杏吧原创

ONE newspaper called it 鈥渁n unusually beautiful slug鈥�. Observers old enough
to remember 1960s TV said it looked like Thunderbird 2. But whatever you call
the 12.2-metre-long SkyKitten, don鈥檛 say it鈥檚 an airship. 鈥淲e call it a hybrid
air vehicle,鈥� says Bruce Wright, programme manager at Advanced Technologies
Group, which showed off its airsh . . . sorry, air vehicle, last summer at
Cardington airfield in Bedfordshire. Even ATG can鈥檛 deny that its SkyKitten owes
something to airships. But it鈥檚 also part hovercraft, part aeroplane,
and鈥攕omewhat bizarrely鈥攑art catamaran. It鈥檚 this double hull that
gives the craft its generic name: Sky Catamaran, or SkyCat for short.

Call it what you like, SkyKitten is trying to revive a business that went
down in flames more than 60 years ago when the Hindenburg crashed and burnt over
Lakehurst, New Jersey. The craft is a small-scale test model of a larger flying
machine which ATG hopes to put into commercial operation later this year.
Already, the company has started building an 82-metre scale-up, and is planning
two even bigger models. One is so big it could swallow London鈥檚 Wembley
Stadium.

ATG is not alone. In Germany, a company called CargoLifter also believes that
airships can once again ply the friendly skies, carrying cargo, construction
gear, military hardware鈥攁nd, yes, maybe passengers. Even the Zeppelin
company, builder of the Hindenburg, has risen from the ashes and is building
airships again.

Airships never quite withered away, of course, though they did shrink
dramatically. Craft bearing the names Goodyear or Fuji can be seen bobbing above
sporting events and entertainment venues. As airborne billboards they are hard
to beat. But to the new breed of airship builders, advertising is a wasted
opportunity. Zeppelin, for one, wants to revive the passenger market. And ATG
and CargoLifter reckon that airships鈥� long range, versatility and lifting
capacity make them superior to any other form of freight transport for big
cargoes. They can travel further than an 18-wheeler truck. They鈥檙e faster than
an ocean-going cargo ship. They can deliver goods for a fraction of the cost of
a plane. And they can carry large loads鈥攔eally, really large loads. If you
want a 68-tonne battle tank in a hurry, a Boeing C-17 military transport
aircraft can get one to you. The full-sized SkyCat will deliver 15 of them at a
time.

Early riser

Airships got off the ground in 1852, when Henri Giffard ascended from a Paris
racecourse in a gondola slung beneath a cigar-shaped balloon 44 metres long.
Giffard鈥檚 airship was simple, but it set the design for future craft. The
balloon鈥攑roperly called an envelope鈥攚as filled with hydrogen for
buoyancy. Attached to the gondola was a 3-horsepower (2.2-kilowatt) steam
engine, which propelled the craft forward at a stately 10 kilometres per
hour.

Early in the 20th century, lighter-than-air craft based on Giffard鈥檚 design
competed with aeroplanes for the burgeoning aviation trade. It was the German
aristocrat Count Ferdinand von Zeppelin who gave airships a name鈥攈is own.
The first Zeppelin, the LZ 1 completed in 1900, was something of an engineering
triumph: 128 metres long with a rigid internal frame carrying 17 hydrogen-filled
cells made from rubberised cotton, all of it covered with canvas and propelled
by twin 16-horsepower engines. By 1910, Zeppelins were carrying passengers
between German cities, and in 1919 a British airship, the R-34, crossed the
Atlantic. The architects of the Empire State Building, the world鈥檚 tallest when
it opened in 1931, even topped off the structure with an airship mooring mast so
that passengers could disembark in midtown Manhattan.

But the 1930s weren鈥檛 kind to airships. The first casualty was the
British-built R-101, which had been lengthened and modified because the original
design was unstable. On 5 October 1930 it left Cardington, bound for India. But
rough weather and engine trouble forced it to low altitude, and over northern
France witnesses saw it pitch and roll, then dive, strike the ground and catch
fire. Just six passengers out of 54 survived. Among the dead were members of the
craft鈥檚 design team and Lord Thompson of Cardington, the Secretary of State for
Air. Two and a half years later, bad weather over the New Jersey coast brought
down the US Navy鈥檚 airship Akron: 70 of the 73-strong crew died. Akron鈥檚 sister
ship Macon went down in 1935 off Point Sur, California, with the loss of two
lives.

The final blow came in 1937. Zeppelin鈥檚 flagship Hindenburg caught fire as it
approached its mooring mast in Lakehurst, New Jersey, killing 35 passengers and
one member of the ground crew. The disaster was captured on newsreel and sent
round the world. Almost immediately, gasbags were relegated to barrage balloons,
and later the advertising blimps. As for the Empire State鈥檚 mast, it was never
used.

