Meeting VSTOL aircraft performance requirements using scheduled H∞ controllers

Meeting required handling qualities for VSTOL aircraft using H_∞, robust control design techniques is discussed. The key characteristic of VSTOL aircraft is widely varying dynamics across the flight envelope. The controller must not only have good robust stability to these changing dynamics, but also exhibit good robust performance so that handling qualities are met at all operating conditions. Here we present an approach to meeting these design aims. The method consists of performing linear H_∞-optimal designs at a set of operating points, and then scheduling the controllers using linear interpolation of the gains. To interpolate the gains an exact observer representation of the controller is used. The possibility of writing the controller in this form follows from the particular optimisation used which makes use of normalised coprime factor plant descriptions.