尾坐式超小型定翼机飞行运动建模与仿真

尾坐式超小型无人定翼机结构简单、飞行效率高、实用性强,其特有的飞行模式与传统飞行器显著不同,分析并掌握其运动特性具有重要意义。提出了一种尾坐式无人定翼机的新方案。为获得其基本气动参数,利用FLUENT进行CFD仿真建立其空气动力学数据库。为分析其各种运动模式,采用四元素法描述其运动姿态,并建立其六自由度飞行运动模型。最后,基于SIMULINK/Aerospace建立运动仿真平台,仿真结果表明该方案垂直起降过程的可行性,为后续控制系统设计与导航奠定了基础。

倾转旋翼飞行器定翼机模态模型预测控制

以XV-15为原型,建立倾转旋翼飞行器纵垂通道三自由度非线性全量模型并线性化。针对其定翼机模态下的纵垂向控制问题,采用级联控制方案,设计基于状态空间模型预测算法的控制器,不同短舱角采用同一组参数,实现无切换控制。仿真结果表明,所设计的飞行控制系统性能好、鲁棒性强,能够满足应用要求。

Z字形折叠无人机气动优化设计

针对Z字形无人机存在滚转力矩和偏航力矩的问题,提出一种基于混合翼型参数化的整机多目标优化方法,以非支配排序遗传算法(NSGA-Ⅱ)为核心与混合翼型参数化、SCDM流场建模、Fluent Meshing网格划分以及Fluent Solution流场计算相结合,建立优化模型,进而开发出基于Isight平台的整机自动优化流程,实现Z字形无人机的气动优化设计。结果表明,基于混合翼型参数化的优化平台,增加了翼型优化的搜索空间,实现了多目标预定数值的优化,减小了Z字形无人机的滚转力矩和偏航力矩,提高了其整体的气动性能。所提方法能消除有限翼展无人机的力矩,为解决不对称无人机滚转和偏航问题提供了技术参考。

A NEW AEROMECHANICAL STABILITY ANALYSIS METHODOLOGY FOR COUPLED ROTOR/FUSELAGE SYSTEM OF HELICOPTERS

The aeromechanical st ability for the coupled rotor/fuselage system of helicopters in forward flight i s investigated. The periodic time-varying equations of motion are developed thr ough building a new 24DOF coupled rigid/elastic blended element based on the fle xible multibody system theory in this paper. It accounts for the effects of prec one, sweep, and the moderately large elastic deflections on the blade and elasti city of shaft and fuselage of the helicopter. The dynamic coupling between the r igid motion of blades about the flap, lag and pitch hinges of articulated rotor and moderately large elastic deflections are included. There is no restriction o n the rotation amplitudes of flap, lag and pitch in the formulation. The stabili ty of periodic solution is studied using the Floquet theory. The transition matr ix is calculated by the Newmark integration method. The aeromechanical stability of a new helicopter is studied. The results show that it is stable in the given forward flight. But the instability arises with the decrease of the bending and torsion stiffness of the shaft.

MULTI-BODY AEROELASTIC STABILITY ANALYSIS OF TILTROTOR AIRCRAFT IN HELICOPTER MODE

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.

ENHANCED UNSTEADY AND NONLINEAR ROTOR WAKE MODEL FOR REAL-TIME FLIG HT SIMULATION

WT5 'BZThis paper presents an unsteady and nonlinear wake model based on th e widely used Peters He finite state dynamic wake model with improvements. The swirl component in the tip trace plane (TTP) can be predicted, nonlinear items are added into the linear theory, and the old small angle assumption use d in matrix prediction is removed. All of these enha ncements are aimed at the low speed flight phase and formulations for the induce d velocity field just in the TTP frame are derived. The corresponding FORTRAN pr ogram is tested and optimized for the real time applications on PCs.

COMPARISON BETWEEN TWO ANALYTICAL MODELS OF HELICOPTER GROUND RESONANCE

The 2-dimensional equivalent model used in helicopter ground resonance analysis is convenient for its simplicity and clarity. The equivalent body mass, the stiffness and the damping are derived from the modal charaCteristics. In this paper, a 3-dimensional space model is constructed to analyse the ground resonance.There is little difference between the calculated results of the 2-dimensional equivalent model and those of the 3-dimensional space model. Hence, the 2-dimensional model is verified for the practical application. Generally, the linear lead-lag damping of the equivalent rotor blade at the modal frequency is derived from the lead-lag damper characteristics by a procedure of iteration. The transformation of the imaginary part of the complex modulus of the viscoelastic damper into a linear velocity damping is complicated in analysis. A method to use the complex modulus directly in the ground resonance analysis is derived and verified.

Dynamic collision avoidance for cooperative fixed-wing UAV swarm based on normalized artificial potential field optimization

Cooperative path planning is an important area in fixed-wing UAV swarm.However,avoiding multiple timevarying obstacles and avoiding local optimum are two challenges for existing approaches in a dynamic environment.Firstly,a normalized artificial potential field optimization is proposed by reconstructing a novel function with anisotropy in each dimension,which can make the flight speed of a fixed UAV swarm independent of the repulsive/attractive gain coefficient and avoid trapping into local optimization and local oscillation.Then,taking into account minimum velocity and turning angular velocity of fixed-wing UAV swarm,a strategy of decomposing target vector to avoid moving obstacles and pop-up threats is proposed.Finally,several simulations are carried out to illustrate superiority and effectiveness.

