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The aerodynamic role of the elytra during a beetle's flapping motion is not well-elucidated, although it is well-recognized that the evolution of elytra has been a key in the success of coleopteran insects due to their protective function. An experimental study on wing kinematics reveals that for almost concurrent flapping with the hind wings, the flapping angle of the elytra is 5 times smaller than that of the hind wings. Then, we explore the aerodynamic forces on elytra in free forward flight with and without an effect of elytron-hind wing interaction by three-dimensional numerical simulation. The numerical results show that vertical force generated by the elytra without interaction is not sufficient to support even its own weight. However, the elytron-hind wing interaction improves the vertical force on the elytra up to 80%; thus, the total vertical force could fully support its own weight. The interaction slightly increases the vertical force on the hind wind by 6% as well.

In recent decades, the take-off mechanisms of flying animals have received much attention in insect flight initiation. Most of previous works have focused on the jumping mechanism, which is the most common take-off mechanism found in flying animals. Here, we presented that the rhinoceros beetle, Trypoxylus dichotomus, takes off without jumping. In this study, we used 3-Dimensional (3D) high-speed video techniques to quantitatively analyze the wings and body kinematics during the initiation periods of flight. The details of the flapping angle, angle of attack of the wings and the roll, pitch and yaw angles of the body were investigated to understand the mechanism of take-off in T. dichotomus. The beetle took off gradually with a small velocity and small acceleration. The body kinematic analyses showed that the beetle exhibited stable take-off. To generate high lift force, the beetle modulated its hind wing to control the angle of attack; the angle of attack was large during the upstroke and small during the downstroke. The legs of beetle did not contract and strongly release like other insects. The hind wing could be considered as a main source of lift for heavy beetle.

Aerodynamic characteristic of the beetle, Trypoxylus dichotomus, which has a pair of elytra (forewings) and hind wings, is numerically investigated. Based on the experimental results of wing kinematics, two-dimensional (2D) and three-dimensional (3D) computational fluid dynamic simulations were carried out to reveal aerodynamic performance of the hind wing. The roles of the spiral Leading Edge Vortex (LEV) and the spanwise flow were clarified by comparing 2D and 3D simulations. Mainly due to pitching down of chord line during downstroke in highly inclined stroke plane, relatively high averaged thrust was produced in the free forward flight of the beetle. The effects of the local corrugation and the camber variation were also investigated for the beetle's hind wings. Our results show that the camber variation plays a significant role in improving both lift and thrust in the flapping. On the other hand, the local corrugation pattern has no significant effect on the aerodynamic force due to large angle of attack during flapping.

Aerodynamic characteristics of the beetle, Trypoxylus dichotomus, which has a pair of elytra (forewings) and flexible hind wings, are investigated. Visualization experiments were conducted for various flight conditions of a beetle, Trypoxylus dichotomus: free, tethered, hovering, forward and climbing flights. Leading edge, trailing edge and tip vortices on both wings were observed clearly. The leading edge vortex was stable and remained on the top surface of the elytron for a wide interval during the downstroke of free forward flight. Hence, the elytron may have a considerable role in lift force generation of the beetle. In addition, we reveal a suction phenomenon between the gaps of the hind wing and the elytron in upstroke that may improve the positive lift force on the hind wing. We also found the reverse clap-fling mechanism of the T. dichotomus beetle in hovering flight. The hind wings touch together at the beginning of the upstroke. The vortex generation, shedding and interaction give a better understanding of the detailed aerodynamic mechanism of beetle flight.

Detailed 3-Dimensional (3D) wing kinematics was experimentally presented in free flight of a beetle, Trypoxylus dichotomus, which has a pair of elytra (forewings) and flexible hind wings. The kinematic parameters such as the wing tip trajectory, angle of attack and camber deformation were obtained from a 3D reconstruction technique that involves the use of two synchronized high-speed cameras to digitize various points marked on the wings. Our data showed outstanding characteristics of deformation and flexibility of the beetle’s hind wing compared with other measured insects, especially in the chordwise and spanwise directions during flapping motion. The hind wing produced 16% maximum positive camber deformation during the downstroke. It also experienced twisted shape showing large variation of the angle of attack from the root to the tip during the upstroke.

