Design of a composite morphing wing

Abstract

Morphing aircraft components can increase the possibility of optimising the performance of an aircraft at various flight conditions. A morphing aircraft wing can change the wing shape to modify the lift and drag distribution on the wing surface, allowing the lift-to-drag ratio to be tailored to the desired performance. A camber morphing and a trailing edge morphing wing changes the aerodynamic lift by altering the camber and by deflecting the wing trailing edge, potentially reducing the aerodynamic drag by eliminating the gaps; which exist between the main wing and the control surfaces of a conventional wing. Among the technology used to achieve camber morphing and trailing edge morphing, were mechanical and smart actuations, such as piezoelectrics and shape memory alloys (SMAs). Compliant structures, cellular structures, shape memory polymers, and multi-stable structures were exploited to improve the flexibility of the aerofoil sections or wings. SMA wires were one of the smart actuators which had been extensively utilised to morph various aerofoils/wings, mainly due to the high actuation force and compatibility, which reduce the volume and weight of the actuators and the complexity of moving mechanical components. In this research, a user defined material model (UMAT) was developed within the explicit LS-DYNA FE code, for NiTi shape memory alloy (SMA) wires, and used for actuation of the composite morphing wing. The Tanaka SMA constitutive model was implemented in MATLAB and FORTRAN codes for the SMA-actuation of various structures. The UMAT was used to simulate actuations of various complex morphing structures, including several aluminium and composite aerofoils with corrugated sections, and a pre-curved corrugated plate. Actuations of the two aluminium aerofoils, with corrugated sections in the lower surface and the middle cantilever section, by a 0.5mm-diameter SMA wire with a maximum recoverable strain or a pre-strain of 1.6%, resulted in trailing edge (TE) deflections of 7.8 mm and 65.9 mm, respectively. Actuation of the carbon fibre (CF) composite aerofoil, with the corrugated section as a middle cantilever section, and with 8 layers of CF in ±45° directions, produced a TE deflection of 52.0 mm. To demonstrate the SMA-actuated morphing concept, a composite 3D-printing technology was explored to manufacture a carbon fibre (CF) composite structure, consisted of a flat vertical front plate, a corrugated section, and a rear trailing edge (TE) section. Due to the nature of 3D-printing, two layers of CF were 3D-printed along the circumference of the corrugation and the TE section, and the minimum thickness of the structure was 3 mm. Experimentally, actuation of the CF composite corrugated structure by a NiTi SMA wire with a diameter of 0.2 mm and a pre-strain of 4.77%, and with a diameter of 0.5 mm and a pre-strain of 1.68%, aligned in the chordwise direction, resulted in 1.1 mm and 6.0 mm TE deflections, respectively. Cyclic tests (10 and 30 cycles) of the actuation of the CF composite corrugated structure showed the TE deflection converged after few cycles. A 1.25m-span composite morphing wing was finally designed and manufactured, consisted of a CF composite D-nose spar which resisted the main aerodynamic loading, and rear sections which were made of rigid and flexible foams. CF composite spar flanges, spar web, front and rear ribs, were 3D-printed, and were assembled with a CF composite skin which was autoclave-manufactured, to form the CF composite D-nose spar. Sections of rigid and flexible foams were CNC-machined and were attached to the front CF composite D-nose spar, 3D-printed long rear ribs, trailing edge sections and the morphed corrugated structure, to form a complete composite morphing wing.