Saturday, January 12, 2008
Weekend Wings #2: Return Of The Airship?
Airships and balloons have been with us for many centuries. Initially balloons were unpowered and at the mercy of the wind and weather. Both hot air and gas-filled balloons were developed at the same time. The Montgolfier brothers demonstrated their first hot air balloon in 1783, with the first human flight following a few months later.
Jacques Charles demonstrated the first hydrogen balloon in the same year and made the first human flight in it ten days after the Montgolfier brothers.
The first balloon powered by human muscles was built by Jean-Pierre Blanchard in 1784. The following year he crossed the English Channel in a balloon propelled by flapping 'wings'.
It didn't take too long for engines to be married to the balloon. In 1852 Henri Giffard installed a steam engine beneath a balloon and flew successfully from Paris to Trappes, a distance of about 17 miles (27 km.).
Airships soon developed distinct classifications. Balloons were simple 'bags' holding gas or hot air, without a framework. Non-rigid airships (often called 'blimps') used a shaped bag without a framework or supporting structure. Semi-rigid airships used a supporting structure such as a central keel to which the gas bags were attached. Rigid airships such as the famous Zeppelins used a full structure or framework containing the gas bags.
Another distinction must be made between aerostats and airships. In one sense any aircraft remaining aloft due to buoyancy is an aerostat, including airships: but in practice the term has come to be applied to all moored or tethered balloons. Airships are self-propelled and not tethered during flight.
The 'Golden Age' of airships began in 1900 with the flight of the first Zeppelin.
These airships were named for their designer, Count Ferdinand von Zeppelin of Germany. Their military potential was rapidly realized by the German armed forces, and during World War I a large number of Zeppelins carried out bombing raids over England. However, as aircraft performance improved it became clear that the slow, unwieldy airship would never be able to survive in combat against them. Some very rare footage from the period is shown below.
Despite such setbacks, Zeppelin L.59 made a record long-distance flight in 1917 in an attempt to carry supplies from Germany to its armed forces in what is today Tanzania. Although unsuccessful, the mission nevertheless covered over 4,200 miles in five days.
Between the wars intensive efforts were made to develop the airship as a passenger and freight transport. Only Germany achieved any real success in the 1930's. The Graf Zeppelin operated scheduled service between Germany and Brazil and completed the first airborne circumnavigation of the world by an airship.
Later the Hindenburg operated between Germany and the USA. It was destroyed in one of the most horrifying disasters of the period when it caught fire and was completely destroyed on arrival in New Jersey in 1937.
Britain pursued for a time the so-called 'Burney Scheme' for a network of airship routes linking it with the colonies. However, one of the prototypes for the scheme, the R101, crashed and was destroyed with heavy loss of life. The scheme was subsequently abandoned.
The USA pursued airships for military purposes during the 1920's and 1930's, culminating in two remarkable craft, the USS Akron (pictured below) and USS Macon. Both used helium as a lifting gas instead of hydrogen, eliminating the risk of fire. However, helium was so scarce at the time that both airships could not be operated simultaneously. If one was filled with helium there wasn't enough to spare for the other.
Both carried fighter aircraft which could be launched in flight and recovered in mid-air.
However, Akron was destroyed in a storm off New Jersey in 1933 and Macon was lost due to structural failure off California in 1935. That ended military airship development in the USA.
During World War II all sides used so-called 'barrage balloons', tethered aerostats to make it difficult for aircraft to dive on a target. The US Navy used over a hundred and fifty blimps for anti-submarine patrols.
They operated not only along the US coast but also in the Caribbean, off Brazil, and in the Mediterranean theater. They achieved little success in terms of U-boats destroyed, but probably contributed much to the overall safety of the sealanes by forcing enemy submarines to remain submerged where they could not move fast. Only one ship was lost from a blimp-escorted convoy throughout the war.
Both Britain and Japan used balloon-launched bombs against their enemies. Britain launched almost 100,000 against Germany from 1942-1944 in Operation Outward. Japan launched some 9,000 'fire balloons' against the USA in 1944-45.
Only a few hundred reached the US and caused minimal damage. The most serious incident saw five children and a woman killed in Oregon in June 1945. The possibility exists that several hundred of these balloons may yet lie undiscovered in wilderness areas, and their explosive cargoes are likely to be still dangerous.
In the fifty years following World War II airships ceased to be a major factor in air transport. A few were built as blimps for advertising and photography platforms, but in the main the craft were abandoned during the Jet Age. However, that may be about to change. There have been a number of interesting developments in the past decade or so.
Zeppelins are being built again. The Zeppelin NT is in use to carry tourists on sight-seeing tours: one is now in service in Japan.
There has been some interest in using airships to move bulky, heavy cargo, and a Russian company is proposing a model to carry up to 180 tons. However, airships' main application today seems to be in the field of communications and surveillance. An 'Internet Airship' has been proposed to provide wide coverage for wireless networks over Europe. The US Army is testing a remotely-piloted airship as a communications node:
Airships are also under consideration for ultra-high-altitude use. Lockheed-Martin is contracted to build a prototype High Altitude Airship. It will cruise above 60,000 feet altitude and generate its own electricity through conformal solar panels.
Another exciting development has been the hybrid airship: one that derives part of its lift from lighter-than-air gases, and part from a lifting body design that relies on forward movement to generate aerodynamic lift. Lockheed-Martin's 'Skunk Works' recently flew a prototype vehicle of this design to immense interest among those following the genre. A video of the first flight is below.
Lockheed-Martin seems to be investing a great deal of time and trouble into airships. The company recently patented a torpedo-launched high-altitude inflatable endurance airship. The mind boggles at the thought of special forces troops being submarine-launched through a torpedo tube and floating to their target in airships . . . but who knows?
Other possibilities are under investigation around the world. For example, South Africa is considering a maritime surveillance system whereby a radar in orbit would transmit impulses to the surface. Their reflections would be picked up by an airship-mounted antenna at very high altitude. Such a hybrid system could cover hundreds of thousands of square miles of ocean at relatively low cost.
There are more novel ideas out there. One ingenious designer is proposing an airship hotel (pictures and video at the link). There's even been a suggestion that airships could be used to carry heavy cargoes to near-orbital altitudes, there to rendezvous with a docking station and transfer their load to other vessels which would lift them the rest of the way into orbit. It's all theoretical at the moment, but if the many obstacles to such an idea can be overcome it offers a much lower-cost route to orbit than any current technology.
One potential drawback to this upsurge of interest in airships is that the world's supply of helium is strictly limited and is already running low. Either new efforts will have to be made to extract it, or some alternative will have to be found. Still, provided this can be done, a centuries-old technology might just be making a comeback.