Aurora Flight Sciences has provided new details about the demonstrator design it is working on for the Defense Advanced Research Projects Agency’s (DARPA) Liberty Lifter X-plane program. Liberty Lifter’s core goal is to prove out a new ekranoplan flying transport design that employs the wing-in-ground (WIG) effect principle. A future aircraft based on the demonstrator could give the U.S. military a new way to affordably move large amounts of cargo and personnel across long distances, and without the need for traditional runways.
Richard Koucheravy, business development director for manufacturing at Aurora, gave TWZ‘s Howard Altman an update on Liberty Lifter from the floor of the Modern Day Marine exposition today. In 2023, Aurora Flight Sciences and General Atomics received contracts to conduct initial Liberty Lifter work. Last year, DARPA selected Aurora Flight Sciences, which is a wholly owned subsidiary of Boeing, to continue on alone in the development of what is hoped to be a flying demonstrator.
The most recent concept art of Aurora’s Liberty Lifter design shows a flying boat-style arrangement with a v-shaped hull for a fuselage and a large straight main wing with wingtip floats, all powered by eight wing-mounted turboprop engines. It also has twin vertical tails joined at the top by a horizontal stabilizer. Cargo, including light amphibious armored vehicles, has been depicted being unloaded via a large rear ramp, as seen in the video below.
General Atomics had proposed a more radical-looking twin-fuselage design that you can read more about here.
“So we are designing a demonstrator that is roughly about 80 percent scale to the objective airplane,” Aurora’s Koucheravy explained. This is a scale that “is representative enough that you can pull some really good lessons out of it without having to build the full scale objective aircraft.”
“So now we’re talking something that’s closer to C-130 cargo size, 25-ton [payload],” he continued, adding that the demonstrator is expected to have a wingspan of around 216 feet. It will also use U.S. government-supplied engines, and Aurora said it would follow up with TWZ about exactly what type they are expecting to receive.
DARPA has previously said the ultimate vision for Liberty Lifter is a design with a comparable payload capacity to the C-17A Globemaster III cargo aircraft. The C-17’s stated maximum payload weight is some 82 tons, although the planes more typically fly around with around 60 tons or less worth of cargo and personnel inside.
Liberty Lifter requirements that DARPA has released publicly in the past also include the ability to take off and land in open water in conditions up to Sea State 4 and “sustained on-water operation” at up to Sea State 5. These two Sea States are characterized by wind speeds of 11 to 16 knots and 17 to 21 knots, as well as wave heights between three and five feet and six and eight feet, respectively.
“We’re building a demonstrator with an unpressurized cockpit, because the aircraft is primarily intended to fly in ground effect, which, for an aircraft this size, it’s going to be pretty close to the water. You’re going to be within a few 100 feet of the water,” Koucheravy explained. “And in order to do that, if there’s any level of Sea State, you’ve got to have the right technology to enable the aircraft to maintain ground effect for very long distances, even though you’ve got potentially some heavy seas. So that’s one of the technical challenges of the program.”
The idea of a flying platform utilizing the wing-in-ground (WIG) principle is not new, but designs of this kind have been met with very little success historically, especially for military use. The Soviet Union remains the most notable operator of military WIG designs, known in Russian as ekranoplans – a term now widely used as a catch-all for WIG designs – but even there their service was limited. Efforts to revive military ekranoplans in Russia in recent years have so far not produced any operational types.
The video below shows the only Project 903 Lun class ekranoplan, a cruise missile-armed design, that the Soviet Union ever completed being moved in the Caspian Sea in 2020 as part of a plan to put it on display.
In principle, ekranoplans offer a highly efficient over-water craft that can move at high speeds since it does not suffer from the drag associated with typical ship designs, while also benefiting from the lift generated by a wing. At the same time, high-speed sea-skimming flight presents challenges, as Koucheravy highlighted, including the risk of collisions with various objects on the surface or even just high cresting waves.
To help get around these issues, DARPA’s Liberty Lifter program has called for something of a hybrid design that is still capable of operating like a traditional flying boat, if required, at “altitudes up to 10,000 feet mean sea level with a compromise on range.”
