US defense agency contracts out long-range flying boat designs

The Defense Advanced Research Projects Agency (DARPA) granted contracts to two teams to develop plans for a low-flying seaplane that can speedily traverse large distances while carrying heavy loads for its Liberty Lifter program, the agency announced on Wednesday.

One of the teams awarded the contract is a partnership of General Atomics working alongside Maritime Applied Physics Corporation. The other team is Aurora Flight Sciences partnered with Gibbs & Cox and ReconCraft. 

What is DARPA?

DARPA is an official agency of the United States Department of Defense focused on furthering technological research that has prospective military utility. The agency states that, since the launch of the Russian Sputnik satellite in 1957, it has been committed to promoting the American goal of being the initiator, rather than the victim, "of strategic technological surprises."

The Department of Defense agency has also been credited with a number of innovations that have massive global influence. In 2021, the Economist wrote that "Moderna’s covid-19 vaccine... weather satellites, GPS, drones, stealth technology, voice interfaces, the personal computer and the internet [are] on the list of innovations for which DARPA can claim at least partial credit."

Now, the agency is looking to develop a long-range, low-cost flying boat as part of its Liberty Lifter program.

The agency describes the Liberty Lifter program as an initiative "to develop a seaplane that operates efficiently in ground effect," can fly as high as 10,000 feet at mean sea level (MSL), and can transport large payloads across great distances at far greater speeds than similar, current alternatives.

The program aims to do this at low manufacturing cost while maintaining the highest innovation and performance standards.

The teams awarded the DARPA contracts have each proposed their own, distinct design for the long-range flying boat.

The General Atomics team opted for a design that features a twin hull. Their plans include a mid-wing design and rely on propulsion from twelve turboshaft engines.

The Aurora Flight Sciences proposal is single-hulled with a high-wing design. It primarily relies on eight turbine engines for propulsion.

What is ground effect?

DARPA states that the Liberty Lifter program aims to develop a plane that is capable of flight at less than 100 feet from sea level in order to harness the physics of this effect.

Additionally, DARPA states that it aims for its plane to achieve goals including "takeoff and land[ing] in Sea State 4, sustained on-water operation up to Sea State 5."

"Sea state" conditions refer to the overall condition of the surface of a large body of water with regard to environmental circumstances such as wind and waves.

The Beaufort Sea State Code describes a sea state 0 as when the sea is "like a mirror" with no disturbance. A sea state of 4 has "small waves. Fairly frequent white caps." It describes sea state 5 as having moderate waves with lots of white caps, potential spray and wind speeds of 17 - 21 knots.

The Liberty Lifter program is a multi-phase project. The first phase is an 18-month design development and planning period. It will continue until mid-2024.

DARPA announced that phase 2 will continue with "detailed design, manufacturing, and demonstration of a full-scale Liberty Lifter X-Plane." Additionally, they write that "DARPA anticipates teaming with one or more DoD Service and international partners for those activities and further development of the Liberty Lifter concept into an operational vehicle."