Vid A German-American company has successfully tested a prototype unmanned airship of weird and wonderful design. The so-called "Stratellite" craft is composed of gas-filled segments linked in a chain, so it can flex and bend with the wind.

Here's a company flight-test vid (you need Flash and YouTube privileges to see it):

Like many modern lighter-than-air projects, the idea of the Stratellite is to serve as a communications relay or surveillance platform, floating at stratospheric heights for long periods. The cruising height of 65 to 70,000 feet is often chosen for long-endurance unmanned aircraft because of the "wind bucket" found at that height. Low windspeeds mean that an aircraft can stay on station or move about without needing to burn too much fuel.

The Stratellite's tadpole-like segmented design is the brainchild of Dr Bernd Kröplin, president of TAO Technologies GmbH of Stuttgart. The development of the airship is being carried out by a joint venture between TAO and Florida-based Sanswire Corp.

The flexible structure isn't the Stratellite's only special sauce. Aviation Week reports that the ship also uses a cunning method of buoyancy control, one of the great Achilles heels of helium filled lighter-than-air craft. As fuel is burned up, the ship becomes too light to maintain a steady height; but helium is too expensive to be casually vented off.

The Stratellite, however, doesn't have this problem because is runs its Rotax engine on gaseous fuel stored in the ship's cells. The fuel is mixed so that it has exactly the same density as the atmosphere, meaning that the ship's buoyancy is unaffected as it is burned and its place in the cells taken up by air.

Sanswire-TAO refer to this gas-fuel ploy as "the Company’s proprietary propulsion solution" in their press release, but there would seem to be prior art here. The famous 1930s airship liner Graf Zeppelin actually employed the same gambit, running her engines on "Blaugas" specially mixed so as to have the same density as air.

Apart from the bendy structure and buoyancy-compensating gas fuel, Av Week reports that the Stratellite will soon feature powerful engine supercharging in order to operate at its designed cruising height. The ship is also expected to have an option to drop its payload attached to a satnav-guided parawing of the sort now starting to become common in military airdrop operations. This would allow the most expensive part of the ship to be recovered in the event that winds between the stratospheric bucket and the ground didn't permit landing. Alternatively, the entire ship could be deflated at height and parachute itself down, losing only the pricey helium fill.

A 70m-long ship is slated to make stratospheric flights late next year, according to Sanswire-TAO.

The Av Week report is here, and there's more from the company here. ®