Artificial magnetotactic Tetrahymena pyriformis GL (T. pyriformis) cells were created by the internalization of iron oxide nano particles and became controllable with a time-varying external magnetic field. Thus, T. pyriformis can be utilized as a cellular robot to conduct micro-scale tasks such as transportation and manipulation. To complete these tasks, loading inorganic or organic materials onto the cell body is essential, but functionalization of the cell membrane is obstructed by their motile organelles, cilia. Dibucaine HCl, a local anesthetic, removes the cilia from the cell body, and the functional group would be absorbed more efficiently during cilia regeneration. In this paper, we characterize the recovery of artificial magnetotactic T. pyriformis after the deciliation process to optimize a cellular robot fabrication process. After sufficient time to recover, the motility rate and the average velocity of the deciliated cells were six and ten percent lower than that of non-deciliated cells, respectively. We showed that the motile cells after recovery can still be controlled using magnetotaxis, making T. pyriformis a good candidate to be used as a cellular robot.

In this work, a three-dimensional (3D) Computational Fluid Dynamics (CFD) model was built to simulate the tail fin motion of a fish robot actuated by a piezoceramic composite actuator, and to determine the maximum thrust tail-beat frequency. A simulation of the tail fin at a tail-beat frequency was performed to confirm measured thrust data from a previous study. The computed and measured thrusts were in good agreement. A series of thrust simulations were conducted for various tail-beat frequencies to confirm the maximum thrust frequency that was obtained from thrust measurements in the previous study. The largest thrust was calculated at a tail-beat frequency of 3.7 Hz and vortices around the tail were fully separated. The calculated maximum thrust tail-beat frequency was in good agreement with the measured frequency. Flow characteristics during tail fin motion were examined to explain why the largest thrust occurred at this particular tail-beat frequency.

In this paper, we have attempted to improve the aerodynamic force generation ability of an artificial wing by implementing initial wing camber in the flexible artificial wing. This initial camber is used to create passive wing camber during flapping motion. We modified original artificial wing by removing many minor vein structures in the wing and then placed the initial camber between two major veins. Stiffness measurements for the original artificial wing and the present wing with initial camber were conducted to compare the stiffnesses of the two artificial wings, and the similarities of the two wings are discussed. A flapping test was carried out using a previously-built flapper that can flap at higher than 25 Hz flapping frequency to verify the wing camber effect. Finally, a performance comparison between uncambered- and cambered-wings was also undertaken based on observations using a high-speed camera and force measurements from wired-flight tests and swing tests. The comparison showed that the cambered-wing could produce about 10% higher thrust than the uncambered-wing.

We conducted a comprehensive study to investigate the aerodynamic characteristics and force generation of the elytra of a beetle, Allomyrina dichotoma. Our analysis included wind tunnel experiments and three-dimensional computational fluid dynamics simulations using ANSYS-CFX software. Our first approach was a quasi-static study that considered the effect of induced flapping flow due to the flapping motion of the fore-wings (elytra) at a frequency of around 30 Hz to 40 Hz. The dihedral angle was varied to represent flapping motion during the upstroke and downstroke. We found that an elytron produces positive lift at 0° geometric angle of attack, negative lift during the upstroke, and always produces drag during both the upstroke and downstroke. We also found that the lift coefficient of an elytron does not drop even at a very high geometric angle of attack. For a beetle with a body weight of 5 g, based on the quasi-static method, the fore-wings (elytra) can produce lift of less than 1% of its body weight.

We present a new version of a compact insect-mimicking flapping-wing system driven by a small motor, and suggest two testing approaches to measure the thrust or lift generated by a flapping-wing system. Flapping performance tests show the proposed flapping-wing system, which is powered by an onboard battery (lithium, 3.7 V, 180 mAh), could flap at flapping frequency of 25 Hz, and produce an average thrust or lift of about 3 g. In a wired-flight test under constrained conditions, the flapping-wing system could fly at an average forward velocity of 700 mm·s−1. For measuring the average thrust or lift produced by the flapping-wing system, we propose two testing approaches of wired-flight test and swing test with the aid of a high-speed camera and they are compared with a load cell measurement. The average thrust or lift values from the two proposed approaches agree well with the average thrust or lift values measured by a load cell.

In an attempt to realize a flapping wing micro-air vehicle with morphing wings, we report on improvements to our previous foldable artificial hind wing. Multiple hinges, which were implemented to mimic the bending zone of a beetle hind wing, were made of small composite hinge plates and tiny aluminum rivets. The buck-tails of rivets were flared after the hinge plates were assembled with the rivets so that the folding/unfolding motions could be completed in less time, and the straight shape of the artificial hind wing could be maintained after fabrication. Folding and unfolding actions were triggered by electrically-activated Shape Memory Alloy (SMA) wires. For wing folding, the actuation characteristics of the SMA wire actuator were modified through heat treatment. Through a series of flapping tests, we confirmed that the artificial wings did not fold back and arbitrarily fluctuate during the flapping motion.

