The U.S. Navy is building on the successful first flight of the stealthy, tailless Northrop Grumman X-47B demonstrator as a pivotal step toward the long-held goal of marrying persistent, autonomous unmanned intelligence and strike aircraft with the reach of its fleet of aircraft carriers.

“We’re celebrating the centennial of Naval aviation, and if we fast-forward 100 years, then we’ve added three words—unmanned, autonomous and LO [low-observable] relevant,” says Capt. Jaime Engdahl, the Navy’s Unmanned Combat Air System (UCAS) project director. The X-47B flight-test program, which began with a 29-min. flight at Edwards AFB, Calif., on Feb. 4 will answer questions about what it takes “to put unmanned, autonomous and LO-relevant into the carrier environment.”

Though proving the viability of the once unthinkable concept of autonomous combat air operations from the carrier, UCAS is also a critical technology stepping-stone to the Navy’s planned Unmanned Carrier-Launched Surveillance Systems (Uclass) program. “Just as important is the technology we embed into the carrier itself,” says Engdahl, referring to the data link and related communication breakthroughs that UCAS-D is expected to demonstrate as part of a planned seamless integration of unmanned aircraft into carrier air wing operations.

While Engdahl describes the first flight of an unmanned Navy X-plane as a “huge deal,” another industry executive notes its significance as an interim step to a future fleet of carrier-borne unmanned combat vehicles. “It is the start of an intent for unmanned aviation on a carrier. It is not the carrier landing—that will be a big deal, too,” says Carl Johnson, Northrop Grumman’s vice president of program management. But this first flight represents the beginning of unmanned tactical aircraft for the Navy.”

The test program will work toward carrier landings in 2013. It will then turn to prove the concept of aerial refueling, which would eliminate onboard fuel storage as a limiting factor for mission endurance in future combat UAS.

To date, the Pentagon has largely used unmanned aircraft to provide intelligence and—in limited fashion with the Air Force’s General Atomics Predator and Reaper—attack capabilities. In general, unmanned aircraft—also including tiny Boeing ScanEagles, AeroVironment Ravens and AAI Corp. Shadows, as well as Northrop Grumman’s larger Fire Scouts and Global Hawks—have all been designed to function in permissive airspace. Introduction of the stealthy UCAS, however, “represents a significant step in a change in the roles for unmanned vehicles,” an industry executive says.

Success of the demonstrator will be key to achieving the planned follow-on purchase of an interim fleet of Uclass. “What [UCAS] moves us into is Uclass—a carrier based-system—for the first time,” says Rear Adm. Matthew Klunder, director of intelligence, surveillance and reconnaissance (ISR) at Navy headquarters. The service hopes to kick off a competition as soon as this year to field up to eight air vehicles on a carrier in 2018.

Northrop is expected to build off of its X-47B experience, Boeing will use its X-45-based Phantom Ray background and General Atomics will likely use its Avenger concept as a departure for its design. Lockheed Martin is also likely to bid, building off of work on the Polecat demonstrator and the RQ-170 now fielded by the Air Force.

A request for proposals (RFP), which was expected this spring, will slip at least to this fall, says Klunder. The primary mission of Uclass will be to contribute to the carrier’s need for round-the-clock ISR collection in its area of operation. Navy officials declined to provide a schedule for when requirements will be reviewed by the Joint Staff.

But debate is continuing in the Pentagon over what attributes to emphasize in the design. And industry is weighing in.

Endurance appears most highly valued aside from fielding the aircraft in 2018. Navy officials are studying how much onboard fuel could be traded to allow for suitable payload and survivability attributes. Ultimately, it comes down to balancing the requirements.

It is not a foregone conclusion that the vehicle will require a high degree of stealth. According to one industry official, “It is in the mix, but it doesn’t sound like that is one of the top priorities. The real issue here is that a more conventional-looking airframe may be the best option.”

Klunder confirms hopes for growth on the air vehicle.

Incorporation of rigorous stealthy requirements would favor Northrop and Boeing, both of which have vehicle designs already mature. Lockheed’s classified work could provide an advantage. General Atomics’ designs are generally less stealthy but offer high endurance.

