The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
James E. Hubbard - One of the best experts on this subject based on the ideXlab platform.
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Understanding the Relationship Between Pitch Agility and Propulsive Aerodynamic Forces in Bio-Inspired Flapping Wing Vehicles
Volume 2: Integrated System Design and Implementation; Structural Health Monitoring; Bioinspired Smart Materials and Systems; Energy Harvesting, 2015Co-Authors: Zohaib Hasnain, James E. Hubbard, Mary Frecker, Joseph Calogero, Aimy WissaAbstract:Ornithopters, or flapping wing mechanical birds, represent a unique category of aerial vehicles that fill a need for small-scale, agile, long range, and payload-capable Flight vehicles. This study focuses on understanding the relationship between the propulsive aerodynamic forces and pitch agility in these flapping wing vehicles. Using analytical methods, the aerodynamic moment acting upon a wing undergoing elastic flapping was calculated. A method to determine the pitch stiffness of the vehicle was then derived using a preexisting stability analysis. This method was used to demonstrate that pitch agility in flapping wing birds is intricately tied to the flapping cycle with different parts of the cycle creating stabilizing and destabilizing effects. The results indicated that pitch agility, and propulsive force generation, have a dependency on the shape of the wing, and that deformations such as bend and sweep are capable of making the vehicle more agile. Contact-aided compliant mechanisms with nonlinear stiffness were designed and inserted into the wing of an ornithopter to induce controlled morphing. These elements have varying stiffness during the upstroke and downstroke parts of the cycle which introduces an asymmetry between the two halves of the flapping cycle. The resulting flapping motion exhibited a two fold increase in horizontal propulsive force over the baseline case. A motion tracking system was used to capture the free Flight response of the ornithopter in Steady Level Flight. This information was then used to calculate the pitch stiffness of the ornithopter with a rigid spar, and, one with a nonlinear compliant element inserted into the spar to induce a desired shape change. The results revealed that an upstroke in which the aerodynamic forces are similar in magnitude to that of the downstroke, may be necessary to make the vehicle more agile, and, that there is a compromise between vehicle agility and Flight propulsive forces.Copyright © 2015 by ASME
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Stability Analysis of the Wing Leading Edge Spar of a Passively Morphing Ornithopter
Volume 2: Mechanics and Behavior of Active Materials; Integrated System Design and Implementation; Bioinspired Smart Materials and Systems; Energy Har, 2014Co-Authors: Aimy Wissa, James E. Hubbard, Joseph Calogero, Mary FreckerAbstract:This paper presents a stability model for the wing leading edge spar of a test ornithopter. The long-term goal of this research effort is to passively improve the performance of ornithopters during Steady Level Flight by implementing a set of wing kinematics found in natural flyers. The desired kinematics is achieved by inserting a compliant mechanism called a compliant spine into the wing leading edge spar to mimic the function of an avian wrist. The stiffness of the compliant spine is time varying and given the nature of flapping Flight, it is periodic. Introducing a variable stiffness compliant mechanism into the leading edge spar of the ornithopter affects its structural stability. Therefore, a stability analysis is required. In order to start the stability analysis, an analytical model of the ornithopter wing leading edge spar with a compliant spine inserted in is necessary. In the model, the compliant spine is modeled as a torsional spring with a sinusoidal stiffness function. Moreover, the equations of motion of the wing leading edge spar-spine system can be written in the form of non-homogeneous Mathieu’s equations, which has well-known stability criteria. The analytical system response is then validated using experimental data taken at NASA Langley Research Center. Results show that the analytical spine angular deflection agrees with the experimental angular deflection data within 11%. Stability was then demonstrated using both analytical and graphical proving that the response of leading edge spar with a compliant spine design inserted at 37% of the wing half span is bounded.Copyright © 2014 by ASME
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Design, Fabrication and Testing of a Passively Morphing Ornithopter Wing for Increased Lift and Agility