Inspired by the fact that a high flexible wing in nature generates high aerodynamic performance, we investigated the aerodynamic performance of the flapping wing with different chord flexures. The unsteady, incompressible, and viscous flow over airfoil NACA0012 in a plunge motion was analyzed by using Navier-Stokes equation. Grid deformation, in which finite element and interpolation ideas are mixed, was introduced for computing large grid deformation caused by the chord flexures. We explored the optimal phase angle for thrust force and propulsive efficiency by varying the chord flexure from 0.05 to 0.7 when reduced frequency and plunge amplitude were fixed. Throughout parametric study on the phase angle and chord flexure amplitude, the maximum thrust force is achieved near at 0° in all given conditions, meanwhile, it is found that the optimal phase angle has dependency of chord flexure amplitude, which achieves higher aerodynamic performance compared to previous studies. These findings will provide a useful guideline for determining wing flexibility in design of a bio-mimetic air vehicle.

In this work, we first present a method to experimentally capture the free flight of a beetle (Allomyrina dichotoma), which is not an active flyer. The beetle is suspended in the air by a hanger to induce the free flight. This flight is filmed using two high-speed cameras. The high speed images are then examined to obtain flapping angle, flapping frequency, and wing rotation of the hind wing. The acquired data of beetle free flight are used to design a motor-driven flapper that can approximately mimic the beetle in terms of size, flapping frequency and wing kinematics. The flapper can create a large flapping angle over 140° with a large passive wing rotation angle. Even though the flapping frequency of the flapper is not high enough compared to that of a real beetle due to the limited motor torque, the flapper could produce positive average vertical force. This work will provide important experience for future development of a beetle-mimicking Flapping-Wing Micro Air Vehicle (FWMAV).

Biological tiny structures have been observed on many kinds of surfaces such as lotus leaves and insect wings, which enhance the hydrophobicity of the natural surfaces and play a role of self-cleaning. We presented the fabrication technology of a superhydrophobic surface using high energy ion beam. Artificial insect wings that mimic the morphology and the superhydrophobocity of cicada's wings were successfully fabricated using argon and oxygen ion beam treatment on a polytetrafluoroethylene (PTFE) film. The wing structures were supported by carbon/epoxy fibers as artificial flexible veins that were bonded through an autoclave process. The morphology of the fabricated surface bears a strong resemblance to the wing surface of a cicada, with contact angles greater than 160°, which could be sustained for more than two months.

Biological tiny structures have been observed on many kinds of surfaces such as lotus leaves, which have an effect on the coloration of Morpho butterflies and enhance the hydrophobicity of natural surfaces. We investigated the micro-scale and nano-scale structures on the wing surfaces of insects and found that the hierarchical multiple roughness structures help in enhancing the hydrophobicity. After examining 10 orders and 24 species of flying Pterygotan insects, we found that micro-scale and nano-scale structures typically exist on both the upper and lower wing surfaces of flying insects. The tiny structures such as denticle or setae on the insect wings enhance the hydrophobicity, thereby enabling the wings to be cleaned more easily. And the hydrophobic insect wings undergo a transition from Cassie to Wenzel states at pitch/size ratio of about 20. In order to examine the wetting characteristics on a rough surface, a biomimetic surface with micro-scale pillars is fabricated on a silicon wafer, which exhibits the same behavior as the insect wing, with the Cassie-Wenzel transition occurring consistently around a pitch/width value of 20.

In the “modified quasi-steady” approach, two-dimensional (2D) aerodynamic models of flapping wing motions are analyzed with focus on different types of wing rotation and different positions of rotation axis to explain the force peak at the end of each half stroke. In this model, an additional velocity of the mid chord position due to rotation is superimposed on the translational relative velocity of air with respect to the wing. This modification produces augmented forces around the end of each stroke. For each case of the flapping wing motions with various combination of controlled translational and rotational velocities of the wing along inclined stroke planes with thin figure-of-eight trajectory, discussions focus on lift-drag evolution during one stroke cycle and efficiency of types of wing rotation. This “modified quasi-steady” approach provides a systematic analysis of various parameters and their effects on efficiency of flapping wing mechanism. Flapping mechanism with delayed rotation around quarter-chord axis is an efficient one and can be made simple by a passive rotation mechanism so that it can be useful for robotic application.