A corridor-based flight mode transition strategy for agile ducted-fan tail-sitter UAV:Altitude-hold transition

As an attractive transition approach,the altitude-hold transition is a special type of super-maneuvering and the vertical/horizontal flight mode transition that an agile aircraft conducts at fixed altitude.However,it is still challenging to implement an autonomous control of the altitude-hold transition while the existing optimal transition planning methods cannot avoid an evident altitude change during the transition process.This paper proposes a corridor-based flight mode transition strategy and presents a successful flight demonstration of the altitude-hold transition on a small ducted-fan tail-sitter unmanned aerial vehicle.In the proposed corridor-based methodology,we model and analyze the transition corridor,concentrate on the dynamic characteristics of the altitude-hold transition,and emphasize that a valid transition trajectory should be governed by its transition corridor.The identified transition corridor reveals that for a given velocity trajectory,the solution for the corresponding trajectories of pitch angle and thrust is unique.Based on this,the transition trajectory generation problem is addressed simply on the velocity-acceleration plane.Furthermore,a proper flight control scheme is devised to track the generated transition trajectories.Finally,the effectiveness of the proposed method is verified through practical flight tests,in which the altitude change is less than 1.1 m during the entire transition course.

The Importance of Flapping Kinematic Parameters in the Facilitation of the Different Flight Modes of Dragonflies

To better understand dragonflies’remarkable flapping wing aerodynamic performance,we measured the kinematic parameters of the wings in two different flight modes(Normal Flight Mode(NFM)and Escape Flight Mode(EFM)).When the specimens switched from normal to escape mode the flapping frequency was invariant,but the stroke plane of the wings was more horizontally inclined.The flapping of both wings was adjusted to be more ventral with a change of the pitching angle that resulted in a larger angle of attack during downstroke and smaller during upstroke to affect the flow directions and the added mass effect.Noticeably,the phasing between the fore and hind pair of wings varies between two flight modes,which affects the wing-wing interaction as well as body oscillations.It is found that the momentum stream in the wake of EFM is qualitatively different from that in NFM.The change of the stroke plane angle and the varied pitching angle of the wings diverts the momentum downwards,while the smaller flapping amplitude and less phase difference between the wings compresses the momentum stream.It seems that in order to achieve greater flight maneuverability a flight vehicle needs to actively control positional angle as well as the pitching angle of the flapping wings.

Sliding Mode Controller Design for Position and Speed Control of Flight Simulator Servo System with Large Friction

Flight simulator is an important device and a typical high-performance position and speed servo system used in the hardware-in-the-loop simulation of flight control system. Friction is the main nonlinear resistance in the flight simulator servo system, especially in a low-speed state. Based on the description of dynamic and static models of a nonlinear Stribeck friction model, this paper puts forward sliding mode controller to overcome the friction, whose stability is

Dynamic flight stability of a model dronefly in vertical flight

The dynamic flight stability of a model dronefly in hovering and upward flight is studied.The method of computational fluid dynamics is used to compute the stability derivatives and the techniques of eigenvalue and eigenvector used to solve the equations of motion.The major finding is as following.Hovering flight of the model dronefly is unstable because of the existence of an unstable longitudinal and an unstable lateral natural mode of motion.Upward flight of the insect is also unstable,and the instability increases as the upward flight speed increases.Inertial force generated by the upward flight velocity coupled with the disturbance in pitching angular velocity is responsible for the enhancement of the instability.

Dynamic flight stability of a hovering model insect:lateral motion

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.

FUZZY GLOBAL SLIDING MODE CONTROL BASED ON GENETIC ALGORITHM AND ITS APPLICATION FOR FLIGHT SIMULATOR SERVO SYSTEM

To alleviate the chattering problem, a new type of fuzzy global sliding mode controller （FGSMC） is presented. In this controller, the switching gain is estimated by fuzzy logic system based on the reachable conditions of sliding mode controller（SMC）, and genetic algorithm （GA） is used to optimize scaling factor of the switching gain, thus the switch chattering of SMC can be alleviated. Moreover, global sliding mode is realized by designing an exponential dynamic sliding surface. Simulation and real-time application for flight simulator servo system with Lugre friction are given to indicate that the proposed controller can guarantee high robust performance all the time and can alleviate chattering phenomenon effectively.

Nominal Model-Based Sliding Mode Control with Backstepping for 3-Axis Flight Table

Based on nominal model, a novel global sliding mode controller （GSMC） with a new control scheme is proposed for a practical uncertain servo system. This control scheme consists of two combined controllers, One is the global sliding mode controller for practical plant, the other is the integral backstepping controller for nominal model. Modeling error between practical plant and nominal model is used to design GSMC. The steady-state control accuracy can be guaranteed by the integral backstepping control law, and the global robustness can be obtained by GSMC. The stability of the proposed controller is proved according to the Lyapunov approach. The simulation results both of sine signal and step signal tracking for 3-axis flight table are investigated to show good position tracking performance and high robustness with respect to large and parameter changes over all the response time.