2012Co-Authors: James E. Hubbard, Mary FreckerAbstract:Abstract : Over the last few decades, flapping wing Unmanned Aerial Vehicles (UAVs), or ornithopters, have shown the potential for advancing and revolutionizing platform performance in both the civil and military sectors. An ornithopter is unique in that it can combine the agility and maneuverability of rotary wing aircraft with excellent performance in low Reynolds number Flight regimes. The objective of the proposed work was to develop methods to design novel ornithopter wings that allow passive wing morphing. Passive morphing was achieved through an optimally designed compliant spine that mimics the function of a bird s wrist. A multi-objective optimization was carried out and several designs resulting from this optimization were bench-top and free Flight tested. The presence of a 1DOF compliant spine in the ornithopter wing was found to introduce an asymmetry between the upstroke and the downstroke. For any given flapping frequency or throttle setting, the ornithopter with the compliant spine consumed less electric power, produced more mean lift and did not incur any thrust penalties when compared to the ornithopter without the compliant spine. Power reduction of 44.7% was achieved at the Steady Level Flight flapping frequency, lift gains of up to 16% of the ornithopter's weight was also realized without incurring any thrust penalties. Also during the free Flight test, the ornithopter with the compliant spine inserted in its wings reduced the overall negative center of mass acceleration during one flapping cycle by 22 %. The negative acceleration reduction may translate into overall lift gains. Thus the Steady Level Flight performance was improved due to the presence of the compliant spine. Therefore compliant mechanisms proved to be not only feasible, but also beneficial for application to general air vehicle design.
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Passively morphing ornithopter wings constructed using a novel compliant spine: design and testing
Smart Materials and Structures, 2012Co-Authors: James E. HubbardAbstract:Ornithopters or flapping wing uncrewed aerial vehicles (UAVs) have potential applications in civil and military sectors. Amongst the UAVs, ornithopters have a unique ability to fly in low Reynolds number Flight regimes and also have the agility and maneuverability of rotary wing aircraft. In nature, birds achieve such performance by exploiting various wing kinematics known as gaits. The objective of this work is to improve the Steady Level Flight performance of an ornithopter by implementing a continuous vortex gait using a novel passive compliant spine inserted in the ornithopter's wings. This paper presents an optimal compliant spine concept for ornithopter applications. A quasi-static design optimization procedure was formulated to design the compliant spine. Finite element analysis was performed on a first generation spine and the spine was fabricated. This prototype was then tested by inserting it into an ornithopter's wing leading edge spar. The effect of inserting the compliant spine into the wings on the electric power required, the aerodynamic loads and the wing kinematics was studied. The ornithopter with the compliant spines inserted in its wings consumed 45% less power and produced an additional 16% of its weight in mean lift compared to the same ornithopter without the compliant spine. The results indicate that this passive morphing approach is promising for improved Steady Level Flight performance.
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Testing of novel compliant spines for passive wing morphing
ASME 2011 Conference on Smart Materials Adaptive Structures and Intelligent Systems Volume 2, 2011Co-Authors: Aimy Wissa, James E. Hubbard, Mary Frecker, Yashwanth Tummala, Alexander BrownAbstract:Flapping wing Unmanned Aerial Vehicles (UAVs) or ornithopters are proliferating in both the civil and military markets. Ornithopters have the potential to combine the agility and maneuverability of rotary wing aircraft with excellent performance in low Reynolds number Flight regimes. These traits promise optimized performance over multiple mission scenarios. Nature achieves this broad performance in birds using wing gaits that are optimized for a particular Flight regime. The goal of this work is to improve the performance of ornithopters during Steady Level Flight by passively implementing the Continuous Vortex Gait (CVG) found in natural avian flyers. In this paper we present new experimental results for a one degree of freedom (1DOF) compliant spine which was inserted into an experimental test ornithopter leading edge wing spar in order to achieve the desired kinematics. The lift and thrust along with electric power metrics at different flapping frequencies were measured using a six-channel load cell and a current senor, respectively. These metrics were determined for the test ornithopter both with and without the compliant spine insert. Initial results validate the ability of our compliant spine design to withstand the loads seen during Flight at flapping frequencies of up to and including 5 Hz. For the ornithopter test platform used in the study, inserting the compliant spines into the wing leading edge spar accurately simulates the CVG increasing the mean lift by 16%, and reducing the power consumed by 45% without incurring any thrust penalties.Copyright © 2011 by ASME
Kamran Turkoglu - One of the best experts on this subject based on the ideXlab platform.
