Hybrid Design for Aircraft Wind-Tunnel Testing Using Response Surface Methodologies

A response surface methodology approach to wind-tunnel testing of high-performance aircraft is being investigated at the Langley Full-Scale Tunnel. An exploratory study was completed using a newly developed response surface methodology design in an effort to better characterize an aircraft's aerodynamic behavior while simultaneously reducing test time. This new design called a "nested face-centered design" was developed when classic designs were found to have inadequate prediction qualities over a cuboidal design space with factors at five levels. A 19% scale modified X-31 aircraft model was chosen for evaluation of the new response surface methodology design based on its nonlinear aerodynamic behavior at high angle of attack that is representative of modern fighter aircraft and due to a substantial preexisting data base. A five-level nested fractional factorial design, augmented with center points and axial points, produced regression models including pure cubic terms for the characteristic aerodynamic forces and moments over a cuboidal design space as a function of model position and control surface deflections. Model adequacy and uncertainty levels were described using robust statistical methods inherent to response surface methodology practice. Comparisons to baseline data and sample lateral-directional and longitudinal aerodynamic characteristics are given as validation of the new design.