Research On Aeroelastic Dynamics Of Tiltrotor-Wing Coupled System

Tiltrotor aircraft can implement continuous flight conversion between helicopter mode andpropeller plane mode through the pivoting of rotor. Because the tiltrotor is planted at the tip of theelastic wing and the tiltrotor is permitted to flap, tiltrotor aircraft has seriously aeroelastical couplingsbetween rotor and wing. Especially in its conversion flight, inflows and aerodynamics of rotor and thedynamical characteristics of tiltrotor-wing coupled system are varied in dynamic process, which resultin complicated nonlinear and unsteady characteristics of tiltrotor-wing coupled system. This papergives emphasis to the researches on the dynamical characteristics of tiltrotor-wing aeroelasticallycoupled system with analyses and experiments.Basing on Hamilton's principle, a dynamical analysis model of semi-span tiltrotor aircraft isdeveloped by the multi-body method with considerations of complex couplings between tiltrotor andwing due to the nonlinear and unsteady characteristics coming from the complicated aerodynamic andinertial force as well as the complicated structures. In which, all of nonlinearly inertial couplingsbetween the rotating blade and elastic distortions of wing are retained and variations of pivoting androtating speed of rotor are considered. Then, the generalized dynamic inflow model is used with themodification of dynamic wake distortion to wholly take into account the aeroelastical couplingsamong responses, aerodynamics and inflows for the coupled distortion of tiltrotor and wing,especially in conversion flight. Finally, all of the structural dynamic model, aerodynamic model andinflow model are tightly coupled together in time domain to analyze the response with implicatingnumeric integration method。The aeroelastically dynamic analysis model of tiltrotor-wing coupled system was validatedthrough numerical and experimental contrastive analyses. A modal experiment of gimbaled tiltrotorwith advanced geometry blade and aeroelastically dynamical experiments with reduced scale modelof semi-span tiltrotor have been completed in wind tunnel of LORA NUAA to support the validation.Contrastive analyses achieved good correlations between numerical and experimental results, whichindicate that the multi-body analytical model represented in this paper has capacities to analyzeaeroelastically dynamic characteristics of coupled tiltrotor-wing coupled system.The dynamic characteristics of tiltrotor aircraft in conversion flight and the mechanism of whirlflutter in prop-plane forward flight have been simulated by the method of transient responsecalculated with the validated analysis model. As to the conversion flight, effects of variations ofpivoting and rotating speed of rotor were analyzed first, and then, aeroelastic coupling responses oftiltrotor and wing during transition flight with varying rotational speed and varying pitch controls were simulated. The mechanism of whirl flutter simulated in transient response indicated that physicalphenomena of tiltrotor aircraft's whirl flutter was the aeroelastic coupling radiation between the flapof tiltrotor and the vertical bending and torsion of elastic wing when flight velocity upon the boundaryspeed. Aiming at the mechanism of whirl flutter, the potential application of aeroelastically tailoringcomposite wing beam was analyzed.Aeroelastical stability of tiltrotor wing coupled system was analyzed with the analysis modeldeveloped in this research. The studied parameters included: the elastic and coupling stiffness of wing,structural geometry parameters of wing, the layer parameters of composite material of wingcrossbeam, the inertia of tilting nacelle, the length of hub to tilting hinge and the position of the tiltinghinge, structural parameters of hub and the coupling between flap and pitch. Some useful conclusionsand disciplines have been obtained which can be used to provide the guide to dynamic design oftiltrotor aircraft.