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Real-Time First Order Guidance Strategies for Trajectory Optimization in UAVs by Utilizing Wind Energy
Journal of Aircraft, 2017Co-Authors: Kamran TurkogluAbstract:This paper presents real-time guidance strategies for unmanned aerial vehicles (UAVs) that can be used to enhance their Flight endurance by utilizing {\sl insitu} measurements of wind speeds and wind gradients. In these strategies, periodic adjustments would be made in the airspeed and/or heading angle command for the UAV to minimize a projected power requirement at some future time. In this paper, UAV Flights are described by a three-dimensional dynamic point-mass. Onboard closed-loop trajectory tracking logics that follow airspeed vector commands are modeled using the method of feedback linearization. A generic wind field model is assumed that consists of a constant term plus terms that vary sinusoidally with respect to the location. To evaluate the benefits of these strategies in enhancing UAV Flight endurance, a reference strategy is introduced in which the UAV would seek to follow the desired airspeed in a Steady Level Flight under zero wind. A performance measure is defined as the average power consumption both over a specified time interval and over different initial heading angles of the UAV. A relative benefit criterion is then defined as the percentage improvement of the performance measure of a proposed strategy over that of the reference strategy. Extensive numerical simulations are conducted. Results demonstrate the benefits and trends of power savings of the proposed real-time guidance strategies.
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ACC - Real-time guidance strategies for optimizing aircraft performance in stochastic wind conditions
2014 American Control Conference, 2014Co-Authors: Kamran TurkogluAbstract:This study presents real-time guidance strategies for unmanned aerial vehicles (UAVs) that can be used to enhance their Flight endurance by utilizing insitu measurements of wind speeds and wind gradients. In these strategies, periodic adjustments can be made in the airspeed and/or heading angle command for the UAV to minimize a projected power requirement at some future time. In this research, UAV Flights are described by a three-dimensional dynamic point-mass model. Onboard closed-loop trajectory tracking logics that follow airspeed vector commands are modeled using the method of feedback linearization. To evaluate the benefits of these strategies in enhancing UAV Flight endurance, a reference strategy is introduced in which the UAV would follow the optimal airspeed command in a Steady Level Flight under zero wind conditions. A performance measure is defined as the average power consumption both over a specified time interval and over different initial heading angles of the UAV. A relative benefit criterion is then defined as the percentage improvement in the performance measure of a proposed strategy over that of the reference strategy. Extensive numerical simulations are conducted to show efficiency and applicability of the proposed algorithms. Results demonstrate the efficiency, benefits and trends of power savings of the proposed real-time guidance strategies in Level Flights.
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Real-Time Second-Order Optimal Guidance Strategies for Optimizing Aircraft Performance in Stochastic Wind Conditions
arXiv: Optimization and Control, 2014Co-Authors: Kamran TurkogluAbstract:This study presents a real-time guidance strategy for an unmanned aerial vehicles (UAVs) that can be used to enhance their Flight endurance by utilizing insitu measurements of wind speeds and wind gradients. In these strategies, periodic adjustments are made in the airspeed and/or heading angle command, in Level Flights, for the UAV to minimize a projected power requirement. In this study, UAV dynamics are described by a three-dimensional dynamic point-mass model. A stochastic wind field model has been used to analyze the effect of the wind in the process. Onboard closed-loop trajectory tracking logics that follow airspeed vector commands are modeled using the method of feedback linearization. To evaluate the benefits of these strategies in enhancing UAV Flight endurance, a reference strategy is introduced in which the UAV would follow the optimal airspeed command in a Steady Level Flight under zero wind conditions. A performance measure is defined as the average power consumption with respect to no wind case. Different scenarios have been evaluated both over a specified time interval and over different initial heading angles of the UAV. A relative benefit criterion is then defined as the percentage improvement in the performance measure of a proposed strategy over that of the reference strategy. Extensive numerical simulations are conducted to show efficiency and applicability of the proposed algorithms. Results demonstrate possible power savings of the proposed real-time guidance strategies in Level Flights, by utilization of wind energy.
