Abstract: he problem of how to depress the limit cycle oscillation of flight control system must be solved in the design of DFBW system. For uncertain nonlinear factors of flight control system, a new idea of the imitative linear unit is put forward to realize the desired stability mar-gin of the system and overcome the effects of nonlinearities. On the other hand, to the known nonlinear factors,the concept of mendability is discussed and used in the controller to compen-sate for the nonlinearities.Both methods used in flight control system are valid to depress the limit cycles as a result of the simulation.

Key words: limit-cycles, nonlinearity, stability