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Structural stability margin criteria for accelerated clearance of developmental flights

机译：加快清理发展飞行的结构稳定裕度标准

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摘要

Inertial motion sensors in the flight control system pick up high frequency signals due to the flexible modes in addition to the rigid body responses and could lead to instability at the structural frequencies when the rigid body stability augmentation feedback loops are closed. To attenuate the effects of this structural coupling, notch filters are designed and placed in series with the inertial sensors in each of the feedback paths. During the initial phase of control law design and development, aircraft structural response data is generally not available. Therefore, while designing the rigid body control laws, an additional budget is allocated for phase lags introduced by the structural notch filters. Once the structural coupling tests are carried out on the aircraft, structural filters are designed in order to meet the certification requirements. During developmental flight tests with multiple prototype vehicles there are likely to be variations in the structural response characteristics as the production processes are maturing and also, due to minor updates to the aircraft standard of preparation and addition of different external stores. This calls for the redesign of structural filters and subsequent onboard software development and testing which is a lengthy process. Hence, in order to meet project schedules without compromising safety, the clearance procedure was modified so that it could be efficiently used for flights during the development phase. This paper presents a revised clearance procedure based not only on values of the nominal stability margins, but also on the sensitivity of structural stability margins to the modal frequency perturbation. This change in the clearance philosophy was considered acceptable for the developmental phase of flights but for the final production vehicle standard one would need to strictly follow the MIL-F 9490 D Standard guidelines. This paper discusses the changes carried out to the clearance procedure, the rationale behind the changes made, and also gives directions for future research in robust stabilization of structural modes as well as notch filter design.
机译：飞行控制系统中的惯性运动传感器除了具有刚体响应之外还具有灵活的模式，还可以获取高频信号，并且当刚体稳定性增强反馈回路闭合时，可能会导致结构频率处的不稳定性。为了减弱这种结构耦合的影响，设计陷波滤波器，并将其与每个反馈路径中的惯性传感器串联放置。在控制法设计和开发的初始阶段，飞机结构响应数据通常不可用。因此，在设计刚体控制律时，会为结构陷波滤波器引入的相位滞后分配额外的预算。在飞机上进行结构耦合测试后，将设计结构过滤器以满足认证要求。在使用多个原型飞行器进行的开发性飞行测试中，随着生产过程的日趋成熟，结构响应特性可能会发生变化，此外，由于飞机准备标准的微小更新以及增加了不同的外部商店，因此结构响应特性可能也会有所变化。这要求重新设计结构过滤器，并随后进行车载软件开发和测试，这是一个漫长的过程。因此，为了在不影响安全性的前提下满足项目进度，对通关程序进行了修改，以便在开发阶段可以有效地用于飞行。本文不仅基于标称稳定裕度的值，而且还基于结构稳定裕度对模态频率扰动的敏感性，提出了一种修订的间隙程序。在飞行的开发阶段，这种许可原则的改变被认为是可以接受的，但对于最终生产车辆的标准，则必须严格遵守MIL-F 9490 D标准的准则。本文讨论了对清除程序进行的更改，所做更改的理由，并为今后在结构模式的稳固稳定以及陷波滤波器设计方面的研究提供了方向。

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