Model reference control (MRC) is a widely used approach in helicopter flight control to impose
desired dynamic behaviour – such as specified damping and natural frequencies – on the actual
nonlinear and complex helicopter system. In this work, the entire closed-loop system consists of
a trajectory planner, which defines simple and well-behaved reference dynamics, and the actual
flight control law, which ensures that the helicopter follows these reference trajectories. The
trajectory planner generates a trajectory from the target flight state specified by the pilot, e.g., the
vertical speed, delivering feasible reference states for the lower-level controller. For unconstrained
trajectories, the closed-loop stability can be verified using conventional linear control engineering
methods such as, e.g., the Hurwitz criterion. However, these methods are not applicable if the
trajectories are constrained by state limits such as the maximum and minimum vertical speed of
the helicopter. For constrained trajectories, nonlinearities such as saturations are often inserted
into the control loops to consider the helicopter's state limits. These nonlinearities complicate the
proof of stability, and thus an alternative approach is required for the stability analysis. In this
work, an analytical approach is presented to generate a trajectory that respects input and state
constraints while applying a linear control law with the help of the invariant set theory and linear
control methods. The method is applied on a model of the Airbus H145 to analyse its control
performance.