Analysis and Research on Aerodynamic Characteristics of Quad Tilt Rotor Aircraft

For the quad tilt rotor aircraft, a computational fluid dynamics method based on multiple reference frames (MRF) was used to analyze the influence of aerodynamic layout parameters on the aerodynamic characteristics of the quad tilt rotor aircraft. Firstly, a numerical simulation method for the interference flow field of the quad tilt rotor aircraft is established. Based on this method, the aerodynamic characteristics of isolated rotors, rotor combinations at different lateral positions on the wing, and rotor rotation directions under different inflow velocities were calculated and analyzed, in order to grasp their aerodynamic interference laws and provide reference for the design and control theory research of such aircraft.

Design of Flight Control System for a Small Unmanned Tilt Rotor Aircraft

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 ...

Multi-body Motion Modeling and Simulation for Tilt Rotor Aircraft

The previous study on modeling of the tilt rotor aircraft used to put a premium on the complicated aerodynamic computation, and the research on the motion equations is often constrained to frequently use the oversimplified 6-degree of freedom （DOF） rigid body equations. However, the transfiguration of aircraft during transition stage, is complicated due to the aerodynamic interference and the change of center of gravity （CG）. Moreover, the gyroscopic moment caused by tilting the high-speed revolving rotors seriously interferes with the aircraft attitude. The above-cited 6-DOF single rigid body equations do not take the inertia coupling effects into account during transition. For this sake, the article, reckoning the body, the nacelles and the rotors to be independent entities, establishes a realistic model in the form of multi-body motion equations. First, by applying Newton＇s laws and angular momentum theorem to a mass of elements of the aircraft, the multi-body motion equations in inertial flame as well as in body frame are obtained by integrating over all elements. As the equations are of implicit nonlinear differential type, the consistent initial value problem should be solved. Then, a numerical simulation of the differential equations is conducted by means of the Runge-Kutta-Felhberg integral algorithm. The modeling and the simulation algorithm are verified against the data of XV-15 as an example. The model can be used in the area of flight dynamics, flight control and flight safety of tilt rotor air- craft.

Control techniques of tilt rotor unmanned aerial vehicle systems： A review

The tilt rotor unmanned aerial vehicle（TRUAV） exhibits special application value due to its unique rotor structure. However, varying dynamics and aerodynamic interference caused by tiltable rotors are great technical challenges and key issues for TRUAV＇s high-powered flight controls, which have attracted the attention of many researchers. This paper outlines the concept of TRUAV and some typical TRUAV platforms while focusing on control techniques. TRUAV structural features, dynamics modeling, and flight control methods are discussed, and major challenges and corresponding developmental tendencies associated with TRUAV flight control are summarized.

Numerical simulation of aerodynamic interaction for a tilt rotor aircraft in helicopter mode

A rotor CFD solver is developed for simulating the aerodynamic interaction phenomenon among rotor, wing and fuselage of a tilt rotor aircraft in its helicopter mode. The unsteady Navier-Stokes equations are discretized in inertial frame and embedded grid system is adopted for describing the relative motion among blades and nacelle/wing/fuselage. A combination of multi-layer embedded grid and 'extended hole fringe' technique is complemented in original grid system to tackle grid assembly difficulties arising from the narrow space among different aerodynamic components, and to improve the interpolation precision by decreasing the cell volume discrepancy among different grid blocks. An overall donor cell searching and automatic hole cutting technique is used for grid assembly, and the solution processes are speeded up by introduction of OpenMP parallel method. Based on this solver, flow fields and aerodynamics of a tilt rotor aircraft in hover are simulated with several rotor collective angles, and the corresponding states of an isolated rotor and rotor/wing/fuselage model are also computed to obtain reference solution. Aerodynamic interference influences among the rotor and wing/fuselage/nacelle are analyzed, and some meaningful conclusions are drawn. (C) 2016 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd.

Analysis of Flight Dynamics Characteristics of Tilt Quad Rotor with Partial Tilt-Wing

The aerodynamic model of propeller,wing,fuselage and vertical tail are established for the tilt quad rotor(TQR)with partial tilt-wing,and then the flight dynamic model is established.Based on the six-degree-of-freedom equation and the small disturbance linearization assumption,the trimming and stability of the tilt quad rotor with partial tilt-wing and the tilt quad rotor without tilt-wing are analyzed.The results show that in the hovering state,due to the existence of tilt-wing,the propeller wake reduces the downwash on the wing,thereby reducing the vertical weight gain of the aircraft.It is beneficial to increase the endurance time and improve the endurance performance.The transition corridor of the TQR with tilt-wing is narrower than that of the TQR without tilt-wing,but the transition corridor of TQR with tilt-wing still has a large space for design.Furthermore,the stability analysis shows that the Dutch roll damping ratio is larger,and in other modes the aircraft has a certain stability.The manipulation response analysis shows that in the transition mode the lateral-directional coupling is strong.

