The replacement of hydrogen with helium to fill the airships meant that the dangers of catastrophic fire which beset the R101 - and more famously the Hindenburg seven years later - were removed. But beyond the use of airships as tourist attractions, and even then not in the UK, it is a sector that has failed to take off again, all previous attempts having fallen victim to financial difficulties.
Despite the adoption of helium the other problems with airships remained and were identified by Sir Barnes Wallis. Although more famous for his later work on the bouncing bomb, Wallis had led the design team on the R100, the rather more successful branch of the twin track development plan for British airships. In fact the R100 had made a return trans Atlantic crossing, and it was suspected that this success hastened the R101s development, as both were effectively in a race to prove which had the better design. The consequent premature flight of the R101 and its tragic outcome therefore resulted in the loss of some more promising technology in the R100.
However Wallis remained interested in lighter-than-air travel and appreciated some of the fundamental problems that remained, particularly concerning the manoeuvrability of the airship on the ground – the traditional method of throwing out hundreds of ropes to a waiting team of people below was clearly not viable. Other concerns were the avionics systems and the materials used. Wallis shared these thoughts with a designer called Roger Munk, who continued to work on airship theory but as long as the core product was to be an improved airship those fundamental problems remained unresolved. The breakthrough came with the idea of developing a hybrid aircraft and in 2007 he launched a company, Hybrid Air Vehicles (HAV), aimed at making the theory a reality.
The fundamental premise of the hybrid was to combine the lighter-than-air properties of an airship with the aerodynamics of an aeroplane wing.
"The thought process behind the hybrid was something that Roger and myself were having in the early 90s," said Mike Durham, HAV's technical director. "We built our first sub-scale demonstrator, a 40ft long remote controlled vehicle, in the late 90s and we have been developing it since then. The hybrid is what makes it possible to fix all of Barnes Wallis' problems."
"Mixing an aeroplane wing shape with an airship allows you to make an airship heavier than air," explained Chris Daniels, head of partnerships and communications at HAV, "and as soon as it is heavier than air it is controllable. You can land it easily and take off in a more controlled manner. It is less dependent on weather and in particular cross winds. So that is why we set up as a hybrid and all the evidence we have points to that being the future for lighter-than-air."
That evidence includes a study by one of the world's biggest aircraft manufacturers who independently suggested that there would be an initial demand for around 600 such airships and that the market would be worth £50bn within 10 years. Daniels added: "Another independent report, from a well-known British billionaire, suggested that we were three years ahead of the competition. So we know there is a market, we know we are ahead of the game, but we are not complacent, we just want to do things right. It is about measured development and getting the right aircraft flying. The only thing that is slowing development is money. It is just the economics of a small business - the more engineers we have working on this the quicker we get it in the air."
The aircraft, the Airlander 10, has already flown. HAV initially won a contract in 2010 from the American military, beating offerings from the Lockheed Martin Skunk Works, with a very fast development schedule aimed at deployment in Afghanistan. Withdrawal of troops followed by defence cuts in 2013 meant the project was pulled just when trial flights were taking place. It was fit to fly back across the Atlantic but was not allowed to for regulatory reasons.
"What we have is a kit that has already flown but we now need to test every single item to prove that it is airworthy," said Daniels. "So for example we have a big engine test rig that we will be using in January and running them to make sure we have got the right amount of thrust and so on."
The engines themselves are standard light aircraft engines from Technify, which, claims Daniels, is: "the only credible solution for 300hp+ diesel engines providing efficiency at a wide range of speeds. Xtrac, the gearbox provider for F1 cars, has provided gear boxes to us in F1 timescales too. They are reliable and flexible and therefore allows us to have a large electrical power generation."
Each of the four engines provides forward thrust but can be manoeuvred to provide low speed vehicle control. Each is also fitted with four vectoring vanes for control in normal flight conditions.
The hull is made of a specialist strong and lightweight material, supplied by Warwick Mills, which is based on carbon fibre, three layers of Mylar and a layer of Kevlar. The resulting material is no thicker than shoe leather. NASA spacesuit manufacturer ILC Dover built the hull, which has no internal structure but is instead what HAV engineers call a double-bubble hull. It is two separate gas volumes that are blended together to form a slightly corrupted figure eight. Durham commented: "The Airlander 10, although it looks like a big bubble, already produces five or six times the lift of an ordinary airship. In a cigar-shaped airship you might get 5 or 6% of your lift from aerodynamics, in a hybrid vehicle you can get up to 40%, which is why the hybrid shape is more efficient."
