DARPA Chooses Geпeral Atomics aпd Aυrora fɩіɡһt Systems for Liberty Lifter Seaplaпe Wiпg-iп-Groυпd Effect Developmeпt
The Liberty Lifter is designed to carry heavy payloads over long distances.
In 2022, DARPA announced its project to develop an aircraft named the Liberty Lifter. This aircraft is designed to have the size and capacity of a C-17 Globemaster III transport aircraft, yet it could lift over 100 tonnes of payload. This is particularly impressive considering that a C-17 can only manage about 77 tonnes on its best day, and the Liberty Lifter is intended to be a seaplane with a ferry range of 6,500 nautical miles (7,500 miles, 12,000 km) – sufficient to fly from the North Pole to the Equator with a bit to spare.
The secret behind this remarkable performance lies in what is known as “ground effect” or “wing-in-ground effect,” which is an esoteric aerodynamic phenomenon that was at the center of one of the great mysteries of the Cold War.
In the late 1960s, American spy satellites observing the Soviet Union spotted a peculiar, exceptionally large aircraft maneuvering around the Caspian Sea. Dubbed the Caspian Sea Monster by the intelligence community, this colossal aircraft, weighing over 500 tonnes, perplexed analysts due to its thick, stubby wings that seemed incapable of supporting it in flight.
The Aurora Concept
It turned out that the enigmatic craft was an ekranoplan, part of a series of ground-effect vehicles being developed by the Soviet military. These vehicles were designed to evade radar detection while carrying a substantial missile load by flying at very low altitudes.
The crucial element was the extremely low altitude. Ground effect occurs when an aircraft is flying very close to the ground or, preferably, water. Without delving into too much technical detail, when an airplane is moving forward at low altitude, it creates a cushion of air trapped between it and the ground. As a result, drag is reduced, and lift is increased, allowing the aircraft to either have smaller wings, carry a heavier load, or a combination of both.
This is why the Caspian Sea monster could be so large and fly with such stubby wings. Unfortunately, such ground-effect craft have severe limitations. One of the biggest of these is that they work best flying over a surface of flat calm water, and they definitely don’t like rough seas.
DARPA’s Liberty Lifter project hopes to not only overcome some of these shortcomings but also to take the technology a step further to create an aircraft that can ferry heavy loads over a great distance, can land and take off on water to eliminate the need for runways, can be put together using inexpensive boat-building techniques, and can operate for weeks without maintenance.
The General Atomics concept
In addition, it must be able to take off and land in Sea State 4, where the waves reach as high as 8.4 ft (2.5 m) and operate on water in Sea State 5 with waves up to 13.1 ft (4 m). It must also be able to function as a low-altitude aircraft that can fly out of ground effect to an altitude of 10,000 ft (3,000 m) above sea level.
For Phase 1 of the project, Aurora Flight Sciences, leading Gibbs & Cox, and RecoCraft are developing a craft that resembles a traditional flying boat, with a single hull, high wing, and eight turboprop engines. Meanwhile, General Atomics and Maritime Applied Physics Corporation are working on a more exotic twin-hull, mid-wing design for better water stability and seakeeping, while propulsion is provided by 12 turboshaft engines.
Phase 1 is expected to last 18 months, with six months of conceptual design work and nine months of design maturation before the results are submitted for a preliminary design review and test/demonstration planning reviews three months later. This will be followed by Phase 2 in 2024 when the successful design will go forward to design, manufacture, and demonstrate a full-scale Liberty Lifter X-Plane.
“We are excited to kick off this program and looking forward to working closely with both performer teams as they mature their point-of-departure design concepts through Phase 1,” said DARPA Liberty Lifter Program Manager Christopher Kent. “The two teams have taken distinctly different design approaches that will enable us to explore a relatively large design space during Phase 1.”