Structural design optimisation and aerothermoelastic analysis of LAPCAT A2 mach 5 cruise vehicle

Structural design of hypersonic aircraft is highly affected by their non-conventional shapes and dimensions, and especially by the very high temperature loads encountered during flight. Indeed, compared to classical aircraft, the non-conventional configurations may lead to largely different internal structural stresses, and the temperatures would lead to high thermal stresses and a significant reduction in material strength and stiffness, resulting in innovative concepts. Moreover, the reduction in structural rigidity requires a stronger focus on aerothermoelastic deformations in the design and optimisation of the aircraft structure. This imposes the need for a closer coupling of the aerodynamic and structural tools than current practice. The current paper presents how the different sizing, analysis, design and optimisation tools are coupled in the design of the structure for the LAPCAT A2 vehicle and gives results of the optimisation of the A2 canard and wing. A wing structure with 6 spars and 6 ribs with cross-grid stiffeners, and a movable canard structure with 3 spars and 7 ribs and an ortho-grid stiffened skin lead to the lightest solutions. Buckling has been identified as the main weight driver for both cases, regardless of the number of ribs and spars used. The design and optimisation of the fuselage (ring frames, longerons and skin) is in progress. The aerothermoelastic module has also been implemented and applied successfully to the A2 wing, leading to the static aerothermoelastic solution after only 4 iterations.