# Savoia-Marchetti S.55

The Savoia-Marchetti S.55 is a double-hulled monoplane flying boat designed and produced by the Italian aircraft manufacturer Savoia-Marchetti. It was designed to perform both commercial and military applications.
The S.55 had several innovative design features. While the passengers and cargo were housed in the twin hulls, the flight crew occupied a cockpit located in the thicker section of the wing between the two hulls. The S.55 had two inline contra-rotating propellers, mounted in tandem. The engines are canted sharply at an upward angle. Two wire-braced booms connected the triple-finned tail structure to the twin hulls and wing.
The S.55 made its maiden flight during August 1924. Shortly after its introduction, the S.55 set records for speed, payload, altitude and range. Many saw service with the Regia Aeronautica and foreign operators including the Spanish Air Force and Royal Romanian Naval Aviation as bombers and maritime patrol aircraft. While some examples were active by the outbreak of the Second World War, the type only played a marginal role in the conflict due to their age.

## Design and development

The Savoia-Marchetti S.55 is a double-hulled thick-section cantilever monoplane flying boat designed to perform both civilian and military operations. Its design was largely original and had numerous features which increased its practicality as a platform for naval military tasks such as minelaying and torpedo attacks. Various aspects of the flying boat eased aspects of its operation; it was relatively easy to dismantle for ground transport; the wings comprised three detachable sections and each of the hulls could be entirely detached from the centre section along with the tail unit. The engines could be readily inspected at all times, even during flight.
The twin hulls are spaced about 4 metres (13 feet) apart and extend for just over half of the total length of the aircraft, and have a single-step V-shaped bottom. They are constructed in a manner that permits the internal space to be configured into a series of cabins, accommodating a maximum of 12 passengers if so required. The cockpit is positioned in the centre section of the leading edge between the two hulls; a passageway allows movement between the cockpit and the cabin space. On militarised aircraft the stern of each hull accommodated a tail gunner. Underneath the middle of the centre section was a clear space of about 2.4 m (8 ft) foot; this was suitable for the mounting of either torpedoes or mine-laying apparatus.
The outer wing sections has a pronounced dihedral and are tapered from root to tip. The leading edges are swept back about 15 degrees while the trailing edge is only slightly inclined. The wing have balanced ailerons which had an inclined axis. The tail surfaces are carried by two pairs of booms; the upper pair attached to the upper surface of the centre section near the rear main spar, and the lower beam to the sternpost of the hull. They are cross-braced and each has a vertical strut at its forward and rear ends. Mounted on top of the rectangular horizontal stabilizing surface are three triangular vertical fins, each with a balanced rudder.
It is powered by a pair of Isotta Fraschini Asso 500 V-12 piston engines, each capable of providing up to 300 kilowatts (400 hp). These are arranged in tandem in a streamlined nacelle which is mounted above the centre section of the aircraft, supported by a series of struts. Both engines are cooled by a single radiator mounted in the nose of the nacelle. The nacelle is inclined, placing the line of thrust from the engines at about eight degrees over the horizontal. The main reason for this arrangement is to direct the slipstream onto the tail surfaces. Level flight could be maintained on a single engine.

