Airships were once considered the future of flight. Now, they are being touted as a greener method of transport.
A solar-powered airship being built by UK-based firm Varialift Airships could eventually be used as a low-emissions way to freight cargo internationally. On a transatlantic flight between the UK and the US, the airship would use 8 percent of the fuel of a conventional jet aeroplane, says Varialift CEO Alan Handley.
Airships 鈥� lighter-than-air vehicles that rely on gas to lift them into flight 鈥� were common until the 1940s, when they were supplanted by jet engine aeroplanes.
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The advantage of airships is that they don鈥檛 require dedicated runways to take off and land, meaning that they can travel to areas with poor infrastructure. 鈥淲e can take it to point A to point B where it鈥檚 required, without any transfer from aircraft to lorries,鈥� says Handley.
They are, however, far slower than jet engines. Handley says the Varialift airship would travel at roughly half the speed of a Boeing 747, which has a cruising speed of around 900 kilometres per hour. Made from a solid aluminium exterior, it would be capable of carrying 50 tonnes of cargo.
The airship contains tanks filled with compressed helium, which it relies on for buoyancy. When the helium is transferred from the tanks into a larger chamber, it expands and pushes air out, thereby generating lift.
Once it reached a height of around 10,000 metres, it would be propelled forward by a combination of two solar-powered and two conventional jet engines. Because there is no on-board battery, the solar-powered engines would be limited to daylight hours.
Varialift has not yet begun constructing a production model. At an airfield at Ch芒teaudun, France, they are currently building a pilot training prototype that is 140 metres long, 26 metres wide and 26 metres high. It is set to be completed in the next nine months.
Robert Hewson at Imperial College London says manoeuvring an airship of this size poses significant challenges, because of the forces involved.
Elsewhere, UK manufacturer Hybrid Air Vehicles has been developing Airlander, a hybrid airship 鈥� one that combines lighter-than-air lift and aerodynamic lift 鈥� that uses four diesel engine-powered propellers. Global aerospace firm Lockheed Martin has also been developing a hybrid airship for several years, but has not yet launched production.
A team at the University of the Highlands and Islands in the UK has developed a solar-powered aircraft that is propelled by changes in buoyancy. The aircraft alternates its buoyancy between positive and negative, propelling itself forward on each descent by compressing air.
For the moment, airships remain a niche industry, says Hewson. They may be useful for transporting oversized cargo and large structures, such as gas turbines and nuclear reactors, to inaccessible places, he says. Surveillance and broadcasting are two other possible uses.
But it is unlikely that we will see the return of airships as a serious means of transporting passengers on commercial flights. The significant speed disadvantage would be a deterrent, says Hewson. 鈥淚t would take days to fly to Australia, for example,鈥� he says. 鈥淚 think it鈥檚 just not feasible.鈥�
Instead, conventional aeroplanes that are powered by hybrid or purely electric engines may help to reduce the carbon emissions associated with commercial air travel.
