Recent studies have considered the use of flared folding wingtips (FFWTs) to enable higher aspect ratios -reducing overall induced drag -whilst reducing gust loading and meeting airport operational requirements. The majority of these analyses have been conducted using linear assumptions despite the presence of large wingtip deformations. The aim of this work is to assess the effect of geometric nonlinearities introduced by an FFWT on the static and dynamic aeroelastic response of a wing. In this paper, a geometrically exact expression was formulated to describe the change in both the local Angle of Attack (AoA) and sideslip angle across all fold angles. This expression highlighted that the aerodynamic stiffness of an FFWT, and therefore quantities such as the linear flutter speed, are a function of the fold angle and therefore, the attitude of the wing. This effect was then verified using both: a wind tunnel model of a flexible semi-span wing incorporating an Flared Folding Wingtip (FFWT), and a new numerical modelling technique, utilising MSC Nastran, which linearised the model about the equilibrium position of the wingtip. The results of these experiments show that the geometric nonlinearities introduced due to the large deformations of FFWTs can significantly affect the dynamics of the system, with flutter speeds varying by over 25%, simply by changing the root angle of attack of the model. Furthermore, good agreement was found between the experimental results and numerical predictions.
Future aircraft designs look set to use longer wing spans to increase the aspect ratio and therefore overall aerodynamic efficiency of the airframe. Such larger wing spans also reduce roll rates and require increased control surface area to achieve the roll maneuver requirements for certification. In this work, the effect of using flared folding wingtips (FFWTs) on the roll performance of simple aircraft wings is investigated numerically and experimentally. A unique rolling rig is designed, manufactured and tested, with a series of steady roll and transient tests performed for different wing spans, with and without folding wingtips. It is shown that the use of FFWTs on aircraft wings can enable improved aerodynamic performance due to the increased span whilst also significantly reducing the aerodynamic damping due to roll, such that the roll performance of a wing incorporating FFWTs is comparable to that of one without the additional span.
Recent developments in morphing wing technologies are routinely tested using Unmanned Aerial vehicles (UAVs) due to their relatively low cost and time to manufacture. However, atmospheric flight tests limit both the repeatability of the recorded data sets, as well as the bounds of the flight envelope willing to be explored, due to the risk of destroying the UAV. In this paper, a novel flight test method is described, which consists of flying a UAV constrained by a tether, resulting in a steady, controlled, elliptical flight paths. The benefits of such a method are explored numerically to characterise the static and dynamic testing capabilities of such a system. This is then followed by an experimental investigation into the behaviour of semi-aeroelastic hinged (SAH) wingtips, employing the AlbatrossOne remotely piloted vehicle. The tethered model was used to explore the static effect of angle of attack and sideslip angle on the both the equilibrium position of the wingtips and the wingtips stability boundary.
Future aircraft designs look set to use longer wing spans to increase the aspect ratio and therefore overall aerodynamic efficiency of the airframe. Such larger wing spans also reduce roll rates and require increased control surface area to achieve the roll maneuver requirements for certification. In this work, the effect of using flared folding wingtips (FFWTs) on the roll performance of simple aircraft wings is investigated numerically and experimentally. A unique rolling rig is designed, manufactured and tested, with a series of steady roll and transient tests performed for different wing spans, with and without folding wingtips. It is shown that the use of FFWTs on aircraft wings can enable improved aerodynamic performance due to the increased span whilst also significantly reducing the aerodynamic damping due to roll, such that the roll performance of a wing incorporating FFWTs is comparable to that of one without the additional span.
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