Airships came to prominence in the First World War when they were used for bombing raids. Today the airship concept is undergoing a revival. But what is the technology like, and what will they be used for?
In 1914, the sight of airships in the skies of Europe was becoming a regular occurrence. The first Zeppelin raid came when Germany bombed the Belgian town of Liege in August 1914. Britain retaliated by bombing a Zeppelin factory in November of the same year. Germany responded with the first Zeppelin air raid in Britain on 19 January 1915.
When airships first started appearing overhead, sightings were a hot topic and often made the news, "much like UFO sightings do today", says Terry Charman, senior historian at the Imperial War Museum and author of the recently published 'The First World War on the Home Front'. But commentators of the day thought they would never be used in wartime to bomb civilians.
The threat from Zeppelin air raids was very real, though. To head it off, the newly formed Royal Naval Air Service bombed the Zeppelin factory in Friederichshafen in November 1914, as well as sheds housing active airships in Dusseldorf and Cuxhaven. As history shows us, this didn't have much impact in stopping the use of Zeppelins in First World War bombing raids.
Airships weren't just about warfare. They were also used to carry passengers, and by 1914, when they first started to be used in wartime air raids, they had already transported more than 10,000 people on passenger flights within Germany. "Their popularity grew rapidly after the First World War, and the first airship ever to make an east to west Atlantic crossing was British, the R34, in July 1919," Charman explains.
It was the 1930s when the airship really caught the world's imagination. The LZ27-127 Graf Zeppelin was a major PR tool in pre-Nazi Weimar Germany. It was the airship that made the first commercial passenger flight across the Atlantic and the first commercial passenger flight around the world, and it flew a scientific mission over the North Pole. It was also the most successful airship of its time, flying over a million miles on 590 flights and carrying more than 34,000 passengers. But the popularity of airships declined rapidly after 1937 when the infamous Hindenburg, which was also linked with the Nazis in most people's minds, crashed into its mooring mast at a cost of 36 lives.
Now, after virtually vanishing from the skies for more than 70 years, it seems that the airship is coming back into fashion.
Modern era of airships
Back in the original era of airships, of which the Zeppelin was the most successful and well-known rigid airship design, they were essentially a metal framework covered by fabric, and used balloons filled with hydrogen (later helium) for buoyancy. The airships used during the First World War bombing raids were more streamlined than their predecessors and powered by several engines, which were attached to the outside of the framework and housed in an engine car. Some of the engines were used for forward propulsion, others for manoeuvring and yet others for reversing.
Today's airships have come a long way in terms of the technology used to build and power them, while sticking to the same basic design. Some modern airships, the Goodyear Blimps for example, are used for marketing and promotional purposes, while others are set to transform whole industries.
Some of the most promising developments in the airship world are coming from California-based Aeros. The design that the company is so excited about is the Aeroscraft. This is a vertical lift and hover vehicle that can take off and land like a helicopter, meaning it can be used to deliver cargo in areas where there are no airports, such as countries with little or no infrastructure development, or in places where airstrips have been damaged through natural disaster or war.
But while it's hoped that the Aeroscraft will have a hugely positive impact in the humanitarian and military worlds, it was designed to help the logistics sector move heavy and oversized cargo shipments from the point of origin to the point of need.
The plan is for three versions with cargo capacities of 66t, 250t and 500t, all with a maximum altitude of 12,000ft and a cruising speed of 115mph. Although slower than the 500mph of conventional aircraft, the Aeroscraft will use two thirds less fuel, so it could help the logistics sector cut its carbon emissions.
Buoyant and rigid
The single most important difference between the designs of a century ago and the Aeroscraft is its variable buoyancy. Speaking about this breakthrough element of the design, Aeros CEO Igor Pasternak says: "the biggest obstacle that conventional and hybrid airships face when tackling the cargo function is their inability to control buoyancy. The requirement for ballast exchange, ground infrastructure and the need for runways limit the usefulness of traditional lighter-than-air vehicles. By being able control the vehicle's heaviness relative to the outside air, the Aeroscraft has overcome that and also eliminated the need for infrastructure and ground personnel from the equation."
Aeros has achieved this leap forward in airship design through the COSH (control of static heaviness) system. This buoyancy management system, which Aeros has developed in-house, enables the Aeroscraft to operate as a lighter-than-air (LTA) vehicle while also becoming heavier on demand, which allows controlled hovering, making it easier to carry out ground operations.
It does this by pressurising the inert helium in the aeroshell into 'helium pressure envelopes' (HPEs), which suppress the lifting ability of the gas. Then it releases the helium back into the aeroshell, creating added static lift, when it needs to become lighter again. Control panels in the pilot's cockpit allow the COSH system to be configured to provide the amount of static heaviness needed for off-loading personnel or cargo, both with flexibility and without the need to take on external ballast to stay grounded. Energy converters control the compression of helium to a determined pressure and discharge it at high speeds, through a system of pipes and control valves.
Tim Kenny, director of engineering at Aeros, says: "The HPE units contain and control the compressed helium and allow the overall helium volume envelope to be reduced or increased, enabling the air vehicle to become heavy or buoyant in a controlled manner."
