Paris Air Show

Navy sets stiff test for UCAV carrier ops

 - June 9, 2009, 6:20 AM

We all know that unmanned aerial vehicles (UAVs) present operational challenges, and making them into stealthy, tailless jets and asking them to do combat is even more challenging. But what about an unmanned stealthy tailless combat jet that must take off and land on an aircraft carrier?

That is the challenge of the U.S. Navy Unmanned Combat Air System (Navy-UCAS) program, and a team led by Northrop Grumman is trying to meet it with the X-47B, which is due to fly later this year and go to sea in late 2011.

The Navy-UCAS is a six-year development program, which is due to end in 2013. It is worth $636 million to Northrop Grumman and the major subcontractors– Lockheed Martin, Pratt & Whitney and GKN Aerospace–in addition to 10 other contributing aerospace companies.

Anyone who has ever been on an aircraft carrier knows that it is a highly orchestrated and disciplined flying environment. “The Navy has set the safety bar very high for the UCAS,” said Scott Winship, Northrop Grumman vice president and Navy UCAS program manager. Winship and his deputy, Tim Beard, have spent countless hours talking with fleet personnel and feeding their input into modeling performed by the company’s software development laboratory at Rancho Bernardo in California.

“We’ve modeled the approach ad nauseam,” said Beard. The Navy has insisted that no new landing control systems be added to the carriers in order to land a UCAS, he said. Therefore the X-47B will use the proven autothrottle techniques developed for the Navy’s standard automatic carrier landing system (ACLS), combined with inputs from its own precision GPS navigation system. This can guide the UCAV to “within inches” of the centerline, according to Beard.

The landing signal officer (LSO) will be connected to the UCAV by the newly developed TTNT IP datalink. At the decision point, three quarters of a mile to touchdown, the LSO will flick a switch to signal the air vehicle’s mission control. If no signal is received by the X-47B, it will automatically execute a go-around.

Even when the UCAV is on short final, the LSO or the ship’s control will still be able to “wave it off,” he said. The X-47B’s flight control system will contain sophisticated “bolter” and “trap” logic to determine whether it is safely down on the deck.

Once the UCAV is safely trapped, what next? A deck handler will plug a hand-held device into the vehicle to control the brakes and shepherd it to the required position, where the engine may be shut down. With a near-50-foot wingspan and 40-foot length, the X-47B is not small, but its outer wings can fold. According to Beard, Northrop Grumman has found an ingenious solution to the problem of keeping the wing “stealthy” despite the folding mechanism. Three of the UCAVs can fit on the elevators of the Navy’s latest carrier, the U.S.S. Roosevelt; underneath, “it fits very well in all deck spaces,” said Beard.

For takeoff, the UCAV’s flying wing design provides one big advantage–the carrier does not have to turn into the wind. The deck handlers will maneuver the X-47B into position for a catapult launch, then the aircraft will display a blue light to indicate that the mission operator (sitting at a workstation somewhere below the flight deck) has taken control, and the X-47B is ready for launch.

The Navy has signed up for Lockheed Martin’s F-35 fighter program, so why does it need another stealthy carrier-based air vehicle? According to Winship, the Navy needs a UCAV for the superior “all-aspect” stealth that only a tailless, cockpit-less design can provide, and also for its greater range. Because of the growing reach and capability of shore-based threats to the big carriers, they are keeping station much further out to sea, he said. Only the UCAV has enough range to cover the extra distance to land-based targets.

The X-47B has a combat radius of more than 1,500 nm. It can travel at high subsonic speed on the power of a single Pratt &Whitney F100 turbofan. “We can generate a tremendous amount of deep coverage–and stay there,” said Winship.
The two internal weapons bays can carry various payloads of up to 4,500 pounds: JDAMs (joint direct attack munitions) or small diameter bombs (SDBs); intelligence, surveillance and reconnaissance sensors; electronic attack systems; or 400 gallons of fuel for extra endurance.

However, the Navy-UCAS demonstration does not require the X-47B to drop bombs, or to have ISR sensors integrated. Nor will the two air vehicles in the program be measured for stealth: the special edges that Lockheed Martin was to provide have been eliminated to save money. If the demonstration is successful, the Navy could launch a System Design and Development phase in 2014. But it could still be 2025 before an initial operating capability is achieved–an indication of just how difficult this business really is.

Scott Winship and Tim Beard spoke at The UCAV Conference organized annually by IQPC in London. For more details visit –Ed.