Fiat CR.20

The Fiat CR.20 was a biplane fighter designed and produced by the Italian aircraft manufacturer Fiat. It represented an intermediate step from the early biplane CR.1 and the later, successful series CR.30, CR.32 and CR.42.

Development of the CR.20 was headed by the aeronautical engineer Celestino Rosatelli, who selected a traditional sesquiplane configuration. The engine was a water-cooled 306 kW Fiat A.20 V-12 engine. Major variants were the CR.20 Idro, a pontoon floatplane, and the CR.20 Asso, using a more powerful (336 kW/450 hp) Isotta Fraschini engine. CR.20bis, produced from 1930, differed from the original version only with the addition of a more advanced landing gear.

Design and development
The Fiat CR.20 was a sesquiplane fighter that possessed considerable military, aerodynamic, and static characteristics at the time of its introduction. It featured an all-metal framework that comprised both steel and various light metals while the exterior covering was of fireproof fabric, except for the front part of the fuselage close to the engine, which was instead covered by duralumin sheeting. The surface of the fuselage was relatively streamlined, which was obtained via the use of duralumin ribs and tubes that directly supported the fabric covering. The pilot was seated relatively high up in relation to the top of the fuselage; this placement provided an ample field of vision both above and below the upper wing. Overall, the aircraft had a relatively compact form, which had the benefit of minimising inertia in all directions and thus bolstering its manoeuvrability.

The wings were rigidly-braced, staggered, and had a dihedral. The number of wing struts was intentionally minimised as to reduce the drag incurred as well as to simplify the mounting. The ribs employed an arrangement of triangular bracing composed of thin duralumin tubes while the wing spars formed box girders, consisting of two metal strips that were riveted together. shearing stresses were adequately distributed by the twin spar webs, the flanges of which extended along the entire length of the spars and were reinforced at certain points. The stress distribution was designed to require the least possible variation in the cross section of the spars to form a girder of near uniform strength. The wing struts were composed of sheet metal in a conventional manner and possessed an aspect ratio of 2.5, as was then typically used on Fiat-built aircraft. The three struts forming each half of the cabane were joined in a manner that imposed no obstruction to the aircraft's cockpit.

The fuselage framework consisted of four longerons, composed of steel, that were connected via a combination of transverse frames and triangular bracing. The structure of the fuselage's forward section of the fuselage effectively terminated at the second bulkhead, that beyond effectively being a projecting bracket. The mounting for the engine was relatively simplistic in terms of its design; however, attention was paid to providing good accessibility for various elements, including the magnetos, water, fuel, and oil pumps and most aspects of the power plant. No bracing was present between the lower longerons due to the location of the fuel tank; instead, the horizontal girders continued through to the lower wing to join securely with the fuselage. The honeycomb radiator, which was located within the forward fuselage, used specialised elastic supports that avoided any vibration-related disturbances. The air passages of the radiator were arranged to facilitate maximum airflow, and thus the most efficient cooling, while the aircraft was climbing. The pilot could exercise control of the radiator via a shutter.

The powerplant was a Fiat A.20 V-12 water-cooled piston engine, which was capable of routinely producing 410 hp. It drove a twin-bladed fixed-pitch propeller that was relatively efficient and had a high revolution speed. This arrangement was partially attributable for the flying qualities of the aircraft, such as its ability to achieve relatively high speeds for the era. The speed of the engine enabled the attainment of a high specific power despite a relatively small bulk. The front end of the engine was specifically shaped to facilitate the installation of the radiator and thus achieve optimal efficacy, weight, and bulk, as well as protection of vulnerable elements from enemy fire. The twin double-spark high-tension magnetos were located aft of the engine and were relatively easily to inspect. A specialised starter, assisted by starting magnetos, was also present. The armament consisted of four machine guns, all being located within the fuselage. Two of these fired through the propeller arc as they were situated quite close to the pilot and featured an orthodox installation. The other two machine guns were mounted on the either side of the fuselage at the height of the longeron that supported the engine. The ammunition boxes, which were located on the sides of, and underneath, the engine cowling, were suitably protected. The aircraft possessed a relatively large carrying capacity.

Considerable attention was paid to maximising the safety of the aircraft across various aspects, as well as to avoid necessitating high piloting skills to operate it. To minimise the risk of an onboard fire, the pilot was able to direct the aircraft's detachable fuel tank to be dropped. Furthermore, a fire wall separated the engine from the rest of the fuselage. Torque was corrected against by making the left half-cell somewhat longer than the right. Moreover, every couple of gyration was offset via a suitable orientation of the axis of traction without causing drift. Special attention was paid to the positioning of both the fuel and oil tanks with respect to the vertical line that passed through the aircraft's centre of gravity, as well as the location of the landing gear in order to lessen the tendency to capsize on rough ground. The angle of attack was such as to achieve maximum lift and therefore to minimise the aircraft's landing speed. Despite these measures, the CR.20 was readily capable of performing various acrobatic manoeuvres and also possessed relatively high horizontal and climbing speeds.

Operational history
During September 1926, official testing of the CR.20 was performed at Montecelio; various aspects of the aircraft, including its manoeuvrability, ease of operation, responsive controls, and perfect equilibrium in flight, were commonly identified by early pilots.

By 1933, the CR.20 had reached its operational peak, equipping 27 squadrons of the Italian Regia Aeronautica. The aircraft engaged in combat against Libyan rebels as well as during the early stages of the Second Italo-Abyssinian War in the attack role. The CR.20s remained in service with the Regia Aeronautica in the aerobatics and training through much of the 1930s.

In 1933, Italy sold five CR.20s to Paraguay, which was fighting the Chaco War against Bolivia. Thus, these aircraft served as Paraguay's only fighters through to the end of the conflict.

Variants

 * CR.20 Idro : Twin-float seaplane version.
 * CR.20bis : Single-seat fighter biplane, fitted with an advanced landing gear.
 * CR.20bisAQ : CR.20bis aircraft fitted with the Fiat A.20 A.Q. piston-engine.
 * CR.20 Asso : Single-seat fighter biplane, powered by a 336 kW (450 hp) Isotta Fraschini Asso Caccia engine.
 * CR.20B : Two-seat trainer, communications aircraft. Built in small numbers.

Operators

 * Austrian Air Force (1931-1938)
 * 🇭🇺 Hungary
 * Hungarian Air Force
 * Kingdom of Italy
 * Regia Aeronautica
 * Aviazione Legionaria
 * Flag of Lithuania 1918-1940.svg Lithuania
 * Lithuanian Air Force - 15 units, 1928-1940.
 * Paraguayan Air Arm
 * Polish Air Force
 * Spanish Air Force
 * Soviet Air Force - Two aircraft, used for tests and trials.
 * Polish Air Force
 * Spanish Air Force
 * Soviet Air Force - Two aircraft, used for tests and trials.
 * Soviet Air Force - Two aircraft, used for tests and trials.
 * Soviet Air Force - Two aircraft, used for tests and trials.