Electronics and propulsion make possible 'fly-on-the-wall' aircraft

Orlando, FL-Remember MAVs? (see DN 5.18.98 or www.manufacturing.net/dn/index.asp?layout=articleWebzine&articleId=CA117015&stt=001) Well, those Micro Air Vehicles have evolved from prospective hand-launched aircraft a few inches in size to what Sam Wilson, head of the MAV development program at DARPA (the Defense Advance Research Project Agency), calls "flying RUGS," or Relocatable Unattended Ground Sensors.

Originally these model-airplane-appearing hand-sized systems were to be carried by a soldier and launched to scout the local area, including urban and interior spaces. At the AeroSense conference here last week, Wilson highlighted recent technology advances which change the scope and performance of such vehicles. While MAVs were seen as fixed-wing aircraft, such a configuration, without any complex wing flaps, had its top speed and slowest speed (in tens of mph) very close together. This narrow envelope, he pointed out, doesn't work well for maneuvering within confined spaces. Also, a fixed wing has to keep flying to function, limiting its endurance.

What DARPA planners now envision is a more helicopter-like vehicle using a ducted fan (essentially a propeller mounted inside a cylindrical wing), according to Wilson. "It could theoretically go up to 80 knots or hover," he noted. As a video clip demonstrated, the shrouded prop allows an operator to safely snatch the vehicle out of the air or launch it easily. This type of system would not fly constantly but "perch and stare," as Wilson called it, say on the corner of a building or inside it, for extended periods of time-thus the RUGS name.

Contributing to such a scenario are new developments in microelectronics. Wilson cited cameras that weighed 2 grams a few years ago now being "match-head size, 12 to the gram. GPS systems once the size of a cigarette pack are watch-size today" thanks to cell phone electronics that meet Enhanced 911 requirements. And cheap, tiny lasers with only a 30m range will be used for obstacle avoidance, he added.

For propulsion, Wilson said two systems seem most viable: a diesel that runs on readily available JP-8 jet fuel and a thermo-electric device deriving power from heat transfer at an exhaust pipe. Both also offer less noise than other engines.

The perch-and-stare routine and a form of "snooze" mode offer some operational advantages, he noted. For example, a 5-lb, 9-inch diameter baseline vehicle would require 1,500W to fly for an hour. The same MAV could function for a week or up to 3 months in a sensor watching mode, according to Wilson. He cited operation could be modified to achieve 20 minutes of flight, one month of watching, and 2.5 days of transmitting without recovery or refueling. Contributing to this power conservation, algorithms will permit only tracking moving objects (changing pixels) and transmitting such updated information. The baseline vehicle is "dense" enough, Wilson said, to be gust resistant when perched. But if blown off, it should react quickly to restart the engine and reposition itself safely.

Wilson said MAV missions will include working with and aiding ground robotic systems: detecting people around or threatening a ground robot or troops; scouting for hazardous holes a ground vehicle might encounter; and validating selection of firing targets.

Finally, while some components may cost thousands of dollars today, Wilson noted the goal is a vehicle cost of $700 each. To achieve this, volume component production would be needed along with such construction methods as "foaming" the vehicle in place around the wiring and frame structure.