Aerodynamic and Structural Characterisation of a Hinged Folding Wingtip

Abstract

In the last thirty years, massive improvements in flight operations and aircraft technology were implemented, reaching a 54% reduction in specific fuel consumption [1]. However, during the same period, the aviation market has tripled the number of flights per year with a consequent and direct increase in the emissions of greenhouse gasses. To fight against climate change due to the global rise in temperature, international policies are pushing towards a greener future for our society, setting specific objectives for reducing emissions, including aviation ones. In order to achieve the critical goal of climate neutrality by 2050, as stated by the European Green Deal [2], and since the number of total flights is valued will double by that year; significant development steps have to be taken in the aviation industry that has to become greener. The best way to decrease aircraft emissions is to increase its aerodynamic efficiency, so increasing the wingspan of the wing in order to reduce the lift-induced drag. Unfortunately, this has two main problems, the increased total structural weight (that will therefore reduce the payload leading to an increase in the number of flights) and the limited wingspan due to existing airport gate requirements. These issues can be solved using a Hinged Folding Wingtip (HFW) that allows an aerodynamic efficient enormous wingspan during flight operations but will fold on the ground enabling the usage of existing gates. Furthermore, the hinge mechanism improves load alleviation capabilities, particularly during gusts, consequently reducing the bending moment transferred at the root of the wing, allowing beneficial lighter structure. This thesis study focused on a precise aeroelastic characterisation (both aerodynamic and structural) of the hinged folding wingtip device using the instantaneous, non-intrusive and whole-field, large-scale Particle Image Velocimetry (PIV) technique, with the state-of-the-art Shake-The-Box (STB) Lagrangian Particle Tracking (LPT) algorithm in combination with Helium-Filled Soap Bubbles (HFSB) flow tracers and fiducial markers painted on the wing model. This new technique permits the avoidance of intrusive, conventional sensors used for aeroelastic evaluations, like strain gauges, piezoelectric accelerometers, potentiometers, and load cells that alter the structural properties of the tested object but also Pitot tubes that alter the flow behaviour. Furthermore, only pointwise measurements are possible with these devices. Through a wind tunnel campaign at the W-tunnel facility at TU Delft, using a hinged folding wingtip model in both steady and unsteady conditions, it was shown that the implementation of this device shows very promising potential. Not only from an aerodynamic efficiency (due to the increased wingspan) and energy consumption efficiency (due to lower structural weight) points of view but more significantly in the gust alleviation capacities, indeed the peak load and the corresponding root bending moment can be reduced significantly applying a correct timing on the hinge release.