Float? Fly? Glide!

By plane or by ship – those are the options for transporting freight over large bodies of water. Airplanes are fast, of course, but also expensive. Ships are less expensive but much slower. You just can’t have everything, right? Wrong! You can: this is where ground-effect vehicles (also known by the Russian name “ekranoplan”) come into play. These engineering marvels – half ship, half aircraft – make use of a fascinating physical principle. Thanks to the ground effect, ekranoplanes glide comparatively effortlessly just slightly above the water, making them on average 30-50% more efficient than aircraft of an equivalent size and ten times faster than standard ships.

Utilizing the ground effect

But why do these vehicles fly at such a low height over the water? What is the advantage over flying at greater heights or moving through the water?
When using the ground effect, a vehicle profits from the special air flow conditions of a wing close to the ground. Two phenomena apply here to produce lower drag as well as greater lift.

First phenomenon: interruption of something called “wake turbulence.” The pressure difference between the top and bottom sides of an aircraft’s wing generate vortices that produce wake turbulence at the ends of the wings. Positive pressure causes the air to flow from the underside upwards around the ends of the wings, thereby inducing a downward force that is responsible for a large portion of the air resistance. This wake turbulence, however, can only propagate through the air, and is therefore interrupted when flying low over ground or water. This reduces the drag and with it the energy required to propel the vehicle. What this means in practice is a reduction in the vehicle’s fuel consumption.

Crossing the ocean on cushions of air

The second phenomenon produces advantageous lift: close to the ground, the air is trapped under the wing surfaces, forming a kind of “air roll” moving along with the aircraft on which the aircraft can essentially glide. The dynamic lift is therefore higher, increasing the efficiency of the wing. This lift also serves to make the ground-effect vehicle more economical than flying at great heights. Combined, both effects significantly raise the lift-to-drag ratio. As a result, these aircraft travel quickly while also saving on fuel.

An entirely new idea?

Is utilization of the ground effect an entirely new idea? Not really. Seabirds, such as the albatross, have long demonstrated how to use this effect to save strength and energy over long distances. In principle, this effect occurs every time an airplane takes off or lands – a phenomenon aircraft designers have been familiar with for some time. However, ground-effect vehicles are specially designed to make use of the effect over longer distances – and they have existed for some time now. The first true ground-effect vehicles were developed in the 1960s, primarily in the former Soviet Union.

The mystery of the Caspian sea monster

Perhaps the most famous ground-effect vehicle was the “KM” (Russian abbreviation for ship design). This giant was designed by the Russian Soviet ship and aircraft designer Rostislav Evgenievich Alexeyev in 1964. It had a relatively short wingspan of approximately 40 meters, a length of over 100 meters, a payload of 280 tons and a total weight of around 540 tons. This made it twice as heavy as the heaviest aircraft of its day – a record it held until 1988 (first flight of the An-225 Mriya, recently destroyed in Ukraine). It was propelled by ten jet engines, eight of which could be switched off after taking flight just above the surface of the water. It raced across the Caspian sea at 400-500 km/h, but it was extremely sluggish and hard to steer, resulting in a very large turning circle. What’s more, it couldn’t be used in poor weather or in heavy seas.

From a military point of view, it boasted another advantage in addition to its speed and payload in that it had no draft during flight. This meant it was not detectable by the sonar systems of enemy ships while also often remaining below the radar systems of the day due to the low altitude flight.

Western intelligence services gave the unknown ocean vehicle, which they discovered on satellite photos in the 1960s, the name of “Caspian sea monster” and were initially mystified. Only after the fall of the Iron Curtain did more information become public, generating enthusiasm among Western experts.

The future calls

In the 1970s, pure ground-effect vehicles were also designed, tested and improved in the West. Good results were achieved particularly in Germany, if at a significantly smaller scale. In the meantime, interest in these vehicles has died down somewhat, although a number of companies have recently taken up the torch to adapt the concept to the needs of today. In addition to the German “Seafalcon” and the Korean “Wingship,” the “Airfish 8” in Singapore represents another attempt at making ground-effect vehicles ready for practical use. The “Tandem Airfoil Flairboat” – of which a number of prototypes were built in the 1970s by German engineer Günther Jörg – is also getting a fresh new design.

Sea-supported air freight or air-supported sea transport?

The many advantages of these “flying ships” also render them interesting for transporting goods. The advantages: higher speed than ships plus lower fuel consumption, making them on average 30-50% more economical to operate than comparable aircraft. The infrastructure requirements are similar to those of a boat, which is why ground-effect vehicles are classified as watercraft. Ekranoplanes don’t require landing strips and are not subject to any prohibitions on flying at night. In this way, goods could be delivered quickly and inexpensively to coastal locations around the world, potentially as a form of feeder traffic.

One ambitious company is already working hard on this vision and even has an unmanned model. The US-based Flying Ship Technologies “landed” its first large order for its flying ships in 2021. For a price of around 100 million US dollars, 20 vehicles are to be delivered to a global European company by 2024. This could represent the first step towards a possible future of freight transport – initially on a relatively small scale, of course, but impressive nevertheless. In any case, achieving the same transport capacity as an An-124 or A-380 right from the start was never the planned goal.

An unmanned “flying ship”

Designed not for size but maneuverability, speed and efficiency, the base version of the flying ship is driven by electric motors, has a range of approximately 550 km (300 nautical miles), and a cargo capacity of 1.2 t. Future versions are expected to utilize alternative green drive technologies to extend the range to approximately 1,800 km (1,000 nautical miles) and the payload to 2.7 t. These models are not intended to be “big haulers” but are intended to transport smaller but much need cargo to remote areas, for example in the Caribbean or scarcely populated archipelagos.

Whether island taxi, ferry or cargo transport, the potential applications are numerous, and we are excited to discover how far ground-effect vehicles will go in the future.

A “flying ship” in full effect