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View Full Version : Why don't trans-oceanic commercial flights utilize WIG?


Jimbrowski
09-09-2002, 12:46 PM
In this thread http://boards.straightdope.com/sdmb/showthread.php?threadid=134614 Wing In Ground effect is mentioned. Also mentioned is the extraordinary efficiency this affords (one suggestion is as much as a 50% improvement in range when flying long distances over water).

So..... why aren't the airlines doing it over water? Sounds like it would save lots of money in fuel.

I'm thinking of a very long flight, where it would make a difference and be worth the effort. New York to Sydney, for example, via the Pacific. Glasgow to Buenos Aires?

I'm sure there must be a good reason (or several) this is not done, but what is it?

- Might the plane actually hit a large ship? (There are already designated shipping and air-traffic lanes, I suspect we could work an 'air' lane in among the 'surface' lanes.)

- Weather? Wouldn't weather radar be the answer (go around or over)?

- Do large commercial airliners routinely gain and/or lose (!) more than 1-1/2 times their wingspan in altitude in the course of "straight and level" flight? A 747-400 would need to fly about 300ft above the water to take advantage of WIG (or about 1.5 times its wingspan of about 213ft). It that too small for a margin of error?

(Isn't there such thing as "terrain hugging radar" used in military applications to fly a vehicle very close to the ground? The ocean wouldn't be very difficult terrain to follow (as it's mostly flat). Why not equip long-range commercial aircraft with it? If you can set the autopilot to maintain 30,000 feet, why not 300 feet?)

- Would it scare the passengers?

DougC
09-09-2002, 01:20 PM
- - - I'm no pilot, but the main reason I can think of would be that if anything went wrong with the engines, you'd smack the water in just a couple seconds. That would tend to scare the passengers, if it happened or not.
~

racekarl
09-09-2002, 01:32 PM
This is not as far fetched or far off as you might imagine.

The Soviets built a bunch of planes that operated exactly as you imagine, they envisioned them as anti-ship or anti sub missle platforms.

The baton has been picked up by western companies, and we may yet see large WIG planes someday

More info:

Russian site about existing WIG craft
http://www.airforce.ru/english/aircraft/ekranoplanes/index.htm

Boeing site about future plans
http://www.boeing.com/news/frontiers/i_pw.html

Mort Furd
09-09-2002, 01:58 PM
Well, I can think of one reason:
Waves. For WIG to function, you need a decent surface below you. If you've heavy waves, the turbulence might well be enough to kick you out of surface effect - in effect reducing your lift and causing you to drop towards the ocean only a few hundred feet below. This would make the worst turbulence you ever experienced in a normal flight seem smooth by comparison - and god help you if you lose enough altitude to hit the surface. The heavy waves wouldn't even have to be cause by a storm in your direct path.
I think that for the most part, it is better for commercial flights to stay above the weather.

Having said all of that, I've not heard of anyone trying it. The concerns may be purely theoretical and WIG may be the way to go.

World Eater
09-09-2002, 02:24 PM
How fast do these things go?

Robot Arm
09-09-2002, 02:48 PM
That 50 percent range increase was for flying boats in the 1930s. They would have had piston engines and their regular cruising altitude wouldn't be very high. Jet aircraft climb to higher altitudes where they're more efficient. There's probably still some advantage to flying in ground effect, but I would guess it's less than 50 percent now.

Everything I've read about ground-effect flight is about designing planes specifically for it. And they're always able to land on the water if something goes wrong. The safety margin of flying a 747 at 300 feet is just way too slim.

And engineering effeciency isn't always the final word. When jet airliners were introduced in the 1950s, there was concern whether people would trust them enough buy tickets. The technical argument in favor of jet engines was pretty clear-cut, but nobody would put them into service if they didn't think they could fill the seats. Watching the waves skim by at hundreds of miles per hour might be a daunting prospect for some people, very different from the way it is now.

World Eater, my article suggests there's a drop in efficiency above 460 mph. And that number looks like it's for proposed designs only, I don't know what speeds have been attained in actual tests. I'm sure there'd be some data on some of the linked sites.

Milton De La Warre
09-09-2002, 03:54 PM
Mort has it in that if there were heavy seas, it'd be an unacceptably rough ride for commercial passengers, to say the least. It's also likely that in very heavy seas, you could lose the ground effect. I don't know, but it would seem the Soviets had the Caspian, Black, and Baltic seas in mind when they designed their WIGs, as opposed to the Pacific, Atlantic, and Indian Oceans. The former seas would be somewhat calmer (by and large), I think.

Robot Arm also has it even more right in saying that the effeciencies gained from high altitude flight exceed those from the ground effect.

Jimbo: There is no flying over weather when you are in ground effect (only). You'd be hard pressed to "fly over" a fog bank. Flying around weather would really entail taking the long way. Besides, flying at very low altitude would make it difficult at best for on-board weather radar to know wherer to go to do that.

When you think of WIG applications, think of high-speed short to medium range military applications. The closest commercial thing to one would be the hydofoils operated by the Ukraine, Russia, and Greece. But even those go a lot slower with greater safety and economy.

flyboy
09-09-2002, 05:53 PM
I'm not a commercial pilot, but I am a private pilot. I can't tell you how insanely unsafe this concept seems to me.

Rhum Runner
09-09-2002, 06:34 PM
Aside from the problems all ready put forward, I don't think there are too many commercial routes that fly exclusively over water, maybe Sydney to Tokyo or NY to London. But, if the WIG has to take a much longer path to stay over water, (like NY to Sydney, what do you do, fly down to Cape Horn and then over?) it doesn't seem very practical. I could see it on inland seas, or in the Med perhaps as a type of ferry.