Toward Long-Endurance Flight- Tamkang’s Aspect of Micro Ornithopters

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A Study on the Control, Dynamics, and Hardware of Micro Aerial Biomimetic Flapping Wing Vehicles

Biological flight encapsulates 400 million years of evolutionary ingenuity and thus is the most efficient way to fly. If an engineering pursuit is not adhering to biomimetic inspiration, then it is probably not the most efficient design. An aircraft that is inspired by bird or other biological modes of flight is called an ornithopter and is the original design of the first airplanes. Flapping wings hold much engineering promise with the potential to produce lift and thrust simultaneously. In this research, modeling and simulation of a flapping wing vehicle is generated. The purpose of this research is to develop a control algorithm for a model describing flapping wing robotics. The modeling approach consists of initially considering the simplest possible model and subsequently building models of increasing complexity. This research finds that a proportional derivative feedback and feedforward controller applied to a nonlinear model is the most practical controller for a flapping system. Due to the complex aerodynamics of ornithopter flight, modeling and control are very difficult. Overall, this project aims to analyze and simulate different forms of biological flapping flight and robotic ornithopters, investigate different control methods, and also acquire understanding of the hardware of a flapping wing aerial vehicle

Analysis and Experiment of an Ultra-light Flapping Wing Aircraft

II Inspired by flying animals in nature especially birds, human has designed and attempted to achieve man-powered flapping wing aircraft in very early aviation history. Limited by the understanding of the aerodynamic theory and materials in practise, the bird-like aircraft remains as a dream and ambition for over a contrary. As the relevant knowledge and technology are fast developing in the last decade, the research topic becomes attractive again with encouraging results from a few full scale aircraft flight tests. Although it is suspected that a manned scale flapping wing may not be as efficient as fixed wing, the unique advantages of high manoeuvrability and short take-off and landing capability will keep flapping wing as one of the most potential type of personal and aerobatic aircraft in the future market. The aim of this project is to investigate into the feasibility and development of a bio-inspired bird-like man-powered ultra-light flapping wing aircraft (ULFWA). The project is based on analytical and experimental study of a scaled model taking an existing hang glider as the baseline airframe. Based on the characteristics of flying animals in nature and manmade hang glider properties, this thesis focuses its study on evaluating the feasibility and analysis of primarily a human powered aircraft. For this purpose, there are four main features as guidance in the ULFWA design. Firstly the flapping frequency was limited to below 2Hz. Secondly the hang glider airframe was adapted with a simple flapping mechanism design. Thirdly the flapping wing stroke and kinematics has been kept with the simplest and resonant movement to achieve high mechanical efficiency. Finally the wing structure has flexible rib of chord wise unsymmetrical bending stiffness to offset the aerodynamic lift loss in upstroke. An engine powered mechanism design was also studied as additional option of the ULFWA. The initial design and aerodynamic calculation of the ULFWA was based on the hang glider data including dimensions, MTOW (226 kg) and cruising speed. The unsteady aerodynamic lift and thrust forces were calculated based on Theodorsen’s theory and unsteady panel method in 2D and extended to 3D using strip theory. A set of optimal flapping kinematic parameters such as amplitude and combination of the heaving and pitching motion of the 2D wing section were determined by calculation and comparison in the limited range. Considering the maximum power and lag motion that human could achieve, the flapping frequency in the ULFWA design is limited to 1Hz. This slow motion leads to a much lower propulsive efficiency in terms of the optimum Strouhal Number (St=0.2-0.4), which was used as the design reference. Mechanism and structure design with inertia force calculation was then completed based on the kinematics. This led to the evaluation of power requirement, which was divided into two components, drag and inertia forces. The results show that the ULFWA needs minimum 2452.25W (equals to 3.29Bhp) to maintain sustainable cruise flight. In order to demonstrate the ULFWA flapping mechanism and structure design, a 1:10 scaled model with two pairs of wings of different stiffness were built for testing and measurement. Two servomotors were used as to simulate human power actuation. With this model, simplified structure and one of mechanism designs was shown. Four experiments were carried out to measure the model’s lift and thrust force. Because of the limited response of the servo motors, the maximum flapping frequency achieved is only 0.75 Hz in the specified flapping amplitude which is close to reality and has improvement margin. By reducing the flapping amplitude, the frequency can be increased to gain higher thrust. Although it is fund that the result from scaled model test is a little lower than theoretical result, it has demonstrated the feasibility and potential of human powered flapping wings aircraft

