The Airship Chronicles – Basics & Beginnings

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If a film or TV show needs to illustrate that the characters are now in an “alternative” universe or parallel world, one of the first tropes is to fill the sky with airships. They are the primary image of the Steampunk world and even trump the ubiquitous goggles, but what of the reality of airships throughout our history and the reality of airships in our future?

Doctor Who Airships

“The Airship Chronicles” is a series of articles exploring the history of airships and profiling some of the glorious “ships of the sky” that have floated with clouds across oceans and lands afar. To start this series we shall look at what qualifies a lighter then air vehicle as an “airship.”

Montgolfier_brothers_flightAlso known as dirigibles (from the French meaning steerable or navigable), airships are part of the aerostat family of airborne vehicles, named so because they use aerostatic lift which is a buoyant force that does not require movement through the surrounding air mass. This contrasts with the heavy aerodynes that primarily use aerodynamic lift which requires the movement of a wing surface through the surrounding air mass.

The first untethered manned balloon flight was achieved on November 21st, 1783 by the brothers Joseph-Michel and Jacques-Etienne Montgolfier in Annonay, France. As with ballooning technology today, the Montgolfiers used heat to create a pocket of air with a lesser density than that of the surrounding air, thus creating lift. Dirigibles, however, utilize gas bags filled with “lifting gas” such as hydrogen or helium to create lift.

Early airships typically used hydrogen as it has twice the lift of helium, however, as illustrated by the Hindenburg disaster of 1937, hydrogen is highly flammable and extremely dangerous. While helium provides safety, it tends to dictate smaller ship size and limits weight operations. Hot air and steam has been used by some airships, but this has proven far less effective than even helium.

Dirigible design falls into three categories: non-rigid, semi-rigid, and rigid. Non-rigid airships are the most common today, often referred to as “blimps,” they rely on internal pressure to maintain the shape of the ship. Semi-rigid airships maintain the envelope shape by internal pressure, but have some form of supporting structure, such as a fixed keel, attached to it. Rigid airships, such as the Hindenburg have an outer structural framework which maintains the shape and carries all structural loads; the lifting gas is contained in one or more internal gas bags or cells.

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Non-rigid and semi-rigid airships are limited to having its engines, crew, cargo, etc. as part of the gondola that typically hangs beneath the envelope. Rigid airships, however, are capable of containing rooms for engines, accommodation, or cargo actually inside the body of the envelope. Rigid airships were first flown by Count Zeppelin and the vast majority of rigid airships built were manufactured by the firm he founded. As a result, all rigid airships are sometimes called “zeppelins.”

Modern_airship_gondolaThe fins at the rear of the envelope stabilize the airship, allowing it to fly straight; on some smaller designs the fins are themselves part of a gas bag and gain their shape only when inflated.  The engines either side of the ship allow for steering; smaller airships house the engines as part of the gondola, but larger rigid designs can actually have a number of engines attached to its frame. Elevators and swivelling propellers provide fine control of altitude, but larger changes of height used to be controlled by either venting gas to lose altitude or dropping ballast to gain altitude. Large airships typically carried several water tanks fore and aft, allowing them to adjust longitudinal trim as well as height. Some modern designs instead pump lifting gas between the gas bags and storage cylinders.

A few airships have been metal-clad, with rigid and nonrigid examples made. Each kind used a thin gastight metal envelope, rather than the usual rubber-coated fabric envelope. Only four metal-clad ships are known to have been built, and only two actually flew, but we learn more about them later . . . 


 

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