共轴刚性旋翼低阶动载荷特性分析

针对共轴刚性旋翼低阶动载荷问题开展分析研究.建立考虑升力偏置的共轴刚性旋翼气弹配平计算方法,建立含干扰因子的共轴双旋翼气动干扰模型与考虑双旋翼构型的旋翼动力学模型,最终集成共轴双旋翼考虑升力偏置的共轴刚性旋翼气弹配平模型.在分析前进比、转速以及升力偏置参数影响下的旋翼低阶挥舞、摆振弯矩变化特性中发现：在大前进比状态下,桨根挥舞、摆振弯矩大大增加,且均以2/rev谐波载荷为主;而施加升力偏置使得挥舞1/rev谐波载荷增加,而2/rev谐波载荷降低,能整体抑制摆振弯矩.     

System identification and improved internal model control for yaw of unmanned helicopter

The sea breeze is a low-frequency disturbance that severely damages the stability of small unmanned helicopters operating over the sea, especially for the yaw control, which is highly sensitive to disturbance. General internal model control is an appropriate method for dealing with this kind of operation conditions, whereas conventional internal model control cannot eliminate the tracking errors between a nominal model and a real model. In coping with unknown dynamics and low-frequency gust disturbances for small helicopters, this paper proposes a novel robust controller constructed with system identification and integrator-based improved general internal model. As a refinement of the conventional frame, the proposed control scheme extends the applicable scope of a controlled plant from a priori known dynamic to an unknown dynamic. Furthermore, under the proposed controller, it is guaranteed that the tracking error between the actual model and the nominal model converges to zero asymptotically. Finally, the effectiveness and advantage of the proposed control scheme are verified through comparative practical flight tests.     

直升机机载三轴速率陀螺校准技术研究

三轴速率陀螺组件是某型无人直升机飞控系统的重要部件之一,其速率精度直接影响飞机的性能,为此必须定期对其进行校准.为提高三轴速率陀螺的校准精度和效率,提出了一套基于单轴速率转台的半自动校准方法.设计了专门的校准工装,实现了被校三轴速率陀螺3个输出轴的快速切换;开发了校准系统软件,实现了校准数据的自动采集和处理,提高了速率校准效率.对校准结果的不确定度进行了分析评定,评定结果表明,提出的校准方法合理可行,具有较好的实用性.     

Cities under fire: Crisis communication on home front versus frontline cities' Facebook pages during operation ‘guardian of the walls’

Social media has been widely adopted by local governments during emergencies and crises and its role as a communication platform has been discussed in various studies on natural hazards, pandemics and terror attacks. However, research in the field has not addressed how municipalities use social media to communicate valuable information during armed conflicts and military operations. The current study examined the ways five major cities in Israel used their Facebook pages to connect to their residents during operation ‘Guardian of the Walls' in 2021. We examined the social media usage and the strategies of these cities during the 12 days of the operation. The findings revealed significant differences between cities that are considered as home front versus frontline regions regarding content type and information dissemination strategies. Additionally, differences regarding content types in terms of sentiment and overall rates of engagement were also identified. These findings highlight the need to further investigate local municipalities' usage of social media during armed conflicts concerning the civil population.     

Adaptive neural network sliding mode control of a nonlinear two-degrees-of-freedom helicopter system

The helicopter can play an important role in military and civil applications owing to its super maneuvering ability, which is closely related to its control system. To improve control performance, this study presents an adaptive sliding mode control strategy merging an adaptive neural network for a nonlinear two-degrees-of-freedom (2-DOF) helicopter system. By setting up the Lyapunov function, the asymptotic stability of the closed-loop system is guaranteed, the astringency of the neural network weight renewal course is pledged, and the asymptotic attitude adjustment and trajectory tracking for the desired set point are realized. The availability of the adaptive radial basis function sliding mode control is finally verified via the simulation and real implementation on a nonlinear 2-DOF helicopter platform.     

