The drivetrain system of tiltrotor aircraft is a complicated multibody system.Traditionally,rotorcraft drivetrain systems are modeled by the finite element method using an equivalent mathematical model with all the el...The drivetrain system of tiltrotor aircraft is a complicated multibody system.Traditionally,rotorcraft drivetrain systems are modeled by the finite element method using an equivalent mathematical model with all the elements spinning at the same rotational velocity and structural properties scaled according to gear ratios.Such a process can be complex and computationally expensive,especially for large-scale problems.This paper proposes the dynamic analysis of a tiltrotor drivetrain,coupled with flexible blades'lagwise motion,using a novel multibody system modeling and analysis method based on the transfer matrix method.The proposed method eliminates the need for equivalent processing of the drivetrain system components and does not require the derivation of the overall governing equations based on the Hamilton principle.Instead,they are directly formulated according to the system's topology graph.Virtual branch and geometric elements are introduced to decouple any topological structure of the drivetrain system into multiple independent chain systems,further reducing the modeling complexity.展开更多
The muhi-body analysis of the aeroelastic stability of the tiltrotor aircraft is presented. Muhi-body dynamic differential equations are combined with the equations of the unsteady dynamic inflow model to establish th...The muhi-body analysis of the aeroelastic stability of the tiltrotor aircraft is presented. Muhi-body dynamic differential equations are combined with the equations of the unsteady dynamic inflow model to establish the complete unsteadily aeroelastic coupling analytical model of the tiltrotor. The stability of the tiltrotor in the helicopter mode is analyzed aiming at a semi span soft-inplane tihrotor model with an elastic wing. Parametric effects of the lag stiffness of blades and the flight speed are analyzed. Numerical simulations demonstrate that the multibody analytical model can analyze the aeroelastic stability of the tiltrotor aircraft in the helicopter mode.展开更多
An attempt is made to apply modern control technology to the roll and yaw control of a rudderless quad-tiltrotor Unmanned Aerial Vehicle(UAV)in the latter part of the flight mode transition,where aerodynamic forces on...An attempt is made to apply modern control technology to the roll and yaw control of a rudderless quad-tiltrotor Unmanned Aerial Vehicle(UAV)in the latter part of the flight mode transition,where aerodynamic forces on the tiltrotor’s wings start to take effect.A predictor-based adaptive roll and yaw controller is designed to compensate for system uncertainties and parameter changes.A dynamics model of the tiltrotor is built.A Radial-Basis Function(RBF)neural network and offline adaptation method are used to reduce flight controller workload and cope with the nonlinearities in the controls.Simulations are conducted to verify the reference model response tracking and yaw-roll control decoupling ability of the adaptive controller,as well as the validity of the offline adaptation method.Flight tests are conducted to confirm the ability of the adaptive controller to track different roll and yaw reference model responses.The decoupling of roll and yaw controls is also tested in flight via coordinated turn maneuvers with different rotor tilt angles.展开更多
The existing full-span models of the tiltrotor aircraft adopted the rigid blade model without considering the coupling relationship among the elastic blade, wing and fuselage. To overcome the limitations of the existi...The existing full-span models of the tiltrotor aircraft adopted the rigid blade model without considering the coupling relationship among the elastic blade, wing and fuselage. To overcome the limitations of the existing full-span models and improve the precision of aeroelastic analysis of tiltrotor aircraft in forward flight, the aeroelastic stability analysis model of full-span tiltrotor aircraft in forward flight has been presented in this paper by considering the coupling among elastic blade, wing, fuselage and various components. The analytical model is validated by comparing with the calculation results and experimental data in the existing references. The influence of some structural parameters, such as the fuselage degrees of freedom, relative displacement between the hub center and the gravity center, and nacelle length, on the system stability is also investigated. The results show that the fuselage degrees of freedom decrease the critical stability velocity of tiltrotor aircraft, and the variation of the structural parameters has great influence on the system stability,and the instability form of system can change between the anti-symmetric and symmetric wing motions of vertical and chordwise bending.展开更多
