Abstract: The disadvantages of normal aircraft to realize flight path control can be overcome by using direct force control, and some new motion modes can be created. The three principal motion of direct lift control are discussed first, and the direct lift control law design which is a problem of output decoupling is summed up. The main steps of how to use the eigenstructure assignment and model following technique to calculate the feedback and feedforward gain are explained. By using aircraft Citation Ⅱ as an example, the direct lift control law is designed. The computation results are satisfactory, showing that the eigenstructure assignment method is an effective tool for flight control system design.

Key words: direct lift control, output decoupling, eigenstructure assignment, model following