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Small insects with flapping wings, such as bees and flies, have flexible wings with veins, and their compliant motion enhances flight efficiency and robustness. This study investigated the effects of integrating wing veins into soft wings for micro-flapping aerial vehicles. Prototypes of soft wings, featuring various wing areas and vein patterns in both the wing-chord and wing-span directions, were fabricated and evaluated to determine the force generated through flapping. The results indicated that the force is not solely dependent upon the wing area and is influenced by the wing vein pattern. Wings incorporating wing-chord veins produced more force compared to those with wing-span veins. In contrast, when the wing area was the specific wing area, wings with crossed wing veins, comprising both wing-span veins and wing-chord veins, produced more force. Although wing-chord veins tended to exert more influence on the force generated than the wing-span veins, the findings suggested that a combination of wing-span and wing-chord veins may be requisite, depending upon the wing area., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Ishiguro, Kawasetsu and Hosoda.)

Allomyrina dichotoma has a natural ultra-high flying ability and maneuverability. Especially its ability to fly flexibly in the air, makes it more adaptable to the harsh ecological environment. In this study, a bionic flapping-wing micro air vehicle (FMAV) is designed and fabricated by mimicking the flight mode of A. dichotoma . Parametric design was employed for combining the airframe structure and flight characteristics analysis. To improve the transmission efficiency and compactness of the FMAV mechanisms, this study first analyses the body structure of A. dichotoma , and then proposes a novel mechanism of FMAV based on its biological motion characteristics, the flight motion characteristics, and its musculoskeletal system. By optimizing the flapping-wing mechanism and mimicking the flying mechanism of A. dichotoma , the large angle amplitude and the high-frequency flapping motion can be achieved to generate more aerodynamic force. Meanwhile, to improve the bionic effect and the wing performance of FMAV, the flexible deformation of A. dichotoma wings for each flapping period was observed by a high-speed camera. Furthermore, the bionic design of wings the prototype was carried out, therefore the wings can generate a high lift force in the flapping process. The experiment demonstrated that the aircraft can achieve a flapping angle of 160 degrees and 30 Hz flapping frequency. The attitude change of FMAV is realized by mimicking the movement for the change of attitude of the A. dichotoma , by changing the angle of attack of the wing, and executing the flight action of multiple degrees of freedom including pitch, roll and yaw. Finally, the aerodynamic experiment demonstrated that the prototype can offer 27.8 g lift and enough torque for altitude adjustment., (© 2020 IOP Publishing Ltd.)

Membranous hind wings of the beetles can be folded under the elytra when they are at rest, and rotate and lift the elytra up only when they need to fly. This characteristic provides excellent flying capability and good environment adaptability. Inspired by the beetles, the new type of the bionic folding wing for the flapping wing Micro Air Vehicle (MAV) was designed. This flapping wing can be unfolded to get a sufficient lift in flight, and can be folded off flight to reduce the wing area and risk of the wing damage. The relationship between the internal pressures of the hydraulic system for the bionic wing folding varies and temperature was analyzed, the results show that the pressure within the system tends to increase with temperature, which proves the feasibility of the schematic design in theory. Stress analysis of the bionic wing was conducted, it was shown that stress distributions and deformation of the bionic wing under the positive and negative side loading are basically the same, which demonstrates that the strength of the bionic folding wing meets the requirements and further proves the feasibility of the schematic design., (Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)

This study investigates the aerodynamic efficiency of a bioinspired flapping wing rotor kinematics which combines an active vertical flapping motion and a passive horizontal rotation induced by aerodynamic thrust. The aerodynamic efficiencies for producing both vertical lift and horizontal thrust of the wing are obtained using a quasi-steady aerodynamic model and two-dimensional (2D) CFD analysis at Reynolds number of 2500. The calculated efficiency data show that both efficiencies (propulsive efficiency- η p , and efficiency for producing lift- P f ) of the wing are optimized at Strouhal number ( St ) between 0.1 and 0.5 for a range of wing pitch angles (upstroke angle of attack α u less than 45°); the St for high P f ( St  = 0.1 ∼ 0.3) is generally lower than for high η p can be obtained for a wide range of prescribed wing kinematics. This study provides insight into the aerodynamic efficiency of biological flyers in cruising flight, as well as practical applications for micro air vehicle design.St  = 0.2 ∼ 0.5), while the St for equilibrium rotation states lies between the two. Further systematic calculations show that the natural equilibrium of the passive rotating wing automatically converges to high-efficiency states: above 85% of maximum P f can be obtained for a wide range of prescribed wing kinematics. This study provides insight into the aerodynamic efficiency of biological flyers in cruising flight, as well as practical applications for micro air vehicle design., Competing Interests: We declare we have no competing interests.

This paper presents the nonlinear six degrees of freedom dynamic modeling of a fixed wing micro air vehicle. The static derivatives of the micro air vehicle are obtained through the wind tunnel testing. The propeller effects on the lift, drag, pitching moment and side force are quantified through wind tunnel testing. The dynamic derivatives are obtained through empirical relations available in the literature. The trim conditions are computed for a straight and constant altitude flight condition. The linearized longitudinal and lateral state space models are obtained about trim conditions. The variations in short period mode, phugoid mode, Dutch roll mode, roll subsidence mode and spiral mode with respect to different trim operating conditions is presented. A stabilizing static output feedback controller is designed using the obtained model. Successful closed loop flight trials are conducted with the static output feedback controller., Competing Interests: The authors declare no conflict of interest.

