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Boeing this week launched its new 787 Dreamliner aeroplane in the UK.

Lighter than air

The new plane will fly at normal speeds but will use 20% less fuel per passenger - it is specifically designed as a low carbon relative of traditional passenger planes.

But with the government committed to reducing national greenhouse gas emissions by 80% of 1990 levels by 2050 and blocking new airport expansion projects, the Dreamliner alone is not going to get the job done. However, one solution could be found in an altogether different kind of transport.

The idea of using airships as heavy duty freight vehicles is now being brought into the spotlight.

Old ideas made new

While they were the earliest reliable method of manned flight, used as intimidating bombers in the First World War and regularly crossing the Atlantic Ocean by the 1920s, the 1937 Hindenburg disaster destroyed airships’ public image and put paid to their development. The stigma has remained despite flammable hydrogen no longer being used in favour of inert helium for their lifting gas.

But experts are beginning to look again at lighter-than-air craft for their environmentally friendly and infrastructure-light credentials. And a number of companies, including Boeing and Lockheed Martin, currently have modern airships under development.

One keen promoter of the idea is former government chief scientific adviser Sir David King, who told press last month that creating a low carbon transport system will depend on investment and innovation, and “pushing at the boundary of what can be technically managed”.

King said the demand for aviation will only continue to rise - and with Heathrow already frequently running at 100% capacity, he said, something has got to give.

“With modern technology applied to airships we could carry a lot of the freight carried by wide-bellied Boeings,” he says. “We need to think out of the box to find solutions on congestion and carbon emissions.”

Lighter-than-air craft operate by static lift (or buoyancy) using an envelope - the gas containment membrane commonly thought of as a balloon - filled with gases that are lighter than air, often helium. The pilot and passengers are housed underneath in the craft’s gondola. Aeroplanes, however, are heavier than air and fly using aerodynamic lift. Hybrid vehicles that combine the two types of lift by using an envelope together with airfoil or rotorcraft technology are also now being prototyped.

“With modern technology applied to airships we could carry a lot of the freight carried by wide-bellied Boeings”

Sir David King

Airships can vary further by envelope shape - ranging from the spherical to the tubular and lenticular (lens-shaped) according to the preferred trade-off between lift and air resistance - and by envelope type. Rigid airships use a metal framework to keep the envelope’s shape regardless of pressure. Semi-rigid airships have a partial framework with an envelope that can be deflated, and non-rigid airships - better known as blimps - maintain their shape solely by the pressure within the envelope, with no framework.

The main innovation among modern airship designs is the increase in loading capacity. Traditional airships, relying solely on their own buoyancy, could rarely carry a load equal to more than 8% of the airship’s mass.

The addition of extra lifting force through aerodynamic or propulsive means allows airships to carry heavier loads, potentially nine times as much as a Boeing 747-400F freight aircraft.

UK company SkyCat projects that airships would create a 90% reduction in carbon emissions compared to widebody freight aircraft thanks to their low fuel consumption and low altitude flight. And although airships are very slow compared with aircraft, moving at around 140km/h versus 900km/h, they would still offer significant benefits over maritime transport, which is even slower and does not have the as-the-crow-flies advantages.

The potential market is large. Aircraft manufacturer Airbus estimated that 150bn freight tonne kilometres were covered in 2008, with that number expected to rise by 6% annually to 2028. Around 55% of that airfreight is carried in the cargo holds of passenger planes, leaving around 60bn freight tonne kilometres that are covered by dedicated freight aircraft annually and could be transferred to airships.

Stopping aviation stack-ups

But perhaps the biggest advantage of airships is their ability for vertical or short take-off and landing, meaning no runway is needed. The vehicles can take off and land from unprepared strips of land and water with no need for runways, ground crews, hangars or handling equipment - as proven in model tests by SkyCat, which has been developing airships in three lift-sizes: 20t, 220t and 1,000t.

The latter are both impressive compared with the 110t capacity of a 747-400F.

This lack of infrastructure means freight could be carried by airbus directly to and from collection and distribution centres, with no need for additional road freight. In theory, an airship could land in any large, relatively flat space.

University of Oxford Smith School of Enterprise and the Environment aviation and rail researcher Chris Carey says that airships could reach up to 100m in length, meaning landing sites might have to be built. But for UK freight, airships would be “relatively very small” at around 50m long and would be unlikely to require new infrastructure.

This is positive news for developing countries and disaster zones. In the former, a lack of developed infrastructure would not preclude a country from exporting freight, and would allow it to participate in international markets without having to build expensive and carbon-heavy infrastructure projects.

In the case of disasters, airships would be a quick and effective method of delivering aid to areas whose transport infrastructure may have been destroyed. The vehicles could land directly on unprepared terrain. Carey cited the example of Haiti, where airport bottlenecks and infrastructure damage have seriously delayed aid deliveries.

In the case of disasters, airships would be a quick and effective method of delivering aid to areas whose transport infrastructure may have been destroyed. The vehicles could land directly on unprepared terrain.

In the UK, the introduction of freight airships would reduce the need for freight aircraft, freeing up crucially needed capacity at airports, allowing passenger traffic to expand comfortably and reducing the need for airport expansion projects, which might mean fewer major projects happening, but could free up resources to focus on other infrastructure needs.

Moreover, airships could be a great help within engineering projects themselves. Boeing is developing an airship with Canadian firm SkyHook International, and has said the SkyHook airship will “address the limitations and expense of transporting equipment and materials in remote regions”.

It is a hybrid airship, with a helium-filled envelope supporting the SkyHook’s own weight, and four rotors providing the additional lift needed for a 40t load. The ability to transport materials to remote regions could be invaluable for projects taking place in difficult terrain and undeveloped areas - “anywhere where access is difficult”, says Carey.

SkyCat has considered this possibility too, and proposed a hypothetical scenario of a 3,000km pipeline project in a remote area using 49m long pipeline sections. The company says its SkyCat-1000 airship could carry the pipes easily, and they could even be welded at source and transported as 98m sections.

One SkyCat could carry 12 such lengths in a single trip. Using three airships, 4km of pipeline could be transported per day, allowing the project to be completed in two years.

Today, a network of freight-carrying airships is still only a glimmer in the eyes of ambitious engineers. Most models are still at the design or prototype stages, and some projects have run out of steam thanks to the financial crisis - for example, the Advanced Technologies Group which owned SkyCat, is now defunct, leaving SkyCat’s current position unclear.

But the advantages offered by modern airships could make them a viable contender for the low carbon transport system of the future. “New low carbon forms of aviation will not emerge for 20 to 30 years,” says King. “We need to anticipate future directions.”

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