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Real-Time Insitu Strategies for Enhancing UAV Endurance by Utilizing Wind Energy
AIAA Guidance Navigation and Control Conference, 2009Co-Authors: Kamran Turkoglu, Yiyuan J. Zhao, Brian CapozziAbstract:This paper presents real-time practical strategies for enhancing the endurance of Unmanned Aerial Vehicle (UAV) Flights by utilizing wind energy. Consistent with actual Flight, no regional knowledge of the wind field is assumed. Rather, the technique relies solely on making “optimal” decisions at each successive time instant, given the instantaneous values of estimated local wind speeds. Based on these estimates, optimal airspeed and/or heading angle corrections are determined to minimize the instantaneous power requirement for Steady Level Flight. UAV dynamics are described in terms of a dynamic point-mass model, and vehicle motion is constrained via boundary controls to a three-dimensional region around a specified target point. Models of closed-loop trajectory tracking are developed using the method of dynamic inversion for both airspeed vector tracking and boundary trajectory tracking. A nominal reference trajectory is assumed in which the UAV flies a fixed radius, constant altitude orbit with an airspeed that would maximize the endurance in zero wind. Simulations conducted for varying wind patterns compare the average power consumption of the proposed strategy with that of the reference trajectory. Obtained results indicate a potential saving in power consumption and in endurance of the UAV by simply using the appropriate wind component instantaneously during the Flight regime.
Andrew J. Lucas - One of the best experts on this subject based on the ideXlab platform.
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Wave-slope soaring of the brown pelican
Movement Ecology, 2021Co-Authors: Ian A. Stokes, Andrew J. LucasAbstract:Abstract Background From the laboratory at Scripps Institution of Oceanography, it is common to see the brown pelican (Pelecanus occidentalis) traveling along the crests of ocean waves just offshore of the surf-zone. When flying in this manner, the birds can travel long distances without flapping, centimeters above the ocean’s surface. Here we derive a theoretical framework for assessing the energetic savings related to this behavior, ‘wave-slope soaring,’ in which an organism in Flight takes advantage of localized updrafts caused by traveling ocean surface gravity waves. Methods The energy cost of Steady, constant altitude Flight in and out of ground effect are analyzed as controls. Potential flow theory is used to quantify the ocean wave-induced wind associated with near-shoaling, weakly nonlinear, shallow water ocean surface gravity waves moving through an atmosphere initially at rest. Using perturbation theory and the Green’s function for Laplace’s equation in 2D with Dirichlet boundary conditions, we obtain integrals for the horizontal and vertical components of the wave-induced wind in a frame of reference moving with the wave. Wave-slope soaring Flight is then analyzed using an energetics-based approach for waves under a range of ocean conditions and the body plan of P. occidentalis. Results For ground effect Flight, we calculate a ∼15 - 25% reduction in cost of transport as compared with Steady, Level Flight out of ground effect. When wave-slope soaring is employed at Flight heights ∼2m in typical ocean conditions (2m wave height, 15s period), we calculate 60-70% reduction in cost of transport as compared with Flight in ground effect. A relatively small increase in swell amplitude or decrease in Flight height allows up to 100% of the cost of transport to be offset by wave-slope soaring behavior. Conclusions The theoretical development presented here suggests there are energy savings associated with wave-slope soaring. Individual brown pelicans may significantly decrease their cost of transport utilizing this mode of Flight under typical ocean conditions. Thus wave-slope soaring may provide fitness benefit to these highly mobile organisms that depend on patchy prey distribution over large home ranges.
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Wave-slope soaring of the brown pelican.