Development, Design, Manufacture and Test of Flapping Wing Micro Aerial Vehicles

The field of FlappingWing Micro Air Vehicles (FWMAV) has been of interest in recent years and as shown to have many aerodynamic principles unconventional to traditional aviation aerodynamics. In addition to traditional manufacturing techniques, MAVs have utilized techniques and machines that have gained significant interest and investment over the past decade, namely in additive manufacturing. This dissertation discusses the techniques used to manufacture and build a 30 gram-force (gf) model which approaches the lower limit allowed by current commercial off-the-shelf items. The vehicle utilizes a novel mechanism that minimizes traditional kinematic issues associated with four bar mechanisms for flapping wing vehicles. A kinematic reasoning for large amplitude flapping is demonstrated namely, by lowering the cycle averaged angular acceleration of the wings. The vehicle is tested for control authority and lift of the mechanism using three servo drives for wing manipulation. The study then discusses the wing design, manufacturing techniques and limitations involved with the wings for a FWMAV. A set of 17 different wings are tested for lift reaching lifts of 38 gf using the aforementioned vehicle design. The variation in wings spurs the investigation of the flow patterns generated by the flexible wings and its interactions for multiple flapping amplitudes. Phase-lock particle image velocimetry (PIV) is used to investigate the unsteady flows generated by the vehicle. A novel flow pattern is experimentally found, namely “trailing edge vortex capture” upon wing reversal for all three flapping amplitudes, alluding to a newly discovered addition to the lift enhancing effect of wake capture. This effect is believed to be a result of flexible wings and may provide lift enhancing characteristics to wake capture

IMPROVED PREDICTION OF FLAPPING WING AERIAL VEHICLE PERFORMANCE THROUGH COMPONENT INTERACTION MODELING

Flapping wing aerial vehicles offer the promise of versatile performance, however prediction of flapping wing aerial vehicle performance is a challenging task because of complex interconnectedness in vehicle functionality. To address this challenge, performance is estimated by using component-level modeling as a foundation. Experimental characterization of the drive motors, battery, and wings is performed to identify important functional characteristics and enable selection of appropriate modeling techniques. Component-level models are then generated that capture the performance of each vehicle component. Validation of each component-level model shows where errors are eliminated by capturing important dynamic functionality. System-level modeling is then performed by creating linkages between component-level models that have already been individually validated through experimental testing, leading to real-world functional constraints that are realized and correctly modeled at the system level. The result of this methodology is a system-level performance prediction that offers the ability to explore the effects of changing vehicle components as well as changing functional properties, while maintaining computational tractability. Simulated results are compared to experimental flight test data collected with an instrumented flapping wing aerial vehicle, and are shown to offer good accuracy in estimation of system-level performance properties

Computational Fluid Dynamics Simulations of Oscillating Wings and Comparison to Lifting-Line Theory

Computational fluid dynamics (CFD) analysis was performed in order to compare the solutions of oscillating wings with Prandtl’s lifting-line theory. Quasi-steady and steady-periodic simulations were completed using the CFD software Star-CCM+. The simulations were performed for a number of frequencies in a pure plunging setup. Additional simulations were then completed using a setup of combined pitching and plunging at multiple frequencies. Results from the CFD simulations were compared to the quasi-steady lifting-line solution in the form of the axial-force, normal-force, power, and thrust coefficients, as well as the efficiency obtained for each simulation. The mean values were evaluated for each simulation and compared to the quasi-steady lifting-line solution. It was found that as the frequency of oscillation increased, the quasi-steady lifting-line solution was decreasingly accurate in predicting solutions

Classical Engineering Systems Provide Behavioral Analog for Ephemeral Insect and Plant Biomechanics

In this dissertation we consider ephemeral behaviors of two small-scale living systems, mosquitoes and citrus fruit reservoirs. While these two systems share few obvious commonalities, they both express life events that are complex and conclude within approximately 50 milliseconds. We utilize high-speed videography, between 1,000-16,000 fps, to detail how complex behavior can be modeled as classical engineering systems. Beginning with the larger organism we assessed the landing and takeoff behavior of Aedes aegypti mosquitoes to ascertain the secrets of their covert interaction with humans. At takeoff, mosquitoes decrease pushing contact time with substrates of low friction through a modified takeoff behavior of striking the substrate with a hind-leg prior to a classic push phase. We propose a 2D analog where the striking leg acts as a rotating cantilever about a fixed end that generates upward momentum with a small penalty in body rotation. Landing mosquitoes are filmed in 2D and modeled as a mass-spring-damper system whose natural frequency, damping coefficient, ratio, and spring constant are determined experimentally and validated through a nonlinear least square solver fitting of the free vibration ODE\u27s general solution. Results indicate mosquitoes behave as an underdamped system to scrub their incoming momentum through extending impact duration, effectively reducing temporal impact force. Shrinking in scale we proceed to characterize citrus reservoir rupture as a passive system capable of microjetting oil through expanding orifices at accelerations greater than 5000 gravities. Citrus reservoirs are modeled as ellipsoidal pressure vessels capped by a thin membrane of contrasting stiffness to the surrounding ductile compressible albedo

