Adaptive sliding mode control of a transport aircraft for heavyweight airdrop

This paper investigates the problem of designing a novel sliding mode controller of a transport aircraft for airdrop modes in the presence of bounded nonlinear uncertainty and actuator fault without the prior knowledge of the bounds. On the basis of feedback linearization of the aircraft-cargo dynamic model, an autopilot inner-loop which combines sliding mode control with adaptive function approximation is developed. The complex nonlinear uncertainty of the model is factorized into a known matrix and an uncertainty function. An adaptive approximation approach is used to estimate the function, and it overcomes the conservation drawback of the sliding mode control that relies on the bounds on the uncertainty/actuator fault. Notably, the adaptation law formed using the projection operator can bound the estimated function, and this avoids singularity of the control signal. Simulations verify the good performance of the control system, which can satisfy the airdrop mission performance indexes well, even in the presence of ±20% aerodynamic coefficients uncertainty and 20% actuator fault.