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http://en.wikipedia.org/wiki/Hovercraft

Another discovery was that the total amount of air needed to lift the craft was a function of the roughness of the surface it traveled over. On flat surfaces, like pavement, the needed air pressure was so low that hovercraft were able to compete in energy terms with conventional systems like steel wheels. However, as the hovercraft lift system acted as both a lift and very effective suspension, it naturally lent itself to high-speed use where conventional suspension systems were considered too complex. This led to a variety of "hovertrain" proposals during the 1960s, including England's Tracked Hovercraft and France's Aérotrain. In the U.S., Rohr Inc. and Garrett both took out licenses to develop local versions of the Aérotrain. These designs competed with maglev systems in the high-speed arena, where their primary advantage was the very "low tech" tracks they needed. On the downside, the air blowing out from under the trains presented a unique problem in stations, and interest in them waned in the 1970s.

Now suppose it could operate on drop down electric motorized wheels near stations (thus fans off) and on an air cushion for high speeds. The cost of the "rails" would be about the same as building a roadway.

The question is could it be made to pay?

More:

http://en.wikipedia.org/wiki/Hovertrain

MSimon wrote:http://en.wikipedia.org/wiki/Hovercraft

Another discovery was that the total amount of air needed to lift the craft was a function of the roughness of the surface it traveled over. On flat surfaces, like pavement, the needed air pressure was so low that hovercraft were able to compete in energy terms with conventional systems like steel wheels. However, as the hovercraft lift system acted as both a lift and very effective suspension, it naturally lent itself to high-speed use where conventional suspension systems were considered too complex. This led to a variety of "hovertrain" proposals during the 1960s, including England's Tracked Hovercraft and France's Aérotrain. In the U.S., Rohr Inc. and Garrett both took out licenses to develop local versions of the Aérotrain. These designs competed with maglev systems in the high-speed arena, where their primary advantage was the very "low tech" tracks they needed. On the downside, the air blowing out from under the trains presented a unique problem in stations, and interest in them waned in the 1970s.

Now suppose it could operate on drop down electric motorized wheels near stations (thus fans off) and on an air cushion for high speeds. The cost of the "rails" would be about the same as building a roadway.

The question is could it be made to pay?

More:

http://en.wikipedia.org/wiki/Hovertrain

It's possible it could be made to pay - but there's no guarantees. You're looking at trains, roadways, and most importantly the potential ridership. It's not enough to go 'if you build it, they will come' - what's important is population density at your start and end, distance between the two, and whether it'd be cheaper and more convenient to drive or fly.

Unless there's a radical change, I don't see it becoming the prevailing means of long-distance transport...

I was thinking you would need a freight route where high speed would be important.

Seems to me the best case you can make for hovercraft as civilian transport is where you don't need anything like rails--across the water. Looks like the last of the Hoverspeed Ferries were retired a decade ago. (I'm surprised and disappointed. They were cool.)

http://europeforvisitors.com/cruises/ar ... rspeed.htm

in favor of Super-seacats--I believe these are the Jet boats I have been on in the past, and they are a real kick too:

http://en.wikipedia.org/wiki/SuperSeaCat

But given all that, you might make a separate case for Poly powered Hovercraft. Lots involved there but if you want to go faster than a cargo ship, and have lots of cheap energy, a hovercraft my be economically viable in new ways. The obvious question is, how do you cool it?

Ah, yes... HoverBolos

http://en.wikipedia.org/wiki/Zubr_class_LCAC

Fair the propulsion fans into the hull with propfan tech, swap the cargo for VLS cells, solid-state laser CIWS and heavier armor... and you too can rule the Baltic!

Or, on a more peaceful note, the hover freighters from Clarke's Dolphin Island et al... a teen runaway stows away on one while it's stopped by the roadside for repairs in the midwestern U.S... and hours later the crew are forced to take to the lifeboats when the freighter founders not far from the Great Barrier Reef in the Pacific... the crew unknowingly leaving the teen behind amidst the debris...

(Remember when writing SF... any neat future gear will always be owned and operated by BP, and not by clever and wise Randian entrpreneurs...)

Still, an updated hover freighter can fit in where fusion-powered aircraft can not... as long as it's seaworthy and designed for minimum wear under constant operation i.e. magnetic bearings etc etc..

Randian? Nah, Long. As in Lazarus Long.

MSimon wrote:Now suppose it could operate on drop down electric motorized wheels near stations (thus fans off) and on an air cushion for high speeds.

Read a sci-fi novel many years ago that used a similar concept, except the vehicles switched to air cushion on the freeway, not on a restricted "railway". Don't remember title or author, but it was about EMT first responders who rode hover vehicles to deal with wrecks that occurred at several hundred mph. Survivors were rare. If I remember right, in panic stop situations the vehicles would drop back down onto tracked modules, somewhat like tracks used by snowmobiles.

MSimon wrote:Now suppose it could operate on drop down electric motorized wheels near stations (thus fans off) and on an air cushion for high speeds. The cost of the "rails" would be about the same as building a roadway.

The question is could it be made to pay?

