Flight dynamics modeling for the Mars helicopter faces great challenges.Aerodynamic modeling of coaxial rotor with high confidence and high computational efficiency is a major difficulty for the field.This paper build...Flight dynamics modeling for the Mars helicopter faces great challenges.Aerodynamic modeling of coaxial rotor with high confidence and high computational efficiency is a major difficulty for the field.This paper builds an aerodynamic model of coaxial rotor in the extremely thin Martian atmosphere using the viscous vortex particle method.The aerodynamic forces and flow characteristics of rigid coaxial rotor are computed and analyzed.Meanwhile,a high fidelity aerodynamic surrogate model is built to improve the computational efficiency of the flight dynamics model.Results in this paper reveal that rigid coaxial rotor can bring the Mars helicopter sufficient controllability but result in obvious instability and control couplings in forward flight.This highlights the great differences in flight dynamics characteristics compared with conventional helicopters on Earth.展开更多
In view of engineering application, it is practicable to decompose the aerodynamics into three components： the static aerodynamics, the aerodynamic increment due to steady rotations, and the aerodynamic increment due...In view of engineering application, it is practicable to decompose the aerodynamics into three components： the static aerodynamics, the aerodynamic increment due to steady rotations, and the aerodynamic increment due to unsteady separated and vortical flow. The first and the second components can be presented in conventional forms, while the third is described using a one-order differential equation and a radial-basis-function （RBF） network. For an aircraft configuration, the mathematical models of 6- component aerodynamic coefficients are set up from the wind tunnel test data of pitch, yaw, roll, and coupled yawroll large-amplitude oscillations. The flight dynamics of an aircraft is studied by the bifurcation analysis technique in the case of quasi-steady aerodynamics and unsteady aerodynam- ics, respectively. The results show that： （1） unsteady aerodynamics has no effect upon the existence of trim points, but affects their stability; （2） unsteady aerodynamics has great effects upon the existence, stability, and amplitudes of periodic solutions; and （3） unsteady aerodynamics changes the stable regions of trim points obviously. Furthermore, the dynamic responses of the aircraft to elevator deflections are inspected. It is shown that the unsteady aerodynamics is beneficial to dynamic stability for the present aircraft. Finally, the effects of unsteady aerodynamics on the post-stall maneuverability展开更多
A comprehensive method based on system identification theory for helicopter flight dynamics modeling with rotor degrees of freedom is developed. A fully parameterized rotor flapping equation for identification purpose...A comprehensive method based on system identification theory for helicopter flight dynamics modeling with rotor degrees of freedom is developed. A fully parameterized rotor flapping equation for identification purpose is derived without using any theoretical model, so the confidence of the identified model is increased, and then the 6 degrees of freedom rigid body model is extended to 9 degrees of freedom high-order model. Bode sensitivity function is derived to increase the accuracy of frequency spectra calculation which influences the accuracy of model parameter identification. Then a frequency domain identification algorithm is established. Acceleration technique is developed furthermore to increase calculation efficiency, and the total identification time is reduced by more than 50% using this technique. A comprehensive two-step method is established for helicopter high-order flight dynamics model identification which increases the numerical stability of model identification compared with single step algorithm. Application of the developed method to identify the flight dynamics model of BO 105 helicopter based on flight test data is implemented. A comparative study between the high-order model and rigid body model is performed at last. The results show that the developed method can be used for helicopter high-order flight dynamics model identification with high accuracy as well as efficiency, and the advantage of identified high-order model is very obvious compared with low-order model.展开更多
The robust bounded flight control scheme is developed for the uncertain longitudinal flight dynamics of the fighter with control input saturation invoking the backstepping technique. To enhance the disturbance rejecti...The robust bounded flight control scheme is developed for the uncertain longitudinal flight dynamics of the fighter with control input saturation invoking the backstepping technique. To enhance the disturbance rejection ability of the robust flight control for fighters, the sliding mode disturbance observer is designed to estimate the compounded disturbance including the unknown external disturbance and the effect of the control input saturation. Based on the backstepping technique and the compounded disturbance estimated output, the robust bounded flight control scheme is proposed for the fighter with the unknown external disturbance and the control input saturation. The closed-loop system stability under the developed robust bounded flight control scheme is rigorously proved using the Lyapunov method and the uniformly asymptotical convergences of all closed-loop signals are guaranteed. Finally, simulation results are presented to show the effectiveness of the proposed robust bounded flight control scheme for the uncertain longitudinal flight dynamics of the fighter.展开更多
