Wing Micro Air Vehicle Research Articles

Aerodynamics of a bio-inspired flexible flapping-wing micro air vehicle

MAVs (micro air vehicles) with a maximal dimension of 15 cm and nominal flight speeds of around 10 m s−1, operate in a Reynolds number regime of 105 or lower, in which most natural flyers including insects, bats and birds fly. Furthermore, due to their light weight and low flight speed, the MAVs' flight characteristics are substantially affected by environmental factors such as wind gust. Like natural flyers, the wing structures of MAVs are often flexible and tend to deform during flight. Consequently, the aero/fluid and structural dynamics of these flyers are closely linked to each other, making the entire flight vehicle difficult to analyze. We have recently developed a hummingbird-inspired, flapping flexible wing MAV with a weight of 2.4–3.0 g and a wingspan of 10–12 cm. In this study, we carry out an integrated study of the flexible wing aerodynamics of this flapping MAV by combining an in-house computational fluid dynamic (CFD) method and wind tunnel experiments. A CFD model that has a realistic wing planform and can mimic realistic flexible wing kinematics is established, which provides a quantitative prediction of unsteady aerodynamics of the four-winged MAV in terms of vortex and wake structures and their relationship with aerodynamic force generation. Wind tunnel experiments further confirm the effectiveness of the clap and fling mechanism employed in this bio-inspired MAV as well as the importance of the wing flexibility in designing small flapping-wing MAVs.

Modal Analysis of a Composite Wing of Micro Air Vehicle

Modal Analysis of a Composite Wing of Micro Air Vehicle

Modal Analysis of a Flexible Membrane Wing of Micro Air Vehicles

Modal Analysis of a Flexible Membrane Wing of Micro Air Vehicles

Aeroelastic Analysis of Membrane Microair Vehicles—Part I: Flutter and Limit Cycle Analysis for Fixed-Wing Configurations

This is the first of two papers concerning the fluid and structural dynamic characteristics of membrane wing microair vehicles. In this paper, a (three) batten-reinforced fixed-wing membrane microair vehicle is used to determine the effect of membrane prestrain on flutter and limit cycle behavior of fixed-wing membrane microair vehicles. For each configuration tested, flutter and subsequent limit cycle oscillations are measured in wind tunnel tests and predicted using an aeroelastic computational model consisting of a nonlinear finite element model coupled to a vortex lattice solution of the Laplace equation and boundary conditions. Agreement between the predicted and measured onset of limit cycle oscillation is good as is the prediction of the amplitude of the limit cycle at the trailing edge of the lower membrane. A direct correlation between levels of strain and the phase of the membranes during the limit cycle is found in the computation and thought to also occur in the experiment.

Structural Analysis of a Dragonfly Wing

Dragonfly wings are highly corrugated, which increases the stiffness and strength of the wing significantly, and results in a lightweight structure with good aerodynamic performance. How insect wings carry aerodynamic and inertial loads, and how the resonant frequency of the flapping wings is tuned for carrying these loads, is however not fully understood. To study this we made a three-dimensional scan of a dragonfly (Sympetrum vulgatum) fore- and hindwing with a micro-CT scanner. The scans contain the complete venation pattern including thickness variations throughout both wings. We subsequently approximated the forewing architecture with an efficient three-dimensional beam and shell model. We then determined the wing’s natural vibration modes and the wing deformation resulting from analytical estimates of 8 load cases containing aerodynamic and inertial loads (using the finite element solver Abaqus). Based on our computations we find that the inertial loads are 1.5 to 3 times higher than aerodynamic pressure loads. We further find that wing deformation is smaller during the downstroke than during the upstroke, due to structural asymmetry. The natural vibration mode analysis revealed that the structural natural frequency of a dragonfly wing in vacuum is 154 Hz, which is approximately 4.8 times higher than the natural flapping frequency of dragonflies in hovering flight (32.3 Hz). This insight in the structural properties of dragonfly wings could inspire the design of more effective wings for insect-sized flapping micro air vehicles: The passive shape of aeroelastically tailored wings inspired by dragonflies can in principle be designed more precisely compared to sail like wings —which can make the dragonfly-like wings more aerodynamically effective.

