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First rigid airship since the Hindenburg cleared for outdoor flight trials

Can brand new COSH tech finally revive the aerial leviathans of the 1930s?

By Lewis Page, 11 Sep 2013

Good news for airship fanciers this week, as it appears that the world's first rigid airship since the 1930s will soon take to the skies for flight trials: and better still, this ship has a new piece of technology which could actually change the existing landscape and permit the leviathans of the skies to return.

Rigid ships set to return to the skies - first time since August 1939*

We refer to the Aeroscraft, brainchild of Ukrainian airship visionary Igor Pasternak, and its proprietary Control of Static Heaviness (COSH) tech which apparently lets it do what no other airship has ever been able to. The "Dragon Dream" half-scale demonstrator, which carried out hangar trials earlier this year, has now been certified by the FAA for R&D outdoor trial flights and the first crew to take the ship up has been named.

The lucky three who'll be aboard for the first proper flight

The Aeroscraft, like all the bigger airships of the glorious pre-WWII era, is a rigid ship rather than a blimp. A blimp maintains its shape by the fact that pressure inside its envelope is maintained at a slightly higher level than ambient, keeping it inflated. Blimps can in fact be made pretty large, as the US Navy showed with the ZPG-3W radar ships of 1958-62, but not large enough for really serious air cargo or haulage operations.

A rigid ship, however, keeps its outer envelope in shape by use of a vast, lightweight structure of girders and wires inside which its lifting gas is kept in flexible bags or cells. It can be made truly enormous: perhaps even big enough to lift not only an entire 600-strong battalion of soldiers but also a full complement of heavy weapons, vehicles and supplies for them - all in one load. This was the "Walrus" vision of the US military's DARPA boffinry bureau some years back, anyway, and it would have offered the option of delivering fully concentrated, tooled-up, mobile troops (as opposed to scattered, lightly armed, foot-marching paratroopers or heliborne infantry) across distances much greater than helicopters or even tiltrotors could span.

Non-military airship lovers also found these plans very exciting as a Walrus-type ship could also do various commercial jobs that ordinary planes and helicopters can't: for instance, dropping off or picking up big cargoes in places that normal aircraft can't go. A realistic and prosaic example would be the setting up of drilling rigs and machinery in remote wilderness like the Canadian oil sands. Wilder dreamers would also have seen big ships invading the conventional air cargo market (unlikely, as we've discussed on these pages before) or even carrying people and things in and out of urban centres, where their potential silence and freedom from suddenly-falling-out-of-the-sky issues would perhaps be welcome.

Why airships never really got off the ground

One of the reasons that the DARPA Walrus plans of the noughties never went ahead - despite the appearance of the impressive Lockheed P-791 testbed airship - was that while a big rigid ship could, technically, do the military air-assault job, it would normally have to vent off much of its lifting gas as the troops disembarked so as to avoid soaring disastrously skyward. Nobody any more is really up for using explosive hydrogen as a lifting gas, especially for a ship headed into combat, and simply chucking away huge amounts of expensive helium isn't really on either. On the other hand, if the ship could only deliver its cargo at places where it could rapidly take on vast amounts of water ballast it wouldn't be very useful.

Indeed, with nothing else in the picture, a good deal of lifting gas would generally have to be thrown away on any long airship journey to compensate for the weight of fuel burned by the engines and so let the vessel get down at the end: this too would be unacceptable in a helium ship, or even a hydrogen one aiming to land at a place without a hydrogen supply.

This was the great Achilles heel of the pre-WWII rigids, in fact, though it didn't prevent them being built back then as their rival the long-range aeroplane was in its infancy. Various solutions have been offered: one is the use of gaseous fuel weighing the same as air, stored in the envelope alongside the lifting gas, as seen on the inter-war airliner Graf Zeppelin. Another ploy is the use of condensers to collect water from the engines' exhaust, as used (though apparently their gear didn't work very well) by the US Navy flying aircraft carriers Akron and Macon in the 1930s. Similar machinery was also developed for the ill-fated Hindenburg and her sister ship Graf Zeppelin II, though as it turned out the US wouldn't let the Nazis have any helium. As a result the two ships were hydrogen filled and didn't bother with water-recovery.

