Investigation of Nonlinear Motion Experienced on a Slender-Wing Research Aircraft

A combined experimental and theoretical study is described of the nature of the nonlinear lateral oscillation experienced by a slender-wing aircraft at high angles of attack. Flight tests of the Handley Page 115 research aircraft confirmed the expectation that the Dutch roll oscillation is undamped at high angles of attack, and also showed that a limit cycle develops, with steady amplitude in bank angle of about 30°. The measured stability derivatives are given, together with the responses obtained from the RAE flight dynamics simulator, in which the digital computation of the equations of motion uses the static aerodynamic data directly from a controlled model in a wind tunnel. The motion is also analysed theoretically using a new approximate method for obtaining solutions for nonlinear differential equations. The analysis gives the conditions sufficient for the existence of a sustained oscillation, and its amplitude and frequency in terms of the aerodynamic and inertia properties of the aircraft.