Experimental Flight Dynamics Testing for Highly Flexible Aircraft

航空航天部门在不断寻求提高飞机效率的过程中，正在考虑更灵活和微调的航空结构系统。一种这样的方法是增加机翼的展弦比（AR），即增加翼展，使得机翼更细长。这种更高展弦比的机翼为民用和军用运输机以及某些类型的无人驾驶飞机（例如用于高空长航时感测、环境监测等的无人驾驶飞机）提供了改进的空气动力学效率的前景。高AR机翼通常比常规设计更灵活，以便使结构质量最小化。这反过来又会增加机翼本身和整个飞机动态响应的复杂性。这些响应包括与机体气动弹性有关的不同运动模式（指的是机体气动、结构和惯性特性之间的相互作用）和所谓的“刚体”运动（表示与任何弹性/柔性效应无关的飞行器的行为）和飞行控制模式。对于（更刚性的）飞行器，气动弹性模式通常处于比飞行动力学和控制模式更高的频率，并且通常能够使用线性方法很好地建模;在这种飞行器中，与飞行动力学行为的任何耦合的程度和复杂性都很低。然而，机体越灵活，所有这些模态之间的相互作用（耦合）就越强。此外，非线性的影响也在增加，特别是高AR机翼的几何非线性，沿着其他潜在的非线性特性，如空气动力学和控制系统中的非线性特性。近年来，结合必要的耦合和非线性现象的高柔性飞机的数值建模方法得到了广泛的研究和发展。然而，通过受控实验验证或校准这些预测方法是一个挑战-通常通过在风洞中将机翼作为刚性支撑在其根部的悬臂进行测试来解决。在现有的试验台上，扩展实验方法以适应捕捉飞行动力学和控制模态与气动弹性模态之间的耦合所需的自由度的范围非常有限。这样的装置通常存在的目的是有限的运动幅度，以测试的气动弹性不稳定性的开始，而不是针对大振幅机翼弯曲，扭转和模型运动，利用或探索nonlinear.This建议引入了一个新的实验概念，允许这种耦合行为进行调查，在受控的风洞环境。它需要一个具有挑战性的扩展到目前的测试方法，为布里斯托大学的新型5度的自由动态试验台和设计合适的灵活驱动和仪表模型。该程序将建立在以前的刚体试验成果的基础上，并将扩展早期的主动试验台控制工作，以确保在风洞中看到的耦合动力学现象尽可能与自由飞行的现象相匹配。这项探索性研究的成功结果可能会推动这种新的试验技术的发展，使其在工业风洞中得以实施。它还将评估在柔性机翼中加入减载控制的能力的可行性。此外，它还将生成增强类型的数据，以评价非线性计算建模技术的预测能力，并根据测量的行为调整或校准这些技术。通过这种方式，所提出的研究提供了大幅度提高风洞能力的前景，以支持未来先进飞机机翼/机身复杂动态相互作用的设计和分析。

The aerospace sector, in its ongoing quest to improve aircraft efficiencies, is considering more flexible and finely tuned aero-structural systems. One such approach is to increase the aspect ratio (AR) of the wings, i.e. increase the span such that the wings are more slender. Such higher aspect ratio wings offer the prospect of improved aerodynamic efficiency for civil and military transport aircraft and for certain types of unmanned aircraft, such as those used for high-altitude long-endurance sensing, environmental monitoring, etc.High AR wings are typically more flexible than conventional designs in order to minimise structural mass. This in turn can increase the complexity of the dynamic responses of the wings themselves and the aircraft as a whole. These responses comprise different modes of motion, associated with airframe aeroelasticity (which refers to the interaction between airframe aerodynamic, structural and inertial properties) and with the so-called 'rigid-body' motions (representing the behaviour of the air vehicle independent of any elastic/flexibility effects) and flight control modes.In design and analysis of conventional (more rigid) aircraft, the aeroelastic modes are typically at higher frequencies than the flight dynamics and control modes and are usually able to be well modeled using linear methods; in such air vehicles the extent and complexity of any coupling with the flight dynamics behaviour is low. However, the more flexible the airframe, the stronger the likely interaction (coupling) between all these modes. Furthermore, the influence of nonlinearity increases - in particular geometric nonlinearity in high AR wings, along with other potential nonlinear characteristics such as in the aerodynamics and control system.Methods for numerical modeling of highly flexible aircraft, incorporating the necessary coupling and nonlinear phenomena, have been extensively researched and developed in recent years. Validating or calibrating these predictive methods via controlled experiments is, however, a challenge - usually addressed by testing a wing as a cantilever supported rigidly at its root in a wind tunnel. There is very limited scope in existing test rigs for extending the experimental approaches to accommodate the degrees of freedom needed to capture the coupling between the flight dynamics and control modes and the aeroelastic modes. Such rigs that do exist are usually intended for limited motion amplitudes in order to test for onset of aeroelastic instability, rather than being aimed at large-amplitude wing bending, torsion and model motions to exploit or explore nonlinearity.This proposal introduces a new experimental concept that allows this coupled behaviour to be investigated in a controlled wind tunnel environment. It entails a challenging extension to the current testing approach for the University of Bristol's novel 5-degree-of-freedom dynamic test rig and the design of suitable flexible actuated and instrumented models. The procedure will build on previous rigid-body test accomplishments and will extend earlier work on active rig control to ensure that coupled dynamic phenomena seen in the wind tunnel match those of free flight as closely as possible.A successful outcome of this exploratory research could launch the development of this new test technique towards implementation in industrial wind tunnels. It will also assess the feasibility of extending the capability to incorporate load alleviation control in the flexible wings. Furthermore, it will generate enhanced types of data to evaluate the predictive ability of nonlinear computational modelling techniques and to adapt or calibrate them to measured behaviours. In this way, the proposed research offers the prospect of substantially improved wind tunnel capability to support design and analysis of future advanced aircraft wings/airframes featuring complex dynamic interactions.