Effect of Flying Vehicle Structural Flexibility on Designed Control System

Studying of flying vehicle motion contains many stochastic criteria with which obligates the control system designer to take into consideration the most effective parameters in control system analysis. These criteria changes with the nature, shape and mission required from this flying vehicle. With the introduction of long slender bodies, the problem of structural flexibility became acute. This flexibility causes additional aerodynamic loads, which in turn cause additional flexure. In addition, coupling occurs between the elastic modes and the control system as the gyros and accelerometers sense the flexure and the rigid body motions. In this paper, we demonstrate a method for determining the natural frequencies and mode shapes of the body bending modes. The work resumes with the derivation of the uncoupled body bending equations in normalized coordinates and finally the transfer function for the flexible vehicle is derived and then the flexibility effect on the system responses is presented. This work is mainly contributed to clarify the amount of airframe flexibility effect on control system behavior and if there is need to compensate this effect.