High Hover Finds Hidden Hostiles

Signal, Jun 2007 by Robinson, Clarence A Jr

Rotary-wing unmanned aerial vehicle excels, offers sensor array, communications relay.

Built for intelligence, surveillance and reconnaissance missions, the new A160 Hummingbird unmanned helicopter is designed to fly autonomously with a highaltitude endurance of 20 hours. This aerodynamically clean platform rivals fixed-wing aircraft performance to employ a suite of sensors, including foliage penetration radar that unmasks hidden troops and vehicles.

The A160 radically advances the state of the art in rotary wing aeronautical design and engineering. This $75 million Defense Advanced Research Projects Agency (DARPA)/ Army program employs an optimum variable-speed rigid rotor system that allows slower blade rotation to increase fuel economy and endurance. Designed to loiter at an altitude of 30,000 feet, the Hummingbird's range is 2,200 nautical miles, which is more than twice the endurance of other unmanned helicopters such as the Army's Fire Scout.

This aircraft can be equipped with day or night long-range optics, a laser range finder and target designator, a precision microwave synthetic aperture radar, an electronic intelligence system, a satellite communications link and an electronic countermeasures payload, according to Philip V. Hunt. He is DARPA's A160 program manager. Weapons also can be carried for armed intelligence, surveillance and reconnaissance (ISR). An unmanned aerial vehicle (UAV) ground moving target indicator (GMTI) radar is in parallel development by DARPA. This new sensor system is designed to detect enemy forces deployed beneath trees in forests or jungles (see page 39).

The A160 literally flies itself using preprogrammed autonomous mission plans, Hunt points out. "The aircraft can, however, be dynamically re-tasked from anywhere in the mission area with a network connection to the groundstation. This feature enables smaller organic ground units at various levels of command to exploit the reconnaissance capability. Mission plans include three-dimensional waypoint navigation, heading locks and triggering from external events. The system also includes a programmable lost-link mission plan. The Hummingbird can be preprogrammed to account for high moments caused by winds blowing over a stiff rotor and large changes in lift that any helicopter experiences in winds," he declares.

In addition to variable speed, the lightweight high-stiffness rotor system provides low disk loading, high-lift-todrag blade airfoils and hingeless rigid in-plane rotors for precision control and quiet operations. The rotor speed varies over a range of flight conditions, vehicle weight, altitude, airspeed and load factor to maintain the best lift/drag ratio, Hunt states.

"All of the Hummingbird's features relate to endurance, providing sensors on station for extended periods. The aircraft can fly for 20 hours at sea level with a 300-pound payload or hover out of ground effects at a 15,000-foot altitude, and it has an airspeed of 140 knots," Hunt notes. A former British Royal Navy officer who in 2002 became a U.S. citizen, he originally was assigned to the F-35 Joint Strike Fighter program. Earlier he served as an engineering officer in fixed-wing Sea Harrier and rotarywing squadrons at sea.

"The AloO's carbon fiber fuselage and blade design are unique, achieving the least sum of induced and profile drag," Hunt continues. "The design leads to lower power demands throughout the flight envelope. This reduced drag means the engine works less hard so that you don't require as much fuel, and that extends range and endurance for the fuel carried.

"The aircraft also has built-in survivability features, including a very quiet acoustic signature, in comparison to other helicopter platforms, through its rotor system design," Hunt says. He holds a bachelor of science degree in mechanical engineering from the University of Bristol and a master's of science degree in vibrations and dynamics from the University of Surrey, both in the United Kingdom.

"The Hummingbird is out of the DARPA Amber and Gnat/Predator stable of Abe Karem at Frontier Systems, Irvine, California," Hunt relates. "His design goal reduces the work done to fly the aircraft and employs efficiencies that lead to reduced specific fuel consumption. Boeing Company acquired Frontier, and under an approximately $50 million agreement is now the A160 program's prime contractor." Karem, a former Israeli air force officer before immigrating to the United States, is widely known as an innovative aviation pioneer.

The AloO's airfoil maintains quiet by controlling the velocity over the rotor wing-very low disc loading. The UAV achieves multipoint design performance with the ability to operate at an optimized rotor speed that minimizes the effect on lower altitude performance. As an example, Hunt cites the Navy/Marine Corps CH-53 helicopter's disc loading of 14 to 17 pounds per square foot. By comparison, the A160 flies at 5 to 6 pounds per square foot, creating much less noise. The Hummingbird's acoustic signature is four times less than that of the Bell 407 helicopter, he reports.