Ionic Polymer Metal Composite Flapping Actuator Mimicking Dragonflies

In this study, variational principle is used for dynamic modeling of an Ionic Polymer Metal Composite (IPMC) flapping wing. The IPMC is an Electro-active Polymer (EAP) which is emerging as a useful smart material for `artificial muscle' applications. Dynamic characteristics of IPMC flapping wings having the same size as the actual wings of three different dragonfly species Aeshna Multicolor, Anax Parthenope Julius and Sympetrum Frequens are analyzed using numerical simulations. An unsteady aerodynamic model is used to obtain the aerodynamic forces. A comparative study of the performances of three IPMC flapping wings is conducted. Among the three species, it is found that thrust force produced by the IPMC flapping wing of the same size as Anax Parthenope Julius wing is maximum. Lift force produced by the IPMC wing of the same size as Sympetrum Frequens wing is maximum and the wing is suitable for low speed flight. The numerical results in this paper show that dragonfly inspired IPMC flapping wings are a viable contender for insect scale flapping wing micro air vehicles.

A dragonfly inspired flapping wing actuated by electro active polymers

An energy-based variational approach is used for structural dynamic modeling of the IPMC (Ionic Polymer Metal Composites) flapping wing. Dynamic characteristics of the wing are analyzed using numerical simulations. Starting with the initial design, critical parameters which have influence on the performance of the wing are identified through parametric studies. An optimization study is performed to obtain improved flapping actuation of the IPMC wing. It is shown that the optimization algorithm leads to a flapping wing with dimensions similar to the dragonfly Aeshna Multicolor wing. An unsteady aerodynamic model based on modified strip theory is used to obtain the aerodynamic forces. It is found that the IPMC wing generates sufficient lift to support its own weight and carry a small payload. It is therefore a potential candidate for flapping wing of micro air vehicles.

Numerical and Experimental Simulations of Flapping Wings

This paper presents recent progress in a continuing investigation of the aeromechanical aspects of unsteady flapping wings for micro air vehicles (MAV). Numerical simulations were performed for two-dimensional (2D) pitching-plunging airfoils and three-dimensional (3D) flapping wings, mainly at hover conditions, using an in-house code called INSflow. The results were compared with available experimental data obtained in the water tunnel at the NRC-IAR. The investigation revealed that, at hover conditions, the vortices formed during the airfoil plunging motion may remain near the airfoil and affect new vortex formations, and thus the integral aerodynamic performance. In addition, the flow around the 3D insect-like wing is fully three-dimensional. The tip flow affects the flow separation, reducing the separation intensity. Two-dimensional calculations may over-predict the separation and the shedding vortices, thus affecting the generation of aerodynamic forces.

An overview of experiments on the dynamic sensitivity of MAVs to turbulence

AbstractAspects of the turbulent wind environment Micro Air Vehicles (MAVs) experience when flying outdoors were replicated in a large wind tunnel. An overview of the facility, instrumentation and initial flight tests is given. Piloting inputs and aircraft accelerations were recorded on fixed and rotary wing MAVs and for some tests, measurements of the approach flow (u,v,w sampled at 1,250Hz at four laterally disposed upstream locations) were made. The piloting aim was to hold straight and level flight in the 12m wide × 4m high × ~50m long test section, while flying in a range of turbulent conditions. The Cooper-Harper rating system showed that a rotary craft was less sensitive to the effects of turbulence compared to the fixed wing craft and that while the fixed wing aircraft was relatively easy to fly in smooth air, it became extremely difficult to fly under high turbulence conditions. The rotary craft, while more difficult to fly per. se., did not become significantly harder to fly in relatively high turbulence levels. However the rotary craft had a higher mass and MOI than the fixed wing craft and further work is planned to understand the effects of these differences.

Non-linear Dynamic Analysis of a Piezoelectrically Actuated Flapping Wing

An energy method is used in order to derive the non-linear equations of motion of a smart flapping wing. Flapping wing is actuated from the root by a PZT unimorph in the piezofan configuration. Dynamic characteristics of the wing, having the same size as dragonfly Aeshna Multicolor, are analyzed using numerical simulations. It is shown that flapping angle variations of the smart flapping wing are similar to the actual dragonfly wing for a specific feasible voltage. An unsteady aerodynamic model based on modified strip theory is used to obtain the aerodynamic forces. It is found that the smart wing generates sufficient lift to support its own weight and carry a small payload. It is therefore a potential candidate for flapping wing of micro air vehicles.

Improvement of Artificial Foldable Wing Models by Mimicking the Unfolding/Folding Mechanism of a Beetle Hind Wing

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.

Resonance Type Flapping Wing for Micro Air Vehicle

A resonance type flapping wing, which is suitable for an insect like Micro Air Vehicle, is presented. It utilizes the r esonance phenomenon of a two-degrees of freedom elastic system, that is, the wing is suppor ted by the spr ings for flapping and feathering motions, being oscillated, at the resonance frequency of the system, only by the torque in flapping motion. The amplitudes of flapping and feathering motions and the phase angle between them are controlled by changing the amount of the damping. Optimum design method is applied to determine the structural parameters of the wing, amount of the torque and damping. Using these optimum quantities thus determined, the arbitrary control of the flapping and feather ing motions becomes possible. The paper presents the theoretical bases of the concept, and the results of the numer ical simulation using a Navier-Stokes code, which takes into account the aeroelastic effects, are also presented to verify the concept.

