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The LWS-6 Żubr (PZL.30 Żubr) was a Polish twin-engined medium bomber, produced by the LWS factory before World War II. A short series was used for training only, because it was inferior to the PZL.37 Łoś design. ==Design and development== It was designed by PZL in the early 1930s, initially as a passenger aircraft (the main designer was Zbysław Ciołkosz). Since the Polish Airlines LOT bought Douglas DC-2 planes instead, the project was converted to a bomber aircraft, with a projected bomb load of 1,200 kg. It was developed as an alternative less-advanced design, in case the modern bomber design, PZL.37 Łoś would fail. The first prototype, designated PZL.30 (or PZL.30BI) was flown in March 1936 by Bolesław Orliński (only three months before the PZL.37 prototype). The prototype, initially powered with two 420 hp Pratt & Whitney Wasp Junior engines, was next refitted with much stronger 700 hp Bristol Pegasus VIII (it was known then as PZL.30BII). The plane was accepted for a limited production by the LWS state factory in Lublin, of which Ciołkosz became the main designer. It was planned to produce 16 aircraft for the Polish Air Force, under a designation LWS-6 ''Żubr'' (Polish: ''Wisent''). The serial aircraft incorporated further changes, among others a landing gear folding into a fuselage sides was changed to more conventional one folding into engine nacelles.〔 After a prototype crash on November 7, 1936, caused by a weak construction of a wing, the design had to be strengthened. Due to this increased weight it had a smaller bomb load than expected. An improved prototype was made with a double tail fin, and flown at the end of 1937. The serial variant, however, returned to a single tail fin configuration, but it was enlarged in a course of production. A series of 15 aircraft were built in 1938. The factory continued work on Żubr development, and in 1939 developed a lighter wing of steel construction and a refined fuselage, but these were not built due to the outbreak of World War II. In 1937 the factory proposed to build a floatplane torpedo bomber variant LWS-5, instead of developing LWS-1 (R-XXA) design of Jerzy Rudlicki. At first the Polish Navy revealed interest and works upon the LWS-1 were cancelled despite their progress, but then due to problems with LWS-6 development and its low bomb load, it was rejected by the Navy. Work upon the prototype was canceled in 1938. It was supposed to be fitted with two Short floats of the Lublin R-XX prototype. In many publications, especially older ones, the erroneous designation LWS-4 is used for the Żubr, but in fact it does not come from any documents〔Morgała, Andrzej (2003). ''Samoloty wojskowe w Polsce 1924-1939'' (Military aircraft in Poland 1924-1939). Warsaw: Bellona. ISBN 83-11-09319-9. pp. 159-165〕 and it was a designation of a light fighter project (PZL.39). The Żubr was given a military code number 71 and the series was to have factory numbers 71.1 to 71.17, but the aircraft were given different last numbers eventually due to secrecy.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「LWS-6 Żubr」の詳細全文を読む スポンサード リンク
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