406 MHz ELT signal spectra for SARSAT

The signal format and spectral properties of the 406-MHz emergency locator transmitter (ELT) used in the search and rescue satellite aided tracking (SARSAT) system are examined. The ELT improves location estimate accuracies and can relay information about the particular aircraft and its problem, by means of the digitally modulated message fields. It is shown that due to the RF signal frequency characteristics and the Doppler shift, processing must be performed over a frequency band of approximately 25 kHz. Through the use of the fast Fourier transformation (FFT), the frequency spectrum of the ELT is analyzed, taking account of effects due to noise, multiple simultaneously received signals, and Doppler shift. It is demonstrated that the FFT provides an effective means for detecting and recognizing the presence of one or more ELT signals over this 25-kHz frequency band. Some recommendations are made to improve the spectral characteristics and the performance of the ELT     

Microprocessor Matched Filtering of Emergency Chirp Signals

A microcomputer matched filter solution is suggested for identifying emergency locator transmitter (ELT) signals from aircraft in distress. A sliding fast Fourier transform (FFT) with adjustable delay covers all permissible ELT sweep rates. The sweep rate for optimum response is retained for signal classification purposes. An additional nonsliding FFT is used to test for the possible presence of monotone modulation in the frequency range of the ELT, and an additional uncorrelated test helps establish a background reference level for positive ELT identiflcation.     

民用飞机固定式应急定位发射系统设计

如何在民用飞机遇险迫降或失事后尽快定位搜救,提高机上遇险人员的生存率,是当前民用飞机设计过程中必须考虑的问题。作为民用飞机应急搜救系统,固定式应急定位发射系统(ELT)可以在飞机遇险时通过自动和人工方式触发,在固定的频率上发射搜救信号,以便搜救组织对遇险人员进行救援。首先提出了固定式ELT系统的设计方案及功能,分析了系统部件的构成,进而提出了固定式ELT系统的性能要求,最后重点阐述了固定式ELT系统的机上设计要求和功能验证过程。     

Two Methods of Spectral Estimation for SARSAT Signals

Search and rescue satellite aided tracking (SARSAT) depends on the processing of emergency locator transmitter (ELT) signals which are received by a satellite in low polar orbit. Since the signal from a distressed vehicle is normally immersed in a background of other ELT signals (false alarms), interference, and noise, different methods of spectral estimation can provide advantages in estimating carrier frequency. A comparison between average spectrum and minimum spectrum for several real signals is provided here.     

A novel approach for the SARSAT system

A novel method for determining the location of a 406-MHz emergency locator transmitter (ELT) for the search and rescue satellite aided tracking (SARSAT) system is proposed. The technique uses information from a geostationary satellite (Geosat) link, as well as the conventional polar orbiting satellite links. The method is based on solving a system of equations to determine the range from the ELT to the polar orbiting satellite (Polarsat) for each signal transmitted. Only two pulses need to be received from the ELT in order to obtain a location estimate. The main difference between the procedure outlined and the global positioning system (GPS) is that accurate time information is not available in the transmissions since aircraft and marine vessels seldom have accurate time standards onboard     

Identification Techniques for SARSAT Signals

A process for the identification of emergency locator transmitter (ELT) signals related to search and rescue satellite-aided tracking (SARSAT) is presented. The ELT identification process is particularly important in order to increase the probability of detection and eliminate sources of interference from the data set. A set of ELT signal parameters is introduced and methods for estimating these parameters are developed. A theoretical analysis and performance evaluation of these methods is provided.     