More:

http://en.wikipedia.org/wiki/Hovertrain

Well, the biggest cost point would be the construction of new track, but the per-mile construction and maintenance for a system like this is a lot less than a Maglev track.

The cheapest option would be to develop a system that is also capable of rolling on standard track, so you don't have to rebuild infrastructure from scratch. I'm thinking along the lines of standard railway wheels that allow the train to run on regular track for local, station and switching traffic, but retract when the train enters a dedicated section of transition track. Current high-speed systems do the same when they need to change electrical and safety systems to run on dedicated track at higher speeds.

The transition track could just be built of concrete plates with normal rail recessed into them, like a crossing or tramway. This way the train can start the hover fans to generate lift from the concrete floor, and once lift is sufficient, retract the railway bogies in a similar way to landing gear on an aircraft.

For propulsion, you could think of permanent magnets in the track and repulsive coils on the train's carriages. No moving parts in contact with the track, meaning almost zero wear.

Something like this would be very feasible (and probably realized in an efficient manner) with today's tech, but I'm not sure if it could be made into something economic.

Of course, the "holy grail" would be hover-like grippers that coincide with existing track, so you don't have to build additional rails at all. But things like safety also come into play in this case.

I'm thinking along the lines of standard railway wheels that allow the train to run on regular track for local, station and switching traffic, but retract when the train enters a dedicated section of transition track.

Think of the air blast blowing the ballast from the track. I don't think that will work. Plus I think you will need some kind of half tube (i.e. side rails) to keep the train unequivocally on the track.

Stoney3K wrote: Well, the biggest cost point would be the construction of new track, but the per-mile construction and maintenance for a system like this is a lot less than a Maglev track.

Please look up Inductrack. It will change your mind about that statement. Inductrak is just about the cheapest track around.

MSimon wrote:I was thinking you would need a freight route where high speed would be important.

There's not that much time-sensitive freight - refrigerated cars handle perishables with ease, and anything that needs to go overnight can go FedEx or UPS.

Don't get me wrong - I love the idea from a technical standpoint. It's the practicality and economics that have me thinking it just won't, if you'll pardon the expression, fly.

DeltaV wrote:Read a sci-fi novel many years ago that used a similar concept, except the vehicles switched to air cushion on the freeway, not on a restricted "railway". Don't remember title or author, but it was about EMT first responders who rode hover vehicles to deal with wrecks that occurred at several hundred mph. Survivors were rare. If I remember right, in panic stop situations the vehicles would drop back down onto tracked modules, somewhat like tracks used by snowmobiles.

I remember that story also - "Code Red" was the title if I recall correctly. I think it was from the '70s. Don't know the author, found a link to it on Metafilter a number of years back, and it held up pretty well. Of course, I can't find the fool thing a second time...

KitemanSA wrote:

Stoney3K wrote: Well, the biggest cost point would be the construction of new track, but the per-mile construction and maintenance for a system like this is a lot less than a Maglev track.

Please look up Inductrack. It will change your mind about that statement. Inductrak is just about the cheapest track around.

Well no. Basically it is an all aluminum roadbed. And if a ferrite add on to increase the inductance is used - well there is a reason us electronicers like to use ferrite in small bits.

DeltaV wrote:

MSimon wrote:Now suppose it could operate on drop down electric motorized wheels near stations (thus fans off) and on an air cushion for high speeds.

Read a sci-fi novel many years ago that used a similar concept, except the vehicles switched to air cushion on the freeway, not on a restricted "railway". Don't remember title or author, but it was about EMT first responders who rode hover vehicles to deal with wrecks that occurred at several hundred mph. Survivors were rare. If I remember right, in panic stop situations the vehicles would drop back down onto tracked modules, somewhat like tracks used by snowmobiles.

Okay, had a friend who remembered it. "Code Three", by Rick Raphael, which appeared in the February 1963 issue of Analog. Must have read it when my father was still getting it (he got me hooked at an early age...) and then I remembered it when I ran across it a few years back. I mentioned it up on my blog, and someone recalled the actual title and found it.

It's good to have friends who have encyclopedic knowledge of SF...

Code Three, by Rick Raphael

And many thanks to my friend John Campbell, who found it.

MSimon wrote:

KitemanSA wrote:

Stoney3K wrote: Well, the biggest cost point would be the construction of new track, but the per-mile construction and maintenance for a system like this is a lot less than a Maglev track.

Please look up Inductrack. It will change your mind about that statement. Inductrak is just about the cheapest track around.

Well no. Basically it is an all aluminum roadbed. And if a ferrite add on to increase the inductance is used - well there is a reason us electronicers like to use ferrite in small bits.

Sorry, not catching your point here. The current Inductrack uses some conductive metal in fairly thin strips along the sides that have very little by way of extreme alignment requirement. The track is open between the rails so no cr@p is collected into the roadbed as an air-cushion track would.

I foresee a disaster with the air-cusion rail system. A heavy snow blankets the track and the vehicle on its air-cushion climbs up the snowpack and out of the track. Whoppee! What fun, we're flying...splat!