Non-linear control structures for rotorcraft positioning

Abstract : The purpose of this communication is to apply and compare three different non-linear control approaches to the design of control structures with control laws allowing autonomous positioning and orientation for a four-rotor aircraft. Realistic rotorcraft flight dynamics are established and analyzed so that a reference three-layers control structure is defined. Then are introduced different non-linear control approaches: non-linear inverse control, backstepping control and differential flat control. The compatibility of these control approaches with the three-layer control structure is assessed and adaptations are .proposed so that they can cope with the guidance of the rotorcraft. The corresponding control laws are detailed and their expected performances are discussed. The simplification of these control laws around equilibrium conditions produces close quasi-linear proportional derivative controllers. A careful tuning of one of them provides a reference to evaluate the improvements resulting from the use of full non-linear control laws, when applied to the positioning and orientation problem. This evaluation is performed by simulation and numerical results are displayed for analysis.