Micro new12
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Researchers are developing micro air vehicles (MAVs) that are small enough to fit in the palm of your hand. MAVs would have an operating range of several kilometers and transmit detailed pictures back to a portable base station. They could be used for military surveillance applications and fly at speeds of 10-15 m/s, powered by electric motors or miniature engines. Significant challenges in MAV design include tight packaging to meet weight limits and integrating vehicle elements due to their close coupling.
Micro new12
- 2. ABSTRACT In the last decade researchers have developed increasingly sophisticated unmanned air vehicles (UAV) for military applications. Increased demands for intelligence are spawning the development of a smaller next-generation UAV called the micro air vehicle, or MAV. Small enough to fit in the palm of your hand, an MAV would have an operating range of several kilometers and transmit detailed pictures back to a portable base station. Potential applications for MAVs, both military and civilian, are numerous. For most military applications, MAVs would be controlled by local users, operating covertly, to supply real-time data. This article focuses on a military surveillance application that uses either visible or mid-wavelength infrared imaging sensors. As designed, the MAV would fly in a low Reynolds-number regime at airspeeds of 10 to 15 m/sec. Propulsion would be provided by a combination of an electric motor with either an advanced lithium battery or fuel cell, or by a miniature MEMS engine, which is a more efficient option. Because of the close coupling between vehicle elements, system integration would be a significant challenge, requiring tight packaging and multifunction components to meet mass limitations. Next, we see the robust schemes for the detection of extreme MAV attitudes, where no horizon is visible, and for the detection of horizon estimation errors, due to external factors such as video transmission noise.
- 3. CONTENTS 1. INTRODUCTION 2. MAVs 3. DESIGN ASPECTS 4. PROPULSION 5. FLIGHT CONTROL AND STABILITY 6. COMMUNICATION AND NAVIGATION 7. OPTICAL SENSORS 8. CONCLUSION 9. REFERENCES
- 4. INTRODUCTION The concept of micro-sized Unmanned Aerial Vehicles (UAVs) or micro Air Vehicles (MAVs) has gained increasing interest over the past few years, with the principal aim of carrying out surveillance missions. The primary payload of these tiny aircraft (~15 centimetres or 6 inches wingspan) is usually a miniature image sensor. Operating in an approximate radius of 600 metres from the launch point, 亮AVs are used to acquire real-time visual information for a wide range of applications. According to DARPA (Defense Advanced Research project Agency), 亮AVs are six-degree-of-freedom aerial robots, whose mobility can deploy a useful micro payload to a remote or otherwise hazardous location where it may perform any of a variety of missions, including reconnaissance and surveillance, targeting, tagging and bio-chemical sensing. Equipped with small video cameras and transmitters, MAVs have great potential for surveillance and monitoring tasks in areas either too remote or too dangerous to send human scouts. Operational MAVs will enable a number of important missions, including chemical/radiation spill monitoring, forest-fire reconnaissance, visual monitoring of volcanic activity, surveys of natural disaster areas, and even inexpensive traffic and accident monitoring. Additional on-board sensors can further augment MAV mission profiles to include, for example, airborne chemical analysis. In the military, one of the primary roles for MAVs will be as small-unit battlefield surveillance agents, where MAVs can act as an extended set of eyes in the sky for military units in the field. Virtually undetectable from the ground, MAVs could penetrate potential terrorist camps and other targets prior to any action against those targets, significantly raising the chance for overall mission success. There is now great interest in developing Micro-Air Vehicles (MAVs) that are very small with both fixed and flapping wing designs. As the size of these MAVs decrease, the amount of thrust and lift that can be generated by the wing will also decrease, limiting the weight and payload capacity of the MAV. For very small MAVs with fixed wing designs, this will require critical air velocities that limit the maneuverability of the MAV. Thus, flapping wing designs can be more desirable, enabling the MAV to fly at air velocities approaching 0 (i.e., hovering), much like a rotorcraft structure. However, the flapping motion associated with these wing designs can produce thrust and lift forces that are more unsteady than fixed wing MAVs, which requires new measurement techniques for assessing the transient characteristics of these forces as a function of the flapping wing design.