Stability Analysis on Rotor Systems Supported by Self-acting Tilting-pad Gas Bearings with Frequency Effects

The recent research on stability of gas bearing-rotor systems still mostly adopts the same method as in oil-lubricated bearing-rotor systems.The dynamic coefficients of gas bearings in the case that the perturbation frequencies are same as the rotating speed are used to carry out the stability analysis of rotor systems.This method does not contact the frequency characteristics of dynamic stiffness and damping coefficients of gas bearings with the dynamical behaviors of rotor systems.Furthermore,the effects of perturbation frequencies on the stability of systems are not taken into account.In this paper,the dynamic stiffness and damping coefficients of tilting-pad gas bearings are calculated by the partial derivative method.On the base of solution of dynamic coefficients,two computational models are produced for stability analysis on rotor systems supported by tilting-pad gas bearings according to whether the degrees of the freedom of pads tilting motions are included in the equations of motion or not.In the condition of considering the frequency effects of dynamic coefficients of tilting-pad gas bearings,the corresponding eigenvalues of the rigid and first five vibration modes of the system with the working speeds of 8-30 kr/min are computed through iteratively solving the equations of motion of rotor-system by using two computational models,respectively.According to the obtained eigenvalues,the stability of rotor system is analyzed.The results indicate that the eigenvalues and the stability of rotor system obtained by these two computational models are well agreement each other.They all can more accurately analyze the stability of rotor systems supported by tilting-pad gas bearings.This research has important meaning for perfecting the stability analysis method of rotor systems supported by gas bearings.

不同前倾角度倾转旋翼噪声数值计算分析

基于自由尾迹结合FW-H(Ffowcs Williams-Hawkings)方程的方法建立了倾转旋翼气动噪声计算模型,并采用倾转旋翼模型噪声试验数据验证了计算分析方法的有效性。选取典型过渡路径,进行考虑配平的倾转双旋翼气动噪声特性计算,获得了旋翼桨叶剖面非定常气动载荷以及不同测点气动噪声等计算结果,分析了倾转旋翼在不同前倾角下噪声指向性和噪声声压级的变化。结果表明:由于双旋翼噪声在传播中的叠加和抵消,倾转双旋翼和孤立单旋翼的噪声指向特性存在较大的不同;倾转旋翼噪声随前倾角增加总体上呈现先增加后减小的变化趋势,在前倾角30°附近噪声最强;不同前倾角下噪声声压级和指向性的变化与旋翼桨尖马赫数、气动载荷和桨盘角度等多种因素相关。

直线型倾转多旋翼植保无人机建模与控制

针对直线型倾转多旋翼植保无人机模型耦合复杂、作业时易受施药执行器干扰等问题,提出了一种模型补偿-线性自抗扰控制算法。首先建立无人机运动学和动力学模型,并分析作业时离心喷头产生的力矩作用影响;然后将作业模型中的固定部分作为已知扰动,引入模型补偿-扩张状态观测器估计内外未知总扰动并动态补偿控制系统,完成位姿控制器设计。仿真结果表明,所提出的算法在作业场景下偏航角度误差小于0.2°,恢复时间小于0.55 s,相比于PID算法和线性自抗扰算法最大角度偏差分别降低3.4°和0.9°,恢复时间减少3.1和0.99 s,具有较强的鲁棒性。飞行实验表明,该无人机可以很好地跟踪植保作业轨迹,最大位置稳态误差小于15 cm,满足植保作业需求。

