Savoia-Marchetti S.55

Savoia-Marchetti

Company type	Private company
Industry	Aerospace, Aircraft manufacturing
Founded	1915
Headquarters	Italy
Products	Aircraft, including the Savoia-Marchetti S.55 flying boat

The Savoia-Marchetti S.55 is a twin-hull, twin-engine monoplane flying boat developed and manufactured by the Italian company Savoia-Marchetti. It served in both civil aviation and military capacities.

Its maiden flight took place in August 1924, and soon after, the S.55 established numerous records related to speed, payload, altitude, and range. The aircraft gained particular fame for completing several notable Atlantic crossings, including pioneering large-scale formation flights—giving rise to the term "Balbo" in English, denoting extensive aircraft formations. The Regia Aeronautica employed many units, and the type was also adopted by foreign air forces such as the Spanish Air Force, fulfilling roles as bombers and maritime patrol platforms. Commercial operators like Aeroflot utilized the model as well, with one even operating in Alaska’s bush aviation sector. Although some remained officially active at the onset of the Second World War, their operational relevance had diminished due to obsolescence, with final withdrawals from Italian and Romanian service occurring by 1943.

Design and development

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Typical engine arrangement on an S.55; later models featured a streamlined nacelle enclosure.

The Savoia-Marchetti S.55 is characterized by its twin-engine configuration paired with dual hulls on a cantilever monoplane flying boat platform, produced in variants suited for both commercial and military use. The civilian versions included the S.55C and S.55P, where passenger seating was arranged in the forward compartments of each hull. Military interest was piqued due to the aircraft’s suitability for torpedo bombing; its design allowed a heavy torpedo to be suspended between the hulls without difficulty. Maintenance and transport were simplified by the ability to disassemble the aircraft: the hulls could be detached from the wing structure along with the tail assembly, while the wings themselves separated into a central section plus two outer panels.

The hulls are spaced approximately 4.3 m (14 ft) apart centerline to centerline and extend for more than half of the aircraft’s length. Each hull features a single-step planing bottom; behind this step, a conventional vee shape is present, whereas forward of it, a shallow inverted U-shaped planing surface is typical of Italian flying boats of that era. Internally, configurations could accommodate up to twelve passengers as seen in the S.55C. The cockpit is positioned at the leading edge of the notably thick wing center section situated between the two hulls, with connecting passageways linking each hull’s cabin to the cockpit. Early models had open cockpits, but subsequent versions incorporated enclosed canopies. For military variants, gunner stations were installed at both bow and stern positions on each hull; beneath the wing center section there was a space approximately 2.6 m (8 ft 6 in) wide designed to carry torpedoes or mines. The outer wing panels are tapered with significant dihedral angles. Leading edges are swept back roughly fifteen degrees while trailing edges have a slight forward sweep. Aerodynamically balanced ailerons are fitted to these wings. Except for the metal-skinned S.55M variant, wooden construction predominates in both wing and hull structures.

The tail assembly is supported by robust booms connected from the sternposts of each hull to points near the rear spar of the wing, reinforced further by smaller framing members and cross-bracing wires. The rectangular horizontal stabilizer carries three rudders: two unbalanced outer rudders each with fixed curved fins flank a central rudder equipped with leading-edge aerodynamic balancing.

Propulsion comes from two air-cooled V-12 piston engines arranged in tandem push-pull configuration within a nacelle mounted above the wing center section. Cooling for both engines is managed through a single radiator located at the front of this nacelle; later models featured streamlined nacelle fairings. The entire nacelle assembly is inclined upward between six and nine degrees depending on variant, enhancing takeoff performance and handling characteristics. The aircraft is capable of sustaining level flight on just one operational engine.

Operational history

The prototype of the S.55 took to the skies for the first time in August 1924, and by 1926, it had established 14 distinct world records involving speed, altitude, and payload distance. However, the aircraft’s most notable achievements were its numerous transatlantic flights.

The initial aerial crossing of the South Atlantic occurred in 1922 in stages using three separate Fairey III aircraft. Later, in January 1926, the Dornier Do J Plus Ultra completed a crossing that included a stopover at the Cape Verde Islands. The first S.55 to successfully cross the Atlantic was the Santa Maria, piloted by Francesco de Pinedo in 1927. After flying southward to Bolama in Portuguese Guinea and being forced down at Cape Verde, they ultimately arrived in Brazil on 23 February 1927. The plane was subsequently exchanged for coffee beans with Brazil.

On 24 April 1927, João Ribeiro de Barros and his three-man crew achieved the first nonstop Atlantic crossing in the S.55 Jahú. Their journey began at Santiago Island in Cape Verde and concluded with a landing on Fernando de Noronha Island, Brazil.

File:Savoia-Marchetti S.55 Santa Maria with motor launch (5956308316) (1k version, grayscale, brightness).jpg

Pinedo's S.55 Santa Maria

Francesco de Pinedo and Carlo del Prete departed from Sesto Calende, Italy on 13 February 1927 aboard an S-55. After nearly four months and approximately 48,280 km (30,000 mi) covered over 193 flying hours with just over fifty stops—including Rio de Janeiro, Buenos Aires, and New York City—they returned on 16 June 1927.