But how easy is it to prove something the size of an airship has reached its most efficient design? Durham responded: "Through scale demonstrators, through wind tunnel testing you just get a better and better design. I am sure what we have is not the ultimate design, in 20 years time somebody will have come up with an even more efficient version. But what we have works, and it is good – maybe we have lucked out and got the optimal design but we can't be 100% sure of that at the moment.
"You can't build one of these just on CFD, and you can't build one of these based on just a few test flights of the demonstrator. It is the whole engineering development process that puts it together. We did a lot of wind tunnel modelling back in the late 90s and early 2000s on the concept of a hybrid vehicle. That testing gives you confidence to scale the data up to build a sub-scale demonstrator – the 40ft model. With the information you get from that you can go back to the wind tunnel and to use CFD for a computer simulation – all the pieces fit together. If we had had £100m at the start we could have developed the vehicle much quicker!"
There are currently a dozen engineers and half as many technicians and Durham describes it as a true hands-on engineering role, with CAD terminal being swapped for screwdriver whenever necessary. However, the main design environment is Solidworks although Durham said: "We use everything from Solidworks to Catia. We have CFD and stress analysis tools and the basic shape was established in a Unigraphics package 15 years ago."
The range of engineering disciplines covers mechanical, electrical, avionics, structural, mechanical, fuel systems and propulsion. "We have to have the complete spectrum of engineers because we are unique in the UK in that we design complete aircraft," said Durham. "We are designing a complete vehicle system, everything starts from this office. We may package up the design of a fuel tank for instance, our fuel systems engineer would set all the basic requirements push that spec out to a manufacturing and design company who will do the detailed design on that fuel tank. So we do tend to run a distributed design and manufacture process."
In particular Blue Bear Systems, Tensys and Cranfield University all helped with aspects of design for the hull structure, simulators and wind tunnel models and testing, respectively.
Other notable contributors have been Raytheon, which undertook electrical wiring, and Triumph, which supplied high performance actuators. Beside the hull, most of the aircraft, like the payload modules, fins and engine housings, are made of carbon composites. These materials have come from a variety of carbon composite manufacturers, of whom Forward Composites is the most significant.
The vital statistics of the Airlander 10 are that it is 302ft long, 143ft wide and 85ft high. In manned mode, it can remain airborne for five days and 21 days unmanned. Its maximum payload is 10 tonnes and maximum speed is in the region of 80 knots.
If it was to be used for passenger transport then it would probably, for regulatory reasons, be limited to 48. Daniels commented: "For passengers it is a much more pleasant experience – you can have floor to ceiling windows, and you can open windows. But on short haul routes, like island hopping it can be quicker than having to go through airports, even if the flying speed is slower. It is a different market to a 747 going across the Atlantic, athough you can go around the world. Where that is useful is for tasks like communication or search and rescue where it can be available for weeks at a time."
One project that is planned for next year is shifting wind turbine blades and gear parts to the north of Sweden. The alternative way to transport the equipment would either be to use helicopters, although they can struggle with underslung loads, of start building roads through forests.
Airlander 10 will cost about £25m, which is cheaper than a large aircraft and roughly equivalent to a large helicopter. However it is efficient and HAV claim it has under 20% of the operating costs, so over a 10 year period it will be a lot cheaper than any other aircraft. It is also the safest form of air travel – it can still fly even if all four engines fail.
Under development already is the triple-hulled Airlander 50, which will have more powerful turbofan propulsion and a payload of 50 tonnes, bringing it into direct competition with large cargo planes.
| The Cardington hangars During the first World War, the British airship programme, already over a decade behind the German Zepplin development, was initiated across a handful of sites in the UK. This involved the construction of vast hangars of which only the two at Cardington still exist. The first of the two was built in 1915 by Short Brothers, who had been commissioned by the Admiralty to develop airships, the R31 and R32. A decade later the hangar was extended to 812ft long to accommodate the R101 airship construction. In 1928 the second hangar was disassembled at the Royal Airship Works in Pulham, Norfolk and re-assembled at Cardington. After the collapse of the British airship industry in 1930 the site was used to build barrage balloons but after the Second World War the RAF no longer used the site. Since then the sheds have been used for filming, construction and fire research and an unsuccessful attempt by a company called Airship Industries to resurrect the airship industry in the 1980s. Shed 2 is now home of Hybrid Air Vehicles. |