Quantitative analysis of take-off forces in birds

The increasing interest on Unmanned Air Vehicles (UAV’s) and their several utilities blended with the need of easy carrying and also the stealth, lead to the need to create the concept of Micro Air Vehicles (MAV’s) and the Nano Air Vehicles (NAV’s). Due to the current interest and the present lack of knowledge on the insect’s and bird’s flight, this study was intended to interpret the forces involved on the moment of the take-off of a bird, recurring to an experiment involving a fast data acquisition force sensor and high speed camera, in addition known facts from earlier studies. In order to do that a bibliographic revision was done, to know what was already studied and to find what could yet be studied. That way could be formed a link on the factors involved on the propulsion of a bird at the moment of take-off. The main conclusions obtained by this work is that the bird can produce movements that will enhance the total moment when the bird stretches its neck forward and moving head down followed by stretching even more its neck and moving head up impelling himself into the air, resulting in a main role on the mechanical forces (against perch) for the bird first moments momentum. Columba livia can generate about 4 times its weight worth mechanic force (against perch) and above 8 times its weight during the 2nd downstroke.O interesse crescente nos Veículos Aéreos não Tripulados “Unmanned Air Vehicles (UAV’s)” e suas diversas utilidades em conjunto com a necessidade de seu fácil transporte e furtividade, levaram à necessidade de criar o conceito dos Micro Veículos Aéreos “Micro Air Vehicles (MAV’s)” e os Nano Veículos Aéreos “Nano Air Vehicles (NAV’s)”. Este tipo de veículos tem como fonte inspiradora os insetos e aves devido à necessária produção simultânea de sustentação e propulsão. Tal como no voo convencional, também no voo animal podem ser identificadas as fases de levantamento (descolagem) e aterragem como diferenciadas do voo longe de uma superfície de apoio. Este trabalho é dedicado ao estudo da fase de levantamento de voo de uma ave columba livia. Foram realizadas experiências para medir a força inicial produzida pela ave para iniciar o voo e a respetiva trajetória na zona próxima do ponto de apoio inicial. Estas medidas foram efetuadas com um sensor de força dotado de elevada velocidade de aquisição de dados e uma camara de alta velocidade. As principais conclusões obtidas com a realização deste trabalho é o facto de que a ave consegue produzir movimentos, que aumentar o momento total quando a ave estica o pescoço para a frente e movendo a cabeça para baixo seguido por continuação de esticamento do pescoço e movimento da cabeça para cima impelindo-se para o ar, resultando num papel principal relativamente às forças mecânicas (contra o poleiro) para o momento linear actuante nos primeiros momentos. Columba livia consegue gerar cerca de 4 vezes o seu peso em força mecânica e acima de 8 vezes o seu peso durante o 2º downstroke

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

A Biomimetic, Energy-Harvesting, Obstacle-Avoiding, Path-Planning Algorithm for UAVs

This dissertation presents two new approaches to energy harvesting for Unmanned Aerial Vehicles (UAV). One method is based on the Potential Flow Method (PFM); the other method seeds a wind-field map based on updraft peak analysis and then applies a variant of the Bellman-Ford algorithm to find the minimum-cost path. Both methods are enhanced by taking into account the performance characteristics of the aircraft using advanced performance theory. The combined approach yields five possible trajectories from which the one with the minimum energy cost is selected. The dissertation concludes by using the developed theory and modeling tools to simulate the flight paths of two small Unmanned Aerial Vehicles (sUAV) in the 500 kg and 250 kg class. The results show that, in mountainous regions, substantial energy can be recovered, depending on topography and wind characteristics. For the examples presented, as much as 50% of the energy was recovered for a complex, multi-heading, multi-altitude, 170 km mission in an average wind speed of 9 m/s. The algorithms constitute a Generic Intelligent Control Algorithm (GICA) for autonomous unmanned aerial vehicles that enables an extraction of atmospheric energy while completing a mission trajectory. At the same time, the algorithm automatically adjusts the flight path in order to avoid obstacles, in a fashion not unlike what one would expect from living organisms, such as birds and insects. This multi-disciplinary approach renders the approach biomimetic, i.e. it constitutes a synthetic system that “mimics the formation and function of biological mechanisms and processes.