Nonlinear aerodynamic damping of sharp-edged flexible beams oscillating at low Keulegan–Carpenter numbers

Slender sharp-edged flexible beams such as flapping wings of micro air vehicles (MAVs), piezoelectric fans and insect wings typically oscillate at moderate-to-high values of non-dimensional frequency parameter β with amplitudes as large as their widths resulting in Keulegan–Carpenter (KC) numbers of order one. Their oscillations give rise to aerodynamic damping forces which vary nonlinearly with the oscillation amplitude and frequency; in contrast, at infinitesimal KC numbers the fluid damping coefficient is independent of the oscillation amplitude. In this article, we present experimental results to demonstrate the phenomenon of nonlinear aerodynamic damping in slender sharp-edged beams oscillating in surrounding fluid with amplitudes comparable to their widths. Furthermore, we develop a general theory to predict the amplitude and frequency dependence of aerodynamic damping of these beams by coupling the structural motions to an inviscid incompressible fluid. The fluid–structure interaction model developed here accounts for separation of flow and vortex shedding at sharp edges of the beam, and studies vortex-shedding-induced aerodynamic damping in slender sharp-edged beams for different values of the KC number and the frequency parameter β. The predictions of the theoretical model agree well with the experimental results obtained after performing experiments with piezoelectric fans under vacuum and ambient conditions.

Measurement of Thrust and Lift Forces Associated With Drag of Compliant Flapping Wing for Micro Air Vehicles Using a New Test Stand Design

Compliant wing designs have the potential of improving flapping wing Micro-Air Vehicles (MAVs). Designing compliant wings requires a detailed understanding of the effect of compliance on the generation of thrust and lift forces. The low force and high-frequency measurements associated with these forces necessitated a new versatile test stand design that uses a 250 g load cell along with a rigid linear air bearing to minimize friction and the dynamic behavior of the test stand while isolating only the stationary thrust or lift force associated with drag generated by the wing. Moreover, this stand is relatively inexpensive and hence can be easily utilized by wing designers to optimize the wing compliance and shape. The frequency response of the wing is accurately resolved, along with wing compliance on the thrust and lift profiles. The effects of the thrust and lift force generated as a function of flapping frequency were also determined. A semi-empirical aerodynamic model of the thrust and lift generated by the flapping wing MAV on the new test stand was developed and used to evaluate the measurements. This model accounted for the drag force and the effects of the wing compliance. There was good correlation between the model predictions and experimental measurements. Also, the increase in average thrust due to increased wing compliance was experimentally quantified for the first time using the new test stand. Thus, our measurements for the first time reveal the detrimental influence of excessive compliance on drag forces during high frequency operation. In addition, we were also able to observe the useful effect of compliance on the generation of extra thrust at the beginning and end of upstrokes and downstrokes of the flapping motion.

Integrated Product and Process Design for a Flapping Wing Drive Mechanism

Successful realization of a flapping wing micro-air vehicle (MAV) requires development of a light weight drive mechanism that can convert the continuous rotary motion of the motor into oscillatory flapping motion of the wings. The drive mechanism should have low weight to maximize the payload and battery capacity. It should also have high power transmission efficiency to maximize the operational range and to minimize weight of the motor. In order to make flapping wing MAVs attractive in search, rescue, and recovery efforts, they should be disposable from the cost point of view. Injection molded compliant drive mechanisms are an attractive design option because of manufacturing scalability and reduction in the number of parts. However, realizing compliant drive mechanism using injection molding requires use of multipiece multigate molds. Molding process constraints need to be considered during the design stage to successfully realize the drive mechanism. This paper describes an approach for determining the drive mechanism shape and size that meets both the design and molding requirements. The novel aspects of this work include (1) minimizing the number of mold pieces and (2) the use of sacrificial shape elements to reduce the impact of the weld-lines on the structural performance. The design generated by the approach described in this paper was utilized to realize an operational flapping wing MAV.

