The so-called remote control, is the management of personnel in different places, or through computer networks, both remote dial-up access to Internet and other means need to be controlled by the computer Unicom, will be charged to the computer's desktop displayed on your computer, remote computer through the local computer configuration, software installation, modification and so on. Remote wake-up (WOL), local area network through remote boot.
Remote Control Hovering Ornithopter Christopher N. Deal1 Mechanical Engineering Undergraduate University of Arkansas, Fayetteville, AR 72701 Academic Advisor: Dr. Po-Hao Adam Huang2, Ph.D. Mechanical Engineering Assistant Professor University of Arkansas, Fayetteville, AR 72701 The concept of an ornithopter (flapping-winged aircraft) to fly in a similar manner to that of a hummingbird or bumble-bee has yet to be successfully implemented into an effective design. The design proposed in this paper utilizes a simple proposal while taking into account that much is left to be considered. Basically, the design has been conceptualized around the idea of a passive pendulum, similar to the way a bumblebee uses its thorax. Normally, hover in an ornithopter would require active control in multiple degrees of freedom to provide stable flight. This design is simplified with hovering being the primary flight pattern when the pendulum is “passively hanging”. This will cause the stroke plane, or the path of the wings, to be horizontal and maintain vertical vectors for both lift and thrust. By utilizing the pendulum, this will create a mechanism to actuate from and therefore change the plane of the stroke, initiating forward, backward, and side-to-side flight. Design considerations described in this report include: actuation, wing design, and basic mechanical system design. Also, the limitations of this design are theorized in this report along with proposed changes to solve these problems. Through this design, a basic aircraft can be created to begin mimicking the flight of a hovering bird or insect. Nomenclature Φ = total stroke amplitude Θ = maximum stroke deviation α = mid-stroke angle of attack τo = flip start ∆τ = flip duration J = advance ratio I. Introduction M illions of different types of insects, bats, and birds all fly with flapping wings, so it is therefore logical that scientist, biologist, and aerodynamicist would be interested in learning more about how to create an artificial flapping winged flyer . This form of aircraft is generally known as an ornithopter (from the Greek ornithos “bird” and pteron “wing”) . Most hobbyist build ornithopters for the shear enjoyment of imitating a bird-like or insect-like artificial aircraft, but there has been a recent interest to study ornithopters for practical applications. Ornithopters utilize the flapping wings for lift and thrust, which increases energy efficiency by minimizing flight components. Many practical application involving ornithopters would require it to transition to hovering mode under non-quiescent conditions. So far, none have achieved the ability to transition even in quiescent environments. Although, a few artificial machines have been made with the ability to hover, including the Mentor, built at the University of Toronto Institute of Aerospace Studies (UTIAS) , and the Delfly, built by the Delft University of Technology Aerospace Department . Both aircraft are very limited by their size. Also, by observing video of the Delfly, it tends to be more of a slow hovering flight similar to how a fixed wing aircraft would “hover” with its nose pointed to the sky. 1 Undergraduate Student, Mechanical Engineering Department, University of Arkansas, AIAA Member 2 Assistant Professor, Mechanical Engineering Department, University of Arkansas, AIAA Life Member 1 American Institute of Aeronautics and Astronautics The aerodynamic properties of ornithopters are very complex because steady-state aerodynamics do not accurately account for the required forces . Instead, unsteady aerodynamic modeling is required to understand the leading edge vortices (LEVs), which create the majority of the forces on flapping wings . By effectively manipulating these aerodynamic forces to provide lift, propulsion, stability, and control, an ornithopter can be made to imitate an insect or hummingbird like flight. To be able to fully imitate this type of flyer, would mean to have a way of actively controlling each individual wing’s amplitude and angle of attack along with several other means of control. Because of this difficulty, a design was created to make this type of hovering control by another means. This paper proposes a design to passively control an ornithopter to mimic a hummingbird type flight. II. Practical Applications Applications typically include the use of ornithopters in the form of micro air vehicles (MAVs) for gathering surveillance information such as audio, video, or photo on targets of interests. Key requirements for an ornithopter in such missions would be its ability to hover with high maneuverability and be extremely power-efficient. Although small helicopters on the order of a few grams have been demonstrated to be able to hover, it does not possess the ability to maneuver in gust conditions