Military

DARPA selects competitors for its Liberty Lifter seaplane project

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The Liberty Lifter is designed to carry heavy payloads over long distances
DARPA
The Liberty Lifter is designed to carry heavy payloads over long distances
DARPA
The Aurora concept
DARPA
The General Atomics concept
DARPA
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DARPA has chosen two radically different designs from teams led by General Atomics and Aurora Flight Systems for development of the Liberty Lifter Seaplane Wing-in-Ground Effect full-scale seaborne strategic and tactical heavy lift demonstrator.

In 2022, DARPA announced its project to develop an aircraft, called the Liberty Lifter, with the size and capacity of a C-17 Globemaster III transport aircraft, yet could lift over 100 tonnes of payload. That's pretty impressive, given that a C-17 can only manage about 77 tonnes on its best day, and that the Liberty Lifter is supposed to be a seaplane with a ferry range of 6,500 nm (7,500 miles, 12,000 km). That's enough to fly from the North Pole to the Equator with a bit to spare.

The secret of this performance is what is called "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 watching the Soviet Union saw a strange, very large aircraft tearing about the Caspian Sea. Dubbed the Caspian Sea Monster by the intelligence community, it had analysts scratching their heads because this monster of an aircraft weighing over 500 tonnes had thick, stubby wings that couldn't possibly support it in the air.

The Aurora concept
DARPA

It turned out that the mystery craft was an ekranoplan, which were a series of ground effect vehicles being developed by the Soviet military that could evade radar detection while carrying a heavy missile load by flying at very low altitude.

It was the very low altitude that was the key. Ground effect occurs when an aircraft is flying very close to the ground or, preferably, water. Without going into too much technical detail, when an airplane is moving forward at low altitude, it acts as if a cushion of air is trapped between it and the ground. As a result, drag is reduced and lift is increased, so the aircraft can either have smaller wings, carry a heavier load, or some combination of both.

This is why the Caspian Sea Monster could be so large and fly with such stubby wings. Unfortunately, such ground effects 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 to also 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
DARPA

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 ReconCraft, is 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."

Source: DARPA

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11 comments
Smokey_Bear
Kinda surprised Scaled Composites (Northrop) isn't in the mix, since it has a striking similarity to the giant Stratolaunch aircraft.
Demosthenes
Just go to russia first and look at the scrap of the ekranoplanes ...
PrometheusGoneWild.com
You mean like the one the Chinese have?
It’s good to see DARPA is still a decade behind everyone else when it comes to platforms.
Here is an idea, make a C-130 size hybrid EVTOL.
Existing technology. 50 people in a garage are making EVTOL aircraft.
Then you don’t have to deal with making it float and it could land anywhere. Including one of the carriers we have. Or a Marine flattop.
But Sikorsky, Bell and Boeing are too busy pimping their antique designs to the Defense Department for billions.
JeJe
History is littered with giant aircraft concepts that lead to cancellation. This project is meant to overcome the same problems Darpa's HULA airship was meant for... that got cancelled...
SeñorCitizen
Have to wonder about the "point" of an American ekranoplan. The C-5 Galaxy, last update more than 30 years ago, could carry 140 tons unrefueled for more than 2000 miles - imagine what a redesign for the 21st century using modern materials and updated engines could do A plane that can fly twice the distance of a "modern C-5" unrefueled, but only when the seas are relatively smooth, doesn't seem like a smart investment. If an opponent can detect and attack a aerial tanker 2000 miles from its destination can attack the transport it is refueling...
Unsold
Looks like that liberty lifter might want the wing flush to the fuselage at the top of the wing.
riczero-b
This reminds me strongly of the Boeing Pelican of about 15 years ago ; there must have been a ton of R&D for that plane that could be accessed for these ideas.
riczero-b
UNSOLD, wing in ground effect planes often have low set wings to increase clearance between the fuselage and flight surface, whilst keeping a strong air cushion trapped. Aurora compensates with the outer wing anhedral.
jerryd
It needs wings that are low and since they want it to fly too, it really needs to be a Manta Ray like blended body shape as the lift works more in low aspect ratio wings.
If just ground effect, a trimaran like ship with 2 sets of winds as crossbeams with props on the front wings.
The props need to be in front blowing air under the wings to get it out of the water 2-3x easier. An engine driving a water prop or jet can help get going a lot and maneuvering in port.
These also are prime EV passenger ships at about 250mph.
Rocky Stefano
An incredible waste of money given the current options