Forebody aerodynamic asymmetry on a full-scale F-15 radome

Abstract

A full-scale F-15 forebody wind tunnel test was conducted at the Langley Full Scale Tunnel. The goal of this program was to assess the impact of radome imperfections on the aerodynamic characteristics at high angles of attack. The results would support the possible revision of fleet F-15 radome maintenance requirements to prevent future high angle of attack departures associated with forebody side force and yawing moment asymmetry. The force and moment data as well as the surface pressure measurement obtained in the wind tunnel indicated that a high angle of attack aerodynamic offset could be triggered by minute forebody surface anomalies. Small imperfections near the apex of the radome caused significant forebody flow asymmetry while gross repair patches and ridges further aft on the forebody had minimal effects. Specifically, the direction and magnitude of the aerodynamic offset were very sensitive to minute geometric anomalies on or near the radome nose cap. Further aft from the radome apex, significantly larger imperfections were required to produce the same offset. These data clearly demonstrated the development of forebody aerodynamic asymmetry is primarily a function of the imperfection's proximity to the apex of the forebody.