Semi-rigid Airship
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A semi-rigid airship is an
airship An airship, dirigible balloon or dirigible is a type of aerostat (lighter-than-air) aircraft that can navigate through the air flying powered aircraft, under its own power. Aerostats use buoyancy from a lifting gas that is less dense than the ...
which has a stiff
keel The keel is the bottom-most longitudinal structural element of a watercraft, important for stability. On some sailboats, it may have a fluid dynamics, hydrodynamic and counterbalancing purpose as well. The keel laying, laying of the keel is often ...
or 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 the non-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 with
rigid airship A rigid airship is a type of airship (or dirigible) in which the Aerostat, envelope is supported by an internal framework rather than by being kept in shape by the pressure of the lifting gas within the envelope, as in blimps (also called pres ...
s. No more were constructed until the semi-rigid design was revived by the Zeppelin NT in 1997. Semi-rigid construction is lighter-weight than the outer framework of a rigid airship, while it allows greater loading than a non-rigid type.


Principle

More or less integrally attached to the hull are the gondola, engines and sometimes the empennage (tail). The framework has the task of distributing the suspension loads of these attachments and the
lifting gas A lifting gas or lighter-than-air gas is a gas that has a density lower than normal atmospheric gases and rises above them as a result, making it useful in lifting lighter-than-air aircraft. Only certain lighter-than-air gases are suitable as lift ...
loads 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 and
non-rigid airship A non-rigid airship, commonly called a blimp ( /blɪmp/), is an airship (dirigible) without an internal structural framework or a keel. Unlike semi-rigid and rigid airships (e.g. Zeppelins), blimps rely on the pressure of their lifting gas (us ...
s is 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 using
ballonet A ballonet is an inflatable bag inside the outer envelope of an airship which, when inflated, reduces the volume available for the lifting gas, making it more dense. Because air is also denser than the lifting gas, inflating the ballonet reduces ...
s (air-filled bags). Ballonets also may serve to provide pitch control. For small types the lifting gas is sometimes held in the hull itself, while larger types tend to use separate gas cells, mitigating the consequences of a single gas cell failure and helping to reduce the amount of overpressure needed.


History

In the first decade of the twentieth century, semi-rigid airships were considered more suitable for military use because, unlike
rigid airship A rigid airship is a type of airship (or dirigible) in which the Aerostat, envelope is supported by an internal framework rather than by being kept in shape by the pressure of the lifting gas within the envelope, as in blimps (also called pres ...
s, they could be deflated, stored and transported by land or by sea.''Flight'' 4 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."
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 the Groß-Basenach design made by Major Hans Groß from the ''Luftschiffer-Bataillon Nr. 1'' in 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. The most advanced construction of semi-rigid airships between the two World Wars took place in Italy. There, the state-factory ''Stabilimento 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 the '' Norge'' and ''
Italia Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...
'', for his overflights of the
North Pole The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's rotation, Earth's axis of rotation meets its surface. It is called the True North Pole to distingu ...
, and the '' W6 OSOAVIAKhIM'', for the
Soviet Union The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
's airship program.


