“…Despite the identified aerodynamic benefits of a joint-driven morphing wing, a major challenge for any bioinspired UAV is to design an efficient actuation mechanism that can realize the proposed benefits in practice. In the past, a non-planar wing design that was indirectly inspired by gulls, the HECS wing (discussed in the Introduction) was shown to yield minimal aerodynamic benefits when it was actively morphed into its furled configuration [41] despite promising rigid model results [20]. This emphasizes the multidisciplinary challenges associated with effective morphing wing design.…”
Section: Discussionmentioning
confidence: 99%
“…In this case, traditional geometric properties including distributions of wing twist, sweep, dihedral and the final wingspan can be approximated as functions of the joint positions [5,18]. Further, these non-planar wing shapes likely have aerodynamic characteristics that differ from comparable planar wing aerodynamic theory [19], as highlighted by the Hyper Elliptical Cambered Span (HECS) wing inspired by gulls, which had improved aerodynamic efficiency (higher lift-to-drag ratio) compared to an equivalent planar wing [20]. Figure 1Gull wings inspired our analyses of how avian joint-driven wing morphing affects longitudinal aerodynamic control, stability and balance.…”
Birds dynamically adapt to disparate flight behaviours and unpredictable environments by actively manipulating their skeletal joints to change their wing shape. This in-flight adaptability has inspired many unmanned aerial vehicle (UAV) wings, which predominately morph within a single geometric plane. By contrast, avian joint-driven wing morphing produces a diverse set of non-planar wing shapes. Here, we investigated if joint-driven wing morphing is desirable for UAVs by quantifying the longitudinal aerodynamic characteristics of gull-inspired wing-body configurations. We used a numerical lifting-line algorithm (MachUpX) to determine the aerodynamic loads across the range of motion of the elbow and wrist, which was validated with wind tunnel tests using three-dimensional printed wing-body models. We found that joint-driven wing morphing effectively controls lift, pitching moment and static margin, but other mechanisms are required to trim. Within the range of wing extension capability, specific paths of joint motion (trajectories) permit distinct longitudinal flight control strategies. We identified two unique trajectories that decoupled stability from lift and pitching moment generation. Further, extension along the trajectory inherent to the musculoskeletal linkage system produced the largest changes to the investigated aerodynamic properties. Collectively, our results show that gull-inspired joint-driven wing morphing allows adaptive longitudinal flight control and could promote multifunctional UAV designs.
“…Despite the identified aerodynamic benefits of a joint-driven morphing wing, a major challenge for any bioinspired UAV is to design an efficient actuation mechanism that can realize the proposed benefits in practice. In the past, a non-planar wing design that was indirectly inspired by gulls, the HECS wing (discussed in the Introduction) was shown to yield minimal aerodynamic benefits when it was actively morphed into its furled configuration [41] despite promising rigid model results [20]. This emphasizes the multidisciplinary challenges associated with effective morphing wing design.…”
Section: Discussionmentioning
confidence: 99%
“…In this case, traditional geometric properties including distributions of wing twist, sweep, dihedral and the final wingspan can be approximated as functions of the joint positions [5,18]. Further, these non-planar wing shapes likely have aerodynamic characteristics that differ from comparable planar wing aerodynamic theory [19], as highlighted by the Hyper Elliptical Cambered Span (HECS) wing inspired by gulls, which had improved aerodynamic efficiency (higher lift-to-drag ratio) compared to an equivalent planar wing [20]. Figure 1Gull wings inspired our analyses of how avian joint-driven wing morphing affects longitudinal aerodynamic control, stability and balance.…”
Birds dynamically adapt to disparate flight behaviours and unpredictable environments by actively manipulating their skeletal joints to change their wing shape. This in-flight adaptability has inspired many unmanned aerial vehicle (UAV) wings, which predominately morph within a single geometric plane. By contrast, avian joint-driven wing morphing produces a diverse set of non-planar wing shapes. Here, we investigated if joint-driven wing morphing is desirable for UAVs by quantifying the longitudinal aerodynamic characteristics of gull-inspired wing-body configurations. We used a numerical lifting-line algorithm (MachUpX) to determine the aerodynamic loads across the range of motion of the elbow and wrist, which was validated with wind tunnel tests using three-dimensional printed wing-body models. We found that joint-driven wing morphing effectively controls lift, pitching moment and static margin, but other mechanisms are required to trim. Within the range of wing extension capability, specific paths of joint motion (trajectories) permit distinct longitudinal flight control strategies. We identified two unique trajectories that decoupled stability from lift and pitching moment generation. Further, extension along the trajectory inherent to the musculoskeletal linkage system produced the largest changes to the investigated aerodynamic properties. Collectively, our results show that gull-inspired joint-driven wing morphing allows adaptive longitudinal flight control and could promote multifunctional UAV designs.