On 20 June 1928, the S.55 I-SAAT Santa Maria, piloted by Tenente Colonnello Umberto Maddalena of the Regia Aeronautica, located survivors from Arctic explorer Umberto Nobile’s airship Italia crash on an ice floe roughly 120 km (75 mi) from Nordaustlandet, Svalbard.

Italian Air Marshal Italo Balbo gained prominence by organizing several transatlantic crossings using Regia Aeronautica S.55 squadrons. His efforts culminated in a formation flight of 24 aircraft from Orbetello, Italy to Chicago’s Century of Progress International Exposition on 1 July 1933. The flight lasted just over 48 hours while maintaining formation throughout. This event popularized the term "Balbo" in English as a descriptor for large aircraft formations.

The Regia Aeronautica operated substantial numbers of S.55s primarily as long-range bombers and patrol planes. By the outbreak of the Second World War, however, the model was considered outdated and only a limited number were retained in reserve.

Variants

File:Savoia-Marchetti S.55M 2006.jpg

SIAI S.55M

File:Savoia Marchetti S.55X 02.jpg

An S.55X aircraft from Balbo's transatlantic expedition

S.55

This includes the prototypes and early production units. The initial prototype was equipped with two 220 kW (300 hp) Fiat A.12bis six-cylinder inline engines, while the second prototype featured two 300 kW (400 hp) Lorraine 12Db V-12 powerplants. Production models were fitted with twin 380 kW (510 hp) Isotta Fraschini Asso 500 V-12 engines. A total of 90 were manufactured between 1927 and 1930, including the prototypes.

S.55C Civile

The first civilian version, powered by a pair of Lorraine 12ED V-12 engines. Eight units were produced from 1925 to 1926.

S.55P Passeggeri

An enhanced civil model featuring enclosed cockpits and a higher hull designed to carry ten passengers. It was powered by either two 380 kW (510 hp) Isotta Fraschini Asso 500, 370 kW (500 hp) Asso 500 Ri, or 520 kW (700 hp) Fiat A.24 V-12 engines. Production totaled 23 units from 1928 through 1932.

S.55A Atlantico

A military version equipped with 418 kW (560 hp) Fiat A.22R engines; sixteen examples were built by Piaggio in 1930.

S.55M Metallico

This variant replaced the wooden structure with metal components and was powered by seven 370 kW (500 hp) Isotta Fraschini Asso 500Ri engines, all manufactured by Piaggio in 1930.

S.55SA Scafo Allargato

Featuring widened and deepened hulls along with enclosed cockpits, this model was powered by two 380 kW (510 hp) Isotta Fraschini Asso 500 or two 370 kW (500 hp) Asso 500 Ri V-12 engines. Production included sixteen units built by Savoia-Marchetti and another sixteen by CANT.

S.55SA Scafo Allargatissimo

A version with significantly enlarged hulls powered by twin 370 kW (500 hp) Asso 500 Ri V-12 engines. Twenty were produced by Savoia-Marchetti, sixteen by Macchi, and six by CANT.

S.55X

Designed for North Atlantic formation flights, this variant was outfitted with two 700 kW (940 hp) Isotta Fraschini Asso 750 W-18 engines; it was later armed for reconnaissance and bombing roles. A total of twenty-five units were built.

P1S

The designation used by Brazilian Naval Aviation for the S.55A model.

Civil operators

Template:Country data Kingdom of Italy

• Aero Espresso Italiana
• Società Aerea Mediterranea

Template:USSR

• Aeroflot

Template:USA

• Aero Transport Company d.b.a. AirVia
• Marine Air Transport Co.
• Alaska Airways

Military operators

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Romanian-operated S.55 in 1943

Template:Country data Kingdom of Italy

• Regia Aeronautica

Template:BRA

• Brazilian Navy (operated eight flying boats)

Nationalist Spain

• Spanish Air Force (from 1937)

Romania

• Royal Romanian Naval Aviation (seven flying boats)

Surviving aircraft

File:Museu TAM - Jahu.JPG

Savoia-Marchetti S.55, registration I-BAUQ at TAM Museum, São Paulo Brazil

The only remaining original example is housed in Brazil, following a comprehensive restoration completed recently at the TAM Asas de um sonho (Wings of a Dream) Museum located in São Carlos, within the state of São Paulo (state), Brazil. This particular S.55, bearing the registration I-BAUQ and painted red, was famously piloted by Commander João Ribeiro de Barros during his 1927 crossing of the South Atlantic. It was christened "Jahú".

A life-size cutaway model replicating the S.55X used by Italo Balbo for his 1933 Transatlantic formation flight is exhibited at the Volandia Museum in Milan, Italy. Constructed by the Savoia Marchetti Historical Group, this replica required over 8,000 man-hours and seven years to complete.

Specifications (S.55)

File:Savoia-Marchetti S.55 ter 3-view L'Aéronautique March,1927.png

See also

• Decennial Air Cruise