发射场航班化发射能力建设思考

航班化发射是构建未来高效航天运输系统的必要前提,是支撑太空产业蓬勃发展的重要基础。针对航班化发射运营对发射场能力的需求,开展了能力规划与建设思考。结合航天发射系统发展现状分析与航班化发射特征要求,描绘了发射场航班化运营的4类典型场景。在此基础上,对航班化发射场景下发射场的班次发射能力、火箭回收能力、综合测试检修能力、体系运营能力进行了规划,并从关键技术实现、基础设施建设两方面开展了能力建设的分析讨论。

不同类型植保无人飞机施药作业对烟草植株的影响

为规范植保无人飞机防治烟草病虫害的技术应用,评估了植保无人飞机在烟草病虫害防治过程中对烟株的安全性,并筛选出适合烟株生长中后期飞防施药的植保无人飞机类型及飞行方式。本试验选用目前主流的9种不同类型的植保无人飞机,分析对比了9种植保无人飞机在烟草成熟期进行飞防作业时对烟草植株形态的影响。结果表明,烟草植株成熟期采用四旋翼植保无人飞机以4 m或3 m的飞行高度垂直于烟草种植垄作业对烟草的损伤较低。

基于模糊PID的球形两栖机器人的设计及控制

为了解决移动机器人对工作环境要求严格的问题,设计了一种适用于多变、狭窄环境的轻小型球形陆空两栖机器人,具有地面滚动和空中飞行两种运动模式,可以自主完成运动模式的切换。首先,设计了机器人的结构,包括滚动部分、飞行部分和模式切换部分。基于拉格朗日方法,建立了不同运动模式下的动力学模型,建立了基于欧拉方程的运动学模型。最后,根据机器人的运动模型,设计了飞行模式和地面滚动模式下的姿态控制器,并对控制器进行了仿真对比实验。在实机上进行了测试,实验结果表明,该机器人能够实现自主模式切换,在不同运动模式下运动稳定、姿态可控,在纯地面模式下具有一定的越障能力。在结构、控制方法及控制策略切换方法上对陆空两栖可变形机器人具有一定借鉴作用。

基于MTRDL的自动飞行系统模式需求建模与验证方法

在民机自动飞行过程中,自动飞行系统模式转换是影响安全的重要因素,随着现代民机机载系统的功能与复杂度的快速增长,在需求阶段对自动飞行系统模式转换的安全性分析和验证成为重要的挑战.飞行模式转换的复杂性不仅体现在自动飞行过程中必需的多重飞行模式之间的交互关系,还体现在模式转换与外部环境之间复杂的数据与控制交联关系,这些交联关系同时隐含了飞行模式转换的安全性质,这些特征提高了形式化方法的应用难度.提出一种领域特定的建模验证框架:首先,提出面向自动飞行系统模式转换的领域需求建模语言MTRDL和基于该语言扩展于SysML上的建模方法;其次,提出基于安全需求模板的安全性质辅助规约方法;最后,通过对某机型的若干条目化需求的实例研究,证明所提方法在自动飞行系统模式转换需求验证中的有效性.

基于EMD分解和Levy-SSA-BP神经网络的齿轮故障诊断

为解决齿轮磨损早期故障诊断问题,提出了一种基于经验模态分解(Empirical Mode Decomposition,EMD)和算法优化反向传播(Back Propagation,BP)神经网络的故障诊断方法。首先,将声发射信号进行经验模态分解,得到本征模函数(Intrinsic Mode Function,IMF);其次,计算各IMF分量与原始信号的相关系数,并对各个分量进行特征提取,构成特征矩阵;最后,将特征矩阵放入经过Levy飞行和麻雀搜索算法优化后的BP神经网络中进行识别。对比BP神经网络和麻雀搜索算法优化后的神经网络,本文提出的算法准确率更高,且对轻微磨损故障的识别能力更好,可以用于早期齿轮故障诊断。

中型无人直升机向心回转机动飞行控制律设计

向心回转是直升机的一个标准机动飞行科目,其可以综合检验直升机各通道的控制性能。针对中型无人直升机向心回转机动中姿态控制和速度控制的问题,提出一种增强飞行过程中稳定性和快速性的控制律设计方法。首先,根据ADS-3E-PRF,设计了向心回转机动的控制指令。随后,在内外环串联的通道控制结构基础上,通过推导得出直升机滑模控制律,从而设计姿态内回路的滑模控制器,对比PID控制器得到了更好的姿态增稳效果和更快的响应速度。最后,通过半物理仿真系统的仿真实验,结合向心回转机动的指标,验证了所设计的方法能有效完成向心回转机动,并达到了满意的标准。

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.

