The Savoia-Marchetti S.55 is a twin-engine twin-hull monoplane flying boat designed and produced by the Italian aircraft manufacturer Savoia-Marchetti. It filled both commercial and military roles. The S.55 first flew in August 1924 and S.55s were soon setting records for speed, payload, altitude and range, and they made a number of successful high profile Atlantic crossings, including the first mass formation crossings. Many saw service with the Regia Aeronautica and foreign operators including the Spanish Air Force as bombers and maritime patrol aircraft, while numerous airlines including Aeroflot also operated the type. Although some were still nominally in service at the start of the Second World War, they played no role due to their age and the last examples were struck off charge by 1943 in Italy and Romania.
Design and development
The Savoia-Marchetti S.55 is a twin-engine twin-hull cantilever-monoplane flying boat that was built in both commercial and military variants. Two airliner version, the S.55C and the S.55P were built, in which the passengers occupied the forward part of each hull. The military soon took interest, as the S.55 was especially suitable for the torpedo bomber role, since a heavy torpedo, which normally posed a problem for designers, could readily be slung between the hulls. Transportation and repair was facilitated as the S.55 could be readily dismantled as the hulls can be separated from the wing along with the tail unit, while the wings split into a centre section and two outer wing panels. The hull centrelines are about 4.3 m (14 ft) apart, and the hulls run over half of the length of the aircraft. They have a single-step bottom, with a conventional vee form aft of the step, while ahead of the step the planing bottom is slightly concave, a common feature on Italian flying boats. The internal space can be configured into a series of cabins to accommodate up to 12 passengers, as with the S.55C. The cockpit is in the leading edge of the thick wing center section between the two hulls and there is a passageway between the cabins in each hull and the cockpit. Early versions had an open cockpit, while later ones were provided with an enclosed canopy. There are gunner's positions on military aircraft at bow and stern of each hull, while under the centre section there is a 2.6 m (8 ft 6 in) wide space suitable for torpedoes or mines. The three-spar outer wing sections have a pronounced dihedral and are tapered. The leading edges are swept back about 15 degrees while the trailing edge is angled forward slightly . The wing have aerodynamically balanced ailerons. Other than in the metalized S.55M variant, the structure of both the wing and hulls is primarily wood, with wood skinning. The tail surfaces are supported by substantial booms attached to the hull sternposts and the wing's rear spar, while smaller frames provide additional bracing, and wires provide the crossbracing. On top of the rectangular horizontal tail are three rudders, with the outer two unbalanced rudders have fixed curved fins, and the inner rudder has an aerodynamic balance area on the leading edge. The S.55 is powered by two air-cooled V-12 piston engines in a tandem push-pull pair, mounted over the wing centre section. A single radiator provides cooling for both engines, and the nacelle was neatly streamlined on later examples. The nacelle and line of thrust from the engines is inclined upward by 6 to 9 degrees, depending on the version, to improve take-off performance and handling. Level flight can be maintained on a single engine.
Operational history The S.55 prototype was first flown in August 1924, and by 1926 had set 14 separate world records for speed, altitude and distance with a payload. The type's greatest successes, however, were its many flights across the Atlantic. The First aerial crossing of the South Atlantic was made in stages in 1922 using three different Fairey IIIs, and a subsequent crossing made by the Dornier Do J Plus Ultra in January 1926 ended in the Cape Verde Islands. A year later, the Santa Maria under Francesco de Pinedo completed the first S.55 crossing. After flying south to Bolama, then to Portuguese Guinea, until it was forced down at Cape Verde: however they reached Brazil on 23 February 1927. The aircraft was later traded to Brazil for coffee beans. The Brazilian João Ribeiro de Barros and his crew of three made the first non-stop crossing in S.55 Jahú on 24 April 1927. Departing from Santiago Island, they crossed the Atlantic and landed at Fernando de Noronha Island, Brazil.
Francesco de Pinedo and Carlo del Prete flew an S-55 from Sesto Calende, Italy on 13 February 1927 and four months later, on 16 June 1927, they returned, having flown nearly 48,280 km (30,000 mi) in 193 flying hours with just over 50 stops, including Rio de Janeiro, Buenos Aires and New York City. On 20 June 1928, S.55 I-SAAT Santa Maria, piloted by Tenente Colonnello Umberto Maddalena of the Regia Aeronautica, located survivors of Arctic explorer Umberto Nobile's crashed airship Italia on an ice floe about 120 km (75 mi) from Nordaustlandet, Svalbard. Italian Maresciallo dell'Aria (Air Marshal) Italo Balbo won fame for organizing multiple Atlantic crossings using a squadron of Regia Aeronautica S.55s. These culminated in a flight from Orbetello, Italy on 1 July 1933 with 24 aircraft to Chicago's Century of Progress International Exposition, in just over 48 hours, while maintaining formation. The term "Balbo" entered the English language as a term to describe a large formation of aircraft. Large numbers of S.55s were operated by the Regia Aeronautica as a long-range bomber and patrol aircraft. By the Second World War, the S.55 was obsolete and only a few were still kept in reserve.
Variants
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