nor transition from horizontal flight. These capabilities can be achieved by small ornithopters given the ability of natural flapping flyers to master the acrobatics of flight. For example, Nathan Chronister has built a 3.8 gram ornithopter (Fig. 1) which has a complete RC system weighing less than a gram . Another possible requirement for reconnaissance would be for the ability of the ornithopter to perch on tree limbs, fences, etc. In any case, the ability for the ornithopter to hover in gust conditiosn is key for most applications, but no current artificial flyer has this practical ability, especially in the sense of Figure 1: Nathan Chronister’s 3.8 MAVs. gram ornithopter  III. Aerodynamics of Ornithopters The aerodynamics in this report are described for FD the concept of hovering flight. The diagram in Fig. 2 shows the stroke of an ornithopter during hovering flight Fnet . The high number of parameters affecting the stroke pattern gives way to a very complicated system. The net force Fnet is a combination of the forces caused by the FU complete cycle of the downstroke force FD and upstroke force FU which balances the weight of the body for hover. This net force, or lift, created by flapping wings is (a) due to the leading edge vortex (LEV) created by the plunging and pitching of the wing, similar to the effect of Figure 2: Schematic diagram of the six parameters the LEV on a delta wing . These similarities can be that were varied in the experiments. This cartoon seen in a comparison of the two in Fig. 3. The LEV is represents a 2-D projection of a 3-D kinematic far more pronounced in the photograph of the delta wing pattern . Personal revisions are in orange. because of steady state nature of fixed wings. Theoretically it seems that flapping wings should stall because of the incredible high angle of attack during the flapping motion. But, the intense LEV provides the high suction lift at the high angles of attack, thus preventing the wings from stalling. Similar to the LEV on delta wing, instead of flow separation, the vortex sticks to the wing traveling along the span and results in the desired maximum lift coefficient at a high angle-of-attack . This accounts for the high lift of a flapping wing. In Figure 3: Similarities in the LEV of a Flapping addition to the stroke path, the ability for the flapping Wing (a)  and Delta Wing (b)  2 American Institute of Aeronautics and Astronautics wings to deform aeroelastically greatly affects the aerodynamic properties. Bats can change the degree of tension in the spars of its wings to change the wing camber and therefore affect the aerodynamic loading. IV. Basic Mechanical System Design Most artificial ornithopter designs consider the forward flight to be primary. As mentioned before, only a few ornithopters come close to having the ability to hover. Most aerodynamic research on hovering insects should lead to designers focusing on the hovering aspect as primary, then finding ways to create thrust in the fore, aft, and lateral directions. The hovering stroke plane can be stabilized by having the body hang below the wing base to benefit from a type of passive pendulum stability . This is similar to how most insects fly and can be seen in Fig. 4 with a horizontal stroke plane while the center of mass is close to the junction of the thorax and abdomen. In hover, the downstroke and upstroke are symmetrical. The pitch and roll can be induced by adjusting the stroke plane. This effectively changes the direction of the net force and creates a component of thrust. The advance ratio J (defined as the ratio of vehicle velocity versus wing flapping velocity) will increase as the thrust component becomes stronger. This can be seen in Fig. 5. Typically, an insect will increase the amplitude or angle of attack of the downstroke. This will increasingly dominate the force balance on the downstroke to unbalance the forces in the horizontal direction and cause forward pitch, and therefore forward thrust. Figure 4: Insect wing flapping Figure 5: The wingtip paths for an motion  insect at different flight speeds . Instead of pitching the stroke plane by means of wing control, it can be changed by simply adjusted the stroke plane by means of actuation. This causes problems because actuation can not be completed in mid-air. This is where the pendulum stability comes into factor. Excluding wind conditions, a pendulum hanging under the stroke plane can provide a semi-stable surface to actuate from. The basic design is shown in Fig. 6. Lift Lift Stroke Plane Thrust Actuators Universal Joint Pendulum Figure 6: Basic Hovering Ornithopter Design 3 American Institute of Aeronautics and Astronautics A. Actuation 1) Shape Memory Alloy (SMA) (Muscle Wires) These wires are high strain, low stress devises that will shorten when the activation temperature is reached. Since they do not push, they can be arranged in a pull-pull configuration or used in conjunction with a spring for the restoring force. The biggest limitation for using these as actuators is that they are either “on” or “off”. This will not give the necessary control unless the amount of deflection can be varied. This would have to be done by controlling the temperature of the muscle wires by applying a specific power. This would prove to be highly difficult because of convection by the varying air flow and the unknown activation temperature range of the material. 