Aviation of World War II
Having considered the proposals received, the Air Force technical commission considered it necessary to begin the construction of two prototypes of the Ro.51, the contract for the production of which under No. 899 was issued on May 29, 1937. The contract amount was 800,000 lire. The Ministry of Aviation assigned two prototypes the numbers of the military register (Matricole Militari) MM.338 and MM.339, respectively.
The assembly of the first prototype was completed quite quickly, so that in the summer of the same year it made its first flight, taking off from the factory airfield in Napoli-Capodichino. On July 6, 1938, the prototype was transferred for testing to the research center in Guidonia, where it showed a maximum speed of 467 km/h at an altitude of 5000 m, which was noticeably less than that of the FIAT G.50 and Macchi C.200.
After several flights by testers Remondino and Mantelli, shortcomings in the flight performance, design and control of the fighter were revealed. The plane was uncontrollable in flight - after landing, Remondino said: I got the impression that I was not flying, but walking on ice.
The reason for this was the very thin wing of the aircraft, which was subject to twisting during flight. The aircraft was returned to the company for modifications, during which a retractable landing gear was installed. But even here there were problems. The fact is that the thin wing of the Ro.51 was not designed for niches for the landing gear and as a result fairings had to be made for the struts: the landing gear struts folded back like on the Seversky P-35 fighter and the Breda Ba.65 attack aircraft. As in the two above cases, the Ro.51 wheels turned out to be semi-retractable. To increase the lateral stability of the fighter, the area of the vertical tail was increased.
After returning to Guidonia on December 20, 1938, flight tests continued. The flight characteristics improved (the speed increased to 489 km/h), but the phenomenon of autorotation still remained when performing rolls. This phenomenon was typical of the first designs of Italian monoplane fighters, but in the Ro.51 it was more pronounced than in the G.50 and S.200. A solution to the autorotation problem was found by using a wing with a variable profile. As a result, IMAM Ro.51 was late and did not receive an order for mass production.
However, the company in Naples did not sit idly by: they decided to convert the second prototype into a seaplane to replace the Ro.44, for which the landing gear with the cleaning system was dismantled and floats were installed: a central one and a pair of side floats.
The main float was connected to the fuselage by an N-shaped frame of six rods, while the underwing floats were mounted on a single strut. The seaplane was tested at the experimental center in Vigna di Valle on Lake Bracciano by test pilot Aldo Ligabò. The replacement led to the fact that the maximum speed dropped to 430 km/h, and the flight range was increased to 1200 km. During the tests, the disadvantages of the side floats were revealed: they were often completely submerged in water. During one of the taxiing operations, one of the wing consoles suddenly went under water, which led to an airplane crash and the closure of the program.
Technical description. Fighter IMAM Ro.51 was a single-engine, single-seat monoplane (low wing) of mixed design. The oval-shaped fuselage is welded from chrome-molybdenum steel pipes, the outer skin is made of duralumin.
The wing is wooden with one spar made of pine or spruce and plywood sheathing, the surfaces are covered with canvas.
The main landing gear was released and retracted by a hydraulic drive, the tail wheel was retractable.
The tail unit was a welded structure made of steel pipes, covered with fabric. The deflecting surfaces covered with canvas are statically and aerodynamically balanced.
The Fighter was equipped with an all-round visibility flashlight made of plexiglass. The pilot's armored back could also serve to protect him when the aircraft was capped.
The main fuel tank is made of light alloy and is located between the pilot's cabin and the engine firewall.
The aircraft was equipped with a two-row 14-cylinder Fiat A.74 R.C.38 engine with a power of 840 hp. with a three-bladed metal variable-pitch propeller.
The aircraft's armament consists of two synchronized Breda-SAFAT machine guns of 12.7 mm caliber, located in the fuselage and fired through recesses in the hood.
In 1936, the Italian Ministry of Aviation (Ministero dell'Aeronautica) announced a development program for the Italian Air Force, called Progetto R. According to this program, 3000 new fighters (Caccia da Combattimento) were required, which could replace outdated ones during 1939-40 Fiat CR.32 Freccia and CR.42 Falco fighters. The requirements included good climb characteristics, armament with one 12.7 mm machine gun, and a limited flight duration. This specification was soon modified by the introduction of an armament of two machine guns and a flight duration of two hours.