Time-Periodic Stability of a Flapping Insect Wing Structure in Hover

The wings of insectlike flapping-wing micro air vehicles experience time-periodic inertial stiffnesses during flapping motion. By modeling the wing structure as a thin beam, a linear time-periodic assumed-modes analysis is developed. The equations of motion of a flapping wing undergoing out-of-plane bending and torsion are derived. The homogeneous assumed-modes equations are nondimensionalized. It is shown that the nondimensional strain stiffness varies with the ratio of the wing's nonrotating natural frequencies to the flapping frequency, whereas the nondimensional, time-periodic inertial stiffnesses vary with the amplitudes of flapping and feathering motion. The parametric stability of a representative wing is assessed by applying Floquet analysis to the nondimensional equations of motion, and a scalable stability diagram is presented. Parametric instabilities of the wing structure, caused by time-periodic stiffnesses, are characterized and plotted in the time domain. The effects of important structural design properties on parametric stability are examined.

Some aspects regarding the adaptive control of a flying wing-micro air vehicle with flexible wing tips

The problem of automatic development of controllers for high maneuverable flexible flying wing micro air vehicles for the situations in which the exact characteristics are not known, has a strong m...

Design of a parallel crank-rocker flapping mechanism for insect-inspired micro air vehicles

In the current paper, a novel micro air vehicle (MAV) flapping mechanism for replicating insect wing kinematics is presented. Insects flap their wings in a complex motion that enables them to generate several unsteady aerodynamic mechanisms, which are extremely beneficial for lift production. A flapping wing MAV that can reproduce these aerodynamic mechanisms in a controlled manner is likely to outperform alternative flight platforms such as rotary wing MAVs. A biomimetic design approach was undertaken to develop a novel flapping mechanism, the parallel crank-rocker (PCR). Unlike several existing flapping mechanisms (which are compared using an original classification method), the PCR mechanism has an integrated flapping and pitching output motion which is not constrained. This allows the wing angle of attack, a key kinematic parameter, to be adjusted and enables the MAV to enact manoeuvres and have flight stability. Testing of a near-MAV scale PCR prototype using a high-speed camera showed that the flapping angle and adjustable angle of attack both closely matched predicted values, proving the mechanism can replicate insect wing kinematics. A mean lift force of 3.35 g was measured with the prototype in a hovering orientation and flapping at 7.15 Hz.

Electrospun non-woven membrane of poly(ethylene covinyl alcohol) end-capped with potassium sulfonate

Electrospinning is a technique used to produce micron to submicron diameter polymeric fibers. The low density of electrospun fibers is important when considering end-use applications as use on filtration material and lightweight wings for micro-air vehicles (MAV). A polymer of poly(ethylene covinyl alcohol) end-capped with sulfonate (EVOH-g-PSN) is synthesized by sulfonification of poly(ethylene-co-vinyl alcohol) (EVOH) with 1,3-propane sultone (PSN) and characterized by Fourier transform infrared spectroscopy. The polymer is soluble in water when the ratio of hydroxyl in EVOH versus PSN is more than 2.5 and insoluble in water when the ratio is less than 2.5. The EVOH-g-PSN non-woven membrane is prepared by electrospinning and the morphology of the membrane is examined using scanning electron microscopy (SEM) to identify any conformational changes that occur due to electrospinning voltage. The molar ratio of sulfur/potassium on the EVOH-g-PSN non-woven membranes were determined using a point scanning analysis with energy dispersive X-ray spectrometer (EDS). The EDS result show that the S/K molar ratios is almost equal to 1.0 indicating that the element of sulfur and potassium in the polymer could exist as the –SO 3K. The SEM shows that the high voltage makes the beaded filaments get into finer fibers.

Dynamics of Micro-Air-Vehicle with Flapping Wings

Small (approximately 6 inch long, or hand-held) reconnaissance micro air vehicles (MAVs) will fly inside buildings, and require hover for observation, and agility at low speeds to move in confined spaces. For this flight envelope insect-like flapping wings seem to be an optimal mode of flying. Investigation of the aerodynamics of flapping wing MAVs is very challenging. The problem involves complex unsteady, viscous flow (mainly laminar), with the moving wing generating vortices and interacting with them. At this early stage of research only a preliminary insight into the nature of the little known aerodynamics of MAVs has been obtained. This paper describes computational models for simulation of the controlled motion of a microelectromechanical flying insect – entomopter. The design of software simulation for entomopter flight (SSEF) is presented. In particular, we will estimate the flight control algorithms and performance for a Micromechanical Flying Insect (MFI), a 80–100 mm (wingtip-to-wingtip) device capable of sustained autonomous flight. The SSEF is an end-to-end tool composed of several modular blocks which model the wing aerodynamics and dynamics, the body dynamics, and in the future, the environment perception, control algorithms, the actuators dynamics, and the visual and inertial sensors. We present the current state of the art of its implementation, and preliminary results.