Investigation of Effects of Extreme Structural Flexibility on Flight Vehicles with Feedback-Control-System Stabilization

摘要

The report presents the results of a study of the effects of extreme structural flexibility on the dynamic characteristics of a flight vehicle that requires an automatic feedback control system for stabilization. The vehicle chosen for this study is a hypothetical missile-type configuration having a long, very slender body with small, rigid aerodynamic surfaces forward and aft, with a first body-bending frequency of one cycle per second, and is to fly at very high dynamic pressure so that aeroelastic instabilities are severe. It is shown that, when the vehicle is unstable in divergence of the coupled pitching and first-bending modes, it can be stabilized with feedback control of the canard surfaces, but feedback control of the tail is generally destabilizing. Furthermore, control by means of one aerodynamic surface (single-actuator control) cannot stabilize the system when a dynamic instability exists in combination with the pitching static instability. Stability and achievable dynamic performance are highly dependent on the locations and areas of the aerodynamic surfaces and the location of the gyroscope. For canard control, the gyroscope must be located well forward, but somewhat aft of the nose.