An American Blimp Corporation A60, the Metlife Snoopy Two^[1]

Steerable ducted fans on a Skyship 600 provide thrust, limited direction control, and also serve to inflate the ballonets to maintain the necessary overpressure

A blimp, or non-rigid airship, is an airship without an internal supporting framework or keel. A non-rigid airship differs from a semi-rigid airship and a rigid airship (e.g., a Zeppelin) in that it does not have any rigid structure, neither a complete framework nor a partial keel, to help the airbag maintain its shape. Rather, these aircraft rely on both a higher pressure of the lifting gas (usually helium) inside the envelope and the strength of the envelope itself.

The term "blimp" refers only to free-flying aircraft. The term is sometimes erroneously used to refer to the tethered craft known as moored balloons. While often very similar in shape, moored balloons have no propulsion and are tethered to the ground.

[edit] Principle

Since blimps keep their shape with internal overpressure, typically the only solid parts are the passenger car (gondola) and the tail fins. A non-rigid airship that uses heated air instead of a light gas (such as helium) as a lifting medium is called a hot-air airship.

A modern blimp from Airship Management Services showing a strengthened nose, ducted fans attached to the gondola under the hull, and cable-braced fins at the tail

Volume changes of the lifting gas, due to temperature changes, is balanced using ballonets (air bags), in order to maintain the overpressure. Without sufficient overpressure, the blimp loses steerability and top speed is degraded. The propeller air stream can be used to inflate the hull. In some models, such as the Skyship 600, differential ballonet inflation can provide a measure of pitch trim control.

The engines driving the propellers are usually directly attached to the gondola, and in some models are partly steerable.

Blimps are the most commonly built airships, because they are relatively easy to build and easy to transport once deflated. However, because of their unstable hull, their size is limited. A blimp with too long a hull will kink in the middle when the overpressure is insufficient or when maneuvered too fast (this has also happened with semi-rigid airships with weak keels). This led to the development of semi-rigids and rigid airships.

Modern blimps launch somewhat heavier than air (overweight), in contrast to historic blimps. The missing lift is provided by lifting the nose and using engine power. Some types also use steerable propellers or ducted fans. Operating in a state heavier than air avoids the need to dump ballast at lift-off and also avoids the need to lose costly lifting gas on landing.

[edit] Etymology of the word "blimp"

The Spirit of Goodyear, one of the iconic Goodyear Blimps.

The term "blimp" is reportedly onomatopoeic, the sound the airship makes when one taps the envelope (balloon) with a finger. Although there is some disagreement among historians, credit for coining the term is usually given to Lt. A.D. Conningham of the British Royal Navy in 1915. ^[2]

A different derivation is given by Barnes & James in Shorts Aircraft since 1900:^[3]

"In February 1915 the need for anti-submarine patrol airships became urgent, and the Submarine Scout type was quickly improvised by hanging an obsolete B.E.2c fuselage from a spare Willows envelope; this was done by the R.N.A.S. at Kingsnorth, and on seeing the result for the first time, Horace Short, already noted for his very apt and original vocabulary, named it 'Blimp', adding, 'What else would you call it?'"

An oft-repeated, but false, alternative explanation for the term says that at some time in the early 20th century, the United States military had two classes for airships: Type A-rigid and Type B-limp (hence "blimp"). In fact,

"there was no American 'A-class' of airships as such—all military aircraft, heavier or lighter-than-air were designated with 'A' until the appearance of B-class airships in May 1917. There was an American B airship—but there seems to be no record of any official designation of non-rigids as 'limp'. Further, according to the Oxford Dictionary, the first appearance of the word in print was in 1916, in England, a year before the first B-class airship." ("Etymology of 'Blimp'" by Dr. A. D. Topping, AAHS Journal, Winter 1963.)

The perpetuation of this erroneous explanation is an example of false etymology.

[edit] Examples of non-rigid airships

A recreational blimp

There are several^[4] blimps worldwide. Some examples include:

• TC-3 and Tc-7, two US Army Corps non-rigid blimps used for parasite fighter trials during 1923–24.
• SS, SSP, SST, SSZ and NS class blimps, convoy escort blimps used by the UK in World War I.
• G class blimp and L class blimp, US training blimps built by Goodyear during World War II.
• K class blimp and M class blimp, US anti-submarine blimps operated during World War II.
• N class blimp (the "Nan ship"), used for anti-submarine and as a radar early-warning platform during the 1950s.
• Goodyear Blimps, a fleet of blimps operated for advertising purposes and as a television camera platform.
• Skyship 600, a private blimp used by advertising companies
• P-791, an experimental aerostatic/aerodynamic hybrid airship developed by Lockheed-Martin corporation.
• SVAM CA-80, an airship manufactured by the Shanghai Vantage Airship Manufacture Co in China

[edit] See also

Wikimedia Commons has media related to: Non-rigid airships

• Airship
• Airship hangar
• Buoyancy compensator (aviation)
• Mooring mast
• Rigid airship
• Zeppelin

[edit] References

Notes

Bibliography