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This paper presents a terrain following controller for rotorcraft that takes into account the terrain characteristics ahead of the vehicle as measured by a Laser Range Scanner. The methodology used to solve the terrain following control problem amounts to posing it as a discrete time path following control problem where a conveniently defined error state space model of the plant is augmented with terrain preview data. A piecewise affine parameter-dependent model representation is used to accurately describe the linearized error dynamics for a pre-defined set of operating regions. For each region, the synthesis problem is stated as a state feedback H2 control problem for affine parameter-dependent systems and solved using Linear Matrix Inequalities (LMIs). An alternative technique to compute the feed-forward preview gain matrix is proposed that avoids solving LMIs involving a large number of unknowns. The resulting nonlinear controller is implemented within the scope of gain-scheduled control theory using the D-methodology. Simulation results obtained with the full nonlinear helicopter model are presented and discussed. I. Introduction Recent advances in sensor technology and the increasing availability of computational capacity are steadily affording Unmanned Air Vehicles (UAVs) higher degrees of robustness and reliability in challenging and uncertain operation scenarios. Model-scale helicopters constitute one of the most versatile and cost-effective UAV platforms with a wide and valuable range of applications, such as crop spraying, fire surveillance, and bridge and building inspection. Unlike fixed-wing aircraft, helicopters were designed to execute vertical flight maneuvers, including hovering and vertical takeoff and landing (VTOL). Moreover, their ability to perform agile maneuvers both at high and low speeds does not undermine the good flying qualities displayed in fast

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