One of the major challenges of evolutionary robotics is to transfer robot controllers evolved in simulation to robots in the real world. In this article, we investigate abstraction of the sensory inputs and motor actions as a tool to tackle this problem. Abstraction in robots is simply the use of preprocessed sensory inputs and low-level closed-loop control systems that execute higher-level motor commands. To demonstrate the impact abstraction could have, we evolved two controllers with different levels of abstraction to solve a task of forming an asymmetric triangle with a homogeneous swarm of micro air vehicles. The results show that although both controllers can effectively complete the task in simulation, the controller with the lower level of abstraction is not effective on the real vehicle, due to the reality gap. The controller with the higher level of abstraction is, however, effective both in simulation and in reality, suggesting that abstraction can be a useful tool in making evolved behavior robust to the reality gap. Additionally, abstraction aided in reducing the computational complexity of the simulation environment, speeding up the optimization process. Preeminently, we show that the optimized behavior exploits the environment (in this case the identical behavior of the other robots) and performs input shaping to allow the vehicles to fly into and maintain the required formation, demonstrating clear sensory-motor coordination. This shows that the power of the genetic optimization to find complex correlations is not necessarily lost through abstraction as some have suggested.

The wings of many insect species including crane flies and damselflies are petiolate (on stalks), with the wing planform beginning some distance away from the wing hinge, rather than at the hinge. The aerodynamic impact of flapping petiolate wings is relatively unknown, particularly on the formation of the lift-augmenting leading-edge vortex (LEV): a key flow structure exploited by many insects, birds and bats to enhance their lift coefficient. We investigated the aerodynamic implications of petiolation P using particle image velocimetry flow field measurements on an array of rectangular wings of aspect ratio 3 and petiolation values of P = 1-3. The wings were driven using a mechanical device, the 'Flapperatus', to produce highly repeatable insect-like kinematics. The wings maintained a constant Reynolds number of 1400 and dimensionless stroke amplitude Λ * (number of chords traversed by the wingtip) of 6.5 across all test cases. Our results showed that for more petiolate wings the LEV is generally larger, stronger in circulation, and covers a greater area of the wing surface, particularly at the mid-span and inboard locations early in the wing stroke cycle. In each case, the LEV was initially arch-like in form with its outboard end terminating in a focus-sink on the wing surface, before transitioning to become continuous with the tip vortex thereafter. In the second half of the wing stroke, more petiolate wings exhibit a more detached LEV, with detachment initiating at approximately 70% and 50% span for P = 1 and 3, respectively. As a consequence, lift coefficients based on the LEV are higher in the first half of the wing stroke for petiolate wings, but more comparable in the second half. Time-averaged LEV lift coefficients show a general rise with petiolation over the range tested.

Evolutionary Robotics allows robots with limited sensors and processing to tackle complex tasks by means of sensory-motor coordination. In this article we show the first application of the Behavior Tree framework on a real robotic platform using the evolutionary robotics methodology. This framework is used to improve the intelligibility of the emergent robotic behavior over that of the traditional neural network formulation. As a result, the behavior is easier to comprehend and manually adapt when crossing the reality gap from simulation to reality. This functionality is shown by performing real-world flight tests with the 20-g DelFly Explorer flapping wing micro air vehicle equipped with a 4-g onboard stereo vision system. The experiments show that the DelFly can fully autonomously search for and fly through a window with only its onboard sensors and processing. The success rate of the optimized behavior in simulation is 88%, and the corresponding real-world performance is 54% after user adaptation. Although this leaves room for improvement, it is higher than the 46% success rate from a tuned user-defined controller.

Insect- and bird-size drones-micro air vehicles (MAV) that can perform autonomous flight in natural and man-made environments are now an active and well-integrated research area. MAVs normally operate at a low speed in a Reynolds number regime of 10(4)-10(5) or lower, in which most flying animals of insects, birds and bats fly, and encounter unconventional challenges in generating sufficient aerodynamic forces to stay airborne and in controlling flight autonomy to achieve complex manoeuvres. Flying insects that power and control flight by flapping wings are capable of sophisticated aerodynamic force production and precise, agile manoeuvring, through an integrated system consisting of wings to generate aerodynamic force, muscles to move the wings and a control system to modulate power output from the muscles. In this article, we give a selective review on the state of the art of biomechanics in bioinspired flight systems in terms of flapping and flexible wing aerodynamics, flight dynamics and stability, passive and active mechanisms in stabilization and control, as well as flapping flight in unsteady environments. We further highlight recent advances in biomimetics of flapping-wing MAVs with a specific focus on insect-inspired wing design and fabrication, as well as sensing systems.This article is part of the themed issue 'Moving in a moving medium: new perspectives on flight'., (© 2016 The Author(s).)

Ornithopters, or flapping-wing aircraft, offer an alternative to helicopters in achieving manoeuvrability at small scales, although stabilizing such aerial vehicles remains a key challenge. Here, we present a hovering machine that achieves self-righting flight using flapping wings alone, without relying on additional aerodynamic surfaces and without feedback control. We design, construct and test-fly a prototype that opens and closes four wings, resembling the motions of swimming jellyfish more so than any insect or bird. Measurements of lift show the benefits of wing flexing and the importance of selecting a wing size appropriate to the motor. Furthermore, we use high-speed video and motion tracking to show that the body orientation is stable during ascending, forward and hovering flight modes. Our experimental measurements are used to inform an aerodynamic model of stability that reveals the importance of centre-of-mass location and the coupling of body translation and rotation. These results show the promise of flapping-flight strategies beyond those that directly mimic the wing motions of flying animals.