Flap Splitting and Setting of the X31 Wing

Rosario Borrelli (CIRA - Italian Aerospace Research Centre)

A common requirement for fighter planes is the ability to reach high roll angle accelerations, as this parameter is one of most important determinants of the plane's maneuverability. If a plane has two edge flaps on the wings, deflecting the two independently will cause a rolling moment to ensue, which in turn induces a roll acceleration. Of course, key factors in determining the roll acceleration are the authorities of the inboard and outboard flaps, and the position of the flap split.








Unfortunately, these parameters cannot be chosen at will, because during the manoeuvre aerodynamic and mass loads are imposed on the structure, creating stress that the structure must be able to withstand. To guarantee the structural integrity is then necessary to add material, increasing the wing weight and reducing the range. Accordingly, the solution must be a good compromise between good roll performance and low structural mass. modeFRONTIER's contribution to its Solution Two conflicting objectives were pursued: maximum roll angle acceleration minimum wing mass DASA's HISSS-D subsonic and supersonic solver was used for the aeroelastic design evaluation, while the structural weight for a given configuration was minimized, while maintaining structural integrity, using LAGRANGE, another proprietary code. The software run on an SGI Origin2000 parallel computer. Optimization results using 16 individuals and 8 generations - using the MOGA algorithm - were sufficient to precisely describe the Pareto Frontier, thus singling out the set of optimal designs for different trade-offs. For a given weight it became then possible to pick the design providing the highest acceleration possible. Conversely, given a desired roll acceleration it was possible to immediately find the design with the lowest weight.