Tiltrotor aircraft have three flight modes:helicopter mode,airplane mode,and transition mode.A tiltrotor has characteristics of highly nonlinear,time-varying flight dynamics and inertial/-control couplings in its tran...Tiltrotor aircraft have three flight modes:helicopter mode,airplane mode,and transition mode.A tiltrotor has characteristics of highly nonlinear,time-varying flight dynamics and inertial/-control couplings in its transition mode.It can transit from the helicopter mode to the airplane mode by tilting its nacelles,and an effective controller is crucial to accomplish tilting transition missions.Longitudinal dynamic characteristics of the tiltrotor are described by a nonlinear Lagrangeform model,which takes into account inertial/control couplings and aerodynamic interferences.Reference commands for airspeed velocity and attitude in the transition mode are calculated dynamically by visiting a command library which is founded in advance by analyzing the flight envelope of the tiltrotor.A Time-Varying Linear(TVL)model is obtained using a Taylorexpansion based online linearization technique from the nonlinear model.Subsequently,based on an optimal control concept,an online optimization based control method with input constraints considered is proposed.To validate the proposed control method,three typical tilting transition missions are simulated using the nonlinear model of XV-15 tiltrotor aircraft.Simulation results show that the controller can be used to control the tiltrotor throughout its operating envelop which includes a transition flight,and can also deal with vertical gust disturbances.展开更多
Tiltrotors have three flight modes that pose control problems and quality defects during the conversion process.To address this,a novel flying qualities-based time-varying stability augmentation system is designed to ...Tiltrotors have three flight modes that pose control problems and quality defects during the conversion process.To address this,a novel flying qualities-based time-varying stability augmentation system is designed to achieve multi-mode,nonlinear,and time-varying stability.The system integrates a nonlinear time-varying control law with the flying qualities requirements for all three flight modes.It consists of an inner and outer loop control framework,where the control law in the inner loop is designed based on the Lyapunov theorem of stability.The reference models in the outer loop are derived from the flying qualities criteria to meet level one flying qualities requirements.To evaluate the conversion process,a time-varying flying qualities evaluation method is developed,which includes the conversion path,pilot model,and time-varying flying qualities index.The proposed time-varying stability augmentation control system is then tested through simulation during the conversion process.A pilot-aircraft closed-loop system is established for conducting experiments.Comparison between simulation results and pilot-in-loop experiment results demonstrates the effectiveness of the proposed control system.Furthermore,it proves that the evaluation method is suitable for analyzing time-varying systems.This research can be valuable in designing and evaluating stability augmentation controls for strongly time-varying systems.展开更多
An analysis has been developed to predict the transient aeroelastic response of gimballed tiltrotors during shipboard engage/disengage operations. A multi blade gimballed rotor is modeled with slender elastic beams ...An analysis has been developed to predict the transient aeroelastic response of gimballed tiltrotors during shipboard engage/disengage operations. A multi blade gimballed rotor is modeled with slender elastic beams rigidly attached to a hub and undergoing flap bending, lag bending, elastic twist, and axial deflection. The gimbal restraint is simulated using a conditional rotational spring. Blade element theory is used to calculate quasi steady loads in linear and nonlinear regimes. The rotor equations of motion are formulated using Hamiltons principle and spatially discretized using the finite element method. The discretized rotor equations of motion are integrated in the modal space for a specified rotor speed run up profile. Studies for a 1/5 size aeroelastically scaled tiltrotor model are conducted to validate the analysis and investigate the transient response and loads of the gimballed rotor during engagement. Blade bending moment and hub moment predictions indicated that gimbal restraint impacts can induce high transient loads on the rotor blades and hub.展开更多
