General Aircraft ST25 Monospar Ambulance, the only surviving ST25 Monospar in the world (an ST12 Monospar is preserved in the UK).
The ST-25 was a low wing cantilever monoplane with a fabric covered metal structure. The monospar name came from the use of a single spar in the wing structure which had been developed by H J Stieger. The cabin was enclosed with five seats. Based on the earlier ST-10 with the addition of folding seat for a fifth passenger and the addition of a radio receiver. First flying on 19 June 1935 the type was named Jubilee and also numbered 25 in honour of the 25th anniversary of the reign of King George V. Powered by two Pobjoy Niagara radial engines.
The Pobjoy Niagara is a British seven-cylinder, air-cooled, radial, aero-engine first produced in 1934, with an unusual offset-from-centre propshaft due to its engine reduction gearing. The Niagara was a popular engine for light and experimental aircraft. The entire series of Pobjoy motors were seven-cylinder radials with compact dimensions and very high rpm. The entire Pobjoy range was well regarded due to its small diameter, smooth operation, low noise and innovative engineering.
The last surviving Monospar, OY-DAZ, an ST-25 Air Ambulance for Zonen, was fully restored during 1989-1999 and today hangs in Egeskov Museum, Denmark.
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