People are familiar with most of the little drones that resemble a tiny helicopter. These machines are remotely controlled and have the ability to land anywhere.
However, a majority of drones that are employed professionally for inspection, surveillance, exploration, mapping, and other offshore missions are self-guided, include fixed wings, and require a small airstrip.
Now, the challenge is that many ships lack the space needed to land, and the operation of landing on ships is invariably complicated if the weather is unfavorable.
A number of solutions are available for effectively catching fixed-wing drones from ships; however, according to scientists at NTNU’s Department of Engineering Cybernetics, their technique is much more better. A couple of autonomous multicopters ascend from the ship with a cable existing between them, and precisely align themselves with the position and planned course of the fixed-wing drone. When these multicopters stretch the cable between them on the same path as the approaching drone, they produce a line that can be used for catching the drone.
Caught at full speed
Upon the approach of the fixed-wing drone, a tiny box opens on the fuselage’s underside and then a catch line drops with a hook fixed on the end. Before the cable contacts the catch line, the autonomous multicopters start to fly in the same course just like the fixed-wing drone so as to decrease the energy of braking. The arresting cable is caught by the hook, causing the drone to lose its speed and end up hanging from the arresting cable before being maneuvered onto the ship’s deck by the autonomous multicopters. In case the arresting cable fails to capture the drone, it is programmed to turn and reattempt, without making anyone to take over with remote control steering.
Well suited for Norway
According to Professor Tor Arne Johansen at NTNU’s Department of Engineering Cybernetics, there are immense possibilities for autonomous drones.
Unmanned, autonomous drones are often portrayed as one of the technologies with the greatest potential in international assessments. This applies especially in Norway, which has rugged geography, great natural resources, high costs and extensive expertise. The technology can reduce the cost of data acquisition, reduce risks and provide important decision-making support for many different purposes.
Tor Arne Johansen, Professor, Department of Engineering Cybernetics, NTNU
The need to land drones offshore
“The difficulty of operating drones from ships is currently the biggest obstacle to using more autonomous drones offshore. New methods that enable efficient and safe take-offs and landings from ships would open up a wide range of new applications.”
The advantage of NTNU’s “line catch” method
“The operation can be performed virtually anywhere, without a runway or other infrastructure. 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.”
Can tolerate bad weather
Johansen informed that the catch approach is scalable. If the drone is massive and flies at extreme speed, a long and strong cable needs to be used, for less abrupt braking, the autonomous multicopters should be able to fly quickly in the same direction. However, this cannot be achieved with landing systems placed on ships, he added.
The drone recovery solution of NTNU can be employed even in bad weather conditions because with extended lines, an extremely precise position is not required, unlike other approaches. Yet, the most standard fixed-wing drones today are not capable of flying in winds over 10 m per second, and they cannot tolerate heavy rainfall and icing. NTNU is currently performing a study on fixed-wing drones and systems that will have the potential to work in more adverse weather conditions.
Just like huge military aircraft that have fixed wings and can take off and land in a vertical direction (VTOL, vertical take-off and landing), certain autonomous drones can perform the same operation. One drawback is that drones like these are more complex and also tend to have a shorter range.
Betting on autonomous crafts
The advancement of drone recovery systems forms just a tiny part of NTNU’s contribution in autonomous vessels. AMOS—one of NTNU’s centers of excellence—is the main force behind the studies conducted on autonomous marine systems and operations. At a single time, the program engages about 100 scientists working with small satellites, drones, and autonomous underwater and surface vessels.
In November 2018, the drone recovery trials were carried out at Eggemoen airport in Hønefoss. The project was supported by the EU Horizon 2020 program and the Research Council of Norway. Maritime Robotics—a Norwegian company—is a partner in the project and has inked a contract with NTNU and NTNU Technology Transfer for the licensing of the technology.
Professor Tor Arne Johansen is responsible for the project, Mads Friis Bornebusch headed the testing at Eggemoen, and Martin Lysvand Sollie, a PhD candidate, is continuing studies on the technology.
Launching fixed-wing drones from ships is easier using different types of catapults. (Video credit: Mads Bornebusch, NTNU)