The dynamical model of an original trirotor helicopter is presented in this paper. The helicopter is composed of three rotors with constant pitch propellers; two fixed rotors turning in opposite directions and one rotor that can be tilted to control the yaw displacement. The dynamical model is obtained via the Euler–Lagrange approach and a nonlinear control strategy is proposed. The roll and the forward displacement are controlled by using a nested saturations control law. The pitch and lateral displacement are controlled in a similar way. The nonlinear controller performance is tested on real experiments using a trirotor rotorcraft. It is shown that the controller is robust to large perturbations on the orientation angles and that it has better behavior than a classical linear state-feedback controller.