The flight-structural dynamics of a high-aspect-ratio wing challenge the flight control design.This paper develops a reduced model of coupled dynamics with stability consideration.The structural dynamics are formulate...The flight-structural dynamics of a high-aspect-ratio wing challenge the flight control design.This paper develops a reduced model of coupled dynamics with stability consideration.The structural dynamics are formulated with dihedrals,and the central loads drive the deformation.The control-oriented model with essential coupled dynamics is formulated.Modal sensitivity anal-ysis and input–output pairing are performed to identify the control structure.Besides,an example of flight control design is provided to discuss the necessity of considering structural dynamics in controller design.Analytical coupled flight dynamics provide a system-theoretic approach for sta-bility and facilitate model-based control techniques.Simulation results reveal the characteristics of flight-structural coupled dynamics and demonstrate that the influence of flexible modes should be considered in control design,especially in lateral dynamics.展开更多
For the research of helicopter/ship dynamic interface,the method of combining steady flow and stochastic flow is adopted to establish a flow field model applied to the flight dynamics analysis of shipborne helicopter....For the research of helicopter/ship dynamic interface,the method of combining steady flow and stochastic flow is adopted to establish a flow field model applied to the flight dynamics analysis of shipborne helicopter.The steady flow is calculated by computational fluid dynamics(CFD)method,while the stochastic flow is composed of the compensation velocity derived from ship motion and turbulence above the deck.The accuracy of the proposed flow field model is verified by comparing the helicopter response in the proposed flow field with the results calculated by US Army′s Military Specifications(MIL)model which is commonly used in engineering.Meanwhile,it also shows the proposed flow field model is more appliable to flight dynamics analysis of shipborne helicopter.On that the basis,ship deck flow field is simulated at different sea conditions by adjusting the wind speed on the deck,mother ship movement and shipboard turbulence,etc.And helicopter angular rate response is calculated.The results show that the difference of dynamic stability between helicopter′s roll and pitch leads to the facts that the influence of above factors on the helicopter′s roll angular rate response is greater than that of pitch angular rate,that the frequency and amplitude of mother ship roll motion are much greater than those of pitch motion,and that the disturbance caused by roll motion on the air has greater influence on the helicopter response.The shipboard turbulence is the main disturbance factor that influences helicopter flight stability and its intensity determines the amplitudes of angular rate response.展开更多
Based on the equations of motion of flexible air vehicles includingrigid-body modes and elastic structural modes, and applying influence coefficients of linearaerodynamics, a set of equations are derived and a method ...Based on the equations of motion of flexible air vehicles includingrigid-body modes and elastic structural modes, and applying influence coefficients of linearaerodynamics, a set of equations are derived and a method is presented for analysis of flight loadsand dynamic characteristics. The problems in the fields of flight mechanics and aeroelasticity suchas static aeroelastic divergence, trim and deformation, aerodynamic loads distribution, flutter andflight dynamics can be solved by the procedure. An airplane with high aspect ratio wings isanalyzed, and the results show that the coupling between rigid -body modes and elastic modes isdistinct and should not be overlooked.展开更多
As all natural laws, Newtonian dynamics should be governed by Einstein’s Covariance Principle;i.e., being covariant under all coordinate transformations, even time-dependent transformations. But Newton’s Second Law,...As all natural laws, Newtonian dynamics should be governed by Einstein’s Covariance Principle;i.e., being covariant under all coordinate transformations, even time-dependent transformations. But Newton’s Second Law, as it is generally understood, is unchanged only under Galilean transformations, which do not include time-dependent coordinate transformations. To achieve the covariant formulation of Newton’s Second Law, a distinction must be made between frames and coordinate systems, as advanced by the Principle of Material Frame-Indifference, and furthermore, the ordinary time derivative must be replaced by the rotational time derivative. Elevating Newton’s Second Law to covariancy has born many fruits in flight dynamics from the theoretical underpinning of unsteady flight maneuvers to the practical modeling of complex flight engagements in tensors, followed by efficient programming with matrices.展开更多
A tilt rotor is an aircraft of a special kind, which possesses the characteristics of a helicopter and a fixed-wing airplane. However, there are a great number of important technical problems waiting for settlements. ...A tilt rotor is an aircraft of a special kind, which possesses the characteristics of a helicopter and a fixed-wing airplane. However, there are a great number of important technical problems waiting for settlements. Of them, the flight control system might be a critical one. This article presents the progresses of the research work on the design of flight control system at Nanjing University of Aeronautics and Astronautics (NUAA). The flight control law of the tilt rotor aircraft is designed with the help ...展开更多