“I think this early in an aircraft design where you have your preliminary design, you basically have the outer mold line of the aircraft, more or less set, you understand your configuration, but there’s still design work to do once you go through that,” Aurora’s Koucheravy said. “And so we’re excited to move into the detail design phase and start building the airplane.”
DARPA is expected to make a decision about whether or not to proceed to the next step with Liberty Lifter this summer. Where Aurora might then begin actually building the demonstrator is still “open question,” according to Koucheravy.
“You know, one of the objectives of the program is to look at maritime manufacturing processes to the max extent possible, rather than approaching this purely from the aerospace build,” he explained. “So the aircraft will be built through a combination of maritime ship-building processes and aircraft build processes.
This “means we’re going to be looking for a location that has a robust maritime workforce” that includes “shipyards [and other] partners on the maritime build side that can help us build and assemble the aircraft close to the water, and then float the airplane,” he continued. “This will not have landing gear. The demonstrator will not be a land based airplane. So it, shortly after build, at some point in the build process, it’ll be floated, and it will live its entire life cycle, pretty much, on the water.”
Naval architecture and marine engineering firm Gibbs & Cox, a subsidiary of Leidos, has notably been part of Aurora’s Liberty Lifter team since the beginning.
The maritime focus of Aurora’s designs speaks to the broader objectives of what DARPA is looking to demonstrate with Liberty Lifter.
“The Liberty Lifter program is currently designing and will build, float, and fly an affordable and innovative seaplane that can potentially transform fast logistics missions for the DOD and commerce,” DARPA states on its current webpage about the program. “Liberty Lifter’s innovative manufacturing techniques and materials offer a path to utilize existing infrastructure to rapidly build – at low-cost – a capability essential for our warfighters, helping to advance the efficacy of our defense industrial base to meet near-term needs. Liberty Lifter could also provide sea-based search and rescue and disaster response at the scale of ships with the speed of air transport.”
Moreso even than offering an alternative to traditional cargo aircraft, Liberty Lifter could provide a new tool for “efficiently transporting large payloads at speeds far exceeding existing sea lift platforms,” according to DARPA.
An over-water logistics capability that is faster than existing cargo ships and is not runway dependent like many traditional cargo planes could be particularly valuable in a future conflict in the Pacific. Especially in a high-end fight against China, U.S. forces in the region would be greatly dispersed, including to more remote locations without well-established infrastructure, to reduce their own vulnerability to attack. Existing traditional airlift and sealift assets would be heavily tasked in general to support those distributed operations.
In addition, Liberty Lifter would be able to avoid many maritime threats like submarines and anti-ship missiles. A very-low-altitude flight profile typically improves overall survivability by helping conceal an aircraft from defenders, especially their radars.
With all this in mind, runway-independent aviation capabilities, or at least ones that are less dependent on traditional airstrips, are of growing interest to the U.S. military. U.S. Special Operations Command had also been working on a floatplane version of the MC-130J Commando II special operations tanker/transport aircraft, but shelved that project last year, citing budgetary issues. The very capable Japanese ShinMaywa US-2 seaplane has also been discussed as another potential path to this kind of capability.
For its part, last year, the state-run Aviation Industry Corporation of China (AVIC) announced the start of series production of the AG600, a large seaplane that has been in development since the late 2000s. TWZ has highlighted in the past how the AG600 would be particularly well suited to supporting far-flung island outposts like the ones China maintains in the hotly contested South China Sea.
Whether or not DARPA decides to proceed with Liberty Lifter and when Aurora’s planned demonstrator may actually fly for the first time remains to be seen. The program is now looking at the potential start of flight testing in the 2028-2029 timeframe, a delay from the original 2027-2028 schedule. DARPA X-plane programs do not always come to fruition, something Aurora is directly familiar with from the cancellation of work on the XV-24 LightningStrike hybrid-electric vertical take-off and landing-capable drone in 2018.
“DARPA is faced with a decision this year, this summer, on whether or not to move forward, execute [the] preliminary design review, and begin the detail design phase and the manufacture of the demonstrator,” Koucheravy acknowledged. “I think we’re as prepared as we can be to give DARPA what they need to make that decision, and we’re excited for the opportunity.”
For now, Aurora’s design for what could be the basis of a new ekranoplan transport for the U.S. military is already becoming firmer.
Contact the author: joe@twz.com