This paper introduces a compliant morphing flap transition that seeks to address a long-standing source of noise and drag in the design of aircraft wingsthe gap present at the spanwise ends of the control surfaces. These gaps create large discontinuities in the flow and allow for pressure leakage from the lower to upper wing surface, generating significant amounts of vorticity, noise, and drag. The concept introduced here seals this gap with a smooth, three-dimensional morphing transition section that elastically lofts between the rigid wing and moving control surface in a passive and continuous manner. Previous transition concepts are first discussed, followed by establishment of an initial desired transition shape. Computational fluid dynamics analysis of the desired transition shape indicates both an increase in lift and a decrease in drag. The morphing, elastically lofted transition concept proposed here will then be introduced. In this concept, the complex three-dimensional shape change required is created with a novel structural architecture that combines material and geometric compliance with geometric bend-twist coupling. The concept design and operating principles will be introduced, relevant geometric parameters will be derived, and an initial prototype demonstrator capable of large deflections and smooth transition surfaces will be shown. Nomenclature Cd drag coefficient Cl lift coefficient ct chordwise length of morphing portion of rib h half-amplitude of control surface displacement l spanwise length of morphing portion oftransition w trailing edge displacement y spanwise distance along transition α skew angle of corrugations β bend-twist coupling ratio ΔCl change in lift coefficient θ rotation angle of trailing edge tip of transition/rib
Morphing technology offers a strategy to modify the wing geometry, and the wing planform and cross-sectional parameters can be optimised to the flight conditions. This paper presents an investigation into the effect of span and camber morphing on the mission performance of a 25-kg UAV, with a straight, rectangular, unswept wing. The wing is optimised over two velocities for various fixed wing and morphing wing strategies, where the objective is to maximise aerodynamic efficiency or range. The investigation analyses the effect of the low and high speed velocity selected, the weighting of the low and high velocity on the computation of the mission parameter, the maximum allowable span retraction and the weight penalty on the mission performance. Models that represent the adaptive aspect ratio (AdAR) span morphing concept and the fish bone active camber (FishBAC) camber morphing concept are used to investigate the effect on the wing parameters. The results indicate that generally morphing for both span and camber, the aerodynamic efficiency is maximised for a 30%-70% to 40%-60% weighting between the low and high speed flight conditions, respectively. The span morphing strategy with optimised fixed camber at the root can deliver up to 25% improvement in the aerodynamic efficiency over a fixed camber and span, for an allowable 50% retraction with a velocity range of 50-115 kph. Reducing the allowable retraction to 25% reduces the improvement to 8%-10% for a 50%-50% mission weighting. Camber morphing offers a maximum of 4.5% improvement approximately for a velocity range of 50-90 kph. Improvements in the efficiency achieved through camber Aerospace 2015, 2 525 morphing are more sensitive to the velocity range in the mission, generally decreasing rapidly by reducing or increasing the velocity range, where span morphing appears more robust for an increase in velocity range beyond the optimum. However, where span morphing requires considerable modification to the planform, the camber change required for optimum performance is only a 5% trailing edge tip deflection relative to cross-sectional chord length. Span morphing, at the optimal mission velocity range, with 25% allowable retraction, can allow up to a 12% increase in mass before no performance advantage is observed, where the camber morphing only allows up to 3%. This provides the designer with a mass budget that must be achieved for morphing to be viable to increase the mission performance.
Aircraft designed to fly a wide mission range will have their design compromised so that they can meet all mission requirements. There has been continued interest in morphing aircraft in recent years. These proposed morphing systems allow for aircraft to undergo large-scale planform shape changes, such that they adopt the optimum shape for the given mission phase. An aircraft that can change wingspan could operate with high aerodynamic efficiency at cruise, due to a large aspect ratio wing. Upon retraction of the wingspan, higher manoeuverability is gained. For a span-changing aircraft, the wing skins must also change geometry with the span change. One proposed type of skin to do this is a corrugated skin, which displays high anisotropy in stiffness, allowing it to take significant aerodynamic pressure loading, whilst being compliant in the spanwise direction to allow for wing morphing. The method of corrugation used produces sharp leading edges, and so different methods for rounding of the leading edge are examined to determine whether lost aerodynamic performance can be recovered. These are analysed first in 2D, and then the simulations are extended to 3D to determine the effects of corrugation wavelength in the spanwise direction, and the effect of corrugation depth. It is found that the leading edge profile can greatly impact performance, that corrugation wavelength has only a minimal effect on aerodynamic efficiency, and finally that corrugation depth can incur a significant performance penalty.
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