airship: the generic term for any dirigible or powered lighter-than-air vehicle, including blimps and zeppelins. Until the 1930s, the word “airship” was used to refer to both lighter-than-air and heavier-than-air craft, but now its use generally implies only LTA craft.
ballast: a weight carried aboard a lighter-than-air vehicle to offset the buoyancy of its lifting gas. Gas balloons commonly use sand, while blimps often carry metal shot in small canvas bags. Water has been the traditional ballast in rigid airships. Ballast is often expendable, being anything with weight that can be jettisoned from the vehicle. Ballast may be dropped by an airship to compensate for lost lifting gas or to ascend more quickly.
balloon: an un-powered lighter-than-air vehicle. Balloons can derive their buoyancy from the confinement of hot air, hydrogen, helium, ammonia or other gas. Balloons can be free (un-tethered and free to drift with the wind) or tethered to the ground (sometimes called captive or kite balloons).
ballonet: an air-filled bladder inside the envelope of a pressure airship used to regulate the gas pressure and maintain the envelope shape.
blimp: a term coined in 1915 as a friendly synonym for a pressure airship. The word is said to have mimicked the sound made when a man snapped his thumb on the airship’s gas-filled envelope. It is not derived from the description of an apocryphal type of World War I British airship, the “Balloon, Type B, limp.” There was never a “Type B” nor a designation “limp” applied to a British airship before, during or after WW I. The term most likely originated with Lieutenant (later Air Commodore) A. D. Cunningham of the Royal Naval Air Service, commanding officer of the British airship station at Capel in December 1915. During a weekly inspection, Lt. Cunningham visited an aircraft hangar to examine a “Submarine Scout” pressure airship, His Majesty’s Airship SS-12. Cunningham broke the solemnity of the occasion by playfully flipping his thumb at the gasbag and was rewarded with an odd noise that echoed off the taut fabric. Cunningham imitated this sound by uttering: “Blimp!” A young midshipman, who later became known as Air Marshal Sir Victor Goddard, repeated the tale of this humorous inspection to his fellow officers in the mess hall before lunch the same day. It is believed that by this route the word came into common usage.
buoyancy: the ability to float due to an object displacing a fluid medium greater than its own weight. Buoyancy can be controlled by the use of ballast.
catenary curtain: a fabric curtain and metal cable structure inside the envelope of a pressure or semi-rigid airship to which an external gondola or control car is attached. A catenary curtain spreads the load across a large part of the envelope to minimize distortions and stretching of the gasbag. Its shape is not a true catenary in the mathematical sense, but it is similar in shape to an inverted rope suspended by its ends.
cruciform fins: a vertical and horizontal “cross-shaped” arrangement of an airship’s empennage or tail fins (+), as opposed to tail fins arranged in “X” configuration.
dirigible: a word that describes any steerable or directable airship, including blimps (pressure airships), semi-rigid airships and zeppelins (rigid airships). The term often is used to describe only rigid airships, but it applies to both. Dirigible is synonym for airship.
duralumin: originally the trade name of a lightweight but strong alloy of aluminum mixed with smaller amounts of copper, magnesium, manganese, iron and silicon. High strength with little weight made the metal a preferred choice for building the structure of rigid airships. Alfred Wilm patented the formula for the alloy in 1909, and granted an exclusive license for its manufacture to the company Dürener Metallwerke. The “duralumin” name was derived from Dürener Metallwerke, and aluminum.
dynamic lift: the vertical movement of an airship created by aerodynamic forces acting on the shape of the vehicle, as opposed to static lift, which is generated by the buoyancy of a lighter-than-air lifting gas.
envelope: the gas bag of a pressure or semi-rigid airship. Unlike a rigid airship gas cell, an envelope forms an external barrier to the elements, and when pressurized, serves an integral role in maintaining the airship’s shape. It also has fittings for attaching the fins, control car and other structural components. The envelope is usually made of a high-strength fabric combined with a sufficiently impermeable barrier coating or film to minimize loss of the buoyant gas it contains. Formerly made of rubberized cotton, envelopes nowadays are constructed mainly of synthetic materials with their seams cemented, glued or sealed.