The low altitude airspace will be open in China, general aviation flights are tremendously increased. Whether aircrafts can fly safely and how to determine the requirements of safety flight are the problems needed to ...The low altitude airspace will be open in China, general aviation flights are tremendously increased. Whether aircrafts can fly safely and how to determine the requirements of safety flight are the problems needed to be confirmed. Under this circumstances, based on the international Civil Aviation Organization（ICAO） criteria and the standards made by CAAC, this paper adopts the ＂See and Avoid＂ principle. Under the binding conditions of flight rules, visibility requirements, responding time, the aircraft speed, circle banking angle or the climbing angle, based on its study on aircraft dynamics principles, this paper establishes a mathematical collision avoidance model for head-to-head traffic and crossing converging traffic at the same level. And the safety separation requirements of the aircrafts in low altitude flight are equantitatively analyzed. Finally, the Matlab software is used to analyze the above method. The result shows that the safe traffic avoidance of the converging traffic at the same level meets certain flight conditions, while intersecting the traffic at the same level can safely avoid the collision.展开更多
During airdrop of heavy load, the flight parameters vary continuously as the load moves in the hold, and change suddenly when the load drops out. This process deteriorates the flight quality and control characteristic...During airdrop of heavy load, the flight parameters vary continuously as the load moves in the hold, and change suddenly when the load drops out. This process deteriorates the flight quality and control characteristic as the load becomes heavier. Based on the simplified airdrop flight equations, the backstepping and switch control methods are developed to tackle the flight state holding and disturbance/uncertainty （such as large-scale flight condition, pilot manipulation error, system measure delay, etc.） attenuation problem in this paper. Moreover, these methods can be used as a reference for pilot manipulating during airdrop. With the backstepping theory, an adaptive controller is synthesized moves in the hold, and then a coordinated switch control method is for the purpose of stabilizing the transport when the load used to control the aircraft when the condition jumps from the existence of load at the rear of fuselage to no load in the fuselage. Simulation results show that the proposed controllers not only provide effective state holding during airdrop, but also achieve robust performance within wide flight conditions.展开更多
To satisfy the validation requirements of flight control law for advanced aircraft,a wind tunnel based virtual flight testing has been implemented in a low speed wind tunnel.A 3-degree-offreedom gimbal,ventrally insta...To satisfy the validation requirements of flight control law for advanced aircraft,a wind tunnel based virtual flight testing has been implemented in a low speed wind tunnel.A 3-degree-offreedom gimbal,ventrally installed in the model,was used in conjunction with an actively controlled dynamically similar model of aircraft,which was equipped with the inertial measurement unit,attitude and heading reference system,embedded computer and servo-actuators.The model,which could be rotated around its center of gravity freely by the aerodynamic moments,together with the flow field,operator and real time control system made up the closed-loop testing circuit.The model is statically unstable in longitudinal direction,and it can fly stably in wind tunnel with the function of control augmentation of the flight control laws.The experimental results indicate that the model responds well to the operator＇s instructions.The response of the model in the tests shows reasonable agreement with the simulation results.The difference of response of angle of attack is less than 0.5°.The effect of stability augmentation and attitude control law was validated in the test,meanwhile the feasibility of virtual flight test technique treated as preliminary evaluation tool for advanced flight vehicle configuration research was also verified.展开更多
To analyze the parachute dynamics and stability characteristics of precision airdrop system, the fluid-structure interaction （FSI） dynamics coupling with the flight trajectory of a para- chute payload system is comp...To analyze the parachute dynamics and stability characteristics of precision airdrop system, the fluid-structure interaction （FSI） dynamics coupling with the flight trajectory of a para- chute payload system is comprehensively predicted by numerical methods. The inflation behavior of a disk-gap-band parachute is specifically investigated using the arbitrary Lagrangian Euler （ALE） penalty coupling method. With the available aerodynamic data obtained from the FSI sim- ulation, a nine-degree-of-freedom （9DOF） dynamic model of a parachute-payload system is built and solved to simulate the descent trajectory of the multi-body dynamic system. Finally, a linear five-degree-of-freedom （5DOF） dynamic model is developed, the perturbation characteristics and the motion laws of the parachute and payload under a wind gust are analyzed by the linearization method and verified by a comparison with flight test data. The results of airdrop test demonstrate that our method can be further applied to the guidance and control of precision airdrop systems.展开更多
Flight data of a twin-jet transport aircraft in revenue flight are analyzed for potential safety problems. Data from the quick access recorder （QAR） are first filtered through the kinematic compatibility analysis. T...Flight data of a twin-jet transport aircraft in revenue flight are analyzed for potential safety problems. Data from the quick access recorder （QAR） are first filtered through the kinematic compatibility analysis. The filtered data are then organized into longitudinal- and lateral-directional aerodynamic model data with dynamic ground effect. The dynamic ground effect requires the radio height and sink rate in the models. The model data are then refined into numerical models through a fuzzy logic algorithm without data smoothing in advance. These numerical models describe nonlinear and unsteady aerodynamics and are used in nonlinear flight dynamics simulation. For the jet transport under study, it is found that the effect of crosswind is significant enough to excite the Dutch roll motion. Through a linearized analysis in flight dynamics at every instant of time, the Dutch roll motion is found to be in nonlinear oscillation without clear damping of the amplitude. In the analysis, all stability derivatives vary with time and hence are nonlinear functions of state variables. Since the Dutch roll motion is not damped despite the fact that a full-time yaw damper is engaged, it is concluded that the design data for the yaw damper is not sufficiently realistic and the contribution of time derivative of sideslip angle to damping should be considered. As a result of nonlinear flight simulation, the vertical wind acting on the aircraft is estimated to be mostly updraft which varies along the flight path before touchdown. Varying updraft appears to make the descent rate more difficult to control to result in a higher g-load at touchdown.展开更多