基于OpenGL的直升机“地面共振”三维动态仿真系统

“地面共振”问题是一种危及直升机安全的自激振动问题。使用数值方法仿真“地面共振”现象是直升机研究过程中经常使用的方法。本文使用Vc＋＋6．0基于开放图形库（Open Graphic Library）和微软基础类库（Microsoft Foundation Classes Library）在Windows NT平台下开发图形仿真系统,用于仿真直升机地面共振过程,通过实践证明该系统稳定可靠。     

Observer-based robust optimal control for helicopter with uncertainties and disturbances

Unknown model uncertainties and external disturbances widely exist in helicopter dynamics and bring adverse effects on control performance. Optimal control techniques have been extensively studied for helicopters, but these methods cannot effectively handle flight control problems since they are sensitive to uncertainties and disturbances. This paper proposes an observer-based robust optimal control scheme that enables a helicopter to fly optimally and reduce the influence of unknown model uncertainties and external disturbances. A control Lyapunov function (CLF) is firstly constructed using the backstepping method, then Sontag's formula is utilized to design an inverse optimal controller to stabilize the nominal system. Furthermore, it is stressed that the radial basis function (RBF) neural network is introduced to establish an observer with adaptive laws, approximating and compensating for the unknown model uncertainties and external disturbances to enhance the robustness of the closed-loop system. The uniform ultimate boundedness of the closed-loop system is ensured using the presented control approach via Lyapunov stability analysis. Finally, simulation results are presented to demonstrate the effectiveness of the proposed control strategy.     

基于电阻应变计的直升机吊挂测力传感器设计

直升机在吊挂起飞、飞行、投放全过程通过监测吊挂物的载荷,可以为正常起吊飞行和飞行员调整飞行姿态提供参考,在到达目的地后,实现半自动化投放,降低人工参与度,保障吊挂飞行安全.将直升机货物挂钩装置中的承载轴销作为测力传感器的弹性体,按照电阻应变式测力传感器工作原理,设计了量程为5 t的测力传感器,实现对货物载荷的实时监测,综合误差小于1％F.S..给出了弹性体设计、应变计选择、灵敏度计算、供桥电压设计、桥路设计和桥路补偿的方法,为其他量程的测力传感器设计提供了参考.     

小型无人直升机分布式飞控系统的设计与实现

基于总线的分布式结构以其结构简单、易于扩展、可维护性强的优点已开始应用于无人机领域。以无人直升机为研究对象，在原有的集中式飞行控制系统的基础上进行技术升级改造，提出了一种基于CAN总线的分布式飞行控制系统设计方案。描述了基于CAN总线的分布式系统总体设计方案、硬件设计、通信机制、软件开发和实现，并进行了半物理仿真验证。测试结果表明，CAN总线实际占用带宽为10.5%，未出现丢帧现象，通信基准时钟同步精度小于150 μs，完全可以满足飞控系统的要求。通过进行全过程飞行半物理仿真，证明基于CAN总线的分布式飞控系统能够满足无人直升机飞控系统的实时性、可靠性等控制需求，设计达到了工程化的要求。     

通过试飞测量大型直升机超短波天线的方向图

超短波天线方向图的精确测量对摸清机载通信系统性能底数,指导部队战术应用具有重要意义.针对传统试飞方法均不适用于大型直升机天线方向图测量的问题,通过分析大型直升机的飞行性能特点,提出了一种新的适用于大型直升机的超短波天线方向图试飞方法.通过分析计算给出了试飞中载机高度、速度、姿态等参数的限制数据,制定了详细的试飞流程,提出了逐架次、逐频点采集校准数据并完成校准曲线拟合的方法,得到了较高的测量精度.该方法已在某大型直升机定型试飞中进行了应用,试飞结果表明该方法的测量结果与传统测量方法之间的标准差在1.6 dB内,试飞效率提高了66%.