Unmanned on Deck
X-47B UCAS Could Remake U.S. Naval Aviation
By MARCUS WEISGERBER
Published: 29 August 2011
Landing a plane on a bobbing aircraft carrier deck is one of the hardest maneuvers for any pilot. It's a tricky dance that's been done for decades, but now that dance is about to get a little trickier.
The task: Land an unmanned, persistent, low-observable aircraft on a moving carrier. And after that's done, refuel the drone from a tanker in flight.
For years, the U.S. Navy and Northrop Grumman have worked on precise navigation technology that will make this possible. This year, the program stepped much closer to making this a reality.
The tailless, bat-winged craft, dubbed the X-47B, flew for the first time in February. And recently, an F/A-18 Hornet fighter jet equipped with an early version of the autonomous guidance software designed for the drone successfully landed on a carrier without a pilot on the stick and throttle.
This precision navigation equipment is a "key technology" that allows the Unmanned Combat Air System Demonstration (UCAS-D) aircraft to navigate on approach with an accuracy of less than 10, said Capt. Jaime Engdahl, UCAS-D program manager at Naval Air Systems Command (NAVAIR).
While the primary goal of the UCAS-D program is to launch and land the aircraft on the carrier, officials must accomplish much more. Upon touchdown, crews must clear the drone from the runway within 45 seconds -- no easy feat - so other aircraft can land.
The Months Ahead
Unlike many of the drones in use today, X-47B is fully autonomous, and special computer software keeps the composite aircraft aloft, according to Keith Carter, NAVAIR's chief engineer on the program.
"There is no pilot flying at all," Carter said. "The aircraft responds to external stimuli."
Instead, waypoints are programmed into a ground-based computer and transmitted to the aircraft through the Rockwell Collins Tactical Targeting Network Technology data link.
While the basic airframe shape, which shares many flight technologies and design similarities with the B-2 bomber, is not groundbreaking, the precision GPS computer system is new technology, according to Janis Pamiljans, Northrop's UCAS-D program manager.
The first of two demonstrator aircraft has been flying test missions at Edwards Air Force Base in California since its first flight in February. Due to the autonomous nature of the aircraft, many hours are spent conducting mission planning for the flight tests, according to Engdahl.
A second aircraft is undergoing tests in preparation for its first flight. The program plans to begin moving aircraft to Patuxent River Naval Air Station, Md., by the end of the year.
Prior to making its first carrier landing, one X-47B will conduct air traffic control exercises, which includes transferring control from a ground station at Patuxent River to a station on the carrier, Engdahl said.
Aside from takeoffs and landings, the X-47B will spend time on the carrier conducting other tests. Before the first flight, program officials plan to put a drone on the flight deck and drive it around using a wireless controller, according to Engdahl.
"You'll get the pitching deck, you'll get the salt air [and] you'll get to exercise with the flight deck directors," he said.
The crew also will conduct maintenance demonstrations in advance of carrier touch-and-goes and landings, which are expected in 2013.
"This program is one to watch in the coming months," Engdahl said.
Computers Are Key
New and precise GPS equipment on the carrier, coupled with an inertial navigation system, will provide the precise position of the carrier deck.
"That gives you [the] … pitch, roll, yaw of the ship," Engdahl said.
Computers pick the landing point, which is then transmitted to the X-47B. "This is forward-leading technology," Engdahl said. "It's relevant to the future of unmanned carrier aircraft."
Three separate computers on the drone evaluate the landing. If they believe a safe landing is not possible, the aircraft climbs and goes around for another approach.
As another safety precaution, a landing signal officer on the ship will hold a controller that will clear the aircraft to land. If a signal is not given to the aircraft, it will circle around and make another attempt.
"If the hook skips over the wires [upon landing] and it bolters, then [the X-47B] will know that it doesn't decelerate and it will go full power," Engdahl said.
And there's more to landing on a carrier than just landing.
"There's an entire dance that takes about 45 seconds to get it trapped, rolled out, pulled back, wings folded, taxi out of the landing area, so that you can land the next airplane," Engdahl said.
In addition to the test of the software on the Hornet, program officials have conducted more than 10,000 simulator lab tests, according to Pamiljans.
"It's part of our validation process to test to the analysis that we've already done, so that we've assured ourselves that before we go to the ship, before the test point, we have already done a rigorous risk analysis," he said.
Refueling Testing, Too
After the carrier landings, the second test aircraft will conduct air-to-air refueling using both U.S. Air Force and Navy refueling systems.
The Air Force system uses a tanker plane equipped with a boom, and the Navy uses a tanker with a probe-and-drogue configuration.
"The Air Force style is pretty easy," Engdahl said. "The Navy style is going to be pretty challenging."
The Air Force test will be done with a KC-135 Stratotanker and the Navy test with a commercial Boeing 707 Omega tanker. Both tanker planes will have special equipment installed that allows crew members on board to take control of the drone during the refueling process.
"We have developed all the [concept of operations] of how we're going to pass control from the ship or the shore to the aircraft, how the aircraft actually rendezvous with the tanker, and how it's going to fly formation with the tanker," he said.
A successful demonstration could revolutionize naval aviation, said Navy and industry officials.
"It truly does portend a significant change in the advantages and the power and the versatility of naval carrier aviation," Adm. Gary Roughead, chief of naval operations, said of the X-47B. "If we can blend the unmanned on an aircraft carrier and the manned [aircraft] on an aircraft carrier, we've changed the dimension of carrier naval aviation in a way that has not happened in decades."