This article first appeared in Aviation Week and Space Technology.

Boeing is poised to attempt a brace of world record endurance flights with its A160T Hummingbird unmanned air vehicle after installing new safeguards to prevent a flight control system failure which led to the loss of a prototype last December.

The accident put a three-month hold on an already aggressive test and demonstration schedule earmarked for the A160T through the rest of 2008. Yet Boeing remains confident it can meet its schedules, as well as set records for rotary UAV payload and endurance that it claims others will find difficult to match.

The record attempt flights will include a hover out of ground effect at 15,000 ft. and an 18-20-hr. flight with a 300.-lb payload. Together they form the final milestones of the Phase 1 demonstration which began in August 2003. Supported by the Defense Advanced Research Projects Agency (Darpa), the tests are intended to prove that a purpose-built, clean-sheet large vertical takeoff and landing unmanned air system (VUAS) can truly go the distance compared to other rotary UAVs that are generally derived from existing manned helicopters.

"We think we've got something different here," says Boeing Advanced Systems' business development director, Grady Eakin. "The range, endurance and payload are unique for a rotary-wing UAV, and we think it can provide a variety of missions all at the same time. We've proved we can get there quickly, stay a long time and fly to places that commanders think are important," he adds.

Although the A160T is aimed squarely at standard UAV roles such as reconnaissance, surveillance, communications relay, resupply and target acquisition, Boeing says the broader capabilities of the turbine-powered helicopter make it capable of much more. One of the initial test vehicles has been mocked-up with stub wings to carry up to eight AGM-114 Hellfire air-to-ground missiles, while another has flown with an aerodynamically-shaped pod large enough to evacuate a wounded soldier or transport a small robotic vehicle.

With Northrop Grumman's MQ-8B Fire Scout already destined for major VUAS roles with the U.S. Navy and Army, Boeing is seeking new niche opportunities for the A160T beginning with the U.S. Special Operations Command (Socom). Initial operational evaluations of the MQ-8B, a modified Schweizer 333, are planned for 2008, while first flight of the Army's MQ-8B variant is slated for the end of 2010, with initial operating capability scheduled for 2014. Demonstrations are also planned to the Navy. Operational tests of the A160T could, by contrast, begin within the next year or so, says Boeing.

Part of the challenge, says Eakin, is making potential users aware of the A160T's capabilities. "There [are] a variety of military and government users that haven't thought yet about how far this has flown and what it can do for them. We've just recently talked to a couple of potential customers and they are surprised that we can carry a couple of payloads, and fly far away from their basing scheme," he adds.

The 35 ft.-long A160T is powered by a Pratt & Whitney Canada PW207D turboshaft driving a 36-ft.-dia., four-blade rotor. The blades, like the fuselage itself, are made from lightweight carbon fiber composites, while the streamlined fuselage shell is designed for both low drag and reduced radar cross-section.

"It's significantly larger than any other VTOL [UAV], but it is significantly lighter as well," says Eakin. "We have a fairly high fuel fraction of more than 50%, which is slightly higher than other UAVs and manned helicopters." Empty weight is 2,500 lb. and the helicopter carries 2,600 lb. of fuel in large tanks clustered around the center of gravity. The forward tank, mounted just ahead of the mostly internally housed rotor mast, occupies almost the whole depth of the fuselage, while a second large tank is sandwiched beneath the engine and transmission housing and the bay in the belly for the retractable gear. Maximum takeoff weight is 6,500 lb. while the largest payload carried to date is around 1,090 lb.

Read more on this story, French amphibious landing craft, an April Fools joke on defense contractors and the many facets of FCS from our friends at Aviation Week on Military.com.

-- Christian