The design of a decoupling compensator for the Apache helicopter is presented. The design is based on linear quadratic regulation with implicit model following. A decoupling compensator is designed for a reduced-order linear model of vehicle dynamics at hover using eigenstructure assignment. The resulting closed-loop system is used as a reference model in the design of a compensator for the full-order system, resulting in a constant state feedback matrix. A feedforward matrix (command mixer) is then designed to diagonalize the system at low frequencies. The design is evaluated with both the full-order linear model and a nonlinear simulation (ARMCOP). It is found to provide desired bandwidth and good decoupling properties with the linear model. The nonlinear simulation shows increased coupling due to the nonlinearities.