| Abstract | Leading-edge high-lift devices increase the angle-of-attack at which the wing stalls. This allows for a greater maximum lift coefficient, and thus more lift for takeoff and landing. The three-position slat is the most common leading-edge highlift device in use on commercial airliners today. Three-position slats have two major limitations: high noise levels, and increased drag. The slot opened during landing creates high noise levels which, due to noise regulations, can limit an aircraft's available approach paths and takeoff/landing hours. In the takeoff position, small discontinuities and leakage of air from the bottom to the top of the wing can increase drag, which is undesirable. These limitations can be mitigated by using a morphing wing design. Current morphing wings are adapted to bend to create a high-lift profile. A flexible leading or trailing edge is bent downward to increase the lift of the wing. One example of a leading-edge morphing wing design is the DLR SADE design. In this design, a flexible composite skin structure surrounds a rigid actuation mechanism. The front 9% of the wing is constructed using the flexible skin, which is discretely-supported at four points by the rigid mechanism. Another example of a bending, morphing, high-lift device is the Flexsys Flexfoil. This design uses a proprietary compliant actuation structure to change the shape of the wing. A collaboration between NASA and the Air Force Flight Research Laboratory was initiated to flight-test the Flexsys Flexfoil morphing trailing edge design, in order to assess the real-world performance of a morphing wing. The trailing-edge Fowler flap of a Gulfstream jet was replaced by the variable-geometry morphing surface developed by Flexsys. The device was successfully flight-tested from -2° to +30° deflection. Although the aforementioned designs have been successful in many regards, they are limited by several factors. The DLR SADE design successfully demonstrated that a flexible leading edge could be optimized to provide reasonable fidelity to a target shape. However, the design suffered from poor shape control at varied angles of attack. In this type of design, the skin thickness and support structure are optimized to provide the desired shape only at selected angles of attack. The varying aerodynamic forces at other angles create undesired deformations in the skin, increasing the amount of deviation from the optimal shape. This is an issue with many morphing wings, since most current morphing designs for high-lift devices have limited mobility. A morphing wing concept is being developed by the National Research Council of Canada (NRC) with the purpose of creating a seamless high-lift device for noise and drag reduction. This project aims to develop a conceptual design which overcomes some of the challenges encountered with the SADE and Flexfoil designs. The NRC project explores the use of an elastomeric skin material and more flexible support structure to design a morphing wing with improved mobility. Initial validation of the morphing wing design performed using finite-element computer simulations will be presented. This paper focuses on the work performed to develop the optimal airfoil shape, and to analyze the integration of the skin with the flexible support structure. The design will allow an increase in chord length, thereby overcoming a performance limitation of existing morphing wing designs. |
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