Movement ecology, 2021Co-Authors: Ian A. Stokes, Andrew J. LucasAbstract:From the laboratory at Scripps Institution of Oceanography, it is common to see the brown pelican (Pelecanus occidentalis) traveling along the crests of ocean waves just offshore of the surf-zone. When flying in this manner, the birds can travel long distances without flapping, centimeters above the ocean's surface. Here we derive a theoretical framework for assessing the energetic savings related to this behavior, 'wave-slope soaring,' in which an organism in Flight takes advantage of localized updrafts caused by traveling ocean surface gravity waves. The energy cost of Steady, constant altitude Flight in and out of ground effect are analyzed as controls. Potential flow theory is used to quantify the ocean wave-induced wind associated with near-shoaling, weakly nonlinear, shallow water ocean surface gravity waves moving through an atmosphere initially at rest. Using perturbation theory and the Green's function for Laplace's equation in 2D with Dirichlet boundary conditions, we obtain integrals for the horizontal and vertical components of the wave-induced wind in a frame of reference moving with the wave. Wave-slope soaring Flight is then analyzed using an energetics-based approach for waves under a range of ocean conditions and the body plan of P. occidentalis. For ground effect Flight, we calculate a ∼15 - 25% reduction in cost of transport as compared with Steady, Level Flight out of ground effect. When wave-slope soaring is employed at Flight heights ∼2m in typical ocean conditions (2m wave height, 15s period), we calculate 60-70% reduction in cost of transport as compared with Flight in ground effect. A relatively small increase in swell amplitude or decrease in Flight height allows up to 100% of the cost of transport to be offset by wave-slope soaring behavior. The theoretical development presented here suggests there are energy savings associated with wave-slope soaring. Individual brown pelicans may significantly decrease their cost of transport utilizing this mode of Flight under typical ocean conditions. Thus wave-slope soaring may provide fitness benefit to these highly mobile organisms that depend on patchy prey distribution over large home ranges.
Mary Frecker - One of the best experts on this subject based on the ideXlab platform.
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Understanding the Relationship Between Pitch Agility and Propulsive Aerodynamic Forces in Bio-Inspired Flapping Wing Vehicles
Volume 2: Integrated System Design and Implementation; Structural Health Monitoring; Bioinspired Smart Materials and Systems; Energy Harvesting, 2015Co-Authors: Zohaib Hasnain, James E. Hubbard, Mary Frecker, Joseph Calogero, Aimy WissaAbstract:Ornithopters, or flapping wing mechanical birds, represent a unique category of aerial vehicles that fill a need for small-scale, agile, long range, and payload-capable Flight vehicles. This study focuses on understanding the relationship between the propulsive aerodynamic forces and pitch agility in these flapping wing vehicles. Using analytical methods, the aerodynamic moment acting upon a wing undergoing elastic flapping was calculated. A method to determine the pitch stiffness of the vehicle was then derived using a preexisting stability analysis. This method was used to demonstrate that pitch agility in flapping wing birds is intricately tied to the flapping cycle with different parts of the cycle creating stabilizing and destabilizing effects. The results indicated that pitch agility, and propulsive force generation, have a dependency on the shape of the wing, and that deformations such as bend and sweep are capable of making the vehicle more agile. Contact-aided compliant mechanisms with nonlinear stiffness were designed and inserted into the wing of an ornithopter to induce controlled morphing. These elements have varying stiffness during the upstroke and downstroke parts of the cycle which introduces an asymmetry between the two halves of the flapping cycle. The resulting flapping motion exhibited a two fold increase in horizontal propulsive force over the baseline case. A motion tracking system was used to capture the free Flight response of the ornithopter in Steady Level Flight. This information was then used to calculate the pitch stiffness of the ornithopter with a rigid spar, and, one with a nonlinear compliant element inserted into the spar to induce a desired shape change. The results revealed that an upstroke in which the aerodynamic forces are similar in magnitude to that of the downstroke, may be necessary to make the vehicle more agile, and, that there is a compromise between vehicle agility and Flight propulsive forces.Copyright © 2015 by ASME
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Stability Analysis of the Wing Leading Edge Spar of a Passively Morphing Ornithopter