A four-cable mount system is proposed for full-model wind tunnel flutter tests,which may adjust the pitch and roll attitude of the aircraft scaled model and ensure that the model is not subjected to cable tension.The ...A four-cable mount system is proposed for full-model wind tunnel flutter tests,which may adjust the pitch and roll attitude of the aircraft scaled model and ensure that the model is not subjected to cable tension.The system provides sufficient support to simulate the free flight of the aircraft by applying appropriate spring stiffness and cable tensions.The proposed fourcable mount system is modeled based on Lagrange mechanics,and its dynamics equations consider aerodynamic effects.The singularity of the system and its bifurcation characteristics under flow conditions are analysed to determine the supercritical bifurcation phenomenon for different tension levels and distances from the front suspension point to the mass centre of the model.The mathematical expressions of the longitudinal flight stability of the cable mount system are derived by linearising the system dynamics equations using small perturbations.The influence of the cable tension,spring stiffness,suspension point position,and other factors on the flight stability of the aircraft are analysed.A feedforward control algorithm is proposed to minimize the total elastic potential energy of the system.The results show that the model is in the level flight state when the elastic potential energy of the four-cable mount system is minimized.A feedback control design method is proposed based on the Lyapunov stability theory to derive the closed-loop stability conditions.The system dynamics model that includes the aircraft rigid body model,flexible cables,pulleys,springs,aerodynamic model,and servo motor control is established using the flexible multibody dynamics method.A multibody dynamics solver and Simulink are used to simulate the attitude adjustment of the model in the wind tunnel and verify the supercritical bifurcation characteristics of the system and the effectiveness of the feedback and feedforward control.展开更多
The lateral dynamic flight stability of a hovering model insect （dronefly） was studied using the method of computational fluid dynamics to compute the stability derivatives and the techniques of eigenvalue and eigen...The lateral dynamic flight stability of a hovering model insect （dronefly） was studied using the method of computational fluid dynamics to compute the stability derivatives and the techniques of eigenvalue and eigenvector analysis for solving the equations of motion. The main results are as following. （i） Three natural modes of motion were identified： one unstable slow divergence mode （mode 1）, one stable slow oscillatory mode （mode 2）, and one stable fast subsidence mode （mode 3）. Modes 1 and 2 mainly consist of a rotation about the horizontal longitudinal axis （x-axis） and a side translation; mode 3 mainly consists of a rotation about the x-axis and a rotation about the vertical axis. （ii） Approximate analytical expressions of the eigenvalues are derived, which give physical insight into the genesis of the natural modes of motion. （iii） For the unstable divergence mode, td, the time for initial disturbances to double, is about 9 times the wingbeat period （the longitudinal motion of the model insect was shown to be also unstable and td of the longitudinal unstable mode is about 14 times the wingbeat period）. Thus, although the flight is not dynamically stable, the instability does not grow very fast and the insect has enough time to control its wing motion to suppress the disturbances.展开更多
In the present paper, the longitudinal dynamic flight stability properties of two model insects are predicted by an approximate theory and computed by numerical sim- ulation. The theory is based on the averaged model ...In the present paper, the longitudinal dynamic flight stability properties of two model insects are predicted by an approximate theory and computed by numerical sim- ulation. The theory is based on the averaged model （which assumes that the frequency of wingbeat is sufficiently higher than that of the body motion, so that the flapping wings＇ degrees of freedom relative to the body can be dropped and the wings can be replaced by wingbeat-cycle-average forces and moments）; the simulation solves the complete equations of motion coupled with the Navier-Stokes equations. Comparison between the theory and the simulation provides a test to the validity of the assumptions in the theory. One of the insects is a model dronefly which has relatively high wingbeat frequency （164 Hz） and the other is a model hawkmoth which has relatively low wingbeat frequency （26 Hz）. The results show that the averaged model is valid for the hawkmoth as well as for the dronefly. Since the wingbeat frequency of the hawkmoth is relatively low （the characteristic times of the natural modes of motion of the body divided by wingbeat period are relatively large） compared with many other insects, that the theory based on the averaged model is valid for the hawkmoth means that it could be valid for many insects.展开更多
基金supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions,China.