Since the disappearance of the great rigids following the Hindenburg disaster, other ploys have been proposed: most notably the use of ships which are actually heavier than air and supplement their gas lift by the use of vertical engine thrust and/or dynamic lift generated as an aeroplane does by flying along. This renders the ship just as vulnerable to disaster following an engine failure as an aeroplane or helicopter is, but it removes some of the ballast problem.

All these plans have circulated for decades, however, without any prospect of a return by proper, heavy-lift big rigid ships: though the US Army's LEMV ship of recent years (now cancelled) - actually aimed at high-flying, light-load spy missions - could potentially have carried out cargo tasks had it survived.

The Aeroscraft, though, is different because it has COSH: we here on the Reg airship desk first reported on this technology a few years back. Essentially what COSH does is take some of the ship's helium and compress it to the point at which it is heavier than air, so removing lift. It seems likely that the gas isn't compressed to any very high pressure, meaning that the tanks in which it is put could be potentially large enough to do the job while remaining acceptably lightweight.

They might well be of fabric construction - this seemed to be the case on initial test blimps. Pressures similar to those seen inside some modern bike tyres would be enough to render helium heavy rather than buoyant, or perhaps the system merely makes it less buoyant.

Looks like rigid tanks these days, but probably not any very high pressure

Pasternak's company nowadays makes bold claims for COSH, saying:

The control of static heaviness is Aeros’ solution to a virtually ballast exchange-free flight. Through a pilot’s control, the vehicle itself can be configured to provide enough static heaviness to offload personnel and cargo, without the limitation of taking on external ballast to stay grounded.

COSH, lift and practical applications

Previous reports had suggested that COSH might need to work in conjunction with other plans such as taking off in a heavy condition, the use of suction landing gear to hold the ship down and perhaps supplementary water-recovery from exhausts to manage a truly major offload, but perhaps the technology has been improved.

COSH also offers the potential to eliminate another problem which contributed to the Walrus project's demise: the fact that a normal heavy-lift airship can't fly very high. If it does, its helium will expand to fill more space than there is inside the envelope and thus will be lost along with its lift as the precious gas bursts cells or escapes through automatic valves. Normally, the only way to get high is to take off with less gas, but that means less payload.

As a result, DARPA's Walrus was only expected to have a ceiling of 10,000 feet - in other words the huge, slow ship could have been hit by even shoulder-launched missiles from the ground all along its flight path. That, quite apart from the ballast issue, was probably a major reason for the project's demise.

But a COSH ship might do better, lifting off with a mostly full envelope and then stuffing the surplus expanding gas away into its internal pressure tanks as it climbed. The resulting loss of lift could be counterbalanced by dynamic lift generated by the ship's speed while it was in transit, perhaps letting it get survivably high up while cruising.

Descending to land, the COSH system would release the gas again to maintain a full envelope at low level and achieve neutral or close-to-neutral buoyancy for vertical landing, before cramming much of the helium away again during unloading. A COSH Walrus could thus be a lot more militarily practical than a non-COSH one.

Regardless of the details, if COSH works to any reasonable degree it is finally a new thing on the airship drawing boards after so many years and as such it could mean a genuine prospect of a return by the big rigids - enough to gladden any airship enthusiast's heart.

But the return will probably not be en masse, even if it comes. There are various possible military/security missions; there is the job of dropping exploratory drilling rigs or suchlike into remote locations. There aren't a whole lot of other likely applications for airships in today's world with its ships and planes, helicopters and roads and rails. It might be that the airship deserves to do some of the jobs that are done today by existing machinery, but not that many, and usually the margin isn't one that would let it break in against the established players. It'll probably be limited - if it comes at all - to jobs that nothing else can do, and there just aren't that many of those.

We're hoping we're wrong, here on the Reg airship desk, but we don't hold out much hope of a sky full of massive rigids any time soon. ®


*The last flight of the Graf Zeppelin II, sister ship to the Hindenburg. We do know about her, though she doesn't make nearly such a good headline.

We also know about the modern day NT Zeppelins and their rigid structures, but they are only semi-rigids: they need envelope inflation too.

No need to write in about those unless you really want to.

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