The focal point of the debate appears to be balancing survivability against endurance. Originally, the Navy’s draft request for information issued last spring called for a vehicle capable of a range of 600 nm and 12 hr. on station. “There isn’t a combination of design parameters that would satisfy the Navy’s requirements,” says one industry executive. “If there is no survivability requirement, then any airplane with a tail can meet the Navy’s requirement,” says another.

The original plans called for an aircraft with a more-than-100-ft. wingspan, but a requirement to allow for landing slightly off the centerline of the carrier will limit the width of the aircraft to 70 ft. UCAS has a 62-ft. wingspan.

The UCAS flight-test Block 1 effort will focus first on the basic airworthiness of the tailless aircraft, as well as envelope expansion with the initial U4.4 vehicle management software load. Following the Feb. 4 first flight, up to three additional flights are scheduled by the end of the month to verify performance before a planned modification period for fuel system-related center-of-gravity changes in March.

The test aircraft, AV1, lifted off from Edwards AFB Runway 4R at 2:09 p.m. PST at a speed of 180 kt, and reached a maximum of 240 kt during its 29-min. flight. The vehicle flew a racetrack pattern at 5,000 ft. over the dry lakebed with the landing gear down. Handling qualities were assessed at reduced speeds of 160 kt and 140 kt during the flight, which included pitch doublets. “The air vehicle performance was rock-solid. It did exactly what was expected, and the preliminary feedback was it matched the aerodynamic modeling very well,” says Engdahl.

On landing, the aircraft touched down around 60 ft. ahead of where it was expected, but “right on the centerline,” says Janis Pamiljans, Northrop Grumman vice president and UCAS-D program manager. The touchdown was the equivalent of catching the “number one wire” in Navy parlance, and gives the flight-test team good input for fine-tuning flight control software, he adds.

After an earlier delay, the aircraft was targeted to fly by late December, but this got pushed back while Northrop Grumman worked to correct an asymmetric braking issue uncovered during taxi tests.

The second aircraft, AV2, has meanwhile completed its design limit load tests up to 130% with “no test anomalies,” says Pamiljans. The test indicates the airframe is able to withstand the 2.4g loads it may see during air-to-air refueling maneuvers. “This aircraft is clearly carrier-capable,” he adds. AV2 is being prepared for the start of fuel testing before being transferred to Edwards around March. First flight is expected in August. “The primary function of AV2 is as a test workhorse to demonstrate carrier landing and launch, as well as operations in and around the carrier. But it is also designed to expand the envelope, with higher g maneuvers and to demonstrate the ability to take on fuel inflight,” says Pamiljans.

AV1 is expected to transfer to Patuxent River, Md., at the end of 2011 where it will undertake Block 2 tests covering shore-based catapult and arrestment evaluations before being hoisted onto a carrier for compatibility tests on deck. In the second half of 2012, the X-47B will conduct a series of shore-based operations from Norfolk in carrier-controlled airspace within the Virginia Capes Range Complex, as well as make the first low approaches to a carrier. Shore-based tests will move to Lakehurst, N.J., at the end of the year for aircraft launch and recovery equipment checks.

In parallel, a program to test and evaluate the carrier element is under way with a Boeing F-18 flying as a UCAS-D surrogate. “We’ve been flying the software in a pallet load with F-18s over the last couple of months,” says Engdahl. Both open- and closed-loop carrier approaches have already been made. “The next milestone [targeted for April] is to take the F-18 surrogate and do actual approaches to the ship using the X-47B software,” he adds. The surrogate will also fly later this year with the early release U5.0 software. Incorporating guidance, navigation and communications protocols to interface with the carrier, as well as air-to-air refueling and full envelope control, U5.0 will be used to guide the F-18 to the first carrier touchdowns in February and March 2013. When four completely autonomous traps have been accomplished, this will clear the way for the first landings by AV1 and AV2. Autonomous aerial refueling tests with a Boeing KC-135 and other tankers will run from late 2013 into mid-2014.