“…Could spanwise camber lead to a second trade-off, one between stability and efficiency during avian gliding? It has been previously demonstrated that engineered wings with spanwise camber do have increased aerodynamic efficiency, but there is no empirical evidence of the effects on static pitch stability [11,27]. Coupling of stability and efficiency is well established for certain aircraft configurations, including box wings and flying wings [28,29].…”
Section: Discussionmentioning
confidence: 99%
“…One type of wing morphing that may allow such a transition is a wing that adjusts the curvature along its span, known as spanwise camber. Spanwise camber has been found to adjust the pressure distribution of aircraft wings, and thus the location of the aerodynamic centre along the wing [11,12]. An iconic example of a bird with spanwise camber is the gull.…”
A gliding bird's ability to stabilize its flight path is as critical as its ability to produce sufficient lift. In flight, birds often morph the shape of their wings, but the consequences of avian wing morphing on flight stability are not well understood. Here, we investigate how morphing the gull elbow joint in gliding flight affects their static pitch stability. First, we combined observations of freely gliding gulls and measurements from gull wing cadavers to identify the wing configurations used during gliding flight. These measurements revealed that, as wind speed and gusts increased, gulls flexed their elbows to adopt wing shapes characterized by increased spanwise camber. To determine the static pitch stability characteristics of these wing shapes, we prepared gull wings over the anatomical elbow range and measured the developed pitching moments in a wind tunnel. Wings prepared with extended elbow angles had low spanwise camber and high passive stability, meaning that mild perturbations could be negated without active control. Wings with flexed elbow angles had increased spanwise camber and reduced static pitch stability. Collectively, these results demonstrate that gliding gulls can transition across a broad range of static pitch stability characteristics using the motion of a single joint angle.
“…A gradient-based method which is well-suited for nonlinear structural minimisation problems with nonlinear inequality constraints is the method of moving asymptotes (MMA) (36) . In this method, the nonlinear optimi-wing (38) . The reason for folding down is that the induced drag is reduced by increasing the aspect ratio of the wing while reducing the increased root bending moment due to the winglet.…”
Lisbon, Portugal in December 2008 (10) . This paper describes a nonlinear aeroelastic model which can calculate morphing deformations of arbitrary planform wings. The morphing deformations are discretised in three distinct morphing modes; wing folding, wing twisting, and wing shearing. With the combination of arbitrary combinations of these three mechanisms, and their distribution over the wing, virtually any morphed wing shape is attainable. The actuator energy consumption associated with the morphing deformations is evaluated as well, including aeroelastic effects. The aeroelastic model consists of a close coupling between a nonlinear beam model, using a corotational approach, and high-subsonic aerodynamics, modelled by the Weissinger method which is corrected using the Prandtl-Glauert correction. Using this aeroelastic analysis code, a morphing winglet, which is retrofitted to a regional airliner, is optimised to minimise the wing drag over an entire flight.The paper is structured as follows. First the morphing wing problem formulation is given, which describes the morphing wing discretisation, and the relevant co-ordinate frames. Next, the nonlinear beam element model is described, followed by the aerodynamic model. The next section elucidates the way both the structural and aerodynamic model are coupled to obtain the aeroelastic solution. Then the mathematical details are given on how the morphing mechanisms are embedded into the aeroelastic solution procedure. This is followed by the results section showing the optimal configuration of the morphing winglet and compare its merits to a fixed winglet equipped wing. Finally an overview of the paper is given, and pertinent conclusions are drawn.
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