An attempt is made to implement a faster level-flight to hover mode transition in tiltrotor’s landing process for the purpose of shortening its landing time. A three-stage tiltrotor landing maneuver is designed, and ...An attempt is made to implement a faster level-flight to hover mode transition in tiltrotor’s landing process for the purpose of shortening its landing time. A three-stage tiltrotor landing maneuver is designed, and corresponding control modules and algorithms are created based on the analysis of the flight dynamics and the required actions of tiltrotor’s landing operation. As the altitude control is vital for tiltrotor’s near-ground landing, an Extended State Observer(ESO) control module of the Active Disturbance Rejection Control(ADRC) is designed to reduce altitude fluctuations in the fast mode transition, which makes the designed maneuver workable at very low altitudes. Simulations are conducted to verify the effectiveness of the designed maneuver and the validity of ESO control in various flight conditions. Flight test results that finally prove the effectiveness of the desired fast transition maneuver are reported.展开更多
Tiltrotor exhibits a conversion mode with strong nonlinear aerodynamic characteristics.The thrust characteristics of propellers are one of the crucial factors determining the performance of tiltrotor with electric pro...Tiltrotor exhibits a conversion mode with strong nonlinear aerodynamic characteristics.The thrust characteristics of propellers are one of the crucial factors determining the performance of tiltrotor with electric propulsion systems in the conversion mode,which is affected by multiple factors such as the advance ratio,tilt angle,and wing blocking effect.In the present study,a numerical method based on the overset mesh method is established to simulate the six degrees of freedom motion of real blade models,which is suitable for simulations of the continuous conversion mode of tiltrotor.Numerical simulations are conducted on the continuous tilting process of the propeller/wing system with various propeller advance ratios to analyze the variation and the underlying principles of propeller dynamic thrust,and to summarize the equivalent inflow velocity under different tilt angles during the conversion process.The results show that the propeller thrust increases as the tilt angle increases and the propeller advance ratio decreases.The uneven force on the advancing and retreating blades causes an increase in thrust oscillation amplitude.The advance ratio influences the total thrust by affecting the forward component of the thrust.The resultant force direction angle of the propeller in the conversion mode is 2°–10°greater than the tilt angle,and the difference in angle increases as the propeller advance ratio increases.A new formula for the equivalent inflow velocity of the propeller during the tilting process is summarized.This could help to estimate the dynamic thrust of the propeller in the conversion mode of tiltrotor.展开更多
The aerodynamics, dynamic responses and aeroelasticity of tiltrotor aircraft in the tilting of rotor i.e. in conversion flight are extraordinarily complicated. The traditional quasi-steady assumption model can not ref...The aerodynamics, dynamic responses and aeroelasticity of tiltrotor aircraft in the tilting of rotor i.e. in conversion flight are extraordinarily complicated. The traditional quasi-steady assumption model can not reflect the unsteady aerodynamic problems in the tilting of rotor. The CFD method based on the vortex theory can get better results, but it consumes a lot of computing resources. In this paper, a wake bending dynamic inflow model of tilting rotor was established firstly based on the Peters-He dynamic inflow model used in helicopter. Then combining with the ONERA unsteady aerodynamic model, a wake bending unsteady dynamic inflow model of tilting rotor in conversion flight of tiltrotor aircraft was established. The wake bending unsteady dynamic inflow model of tilting rotor was verified by using the experimental data of an isolated rotor model in large angle pitching up maneuver and was used to calculate the dynamic responses of tilting rotor in conversion flight of a tiltrotor aircraft model. The calculated results were analyzed to be physically reasonable.展开更多
An analytical model for aeroelastic stability of the wing/pylon/rotor coupled system with elastic bending-twist coupling wing for tiltrotor aircraft in forward flight has been established in this paper. The investigat...An analytical model for aeroelastic stability of the wing/pylon/rotor coupled system with elastic bending-twist coupling wing for tiltrotor aircraft in forward flight has been established in this paper. The investigation is focused on the effectiveness of the wing elastic bending-twist couplings provided by composite wing beam on the aeroelastic stability for the wing/pylon/rotor coupled system. By introducing the different wing elastic bending-twist couplings into the Boeing’s test model, the aeroelastic stability of the Boeing’s test model with different wing elastic bending-twist couplings has been analyzed. The numerical re-sults indicate that the negative wing beamwise bending-twist elastic coupling (the wing upward beamwise bending engenders the nose-down torsion of the wing section) can saliently enhance the stability of the wing beamwise bending modal. The posi-tive wing chordwise bending-twist elastic coupling (the wing forward chordwise bending engenders the nose-down torsion of the wing section) has a great benefit for increasing the stability of the wing chordwise bending modal.展开更多
