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Lift system optimization for hover-capable flapping wing micro air vehicle

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Abstract

A key challenge is using bionic mechanisms to enhance aerodynamic performance of hover-capable flapping wing micro air vehicle (FWMAV). This paper presented a new lift system with high lift and aerodynamic efficiency, which use a hummingbird as a bionic object. This new lift system is able to effectively utilize the high lift mechanism of hummingbirds, and this study innovatively utilizes elastic energy storage elements and installs them at the wing root to help improve aerodynamic performance. A flapping angle of 154° is achieved through the optimization of the flapping mechanism parameters. An optimized wing shape and parameters are obtained through experimental studies on the wings. Consequently, the max net lift generated is 17.6% of the flapping wing vehicle’s weight. Moreover, energy is stored and released periodically during the flapping cycle, by imitating the musculoskeletal system at the wing roots of hummingbirds, thereby improving the energy utilization rate of the FWMAV and reducing power consumption by 4.5% under the same lift. Moreover, strength verification and modal analyses are conducted on the flapping mechanism, and the weight of the flapping mechanism is reduced through the analysis and testing of different materials. The results show that the lift system can generate a stable lift of 31.98 g with a wingspan of 175 mm, while the lift system weighs only 10.5 g, providing aerodynamic conditions suitable for high maneuverability flight of FWMAVs.

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Flying insects are able to hover and perform agile maneuvers by relying on their flapping wings to produce control forces, as well as flight forces, due to the absence of tail control surfaces. Insects have therefore become a source of inspiration for the development of tailless, hover-capable flapping-wing air vehicles (FWAVs). However, the technical difficulty involved in designing and building such a complicated and compact system within a limited takeoff weight for it to remain airborne is a major barrier. Consequently, among the many developed vehicles, only a few are capable of free flight. In this review paper, we survey recent developments of insect-inspired tailless FWAVs in various sizes from micro- to pico-scale, with different types of driving actuator, mechanism design, wing configuration, and control strategy. We discuss the capability of free flight and flight endurance of the FWAVs, which are limited by current electronics and power technologies that severely constrain those vehicles using other driving actuators, rather than conventional electromagnetic motors, to freely take off. Achievements in the development of FWAVs demonstrate their potential for future applications, both in the military and civilian fields. In addition, further integration with other modes of locomotion, such as crawling, jumping, perching, self-wing-folding, and water-diving, can be a future direction of a FWAV to fully adapt the biologically locomotive strategies in nature, and to increase the range of applications.
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From millimeter-scale insects to meter-scale vertebrates, several animal species exhibit multimodal locomotive capabilities in aerial and aquatic environments. To develop robots capable of hybrid aerial and aquatic locomotion, we require versatile propulsive strategies that reconcile the different physical constraints of airborne and aquatic environments. Furthermore, transitioning between aerial and aquatic environments poses substantial challenges at the scale of microrobots, where interfacial surface tension can be substantial relative to the weight and forces produced by the animal/robot. We report the design and operation of an insect-scale robot capable of flying, swimming, and transitioning between air and water. This 175-milligram robot uses a multimodal flapping strategy to efficiently locomote in both fluids. Once the robot swims to the water surface, lightweight electrolytic plates produce oxyhydrogen from the surrounding water that is collected by a buoyancy chamber. Increased buoyancy force from this electrochemical reaction gradually pushes the wings out of the water while the robot maintains upright stability by exploiting surface tension. A sparker ignites the oxyhydrogen, and the robot impulsively takes off from the water surface. This work analyzes the dynamics of flapping locomotion in an aquatic environment, identifies the challenges and benefits of surface tension effects on microrobots, and further develops a suite of new mesoscale devices that culminate in a hybrid, aerial-aquatic microrobot.
Conference Paper
This paper describes the development and design of the Nano Hummingbird, a small hovering ornithopter, which was developed as a part of the Defense Advanced Research Projects Agency (DARPA) Nano Air Vehicle (NAV) program. Announced in 2005, the NAV program goal was defined as a small, biologically inspired, unmanned air vehicle that would sustain hover and fly forward up to 10 m/s, while having a size under 7.5 cm, a total mass under 10g, and a payload of 2g. In 2011, the Nano Hummingbird was unveiled by AeroVironment as the culmination of over four years of work by a small team of engineers, technicians, artists, and modelers. It had a mass of 19 g, a wingspan of 16.5 cm, and the ability to hover for several minutes, fly forward up to 6.7 m/s, and transmit live color video to a remote ground station. Additionally, the vehicle demonstrated the ability to perform controlled hovering flight strictly with the use of its two flapping wings, a feat that was previously only seen in nature. The first part of this paper describes the history of the program, the evolution of the flying prototypes, and highlights the performance and characteristics of the flight vehicle. In the second part, further detailed explanation of the design of the subsystems is provided - including the flapping mechanism, control mechanism, wings, and onboard avionics - and their own paths of development.
Article
Experimental and numerical studies are conducted on the aerodynamic characteristics of a flapping wing of an insect in forward flight. Unsteady aerodynamic forces and flow patterns are measured using a dynamically scaled mechanical model in a water tunnel. The design of the model is based on the flapping wing of a bumblebee. The forces and flow patterns are also computed using a three-dimensional Navier-Stokes code. Comparisons between the experimental and numerical results show good agreement in the time histories of aerodynamic forces and flow patterns in both hovering and forward flight. Aerodynamic mechanisms of a flapping wing in forward flight, such as delayed stall, rotational effect, and wake capture are examined in detail. The results indicate that these aerodynamic mechanisms had an effect on the aerodynamic characteristics of the flapping wing in forward flight; however, these mechanisms function differently during the up- and downstroke, for different stroke plane angles, and for different advance ratios.
Article
Theoretical considerations and available experimental studies are combined for a discussion on the aerodynamic mechanisms of lift generation in hovering animal flight. A comparison of steady-state thin-aerofoil theory with measured lift coefficients reveals that leading edge separation bubbles are likely to be a prominent feature in insect flight. Insect wings show a gradual stall that is characteristic for thin profiles at Reynolds numbers (Re) less than about 105. In this type of stall, flow separates at the sharp leading edge and then re-attaches downstream to the upper wing surface, producing a region of limited separation enclosing a recirculating flow. The resulting leading edge bubble enhances the camber and thickness of the thin profile, improving lift at low Re. Some of the results for bird wing profiles indicate that the complications of leading edge bubbles might even be found in the fast forward flight of birds.
Conference Paper
The Micromechanical Flying Insect (MFI) project aims to create a 25 mm (wingtip to wingtip) flapping wing micro air vehicle inspired by the aerodynamics of insect flight. A key challenge is generating appropriate wing trajectories. Previous work showed a lift of 506 mu N at 160 Hz using feedforward control. In this paper, refinements to the MFI design including those in [2] increased wing beat frequency to 275 Hz and lift to 1400 mu N using pure sinusoidal drive for a fixed benchtop experiment. We show through simplified aerodynamic models that not only do sinusoidal actuator drives produce close to maximal lift, but significantly improved wing trajectories due to non-sinusoidal actuator drives are practically unobtainable due to actuator limitations.
Structural design and aerodynamic characteristics of two types of fold-able flapping-wings
  • X X Mu
  • S Xu
  • X Y Wu
  • H H Liu
  • Z P Yin
  • L Q Liu
  • L Jiang
  • G Y Gu
  • X Wu
A review of bird-inspired flapping wing miniature air vehicle designs
  • J W Gerdes
  • S K Gupta
  • S A Wilkerson