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Wind In Ground (WIG), is an old concept.

In short: Wing-tip vortices create an additional drag on the aircraft known as the induced drag. However, when the flying craft (or bird) flies close to the ground or water, these vortices don't get enough space to develop which results in additional lift and reduced drag. This phenomenon has been effectively used in transportation vehicles to create ground effect or WIG crafts.

Although a paper titled 'Wing-in-ground effect vehicles' declares that many technical difficulties have either been solved or can be solved, according to this wiki article, there are some practical issues in using these crafts for regular passenger traffic.

Since hovercrafts also glide on air cushion, and yet they are not that rare, what makes WIG so uncommon? (Analogy wise, hovercraft is like helicopter while WIGcraft is like airplane)

Is it the engineering aspects that makes them uncommon? If yes, which aspects?

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  • $\begingroup$ Working a bit from memory here, but the wiki supports: You need a fairly well behaved "ground" in order to be able to operate very reliably. This mostly limits them to smaller bodies of water with decent weather. I think that it comes down to a question of usefulness vs. cost of development. $\endgroup$ – Dan Jan 28 '15 at 6:26
  • $\begingroup$ Back in the day, the Russians built some very large ones, as prototypes. But either the ground needs to be very flat, or the aircraft must be small and maneuverable in order to follow hilly ground, both of which limit the overall usefulness of the craft too much. Also, regular aircraft can simply fly over any obstructions, while a WIG craft would require dedicated pathways. $\endgroup$ – Dave Tweed Jan 28 '15 at 12:07
  • $\begingroup$ @DaveTweed Practically all WIG vehicles (Ekranoplan in Russian nomenclature) were intended for use over water. That answers the issue with flatness of the ground. Some of the proposed WIG vehicles had a reserve in engine output, which allowed them to temporarily increase altitude (to the point where ground effect no longer applies). For example, the recently proposed Pelican concept had such capability. $\endgroup$ – Nick Alexeev Feb 1 '15 at 5:04
  • $\begingroup$ This might be oversimplifying things but WIG vehicles were effectively short winged extremely low flying aircraft. If anyone is going to go to the trouble of making an aircraft why not make so it can fly at an elevation of 40,000 ft instead if something like 5 ft - there's more usage out of it and the pay-off is greater. $\endgroup$ – Fred Feb 2 '15 at 7:10
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This is mostly an issue of safety trade-offs and not necessarily technical shortcomings. While a WIG vehicle, often referred to as a Ground Effect Vehicle (GEV), has improved efficiency it is also forced to fly very low. Above around 50 feet (wingspan-dependent) you will not see much in the way of ground effect benefits.

The problem is that, even over water, there are numerous obstacles that could be in a WIG vehicle's flight path. Commercial aircraft normally fly above 18,000 feet (5,500 meters) so that they stay in Class A airspace. This allows them to remain far above obstacles and it also allows air traffic control to deconflict air traffic and prevent dangerous proximity. There is no practical way to deconflict like this near the surface of the water where ubiquitous craft such as sailboats would pose deadly peril to a WIG vehicle.

Furthermore, it is very difficult to maneuver at such a low altitude. Aircraft can only safely pull upwards from a WIG vehicle flight altitude and that is the least-advantageous direction from an aircraft power perspective. Also, due to the low altitude, an obstacle may not be visible until very shortly before a possible impact; even on a clear day with good visibility.

As for why hovercraft are more common: they are able to (and typically do) move at relatively slow speeds, and even stop on the water. They can slow down, stop, and make sharp turns more easily and more safely than a WIG vehicle. Due to their relatively slow speed, they also typically have more time to react to an emergency situation. Finally, hovercraft technology is much less complex and much less expensive.

Reference: Aeronautical engineering experience and pilot experience

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  • $\begingroup$ But in flat areas one could maybe build special "lanes" which are free from obstacles (like high buildings, ...), i.e. like when you want to cross a lake or a small sea (Sweden - Danmark for example). $\endgroup$ – Trilarion Feb 3 '15 at 16:52
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    $\begingroup$ Also, bad turbulence. I believe a B52 had its tail sheared off due to flying under the radar. $\endgroup$ – Sanchises Jun 6 '15 at 21:35
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I don't think there are any engineering issues with them, I just think there is no economic or operational niche for them.

They have the operational overhead of aircraft so why not just use a plane to begin with? They can only be used over relatively flat terrain or still water but is there anyplace in the world where the necessary terrain and economic need for ground hugging fast transport exists? I doubt it. E.g. I can't see them working as reliable ferries in populated areas for example.

I also see WIGs as one of those 90% great, 10% deal breaking suck technologies. The deal breaking suck is the limitation on terrain which even over water, will be unpredictable. Just a bit of wave toss up and suddenly you might as well be flying.

Another problem, rarely discussed is that these things are LOUD because the big ones are fully revved jets operating right on the ground. Read up on the first hand accounts of Soviet test observers on the Caspian sea. No way your getting those operating near populated areas these days.

I also suspect that over land they have a similar problem to hovercraft in that the powerful downdrafts that keep them lofted turn almost anything they fly over that isn't nailed down into a projectile. Imagine a huge WIG flying up over a gravel beach. It'd be like a a machine gun.

It only take a one big negative to render a design or technology useless and I think WIGs have several big negatives.

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