But exactly a century after the first Zeppelin flew, giant airships are
staging a comeback. Last October, the 41-metre, helium-filled Mineseeker arrived
in Kosovo on a six-week mission to search for unexploded mines and cluster
bombs. Equipped with radar, TV cameras and infrared sensors, the airship is part
of a joint venture between Britain鈥檚 Defence Evaluation and Research Agency and
the Lightship Group, which builds illuminated advertising blimps.

Like the CargoLifter and Zeppelin craft, Mineseeker is an update of
traditional designs. ATG, meanwhile, is practically reinventing the genre. With
their twin hulls, the SkyCats look like two airships melded together. The double
envelope means there鈥檚 a lot more room for helium. But it has another more
radical role, one that justifies ATG鈥檚 proud 鈥渉ybrid鈥� boast. Curved on top and
flattened below, the hull forms a giant aerofoil. When the craft is moving
forward, its whole body generates lift. Says Wright: 鈥�60 per cent of its lift is
developed in the envelope, and 40 per cent is aerodynamic.鈥� The twin hull, he
explains, gives more aerodynamic lift than a single hull of the same length
would, and it鈥檚 more stable.

Another plus of the SkyCat design is the absence of the struts and hoops that
keep a traditional airship in shape. The keel beneath the ship provides rigidity
without the weight of a full frame. What structure it has is made from
composites, and with so little metal it鈥檚 鈥渆lectronically transparent鈥�. That
makes it a promising platform for broadcast antennas or eavesdropping equipment.
And it鈥檚 stealthy, which ATG says makes it a shoo-in for military operations.
Its secret is an envelope of strong, composite fabrics, including Kevlar, which
will bear the load鈥攁nd stop any bullets鈥攐nce it鈥檚 airborne. The
envelope is split onto three longitudinal cells to minimise the risk of a
catastrophic puncture.

SkyCat can also land almost anywhere. 鈥淲e do not use landing gear,鈥� Wright
says. 鈥淲e use the same air cushion system that鈥檚 used on hovercraft, so we can
take off and land on grass, sand, water, swamps鈥攜ou name it.鈥� Once SkyCat
is where the pilots want it, Wright says, they can reverse the direction of the
fans so the hovercraft skirt creates suction that holds the craft in place.
That鈥檚 better than the airships of old, which had to be tethered to a pole where
they bobbled around like party balloons tied to a pushchair. 鈥淲e don鈥檛 have to
tie it up or anything,鈥� Wright adds. 鈥淪o it鈥檚 a stable platform to load cargo,
or people, or whatever you鈥檙e transporting.鈥� One minor drawback compared with
old airships is that the SkyCat has to move forward to generate the aerodynamic
lift it needs to leave the ground. But given the all-terrain capability of
its hovercraft-style undercarriage, that鈥檚 no big handicap.

After the SkyKitten, ATG envisions three progressively larger models: SkyCat
15, which will lift a 15-tonne load, SkyCat 200 with a 200-tonne capacity, and
finally SkyCat 1000鈥攚ell, no prizes for guessing how much that one will
carry. All will share the twin-hull configuration. There is already a customer
for a SkyCat 15, and the craft is being built in one of ATG鈥檚 hangars at
Cardington. The company says SkyCat 15 could fly sometime this year.

Faster and cheaper

The bigger models are still on the drawing board, but ATG reckons they will
find buyers. The 200 has triple the carrying capacity of a C-17 cargo plane,
which its designers claim will make it ideal for delivering freight, or dropping
battle-ready troops and military hardware right onto the battlefield. The same
goes for the gargantuan SkyCat 1000. At 307 metres long, it will be the largest
flying machine ever built鈥攎ore than four times the length of a Boeing 747.
It will fly faster than the old airships: top speed will be 110 knots (a shade
over 200 kilometres per hour), compared with 68 knots for the Hindenburg. That鈥檚
four times as fast as the fastest ship. And its range is a massive 9650
kilometres, more than twice that of a C-17.

Why go to all this trouble to revive airships? Simple: economics. Today there
are two ways to move large, heavy cargo from continent to continent. The quick
way is to use airfreight. Carriers charge about $3.50 to fly a kilogram
of cargo the 6500 kilometres across the Atlantic, and they鈥檒l deliver the goods
in as little as a day. The cheap way is to send it by ship, which takes 10 to 25
days, and costs about 60 cents a kilogram. An airship (or hybrid air vehicle)
will be faster than a ship, making the ocean crossing in just 40 hours, and
cheaper than a plane at around a dollar a kilogram. 鈥淲e鈥檙e looking for a middle
ground,鈥� explains Wright. 鈥淚t gives transportation managers another option.
That鈥檚 the driving force for this class of vehicle.鈥�

CargoLifter reckons that the heavy-lifting market is worth a billion
dollars a year in the US alone, and that airships could grab one-tenth of that
with ease. Its CL 160鈥攃arrying capacity 160 tonnes, or almost two and a
half battle tanks鈥攎ay not be as radical a design as the SkyCat, but it is
still a contender for the title of biggest aircraft ever constructed. At 260
metres, it鈥檚 15 metres longer than the Hindenburg, which still holds the record.
And its manufacturer says it will be much safer than the old Zeppelin. 鈥淔irst of
all, today we are able to use helium,鈥� says CargoLifter鈥檚 spokeswoman Silke
R枚sser. 鈥淭hat was the thing that they didn鈥檛 have when the Hindenburg
exploded.鈥� Helium gives comparable lift to hydrogen鈥攁bout one kilogram per
cubic metre鈥攁nd it鈥檚 inert. CargoLifter has also eliminated another
potential fire hazard. CL 160鈥檚 envelope will be made of flameproof composites
rather than the linen which burnt so quickly in the Hindenburg fire. The same
goes for the SkyCats.

Like the SkyCat, the CL 160 has a central keel and no internal frame. The
keel, built from composites, houses the crew compartment, four 450-horsepower
diesel engines and propellers, and the cargo deck. Its designers see the craft
as a means to lift heavy and bulky items, such as generators and oil refinery
equipment, into remote regions. CargoLifter has finished a huge hangar at its
airship centre in Brand, 50 kilometres south of Berlin, and its prototype CL 160
is due for completion at the end of the year. A 32-metre scale model鈥攏amed
Joey, after the offspring of a kangaroo, since it would fit snugly into the
cargo bay of the full-sized ship鈥攎ade its maiden flight in October
1999.

Not everyone is bowled over by CargoLifter鈥檚 progress. 鈥淭hey have a very
impressive hangar, but not an airship,鈥� says Jeannine Meigh枚rner of rival
company Zeppelin, based in Friedrichshafen in southern Germany. Zeppelin has had
a prototype airship, the NT (for 鈥渘ew technology鈥�), in the air since September
1997. The new Zeppelin has logged more than 760 hours in the air, and its
builders say it will receive government certification early this year, allowing
it to fly commercially.

True to its heritage, Zeppelin鈥檚 target market is not freight, it鈥檚 people.
But, explains Bernd Str盲ter, chief executive of the company, this is not
your grandfather鈥檚 Zeppelin. For one thing, it won鈥檛 ply commercial air routes.
The customers it hopes to attract are sightseers. It鈥檚 also much smaller, just
75 metres, and more nimble than its mighty ancestor. While the Hindenburg had to
be tethered to a mooring mast, the Zeppelin NT can land straight onto the ground
thanks to its swivelling engines. By pointing these skyward, the ship can force
itself onto the ground even though it鈥檚 lighter than air.

Zeppelin NT can lift around a tonne, enough to accommodate 12 passengers and
two crew. Of course, that capacity could be used for freight. But as
Str盲ter points out, there is a problem with that. An airship, naturally, is
lighter than air; offloading anything more than a few kilograms will produce
buoyancy, so the ship will try to lift off. 鈥淚f you want to take a cargo off,
you have to put another cargo on,鈥� he explains. Zeppelin NT鈥檚 swivelling engines
can hold it down long enough for passengers to disembark, but to land for good
it needs ballast.

The other ships suffer from the same problem. CL 160 solves it with a water
ballast system that pumps water on board while the cargo is being offloaded. But
that means the ship is tied to special landing sites and needs a ground crew to
service it. SkyCat gets round the problem in two ways. First of all, its
hovercraft undercarriage can suck it onto the ground while the cargo is taken
off, allowing it to offload anywhere then fly away. Its unusual shape also
helps. Because the aerofoil body generates lift, it can fly when it鈥檚 heavier
than air, so offloading cargo doesn鈥檛 instantly make it float. But to put down
permanently, SkyCat still has to suck up water from a nearby lake or
reservoir.

Given the fate of the past generation of airships, there鈥檒l be some nervous
observers when the new giants take to the air, especially in stormy weather. But
the companies are confident their machines will cope. Zeppelin says the NT can
land in a force 7 near-gale. 鈥淥f course, a storm can harm the airship,鈥� says
Meigh枚rner. 鈥淏ut this is a high-tech airship. Lakehurst won鈥檛 happen again,
it really won鈥檛.鈥�

Wright, meanwhile, says SkyCat aircrews could 鈥渟uck the aircraft down鈥� and
withstand winds up to 125 kilometres per hour鈥攖hat鈥檚
hurricane-force鈥攐n the ground. If one of its helium cells were holed in
flight it would take two or three hours to deflate, and an engine failure
wouldn鈥檛 be catastrophic because the craft only uses two of its four once it鈥檚
airborne. The pilots will have to avoid storms, but that should be easier than
it was in the 1930s thanks to modern weather maps. But why talk about the 1930s
at all? That was the age of the airship鈥攁nd SkyCat isn鈥檛 one of those.