## Operational history

During August 1924, The S.55P prototype was first flown in August 1924. Throughout 1926, the prototype set 14 separate world records for speed, altitude and distance with a payload. The type's greatest successes, however, were its many flights between Europe and the Americas.
The First aerial crossing of the South Atlantic had been made in stages in 1922 using three different Fairey III machines, and a subsequent crossing was made by the Dornier Do J Plus Ultra in January 1926 with a single stop at the Cape Verde Islands. One year later, the first S.55 crossing was made by the Santa Maria under Francesco de Pinedo. After flying south to Bolama, at that time in Portuguese Guinea, they hoped to cross the ocean without another stop but were forced down at Cape Verde, reaching Brazil on 23 February 1927. After the crossing, the aircraft was traded to Brazil for coffee beans.
The Brazilian João Ribeiro de Barros and his crew of three made another crossing in S.55 "Jahú" on 24 April 1927. Departing from Santiago Island, they crossed the Atlantic in "Jahú" and landed at Fernando de Noronha Island, Brazil.
Pilots Francesco de Pinedo and Carlo del Prete took off from Sesto Calende, Italy, in an S-55 on 13 February 1927. Four months later, on 16 June 1927, they arrived back in Italy, having flown nearly 48,280 km (30,000 mi) in 193 flying hours and having made 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 Ten. Col. Umberto Maddalena of the Italian air force, located survivors of Arctic explorer Umberto Nobile's crashed airship Italia on an ice floe about 120 km (75 mi) northeast of Nordaustlandet, Svalbard.
The Italian Air Marshal of the time, Italo Balbo, became famous for organizing a squadron of S.55s for Atlantic crossings, culminating in his 1933 flight with 24 aircraft to Chicago's Century of Progress International Exposition. On 1 July 1933, General Balbo commanded a flight of S-55s from Orbetello, Italy, completing the flight in just over 48 hours, maintaining a tight "V" formation. These large fleets of aircraft were sometimes called a "Balbo".
Numerous aircraft were introduced by the Regia Aeronautica and served as a long-range bomber and patrol aircraft. By the Second World War, the service's S.55 fleet was no longer considered to be serviceable and the type was only ever held in reserve.

## Variants
### S.55

    Prototypes and original production model delivered from 1927 to 1930, 90 built, including two prototypes.

### S.55C

    Civil variant delivered from 1925 to 1926, eight built.

### S.55P

    Improved civil variant with enlarged hull for ten passengers and enclosed cockpits delivered from 1928 to 1932, 23 built.

### S.55A

    Military variant delivered with 418 kW (560 hp) Fiat A.22R engines, 16 built.

### S.55M

    Variant with some wood structures replaced by metal, seven built by Piaggio in 1930.

### S.55 Scafo Allargato

    Widened and deepened hull and enclosed cockpits, 16 built by Savoia-Marchetti and 16 built by CANT.

### S.55 Scafo Allargatissimo

    Variant with greatly enlarged hull, 20 built by Savoia-Marchetti, 16 built by Macchi and six built by CANT.

### S.55X

    Variant fitted with Isotta Fraschini Asso 750 engines for North Atlantic formation flights, later armed and used as a reconnaissance-bomber. 25 built.

### P1S

    Brazilian Navy designation of the S.55A.

## Operators
### Civil operators
#### Kingdom of Italy

* Aero Espresso Italiana
* Società Aerea Mediterranea

#### Soviet Union

* Aeroflot

#### United States

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

### Military operators
#### Kingdom of Italy

* Regia Aeronautica

#### Brazil

* Brazilian Navy (eight flying boats)

#### Spain (1937)

* Spanish Air Force

#### Romania

* Royal Romanian Naval Aviation (seven flying boats)

## Surviving aircraft

The last remaining example is preserved in Brazil, at the TAM "Asas de um sonho" museum, at São Carlos, São Paulo. The aircraft, registered I-BAUQ and named "Jahú", was the S.55 used by Commander João Ribeiro de Barros in his crossing of the South Atlantic in 1927.

## Specifications (S.55)

Data from Jane's all the World's Aircraft 1928, National Advisory Committee for Aeronautics
General characteristics
* Crew: Two pilots and 3-4 other crew members
* Length: 16.5 m (54 ft 2 in)
* Wingspan: 24 m (78 ft 9 in)
* Height: 5 m (16 ft 5 in)
* Wing area: 92 m$^2$ (990 sq ft)
* Empty weight: 5,750 kg (12,677 lb)
* Max takeoff weight: 8,260 kg (18,210 lb)
* Powerplant: 2 × Isotta Fraschini Asso 500 V-12 water-cooled piston engines, 370 kW (500 hp) each mounted in tandem, plus one Garelli piston engine driving oil distribution placed between the two main engines
* Propellers: 2-bladed fixed pitch tractor and pusher propellers
Performance
* Maximum speed: 205 km/h (127 mph, 111 kn)
* Stall speed: 105 km/h (65 mph, 57 kn)
* Range: 1,200 km (750 mi, 650 nmi) to 2,200 km (1,400 mi; 1,200 nmi)
* Time to altitude: 1,000 m (3,300 ft) in 9 minutes; 2,000 m (6,600 ft) in 25 minutes; 3,000 m (9,800 ft) in 45 minutes