Improving flight control laws for load alleviation

This paper proposes a methodology to improve a given controller by taking into account additional H2 (H1) specifications. From a given model of the system and a givenlow-order controller, a particular augmented standard control problem, called Cross Standard Form (CSF), is built. The main property of this new standard problem is that the unique H2 (H1) optimal controller is the given controller. This problem is then completed by an additional H2 (H1) channel between new exogenous inputs and new controlled outputs. The weight on this new channel allows a trade-off, between the minimization of this channel and the respect of the initial controller bahavior, to be tuned. This methodology is then applied to the longitudinal flight control of a large aircraft, whose initial design was based on an industrial practical know-how (eigenvalue assignment), in order to reduce loads in turbulence