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Aircraft of the Month for July 2000

SIAI Marchetti SM.55

by Alex Stoll

The SM.55 was designed as a torpedo bomber by Alessandro Marchetti. It was built entirely from spruce and ash with a plywood coverin, except for the alluminum alloy propellers, engines, cabins, and hatch seals. It had two fins but three rudders for more stability. Several high officers of the Italian Air Force did not approve of it though: it was almost all wooden and the big wing was deemed too big and since it was all wood they thought it would warp easily and quickly. So Marchetti installed Issotta F. Asso engines, and the SM.55 broke 14 records for speed, altitude, load carrying, and distance. Equipment on the modified trans-Atlantic versions included a Sperry artificial horizon, a Pioneer change course indicator, and Marconi radio and wireless transmitters and receivers. Transmissions could be received up to 2000 mi, and could be transmitted to up to 2000 mi for short wave and 500 mi for long wave. Backup radios were also carried.

SM.55X's on their way to Cartwright, Labrador, from Reykjavik, during the longest (1500 mi) leg of the 1933 flight to Chicago.

In 1929, Francesco De Pinedo, who had flown 34,000 miles from Italy to Japan and back in 1925, flew an improved SM.55, the Santa Maria (named after Colombus' flagship), 28,000 miles to all the countires on the North Atlantic rim. In September 1930 Italo Balbo led 14 SM.55s 6500 mi from Rome to Rio de Janeiro and back. In 1932, a SM.55 purchased by the USSR flew 14,000 mi from the Savoia-Marchetti factory outside Florence across Sibera to Petropavlovsk on the Kamchatka Peninsula. From 1 July - 21 August, 1933, Balbo led 24 SM.55s on a round trip from Rome to Chicago for the Chicago World's Fair Exposition, a distance of almost 11,500 mi.

Map of the trip to and from Chicago

More photos
Close-up of the Asso 750 installation on a SM.55X
SM.55X's at Orbetello (outside Rome) before their flight to Chicago in 1933
Leaving in formation
SM.55X's flying in formation


(Note the facist symbols at the bow of the hulls on this SM.55X)
Prototype1923Two 224kW (300hp) Fiat A.12 bis engines; max speed 190km/h
?1925Patrol bomber and mine layer; two 298kW (400hp) Lorraine-Dietrich engines
M1926Initial military version; two 373kW (500hp) Isotta Fraschini 12-cyl Asso (Ace) engines; max speed 210 km/h
P1928Passenger version
A1930First trans-atlantic version; two 418kW (560hp) Fiat A.22R engines
C1932Commericial version; two 522kW (700hp) Fiat A.24R engines; max speed 240 km/h
X1933Tenth version; incorperated many design improvements, including three-blade props, smoother fairing, and experimental concave hull bottoms (more info below)
Piaggio 9?All-metal version; 7% lighter but 19 km/h (10 kts; 12mph) slower and with a 457m (1500ft) lower service ceiling

SM.55X Specifications
TypeTwin-hull monoplane flying boat
PowerplantTwo 18-cyl. Isotta Fraschini Asso 750 engines, 597 kW (800hp) each
AccommodationTwo pilots, a radioman and a flight engineer/mechanic
Max fuel3780L (1000 gal) carried in seven tanks in each hull
Max speed at sea level280 km/h (151 kts; 174 mph)
Cruise speed217 km/h (117 kts; 135 mph)
Service ceiling5000m (16,400 ft)
Ceiling, fully loaded4115m (13,500 ft)
Range3000km (1620 nm; 1863 mi)
Fuel consumption during cruise30 gph per engine
Takeoff speedJust under 113 km/h (61 kts; 70 mph)
Empty5760 kg (12,686 lb)
MTOW8263 kg (18,200 lb)
Wingspan24m (78 ft 8.5 in)
Wing area93m² (990 sq ft)

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