基金the National Natural Science Foundation of China(No.12272169)the Project of Key Laboratory of Cross-Domain Flight Interdisciplinary Technology,China(Nos.2024-KF03001 and 2024-KF03003)Technology Development Project,China(No.XYZX040401)for the financial support。
文摘The drivetrain system of tiltrotor aircraft is a complicated multibody system.Traditionally,rotorcraft drivetrain systems are modeled by the finite element method using an equivalent mathematical model with all the elements spinning at the same rotational velocity and structural properties scaled according to gear ratios.Such a process can be complex and computationally expensive,especially for large-scale problems.This paper proposes the dynamic analysis of a tiltrotor drivetrain,coupled with flexible blades'lagwise motion,using a novel multibody system modeling and analysis method based on the transfer matrix method.The proposed method eliminates the need for equivalent processing of the drivetrain system components and does not require the derivation of the overall governing equations based on the Hamilton principle.Instead,they are directly formulated according to the system's topology graph.Virtual branch and geometric elements are introduced to decouple any topological structure of the drivetrain system into multiple independent chain systems,further reducing the modeling complexity.
文摘The muhi-body analysis of the aeroelastic stability of the tiltrotor aircraft is presented. Muhi-body dynamic differential equations are combined with the equations of the unsteady dynamic inflow model to establish the complete unsteadily aeroelastic coupling analytical model of the tiltrotor. The stability of the tiltrotor in the helicopter mode is analyzed aiming at a semi span soft-inplane tihrotor model with an elastic wing. Parametric effects of the lag stiffness of blades and the flight speed are analyzed. Numerical simulations demonstrate that the multibody analytical model can analyze the aeroelastic stability of the tiltrotor aircraft in the helicopter mode.
文摘An attempt is made to apply modern control technology to the roll and yaw control of a rudderless quad-tiltrotor Unmanned Aerial Vehicle(UAV)in the latter part of the flight mode transition,where aerodynamic forces on the tiltrotor’s wings start to take effect.A predictor-based adaptive roll and yaw controller is designed to compensate for system uncertainties and parameter changes.A dynamics model of the tiltrotor is built.A Radial-Basis Function(RBF)neural network and offline adaptation method are used to reduce flight controller workload and cope with the nonlinearities in the controls.Simulations are conducted to verify the reference model response tracking and yaw-roll control decoupling ability of the adaptive controller,as well as the validity of the offline adaptation method.Flight tests are conducted to confirm the ability of the adaptive controller to track different roll and yaw reference model responses.The decoupling of roll and yaw controls is also tested in flight via coordinated turn maneuvers with different rotor tilt angles.
基金supported by the National Natural Science Foundation of China (No. 11572150)
文摘The existing full-span models of the tiltrotor aircraft adopted the rigid blade model without considering the coupling relationship among the elastic blade, wing and fuselage. To overcome the limitations of the existing full-span models and improve the precision of aeroelastic analysis of tiltrotor aircraft in forward flight, the aeroelastic stability analysis model of full-span tiltrotor aircraft in forward flight has been presented in this paper by considering the coupling among elastic blade, wing, fuselage and various components. The analytical model is validated by comparing with the calculation results and experimental data in the existing references. The influence of some structural parameters, such as the fuselage degrees of freedom, relative displacement between the hub center and the gravity center, and nacelle length, on the system stability is also investigated. The results show that the fuselage degrees of freedom decrease the critical stability velocity of tiltrotor aircraft, and the variation of the structural parameters has great influence on the system stability,and the instability form of system can change between the anti-symmetric and symmetric wing motions of vertical and chordwise bending.