文摘Flight dynamics modeling for the Mars helicopter faces great challenges.Aerodynamic modeling of coaxial rotor with high confidence and high computational efficiency is a major difficulty for the field.This paper builds an aerodynamic model of coaxial rotor in the extremely thin Martian atmosphere using the viscous vortex particle method.The aerodynamic forces and flow characteristics of rigid coaxial rotor are computed and analyzed.Meanwhile,a high fidelity aerodynamic surrogate model is built to improve the computational efficiency of the flight dynamics model.Results in this paper reveal that rigid coaxial rotor can bring the Mars helicopter sufficient controllability but result in obvious instability and control couplings in forward flight.This highlights the great differences in flight dynamics characteristics compared with conventional helicopters on Earth.
文摘In view of engineering application, it is practicable to decompose the aerodynamics into three components： the static aerodynamics, the aerodynamic increment due to steady rotations, and the aerodynamic increment due to unsteady separated and vortical flow. The first and the second components can be presented in conventional forms, while the third is described using a one-order differential equation and a radial-basis-function （RBF） network. For an aircraft configuration, the mathematical models of 6- component aerodynamic coefficients are set up from the wind tunnel test data of pitch, yaw, roll, and coupled yawroll large-amplitude oscillations. The flight dynamics of an aircraft is studied by the bifurcation analysis technique in the case of quasi-steady aerodynamics and unsteady aerodynam- ics, respectively. The results show that： （1） unsteady aerodynamics has no effect upon the existence of trim points, but affects their stability; （2） unsteady aerodynamics has great effects upon the existence, stability, and amplitudes of periodic solutions; and （3） unsteady aerodynamics changes the stable regions of trim points obviously. Furthermore, the dynamic responses of the aircraft to elevator deflections are inspected. It is shown that the unsteady aerodynamics is beneficial to dynamic stability for the present aircraft. Finally, the effects of unsteady aerodynamics on the post-stall maneuverability
基金the support of the Fund of Key Laboratory of Chinaa Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions of China
文摘A comprehensive method based on system identification theory for helicopter flight dynamics modeling with rotor degrees of freedom is developed. A fully parameterized rotor flapping equation for identification purpose is derived without using any theoretical model, so the confidence of the identified model is increased, and then the 6 degrees of freedom rigid body model is extended to 9 degrees of freedom high-order model. Bode sensitivity function is derived to increase the accuracy of frequency spectra calculation which influences the accuracy of model parameter identification. Then a frequency domain identification algorithm is established. Acceleration technique is developed furthermore to increase calculation efficiency, and the total identification time is reduced by more than 50% using this technique. A comprehensive two-step method is established for helicopter high-order flight dynamics model identification which increases the numerical stability of model identification compared with single step algorithm. Application of the developed method to identify the flight dynamics model of BO 105 helicopter based on flight test data is implemented. A comparative study between the high-order model and rigid body model is performed at last. The results show that the developed method can be used for helicopter high-order flight dynamics model identification with high accuracy as well as efficiency, and the advantage of identified high-order model is very obvious compared with low-order model.
基金supported by the National Natural Science Foundation of China(61174102)the Jiangsu Natural Science Foundation of China(SBK20130033)+1 种基金the NUAA Fundamental Research Funds(NS2013028)the Specialized Research Fund for the Doctoral Program of Higher Education(20133218110013)
文摘The robust bounded flight control scheme is developed for the uncertain longitudinal flight dynamics of the fighter with control input saturation invoking the backstepping technique. To enhance the disturbance rejection ability of the robust flight control for fighters, the sliding mode disturbance observer is designed to estimate the compounded disturbance including the unknown external disturbance and the effect of the control input saturation. Based on the backstepping technique and the compounded disturbance estimated output, the robust bounded flight control scheme is proposed for the fighter with the unknown external disturbance and the control input saturation. The closed-loop system stability under the developed robust bounded flight control scheme is rigorously proved using the Lyapunov method and the uniformly asymptotical convergences of all closed-loop signals are guaranteed. Finally, simulation results are presented to show the effectiveness of the proposed robust bounded flight control scheme for the uncertain longitudinal flight dynamics of the fighter.
