Blimp

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.

Principle

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 its ability to be steered 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 may 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.

Etymology

A 1943 etymology published in the New York Times confirms the British origin during the First World War when the British were experimenting with lighter-than-air craft. The initial non-rigid aircraft was called the A-limp; and a second version called the B-limp was deemed more satisfactory.

A different derivation is given by Barnes & James in Shorts Aircraft since 1900:

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,

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

Examples of non-rigid airships

See also

Notes

References

External links

Category:Airship configurations