An Investigation into the Effects of Lateral Aerodynamic Asymmetries, Lateral Weight Asymmetries, and Differential Stabilator Bias on the F-15 Directional Flight Characteristics at High Angles of Attack

Abstract

The F-15 is a stable aircraft throughout most of its flight envelope. However, it still exhibits an uncommanded yawing and rolling tendency at high angles-of-attack. Identified influencing factors of this uncommanded motion are lateral aerodynamic asymmetries, lateral weight asymmetries, and differential stabilator bias. Previous research into the effects of these influencing factors has been qualitative. This thesis quantifies the effects and then identifies a symmetric F-15 configuration. The quantifying metric presented is net yaw acceleration. This thesis used both computer simulation and experimental flight test to quantify these effects. A discussion of each influencing factors effects on the F-15B high AOA net yaw acceleration is presented. Aerodynamic asymmetries of the baseline F-15B are shown to cause a right yaw. Lateral weight asymmetries are shown to cause yaw acceleration away from the weight asymmetry. And, small changes in differential stabilator bias are shown to have little influence on net yaw acceleration. Considering these discussions, the baseline F-15B is identified as the symmetric F-15B. Finally, this thesis identifies two possible causes for F-15 departures, transient net yaw acceleration and combined sense of yaw and roll rate. The understandings of these possible causes on F-15 departures are just beginning to be evaluated