基金co-supported by the Natural Science Founda-tion of Jiangsu Province,China(No.BK20200437)the National Natural Science Foundation of China(No.62103187)the Fundamental Research Funds for the Cen-tral Universities,China(No.NT2022025).
文摘The flight-structural dynamics of a high-aspect-ratio wing challenge the flight control design.This paper develops a reduced model of coupled dynamics with stability consideration.The structural dynamics are formulated with dihedrals,and the central loads drive the deformation.The control-oriented model with essential coupled dynamics is formulated.Modal sensitivity anal-ysis and input–output pairing are performed to identify the control structure.Besides,an example of flight control design is provided to discuss the necessity of considering structural dynamics in controller design.Analytical coupled flight dynamics provide a system-theoretic approach for sta-bility and facilitate model-based control techniques.Simulation results reveal the characteristics of flight-structural coupled dynamics and demonstrate that the influence of flexible modes should be considered in control design,especially in lateral dynamics.
基金supported by the Aviation Science Fund(20145784010)
文摘For the research of helicopter/ship dynamic interface,the method of combining steady flow and stochastic flow is adopted to establish a flow field model applied to the flight dynamics analysis of shipborne helicopter.The steady flow is calculated by computational fluid dynamics(CFD)method,while the stochastic flow is composed of the compensation velocity derived from ship motion and turbulence above the deck.The accuracy of the proposed flow field model is verified by comparing the helicopter response in the proposed flow field with the results calculated by US Army′s Military Specifications(MIL)model which is commonly used in engineering.Meanwhile,it also shows the proposed flow field model is more appliable to flight dynamics analysis of shipborne helicopter.On that the basis,ship deck flow field is simulated at different sea conditions by adjusting the wind speed on the deck,mother ship movement and shipboard turbulence,etc.And helicopter angular rate response is calculated.The results show that the difference of dynamic stability between helicopter′s roll and pitch leads to the facts that the influence of above factors on the helicopter′s roll angular rate response is greater than that of pitch angular rate,that the frequency and amplitude of mother ship roll motion are much greater than those of pitch motion,and that the disturbance caused by roll motion on the air has greater influence on the helicopter response.The shipboard turbulence is the main disturbance factor that influences helicopter flight stability and its intensity determines the amplitudes of angular rate response.
文摘Based on the equations of motion of flexible air vehicles includingrigid-body modes and elastic structural modes, and applying influence coefficients of linearaerodynamics, a set of equations are derived and a method is presented for analysis of flight loadsand dynamic characteristics. The problems in the fields of flight mechanics and aeroelasticity suchas static aeroelastic divergence, trim and deformation, aerodynamic loads distribution, flutter andflight dynamics can be solved by the procedure. An airplane with high aspect ratio wings isanalyzed, and the results show that the coupling between rigid -body modes and elastic modes isdistinct and should not be overlooked.
文摘As all natural laws, Newtonian dynamics should be governed by Einstein’s Covariance Principle;i.e., being covariant under all coordinate transformations, even time-dependent transformations. But Newton’s Second Law, as it is generally understood, is unchanged only under Galilean transformations, which do not include time-dependent coordinate transformations. To achieve the covariant formulation of Newton’s Second Law, a distinction must be made between frames and coordinate systems, as advanced by the Principle of Material Frame-Indifference, and furthermore, the ordinary time derivative must be replaced by the rotational time derivative. Elevating Newton’s Second Law to covariancy has born many fruits in flight dynamics from the theoretical underpinning of unsteady flight maneuvers to the practical modeling of complex flight engagements in tensors, followed by efficient programming with matrices.
基金National Natural Science Foundation of China (60705034)
文摘A tilt rotor is an aircraft of a special kind, which possesses the characteristics of a helicopter and a fixed-wing airplane. However, there are a great number of important technical problems waiting for settlements. Of them, the flight control system might be a critical one. This article presents the progresses of the research work on the design of flight control system at Nanjing University of Aeronautics and Astronautics (NUAA). The flight control law of the tilt rotor aircraft is designed with the help ...