Volume 2: Mechanics and Behavior of Active Materials; Integrated System Design and Implementation; Bioinspired Smart Materials and Systems; Energy Har, 2014Co-Authors: Aimy Wissa, James E. Hubbard, Joseph Calogero, Mary FreckerAbstract:This paper presents a stability model for the wing leading edge spar of a test ornithopter. The long-term goal of this research effort is to passively improve the performance of ornithopters during Steady Level Flight by implementing a set of wing kinematics found in natural flyers. The desired kinematics is achieved by inserting a compliant mechanism called a compliant spine into the wing leading edge spar to mimic the function of an avian wrist. The stiffness of the compliant spine is time varying and given the nature of flapping Flight, it is periodic. Introducing a variable stiffness compliant mechanism into the leading edge spar of the ornithopter affects its structural stability. Therefore, a stability analysis is required. In order to start the stability analysis, an analytical model of the ornithopter wing leading edge spar with a compliant spine inserted in is necessary. In the model, the compliant spine is modeled as a torsional spring with a sinusoidal stiffness function. Moreover, the equations of motion of the wing leading edge spar-spine system can be written in the form of non-homogeneous Mathieu’s equations, which has well-known stability criteria. The analytical system response is then validated using experimental data taken at NASA Langley Research Center. Results show that the analytical spine angular deflection agrees with the experimental angular deflection data within 11%. Stability was then demonstrated using both analytical and graphical proving that the response of leading edge spar with a compliant spine design inserted at 37% of the wing half span is bounded.Copyright © 2014 by ASME
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Design, Fabrication and Testing of a Passively Morphing Ornithopter Wing for Increased Lift and Agility
2012Co-Authors: James E. Hubbard, Mary FreckerAbstract:Abstract : Over the last few decades, flapping wing Unmanned Aerial Vehicles (UAVs), or ornithopters, have shown the potential for advancing and revolutionizing platform performance in both the civil and military sectors. An ornithopter is unique in that it can combine the agility and maneuverability of rotary wing aircraft with excellent performance in low Reynolds number Flight regimes. The objective of the proposed work was to develop methods to design novel ornithopter wings that allow passive wing morphing. Passive morphing was achieved through an optimally designed compliant spine that mimics the function of a bird s wrist. A multi-objective optimization was carried out and several designs resulting from this optimization were bench-top and free Flight tested. The presence of a 1DOF compliant spine in the ornithopter wing was found to introduce an asymmetry between the upstroke and the downstroke. For any given flapping frequency or throttle setting, the ornithopter with the compliant spine consumed less electric power, produced more mean lift and did not incur any thrust penalties when compared to the ornithopter without the compliant spine. Power reduction of 44.7% was achieved at the Steady Level Flight flapping frequency, lift gains of up to 16% of the ornithopter's weight was also realized without incurring any thrust penalties. Also during the free Flight test, the ornithopter with the compliant spine inserted in its wings reduced the overall negative center of mass acceleration during one flapping cycle by 22 %. The negative acceleration reduction may translate into overall lift gains. Thus the Steady Level Flight performance was improved due to the presence of the compliant spine. Therefore compliant mechanisms proved to be not only feasible, but also beneficial for application to general air vehicle design.
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Testing of novel compliant spines for passive wing morphing
ASME 2011 Conference on Smart Materials Adaptive Structures and Intelligent Systems Volume 2, 2011Co-Authors: Aimy Wissa, James E. Hubbard, Mary Frecker, Yashwanth Tummala, Alexander BrownAbstract:Flapping wing Unmanned Aerial Vehicles (UAVs) or ornithopters are proliferating in both the civil and military markets. Ornithopters have the potential to combine the agility and maneuverability of rotary wing aircraft with excellent performance in low Reynolds number Flight regimes. These traits promise optimized performance over multiple mission scenarios. Nature achieves this broad performance in birds using wing gaits that are optimized for a particular Flight regime. The goal of this work is to improve the performance of ornithopters during Steady Level Flight by passively implementing the Continuous Vortex Gait (CVG) found in natural avian flyers. In this paper we present new experimental results for a one degree of freedom (1DOF) compliant spine which was inserted into an experimental test ornithopter leading edge wing spar in order to achieve the desired kinematics. The lift and thrust along with electric power metrics at different flapping frequencies were measured using a six-channel load cell and a current senor, respectively. These metrics were determined for the test ornithopter both with and without the compliant spine insert. Initial results validate the ability of our compliant spine design to withstand the loads seen during Flight at flapping frequencies of up to and including 5 Hz. For the ornithopter test platform used in the study, inserting the compliant spines into the wing leading edge spar accurately simulates the CVG increasing the mean lift by 16%, and reducing the power consumed by 45% without incurring any thrust penalties.Copyright © 2011 by ASME
