After a gap of several years, airship production is returning to the Cardington sheds - birthplace of the historic R101in the 1930s - near Bedford, 70km (45 miles) north of London in the UK. The airship under construction there today is a totally new design which will have a 14,200m3 (500,000ft3) envelope and be capable of carrying up to 52 passengers. With a length of 81m, it will be the biggest airship in the world.
The manufacturer, headed by Air Marshal Sir John Walker, is Airship Technologies - a company built on the foundations of the UK's Airship Industries, which collapsed in the wake of the disintegration of Australian entrepreneur Alan Bond's business empire in the early 1990s.
The Airship Technologies design team, headed by chief designer Roger Munk, has already achieved full US Federal Aviation Administration certification for five airship designs (the Skyship 500, 500 HL, 600, 600B and Sentinel 1000) since the 1970s.
Non-rigid structure
The latest project - the AT-04 - is constructed from a totally non-rigid structure with composite battens and fins. It will be powered by three Zoche diesel engines with vectored thrust, plus a bow thruster for docking. Each Zoche will deliver a maximum 260kW (350hp), and 185kW continuous. The AT-04 is designed to cruise at 45kt (85km/h) on the stern engine alone, allowing virtually silent, vibration-free flight. Maximum continuous cruise is expected to be 75kt.
A new fabric is being used for the main body, which, in conjunction with a revamped envelope design, has more than doubled the payload of the 600-series ships. The fabric was previously used on tethered aerostat balloons, and it is lighter and more durable. This is an important factor, given that 15% of an airship's cost is that of the envelope. Older fabrics used to last only four years in high ultra-violet (UV) environments and needed repainting every year, so incurring hangarage costs.
Every repaint added 90kg to the weight of a 600-series airship. Tests have shown that the new fabric, which incorporates a UV blocker, should last for a decade at least.
The prototype AT-04 is now under construction, and Walker is bullish about the rate of progress. "We estimate one year from an order being placed to first flight, plus six months for certification. We anticipate that the first flight of the prototype will be summer 1998," he says.
Airship Technologies uses what Walker terms the "Airbus principle" to control costs. Much of the work is subcontracted and, wherever possible, a modular approach is taken to maintain flexibility and so reduce construction and maintenance costs. For example, all three engines are identical and totally interchangeable, allowing for fast, low-cost replacement. The gondola, too, is designed in modular fashion, with the potential for extra identical sections to be added or subtracted, according to the needs of the customer.
Initially, the envelope will be built in the USA, the engines in Germany and the gondola in the UK, where a production line is being laid down at Cardington. Final assembly will take place at Weeksville, North Carolina, before the airship is ferried across the Atlantic to European customers. The AT-40 will be able to carry out the transatlantic trip non-stop without refuelling on its standard 3,000litre fuel capacity.
European base
The plan is to re-establish Cardington as a base for European airship assembly, and Airship Technologies is negotiating with the Bedford Development Agency to help bring this about. It is likely that the FAA in Atlanta, Georgia, will carry out the certification as it has most experience of modern airships, and the US market has to date been the largest.
US military chiefs believe that the airship's day will return. There is a need to develop effective early-warning systems to defend against surface-skimming cruise missiles. This requires a stable radar platform capable of looking as far as possible over the horizon - a function demonstrated on aerostats. The US Department of Defense has invited tenders for a $600 million cruise-missile programme for which Airship Technologies will bid.
Apart from its ability to stay on station for hours, or even days, and move independently under its own power, the shape of the airship bestows an advantage in missile detection where horizontal and vertical signal-polarisation is needed: a wide horizontal antenna can be mounted on an aircraft, but with very little height, whereas the AT-04 can accommodate the 30m2 (323ft2) Westinghouse ASSR-1000 parabolic elliptical reflector within its envelope, with room to spare. The importance of antenna height is such that the US Navy planned to Ìt a three-face, 270m2 per face, antenna in a 50,000m3 airship.
Munk is optimistic about Airship Technologies' chances of securing the contract. "We believe we have a design team here in Bedford which is at the worldwide cutting edge of airship technology, and we have a huge amount of experience from the days when Airship Industries and Westinghouse worked together on a previous US Navy contract and overcame many technological barriers. We can effectively pick up where we left off with that technology for a few million dollars, and that has to make more sense than the US Department of Defense starting from scratch," he says.
Airship Technologies seems to have developed a technology portfolio which addresses many of the problems associated with the previous generation of airships. Munk adds: "Traditionally, airships need large groundcrews, all of whom have to be fed and watered. Our development of vectored-thrust engines which can turn through 90í led to a lot of military contracts early on. We have now combined that with a bow-thruster system that only cost us $5 million to develop and which allows us to ground-handle an airship for the first time ever without a groundcrew - and that absolutely transforms airship operating economics."
Airship Technologies uses "fly-by-light" flight-control technology: the first-ever certificated fly-by-light system was developed for airship use, as these vehicles were seen as stable testbeds with long control runs ideal for such experimental technology. As a proof- of-concept exercise to demonstrate ground-handling controllability in a highly regulated environment, a Skyship 600 has been operated at Charles de Gaulle Airport, in Paris, France. Air traffic controllers are reported to have been surprised and impressed by the airship's manoeuvrability and its ability to fit in with normal traffic patterns at an international airport.
Military configuration
In its military configuration, the AT-04 will be able to stay on station for two or more days - a distinct advantage over helicopter operations, where, for example a Westland Sea King helicopters can be flown 230km (425nm) and stay on station for only 2h before returning.
The AT-04 may be an attractive proposition for operations in which helicopter use is not practical. In addition, the side of an airship makes a prominent advertising hoarding.
As far as larger airships are concerned, structural problems decrease as the scale of the airship increases. More speed is possible with proportionately less power. Munk says that the military learned in the Gulf War that 100t payloads were not a good idea.
"On occasions, they need to lift 500-1,000t at a time," he says. Airship Technologies is studying a way to satisfy that need.
The last word should go to Walker, who, as an Air Commodore, was a sponsor of a Ministry of Defence airship trial carried out in 1984. As he said then, it is sometimes "-wise to quietly ponder on what new technologies can do for old, but basically sound, ideas. That is what offers a new dawn for airships".
Source: Flight International
