City streets pose problems for unmanned aircraft.

THE DREAM IS A fully autonomous rotary-wing unmanned aerial vehicle--one capable of flying through urban canyons, hovering above city streets or perching on building ledges as it gathers intelligence.

Researchers at the Georgia Tech's Center of Excellence in Rotorcraft Technology took one step toward that dream in August 2004 when they flew the GTMAX drone in two Defense Advanced Research Projects Agency demonstration missions at the Fort Benning military operations urban training site in Georgia.

The 160-pound aircraft with a 10-foot rotary diameter flew itself to pre-set coordinates and delivered medical supplies to a soldier within five seconds of its scheduled drop time. It later showed the ability to detect and avoid gunfire from a mock insurgent's gun.

While the demonstrations were a success, there "is a long way to go" before the goal of full autonomy is achieved, said the center's director, Daniel Schrage. It will take at least another five to 10 years of software development before rotary-wing UAVs can swoop among tall buildings searching for insurgents completely independent of operators, he said at an Institute for Defense and Government Advancement conference.

Smoke and dust, electrical wires and the limitations of global positioning system technology in proximity to buildings are among the obstacles, he added.

Rotorcraft UAVs that can freely operate in an urban environment are high on the Army's wish list, Paul Bogosian, aviation program executive officer, told reporters at a briefing.

"There's no question it offers attributes that any hovering platform can offer in that kind of [urban] environment," he said.

Pentagon planners see rotary-wing UAVs as part of a suite of unmanned sensors. Ideally, fixed-wing drones will cruise at higher altitudes while the helicopters maneuver in for closer looks. The ability to hover and perch gives them an advantage over higher-flying aircraft.

"If you're going to really have to hover and spend much time with staring sensors and zero-ground speed sensors, then you're going to want a hovering capability," said Schrage.

The four-year, DARPA-funded project involved about a half-dozen research universities, with each taking responsibility for developing software programs that demonstrated different capabilities. Georgia Tech integrated the package onto a Yamaha RMAX drone normally used for agricultural applications.

The effort required a mix of software programmers, and aeronautical, electrical and computer engineers.

"A lot of UAVs today don't fly very aggressively," said Schrage. Human operators don't have as quick a reaction time as an on-board computer, and they may fear causing an accident.

Among the software tested were programs that could detect gunfire and carry out evasive maneuvers, including the ability to hover in one position during gusts of wind and to make corrections in mid-flight in the event the UAV is struck by gunfire and damaged. These capabilities exceed the skills of human pilots, Schrage noted. The ultimate goal is flying complete missions without human interaction. Wire avoidance is still a major issue, as is flying near buildings where GPS signals are weak, he added.

GTMAX demonstrated the ability to launch a smaller drone, the GTspy, in mid-flight. Schrage said this is the first time a UAV has been launched from a UAV. The goal is to be able to send the smaller vehicle through a window.

DARPA's involvement in the project ended after the demonstration, although its interest in rotary-wing UAVs continues. The agency gave soldiers deployed in Iraq a micro air vehicle (MAV] to field-test. The aircraft is described as a 17-pound, 13-inch diameter rotary-wing reconnaissance platform with two sensors that can hover and stare in urban environments. Soldiers used the MAV to conduct aerial reconnaissance ahead of a convoy and to search for enemy forces. DARPA will send 25 upgraded units to Iraq this summer for further field-testing.

Bill Philips, deputy program executive officer for Army aviation, said the service is looking to expand the MAV program as soon as it is "sustainable and supportable."

Bogosian said there are no other funded Army rotary-wing UAV programs in development at this time other than the joint Army-Navy Fire Scout. With a 28-foot wide rotary diameter and a length of 23 feet, the aircraft was not designed to be a stealthy drone that can easily maneuver through tight urban environments.

DARPA spokeswoman Jan Walker said she does not know of a program intending to take software enabled control to the next level needed for rotorcraft to maneuver in urban environments. However, the software was successfully tested last summer on a Robinson-built R22 manned helicopter adapted to unmanned use, according to the Air Force Research Laboratory.

"We're still along way to becoming completely autonomous, but we need to continue this as a community," Schrage said.--STEW MAGNUSON