文摘The low altitude airspace will be open in China, general aviation flights are tremendously increased. Whether aircrafts can fly safely and how to determine the requirements of safety flight are the problems needed to be confirmed. Under this circumstances, based on the international Civil Aviation Organization（ICAO） criteria and the standards made by CAAC, this paper adopts the ＂See and Avoid＂ principle. Under the binding conditions of flight rules, visibility requirements, responding time, the aircraft speed, circle banking angle or the climbing angle, based on its study on aircraft dynamics principles, this paper establishes a mathematical collision avoidance model for head-to-head traffic and crossing converging traffic at the same level. And the safety separation requirements of the aircrafts in low altitude flight are equantitatively analyzed. Finally, the Matlab software is used to analyze the above method. The result shows that the safe traffic avoidance of the converging traffic at the same level meets certain flight conditions, while intersecting the traffic at the same level can safely avoid the collision.
基金Foundation items： Aeronautical Science Foundation （2007ZD53053） National Natural Science Foundation of China （60134010）
文摘During airdrop of heavy load, the flight parameters vary continuously as the load moves in the hold, and change suddenly when the load drops out. This process deteriorates the flight quality and control characteristic as the load becomes heavier. Based on the simplified airdrop flight equations, the backstepping and switch control methods are developed to tackle the flight state holding and disturbance/uncertainty （such as large-scale flight condition, pilot manipulation error, system measure delay, etc.） attenuation problem in this paper. Moreover, these methods can be used as a reference for pilot manipulating during airdrop. With the backstepping theory, an adaptive controller is synthesized moves in the hold, and then a coordinated switch control method is for the purpose of stabilizing the transport when the load used to control the aircraft when the condition jumps from the existence of load at the rear of fuselage to no load in the fuselage. Simulation results show that the proposed controllers not only provide effective state holding during airdrop, but also achieve robust performance within wide flight conditions.
基金supported by the National Key Basic Research Program of China(No.2015CB755800)
文摘To satisfy the validation requirements of flight control law for advanced aircraft,a wind tunnel based virtual flight testing has been implemented in a low speed wind tunnel.A 3-degree-offreedom gimbal,ventrally installed in the model,was used in conjunction with an actively controlled dynamically similar model of aircraft,which was equipped with the inertial measurement unit,attitude and heading reference system,embedded computer and servo-actuators.The model,which could be rotated around its center of gravity freely by the aerodynamic moments,together with the flow field,operator and real time control system made up the closed-loop testing circuit.The model is statically unstable in longitudinal direction,and it can fly stably in wind tunnel with the function of control augmentation of the flight control laws.The experimental results indicate that the model responds well to the operator＇s instructions.The response of the model in the tests shows reasonable agreement with the simulation results.The difference of response of angle of attack is less than 0.5°.The effect of stability augmentation and attitude control law was validated in the test,meanwhile the feasibility of virtual flight test technique treated as preliminary evaluation tool for advanced flight vehicle configuration research was also verified.
基金co-supported by Research Project of Chinese National University of Defense Technology(No.:JC13-0104)the National Natural Science Foundation of China(Nos.:51375486 and 11272345)the found support from China Scholarship Council(CSC)
文摘To analyze the parachute dynamics and stability characteristics of precision airdrop system, the fluid-structure interaction （FSI） dynamics coupling with the flight trajectory of a para- chute payload system is comprehensively predicted by numerical methods. The inflation behavior of a disk-gap-band parachute is specifically investigated using the arbitrary Lagrangian Euler （ALE） penalty coupling method. With the available aerodynamic data obtained from the FSI sim- ulation, a nine-degree-of-freedom （9DOF） dynamic model of a parachute-payload system is built and solved to simulate the descent trajectory of the multi-body dynamic system. Finally, a linear five-degree-of-freedom （5DOF） dynamic model is developed, the perturbation characteristics and the motion laws of the parachute and payload under a wind gust are analyzed by the linearization method and verified by a comparison with flight test data. The results of airdrop test demonstrate that our method can be further applied to the guidance and control of precision airdrop systems.