基于导波传播模型的MUSIC损伤识别算法

针对结构健康监测领域的损伤近场定位问题,提出了适用于复合材料结构损伤识别的近场二维多重信号分类（MUSIC）损伤识别算法。该损伤识别算法将导波传播模型引入近场二维MUSIC损伤识别模型,构造损伤散射信号与实验差信号的互相关矩阵,通过信号子空间与噪声子空间正交特性构造近场二维MUSIC空间谱。通过数值仿真和实验验证了所提出的损伤识别算法能够有效地识别复合材料结构损伤位置信息,具有很高的定位精度和分辨率。针对飞机垂直尾翼的加强筋结构对导波传播特性影响较大的问题,提出了分区域监测的损伤检测策略,并利用基于导波传播模型的二维MUSIC空间谱损伤识别算法成功地识别飞机垂直尾翼结构损伤,实现了复杂复合材料结构损伤识别的工程验证。     

发动机振动诊断及振源分析法

近几年来,现役某小型战斗机已有十多架次因飞行员反映空中振动大而停飞。由于没有空测手段,无法作出确切判断,致使有的飞机停飞长达一年之久,直接影响部队飞行训练。为此,研制了“机载振动数据采集系统”及“地面分析设备”和提出了空中振动大的故障诊断及振源分析方法与诊断程序。(1)为研究解决空中振动大的故障提供检测手段、定量数据和分析方法;(2)为处理因反映空中振动大而停飞问题提供科学依据;(3)对保证飞行安全和提高飞机良好率有直接作用;(4)可推广到其它现役机种的振动监控和振动诊断,也可应用于新机试飞,以便评定空中振动品质。      

Interception Algorithm of S-cubed Signal Model in Stealth Radar Equipment

Radar equipment of stealth platforms such as aircraft have adopted the newest modern technology to design the signal waveforms. One of the important and effective methods is the hybrid waveform called spread spectrum stretch (S-cubed) which combines linear frequency modulation (LFM) and discrete phase code. In order to investigate the function of enemy’s stealth radar equipment, the interception algorithm of S-cubed is needed. In this paper, a novel detection and parameter estimation approach for the reconnaissance S-cubed radar signal is presented. First, the generalized time-frequency representation of Zhao, Atlas, and Marks (ZAM-GTFR) and Hough transforms (HT) are applied to detecting the signal, and then the initial frequency and modulation slope of LFM are estimated from the ZAM-GTFR. On the basis of LFM information, the reconstructing signal is generated. Finally, the code rate of discrete phase code is extracted from the negative peaks of the ZAM-GTFR. Simulation results show that the proposed algorithm has higher estimation accuracy when the signal to noise ratio (SNR) is above 3 dB.     

飞机地面局部气候环境研究

飞机结构腐蚀疲劳寿命研究主要依靠典型结构件(疲劳+腐蚀)代替全尺寸机体结构进行试验和分析,因此,在机场总体环境谱基础上进一步分析飞机局部环境谱有着重要意义。首先根据模糊聚类分析方法,将飞机舱室压缩、简化分类为3种状态:开式、半开式和封闭式,然后采用实测温度、相对湿度的方法,获得飞机地面停放局部气候环境参数的大量数据,并建立气象参数与飞机各类舱室以及同类舱室参数间的线性关系。通过这些关系式和机场环境谱,就可以确定飞机局部舱室所经受的腐蚀环境历程,编制局部环境谱,为进一步选择典型结构件提供依据。     

飞机载荷/环境谱编制研究及应用

阐明了编制恰当的载荷/环境谱是飞机结构疲劳、损伤容限和耐久性设计或现有机种寿命评定中的首要工作,它对后续的分析和试验工作的成败、经费、工作量和时间都有重大的影响。介绍了根据不同的工作任务和技术要求,有多种形式的载荷/环境谱及相应的编谱方法,主要对载荷/环境谱的编制技术进行了研究,提出了具有指导意义的一般性方法,最后给出了某型飞机的载荷环境谱。     

飞机发动机混沌振动信号盲分离检测方法

发动机混沌振动信号携带着丰富的状态信息,依据混沌振动信号进行状态监测及故障诊断是一种很有前途的技术手段,但由于混沌信号具有伪随机特性及在低频段具有宽频谱等特点,使得传统的方法很难将其从振动信号中分离。在提取混沌振动信号方面,使用快速独立分量分析（Fast ICA）盲分离方法分离出飞机发动机振动信号中的混沌信号。利用功率谱和Lyapunov指数（LE）方法进行了判定,根据计算结果对发动机状态做出判断,验证了盲分离方法分离混沌振动信号的有效。盲分离检测混沌振动信号的方法不仅使依据混沌信号判断飞机发动机状态成为可能,也为利用混沌信号进行状态预测和控制提供了一种方法。     