多节链式倾转旋翼飞行器重构控制与运动仿真

多节链式旋翼飞行器具有构形可变换的特点,是应对运动空间变化的一种有效构形设计方式。受限于构形变化下电机共轴带来的横向转动力矩的缺失,多节链式旋翼飞行器的动态重构飞行具有无法达成的临界构形区间。为此,设计了具备横向倾转的链式旋翼机体结构,以单机臂为模块化结构基本单元,通过旋转关节实现水平向的构形变化,机臂中段配置倾转矢量关节,用以提供滚转力矩支撑。在机体运动学、动力学模型推导的基础上,引入虚拟控制量对控制分配进行线性化处理,利用Moore-Penrose伪逆求解控制效率矩阵,面向全构形变换设计了基于全驱动控制的飞行控制律。对飞行器典型构形位姿控制的稳定性、构形变换控制的可行性进行实验论证,仿真结果表明:在飞行器各典型构形飞行状态下,姿态各轴向角度跟踪最大误差不超过0.05°,构形变换过程中,姿态各轴向角度跟踪误差不超出0.1°,2种情况下,位置偏差均能控制在1 mm以内,飞行器具备各构形下稳定飞行及构形变换的能力,为进一步开展动态重构及稳健飞行提供了必要条件。

倾转旋翼机齿轮-丝杠作动器动力学建模及响应分析

倾转旋翼机的倾转机构是由齿轮副与滚珠丝杠副组成的复杂结构,动力学问题较为突出。为准确分析其动态行为并探明振动机制,考虑丝杠副的滚珠冲击激励以及齿轮副的准静态传动误差激励耦合作用,提出了一种齿轮-滚珠丝杠作动器系统动力学耦合建模方法。基于系统动力学方程求解特征值问题,得到了系统各阶固有频率与振型;对比有限元模态分析结果,验证了理论模型的准确性;在此基础上,分析了齿轮-滚珠丝杠作动器系统的动态行为,研究了丝杠副结构参数对输出响应的影响。结果表明,丝杠轴向振动响应随着螺旋升角的增大而减小,随着接触角的增大呈现先增大后减小的趋势。

基于改进遗传算法的倾转旋翼无人机区域覆盖路径规划

基于改进遗传算法研究倾转旋翼无人机(TRUAV)在多障碍物约束下的区域覆盖路径规划问题.运用最小跨度算法和往返路径生成算法进行任务区域内的覆盖路径初规划,将区域覆盖问题转化为旅行商问题以优化覆盖路径顺序.为了避开区域内的障碍物,提出鱼尾形避障策略.引入最近邻算法,生成比传统遗传算法质量更高的初始种群,设计三点式交叉算子和动态区间变异算子进行遗传操作以提高所提算法的全局搜索能力,避免算法陷入局部最优.在含多个障碍物的多边形区域算例内仿真验证所提算法的性能.结果表明,相比于逐行路径覆盖算法和传统遗传算法,所提算法的覆盖路径长度减少了7.80%,TRUAV的任务区域覆盖效率显著提升.

基于串级模型预测控制的倾转旋翼机过渡段控制

针对倾转旋翼机过渡阶段存在的纵垂向控制通道切换问题,基于串级控制框架提出了一种具有自适应权重矩阵的模型预测控制(model predictive control,MPC)策略。首先,通过分析直升机模态和定翼机模态的控制结构差别,构造了兼容全部飞行模态的增广串级控制结构。然后,在确立了倾转旋翼机的模糊建模策略后,设计了MPC目标函数中权重矩阵的参数自适应变化律,从而使内环和外环中高度、前飞速度的跟踪误差惩罚项根据所处模态的不同有着不同的惩罚占比。这样可以使在过渡阶段设计的增广串级控制结构能始终满足时标分离原则。该控制方案将2个飞行模态和过渡阶段的控制纳入一个统一的控制结构中,实现了各飞行模态间的自由切换。仿真结果表明,所提控制方案有良好的控制效果,控制量较为平滑。

倾斜转子-蜂窝密封系统动力学特性

建立了蜂窝密封三维数值模型,采用计算流体力学方法分析了转子倾斜对蜂窝密封泄漏特性和动力稳定性的影响。结果表明:转子倾斜导致蜂窝密封泄漏量减少,倾斜角由0°增加到0.3°,泄漏量降低了1.9%~6.5%;转子倾斜角越大,密封直接刚度系数越大,直接阻尼系数越小;在高频(f>130 Hz)时转子倾斜会导致密封有效阻尼系数减小,易引发轴系稳定性恶化;当转子倾斜时,沿周向同一腔室(2号、7-8号、13号)内的压力均呈正弦规律变化,且随着倾斜角的增大,周向压力绝对幅值增大,同一轴向位置间隙处的压力差增大,密封越易失稳。

