Research On Structural Design And Shape Morphing Techniques For Morphing Aircraft At Midium Scale Deformation Level

Morphing aircraft is a kind of multi-role aircraft which can automatically change external shape to adapt to a variable mission environment during flight. The development of morphing techniques can help aircraft enhance the multi-task ability, improve the overall performance in the whole envelope and reduce the cost, which meets both military and civilian needs of future advanced aircraft. Recently the studies on morphing aircraft structural design and shape morphing techniques based on smart materials and structures have become hot topics.In this dissertation, some basic researches have conducted on structural design and shape morphing techniques of morphing aircraft at medium scale deformation level. Targeting morphing wing and morphing inlet, a series of studies are carried out including: design and property analysis of a composite flexible skin based on deformable honeycombs, design and analysis of a kind of distributed pressurized telescopic tube actuator, structural design and experimental demonstration of a compliant variable camber wing based on deformable honeycombs, and deformation analyses on a morphing surface of morphing bump inlet based on bi-stable structures. The main research contents and contributions are as follows:(1) Aiming at the conflict between structural in-plane deformation and out-of-plane bearing of current morphing structure design, a kind of cross-shaped flexible honeycomb is designed and manufactured based on the analysis of the deformation mechanism of the conventional hexagon honeycomb. The designed flexible honeycomb has a light weight, good in-plane deformation ability and certain out-of-plane bearing capacity. The in-plane deformation mechanism, mechanical properties and parameters effects are analyzed by representative volume element method. The honeycomb could be considered as three dimensional orthotropic material and its equivalent moduli expressions are theoretically derived. The mechanical tests are conducted on the cross-shaped honeycomb specimens and the experimental data are accordant with the analytical and simulation values. A kind of composite flexible skin based on cross-shaped honeycomb and its design method are proposed. According to the skin design requirements of in-plane deformation and out-of-plane bearing in a variable camber scheme, the design works are conducted on the geometric parameters of the composite skin including the honeycomb cell size, the thickness of the upper panel and so on. Some suitable parameter ranges are given to meet the usage requirements of flexible skin, which could provide theretical basis for the application of the designed composite flexible skin.(2) In order to meet the distributed actuation requirement of morphing aircraft, a kind of innovative flexible pressurized telescopic tube actuator is developed, motivated by the motion manner of the telescopic antenna structure. The telescopic tube actuator which has a light weight is made up of the spool, inner rubber tube, outside aluminum protecting sleeves and lock nut. The actuator could provide a large axial driving force and drive displacement as well as certain compression stiffness by changing the pressure of the inner tube. The working principle of the pressurized telescopic tube actuator is introduced and its structural model is established, including the hydraulic oil column, flexible inside wall and rigid outer wall. The driving force and equivalent compression stiffness are analyzed, which are functions of the pressure and geometric parameters of the telescopic tube. The simplified engineering expression of the equivalent compression stiffness is given. The telescopic tube actuator specimens are manufactured and the experimental system consisting of hydraulic source, supporting and measuring devices are made. Experiments are conducted on the driving ability and mechanical properties of the actuator, which could provide a certain technical reference for the application of the telescopic tube actuator.(3) The conceptual design of a compliant variable camber wing based on deformable honeycombs is proposed, in which full height cross-shaped flexible honeycombs are used as morphing structures, and flexible pressurized telescopic tube actuators are distributedly embedded in the morphing structure. According to the deformation and bearing requirements of the flexible trailing edge, parameters design and analysis are carried out on the components including deformable honeycombs, telescopic tube actuators, supporting webs and bearing horizontal plate. The finite element model of the flexible trailing edge is established, and its deformation and bearing characteristics are analyzed. The results show that the designed trailing edge has good deformation and bearing capacities, and could effectively resist certain perturbation air load, which satisfy the usage requirement under expected flight conditions. The sample of the flexible trailing edge wing is manufactured, and experimental demonstration is conducted on its deformation ability under no flow condition. The test data are accordant with the simulation results, which validates the effectiveness of the design and analysis on the trailing edge. The design concept and analysis method of the compliant wing could provide a new design approach for the engineering application of camber variation.(4) In order to improve the inlet-engine match performance of the non-adjustable bump inlet at non-design point, a conceptual design is proposed in which a bistable morphing bump surface is used to replace the original non-deformable bump surface in the throat region of the inlet. The air inflow of the inlet could be adjusted by shifting two stable configurations of the morphing surface. The transition mechanism of the morphing bump surface and its bistability existing conditions including geometric parameters and boundary constraint are studied by simulation method. Two preliminary loading schemes are proposed, which include applying uniform line load on the morphing surface by rigid frame and applying bending moment at the edge of the surface through rigid discs. The deformation process types of the morphing bump surface under the two loading methods are discussed, which show that the deformation type could be controlled by loading position and structural geometric parameters. For the uniform line loading case, effects of loading position and structural parameters on the critical driving force, input energy and structural strain level are studied for the transition of the morphing bump surface. Suitable loading position and structural material selection are given. The analysis on the bistable behavior of the morphing bump surface could provide some basic data for further driving scheme and material design of the morphing bump inlet.