A Tale of Two UCAV Wing Designs

This paper is via the initiative of the NATO RTO-AVT-161 Task group. The group is aimed at assessment of Stability and Control Prediction Methods for NATO Air and Sea Vehicles (essentially complex configurations). The assessments need to include the absolute values of forces and moments as well as the various symmetric and asymmetric stability derivatives, both steady and unsteady. This paper relates to the UCAV wing design aspects. A UCAV needs to be as light and small as possible for a given mission flight envelope. It is a compromise between efficient high-speed flight, loiter and good stability and handling at low speeds. We look at a planar wing (P0) and two designs: a notional intuitive design (BG2) and a modal "compromise" design (C1) enabling low and high speed flight. Low speed experimental data is available on the BG2 wing model tested by DLR. Results are compared with experiment (on BG2) and CFD methods utilizing structured (ENSOLV, NLR) and unstructured (EDGE, FOI) grids and various turbulence models. The emphasis is on symmetric longitudinal stability aspects. It is inferred that CFD reflects the main character of the BG2 wing and that the behaviour of the designed UCAV wing (C1) in reality can be predicted well by these CFD methods. The work so far has been interesting and encouraging. It has led to an improved understanding of the complex configurations with strongly interacting and separating / moderate sweep vortical flows. In the wider perspective, for the future, an understanding has evolved for either exploitation or avoidance of the complex flows. This is an important motivation. NOMENCLATURE