Original URL: http://www.theregister.co.uk/2010/05/20/bullet_580_inflated/

'World's largest' airship inflated in colossal Alabama cowshed

New NASA ship features hover-slats, water harvesting

By Lewis Page

Posted in Science, 20th May 2010 15:01 GMT

The "world's largest airship" - according to its makers - was inflated for the first time yesterday and is undergoing ground tests inside a mighty roofed exhibition hall in Alabama which in normal times offers "the space for 1500 cattle".

The "Bullet 580" ship measures 235 feet long and 65 feet in diameter. It is intended to carry payloads of almost one tonne to altitudes of 20,000 feet on surveying or surveillance missions.

The Bullet design was developed in Canada by a company called 21st Century Airships, spawned by well-known ballooning and airship enthusiast Hokan Colting (he was partnered in the balloon biz with fellow Swede Per Lindstrand - noted aerial daredevil and chum of beardy bizlord Richard Branson - in 1970s Britain). Colting achieved a 20,000-foot-plus airship height record in a spherical 21st-century airship above Alberta in 2003.

The Bullet design, based on a 21st-century flying prototype called Voyager, offers various special sauces compared to a standard helium-filled blimp. Its propelling ducted fans are mounted along the centreline of the hull rather than beneath it, so that the nose doesn't lift when more power is applied.

Concept art of the proposed Bullet airship. Credit: E-Green

The zeppelin - finally sorted out?

Slats also allow the pilot to control the airflow emitted by the ducted fans, meaning that traditional tailplanes and rudders aren't required - and that the ship can still be controlled even when not moving foward through the air. This is supposed to offer good manoeuvrability even when hovering, and to mean that the large ground handling crews required by normal airships are unnecessary.

1930s flying-aircraft-carrier trick revisited?

After 21 years in operation during which it flew some 14 airships, 21st Century was bought last year by Alabama firm E-Green Technologies, which had previously been involved in trying to market 21st Century airships to US government customers. E-Green says that the new Bullet 580 is being built to carry a joint NASA and academic survey payload intended to measure soil moisture.

E-Green adds that the Bullet will be equipped with a "Water Condensate Recovery System [which] reduces need for helium replenishment", a key requirement for airships not filled with hydrogen or hot air. Helium is expensive: but in general a ship gets lighter as it burns fuel and thus gas will probably have to be vented off to make a landing. Replacing the lost helium for another flight is costly and troublesome.

Concept art of the proposed Bullet airship. Credit: E-Green

Samantha was a little disappointed at the lack of gaiety aboard.

This snag can be mitigated by the use of vertical thrust, dynamic lift generated in forward flight and/or ground effects hover/suck ducts (as seen on the Lockheed P-791 demonstrator in recent years). But a more conventional vessel like the Bullet would need an answer to the static lift problem. Most airship designers claim some trick up their sleeve in this area, usually treated as a deep secret: Colting would never divulge what approach 21st Century was taking.

However the term "water condensate" probably means the harvesting of steam from the craft's diesel exhausts to fill water ballast tanks and compensate for burned-up fuel. The US Navy's flying aircraft carriers of the 1930s used such a system, but it was an acknowledged Achilles heel of theirs. Alternative approaches include the use of neutral-buoyancy gaseous fuel (like the Graf Zeppelin in the 1930s and the TAO sperm-ship nowadays) or the mysterious "Control of Static Heaviness" gas-squash kit touted by Russo-Californian engineer Igor Pasternak.

With its NASA contract, it seems that E-Green has managed to get together enough cash to build a full-size version of Colting's design. The test inflation is being carried out inside the Garrett Coliseum in Montgomery, Alabama - "one of the few facilities large enough to host the operation". The Coliseum is more normally used for agricultural shows and the like: its proprietors proudly state that it can hold 13,500 people, more than 600 horses, as many as 1500 cattle ("with milking parlor") and/or unspecified numbers of swine.

"The first flight of the Bullet 580 is planned for later this year", according to E-Green. ®