West Bethesda, Md. –
Naval Information Warfare Center (NIWC) Pacific (PAC) and Naval Surface Warfare Center, Carderock Division engineers conducted tests of a drone tether management system at Carderock’s 8 feet by 10 feet Subsonic Wind Tunnel from Sept. 6-9, 2022.
Dr. Jared Soltis, aerospace engineer with the Sea-Based Aviation and Aeromechanics Branch, led the Carderock team that developed and provided enhanced testing capabilities at the Subsonic Wind Tunnel, and Dr. Kurt Talke led the NIWC PAC team that developed and provided the Unmanned Aerial Systems (UAS) and tether control system. This project is a Naval Innovative Science and Engineering project on which NIWC PAC and Carderock spent years collaborating, including an experiment in the Maneuvering and Seakeeping Basin (MASK) at Carderock in September 2021.
“The NIWC PAC researchers came up with this and have been developing it for a couple of years,” Soltis said. “Our role in the project is to test it in our facilities – the MASK last year and the Wind Tunnel this year.”
The experiment will eventually support the Naval Sea Systems Command Unmanned Maritime Systems (PMS 406) Program Office. As the Integrated Product Team Lead for PMS 406’s payload integration, Soltis works with other engineers across the Navy to integrate these systems onto PMS 406’s unmanned surface vehicles.
Tethered aerial systems come in many forms and are being adopted by the U.S. Navy for different missions. The aircraft tested in Carderock’s wind tunnel was a multirotor configuration, one of the most common. Commercial systems exist, but many are not adequate for naval ship integration due to insufficient tether control systems.
“Kurt Talke, NIWC PAC’s primary investigator in the program, came up with the idea to use a slack tether instead of a taut tether,” Soltis said. “Instead of pulling on the drone with a constant amount of tension, the tether hangs slack, which reduces the amount of force pulling down on the drone. You get better performance, better payload capability and other advantages.”
A tethered drone system provides benefits such as power, secure communications and greater bandwidth. They’re also less expensive than a manned helicopter and can have fewer requirements for the ship to operate compared to a very large drone.
“You can provide power and communications control through the tether so you don’t ever have to land,” Soltis said. “That’s great in establishing a communications relay or persistent observation node near the host vessel. This increases communication distances and you get a camera up high, allowing you to see more than from the ship’s deck. It’s the elevated position of whatever it is you’re carrying with an effectively unlimited endurance.”
Carderock’s Subsonic Wind Tunnel facility can test the drones in flight at wind speeds up to about 45 miles per hour.
“We’re flying in the largest cross section of the tunnel circuit, which is not usually used for testing,” Soltis said. “This large volume provides enough space for free-flight UAS and a motion-tracking system to measure UAS and tether dynamics.”
Last year’s collaboration focused on how the system responded to waves, and was conducted in the MASK. This year’s experiment focused on the impact of wind.
In some tethered systems, aerodynamic drag can generate enough force to pull the tether out and even lead to a runaway situation where it can’t be controlled. A slack tether management system can reduce the forces on the tether and alleviate some of these issues.
NIWC PAC brought the drone and tether management system while Carderock provided the facilities and motion tracking and control system. Operating the UAS and tether control system inside the Subsonic Wind Tunnel required that Carderock’s motion capture system broadcast the UAS position with the NIWC PAC drone and tether controller in real-time. Because the test leg of the wind tunnel had to be closed during testing, the pilot needed to fly the drone by using cameras installed in the section and coordinate with the motion tracking system operator and tether system operator to ensure successful flights.
Eventually the team wants to combine the wind and motion components together in new testing facilities or in the real world.
“Tethered UAS are being used on a number of different vessels for multiple purposes, so we expect there is going to be more testing of new concepts and development,” Soltis said. “Now that we enhanced the wind tunnel with motion tracking capabilities, we expect more testing of unmanned aerial systems in the wind tunnel and doing things like swarming – multi-aircraft operations in challenging environments.”