List of other semi-rigid airships

Pre-War and WWI * '' Bartolomeu de Gusmão'' from Augusto Severo de Albuquerque Maranhão in Brazil in 1894, destroyed in March 1894 by a gust of wind * ''Pax'' from Augusto Severo de Albuquerque Maranhão in France in 1902, caught fire at its first ascent, killing the pilot * '' Le Jaune'' - Built by Lebaudy Frères in France, first flight: 1902-11-13.Scientific American, 31 December 190
'The Lebaudy Airship, "Le Jaune" Ascending From the Meadows of Moisson,' France
/ref> Lebaudy built many other semi-rigid airships, among them the '' Patrie'' and the '' République''. * British Army Dirigible No 1, often called the Nulli Secundus. * Forlanini F.1 ''Leonardo da Vinci'', Italy, 3265 m3, 40 PS, first ascent: 1909; 1910-02-01 damaged beyond repair * The Groß-Basenach-type airship (5 built for the Prussian army) * The ''Luftschiff von Veeh'' (also ''Veeh 1'' or ''Stahlluftschiff'') built by Albert Paul Veeh from Apolda in Düsseldorf in the 1910s * Siemens-Schuckert I (1911), * M.1, Italian, first flight 1912, 83-metre long, 17-metre diameter, 2× 250 PS Fiat SA.76-4 engines each with one airscrew, payload: 3800 kg, first with the Army then the Navy, 164 flights, decommissioned 1924 * M.2, ''Città di Ferrara'', Italian, first flight 1913, hull identical to the M.1, 83-metre long, 17-metre diameter, 4×125 PS driving two airscrews, payload 3000 kg, speed: 85 km/h, a Navy airship, stationed in Jesi, on 1915-06-08 shot down by an Austrian flying boat * Forlanini F.2 ''Città di Milano'', Italy, 11,500 m3, 2×85 PS, first flight: 1913-04-09, destroyed 1914-04-09 at Como * SR.1 (M-class) built by Italy for England 1918, 12,500 m3, 83 m long, 17 m Diameter, 9-man crew, internal keel of triangular steel components 1920s and 1930s * Among the Parseval airships designed by August von Parseval in the 1900s-1930s: ** PL 26 and PL 27 ** Parseval-Naatz designs * Zodiac V10 was built 1930 for the French Navy * O-1 (airship) built by SCDA, Italy, and the only true semi-rigid airship to serve with
United States Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...
. * RS-1 was the only American-built semi-rigid military airship (flown by the
United States Army The United States Army (USA) is the primary Land warfare, land service branch of the United States Department of Defense. It is designated as the Army of the United States in the United States Constitution.Article II, section 2, clause 1 of th ...
) Manufacturer: Goodyear, maiden flight: 1926. * Raab-Katzenstein 27 - maiden flight: 1929-05-04 Nobile's company designed or built the following airships: * T 34 ''Roma'', 33,810 m3, sold to US Army in 1921 and destroyed in 1922 after rudder malfunction caused collision with high tension wires * N 1 ''Norge'', 19,000 m3, reached the North Pole in 1926 * N 2 a 7000 m3-airship built in hangars at
Augusta, Sicily Augusta (, archaically ''Agosta''; ; Ancient Greek, Greek and , Medieval: ''Augusta'') is a town and in the province of Syracuse, Italy, Syracuse, located on the eastern coast of Sicily (southern Italy). The city is one of the main harbours in ...
* 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 4 ''Italia'' Flew to
Svalbard Svalbard ( , ), previously known as Spitsbergen or Spitzbergen, is a Norway, Norwegian archipelago that lies at the convergence of the Arctic Ocean with the Atlantic Ocean. North of continental Europe, mainland Europe, it lies about midway be ...
for 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 the Russian airship program, such as the Soviet SSSR-V6 OSOAVIAKhIM (1934–1938) * The Fujikura company built the ''No. 8'' semi-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 Soviet ''OSOAVIAKhIM''.


Current developments

, the only manned semi-rigid model of airship in active operation is the Zeppelin 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 these will be American-based airships. CL160 "Cargolifter" was an unrealised design of the now liquidated German Cargolifter AG (1996–2003).CargoLifter CL160 P1 Super Heavy-Lift Cargo Airship, Germany - Aerospace Technology
/ref> ''Cargolifter Joey'' was a small semi-rigid experimental airship produced to test the design.


See also

* Airship hangar *
Rigid airship A rigid airship is a type of airship (or dirigible) in which the Aerostat, envelope is supported by an internal framework rather than by being kept in shape by the pressure of the lifting gas within the envelope, as in blimps (also called pres ...
*
Non-rigid airship A non-rigid airship, commonly called a blimp ( /blɪmp/), is an airship (dirigible) without an internal structural framework or a keel. Unlike semi-rigid and rigid airships (e.g. Zeppelins), blimps rely on the pressure of their lifting gas (us ...


References


Citations


General and cited references

* Belokrys, Aleksei (2017). ''Nine Hundred Hours in the Sky: The Unknown History of the Airship "SSSR-V6"''. Moscow, Russia: Paulsen. . .


External links


Images of a Flight Simulator model of Nobile's N5
() {{DEFAULTSORT:Semi-Rigid Airship Airship configurations