, rectangular wing, wind tunnel model. The model is designed so that the outboard, trailing edge control surface will reverse at two separate conditions within the envelope of a low speed wind runnel. Two methods will be examined to change the spar stiffness and thus the reversal dynamic pressure: changing the length of the leaf springs that control pitch stiffness at the root, and replacing the baseline stiffness spar with a reduced stiffness spar. This paper presents the design of both of these methods and the results of a wind tunnel test which implemented the first method.