Span morphing using the GNATSpar wing

Abstract

Rigid wings usually fly at sub-optimal conditions generating unnecessary aerodynamic loses represented in flight time, fuel consumption, and unfavourable operational characteristics. High aspect ratio wings have good range and fuel efficiency, but lack manoeuvrability. On the other hand, low aspect ratio wings fly faster and are more manoeuvrable, but have poor aerodynamic performance. Span morphing technology allows integrating both features in a single wing design and allows continuously adjusting the wingspan to match the instantaneous flight conditions and mission objectives. This paper develops, a novel span morphing concept, the Gear driveN Autonomous Twin Spar (GNATSpar) for a mini-UAV. The GNATSpar can be used to achieve span extensions up to 100% but for demonstration purposes it is used here to achieve span extensions up to 20% to reduce induced drag and increase flight endurance. The GNATSpar is superior to conventional telescopic and articulated structures as it uses the space available in the opposite sides of the wing instead of relying on overlapping structures and bearings. In addition, it has a self-locking actuation mechanism due to the low lead angle of the driving worm gear. Following the preliminary aero-structural sizing of the concept, a physical prototype is developed and tested in the 7 × 5 wind-tunnel at the University of Southampton. Finally, benefits and drawbacks of the design are highlighted and analysed.

A review of modelling and analysis of morphing wings

“…More fight tests should be conducted for morphing wing aircrafts to verify the modelling and analysis methods. Fully stressed design [20] 3D FEM: shell elements Steady CFD [27] 3D FEM: shell elements Simplex search [29] Steady CFD [30] Analytical (Bernoulli's theory) [32] 3D FEM: shell elements DLM [33] Internal model control [34] PID & an on/off switch controlling the SMA heating [35] Fuzzy PID [37] PID & self-tuning [40] XFoil Hill climbing method, simulated annealing search [46] 3D FEM: rigid rib elements XFLR5 [55] 3D FEM: solid elements Steady CFD Quadratic Lagrangian algorithm [56] Steady VLM [58] 3D FEM: shell and solid elements XFoil [67] Analytical (Lagrange's equations) [73] Steady CFD [74] 3D FEM: beam, shell and solid elements…”

“…References [43] and [44] described the implementation of a continuous span morphing wing with two primary 17% in endurance. In [46], the compliant spar concept was developed and modelled to allow the wingspan to be varied, providing roll control and enhancing the operational performance for a medium altitude long endurance unmanned aerial vehicle (UAV). The compliant spar is made of compliant joints arranged in series to allow the partition to be flexible under span-wise loads, yet stiff enough to resist bending loads.…”

“…The compliant spar is made of compliant joints arranged in series to allow the partition to be flexible under span-wise loads, yet stiff enough to resist bending loads. Reference [46] developed a novel span morphing concept, referred to as the gear driven autonomous twin spar (GNATSpar), for a mini-UAV. The GNATSpar can be used to achieve span extensions up to 20% to reduce induced drag and increase flight endurance.…”

Recent researches on morphing aircraft technologies in Japan and other countries

“…The VCCTEF system achieved the circular wing camber by implementing three chordwise control surface segments of equal chord length, which resulted in a smooth chordwise Tsushima and Tamayama, Mechanical Engineering Reviews, Vol.6, No.2 (2019) [DOI: 10.1299/mer.19-00197] pressure distribution. For a small UAV, Ajaj et al (Ajaj et al, 2016) developed a span length morphing concept named the Gear driveN Autonomous Twin SPAR (GNATSpar). The design augmented the span morphing capability to their rigid wings with a rack and pinion actuation system.…”

The Transformer aircraft: A multimission unmanned aerial vehicle capable of symmetric and asymmetric span morphing

“…These designs include the Zigzag Wingbox concept (Ajaj et al, 2013), the Compliant Spar concept , and the Gear driveN Autonomous Twin Spar (GNATSpar) (Ajaj et al, 2016b). Most of the concepts developed by Ajaj et al (2013Ajaj et al ( and 2016b) used a hybrid structural design philosophy where the wing structure is at the same time the mechanism and the actuator. The structure was then covered by flexible material (mainly elastomeric) to provide and maintain the aerodynamic profile.…”