Numerical Tools for the Control of the Unsteady Heating of an Airfoil

This paper concerns the real time control of the boundary layer on an aircraft wing. This new approach consists in heating the surface in an unsteady regime using electrically resistant strips embedded in the wing skin. The control of the boundary layer＇s separation and transition point will provide a reduction in friction drag, and hence a reduction in fuel consumption. This new method consists in applying the required thermal power in the different strips in order to ensure the desired temperatures on the aircraft wing. We also have to determine the optimum size of these strips （length, width and distance between two strips）. This implies finding the best mathematical model corresponding to the physics enabling us to facilitate the calculation for any type of material used for the wings. Secondly, the heating being unsteady, and, as during a flight the flow conditions or the ambient temperatures vary, the thermal power needed changes and must be chosen as fast as possible in order to ensure optimal operating conditions.

Numerical simulation of the influence of ground effect on the performance of multi section wings

the establishment of multi-element airfoil in steady and unsteady ground effect N-S equation turbulence model, the S-A model of multi element airfoils during takeoff and landing high attack angle change numerical simulation analysis, the calculation results show that the lower altitude, lift and drag wing angle decreased; the greater the ground the effect is more obvious, the greater the loss of lift. The simulation results show that the lift coefficient is slightly less than that of unsteady numerical simulation, and the drag coefficient is slightly less than that of unsteady numerical simulation. The ground disturbance to the wing not only affects the steady state flow field, but also is closely related to the unsteady aerodynamic performance. The results of this study can provide a reference for the design and flight control of large aircraft wings.

Vision algorithms for fixed-wing unmanned aerial vehicle landing system

Autonomous landing has become a core technology of unmanned aerial vehicle（UAV）guidance,navigation and control system

A novel posture alignment system for aircraft wing assembly

A novel 6-degree of freedom (DOF) posture alignment system, based on 3-DOF positioners, is presented for the assembly of aircraft wings. Each positioner is connected with the wing through a rotational and adsorptive half-ball shaped end-effector, and the positioners together with the wing are considered as a 3-PPPS (P denotes a prismatic joint and S denotes a spherical joint) redundantly actuated parallel mechanism. The kinematic model of this system is established and a trajectory planning method is introduced. A complete analysis of inverse dynamics is carried out with the Newton-Euler algorithm, which is used to find the desired actuating torque in the design and path planning phase. Simulation analysis of the displacement and actuating torque of each joint of the positioners based on inverse kinematics and dynamics is conducted, and the results show that the system is feasible for the posture alignment of aircraft wings.

Aeroelastic stability of wing/pylon/rotor coupled system for tiltrotor aircraft in forward flight

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.

Linearization method of nonlinear aeroelastic stability for complete aircraft with high-aspect-ratio wings

A linearization method and an engineering approach for the geometric nonlinear aeroelastic stability analysis of the very flexi- ble aircraft with high-aspect-ratio wings are established based on the little dynamic perturbation assumption.The engineering practicability of the method is validated by a complex example.For a high-altitude long-endurance unmanned aircraft,the nonlinear static deformations under straight flight and the gust loads are calculated.At the corresponding nonlinear equilibrium state,the complete aircraft is linearized dynamically and the vibration modes are calculated considering the large deformation effects.Then the unsteady aerodynamics are calculated by the double lattice method.Finally,the aeroelastic stability of the complete aircraft is analyzed.The results are compared with the traditional linear calculation.The work shows that the geometric nonlinearity induced by the large structural deformation leads to the motion coupling of the wing chordwise bending and the torsion,which changes the mode frequencies and mode shapes.This factors change the aeroelastic coupling relationship of the flexible modes leading to the decrease of the flutter speed.The traditional linear method would give not only an imprecise flutter speed but also a possible dramatic mistake on the stability.Hence,for a high-altitude long-endurance unmanned aircraft with high-aspect-ratio wings,or a similar very flexible aircraft,the geometric nonlinear aeroelastic analysis should be a necessary job in engineering practice.

Quadratic stabilization of a nonlinear aeroelastic system using a novel Neural-Network-based controller

This contribution proposes a novel neural-network-based control approach to stabilize a nonlinear aeroelastic wing section. With the prerequisite that all the states of the system are available, the proposed controller requires no comprehensive information about structural nonlinearity of the wing section. Furthermore, the proposed control approach requires no human intervention of designing goal dynamics and formulating control input function, which is difficult to be realized by the typical neural-network-based control following an inverse control scheme. Simulation results show that the proposed controller can stabilize the aeroelastic system with different nonlinearities.

Numerical Investigation of Influence of Rotor/Stator Interaction on Blade Boundary Layer Flow in a Low Speed Compressor

Numerical method was applied to the unsteady flow simulation at the mid span of a two-stage low speed compressor,and the blade boundary layer flow under rotor/stator interaction was investigated.By the model of wake/boundary layer interaction provided in this paper,the simulated blade frictional force and the boundary layer turbulent kinetic energy,the influence of wake/potential flow interaction on the blade boundary layer flow was analyzed in detail.The results show that under the condition of rotor/stator interaction,the wake is able to induce the stator laminar boundary layer flow to develop into turbulent flow within a certain range of wake interaction.In the stator suction boundary layer,an undisturbed region occurs behind the rotor wake,which extends the laminar flow range,and the wake with high turbulent intensity has the capability to control the boundary layer separation under adverse pressure gradient.