Riding the wave
© Regent
October 2021

Riding the wave

By Volker Paulun
Half airplane, half ferry: Wing-in-ground (WIG) craft efficiently “surf” an air cushion and are poised to play an important part in interurban mobility. The principle, though, has been around for a while.

The western world is shocked. In the middle of the Cold War, in September 1966, U.S. satellites are taking pictures of a …. well, what …? Is it an airplane floating in the harbor basin of a Soviet naval base? Or a new boat class? Well, it’s a hybrid of both, a wing-in-ground (WIG) craft. And it boasts such mammoth dimensions that U.S. intelligence officials reverentially dub it “Caspian Sea Monster.” The behemoth is 100 meters (328 ft) long, while the biggest Boeing 747 merely measures 78 meters (256 ft) in length. Its takeoff mass of 550 metric tons (606 short tons) is around 100 tons (110 short tons) higher than that of a jumbo jet. But what worries western military experts most is the fact that as a WIG craft it flies at a maximum altitude of 14 meters (46 ft), literally under their radar – at a speed of up to 500 km/h (310 mph).

Surfing a “rolling air cushion”

Today we know that their fears were unfounded. The Sea Monster was built only once and finally sank in 1980 after a pilot error. The few WIG craft that were to succeed it can only be found in museums today. Engineers in other countries pursued the idea as well, albeit a major commercial success has not materialized so far, even though these “wingships” are epitomes of efficiency due to the ground effect they use. As a result of this aerodynamic effect, a “rolling air cushion” forms underneath the wings and the fuselage on which the WIG craft can ride in an energy-saving way. Another efficiency benefit is the fact that, unlike normal aircraft, a WIG craft is not affected by wake turbulence. In total, the ground-effect gliding is supposed to be up to 40 percent more efficient than flying at higher altitudes.

This inevitably raises the question why this principle has not caught on so far. A decisive reason is that the higher the ground effect the lower the craft flies. Altitudes of clearly less than one meter (3 ft) are ideal in terms of efficiency. Such low flying altitudes practically exclude the use of WIG craft on land, which typically bristles with all kinds of obstacles. But even water is not always perfectly smooth. Waves, buoys, ships, offshore wind farms or bridges – a lot of things can get in the way of a WIG. The air cushion rolling in front of these gliders can also cause severe storm damage, plus flying extremely close to the surface used to have some pitfalls.

Buoyed up by new conditions and technologies

All in all, a plethora of disadvantages caused the efficiency advantage over airplanes to melt away, especially since aircraft fuel was cheap. Climate change and the resulting stricter emission limits, plus rising energy costs, now seem to buoy up the WIG idea again.

WIG craft have a major advantage: Thanks to their higher efficiency they’re clearly better suited for switching to battery-electric propulsion systems than airplanes. In addition, the important self-regulating stabilization programs have become increasingly better and cost-efficient due to technological progress.

Riding the wave© privat

The electrification of aviation enables new and revived concepts such as WIG craft. Power density and reliability of the electric propulsion units play a major part in this context. Schaeffler will continue to monitor these technologies

Dr. Peter Glöckner,
Director R&D, Engineering and OEM Sales Schaeffler Aerospace
Projects around the world

Brittany Ferries in France has recently signed a letter of intent for zipping across the Channel with Seagliders starting in 2028 at a top speed of 290 km/h (180 mph) and with up to 150 passengers on board. Regent, the Boston-based manufacturer of the flying boat, is even planning to start regular service with a smaller version in 2025. However, both companies said that the project raised “many technological, practical and regulatory questions.” Jonathan Ridley, Head of Engineering at the renowned Warsash Maritime Academy, commented to the BBC that in spite of all obstacles the plans were “really quite viable.”

Equally convinced of the idea is U.S. billionaire Mark Cuban, the owner of the Dallas Mavericks basketball team, who is a member of a group of companies and investors that were leading the most recent financing round for Regent. “The efficiency of coastal transportation will be 100 times greater with Regent. There is no other way to describe it. The idea of having to get between two coastal points is always stress-inducing. Regent changes all that and makes it fast and easy.” It’s conceivable that Cuban has set his sights on coastal points such as Los Angeles, San Francisco, New York and Miami.

  • The Seaglider from U.S. manufacturer Regent is supposed to cost half as much as a comparable airplane and be six times faster than a ferry

  • At a top speed of 290 km/h (180 mph), the Seaglider is supposed to achieve a range of 290 kilometers (180 miles), twice as much as that of a comparable electric aircraft

  • A little bit of air beneath the fuselage: the closer to the surface a WIG craft flies, the more efficient it is

Tallinn, the capital of Estonia, might also be one of such coastal points. In 2019, Sea Wolf Express, a company based there, announced that they would establish a high-speed connection across the Baltic Sea to Helsinki. Their WIG craft that comes from Russia is supposed to zip across the Gulf of Finland at 200 km/h (125 mph). This is another project that’s still in the planning stage and the company is in the process of exploring regulatory issues with the relevant government authorities. At least the Finnish side is open-minded toward the plans, according to a government spokesperson, but particularly safety issues such as flying over frozen water still require basic clarification.

Riding the wave
As early as in 2017, the Airfish8 from Wigetworks in Singapore was deployed on a test flight to the Malaysian tourist resort Langkawi© Wigetworks

In Singapore, the Airfish8 WIG craft from Wigetworks is being prepared for launch and completed initial test flights as early as in 2017. In the same year its Chinese counterpart, Xiangzhou 1, took off for initial test glides. The U.S. manufacturer Regent is in negotiations with several transportation companies. In addition to Brittany Ferries, they include a provider from the Bahamas, a U.S. charter airline with bases in New York, the Hamptons, Miami and the Virgin Islands, and the Croatian ferry operator Split Express, so there are many indications that new vehicles will be navigating ocean routes in the near future.