Because fixed-wing drones are faster and more energy-efficient than multicopters, they're often used for tasks such as mapping areas of the ocean. Many of them do require landing strips, however, which there isn't always room for on ship decks. A clever new technique gets around that problem, using copters to catch them.

Developed by a team at the Norwegian University of Science and Technology, the system requires fixed-wing drones to be equipped with a small box on their underside. As one of these drones approaches its host vessel at sea, that box opens, and a catch line with a hook at the end drops out and hangs down.

At the same time that the fixed-wing drone is nearing the ship, two autonomous multicopter drones take off from the vessel. They proceed to hover side-by-side just below the path of the incoming drone, with a cable stretched horizontally between them. As the drone's catch line closes in on that cable, the copters start flying in the same direction as that drone.

This results in the line getting hooked on the cable, but not too abruptly. The drone subsequently shuts off its motor, and ends up swinging down to dangle beneath the cable. It's then gently lowered to the deck of the ship by the multicopters, which also proceed to land on the vessel.

"The operation can be performed virtually anywhere, without a runway or other infrastructure," says the university's Prof. Tor Arne Johansen. "The method requires minimal modifications to any fixed-wing drone, as opposed to more traditional methods that recover fixed-wing drones in nets or vertical lines. These require the drone to be designed to withstand the heavy loads encountered during landings."

And while there are fixed-wing drones that can perform vertical take-offs and landings, these tend to be more complex and have a shorter range than their conventional counterparts. There is also at least one model that can perform belly landings on the water, although rough seas would pose a challenge for it – plus it has to be retrieved from the water after landing.

The new Norwegian "linecatch" system is demonstrated in the video below.

Source: Gemini