DARPA’s Liberty Lifter seaplane aims to tap ‘ground effect’

The United States is seeking to develop a massive new seaplane known as the Liberty Lifter that will harness the ground effect to transport military payloads over long distances.

An X-plane project under the direction of DARPA (Defense Advanced Research Projects Agency), Liberty Lifter will be designed to operate at sea for weeks at a time, capable of both water and traditional runway landings. When traversing long distances across water, the seaplane will seek to exploit the ground effect, flying just a few metres above the sea’s surface to reduce drag and allow the aircraft to operate with high efficiency.

The concept has been successfully exploited in the past by the Soviet-era ekranoplans. Known as Project 903, the Lun-class ekranoplan MD-160 came into service in 1987, using the ground effect for efficient military logistics in and around the Caspian Sea. Just one model was ever fully built, with a second due to be developed into a flying field hospital before the collapse of the Soviet Union ended the programme.

Whereas the ekranoplans were designed only to operate low across water and in calm seas, the Liberty Lifter will be capable of reaching heights of 10,000 feet across sea and land, as well as take off and land in rougher waters and congested, active military theatres. According to DARPA, the plane will also be developed with a low-cost design and construction philosophy.

“This first phase of the Liberty Lifter program will define the unique seaplane’s range, payloads, and other parameters,” said Alexander Walan, a programme manager in DARPA’s Tactical Technology Office. “Innovative advances envisioned by this new DARPA program will showcase an X-plane demonstrator that offers warfighters new capabilities during extended maritime operations.”

The three key challenges for the Liberty Lifter programme have been outlined by DARPA as follows:

Extended Maritime Operations: Emphasis will be placed on operating in turbulent sea states by creating high-lift abilities at low speeds to reduce wave impact load during takeoff/landing, and innovative design solutions to absorb wave forces. In addition, the project will address risks of vehicle collision during high-speed operation in congested environments. Finally, the aim is for the vehicle to operate at sea for weeks at a time without land-based maintenance activities.

Full-Scale Affordable Production: Construction will prioritise low-cost, easy-to-fabricate designs over low-weight concepts. Materials should be more affordable than those in traditional aircraft manufacturing and available to be purchased in large quantities.

Complex Flight and Sea Surface Controls: Advanced sensors and control schemes will be developed to avoid large waves and to handle aero/hydro-dynamic interactions during take-off/landing.