Abstract
The objectives of the present study on Unmanned Combat Air Vehicles (UCAVs) are two-fold: first to control the flow by inserting leading-edge and cross-flow slots and analysing the viscous flow development over the outer panels of a flying-wing configuration to maximise the performance of the elevons control surfaces; second to predict high-lift performance particularly the maximum-lift characteristics. This is demonstrated using a variety of inviscid Vortex Lattice Method (VLM) and Euler, and viscous CFD Reynolds Averaged Navier-Stokes (RANS) methods. The computational results are validated against experiment measured in a wind tunnel. Two flying-wing planforms are considered based around a generic 40 edge-aligned configuration. The VLM predicts a linear variation of lift and pitching moment with incidence angle, and substantially under-predicts the induced drag. Results obtained from RANS and Euler agree well with experiment.
Highlights
The current generation of flying-wing Unmanned Combat Air Vehicles (UCAVs) lack conventional stabilising surfaces or the associated control surfaces, and as a result in its purest form air vehicles suffer from the inherent disadvantage of being unstable and difficult to control [1]
Linear computational results were investigated with the Vortex Lattice Method (VLM) Tornado code, and non-linear computational studies were performed with in-house and commercial computational fluid dynamics (CFD) codes
The freestream conditions are provided by the wind tunnel tests where Mach number was 0.1 and the Reynolds number based on aerodynamic mean chord length was 5×105
Summary
The current generation of flying-wing UCAVs lack conventional stabilising surfaces or the associated control surfaces, and as a result in its purest form air vehicles suffer from the inherent disadvantage of being unstable and difficult to control [1]. These aerial vehicles are largely similar in design with geometric features chosen for stealth reasons. Due to Radar Cross Section (RCS) signature and weight constraints, leading and trailing edges have to be aligned at a common angle of between 40° and 60°, resulting in aerodynamic design between pure deltas, diamond and lambda wings. These delta shaped flying-wing configurations allow the air vehicle to operate at near and post stall regimes taking advantage of the additional lift generated by the leading edge vortices [1]. Detailed understanding of the leading edge vortices behaviour becomes mandatory in order to enhance the air vehicle’s performance and manoeuvrability
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