In 1919, Alessandro Marchetti designed the Marchetti MVT fighter, renamed the SIAI S.50 in 1922 when Marchetti joined the SIAI company as its chief designer. SIAI entered the S.50 in the 1923 Regia Aeronautica fighter contest, even though the S.50 was powered by a 212-kilowatt SPA 62a six-cylinder engine instead of the 224-kilowatt Hispano-Suiza HS 42 eight-cylinder water-cooled engine required by the Italian Air Ministrys specification for entrance in the contest. Despite this, the S.50 attracted enough Regia Aeronautica interest to prompt it to acquire three S.50 fighters from SIAI for evaluation, although a proposal to order twelve S.50 aircraft never bore fruit. Marchetti decided to design a derivative of the S.50 powered by the HS 42 engine for entry in the 1923 fighter contest. The resulting S.52 was a single-seat, all-metal biplane with its fuselage suspended between the upper and lower wings. The after part of the fuselage itself was flattened to serve as an airfoil. The semi-elliptical wings were extremely thin in section and larger in area than those of the S.50, and used ailerons to allow lateral control rather than the wing warping the S.50 employed. The S.50s all-moving tail surfaces were replaced in the S.52 by a conventional tail unit which combined fixed and moving surfaces. The engine drove a two-bladed propeller, and the S.52 was armed with two fixed, forward-firing 7.7-millimeter Vickers machine guns synchronized to fire through the propeller.
Operational history
The S.52 was too late for the 1923 fighter contest, first flying in 1924. Two prototypes – designated MM.3 and MM.4 – were built, but no Italian production order ensued. In 1925, a proposal was made to re-engine one of the prototypes with a 306-kilowatt FiatA 20 engine, which was projected to give it a top speed of 285 kilometers per hour. This conversion never took place. The other prototype was shipped to Latin America for demonstration flights, one of which was a 1927 flight from Argentina to Paraguay. SIAI had learned that the Paraguayan Air Arm was purchasing airplanes, so the S.52 made a series of successful flights at the Paraguayan Military Aviation School. The Paraguayan government decided to buy it in 1927 – the first fighter Paraguay had ever bought and its only fighter until the arrival of sevenWibault 73 C.1 aircraft in 1928 – but placed no order for additional S.52s. The Paraguayan S.52 received the serial number 16 in 1932. It apparently took no part in the Chaco War, but saw intensive use as a fighter trainer at Paraguays Ñu-Guazú Military Aviation School until it was destroyed in an accident on 8 May 1933 at the Ñu-Guazú airfield. Its pilot, Lieutenant Emilio Rocholl, survived the crash.
