The goal of the present paper was to understand the effects of different approximations considered in the analytical expressions of rotor disc tilt angles when developing a piloted simulation model for helicopter manoeuvring flight. The paper investigated five cases: 1) a classical formulation of the rotor disc ti 2) effects of non-uniform induced velocity distribution along the rotor disc introduced in the form of a dynamic inflow correction factor in the lateral disc-ti 3) effects of unsteady flow along the rotor blade introduced in the form of a sweep correction factor in the rotor disc-tilt angles; 4) effects of both sweep and dynamic inflow corrections in the formulae of the rotor disc-ti 5) effects of high-order coupling terms included in the analytical expressions of the rotor disc-tilt. The paper developed a six degree-of-freedom (6-dof) non-linear helicopter model and implemented these approximations in the model. With respect to the simulated trimmed flight solution, it was demonstrated that using both sweep and dynamic inflow corrections in the analytical expressions of the rotor disc tilt angles resulted in accounting for the experimentally measured peak of the lateral tilt in the region of low flight velocities. This peak is theoretically still unexplained and the above conclusion suggests that the discrepancy may be searched in both modelling the dynamic inflow and the sweep effects on the rotor blade. Using both sweep and dynamic inflow corrections resulted in overpredicted lateral disc-tilt for trimming at high flight speeds. With respect to the manoeuvring flight simulations, three manoeuvres were performed: a doublet in the longitudinal cyclic, a doublet in the lateral cyclic and the acceleration/deceleration manoeuvre from the ADS-33 standard. It was demonstrated that for a pitch axis manoeuvre, the results are mainly affected by dynamic inflow modelling. For a manoeuvre in the roll axis, the coupling between the longitudinal and lateral plane was important and thus the high-order coupling terms considered in the analytical expressions of the rotor disc-tilt played an important role. For a more elaborate manoeuvre such as acceleration/deceleration, the effects of dynamic inflow correction, high-order coupling terms and sweep correction contributed all to the prediction of the flying parameters.
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