- 5. MAVs The MAV has a variety of potential uses in military operations, including local reconnaissance, fire control, and detection of intruders. Law enforcement organizations could use MAVs for hostage rescue, border patrol, traffic surveillance, and riot control. For most of these applications, a swarm of MAVs could provide wide-area coverage. Much of the appeal of the MAV for covert operations comes from its small size. To determine how invisible the MAV would be on the battlefield, we examined the various means of detection available to potential adversaries. To the human eye, an MAV in flight would resemble a small bird. MAV radar signatures would be similar to those of small birds and are thus likely to be lost in clutter. Furthermore, the projected MAV airspeed of 10 to 15 m/sec is below the minimum detectable velocity for most radars. Infrared search-and-track units would be able to detect an MAV only at short ranges because of its low power. For an electrically powered MAV, the acoustic signature would be dominated by the aerodynamic noise of the propeller, and would be audible only at close range. An MAV powered by an internal-combustion engine with a muffler could achieve similar acoustic performance.
- 6. PROPULSION Having explored the predicted lift-to-drag ratio and propeller efficiency for the MAV, we now consider the power required to fly one. Figure 7 shows the flight power (airspeed times thrust), shaft power, and electric power needed for a range of MAV sizes, with the requirements for our baseline 15-cm wingspan highlighted. For conservative choices of lift-to-drag ratio and CL, the baseline flight power is 1.25 W. For a propeller efficiency of 50%, the baseline shaft power is 2.5 W. If we use an electric motor with 60% efficiency, the baseline electrical power is 4.2 W. These values, however, provide only enough power for level flight, and they must be doubled so that the MAV can turn, climb, and fly in gusty air. To produce this power, we considered a variety of efficient and lightweight propulsion systems, including electric motors powered by batteries or fuel cells, internal-combustion engines, turbines, compressed gas, and power plants using flywheels or capacitors for energy storage. The majority of these systems proved inadequate. Compressed gas is not likely to provide enough endurance, and flywheels and capacitors require significant development to be practical. Microsize turbines under development at MIT could offer robust performance and be used to generate thrust or electrical power; however, they require more than three years of development . Fuel cells, particularly those combining atmospheric oxygen with hydrogen generated by using chemical hydride or methanol oxidation, have promise, but none have been built in the MAV-size range. Consequently, we focused on the most promising near-term candidates for powerbattery- driven electric propulsion and internal-combustion engines. Battery-driven electric propulsion has three advantages: it avoids the need for consumable fuel, is more reliable than internal- combustion engines, and is quiet. Small electric motors with adequate power densities are available.
- 7. DESIGN ASPECTS The simplest design is an MAV that can remain within the line of sight of a small base station that tracks the vehicle, maintains the communications link, and performs navigation calculations. A vehicle that flies behind buildings or hillsbeyond the line of sightmust depend on some other approach to communications and needs an independent means of navigation. One configuration that meets these requirements stores data on board with later readout when the vehicle returns to line of sight. Another configuration includes an overhead communications relay. Without a line of sight for navigation, alternative navigation approaches such as dead reckoning, inertial navigation, and the Global Positioning System (GPS) might be tapped, with the latter two depending on the availability of small components. Intelligence gathering around or within buildings requires a hovering vehicle with a sophisticated navigation system. Alternatively, the MAV might be able to perch, or fasten itself to a fixed object, or turn into a crawler for local sensing. Combined hovering-flying vehicle possibilities include conventional main rotortail rotor helicopters, coaxial rotors, propulsiondriven rotors, ducted fans, and tail-sitter airplanes. For some applications, the vehicle would need to be fully autonomous and able to respond to the data received by onboard sensors.
- 8. MAVs The MAV has a variety of potential uses in military operations, including local reconnaissance, fire control, and detection of intruders. Law enforcement organizations could use MAVs for hostage rescue, border patrol, traffic surveillance, and riot control. For most of these applications, a swarm of MAVs could provide wide-area coverage. Much of the appeal of the MAV for covert operations comes from its small size. To determine how invisible the MAV would be on the battlefield, we examined the various means of detection available to potential adversaries. To the human eye, an MAV in flight would resemble a small bird. MAV radar signatures would be similar to those of small birds and are thus likely to be lost in clutter. Furthermore, the projected MAV airspeed of 10 to 15 m/sec is below the minimum detectable velocity for most radars. Infrared search-and-track units would be able to detect an MAV only at short ranges because of its low power. For an electrically powered MAV, the acoustic signature would be dominated by the aerodynamic noise of the propeller, and would be audible only at close range. An MAV powered by an internal-combustion engine with a muffler could achieve similar acoustic performance.