Fiat AS.6

The Italian aircraft engine Fiat AS.6 was a piston engine with 24 cylinders.

History

The engine was designed by Fiat for the racing aircraft Macchi Castoldi MC72 -, which in September 1931 should attend the Schneider Trophy in Calshot Spit ( UK). The first test run took place on 20 April 1931. The first flight on June 22, 1931 ended by misfires with damage to the new engine. Due to technical problems and a fatal accident the pilot Monti on August 2, 1931 Italy turned down the part.

By the complex development of the first speed record with 682.078 km / h could be placed on the April 10, 1933; the last record was followed on 23 October 1934, and with 709.209 km / h up to now unbeaten in its class.

Construction

The design of the motor by the engineer Tranquillo Serbi followed three development objectives:

  • Small end face to reduce the air resistance
  • No free moments in any load condition
  • Maximum power output

Minimization of the end face

The auxiliaries such as the ignition system, downdraft carburetor and loaders were disposed behind the engine so as not to interfere with the slim silhouette of the V- engine.

The two propeller shafts were designed as coaxial shafts and ran between the cylinder banks of the front cylinder 12 through.

The oil and water cooler on the aircraft were designed as a surface cooler.

Minimizing the free moments

The two crankshafts uncoupled turned in the opposite direction, as well as the propeller shaft and propeller. Thus, first, the moments were eliminated when accelerating the engine and secondly neutralizes the propeller torque.

With only one propeller, the torque of the propeller would be critical for the start: the moment would have to be intercepted by one of the two floats, which would change the depth of immersion and thus the resistance of this float - the aircraft could hardly be kept on track in the starting phase.

Maximize power output

The engine was based on the racing engine Fiat AS.5 with about 1000 hp, which indeed already per two intake and two exhaust valves per cylinder had, but was not charged. With the mechanical supercharger to be achieved for the AS.6 with redoubled Displacement performance of 2500 hp and 3000 hp for racing and record flights. The loader was driven from the rear crankshaft; to the dissipated power offset of about 200 hp, was reduced according to the angle of the front propeller.

The carburetor has been designed as a downdraft carburetor with eight nozzles.

For the formulation of the fuel, the British expert " Rod" Banks was engaged. The composition was 55 % gasoline and 23% alcohol, 22 % benzene and 0.15 % tetraethyl lead.

Technical problems of the engine

The technical problems of the engine could not be solved satisfactorily in spite of great efforts.

  • After the first engine run on 20 April 1931 which ended with a disappointing 2200 hp and two burnt valves, twelve valve combinations and 1000 valves from ten different steels were tested.
  • On June 22, 1931 strong misfire during the first flight forced the pilot to abort Monti. The loader was destroyed.
  • In a hall, a test rig was constructed with two 400 hp and 700 bhp engines to get the problems with the carburetor and the mixture formation at speeds up to 750 km / h in the handle. Cause of the problems of mixture preparation were on the one hand unwanted charging effects due to the high speeds in flight, on the other hand, separation processes in the nearly four meters extremely long intake runners.
  • In 1932, bench tests were performed mainly in order to improve the engine. On February 26, 1932, simulated with 2400 hp record flight over 3 km.

In the end, the engine could be used for only a few flights; further use was no longer after the world record in 1934.

Two pilots died in the testing of MC.72 by accidents that were caused by the engine.

  • On August 2, 1931, the pilot died in an accident at the start Monti
  • On September 10, 1931 Bellini MC.72 exploded during a record attempt at Desenzano del Garda in the air

Specifications

Engines Received

A complete Fiat AS.6 is exhibited in the Italian Air Force Museum Vigna di Valle.

Macchi M.C.72 List of aircraft engines
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