equilibrium: a condition of relative balance in which the forces of lift and gravity are equal.
fineness ratio: the ratio of an airship’s length to its diameter; the higher the number, the longer and more slender the airship.
gas cell: on a rigid airship, the gas-impervious, balloon-like container of lifting gas housed within the rigid framework. These cells were built as light and gas-tight as possible, using a variety of fabrics and gas-barrier materials. They were held in place by wire and cord netting, and their volume could vary with atmospheric pressure. The framework and outer cover of a rigid airship maintained its shape, not the outward pressure exerted by its gas cells.
gondola: a term used to describe the variously-shaped external pods on an airship that house engines or control stations. The earliest airships had open-top, boat-shaped structures holding engines and crew. Later, these structures were enclosed, giving rise to the terms “control car” and “engine car” or simply “car.”
Heavier Than Air (HTA): the branch of aeronautics that includes flight vehicles that require air passing over an airfoil (e.g., a wing) to generate aerodynamic lift. Such vehicles include airplanes, gliders, helicopters and kites, either piloted or un-piloted.
hybrid airship: an airship with features found in more than one type of dirigible construction, for example, an airship having both pressure airship and semi-rigid airship characteristics. The term also applies to “hybrid” vehicles that rely on a combination of lighter-than-air (a gas cell or envelope) and heavier-than-air (stationary or rotary wings) principles to achieve flight.
Lighter Than Air (LTA): the branch of aeronautics (sometimes further confined to aerostatics) that includes flight vehicles that depend upon buoyancy from the displacement of air for their lift. Such vehicles include balloons and dirigibles of all types, piloted or un-piloted. LTA does not include kites (except when referring to tethered “kite” balloons or aerostats).
non-rigid airship: another term for a pressure airship.
pressure airship: a term used to describe an airship whose shape is dependent on the gas inside its envelope having a higher pressure than is found in the atmosphere outside. With no lifting gas in its envelope, a pressure airship is only an empty bag on the ground with its control car, fins and hardware fittings the only rigid structures. Also called a “non-rigid airship.”
pressure height: the maximum altitude at which an airship can no longer contain its lifting gas due to its greater pressure compared to the surrounding atmosphere. At this altitude, the airship’s spring-loaded automatic valves open to relieve the pressure or else the gas cell or envelope will burst.
rigid airship: an airship whose shape is maintained by an internal framework and whose lifting gas is contained by a separate gas cell or cells within that structure. The external fabric covering on a rigid airship is not completely gas-tight, but it does protect the more delicate gas cells and other interior components from wind and weather and provides a degree of streamlining. Rigid airships include zeppelins and similar aircraft built by other companies. Even the metal skeleton of a “rigid” airship must flex somewhat under loads or else it would break.
Schütte-Lanz: the rigid airship manufacturing company founded in Mannheim-Rheinau, Germany by Johann Schütte and Karl Lanz. From 1909 until shortly after WW I, it was a competitor to the Zeppelin Company and introduced many innovative refinements to rigid airship design. These improvements appeared in Zeppelins due to a wartime patent-sharing agreement. Schütte-Lanz airships generally were more streamlined, but their plywood girders (used instead of duralumin) were weakened by exposure to moisture.
semi-rigid airship: an airship with a rigid keel but whose envelope is maintained by gas pressure. The keel at the bottom of the envelope is used as a support for control car, engines, ballast and sometimes tail surfaces.
static lift: the vertical force exerted on an airship created solely by the buoyancy of its lighter-than-air lifting gas, unlike dynamic lift, which is generated by aerodynamic forces acting on the shape of the vehicle.
streamlined: having a smooth, aerodynamically efficient shape offering minimal wind resistance; a classic example is the elongated tear drop shape.
zeppelin: The often generic term for any rigid airship, derived from the name of its inventor and promoter, Ferdinand Graf von Zeppelin (1838-1917). The first aircraft of this type flew in 1900 near Friedrichshafen, Germany. After many trials and tribulations, Zeppelin was able to form a company, Luftschiffbau-Zeppelin, to manufacture this type of airship. The word is properly capitalized when referring to airships produced by the Zeppelin Company, but may be used lower-case to describe generically any similar, cigar-shaped rigid airship.