基金supported by the National Natural Science Foundation of China(No.11502008)
文摘Tiltrotor aircraft have three flight modes:helicopter mode,airplane mode,and transition mode.A tiltrotor has characteristics of highly nonlinear,time-varying flight dynamics and inertial/-control couplings in its transition mode.It can transit from the helicopter mode to the airplane mode by tilting its nacelles,and an effective controller is crucial to accomplish tilting transition missions.Longitudinal dynamic characteristics of the tiltrotor are described by a nonlinear Lagrangeform model,which takes into account inertial/control couplings and aerodynamic interferences.Reference commands for airspeed velocity and attitude in the transition mode are calculated dynamically by visiting a command library which is founded in advance by analyzing the flight envelope of the tiltrotor.A Time-Varying Linear(TVL)model is obtained using a Taylorexpansion based online linearization technique from the nonlinear model.Subsequently,based on an optimal control concept,an online optimization based control method with input constraints considered is proposed.To validate the proposed control method,three typical tilting transition missions are simulated using the nonlinear model of XV-15 tiltrotor aircraft.Simulation results show that the controller can be used to control the tiltrotor throughout its operating envelop which includes a transition flight,and can also deal with vertical gust disturbances.
基金co-supported by the Fundamental Research Funds for the Central Universities of China(No.YWF-23-SDHK-L-005)the Aeronautical Science Foundation of China(Nos.20220048051001,20230013051002)+2 种基金National Key Laboratory of Science and Technology on Rotorcraft AeromechanicsChina(Nos.61422202205,61422202106)the 1912Project,China。
文摘Tiltrotors have three flight modes that pose control problems and quality defects during the conversion process.To address this,a novel flying qualities-based time-varying stability augmentation system is designed to achieve multi-mode,nonlinear,and time-varying stability.The system integrates a nonlinear time-varying control law with the flying qualities requirements for all three flight modes.It consists of an inner and outer loop control framework,where the control law in the inner loop is designed based on the Lyapunov theorem of stability.The reference models in the outer loop are derived from the flying qualities criteria to meet level one flying qualities requirements.To evaluate the conversion process,a time-varying flying qualities evaluation method is developed,which includes the conversion path,pilot model,and time-varying flying qualities index.The proposed time-varying stability augmentation control system is then tested through simulation during the conversion process.A pilot-aircraft closed-loop system is established for conducting experiments.Comparison between simulation results and pilot-in-loop experiment results demonstrates the effectiveness of the proposed control system.Furthermore,it proves that the evaluation method is suitable for analyzing time-varying systems.This research can be valuable in designing and evaluating stability augmentation controls for strongly time-varying systems.
文摘An analysis has been developed to predict the transient aeroelastic response of gimballed tiltrotors during shipboard engage/disengage operations. A multi blade gimballed rotor is modeled with slender elastic beams rigidly attached to a hub and undergoing flap bending, lag bending, elastic twist, and axial deflection. The gimbal restraint is simulated using a conditional rotational spring. Blade element theory is used to calculate quasi steady loads in linear and nonlinear regimes. The rotor equations of motion are formulated using Hamiltons principle and spatially discretized using the finite element method. The discretized rotor equations of motion are integrated in the modal space for a specified rotor speed run up profile. Studies for a 1/5 size aeroelastically scaled tiltrotor model are conducted to validate the analysis and investigate the transient response and loads of the gimballed rotor during engagement. Blade bending moment and hub moment predictions indicated that gimbal restraint impacts can induce high transient loads on the rotor blades and hub.