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DESIGN OF A PASSIVELY MORPHING ORNITHOPTER WING USING A NOVEL COMPLIANT SPINE
ASME 2010 Conference on Smart Materials Adaptive Structures and Intelligent Systems Volume 1, 2010Co-Authors: Yashwanth Tummala, Mary Frecker, Aimy Wissa, James E. HubbardAbstract:A new scheme to design morphing ornithopter wings using a passive compliant spine is presented in this paper. The objective of this work is to optimize Steady Level Flight performance of an ornithopter by passively implementing the Continuous Vortex Gait (CVG) which requires bending, twist and sweep coupling during the upstroke. An optimization problem is formulated to design a compliant spine for pre-specified bending, sweep, and twist deflections. As a first step to achieving these 3 DOF kinematics, a 1 DOF compliant spine is considered to produce a specified bending deflection during the upstroke for drag reduction while remaining stiff during the downstroke for increased lift. The effect of the relevant geometric design parameters, namely contact gap, angle, and hinge geometry, are considered and optimized to achieve the aforementioned kinematics for both single and multiple joints, which make up a compliant spine. Results presented include the spine design optimization procedure, as well as a complete analysis for a 1DOF compliant spine to illustrate the efficacy of the methodology. This compliant spine design methodology and optimization procedure will be used, in the future, to design the 3-DOF compliant spine for the passively morphing ornithopter.© 2010 ASME
Aimy Wissa - One of the best experts on this subject based on the ideXlab platform.
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Understanding the Relationship Between Pitch Agility and Propulsive Aerodynamic Forces in Bio-Inspired Flapping Wing Vehicles
Volume 2: Integrated System Design and Implementation; Structural Health Monitoring; Bioinspired Smart Materials and Systems; Energy Harvesting, 2015Co-Authors: Zohaib Hasnain, James E. Hubbard, Mary Frecker, Joseph Calogero, Aimy WissaAbstract:Ornithopters, or flapping wing mechanical birds, represent a unique category of aerial vehicles that fill a need for small-scale, agile, long range, and payload-capable Flight vehicles. This study focuses on understanding the relationship between the propulsive aerodynamic forces and pitch agility in these flapping wing vehicles. Using analytical methods, the aerodynamic moment acting upon a wing undergoing elastic flapping was calculated. A method to determine the pitch stiffness of the vehicle was then derived using a preexisting stability analysis. This method was used to demonstrate that pitch agility in flapping wing birds is intricately tied to the flapping cycle with different parts of the cycle creating stabilizing and destabilizing effects. The results indicated that pitch agility, and propulsive force generation, have a dependency on the shape of the wing, and that deformations such as bend and sweep are capable of making the vehicle more agile. Contact-aided compliant mechanisms with nonlinear stiffness were designed and inserted into the wing of an ornithopter to induce controlled morphing. These elements have varying stiffness during the upstroke and downstroke parts of the cycle which introduces an asymmetry between the two halves of the flapping cycle. The resulting flapping motion exhibited a two fold increase in horizontal propulsive force over the baseline case. A motion tracking system was used to capture the free Flight response of the ornithopter in Steady Level Flight. This information was then used to calculate the pitch stiffness of the ornithopter with a rigid spar, and, one with a nonlinear compliant element inserted into the spar to induce a desired shape change. The results revealed that an upstroke in which the aerodynamic forces are similar in magnitude to that of the downstroke, may be necessary to make the vehicle more agile, and, that there is a compromise between vehicle agility and Flight propulsive forces.Copyright © 2015 by ASME
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Stability Analysis of the Wing Leading Edge Spar of a Passively Morphing Ornithopter
