On the nonlinear dynamics of a rotor in autorotation:a combined experimental and numerical approach

This article presents a systematic assessment of the use of numerical continuation and bifurcation techniques in investigating the nonlinear periodic behaviour of a teetering rotor operating in forward autorotation. The aim is to illustrate the potential of these tools in revealing complex blade dynamics, when used in combination (not necessarily at the same time) with physical testing. We show a simple procedure to promote understanding of an existing but not fully understood engineering instability problem, when uncertainties in the numerical modelling and constraints in the experimental testing are present. It is proposed that continuation and bifurcation methods can play a significant role in developing numerical and experimental techniques for studying the nonlinear dynamics not only for rotating blades but also for other engineering systems with uncertainties and constraints.</jats:p

Experimental Effect of Sideslip Angle on the Dynamic Behaviour of Flared Folding Wingtips

A concept of growing interest in recent years is the Flared Folding Wingtip (FFWT), which can be used in-flight to reduce airframe loading due to gust encounters and augment the handling qualities of an aircraft. The performance of an FFWT is affected by the relative angle between the built-in hinge angle and the flow direction. Therefore, a critical concern is the behaviour of such a device at non-zero sideslip angles, such as experienced by aircraft in crosswind landings. In this paper, a specially designed wind tunnel model capable of large wingtip rotations, and a geometrically nonlinear numerical model, are utilised to explore how sideslip angle affects both the static and dynamic behaviour of such a system. It is shown that stable equilibrium positions exist up to and beyond a fold angle of 90 degrees, even when the effective flare angle is zero or switches sign. Additionally, to accurately capture the variation in the frequency of the wingtip with sideslip angle, it is shown factors such as the change in sweep angle of the wing must be accounted for. Furthermore, it is shown that these changes in frequency with sideslip angle can lead to a reduction in the flutter speed, but do not have a significant impact on the gust load alleviation of wings incorporating FFWTs, when exposed to one-minus-cosine gust encounters

Sizing of High-Aspect-Ratio Wings with Folding Wingtips

High-aspect-ratio wings are of particular interest to modern aircraft design due to the inherent reduction in induced drag that they provide. However, such wing configurations often come with problems such as increased structural weight and oversized wingspans for existing airport facilities. Unlike conventional folding wingtips, as used on the 777-X, this paper demonstrates the use of semi-aeroelastic hinge devices that enable aircraft incorporating high-aspect-ratio wings not only to fit into airport gates, but also to alleviate aerodynamic loads by allowing floating wingtips to be used in-flight. This study establishes a preliminary design process for such a wing configuration and undertakes a comprehensive sizing process to investigate the impact of the device on wing weight and aircraft performance. For the cases considered, a reduction in wing weight of approximately 25% can be achieved by utilizing the semi-aeroelastic hinge, which can lead to more than 5% improvement in aircraft range