基金co-supported by the Beijing Municipal Sci-Tech Program (No. Z181100003218015)the Fundamental Research Funds for the Central Universities, China (No. YWF-20-BJ-J-542)。
文摘An attempt is made to implement a faster level-flight to hover mode transition in tiltrotor’s landing process for the purpose of shortening its landing time. A three-stage tiltrotor landing maneuver is designed, and corresponding control modules and algorithms are created based on the analysis of the flight dynamics and the required actions of tiltrotor’s landing operation. As the altitude control is vital for tiltrotor’s near-ground landing, an Extended State Observer(ESO) control module of the Active Disturbance Rejection Control(ADRC) is designed to reduce altitude fluctuations in the fast mode transition, which makes the designed maneuver workable at very low altitudes. Simulations are conducted to verify the effectiveness of the designed maneuver and the validity of ESO control in various flight conditions. Flight test results that finally prove the effectiveness of the desired fast transition maneuver are reported.
基金co-supported by the National Natural Science Foundation of China(No.52236002)the specialized research projects of Huanjiang Laboratory。
文摘Tiltrotor exhibits a conversion mode with strong nonlinear aerodynamic characteristics.The thrust characteristics of propellers are one of the crucial factors determining the performance of tiltrotor with electric propulsion systems in the conversion mode,which is affected by multiple factors such as the advance ratio,tilt angle,and wing blocking effect.In the present study,a numerical method based on the overset mesh method is established to simulate the six degrees of freedom motion of real blade models,which is suitable for simulations of the continuous conversion mode of tiltrotor.Numerical simulations are conducted on the continuous tilting process of the propeller/wing system with various propeller advance ratios to analyze the variation and the underlying principles of propeller dynamic thrust,and to summarize the equivalent inflow velocity under different tilt angles during the conversion process.The results show that the propeller thrust increases as the tilt angle increases and the propeller advance ratio decreases.The uneven force on the advancing and retreating blades causes an increase in thrust oscillation amplitude.The advance ratio influences the total thrust by affecting the forward component of the thrust.The resultant force direction angle of the propeller in the conversion mode is 2°–10°greater than the tilt angle,and the difference in angle increases as the propeller advance ratio increases.A new formula for the equivalent inflow velocity of the propeller during the tilting process is summarized.This could help to estimate the dynamic thrust of the propeller in the conversion mode of tiltrotor.
文摘The aerodynamics, dynamic responses and aeroelasticity of tiltrotor aircraft in the tilting of rotor i.e. in conversion flight are extraordinarily complicated. The traditional quasi-steady assumption model can not reflect the unsteady aerodynamic problems in the tilting of rotor. The CFD method based on the vortex theory can get better results, but it consumes a lot of computing resources. In this paper, a wake bending dynamic inflow model of tilting rotor was established firstly based on the Peters-He dynamic inflow model used in helicopter. Then combining with the ONERA unsteady aerodynamic model, a wake bending unsteady dynamic inflow model of tilting rotor in conversion flight of tiltrotor aircraft was established. The wake bending unsteady dynamic inflow model of tilting rotor was verified by using the experimental data of an isolated rotor model in large angle pitching up maneuver and was used to calculate the dynamic responses of tilting rotor in conversion flight of a tiltrotor aircraft model. The calculated results were analyzed to be physically reasonable.
文摘An analytical model for aeroelastic stability of the wing/pylon/rotor coupled system with elastic bending-twist coupling wing for tiltrotor aircraft in forward flight has been established in this paper. The investigation is focused on the effectiveness of the wing elastic bending-twist couplings provided by composite wing beam on the aeroelastic stability for the wing/pylon/rotor coupled system. By introducing the different wing elastic bending-twist couplings into the Boeing’s test model, the aeroelastic stability of the Boeing’s test model with different wing elastic bending-twist couplings has been analyzed. The numerical re-sults indicate that the negative wing beamwise bending-twist elastic coupling (the wing upward beamwise bending engenders the nose-down torsion of the wing section) can saliently enhance the stability of the wing beamwise bending modal. The posi-tive wing chordwise bending-twist elastic coupling (the wing forward chordwise bending engenders the nose-down torsion of the wing section) has a great benefit for increasing the stability of the wing chordwise bending modal.
