Wikipedia

Semi-rigid airship

Asemi-rigid airshipis anairshipwhich has a stiffkeelor truss supporting the main envelope along its length. The keel may be partially flexible or articulated and may be located inside or outside the main envelope. The outer shape of the airship is maintained by gas pressure, as with thenon-rigid"blimp". Semi-rigid dirigibles were built in significant quantity from the late 19th century but in the late 1930s they fell out of favour along withrigid airships.No more were constructed until the semi-rigid design was revived by theZeppelin NTin 1997.

Internal structure of semi-rigid airship

Semi-rigid construction is lighter-weight than the outer framework of a rigid airship, while it allows greater loading than anon-rigid type.

Principle

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More or less integrally attached to the hull are the gondola, engines and sometimes theempennage(tail). The framework has the task of distributing thesuspension loadsof these attachments and thelifting gasloads evenly throughout the whole hull's surface and may also partially relieve stresses on the hull during manoeuvres. In early airships which relied on nets, fabric bands, or complicated systems of rope rigging to unite the lifting envelope with the other parts of the ship, semi-rigid construction was able to achieve improvements in weight, aerodynamic, and structural performance. The boundary between semi-rigid andnon-rigid airshipsis vague. Especially with small types, it is unclear whether the structure is merely an extended gondola or a proper structural keel.

As in non-rigid airships, the hull's aerodynamic shape is maintained by an overpressure of the gas inside and light framework at the nose and tail. Changes in volume of the lifting gas are balanced usingballonets(air-filled bags). Ballonets also may serve to providepitch control.For small types the lifting gas is sometimes held in the hull itself, while larger types tend to use separategas cells,mitigating the consequences of a single gas cell failure and helping to reduce the amount of overpressure needed.[1]

History

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Italian explorerUmberto Nobilecrossed the North Pole in his semi-rigid airshipNorgein 1926.

In the first decade of the twentieth century, semi-rigid airships were considered more suitable for military use because, unlikerigid airships,they could be deflated, stored and transported by land or by sea.[2]Non-rigid airships had a limited lifting capacity due to the strength limitations of the envelope and rigging materials then in use.

An early successful example is theGroß-Basenachdesign made by MajorHans Großfrom theLuftschiffer-Bataillon Nr. 1in Berlin, the experimental first ship flying in 1907. It had a rigid keel under the envelope. Four more military airships of this design were built, and often rebuilt, designated M I to M IV, up to 1914.[3]

The most advanced construction of semi-rigid airshipsbetween the two World Warstook place in Italy. There, the state-factoryStabilimento di Costruzioni Aeronautiche(SCA) constructed several.Umberto Nobile,later General and director, was its most well-known member, and he designed and flew several semi-rigid airships, including theNorgeandItalia,for his overflights of theNorth Pole,and theW6 OSOAVIAKhIM,for theSoviet Union'sairship program.

List of other semi-rigid airships

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Pre-War and WWI

1920s and 1930s

Nobile's company designed or built the following airships:

  • T 34Roma,33,810 m3,sold to US Army in 1921 and destroyed in 1922 after rudder malfunction caused collision with high tension wires
  • N 1Norge,19,000 m3,reached the North Pole in 1926
  • N 2 a 7000 m3-airship built in hangars atAugusta, Sicily
  • N 3 Sold to Japan as naval Airship No. 6, first flight on 1927-04-06. It was lost in 1927 after encountering a typhoon in the Pacific. There were no fatalities
  • N 4ItaliaFlew toSvalbardfor Arctic expedition 1928, crashed after third polar flight on return from North Pole
  • N 5 was a project for a 55,000 cubic metre keel airship, many times interrupted, eventually abandoned 1928
  • Nobile-designed airships of theRussian airship program,such as the SovietSSSR-V6 OSOAVIAKhIM(1934–1938)
  • The Fujikura company built theNo. 8semi-rigid airship for the Japanese Navy to replace the Nobile N 3, basing the design on the latter airship. The airship set a record for an endurance flight of 60 hours and 1 minute on 17 July 1931, a record later broken by the SovietOSOAVIAKhIM.

Current developments

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As of 2008,the only manned semi-rigid model of airship in active operation is theZeppelin NT.It comprises a single gas cell kept at a slight over-pressure, ballonets to maintain constant volume, and a triangular keel structure internal to the cell.Three of thesewill be American-based airships.

CL160 "Cargolifter" was an unrealised design of the now liquidated GermanCargolifter AG(1996–2003).[5][unreliable source?]Cargolifter Joeywas a small semi-rigid experimental airship produced to test the design.[5]

See also

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References

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Notes

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  1. ^U. Nobile"Semi-Rigid v. Rigid Airships"FLIGHT,22 January 1922
  2. ^Flight4 July 1909 Flight Magazine Global Archive:"The dirigible must be of the frameless or of the semi-rigid sort, because experience on the Continent has proven that for military service the rigid type, exampled more particularly by the Zeppelin school, cannot be collapsed and packed into small compass for the purposes of transport, which are among the War Office requirements."
  3. ^pilotundluftschiff.de.Halbstarre Luftschiffe vom Typ Groß Basenachlast accessed 2008-07-05
  4. ^Scientific American, 31 December 1904:'The Lebaudy Airship, "Le Jaune" Ascending From the Meadows of Moisson,' France
  5. ^abCargoLifter CL160 P1 Super Heavy-Lift Cargo Airship, Germany - Aerospace Technology

Bibliography

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  • Belokrys, Aleksei.Deviat'sot chasov neba. Neizvestnaia istotriia dirizhablia "SSSR-V6"[Nine Hundred Hours in the Sky. The Unknown History of the Airship "SSSR-V6" ]. Moscow, Russia: Paulsen, 2017.ISBN978-5-98797-174-1(in Russian).
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