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MIRACULOUS new AIRSHIP set to fly by 2013

Helium buoyancy issue solved at last?

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Intriguing news on the airship beat today, as it is reported that a mysterious, well-nigh miraculous new technology – one which could potentially lead to the appearance of enormous aerial vessels fit to dwarf even the zeppelin leviathans of the 1930s – is to get flight trials within two years.

Concept for a heavy-lift military 'Aeroscraft' airship. Credit:Aeros

Walrus isn't dead, just resting.

The technology in question is the enigmatic Control Of Static Heaviness (COSH) kit developed by Ukrainian airship visionary and entrepreneur Igor Pasternak at his Californian firm Aeros, which the Reg reported on a couple of years ago.

COSH purports to offer an answer to one of the knottiest problems facing airship designers today: that of controlling buoyancy while losing weight. In order to move about, an airship must burn fuel, so becoming lighter. More seriously, in order to operate, it will often need to drop off cargo or passengers. In either case the ship will become more buoyant and tend to ascend more and more powerfully.

This is bad, because pressure decreases as the ship soars upward, causing the lifting-gas cells inside it to expand. It's normal for part of the ship to hold air at surface level, allowing the ship to reach a decent altitude safely, but enough uncontrolled buoyancy will loft the vessel to "pressure height", where expanding gas cells have driven out all the air and fill the ship completely.

At pressure height, automatic valves open and start venting off lifting gas to prevent the ship bursting. It may be possible to regain control and achieve a safe landing in the end – though not always – but a lot of gas will definitely be gone until the ship can be refilled. This will also be true if the pilot vents gas in advance, so as to prevent a dangerous excursion above pressure height. Either case is unacceptable, as nice safe helium costs far too much to be thrown away whenever cargo is dropped off or fuel burned. Nobody has been willing to use cheap but highly-flammable hydrogen since the Hindenburg disaster.

There are various existing solutions to this problem, but all have their disadvantages. If a ship is delivering people and cargo at a properly-equipped mooring mast, it can take on water ballast through a nose connection at the same time, so remaining neutrally buoyant. Fuel burn while airborne can be dealt with by recovering an equal weight of water from engine exhaust using condensers. These systems were used successfully in the US Navy's 1930s helium airships, USS Akron and Macon.

One can also deal with fuel burn – though not cargo dropoff – by running one's engines on gaseous fuel mixed to have the same density as air and stored within the envelope. The famous interwar dirigible airliner Graf Zeppelin used this system, filling about a third of its hull with "Blaugas". As this was burned in the ship's diesels it was replaced by air weighing the same amount, and so the zeppelin's buoyancy was unchanged: this meant no need to vent off lifting gas during a voyage and thus no need to replenish it afterwards. Though the Graf used cheap hydrogen for lift rather than scarce, expensive helium, laying on hydrogen supplies at the ship's Latin American destinations was seen as unacceptably troublesome.

Some modern airships have been built using neutrally buoyant fuel gas, but on the whole in today's era of helium lift designers are reluctant to return to building huge aerial bags of explosive gas – and in any case the fuel-gas system offers no help in the matter of unloading at locations where ballast can't easily be taken on.

But one of the main selling-points of an airship in today's world is its ability – potentially – to deliver heavy cargoes to places without runways, mooring masts and water-ballast supplies. That's certainly a major role seen for them by the US military today, so airship designers need to think of ways to do without such luxuries.

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