Tilt-rotor aircraft combine the helicopter’s benefit of VTOL capability and the flight performance that turboprops possess on range, speed and endurance. Tilt-rotor aircraft have the potential to decrease airport congestion and average flight delay in passenger transportation, while benefits are numerous in i.e. search and rescue, disaster relief and military application. Time, money and risk can be significantly reduced through the application of flight trajectory optimization and assessment prior to flight, as this can accurately simulate flight and its related performance limits. A numerical three-dimensional pointmass model for a tilt-rotor type aircraft has been derived to fill the gaps that currently exist in tilt-rotor modelling and the understanding of their flight mechanics. After validation, the model is applied to optimize integral flight trajectories using optimal control theory in GPOPS. It was concluded that the derived model is valid under its assumptions and limitations. From the tilt-rotor flight behaviour it was assessed that specific nacelle tilting behaviour could be observed, as the tilt-rotor can exploit its unique rotor tilting capability. Since the power required is the driving factor in most flight optimization, the nacelle angle is driven by the aircraft’s velocity and altitude. This model can be used in theoretical flight trajectory optimization studies. The model can be adapted to account for specific requirements and aircraft types.