民机结构外露关键部位涂层加速腐蚀环境谱研究

 结合民机结构使用特点,参考国内外已有研究成果,提出了适用于民机结构外露腐蚀关键部位的涂层加速环境谱。该谱由温湿暴露、紫外照射、低温疲劳和盐雾4个环境块构成。给出了各环境块参数的确定方法及加速谱与外场实际使用环境的当量加速关系。通过民机机翼下翼面典型模拟试件加速腐蚀若干周期的试验,验证了该加速谱和当量加速关系的合理性。该谱的提出为腐蚀条件下民机结构日历寿命评定提供了重要的依据。     

飞机日历寿命确定的区域定寿法

给出一种飞机结构日历寿命的区域定寿法,该方法根据腐蚀环境的差异,把全国各型飞机划分成若干个区域,分别编制出每个区域的腐蚀环境谱,然后用每个区域的腐蚀环境谱,分别进行该区域中的各种机型飞机的日历寿命确定,这与飞机疲劳寿命确定方法有较大不同。用该方法确定飞机日历寿命可以提高定寿效率,缩短定寿时间,节约定寿经费。     

飞机环境振动状态-时间谱的编制与应用

 飞机环境振动状态-时间谱是飞机的一种重要的统计参数。它是运用状态归纳法进行环境振动数据归纳所必不可少的先知条件。本文提出了飞机环境振动状态-时间谱的一个编制方法。该法建立在大量飞行统计数据的基础上,并全面考虑了空中飞行和地面试车两种情况。由此编制出来的飞机环境振动状态-时间谱能较真实地反映飞机实际使用的情况。这个编制方法已用于工程实践中。     

航空发动机飞行载荷谱的预测

提出了基于飞机的设计飞行任务剖面、飞行力学及发动机原理的发动机飞行载荷的预测方法,即首先将飞机的设计飞行任务剖面通过飞行力学的基本原理转化为发动机的推力（或油门）剖面,然后通过发动机性能计算获得发动机的其它工作状态参数,从而获得发动机的飞行载荷谱。      

K8飞机活动舱盖压力谱编制

根据活动舱盖压力谱Ｐ－ｔ曲线特点,通过任务类型划分、异常信号剔除、滤波、雨流计数和计数结果统计处理以及等损伤折算等工作,结合巴基斯坦空军提供的Ｋ８飞机各任务类型飞行小时和起落次数的统计结果,编制了Ｋ８飞机活动舱盖压力谱。     

疲劳开裂结构等效分析谱构造方法

为了解决外场疲劳裂纹排故中结构疲劳载荷谱数据不全或过于复杂的问题,提出了一种适用于飞机外场疲劳开裂结构的等效分析谱构造方法。该方法以细节疲劳额定值(DFR)法和结构细节有限元分析为基础,构建地—空—地最大应力与结构疲劳寿命的变化曲线,进而通过寿命反推,获取适用的地—空—地损伤比,以此构建等效分析谱,谱型为等幅谱。通过应用实例,将该方法构造的载荷谱与实测谱进行了对比,确认了该方法的正确性和有效性。     

X型飞机机动载荷谱的编制

一、前言 为了编制X型飞机载荷谱和强度规范,先后在6个机场23架飞机上得到509个起落、304小时的VGH三参数时间历程记录,加上调查获得的实际使用资料,按飞-续-飞的编谱方法,编制了该型飞机的机动载荷谱。     

飞机噪声预测和分析

根据中国民航规章中有关飞机适航噪声审定的要求和噪声预测原理建立了飞机噪声预测系统软件。该软件除可预测飞机适航噪声审定的起飞、进场和边线有效感觉噪声级外,还可计算巡航过程机体表面声压分布。各种噪声源的声功率在软件中均可单独计算,因此改变发动机和飞机参数可以考查这些参数对声功率的影响;对发动机和飞机设计有参考价值。通过算例计算出的起飞、进场和边线有效感觉噪声级与实测结果符合较好,能很好地满足工程应用需要。