Comment by j9461701 | Hacker News Reader

Comment by j9461701 | Hacker News Reader

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Theoretically you could fly over most waves, as some designs allow fleet height equal to 1/2 wingspan - so dozens of meters of height. The issues with ground effect vehicles are several:

A plane takes advantage of the much thinner atmosphere higher up to go farther easier, while an ekranoplan has to plum along under an ocean of air sapping its fuel efficiency. No GEV design I'm aware of (feel free to correct!) could make it across any ocean without stopping for refueling, and many can't even island-hop across the ocean. You'd need to construct refueling stations in the middle of the ocean.

GEVs need calm, flat water to take off. This makes the above refueling stations even more challenging, as any vehicle that lands to top up may not be able to get airborne again. This seems a minor point, but it's why we abandoned seaplanes - it's just not worth the effort of waiting for the seas to calm when a plane on an asphalt runway is always ready to go.

GEVs are awkward to maneuver and very slow to turn, so if a pilot does happen to see a rogue 30 meter wave up ahead he has very little he can do to avoid it. Everyone just dies.

Taking off in light wind is difficult, as wave direction is inconsistent. Taking off in heavy wind is a miserable, bumpy experience for the passangers. Sort of damned if you do, damned if you don't situation.

I do think there might be something to GEVs, but it would require someone to invent a design that combined 1) 30+ meter flight height with 2) 3000 km range on one fuel tank. The ability to hop from bay to bay is critical to the design becoming practical.

> GEVs are awkward to maneuver and very slow to turn, so if a pilot does happen to see a rogue 30 meter wave up ahead he has very little he can do to avoid it. Everyone just dies.

Wouldn't most GEV be able to temporarily "jump" out of ground effect for emergencies like that, or at least wouldn't require much change to gain that capability? But that ability wouldn't really make a difference, not without solving all the other issues as well.

What I could imagine, as a narrow niche, is a short range regional plane designed to be good at utilizing ground effect on routes that are too short for the "ascend into thinner air" trick to work out and that happen to go over water. Not being seaplanes those wouldn't require sufficiently calm seas for aquatic start and landing. I think that this might be able to occupy an attractive sweet spot between the fuel economy of surface boats and the speed of aircraft in intra-archipelago traffic. Flying slow in ground effect could even be the missing link for creating a niche where electric flying is economically viable. Perhaps a "plug in hybrid" that goes purely electric on short hoops, stays purely electric on longer connections if the sea is sufficiently calm and that can spin up the RX if it is forced to fly the whole distance out of ground effect.

I think that the main economic issue with this concept is that fuel isn't that much of a cost factor in short distance flying, but I might be completely wrong with this.

>Wouldn't most GEV be able to temporarily "jump" out of ground effect for emergencies like that, or at least wouldn't require much change to gain that capability? But that ability wouldn't really make a difference, not without solving all the other issues as well.

Consider these vehicles can travel up to 500 km/h and operate very near to the ground, meaning

1) Vision-obscuring weather like fog or rain

2) A plethora of objects to smack into

3) Very low time to react due to high speed

This is why we generally avoid flying planes this low, unless forced to by circumstances. An example of such circumstances is found in military aviation, in which military aircraft fly very low to the earth to avoid detection (a strategy rendered somewhat less effective modernly due to the invention of light-weight Pulse-Doppler radar). In this case the danger from crashing the plane is judged less than the danger from enemy missiles.

GEVs take this already challenging and dangerous task, which the military only does because they are being shot at, and then make everything that much more difficult by having the vehicle control like a cow.

> 2) A plethora of objects to smack into

On the ocean? I'd say that not running into objects that raise high from an ocean would rank pretty low on the scale of control problems that are hard in 2020.

"up to 500 km/h" are military devices built for maximum speed at minimal distance from the surface. A short distance people mover aircraft that tries to trade speed for energy conservation would have very different numbers. And it would be far more nimble, by being able to quickly raise out of the ground effect level, than swimming ocean-surface vessels that are already quite capable of not hitting objects on the ocean (you'd definitely want to improve on the state of that art though).

The biggest issue with this concept, outside of the clearly problematic cost/market size ratio (because designing planes is never cheap) would surely be that an aircraft traveling in ground effect lacks the altitude energy store that allows conventional aircraft to deal surprisingly well with engine outages (or sensor issues) outside of short time windows during start and landing. You'd probably need to spend a lot of mass and effort on making the fuselage properly boatable in emergencies even if it's never intended to swim more than once.

Crossing the North Sea might be perfect. At the moment, a ferry takes almost a day, and planes are very inefficient because they spend half the time climbing and can immediately start landing again.

And there's tons of traffic of all sorts across the North Sea. It's the perfect case for large short-range transport.

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