基金Foundation item： National Natural Science Foundation of China （60832012）
文摘Flight data of a twin-jet transport aircraft in revenue flight are analyzed for potential safety problems. Data from the quick access recorder （QAR） are first filtered through the kinematic compatibility analysis. The filtered data are then organized into longitudinal- and lateral-directional aerodynamic model data with dynamic ground effect. The dynamic ground effect requires the radio height and sink rate in the models. The model data are then refined into numerical models through a fuzzy logic algorithm without data smoothing in advance. These numerical models describe nonlinear and unsteady aerodynamics and are used in nonlinear flight dynamics simulation. For the jet transport under study, it is found that the effect of crosswind is significant enough to excite the Dutch roll motion. Through a linearized analysis in flight dynamics at every instant of time, the Dutch roll motion is found to be in nonlinear oscillation without clear damping of the amplitude. In the analysis, all stability derivatives vary with time and hence are nonlinear functions of state variables. Since the Dutch roll motion is not damped despite the fact that a full-time yaw damper is engaged, it is concluded that the design data for the yaw damper is not sufficiently realistic and the contribution of time derivative of sideslip angle to damping should be considered. As a result of nonlinear flight simulation, the vertical wind acting on the aircraft is estimated to be mostly updraft which varies along the flight path before touchdown. Varying updraft appears to make the descent rate more difficult to control to result in a higher g-load at touchdown.
文摘A four-cable mount system is proposed for full-model wind tunnel flutter tests,which may adjust the pitch and roll attitude of the aircraft scaled model and ensure that the model is not subjected to cable tension.The system provides sufficient support to simulate the free flight of the aircraft by applying appropriate spring stiffness and cable tensions.The proposed fourcable mount system is modeled based on Lagrange mechanics,and its dynamics equations consider aerodynamic effects.The singularity of the system and its bifurcation characteristics under flow conditions are analysed to determine the supercritical bifurcation phenomenon for different tension levels and distances from the front suspension point to the mass centre of the model.The mathematical expressions of the longitudinal flight stability of the cable mount system are derived by linearising the system dynamics equations using small perturbations.The influence of the cable tension,spring stiffness,suspension point position,and other factors on the flight stability of the aircraft are analysed.A feedforward control algorithm is proposed to minimize the total elastic potential energy of the system.The results show that the model is in the level flight state when the elastic potential energy of the four-cable mount system is minimized.A feedback control design method is proposed based on the Lyapunov stability theory to derive the closed-loop stability conditions.The system dynamics model that includes the aircraft rigid body model,flexible cables,pulleys,springs,aerodynamic model,and servo motor control is established using the flexible multibody dynamics method.A multibody dynamics solver and Simulink are used to simulate the attitude adjustment of the model in the wind tunnel and verify the supercritical bifurcation characteristics of the system and the effectiveness of the feedback and feedforward control.
基金supported by the National Natural Science Foundation of China(10732030)the 111 Project(B07009)
文摘The lateral dynamic flight stability of a hovering model insect （dronefly） was studied using the method of computational fluid dynamics to compute the stability derivatives and the techniques of eigenvalue and eigenvector analysis for solving the equations of motion. The main results are as following. （i） Three natural modes of motion were identified： one unstable slow divergence mode （mode 1）, one stable slow oscillatory mode （mode 2）, and one stable fast subsidence mode （mode 3）. Modes 1 and 2 mainly consist of a rotation about the horizontal longitudinal axis （x-axis） and a side translation; mode 3 mainly consists of a rotation about the x-axis and a rotation about the vertical axis. （ii） Approximate analytical expressions of the eigenvalues are derived, which give physical insight into the genesis of the natural modes of motion. （iii） For the unstable divergence mode, td, the time for initial disturbances to double, is about 9 times the wingbeat period （the longitudinal motion of the model insect was shown to be also unstable and td of the longitudinal unstable mode is about 14 times the wingbeat period）. Thus, although the flight is not dynamically stable, the instability does not grow very fast and the insect has enough time to control its wing motion to suppress the disturbances.
基金supported by the National Natural Science Foundation of China (10732030) and the 111 Project (B07009)
文摘In the present paper, the longitudinal dynamic flight stability properties of two model insects are predicted by an approximate theory and computed by numerical sim- ulation. The theory is based on the averaged model （which assumes that the frequency of wingbeat is sufficiently higher than that of the body motion, so that the flapping wings＇ degrees of freedom relative to the body can be dropped and the wings can be replaced by wingbeat-cycle-average forces and moments）; the simulation solves the complete equations of motion coupled with the Navier-Stokes equations. Comparison between the theory and the simulation provides a test to the validity of the assumptions in the theory. One of the insects is a model dronefly which has relatively high wingbeat frequency （164 Hz） and the other is a model hawkmoth which has relatively low wingbeat frequency （26 Hz）. The results show that the averaged model is valid for the hawkmoth as well as for the dronefly. Since the wingbeat frequency of the hawkmoth is relatively low （the characteristic times of the natural modes of motion of the body divided by wingbeat period are relatively large） compared with many other insects, that the theory based on the averaged model is valid for the hawkmoth means that it could be valid for many insects.
