Computational Prediction of Nose-Down Control for F/A-18E at High Alpha

Abstract

Computational fluid dynamics was used to predict the longitudinal stability and control characteristics of the preproduction F/A-18E Super Hornet configuration with neutral and full nose-down control at high angle of attack, subsonic conditions. Such data contribute to an analysis of the ability of the pilot to recover from extreme angles of attack and are usually obtained and extrapolated from wind-tunnel tests. The current computational study was intended to be an exploratory study of the usefulness of computational fluid dynamics to aid the designer and analysts in predictions of flight behavior. The calculations were made for Mach 0.082 at a Reynolds number of 1.15 x 10 6 based on mean aerodynamic chord at angles of attack between 0 and 60 deg. The F/A-18E was modeled with 34-deg leading-edge flaps, 4-deg trailing-edge flaps, 0-deg aileron deflection, a rudder deflection of 30 deg, a spoiler deflection of 60 deg, and horizontal-tail deflections of 0 and 20 deg. The flow conditions and configuration corresponded to those used in tests of a 15%-scale F/A-18E wind-tunnel model tested at the 30- by 60-ft full-scale wind tunnel at the NASA Langley Research Center in Hampton, Virginia. The flow solver used during this project was USM3D, which was developed by the NASA Langley Research Center. The forces and moments predicted by USM3D compared well to the wind-tunnel data for angles of attack between 0 and 40 deg. For angles of attack from 40 to 60 deg, however, the results from USM3D differed from the wind-tunnel data. These differences are attributed to the unsteady nature of the flow and turbulence effects not adequately captured by the computations.