Purpose

The paper describes the application of two different vibration measurement methods for the identification of natural modes of the miniature unmanned aerial vehicle (UAV). The purpose of this study is to determine resonant frequencies and modes of mini-airplane within the specified range of frequency values.

Design/methodology/approach

Special measuring equipment was used including both contact and non-contact techniques. The measuring systems on equipment of the Institute of Aviation Technology in the Faculty of Mechatronics, Armament and Aerospace of Military University of Technology (Warsaw, PL) were used to conduct measurements. In traditional ground vibration testing (GVT) methods a large number of sensors should be attached to the aircraft. The weight of sensors and cables is negligible in relation to the mass of the large aircraft. However, for small and lightweight unmanned aerial vehicles, this could bring a significant mass component in relation to the total mass of the tested object.

Findings

The real mini-UAV construction was used to investigate its resonant modes in the range of frequencies between 0 and 50 Hz. After receiving the output values it is possible to perform some flutter calculations within the range of operational velocities. As there is no certainty that the computed modes are in accordance with those natural ones some parametric calculations are recommended. Modal frequencies depend on structural parameters which are quite difficult to identify. Adopting their values from the reasonable range it is possible to assign the range of possible frequencies. The frequencies of rudder or elevator modes are dependent on their mass moments of inertia and rigidity of controls. The critical speeds of tail flutter were calculated for various combinations of stiffness or mass values.

Practical implications

In this paper, some specific techniques of performing the GVT test were presented. Two different measuring methods were applied, i.e. the contact method and the non-contact method. Using the dedicated apparatus in relation to the mini-airplane, properly prepared in terms of mass distribution, rudders deflection stiffness and proper support, some resonant characteristics can be determined. The contact measuring system consists of a multi-channel analyzer, piezoelectric accelerometers, electrodynamic exciters, amplifiers, impedance heads and a computer with the Test.Lab Software. As the non-contact method, a laser scanning vibrometer was used. The principle of its operation is based on the separation of the emitted laser beam. The returning beam reflected from a vibrating object is captured by the camera and compared to the reference beam. Dedicated software analyzes collected data and on the basis of it creates animations of structural vibrational shapes and spectral plots within the investigated frequency range.

Originality/value

The object used for research is the mini-UAV Rybitwa – composite mini-plane with a classic aerodynamic layout manufactured in Institute of Aviation Technology Military University of Technology. In the work, both measurement methods and some sample results were presented. Results referenced to dynamic properties of the mini-UAV can be applied in the future for its finite element model tuning, what would be useful for the needs of some parametric analyzes in case of some UAV modifications because of its structural or equipment modifications.

中文翻译：

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接触式和非接触式测量技术在小型无人机地面共振测试中的应用

目的

本文介绍了两种不同的振动测量方法在识别微型无人驾驶飞行器 (UAV) 固有模态方面的应用。本研究的目的是确定微型飞机在指定频率值范围内的共振频率和模式。

设计/方法/方法

使用了特殊的测量设备，包括接触式和非接触式技术。使用军事技术大学（波兰华沙）机电一体化、武器装备和航空航天学院航空技术研究所的设备测量系统进行测量。在传统的地面振动测试 (GVT) 方法中，应将大量传感器连接到飞机上。与大型飞机的质量相比，传感器和电缆的重量可以忽略不计。然而，对于小型和轻型无人机，这可能会带来相对于被测物体总质量的显着质量分量。

发现

真正的微型无人机结构用于研究其在 0 到 50 Hz 频率范围内的谐振模式。接收到输出值后，可以在操作速度范围内执行一些颤振计算。由于不确定计算模式是否与那些自然模式一致，因此建议进行一些参数计算。模态频率取决于很难识别的结构参数。在合理范围内采用它们的值，可以分配可能的频率范围。方向舵或升降舵模式的频率取决于它们的质量惯性矩和控制装置的刚性。尾颤的临界速度是针对刚度或质量值的各种组合计算的。

实际影响

在本文中，介绍了执行 GVT 测试的一些具体技术。应用了两种不同的测量方法，即接触法和非接触法。使用与微型飞机相关的专用设备，在质量分布、方向舵偏转刚度和适当的支撑方面进行适当准备，可以确定一些共振特性。接触式测量系统由多通道分析仪、压电加速度计、电动激励器、放大器、阻抗头和带有 Test.Lab 软件的计算机组成。作为非接触式方法，使用激光扫描测振仪。其工作原理基于发射激光束的分离。从振动物体反射的返回光束被相机捕获并与参考光束进行比较。

原创性/价值

用于研究的对象是微型无人机 Rybitwa——由航空技术研究所制造的具有经典空气动力学布局的复合微型飞机。在这项工作中，介绍了两种测量方法和一些样本结果。参考迷你无人机的动态特性的结果可以在未来应用于其有限元模型调整，这将有助于某些参数分析的需要，以防某些无人机由于其结构或设备修改而进行修改。