DARPA selects competitors for its Liberty Lifter seaplane project

DARPA chose two radically different designs from groups led by General Atomics and Aurora Flight Systems to develop a full-scale maritime demonstrator of the Liberty Lifter strategic and tactical heavy cargo aircraft with a wing-in-ground effect.

In 2022, DARPA announced its project to develop an aircraft called the Liberty Lifter, similar in size and capacity to the C-17 Globemaster III transport aircraft, but capable of lifting more than 100 tons of payload. This is impressive considering that the C-17 can only lift about 77 tons on its best day, and that the Liberty Lifter is supposed to be a seaplane with a range of 6,500 nautical miles (7,500 miles, 12,000 km). This is enough to fly from the North Pole to the equator with a small margin.

The secret of this notion lies in the so-called “ground effect” or “wing-in-ground effect”, an esoteric aerodynamic phenomenon that was at the center of one of the greatest mysteries of the Cold War.

In the late 1960s, American spy satellites monitoring the Soviet Union saw a strange, very large aircraft hurtling across the Caspian Sea. Dubbed the Caspian Sea Monster by the intelligence community, it left analysts scratching their heads because this 500-ton-plus aircraft-shaped monster had thick, stubby wings that couldn’t keep it aloft.

It was revealed that the mysterious ship was an ekranoplan, which is a series of ekranoplans developed by the Soviet military that could evade radar detection by carrying a heavy missile load while flying at very low altitude.

It was the very low altitude which was the key. The ground effect occurs when an aircraft flies very close to the ground, or preferably water. Without getting into technical details, when an airplane moves forward at low altitude, it acts as if there is a cushion of air between it and the ground. As a result, drag is reduced and lift is increased, so the aircraft can have smaller wings, carry a heavier load, or a combination of both.

This is why the Caspian sea monster could be so big and fly with such short wings. Unfortunately, such ekranoplans have serious limitations. One of the biggest ones is that they work best when flying over the 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 take the technology one step further to create an aircraft that can carry heavy loads over long distances, land and take off on water to eliminate the need for runways. . , can be assembled using inexpensive shipbuilding methods and can run for weeks without maintenance.

DARPA

In addition, it must be able to take off and land in sea 4 when the waves reach 8.4 feet (2.5 m), and operate on the water in sea 5 with seas up to 13.1 feet (4 m). It must also be able to function as a low-altitude aircraft that can fly without ground influence to an altitude of 10,000 feet (3,000 m) above sea level.

For the first phase of the project, Aurora Flight Sciences, which leads Gibbs & Cox and ReconCraft, is developing a craft resembling 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 seaworthiness, and 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 refinement, before results are submitted for preliminary design review and test/demonstration planning review three months later. This will be followed by Phase 2 in 2024, when the successful project will move on to the development, production and demonstration of the full scale Liberty Lifter X-Plane.

“We are excited to launch this program and look forward to working closely with both execution teams as they refine their Stage 1 Starting Point design concepts,” said Christopher Kent, DARPA Liberty Lifter Program Manager. “The two teams took completely different design approaches, which will allow us to explore a relatively large design space in Phase 1.”

Source: DARPA