Savoia-Marchetti SM.78

SIAI (later Savoia-Marchetti)

Industry	Aircraft manufacturing
Founded	1915
Headquarters	Italy

The Savoia-Marchetti SM.78 was a biplane flying boat developed in Italy during the early 1930s, designed for bombing and reconnaissance missions.

Development

Designed as a maritime patrol bomber, the SM.78 took to the skies for the first time in late 1932. It belonged to a series of flying boats produced by SIAI (later known as Savoia-Marchetti), a company that began manufacturing licensed foreign aircraft in 1915 before creating its own original designs two years afterward.

The SM.78 originated as an evolution of the SM.62bis. The prototype, identified by the serial number MM222, completed its maiden flight at the end of 1932 and was subsequently sent to Vigna di Valle in the following year for testing and assessment. Marking the final biplane flying boat to be mass-produced or widely employed by Italy, a total of 49 units were built—32 constructed by Piaggio and 17 by SIAI.

Technical description

Featuring a single-bay biplane configuration, the SM.78 possessed an elongated and slender rear fuselage topped with a tall welded steel vertical stabilizer and a centrally mounted wooden horizontal tailplane. Its hull incorporated two steps on the underside to facilitate water takeoffs.

This model retained essentially the same wing, tail, and fuselage design as the SM.62bis but introduced a different variant of Handley Page flaps.

The hull framework was crafted from poplar wood, while ash was used for the longerons. The hull’s exterior was covered with plywood featuring a double-layered bottom; cedar wood formed the outermost layer, and the sides consisted of orthogonally arranged cedar laminates. The wings were fabric-covered with spruce longerons and poplar ribs, selected for their combination of lightness and strength, and treated with paint to ensure water resistance. Mid-wing-mounted twin stabilizing floats provided additional support on water.

Although the prototype housed pilot and co-pilot side-by-side within an enclosed cockpit, production models replaced this with an open cockpit arrangement. A forward crew station located in the nose accommodated a 7.7 mm (0.303 in) Lewis gun alongside two cameras; this position was operated by the co-pilot when necessary, forming part of a three-person crew. An additional enclosed dorsal turret armed with another 7.7 mm (.303 in) Lewis machine gun was manned by the gunner/radio operator, who also managed communications equipment consisting of an R.A.350 transmitter and an A.R.4 receiver. Despite lacking an intercom system, pilots could relay messages to the nose gunner through a pneumatic tube system.

The forward Lewis gun had access to 564 rounds distributed across twelve magazines, while the rear gun carried 470 rounds in ten magazines. Bombs were housed in an internal bomb bay positioned within the lower wing near the fuselage, with a maximum payload capacity of 700 kg (1,540 lb). Typical bomb loads included combinations such as two 250 kg (550 lb) bombs paired with two 100 kg (220 lb) bombs; six 100 kg (220 lb) bombs; four 70 kg (150 lb) depth charges; or six training bombs weighing 12 kg (26 lb) each. Additionally, smoke generators could be installed on inner hardpoints for signaling or concealment purposes. A "Jozza" bombsight was mounted on the right side of the cockpit behind a glazed panel.

Propulsion was provided by a single Isotta Fraschini Asso 750 W18 engine delivering 671 kW (900 hp) at takeoff power. This engine was mounted on a steel frame between the upper and lower wings and drove a four-bladed variable-pitch propeller adjustable prior to flight. Combined with its aerodynamically refined hull design, these features afforded respectable performance for its era. A carbon dioxide (CO₂) fire extinguisher was installed adjacent to the engine compartment for safety.

Fuel capacity totaled 2,200 liters (580 US gallons), stored within six unarmored duralumin tanks distributed throughout the fuselage—two located aft, two centrally, and two forward positions.

Operational history

Manufactured between 1932 and 1935, the SM.78 saw production of just 16 units by SIAI and an additional 32 by Piaggio. It was assigned to several squadrons, including the 141° Squadriglia stationed at La Spezia, the 144° at Livorno, the 182° based in Nisida, and the 189° located at Syracuse. The aircraft remained active until 1938, when it was superseded by the more advanced CANT Z.501, a monoplane featuring enhanced capabilities. A number of SM.78s continued operating in the initial stages of World War II, primarily fulfilling air-sea rescue missions. Although Spain, an operator of SM.62 models, sought to obtain a license for SM.78 production, this effort was unsuccessful, leaving Italy as the sole user.

Operators

Template:Country data Kingdom of Italy

• Regia Aeronautica

Additional reading

• Donald, David, editor. The Encyclopedia of World Aircraft. London: Aerospace Publishing, 1997. ISBN 1-85605-375-X.
• Lembo, Daniele. "SM.78 (Italian language)." Storia Militare No.19, Westward editions, pp. 43–49.