Another difference in the Aeroscraft is its rigid structure. Modern airships tend to have a non-rigid structure, relying on the gases that fill them to help them maintain their shape. But just like in the Zeppelin era, the Aeroscraft has a rigid structural design and it is currently the only rigid-structured variable-buoyancy air vehicle of its kind.
The Aeroscraft has made use of some of the impressive material innovations that have come along in the past fifty years to help it balance utility with weight budget management. The rigid structure is made of ultra-light carbon fibre and aluminium trusses, which are reinforced with high-'strength composite tensioned cables.
This truss structure is essential for the cargo applications that the Aeroscraft has been designed for, as it helps it shoulder the burden of cargo loads, enables it to achieve a faster cruising speed by combatting aerodynamic forces in forward flight, and improves its weather resilience compared with traditional LTA vehicles. It also provides a range of hard points for mounting engines, canards, cockpit, propulsion systems and other auxiliary systems both inside and outside the hull mould line.
The rigid structure for the Aeroscraft advanced prototype, called Dragon Dream, contains 200 trusses of varying lengths from 5.5m to 16.8m. They give the airship the strength it needs with a lightness that was not possible in the days of the early airships.
The Aeroshell is the major external framework of the Aeroscraft, which can be thought of as the vehicle's muscle and skin that fits over the bones of the internal rigid truss structure. This is how it keeps its shape whatever buoyancy levels are being provided by the HPEs. It's made up of two main elements. First, the honeycomb aluminium panels (the muscles). These geometric panels are ultra-light-weight and sandwiched between sheets of aluminium to provide a structural element that has an excellent strength to weight ratio. Second, the 'skin', which fits over the top of the honeycomb aluminium panels, is a combination of Mylar and other lightweight fibre-based materials, all of which were chosen for characteristics such as solar reflectivity, helium retention, strength, and durability.
As well as these advances in buoyancy and framework design, the Aeroscraft also has vectored thrust engines that rotate to allow for advanced manoeuvrability and provide its VTOL (vertical take off and landing) flight operations. These vectored thrust engines mean that the Aeroscraft can propel itself in forward flight and also help with hover operations and any ground-based taxiing manoeuvres.
The Aeroscraft will have multiple electric propulsion units for 360-degree flexibility, powered by diesel generators. Using a diesel-to-electric propulsion system overcomes the aviation fuel distribution limitations.
'Super manoeuvrability' is also supported by the avionics system, which was designed with a focus on streamlining pilot control to make flying more manageable. Unlike the conventional fixed-wing yoke, the Aeroscraft has a side-stick controller that allows both pilot and co-pilot a full range of control from either seat. Onboard cameras make it easier for pilots to see exactly what the airship's position is by giving instant perspective both inside and outside the airship.
"Reducing the workload of pilots is what we are aiming to achieve," says aerospace control engineer Louis Pu. "By combining a standard suite of flight technologies with the technologies of the vehicle management system, the Aeroscraft's avionics system will provide a more manageable, user-friendly experience."
The Aeroscraft's engines are controlled and backed up by standard throttle levers and hard switches. What sets its systems apart is that everything is communicated through a vehicle management system, removing the need for extra support from flight engineers. This centralised VMS allows pilots to interact with all vehicle subsystems, at any stage of flight, through touchscreen controls. If Aeroscraft goes into production the avionics system will also include onboard weather systems and automated cargo handling systems, which will eliminate the need for loadmasters.
Rounding off the design is the air-bearing landing system, which eliminates the need for runways and allows landing on virtually any surface, including water.
The landing system is equipped with powerful gripping and suction capabilities that play a major role in enabling the Aeroscraft to stay grounded for cargo transfer. It can absorb energy during vertical landings and provides suction between the airship and the ground to stabilise the vehicle during passenger/cargo unloading and high wind conditions. It also provides positive buoyancy to reduce friction and allow the Aeroscraft to taxi.
"What makes the landing cushions unique is their ability to inflate and deflate based on surface conditions," says Alex Canto, director of quality control at Aeros. "The sides of the landing systems can be simply deflated and inflated to compensate for uneven terrain, which means the Aeroscraft behaves and appears as though it has just landed on an even surface."
We have lift off
Aeros also has ambitions in Europe, and this year supported the establishment of the European Consortium of Aircraft Operations. ECAO will be carrying out a study of the Aeroscraft's potential for cutting carbon emissions in the logistics and humanitarian response sectors, and its operational role in the international air traffic and cargo logistics systems in and surrounding the European Union.
The ECAO study, which will be completed in early 2016, will investigate the economic and environmental benefits, trends in logistics, and potential impacts on redistribution of manufacturing, as well as supply chain integration and usage in various humanitarian aid and relief operations. Aside from attempting to quantify the emissions, noise and other environmental advantages, researchers will conduct cost analysis, evaluate promising applications for economic development and commercial value creation, and potential infrastructure cost savings.
The structural and COSH elements of the Aeroscraft are now in testing and Aeros is committed to having its first commercial vehicle certified and ready to fly by 2017 – or sooner if the US Congress fast-tracks approval.
It seems that airships may soon appear in our skies again, but now in cargo and humanitarian roles. They have come a long way since the Zeppelin days.