倾转三旋翼无人机控制设计与飞行实验

针对倾转三旋翼无人机的飞行控制问题,本文围绕控制分配算法、控制权重设计和模态转换策略3个方面开展研究.首先,分析飞行控制原理,构建模态转换飞行控制框架;其次,为提高控制分配鲁棒性,设计串级解耦控制分配算法并提出两种控制分配参数修正方法;为实现稳定的模态转换飞行,引入可达力矩集设计控制权重,并提出基于时间和倾转角度的模态转换策略;最后,分别开展旋翼模态与模态转换飞行试验,验证了控制方法的有效性.试验结果表明:引入参数修正的串级解耦控制分配算法可有效提高控制分配鲁棒性,并改善姿态控制性能,基于设计的控制权重与模态转换策略可确保模态转换飞行的安全性、稳定性.

考虑瓦块磨损的可倾瓦径向轴承-转子系统动态特性研究

针对含有瓦块磨损故障的可倾瓦径向轴承-转子系统润滑和振动特性耦合建模问题,考虑了瓦块磨损、转子与瓦块平摆振动和轴承混合润滑的影响,提出了可倾瓦径向轴承-转子系统的混合润滑动力学模型,研究了不同磨损率下转子振动特性和轴承润滑性能的动态响应,探明了转子偏心量、转速和预载荷系数等参数与磨损率的耦合作用对轴承-转子系统动态特性的影响。结果表明:转子在磨损瓦块位置的振动位移和振动加速度随磨损率的增加而增大;与无磨损轴承相比,磨损轴承的转子加速度峰值频率会额外激起转频的偶次倍频;多瓦块磨损会导致转子振动响应和轴承油膜压力显著增大。该研究结果可为可倾瓦径向轴承-转子系统的状态监测及故障识别提供理论参考依据。

倾转旋翼无人机过渡段控制策略研究

针对倾转旋翼无人机过渡段的纵向控制问题,以某型倾转旋翼无人机为研究对象,综述了国内倾转旋翼机的发展趋势。利用Rotorlib软件建立倾转旋翼无人机的6自由度刚体模型;通过频域和时域对过渡段的特性进行分析,设计出过渡段的舵面操纵分配策略;对总距控制通道的控制结构进行设计。由于倾转旋翼在过渡过程中总距控制通道存在严重的耦合,根据动力学方程分析提出余弦分配的策略来改进耦合问题。通过仿真验证了余弦分配对于总距控制通道的耦合问题有明显的改善。

一种大型倾转旋翼飞机倾转结构设计及力学分析

倾转旋翼飞机翼尖有一台可旋转的发动机带动两旋翼,实现飞机垂直起降和水平飞行,倾转部分是其区别于普通飞机的独特结构。通过对比研究,设计了一种可以实现旋翼旋转的结构,以及发动机布置等相关结构,该结构使用三只行星齿轮,满足载荷均布性,使结构具备实用性、稳定性和可靠性,设计可以模块化生产。采用定量研究,对相关结构在飞机几种主要飞行状态时的受力情况进行了简单的力学分析,对转轴强度、转轴直径、旋转用电机、机翼末端的强度要求等进行初步的理论计算。研究发现,倾旋转部分和机体部分的重心相对于机翼转轴的位置,对机翼的扭矩大小有重大影响。本研究为此类飞机的研发提供一些基础的设计及理论数值计算。

基于文献计量分析的倾转旋翼动态发展分析

倾转旋翼机作为一种结合了直升机和固定翼飞机优点的飞行器,在军事和民用领域都取得了显著进展。本文基于文献计量法对Web of Science网站2013—2022年关于倾转旋翼的文献进行了分析,研究并总结倾转旋翼领域近十年的发展动向,以期为我国倾转旋翼发展和相关工作提供参考和借鉴。

基于LQR的倾转旋翼机过渡段控制律设计

倾转旋翼机具有直升机模态、过渡段模态和定翼机模态,既有直升机的悬停和垂直起降性能,又有定翼机的高速巡航飞行能力,在过渡段模态,气动干扰严重且稳定性较差,因此,设计过渡段的控制律具有一定意义。以XV-15倾转旋翼机作为原型,首先用MATLAB建立飞机的气动模型,然后基于LQR最优控制算法对过渡段的纵垂向飞行姿态进行控制律的设计,最后进行模拟仿真。结果表明,LQR控制器对倾转旋翼机的飞行姿态具有较好的控制效果。