The research arm of the US Department of Defense promises the first prototype by 2027. Most pilots are aware of the phenomenon that when they fly their aircraft close to the ground, they can glide much further than usual. This is because the proximity to the ground breaks the turbulence created by the wings in such a way that it results in reduced friction.
This phenomenon has already been recognised by designers and led to the first boundary-wing aircraft, or ekranoplanes, which combine the characteristics of hovercraft with those of aeroplanes. However, one important difference compared to aircraft is that while in conventional aircraft much of the lift is due to a reduction in pressure above the wing, in ekranoplanes the lift is due more to an increase in pressure below the wing.
By exploiting this phenomenon, ekranoplanes can theoretically travel faster than a ship, but can be operated more economically than an aircraft. DARPA, the research arm of the US Department of Defense, is now developing a new ekranoplanet under the newly announced Liberty Lifter programme, IEEE Spectrum reports.
The objectives of the DARPA Liberty Lifter programme are that the vehicle should be cheap and easy to manufacture – something that has not been the case with DARPA’s development of the eponymous Liberty-class warships of the same name, used in the Second World War. According to DARPA’s call for proposals, the following criteria must be met by the applicant manufacturers’ vehicles:
- have a minimum range of 7,500 km.
- be able to climb to an altitude of 3000m if necessary.
- be capable of carrying a minimum of 90 tonnes.
- be able to carry, receive and launch amphibious vehicles.
- be capable of operating on the high seas and oceans.
- be able to spend up to 4-6 weeks at a time on the high seas.
The Liberty Lifter programme will select two of the applicants and allocate the USD 15 million for the development of the vehicle. DARPA hopes that by around 2025, there will be concepts with at least one of them passing the review. If successful, the first prototype could be airborne by 2027. Interestingly, the DAPRA video published on the programme shows a twin-turret concept – a configuration that has not been built before.
This is not the first time that DARPA has flirted with the idea of a similar vehicle: in the mid-1990s, they designed the Aerocon Dash 1.6 wingship, which would have dwarfed even the largest ekranoplanes ever built: it would have had a wingspan of 100 metres, 20 jet engines and the capacity to carry 3,000 people or 1.4 million kg of cargo. The plane was ultimately deemed too dangerous and too expensive, and remained only a blueprint, never built.
One of the first jet-powered ekranoplanes was the VVA-14, designed by an Italian-born designer, Robert Bartini, and built in the Soviet Union in the 1970s. It first took to the skies from a runway in 1972, but in the years that followed it was tested numerous times in water. But with Bartini’s death in 1974, the programme died. However, the last of the aircraft remained in service until 1987. Another Soviet ekranoplanet, also from the 1970s, was the A-90 Orlyonok, but this one had propeller propulsion instead of jet engines.
The most famous ekranoplanet, however, was the Ekrano monster, also built by the Soviets and known simply as the “Caspian Sea Monster”, which was equipped with 10 jet engines and could travel at speeds of up to 550 km/h. The A-90 was a Soviet-built ekrano, which was also a Soviet-built ekrano. Only one of the Luny-class ekranoplans was built, which entered service in 1987 and remained in service until the late 1990s.