Aeroelastic Responses Of Coupled Rotor-Nacelle-Wing Structures For Tiltrotor Aircraft In Conversion Flight

Tiltrotor aircraft possess excellent vertical/short takeoff and landing and high speed cruising performances. During the tilting process (conversion flight), rotors are in a complex unsteady aerodynamics condition. The dynamic model of the coupled tilting rotor, nacelle and wing structures for tiltrotor aircraft can be used for analysis of aeroelastic response during tilting, and also for analysis of stability and modeling of control system.In this thesis, rotors and nacelles'tilting DOF has been added based on dynamic model of tiltrotor aircraft in cruising presented by Johnson to establish a dynamic model of coupled rotor, nacelle and wing structures for tiltrotor aircraft during tilting process. During the tilting process, the most notable feature of aerodynamic model is the wake bending caused by rotor tilting, which has significant effects on the induced velocity of rotor. By using the Peters-He unsteady dynamic inflow model and considering the wake bending effects, a rotor wake bending unsteady dynamic inflow model for computing the induced velocity during tilting process has been established. Aerodynamic forces on the rotor blade were computed by using the ONERA unsteady aerodynamic model. The flap and lag motion equations during tilting were derived. By using the finite element method, the dynamic equations of wing and nacelle systems have been established, including the coupling motion caused by nacelle's inertia and simulating the bending-torsion coupling characteristic of the composite box-shaped beam of the wing. Based on the developed dynamic equations of the coupled rotor, nacelle and wing structures, a MATLAB program was compiled to conduct the model trimming and response computation. The wind tunnel model test for the dynamic response during rotor tilting was conducted to validate the theoretical models.A few of conclusions have been obtained by the theoretical analysis and experiment:(1) The established dynamic model of coupled tilting rotor, nacelle and wing structures for the tiltrotor aircraft in this thesis can accurately reflect the aeroelastic characteristics of the coupled rotor, nacelle and wing structures during the tilting process;(2) During the tilting process, considering the wake bending can improve computational precise of the rotor disk induced velocity. Wake bending parameters are related to rotor shaft's tilting angular velocity, rotor disk tilt (flap) angular velocity, rotor's induced velocity and forward flight velocity. During tilting process in forward flight with high speed, while rotor shaft tilts to a particular angle, wake skew angle has a peak value and rotor disk has a high tilting angular velocity, which may produce a substantial dramatic oscillation of the wake bending, and the aerodynamic forces on the blades and wing and their dynamic responses all appear short term oscillations;(3) During tilting process, a sudden change of the rotor tilting angular velocity would cause the sudden oscillations of the rotor and wing responses. Hence, changes of the rotor angular velocity should be as smooth as possible;(4) During tilting process, the flapping and lagging motions of rotor blades are important for computation of the aerodynamic and inertia forces on the rotor disk. As the nacelle's center of gravity is not at the extended line of wing elastic axis, the nacelle's inertia may cause the wing elastic bending and torsion coupling which may lead to flutter occurring. By using the bending-torsion characteristic of the composite material reasonably can delay the occurrence of flutter and can also reduce the amplitude of wing torsional response;(5) Wing's elastic vibration will delay the occurrence of rotor wake skew angle's peak point and the oscillations of other parameters also lag correspondingly.The innovation points of the research in this thesis are as follows:(1) The dynamic model of coupled rotor, nacelle and wing system during tilting process has been established based on the dynamic model of tiltrotor aircraft in cruising model, and the motion equations of coupling system during the rotor tilting process has been derived;(2) Adding the wake bending effects to the Peters-He unsteady dynamic inflow model, a rotor wake bending unsteady dynamic inflow model has been established. The induced velocity during tilting process can be calculated by using the established model;(3) The analytical methods for the aeroelastic responses of the coupled tilting rotor, nacelle and wing system of tiltrotor aircraft has been established and can be used to compute the aeroelastic responses of wing and rotor during rotor tilting.