The competition to create fighters under this program included Macchi MC-200 Saetta, Caproni-Vizzola F-4 and F-5, IMAM-Romeo Ro-51, FIAT G-50 Freccia, Reggiane Re-2000 Falco and AUSA AUT .18. During the tests, the Macchi MC-200 Saetta was selected for production. Its closest competitor, the Reggiane Re.2000, which had good maneuverability at altitude and better handling at low speed, was rejected due to the severe vulnerability of its wing fuel tanks and due to doubts about their structural strength. However, due to the behind-the-scenes struggle between lobbyists, the Macchi MC-200 Saetta, the FIAT G-50 Freccia, and the Reggiane Re-2000 Falco went into production, each of which produced a line of fighters or fighter-bombers. The losers of the competition remained in the shadows - the cars are no less interesting and worthy of careful consideration.
AUSA AUT.18 has an extremely long design period: conceived by engineer Felice Trojani back in 1934, the project was constantly reworked over three years based on the results of a large number of tests and blowing models in the wind tunnel. Construction of the prototype took place at the Aeronautica Umbra S.A plant in Foligno, of which Troiani was the technical director. The aircraft designation is an abbreviation of the name of the company, the name of the designer and the wing area in square meters.
AUT.18, originally conceived as a two-seat fighter, was built in a single-seat configuration. Compared to the previous generation fighters, it was heavier and used a more powerful FIAT A.80 engine with 1044 hp. and was armed with two 12.7 mm machine guns located outside the propeller sweep zone. Taxi tests of the MM prototype. 363 (the car received this number from the Italian Air Force) began on March 21, 1939, at the factory airfield in Foligno. For flight testing, out of precaution, it was decided to move the aircraft to the larger Viterbo airfield. This was followed by a difficult transportation operation over a distance of about 120 km. After delivery to Viterbo on April 22, 1939, the first flight took place under the control of Umbra test pilot Roccato.
In the summer of 1939, military tests of the aircraft began: on July 20, AUT.18 was transferred to the flight test center of the Italian Air Force (Regia Aeronautica) Guidonia and on August 18, a short cycle of firing tests began at the Furbara airfield, with a positive result. To improve the aircraft's performance, the cowling was replaced with a new, aerodynamically cleaner one. The frontal projection of the engine was reduced, the cylinder heads were covered with convex fairings, and a swept spinner was installed on the propeller hub.
To carry out this work, on February 23, 1940, the aircraft was delivered to the plant in Foligno. Thanks to the new hood configuration, the AUT.18 is 15 km/h faster. - now the maximum speed was 489 km/h. On June 21, the aircraft was returned to Guidonia and on July 12, after 49 flights, Rocciato completed flight tests. Flight testing was carried out with extreme caution due to an unwillingness to risk the only existing machine.
Colonels Tondi, Mantelli, Vignoli flew at the flight test center on AUT.18 and their assessment of the aircraft was quite high. There was a proposal to replace the Breda Ba.65 attack aircraft with it: one of Adriano Manteli’s test reports contains specific references to this possibility. The aircraft, heavier than other modern fighters, offered good opportunities as a successor to the Ba. 65, having better speed characteristics.
On November 5, 1940, the official transfer of AUT.18 to the Regia Aeronautica took place, and on the same day Manteli received instructions to relocate the aircraft to the Orvieto airfield for use as an air defense fighter. Due to alterations and bureaucratic delays during testing (Mackey MC.200 had already completed its first flight in 1937), this fighter was not proposed to be put into mass production. The reasons were primarily political - in the series there were already 3 types of fighter (instead of one), two of which were at least slightly superior to the AUT.18.
Little is known about the fate of the prototype. Troiani wrote in his memoirs that the aircraft was transported to Germany for testing after the armistice, but it is more likely that it was destroyed in a raid after its transfer to Orvieto. There is a version that it was captured by the Allies for study. It should be noted that the British Royal Air Force already knew about this type of aircraft in 1936 and noted it among the known Italian types.
Technical description. The AUT.18 fighter was a single-engine, single-seat, all-metal monoplane with a low wing. The triangular-section fuselage was autogen-welded from steel chromium-molybdenum pipes, the outer skin was made of duralumin.
The wing was a structure made of chrome-molybdenum steel pipes connected by spot welding. The wing skin is made of duralumin, the surfaces are covered with canvas.
The armament consists of two 12.7-mm Breda-SAFAT machine guns, located in the central part of the wing and firing outside the propeller sweep plane. The ammunition capacity of machine guns is 300 rounds per barrel. The landing gear of the aircraft is retractable with its wheels facing the axis of the aircraft. The landing gear retraction mechanism is equipped with a hydraulic drive and booster pumps. The wheels are equipped with "FAST" shock absorbers. The tail wheel is retractable.
The tail unit is made of duralumin (spars and ribs), the deflecting surfaces covered with canvas are statically and aerodynamically balanced.
The fuel tanks are located in the fuselage immediately behind the cockpit.
FIAT A.80 engine with 1044 hp. with a three-blade metal Alfa Romeo propeller with variable pitch in flight.