Volume 2: Mechanics and Behavior of Active Materials; Integrated System Design and Implementation; Bioinspired Smart Materials and Systems; Energy Har, 2014Co-Authors: Aimy Wissa, James E. Hubbard, Joseph Calogero, Mary FreckerAbstract:This paper presents a stability model for the wing leading edge spar of a test ornithopter. The long-term goal of this research effort is to passively improve the performance of ornithopters during Steady Level Flight by implementing a set of wing kinematics found in natural flyers. The desired kinematics is achieved by inserting a compliant mechanism called a compliant spine into the wing leading edge spar to mimic the function of an avian wrist. The stiffness of the compliant spine is time varying and given the nature of flapping Flight, it is periodic. Introducing a variable stiffness compliant mechanism into the leading edge spar of the ornithopter affects its structural stability. Therefore, a stability analysis is required. In order to start the stability analysis, an analytical model of the ornithopter wing leading edge spar with a compliant spine inserted in is necessary. In the model, the compliant spine is modeled as a torsional spring with a sinusoidal stiffness function. Moreover, the equations of motion of the wing leading edge spar-spine system can be written in the form of non-homogeneous Mathieu’s equations, which has well-known stability criteria. The analytical system response is then validated using experimental data taken at NASA Langley Research Center. Results show that the analytical spine angular deflection agrees with the experimental angular deflection data within 11%. Stability was then demonstrated using both analytical and graphical proving that the response of leading edge spar with a compliant spine design inserted at 37% of the wing half span is bounded.Copyright © 2014 by ASME
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Testing of novel compliant spines for passive wing morphing
ASME 2011 Conference on Smart Materials Adaptive Structures and Intelligent Systems Volume 2, 2011Co-Authors: Aimy Wissa, James E. Hubbard, Mary Frecker, Yashwanth Tummala, Alexander BrownAbstract:Flapping wing Unmanned Aerial Vehicles (UAVs) or ornithopters are proliferating in both the civil and military markets. Ornithopters have the potential to combine the agility and maneuverability of rotary wing aircraft with excellent performance in low Reynolds number Flight regimes. These traits promise optimized performance over multiple mission scenarios. Nature achieves this broad performance in birds using wing gaits that are optimized for a particular Flight regime. The goal of this work is to improve the performance of ornithopters during Steady Level Flight by passively implementing the Continuous Vortex Gait (CVG) found in natural avian flyers. In this paper we present new experimental results for a one degree of freedom (1DOF) compliant spine which was inserted into an experimental test ornithopter leading edge wing spar in order to achieve the desired kinematics. The lift and thrust along with electric power metrics at different flapping frequencies were measured using a six-channel load cell and a current senor, respectively. These metrics were determined for the test ornithopter both with and without the compliant spine insert. Initial results validate the ability of our compliant spine design to withstand the loads seen during Flight at flapping frequencies of up to and including 5 Hz. For the ornithopter test platform used in the study, inserting the compliant spines into the wing leading edge spar accurately simulates the CVG increasing the mean lift by 16%, and reducing the power consumed by 45% without incurring any thrust penalties.Copyright © 2011 by ASME
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DESIGN OF A PASSIVELY MORPHING ORNITHOPTER WING USING A NOVEL COMPLIANT SPINE
ASME 2010 Conference on Smart Materials Adaptive Structures and Intelligent Systems Volume 1, 2010Co-Authors: Yashwanth Tummala, Mary Frecker, Aimy Wissa, James E. HubbardAbstract:A new scheme to design morphing ornithopter wings using a passive compliant spine is presented in this paper. The objective of this work is to optimize Steady Level Flight performance of an ornithopter by passively implementing the Continuous Vortex Gait (CVG) which requires bending, twist and sweep coupling during the upstroke. An optimization problem is formulated to design a compliant spine for pre-specified bending, sweep, and twist deflections. As a first step to achieving these 3 DOF kinematics, a 1 DOF compliant spine is considered to produce a specified bending deflection during the upstroke for drag reduction while remaining stiff during the downstroke for increased lift. The effect of the relevant geometric design parameters, namely contact gap, angle, and hinge geometry, are considered and optimized to achieve the aforementioned kinematics for both single and multiple joints, which make up a compliant spine. Results presented include the spine design optimization procedure, as well as a complete analysis for a 1DOF compliant spine to illustrate the efficacy of the methodology. This compliant spine design methodology and optimization procedure will be used, in the future, to design the 3-DOF compliant spine for the passively morphing ornithopter.© 2010 ASME