自动飞行系统飞行模式操作验证方法研究

现代民用飞机的自动飞行控制系统是主要的人机交互系统之一,其飞行模式操作控制功能由两大物理部分组成:FMCP硬件与自动飞行控制软件。对于复杂的人机交互功能的验证,需要采用面向开发过程的模型验证方法,首先由系统功能层级到功能模块层级逐级分解飞行模式操作控制功能开发架构,进而从功能模块层级到系统功能层级自下而上设计飞行模式操作控制功能验证架构,最后针对功能验证架构中的集成模型测试阶段,以FMCP速度视窗功能为例,通过对所有相关的人机操作进行分类定义,分别定义了速度目标值的状态转换与动作响应,进而针对定义梳理出完整的速度目标值状态转换与动作响应矩阵,矩阵中的每一个表格均对应着速度目标值的状态转换或者动作操作及其对应的响应情况。为自动飞行模式操作控制的集成模型验证提供了参考。

考虑模态转换的组合动力飞机任务性能快速评估方法

工作在较宽飞行范围的高马赫数组合动力飞机,其动力性能受到飞行条件/飞行姿态以及模态转换的影响,并进一步影响其飞行任务性能。为尽可能真实并快速地评估组合动力飞机的飞行任务性能,提出了一种考虑模态转换的组合动力飞机任务性能快速评估方法,并量化研究了不同飞行轨迹、不同模态转换区间对飞行任务性能的影响。首先建立了高马赫数飞机的飞行动力学模型,将飞行姿态考虑进任务分析中;随后建立了组合动力的非安装及安装性能计算模型,飞行轨迹中可实时模拟动力装置的性能;最后建立了模态转换模拟模型,可分析模态转换过程对飞行任务性能的影响。结果表明:该文研究的飞行马赫数为5的组合动力飞机,巡航高度由海拔20 km升高至27 km,巡航距离增加18.3%,总航程增加21.9%;将模态转换马赫数区间由低马赫数2~2.3向高马赫数2.2~2.5范围移动,爬升加速段距离增加8.4%,爬升加速时间增加5.8%。

线性碲镉汞APD的高速焦平面读出电路研究

设计了一款针对线性模式碲镉汞APD的高速成像读出电路。像元内基于三级推挽放大器级联的电阻反馈跨导放大器(RTIA),实现了光电流的实时线性转换,并利用工作于亚阈值区的MOS管作为反馈电阻实现跨阻增益可调;利用电容补偿法对RTIA的相位裕度进行优化,解决了低增益下的输出振荡现象。结果显示,像元内RTIA跨阻增益可调范围达100~140 dB,增益带宽积可达10^(14)数量级,像元电路输出延时低于1.8 ns。设计了像素外的飞行时间测量电路,采用两段式时间数字转换器分别进行飞行时间的大范围粗量化和高精度细量化,测量范围可达1530 m,测量精度为106.5 cm,线性度高于99.99%。

国内商业航天对航班化重复使用运载火箭的探索实践

为实现航天运输系统航班化的终极发展目标,从复用频次与飞行后维护检修角度调研了行业现状,提炼了面向航班化重复使用运载火箭技术的重点发展方向。首次对外公开介绍了星际荣耀垂直起降验证飞行器在复飞准备阶段的探索实践,国内商业航天所采用的重复使用液体火箭方案及快速复用能力得到验证。

MAGIC CARPET着舰对甲板运动的控制策略

MAGIC CARPET是美国最近几年非常成功的舰载机着舰控制技术,是未来主要的着舰方式。MAGIC CARPET着舰性能很优秀,但受甲板运动的影响较大,因此研究应对甲板运动的策略十分有必要。首先,分析了航母运动和光学下滑道稳定方式;然后,分别研究了下滑道惯性稳定、下滑道线稳定时的MAGIC CARPET着舰,并得到了相关结论;理论分析和实时仿真表明该策略与美军试飞结果具有很好的一致性;最后,分析了下滑道稳定方式的选择方法。研究结果为飞机着舰和直接力控制提供了参考。

舰载机着舰侧向轨迹增量控制

针对舰载机着舰侧向控制难度较大的问题,借鉴美国海军的“魔毯”(MAGIC CARPET)着舰的先进理念,提出了1种新的着舰控制方法,即侧向轨迹增量控制。首先,分别从理论上分析了侧向常规控制、侧向轨迹增量控制的控制结构和着舰性能;然后,对HUD显示符号进行改进;最后,通过实时仿真,比较了这2种方法的着舰控制效果。结果显示,着舰侧向轨迹增量控制具有3个优点:1)简易,降低了飞行员的操纵频次和负担;2)直观,着舰侧向操纵更直观,侧向杆量与飞机侧偏修正速率成正比例,而且当横杆回中时飞机能自动跟踪跑道中心线的横向漂移;3)鲁棒,显著提高了对侧风和舰尾流的抑制能力,即使在飞行员不操纵的情况下,飞机也能迅速反应和抑制风干扰。因此,建议在着舰工程中采用侧向轨迹增量控制。