STUDYING OF A FORCE EQUALIZATION ALGORITHM FOR TWO ACTUATORS SIMULTANEOUSLY TURNING ASIDE THE FLIGHT CONTROL SURFACE OF NARROW-BODY CIVIL AIRCRAFT

Abstract

Some civil aircraft assume two actuators simultaneously turning aside the flight control surface (rudder, in some cases aileron or elevator). Thus resulting in onset of the force fighting (mutual loading force). There are several ways to reduce the mutual loading force. One of them is to insert specific force equalization algorithm in actuators steering. This article deals with effectiveness of force equalization algorithm as well as its influence on system “2 active actuators - elevator”. Mathematic model of two actuators on elevator has been formed and tested by the developed testing method that reproduces the most severe operation conditions. There are several nonlinearities which is contained in mathematic model: sleeve-travel physical limits, nonlinear effects of fluid foil, rod-travel physical limits and attachment rigidity. Force equalization algorithm comprises a pressure differential feedback loop with PID regulator. The results show that force equalization algorithm is highly efficient (mutual loading force has been reduced over than 90%) in mode test without external load. However, in test mode with external load it is necessary to introduce a limitation on the magnitude of the corrective signal so as decrease the rod drop to level specified in terms of reference. Algorithm has no effect on stability margin of the system. In conclusion, results of this study could also be useful to expand the test program for two actuators simultaneously turning aside the flight control surfaces to further simplify the implementation of the force equalization algorithm.