introduction

1.0 INTRODUCTION

The Defense Advanced Research Projects Agency (DARPA) is working on the development of a new class of flight vehicles called micro air vehicles (MAVs). The high level of current interest in developing small flight vehicles is the result of the nearly simultaneous emergence of their technological feasibility and an array of compelling new military needs, especially in urban environments [1]. Technological feasibility follows from advances in several micro-technologies, including the rapid evolution of micro-electromechanical systems, also known as MEMS. Military needs follow from a shift toward a more diverse array of military operations and the predicted spectrum of conflict in non-traditional environments (e.g. urban centers) for 21^st-Century warfighters.

The Rand Corp., a research organization, first raised the possibility of miniature flying vehicles in 1992. They presented a report to the Pentagon that examined a range of microdevices for defense applications [2]. Engineers from the Massachusetts Institute of Technology examined the idea more closely, and enthusiasm for the concept grew. The outcome of the effort was a newly created DARPA program which was developed for this new dimension of flight. The DARPA program was initiated through the agency’s Small Business Innovation Research Program, and in the Fall of 1997, the research agency began a three-year, $35 million effort to have industry and academia develop prototypes [2].

1.1 Military Interest MAVs are not small versions of larger aircraft, but they are fully-functional, militarily capable, six-degree-of-freedom aerial robots. Their mobility provides the capability of deploying a useful micro payload to a remote or otherwise hazardous location where it may perform any of a variety of missions. Such missions may include reconnaissance and surveillance, targeting, tagging, and bio-chemical sensing [1]. Initial missions for MAVs would include reconnaissance and surveillance, but they also could encompass targeting artillery and mortars, assessing battle damage, carrying acoustic sensors to listen for the movement of heavy equipment, and transporting detectors to sense radiation or biological and chemical weapons.

Initial development of the MAVs has been spurred on by military interest in producing miniature intelligence-gathering planes. The Pentagon hopes that the devices will give small military units direct access to reconnaissance data. MAVs could help them in battling an enemy just over a hill or in engaging them in street-to-street fighting in an urban setting. MAVs are envisioned as an asset at the platoon level or below giving the individual soldier on-demand information about his surroundings and for providing increased situational awareness which results in greater effectiveness and fewer casualties.

1.2 Other Applications Ultimately, MAVs could also be adapted to many civilian applications including guiding fire and rescue operations, monitoring traffic, forestry and wildlife surveys, border surveillance, observing crops, real estate aerial photography, and furnishing information to police patrols.

Figure 1.1: An "Over-The-Hill Reconnaissance" Mission for the MAV [1]
The U.S. Navy is interested in developing small, unmanned vehicles to serve in reconnaissance missions too hazardous for human pilots. MAVs could also serve during wartime in order to determine if areas are clear of hostile forces as shown in Figure 1.1. Another possible application of MAVs is in the area of chemical leak zones. In these situations, it is very important that the situation be assessed first without the risk of exposure to people. A danger assessment can be performed with small sensing equipment as a payload on the MAV.

Additionally, MAVs have fire-fighting applications. A small, maneuverable MAV with an infrared camera could locate people still in a building while keeping firefighters safely away from danger. Finally, an MAV could be a target designator. The MAV could eliminate targets without involving humans [3].

1.3 MAV Requirements The definition employed in DARPA’s program limits these aircraft to a size less than 15 centimeters (6 in.) in length, width, or height [1]. MAVs must have a weight of 50 grams or less and must be capable of staying aloft for 20 to 60 minutes for a distance of 10 kilometers. The aircraft will have to be light and small enough to fit in a soldier’s backpack, yet be capable of carrying a solid-state camera, infrared sensor or radar detector on flights of several kilometers. The MAV would have to carry out most of its operations autonomously, controlled by an on-board computer that would use the sensory data collected to fly around hazards such as trees and buildings. MAVs must carry a power supply that will keep them in the air long enough to complete their mission, and MAV engines will have to be powerful enough to propel each aircraft at more than 30 kilometers per hour. 1.4 MAV Configurations Interest groups from the military, universities, and private companies have proposed multiple designs of MAVs. These vehicles may display a wide variety of configurations depending on specific mission requirements. Design proposals differ in both outward and inward appearances. Some designs have wings and tails similar to conventional aircraft, while others take the configurations of tail-less flying wings, oval disks, insects, or other miscellaneous shapes [2].

Intelligent Automation Inc. is proposing a conventional looking aircraft that will be powered by a small piston engine driving a two-inch propeller. The design uses available technology to develop its small alcohol-fueled engine. Aerodyne Research Inc. has proposed a spheroid craft powered by several microturbofan jet engines that fire downward from its circular bottom. The advantage of a spheroid craft is its ability to hover in flight gathering reconnaissance data.

Robert Michelson of the Georgia Tech Research Institute, envisions the MAV as a multi-mode vehicle capable of flying and crawling. The entomopter design, as seen in Figure 1.2, was inspired by insects and uses a reciprocating chemical muscle to generate an up-and-down motion, such as beating wings or scurrying feet.

Figure 1.2: Robert Michelson's Entomopter Design [4]

1.5 The Hummingbird Configuration

Figure 1.3: The Micro Air Vehicle Flight Regime Compared to Existing Flight Vehicles [1]. The new MAVs could take on several model variations. Some possible sources include insects, birds, and small aircraft. Ultra Flite plans to use the hummingbird as their modeling source. First, a hummingbirds’ characteristics make them a perfect candidate for MAV modeling. The most impressive capability is that it can maintain hovering flight. This would be especially useful in several MAV applications such as battlefield assessment and surveillance. Also, hummingbirds are small in size and quiet, which makes them prime choices for the above applications. Finally, the hummingbird is a highly efficient system. Their unmatched maneuverability and their ability to instantly transition between flight modes make hummingbirds an excellent choice for MAV modeling. Figure 1.3 shows how the hummingbird is within the perfect range of micro air vehicle design parameters.