Practical Flapping Mechanisms for 20cm-span Micro Air Vehicles

[[abstract]]In the body of research relevant to high-performance flapping micro air vehicles (MAV), development of light-weight, compact and energy-efficient flapping mechanisms occupies a position of primacy due to its direct impact on the flight performance and mission capability. Realization of such versatile flapping mechanism with additional ability of producing thrust levels that fulfill requirements of cruising forward flight and vertical take-off and landing (VTOL) conditions demand extensive design validation and performance evaluation. This paper presents a concerted approach for mechanism development of a 20 cm span flapping MAV through an iterative design process and synergistic fabrication options involving electrical-discharge-wire-cutting (EDWC) and injection molding. Dynamic characterization of each mechanism is done through high speed photography, power take-off measurement, wind tunnel testing and proof-of-concept test flights. The research outcome represents best-in-class mechanism for a 20 cm span flapping MAV with desirable performance features of extra-large flapping stroke up to 100°, minimal transverse vibrations and almost no phase lag between the wings.[[notice]]補正完畢[[journaltype]]國外[[incitationindex]]SCI[[ispeerreviewed]]Y[[booktype]]紙本[[countrycodes]]US

Experimental and computational analysis for insect inspired flapping wing micro air vehicles

Many creatures in nature have evolved the ability to fly and some seem to do so effortlessly with captivating movement. The flight characteristics of these natural fliers have greatly fascinated biologists and engineers for a long time that to this day researchers continue to actively work in this field of science with the aim of one day developing a Flapping Wing Micro Aerial Vehicle (FWMAV) which can replicate the flight of nature's creatures. These types of autonomous robotic vehicles can fulfil tasks which are not suitable for manned vehicles especially when risks to human safety are present. Flight techniques such as control, stability and manoeuvrability are flight characteristics which an FWMAV must possess if such a device is employed for various rescue missions. With this in mind symmetrical and asymmetrical wing motions are studied experimentally in the current research programme in such a way that the methodology employed for this type of flight can be implemented into future FWMAVs. In summary, the research performed during the course of this project produced innovative results in the form of the creation of two micro air vehicles with a thorough explanation of the development process and examination under experimental tests. Various parameters were analysed during the experimental tests such as force, moment, power and wing position measurements. The tests were performed on both models, one of which has the functionality to perform asymmetrical flapping and successfully generate moments about two different axes. A unique wing motion which favoured the upward vertical force production was investigated under various scenarios. The wings keep a fixed angle of attack during the downwards flapping motion and are allowed to passively rotate during the upstroke motion. Computational simulations were performed to investigate the hovering fluid dynamics, forces, moments and power required for various chordwise rotational positions and durations of wing rotation. This investigation aided in understanding the full effects of altering these parameters under hovering conditions for a rectangular wing. The valuable results found from this research program provide a better insight into various topics involving micro air vehicles in addition to developing future flight worthy insect inspired vehicles

Experimental And Numerical Investigations On The Performance Of Flexible Skin Flapping Wing For Micro Aerial Vehicle Application

Flapping-wing micro air vehicles are small, hand-held flying vehicles that can maneuver in a constrained space because of its lightweight, low aspect ratio, and ability to fly in low Reynolds number environment. Flying mammals such as bats, and flying squirrels share a unique feature that allows them to fly with amazing agility and maneuverability unmatched by other flying animals of the same size. The unique feature that allows these animals to have such fight capabilities is their thin and flexible membrane wings. In this work, the unique characteristic features of flexible membrane wings associated with flying mammals such as bats are investigated for their highly efficient aerodynamic abilities. The primary goal of this study is to incorporate the mechanism involved in these flying mammals for improved aerodynamic performance of MAV’s. An Electronic Control System (ECS) was introduced to control a proper flapper wing mechanism to emulate the wing flapping of bats for the ongoing micro air vehicle (MAV) research. Besides, aerodynamic tests were carried out in an open-air wind chamber to investigate the aerodynamic characteristics, particularly the wing skin flexibility and camber effect. Furthermore, the optimization using response surface methodology (RSM) was carried out to investigate the interactive relationship of each factor and optimize the aerodynamic performance. In addition to this, three-dimensional numerical simulation was also accomplished on flat and camber wing using FLUENT software. UDFs were written to mimic the harmonic motion of the flapping wing and the dynamic mesh model was utilized. The aerodynamic performance based on lift and drag coefficient were investigated as functions of AoA, frequency, and velocity. Advance ratio parameter was adopted to study the effects of unsteady flow for flexible and camber wing. The proposed ECS demonstrates efficient control and accurate measurement. Moreover, the tedious procedure involved in the repeated calibrations for the manual system was totally eliminated by ECS. It was found that the most flexible wing skin was best suited for unsteady state with low advance ratio, whereas the least flexible wing was preferred for higher ranges. Furthermore, the experimental results showed that the cambered wings have significantly higher lift and drag when compared to that observed in case of flat wings. Moreover, the optimum result for the aerodynamic performance of the flapping wing characterized based on optimum camber, velocity, and frequency was found to be 15%, 4.29 m/s, and 9 Hz respectively. The numerical results were in good agreement with the experimental findings. The numerical results confirmed the enhancement of aerodynamic performance and camber wing was able to increase by as much as 1.12 times when compared to the flat wing. Investigation on the formation of vortices as well as its strength revealed that a higher camber wing was able to generate a higher LEV strength, provided the shape of the vorticity pattern was more compact, more attached, and more concentrated

An Analytical Investigation of Flapping Wing Structures for Micro Air Vehicles

An analytical model of flapping wing structures for bio-inspired micro air vehicles is presented in this dissertation. Bio-inspired micro air vehicles (MAVs) are based on insects and hummingbirds. These animals have lightweight, flexible wings that undergo large deformations while flapping. Engineering studies have confirmed that deformations can increase the lift of flapping wings. Wing flexibility has been studied through experimental construction-and-evaluation methods and through computational numerical models. Between experimental and numerical methods there is a need for a simple method to model and evaluate the structural dynamics of flexible flapping wings. This dissertation's analytical model addresses this need. A time-periodic assumed-modes beam analysis of a flapping, flexible wing undergoing linear deformations is developed from a beam analysis of a helicopter blade. The resultant structural model includes bending and torsion degrees of freedom. The model is non-dimensionalized. The ratio of the system's structural natural frequency to wingbeat frequency characterizes its constant stiffness, and the amplitude of flapping motion characterizes its time-periodic stiffness. Current flapping mechanisms and MAVs are compared to biological fliers on the basis of the characteristic parameters. The beam analysis is extended to develop an plate model of a flapping wing. The time-periodic stability of the flapping wing model is assessed with Floquet analysis. A flapping-wing stability diagram is developed as a function of the characteristic parameters. The analysis indicates that time-periodic instabilities are more likely for large-amplitude, high-frequency flapping motion. Instabilities associated with the first bending mode dominate the stability diagram. Due to current limitations of flapping mechanisms, instabilities are not likely in current experiments but become more likely at the operating conditions of biological fliers. The effect of structural design parameters, including wing planform and material stiffness, are assessed with an assumed-modes aeroelastic model. Wing planforms are developed from an empirical model of biological planforms. Non-linearities are described in the effect of membrane thickness on lift generation. Structural couplings due to time-periodic stiffness are identified that can decrease lift generation at certain wingbeat frequencies