A technologically advanced cousin of the balloon,
airships are streamlined vessels buoyed by gases and
controlled by means of propellers, rudders, and pressurized
air systems. More commonly referred to as blimps
and dirigibles, the airship is comprised of non-rigid,
semi-rigid, and rigid types that rely on lighter-than-air
gases such as helium and hydrogen for lift. Since the
turn of the twentieth century, they have been engaged
commercially in the transport of passengers and cargo
and have proven a successful means of advertising.
Airships derive their lift from forward motion, just as an airplane does, and all three types have long used the internal combustion engine, like the type used in automobiles, to propel their massive bodies through the air. These have included the earliest motorcycle engines, the diesel engines of the mammoth American ships Akron and Macon, and the beefed-up Porsche engines used to power a new generation of airships. Traditional pressure airships house the engine, propeller, and gear box on an outrigger that extends from the side of the car, while the modern British Skyship’s 500 and 600 use inboard engines that turn long prop shafts which allow the propellers to be vectored outboard. The introduction of pivoted, or vectored, engines gave airships the ability to change the direction of thrust and afforded it such amenities as near-vertical lift-off, thus reducing the need for long runways. Capable of airborne refueling, airships can remain aloft for weeks at a time, reaching an average airspeed of 60 MPH (96.5 km/h).
with French inventors in the latter half of the eighteenth
century. In 1783, Jacques and Joseph Montgolfier
designed the first balloon used for manned flight, while
concurrently, Jean-Baptiste-Marie Meusnier had thought
to streamline the balloon and maneuver it by some
mechanized means. While several airships of similar design
met with limited success from 1852, Meusnier’s
idea did not officially get off the ground until 1898. That year, the Brazilian aeronaut Alberto Santos-Dumont became the first pilot to accurately navigate a hydrogenfilled
envelope and basket by means of a propeller
mounted to a motorcycle engine.
Because of their non-rigid structure, the first blimps, like the balloon, were prone to collapsing as the gas contracted during descent. To counter this, Santos-Dumont introduced the ballonet, an internal airbag that helps maintain the envelope’s structure and regulates pitch as well as lift, or buoyancy. Modern blimps continue to use ballonets positioned at the front and rear of the envelope, permitting the engineer to pump air into one or the other to change the pitch angle. For example, by increasing the amount of air in the aft ballonet, the airship becomes tail heavy, thus raising the nose skyward. Steering is further achieved by controlling rudders affixed to one of several types of tail fin configurations, allowing for basic left, right, up, and down directions.
The long standard cross-shaped fin is slowly being replaced by an Xshaped configuration. While the X is more complicated, requiring a combination of rudders to complete a maneuver, it provides better ground clearance. The car or gondola serves as the control center, passenger quarters and cargo hold of the airship. The envelope and car are connected by a series of suspended cables attached to the envelope by different types of load-sharing surfaces. Many modern airships use a curtain structure glued or bonded along the length of the envelope which evenly distributes the weight of the car and engines.
The German inventor, Count Ferdinand von Zeppelin
took the guesswork out of airship aerodynamics by
building a rigid structure of lightweight aluminum girders
and rings that would hold the vessel’s streamlined
shape under varying atmospheric conditions. Unlike Dumont’s
single-unit envelope, Zeppelin incorporated a
number of drum-shaped gasbags within compartments of
the structure to maintain stabilization should one of the
bags become punctured or deflate. The dirigible was then
encapsulated by a fabric skin pulled tightly across its
framework. Buoyancy was controlled by releasing water
ballast to ascend or by slowly releasing the hydrogen gas
through a venting system as the ship descended.
Zeppelin was among the first airship designers to realize, in practice, the functionality of greater size in lighter-than-air vessels. As he increased the surface area of the envelope, the volume increased by a greater proportion. Thus, a larger volume afforded better lift to raise the aluminum hull and maximized the dirigible’s cargo carrying capacity. Airships like the Graf Zeppelin, the Hindenburg, and their American counterparts, the Macon and the Akron, reached lengths of up to 800 ft (244 m) with volume capacities nearing seven million cubic feet. Hydrogen was, in part, responsible for such engineering feats because it is the lightest gas known to man and it is inexpensive. Its major drawback, one that would virtually close the chapter on non-rigid airship aviation, was its flammability. While passenger quarters, cargo, and fuel could be secured to or stored within the dirigible’s metal structure, its engines were housed independently and suspended to reduce the possibility of friction-caused ignition of the gas.
Little did English writer Horace Walpole know how closely he had prophesied the future of airships when, upon the launch of the Montgolfier balloon, he wrote, “I hope these new mechanic meteors will prove only playthings for the learned or the idle, and not be converted into engines of destruction...” While zeppelins, as they had become known, were initially put into commercial service, successfully completing nearly 1,600 flights in a four-year period, they were engaged in the service of Germany during World War I as giant bombers, raiding London itself in May of 1915. After the war, the rigid dirigible was employed as both a trans-Atlantic luxury liner and airborne aircraft carrier, but eventually fell out of favor after the Hindenburg disaster in Lakehurst, New Jersey, on May 6, 1937.
An intermediate version of the rigid and non-rigid types, the envelope of the semi-rigid airship was fitted with a keel similar to that of a boat. The keel acted as a sort of metal spine which helped maintain the envelope’s shape and supported the gondola and engines. Interest in the semi-rigid airship was short-lived, though it met with some success. In 1926, the Italian pilot Umberto Nobile navigated the airship Norge across the North Pole, accompanied by the Norwegian explorer Roald Amundsen.
following generation of airships and continues as
such in the early twenty-first century. Though its lifting
capacity is less than that of hydrogen, helium is considered
a safe resource because it is inflammable. During the
1920s, the United States discovered an abundant source
of the gas in its own backyard and reinstated the blimp as
a surveillance mechanism during World War II, maintaining
a fleet of some of the largest non-rigid airships ever
built. “It was the American monopoly of helium that
made possible this Indian Summer of the small airship—
long after every other country had abandoned the whole
concept,” wrote Patrick Abbott in his book Airship.
By the 1950s, the Goodyear Tire and Rubber Co. had become involved in the production of airships as part of the Navy’s intended early warning defense system, and remained one of the largest manufacturers of blimps until the late 1980s. The Goodyear blimp is probably most noted as a high-flying billboard and mobile camera that has offered millions of television viewers a bird’seye view of sporting events for several decades.
The early 1990s marked a resurgence in airships with the design of such models as the 222-ft (67.6-m) long Sentinel 1000. Built by Westinghouse Airships, Inc., its envelope is made of a lightweight, heavy-duty Dacron/Mylar/Tedlar composite that may eventually replace the traditional rubberized fabrics used by the Sentinel’s predecessors. According to Aviation Week and Space Technology, the craft “has a 345,000-cu.-ft. envelope and is powered by two modified Porsche automotive engines fitted with propellers that can be tilted through a range of plus 120 to minus 90 degrees.” Its potential for transporting heavy payloads, its quietness, and relative stability, have brought the airship back to design rooms around the world. Based partly on its fuel efficiency and the fact that its shape and skin make it virtually invisible to other radar, the United States has plans to reintroduce the blimp as a radar platform for its Air Defense Initiative. French scientists have used the airship to navigate and study rainforests by treetop, while environmentalists have considered its usefulness as a means of monitoring coastal pollution. The future may see airships powered by helicopter rotor systems and solar power, as well as the return of the rigid airship.
There is a moment in the life of any aspiring astronomer that it is time to buy that first telescope. It’s exciting to think about setting up your own viewing station.
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