Caproni Ca.90

Caproni

Industry	Aerospace, Aircraft manufacturing
Founded	1908
Headquarters	Italy

The Caproni Ca.90 was an experimental heavy bomber crafted by the Italian firm Caproni. When it took to the skies for the first time on 13 October 1929, it held the distinction of being the largest land-based aircraft globally at that moment, surpassed only by the slightly bigger Siemens-Schuckert R.VIII from the First World War era. Only a single unit of the Ca.90 was ever produced.

Despite the Dornier Do X flying boat debuting later in 1929 with a greater wingspan and weight, the Ca.90 retained its status as the largest landplane until the Tupolev ANT-20 appeared in 1934.

Design and development

The Caproni Ca.90 featured a six-engine inverted sesquiplane configuration intended for heavy bombing missions. Its structure mainly consisted of steel tubing, chosen for its superior strength and flexibility compared to aluminium or duralumin. The key joints were precision-machined from chrome-nickel steel alloys. Most of the fuselage and wing surfaces were covered with simply treated fabric, except for the forward section which used corrugated duralumin sheeting. Comprehensive testing of all components occurred at the experimental division of the Polytechnic University of Milan.

Its fuselage had a large square cross-section, suspended beneath the lower wing and integrated into the central wing structure. The nose was equipped with a turret armed with a machine gun, positioned ahead of a sizable fuel tank; above this tank was the cockpit where the pilot controlled the plane. Behind this area were additional fuel tanks and a bomb bay capable of carrying bombs in various sizes—800 kg, 500 kg, 250 kg, and 100 kg—for a total payload capacity of up to 8,000 kg on typical missions. Defensive armament included seven machine guns distributed across multiple rear positions to provide comprehensive fire coverage.

Propulsion came from six water-cooled Isotta Fraschini Asso 1000 W-18 piston engines. These were arranged as two tandem pairs mounted above the lower wing, each pair driving one four-bladed pusher propeller and one two-bladed tractor propeller, while a third pair was situated above the fuselage. The Asso 1000 engines were among the most powerful available at that time; although their power-to-weight ratio was moderate, they offered relatively efficient fuel consumption. Radiator airflow could be regulated by the pilot to manage engine cooling effectively. Fuel was stored extensively within both wings and fuselage compartments. Caproni noted that an excessive number of engines complicated control and reduced safety; during flight tests, it was suggested that future engines producing up to 2,000 hp might enable reducing engine count on this airframe to as few as three.

The aircraft's wingspan was notably large for its period. It employed a monoplane tail assembly fitted with balanced control surfaces; the rudder’s balanced area also provided in-flight vertical fin adjustments. The landing gear featured a wide track designed for handling uneven terrain, consisting of two independent pairs of large wheels mounted on ball bearings with oleo-rubber shock absorbers. A tail wheel was installed beneath the rear fuselage section.

Considered a technological milestone at its time, the Ca.90 demonstrated that landplanes could reach such immense sizes without significantly increasing takeoff or landing challenges. Its handling characteristics were not markedly different from smaller aircraft despite its massive scale and weight; during trials, it was often flown solo by a single pilot. This was partly due to extensive research and incorporation of special balancing surfaces on flight controls to minimize pilot fatigue. Additionally, all instrumentation and engine controls were arranged thoughtfully to facilitate ease of operation. Flight controls typically operated via steel cables, and dual flying controls were installed in the cockpit to accommodate a second pilot if needed.

The Ca.90 underscored several advantages large land-based aircraft had over similarly sized flying boats—particularly regarding weight savings since flying boats required heavy and complex hulls capable of enduring harsh sea conditions and water impact stresses, whereas landplanes could utilize simpler, lighter fuselages resulting in greater payload capacities for equivalent engine power. Land operations also avoided weather-related delays common to flying boats caused by rough seas. Nonetheless, it was proposed that relatively minor modifications could convert the Ca.90’s fuselage into a watertight hull suitable for amphibious operation.

In its bombing role, the Ca.90 boasted an effective operational radius of approximately 2,000 km (1,243 miles) while carrying an 8,000 kg (17,600 lb.) bomb load. It was promoted as capable of defending itself against enemy fighters due to its robust structure tolerating combat damage and possessing sufficient range to strike distant targets without escort support. Moreover, its spacious fuselage made it adaptable for alternative uses such as passenger transport, air mail delivery, or freight carriage; configured as an airliner, it could undertake extended nonstop flights including potential transatlantic routes with reduced payloads to accommodate additional fuel requirements. The sheer scale of the Ca.90 made it a source of pride for Italy’s aerospace industry and national prestige for both Caproni and Italy as a whole.

Specifications

Appearances in media

The Ca.90 is depicted in animated form within the Studio Ghibli production The Wind Rises. It features during a dream sequence where Jiro Horikoshi encounters and engages in a significant dialogue with his muse, Count Caproni.

See also

• Beardmore Inflexible

Bibliography

• Angelucci, Enzo. The Rand McNally Encyclopedia of Military Aircraft, 1914-1980. San Diego, California: The Military Press, 1983. ISBN 0-517-41021-4.
• The Illustrated Encyclopedia of Aircraft (Part Work 1982–1985). London: Orbis Publishing, 1985.
• "The Caproni "90 P.B." military airplane (Italian) : a giant biplane of 6000 horsepower" National Advisory Committee for Aeronautics, 1 July 1930. NACA-AC-121, 93R19696.