Europe's long-standing interest in maritime unmanned aircraft continues to build, and its industry is hoping to catch up with and surpass U.S. rivals by cracking the technological challenge of operating from warships in high seas.

Automatic launch and recovery of unmanned rotorcraft is a major challenge in the operational environment that is a ship at sea. But when it comes to the delicate maneuvering required to land helicopters onboard patrol boats and frigates—especially in rough weather—machines may soon outperform their masters.

“Today, ship-landing unmanned helicopters requires calm sea, good weather, with an external pilot. But we are getting rid of these constraints,” says Jean-Noel Stock, vice president of drones, surveillance and intelligence at Thales, which with French shipbuilder DCNS is developing the D2AD automatic deck-landing system for future naval unmanned aircraft systems (UAS).

France has taken a lead in demonstrating technology for automated land- and ship-based vertical-takeoff-and-landing (VTOL) operations, but the U.K.'s Royal Navy has a potential requirement for a rotary-wing shipboard UAS and a joint program looks possible.

Thales, EADS-Astrium and Indra are among a growing number of European companies developing automatic VTOL systems for unmanned rotorcraft operating in challenging sea-state environments (see p. 33). In October, under the D2AD project, French defense equipment agency DGA completed a four-year demonstration of unmanned rotorcraft capable of landing onboard ships in difficult weather conditions. The project culminated in 30 successful takeoffs and landings of a Boeing H-6U Unmanned Little Bird on the Lafayette-class frigate Guepratte off Toulon Sept. 24-Oct. 4.

“The roughest we got to was Sea State 3, but we gathered enough data to put that into our simulation model and demonstrate our system was [capable] up to Sea States 4 and 5,” Stock says. Sea State 5 means waves up to 12 ft., winds to 40 kt. and a frigate flight deck rolling 15-20 deg.

Derived from the launch and recovery system for the Thales Watchkeeper fixed-wing tactical UAS, D2AD includes a shipboard segment using radar sensors for guidance and motion-prediction software to anticipate the ship's movement. The flight segment, which functions independently of GPS and is adaptable to different types of UAVs, involves an airborne beacon and deck-lock harpoon that engages a landing grid and holds the aircraft to the flight deck.

“To the best of our knowledge, even the U.S. today has not gone so far in the experimentation of this system,” says Pierre Legros, senior vice president of the surface ships and naval systems division at DCNS.

DGA awarded the D2AD contract in 2008, giving Thales responsibility for the positioning system and UAS interface, supply of a demonstrator aircraft and slaving of its flight path along a trajectory. Majority-state-owned DCNS is responsible for predicting ship motion, the harpoon system, and system interface and integration with the vessel.

When operating in high seas, the motion of vessels will vary with size, hull design and stabilization system. When alighting on such a platform, a helicopter pilot must observe the heave, pitch and roll motion of the deck to determine when to land through a combination of aircraft capability and gut instinct.

With D2AD, a pilotless aircraft approaching a ship in rough waters and inclement weather begins transmitting its position and heading to a pair of receivers on opposite sides of the flight deck. The receivers triangulate the signal and a correction order is sent to the helicopter.

The system's sophistication, however, has less to do with triangulating sensors than choreographing a sort of dance between the aircraft and the ship using DCNS-developed motion prediction algorithms that make it possible to anticipate the vessel's movement. When this information is conveyed to the helicopter, the aircraft is able in response to mimic the ship's pitch and heave and anticipate roll as it lands.

“The interface is simple, but the intelligence is not in radar, it is in the prediction of movement,” Legros says.

Such delicate maneuvering was performed accurately during the sea trials. Legros says the helicopter was manned to ensure safety during testing, but with “no hands on the controls.” He says the system's demonstrated reliability and precision offers the potential to become a standard component of all naval helicopters.

“The pilot in the helicopter doesn't have any means to anticipate the movement of the platform,” he says. “At the end of the day, this system should be more precise, more accurate and safer than normal helicopter operation.”

However, pilots may be reluctant to trust the notion that technology can beat human ability.

“After some trials they will start to be convinced,” he says. “It is clearly our goal to offer the same system for [manned] helicopters in the future for safer operations.”

Initial flight trials of the D2AD system started in early 2011 using a helium balloon and light aircraft with a platform modeling the ship. Landings in unprepared areas were conducted over the following summer, “just to show there could be some army configurations,” Stock says.

D2AD was also tested with the Unmanned Little Bird in the U.S., with landings on a three-axis motion platform simulating a moving deck and on a trailer towed by a truck at 5-15 kt. to represent a ship under way.

Although sea trials involved a nearly 2,000-kg (4,400-lb.) aircraft, Legros says D2AD can be installed on all types of VTOL UAVs equipped with the harpoon. “We're not integrating into the flight-control software, therefore integration is only a matter of a week or so,” Legros says, adding that installing the sensors and software onboard the Lafayette frigate took four weeks. “[It was] very easy, and very safe.”

Stock says the next step could involve integrating the D2AD system in a smaller UAS for DGA, such as the Austrian Schiebel S-100 Camcopter, which has been used in sea trials for the French and other navies.

“At the moment we anticipate that what the navies in France and the U.K. are looking for is a slightly smaller helicopter of the [1,000-kg] class,” he says.

While the D2AD project is aimed at reducing risk for a future French navy UAS program called SDAMA (for Systeme de Drones Aeriens de la Marine), it could benefit the U.K. defense ministry's planned Rotary-Wing Unmanned Aircraft System (RWUAS) “concept capability demonstration.” When announced in July, a contract for the two-year project was slated to be awarded in January.

As described, the RWUAS demonstration “will inform future maritime UAS requirements, potentially leading to an acquisition program in the second decade,” according to the defense ministry's announcement. The project will involve physical demonstrations and simulation experiments with a VTOL UAS to “assess platform integration issues and the impact . . . of bringing an RWUAS into service.”

An earlier study “identified the potential of a small or medium rotary-wing UAS to deliver the maritime capabilities being sought,” the announcement stated, categorizing the classes as systems weighing 100-1,000 kg and 1,000-3,000 kg, respectively.

EADS Astrium, meanwhile, is developing an automatic landing system for unmanned VTOL aircraft, known as DeckFinder, that makes use of space-based global navigation system technology on a local scale. Six “ground satellites” and corresponding airborne receivers enable fully automatic takeoff and landing for unmanned rotorcraft on fixed and mobile platforms. Using radio-based local positioning for precise near-field navigation, Deckfinder's accuracy exceeds the performance of global navigation satellite systems like GPS and Galileo, according to EADS.

The ground segment can be rapidly deployed or permanently installed around an existing helicopter landing deck, and the airborne segment, consisting of two downward-oriented antennas, a lightweight receiver and an airborne computer, can be configured for any UAS. Weighing as little as 1.2 kg, the system has standardized interfaces to connect to existing autopilot systems and can be installed in a matter of hours, says Julian Steffes, Astrium product manager for navigation applications.

“It provides more precision than a pilot, and you can tailor the algorithm to the platform,” he says.