We consider the problem of controlling the vertical motion of a nonlinear model
of a helicopter during landing, while stabilizing the lateral and longitudinal
position and maintaining a constant attitude. The dynamics of the helicopter
main and tail rotors are often neglected to simplify the control design, but this
reduction has the disadvantage of an unreal choice of the control inputs. We
have solved this contradiction by choosing the main controller required for
performing the secure autonomous landing by neglecting the complex rotors
dynamics, and then we have included these important dynamics in a closed loop
model having real controls determined from an auxiliary controller. Simulation
results show the effectiveness of the method to cope with uncertainties on the
plant and actuator model.