2) Magnetic Servos Small servos at this scale have not been researched to much of an extent so there has not been much determined about how they would compare to using SMA’s. They are much larger in size and could cause the actuation system to be too heavy and bulky. Some servos from airmidimicros.com for planes up to 20 grams were found to be 7 x 8 x 4 mm and 0.4 grams. B. Wing Design Several factors have to be taken into account in the design of the wing. These factors include: size, flapping rate (frequency), stiffness, and mono or bi wings. 1. Size / Frequency / Mass The size of the wing highly depends upon the mass that has to be supported by the wings. A graph created by C. P. Ellington (Fig. 7) can be used to determine the size of the wings according to the projected frequency and mass. For example: a wing that beats at 30 Hz and supports a 10 g load would have to be approximately 75 mm in length. The actual area of the wing is determined by proportionality. 2. Stiffness The stiffness of the wing has the largest effect on the design because it controls the angle of attack and the flip duration. The stiffness can be adjusted in the spanwise and chordwise manner by changing the material used for the wing membrane and the way the spars are made. The spars can be adjusted by the material being chosen, thickness, number, and separation. Some example layouts Figure 7: Wing Frequency vs. are shown if Fig. 8. Support Mass vs. Wing Length.  Figure 8: Example Wing Layouts 3. Mono or bi wings The choice of mono or bi wings primarily depends on how powerful the motor is and required stability. A single set of wings (mono) will cause the body to oscillate because of the shifting forces caused by the downstroke and upstroke. If the wings are larger because frequency is limited, then forces on each stroke would be larger and last for a longer period of time. This could easily cause problems in this design because the effective lift and thrust component need to be effectively stable. A bi wing configuration (similar to a dragonfly) would cancel out this oscillation effect. These configurations are modeled in Fig. 9. 4 American Institute of Aeronautics and Astronautics Figure 9: a) Bi-Wing Design b) Mono-Wing Design C. Flapping Mechanism The flapping mechanism is a simple cam system using a small electric motor and gear. This creates an oscillating motion for the wings and can be seen in Fig. 10. A prototype of this mechanism was created using a rapid prototyping machine and worked despite a few minor problems. A redesign is in the works using more precision parts and a more powerful motor. This prototype can be seen in Fig. 11. Figure 10: Cam Figure 11: Ornithopter Prototype Mechanism for Flapping V. Conclusion The design and testing of the passive pendulum ornithopter is currently under-going at the University of Arkansas. The prototype flapping mechanism has been built with 3D ABS plastic printer and is currently being tested on a miniature 6-component force balance. Tests cases representing hovering and horizontal flights will be performed outside and inside a 1’x1’ low speed wind tunnel, respectively. Preliminary results will be presented at the conference. Acknowledgments The Authors would like to thank the AIAA Region IV for providing the travel support to present this paper at the AIAA Region VI student conference in San Jose. References 1 Ellington CP, (1999), “The Novel Aerodynamics of Insect Flight: Application to Micro-Air Vehicles,” The Journal of Experimental Biology, Vol. 202, pp. 3439-48. 2 “Ornithopter,” Website Reference, http://en.wikipedia.org/wiki/Ornithopter 3 “Mentor the Hovering Ornithopter,” Website Reference, http://www.andrew.cmu.edu/user/deberhar/Mentor.html 4 “DelFly,” Website Reference, http://www.delfly.nl/?lang=en 5 Ho S, Nassef H, Pornsinsirirak N, Tai Y, Ho C, (2003), “Unsteady Aerodynamics and Flow Control for Flapping Wing Flyers,” Progress in Aerospace Sciences, Vol. 39, pp. 635-681. 6 Ramamurti R, Sandberg WC, (2002), “A Three-Dimensional Computational Study of the Aerodynamic Mechanisms of Insect Flight,” The Journal of Experimental Biology, Vol. 205, pp. 1507-18. 5 American Institute of Aeronautics and Astronautics 7 “The Ornithopter Zone,” Website Reference, http://www.ornithopter.org/ 8 Sane SP, Dickinson MH, (2001), “The Control of Flight Force by a Flapping Wing: Lift and Drag Production,” The Journal of Experimental Biology, Vol. 204, pp. 2607-26. 9 Zbikowski R, (2002), “On Aerodynamic Modelling of an Insect-like Flapping wing in Hover for Micro Air Vehicles,” Philosophical Transactions: Mathematical, Physical and Engineering Sciences, Vol. 360, No.1791, Biomimetics: Technology Transfer from Biology to Engineering, pp. 273-290. 10 http://www.nasaexplores.com/show2_articlea.php?id=03-080 11 “Micro-Aerial Vehicle (MAV) Research : Designing An Ornithopter for Urban Search and Rescue,” Website Reference, http://www.eng.unsw.edu.au/current/scholar/tr0506/results/sys/text.htm 6 American Institute of Aeronautics and Astronautics
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