The Fiat A.20 was an Italian aero-engine of the 1920s. It was a water-cooled V12 engine that was used by early versions of the Fiat CR.20 fighter and the Macchi M.41 seaplane.

In 1923, FIAT built the A.15, a 430 hp (320 kW) water-cooled V12 engine. While no production of the A.15 ensued, it formed the basis for the Fiat A.20, which differed in being a Monobloc engine, and delivered a similar power despite a reduction in capacity from 20.3 to 18.7 L (1,239 to 1,141 cu.in).

Applications:
CANT 15
CANT 25
Fiat CR.20
Macchi M.41
Macchi M.71
Piaggio P.6
SIAI S.58 bis
SIAI S.67
Ansaldo AC.4

Specifications:

Fiat A.20
Type: Water-cooled V12 engine
Bore: 115 mm (4.5 in)
Stroke: 150 mm (5.9 in)
Displacement: 18.7 L (1,141 in3)[6]
Length: 1,645 mm (64.8 in)
Width: 645 mm (25.4 in)
Height: 845 mm (33.3 in)
Dry weight: 317.5 kg (699 lb)
Fuel system: twin carburettorss
Cooling system: water-cooled
Power output: 410 hp (306 kW)
Specific fuel consumption: 220 g/hp hour

The Italian 1931 Schneider Trophy entrant, the Macchi M.C.72, required an engine of 2,300 horsepower (1,700 kW) with the capability of producing up to 2,800 horsepower (2,090 kW) while having a weight of not more than 840 kilograms (1,850 lb). The contract was awarded to Fiat, but their most powerful V engine to that date was the 1,000-horsepower (750 kW) 12-cylinder Fiat AS.5 that had also been used for Schneider Trophy racing.

The solution was to couple two AS.5 engines in tandem to produce a V-24 with each engine independently driving one of a pair of contra-rotating propellers through co-axial shafts. The rear engine drove the front propeller through a reduction gearbox, located between the two engines, up to a shaft that passed between the cylinder banks of the reverse-mounted forward engine. The latter’s crankshaft drive faced rearwards and drove the rearmost propeller in a likewise manner, but instead via a hollow shaft through which the rear engine driveshaft passed. A large rear-mounted supercharger was used to boost the engine, with the fuel/air mixture being delivered to the cylinders through a manifold that was centrally mounted between the cylinder banks of both engines.

The apparent advantages were that this configuration maintained a small frontal area, and that Fiat already had previous experience with the AS.5, while having a combined displacement of 50 litres (3,066 cu in) it was thought that the power requirement would be easily met.

In practice the engine was plagued with technical problems that led to the Italian team being unable to compete in the 1931 Schneider Trophy event. On 23 October 1934 however, after backfiring problems had been solved with the assistance of the British engineer “Rod” Banks, the AS.6 was used by Francesco Agello to set a new airspeed record for piston-powered seaplanes at 709.2 kilometres per hour (440.6 mph), a record that still stands today.

Applications
Macchi M.C.72

Specifications:

AS.6
Type: 24-cylinder V-engine
Bore: 138 mm (5.4 in)
Stroke: 140 mm (5.5 in)
Displacement: 50.25 L (3,066 cu in)
Dry weight: 930 kg (2,050 lb)
Valvetrain: Two intake and two exhaust valves per cylinder
Supercharger: Single-stage, centrifugal running at up to 19,000 rpm. Boost pressure 1.82 bar.
Fuel system: Carburettor
Cooling system: Liquid-cooled
Power output: 3,100 hp (2,300 kW) at 3,300 rpm
Compression ratio: 7:1
Power-to-weight ratio: 2.47 kW/kg (1.5 hp/lb)

The Fiat AS.5 was an Italian 12-cylinder, liquid-cooled V engine designed for the 1929 Schneider Trophy contest Fiat planned a new seaplane to counter the British challengers from Gloster and Supermarine. To minimise frontal area they chose a compact V-12 engine design that set new size standards for a 1,000-horsepower (750 kW) class engine. This unsupercharged engine had a high power-to-weight ratio due to the use of a high compression ratio and a special fuel blend containing a 50/50 mix of petrol and benzole.

A problem encountered with the AS.5 was that it developed maximum power at high crankshaft speeds (3,000 rpm) but lacked output gearing, so that great care had to be taken with the choice of propellers. The production version did feature a reduction gear. The AS.5 was developed into the AS.6, essentially a tandem-coupled combination of two AS.5 units.

Applications
Fiat C.29

Specifications:
AS.5
Type: 12-cylinder V-engine
Bore: 138 mm (5.4 in)
Stroke: 140 mm (5.5 in)
Displacement: 25.13 L (1534 cu in)
Dry weight: 348 kg (767 lb)
Valvetrain: Two intake and two exhaust valves per cylinder
Fuel system: Carburettor
Cooling system: Liquid-cooled
Power output: 1,000 hp (750 kW) at 3,200 rpm
Compression ratio: 8:1
Power-to-weight ratio: 2.15 kW/kg (1.3 hp/lb)

The Fiat AS.2 was an Italian 12-cylinder, liquid-cooled V engine designed for the 1926 Schneider Trophy contest held at Hampton Roads, Virginia, the AS.2 featured separate steel cylinders and cast aluminium alloy cylinder heads. The starting point for the Italian engine was the earlier Fiat A.22. The ‘S’ in AS stood for ‘Spinto’ (thrust). A weakness of the engine was its magnesium alloy pistons, a new engineering material at the time. Many pistons were holed. Despite the engine’s technical problems it was successful at the Schneider Trophy event, winning on 13 November 1926, with a second AS.2 powered aircraft placing third.

Applications
Macchi M.39

Specifications:

AS.2
Type: 12-cylinder V-engine
Bore: 140 mm (5.5 in)
Stroke: 170 mm (6.7 in)
Displacement: 30.955 litres (1,889 cu in)
Width: 720 mm
Height: 850 mm
Dry weight: 408 kg (900 lb)
Valvetrain: Two intake and two exhaust valves per cylinder
Fuel system: Carburettor
Cooling system: Liquid-cooled
Power output: 596 kW (800 hp) at 2,500 rpm
Compression ratio: 6:1
Power-to-weight ratio: 1.46 kW/kg (0.9 hp/lb)

Fiat’s interest in Diesel engines dated from 1907, initially focused on slow turning factory engines then moving to higher speed marine and railway motors. The water cooled straight six cylinder AN.1 was their first foray into Diesel aero-engines. To shorten its development time and to concentrate on the higher combustion chamber pressures, different burning temperatures and fuel supply systems of the Diesel cycle, they based its design on the Fiat A.12. This was a petrol engine first run in 1916 and produced in large numbers during World War I, a water-cooled, upright, overhead camshaft straight six. The AN.1 kept the external dimensions and the lower section, crankshaft, crankcase, sump, plus the lubrication and water-cooling supplies of the older engine but required new cylinders, pistons, valve gear and fuel delivery systems to replace carburettors and magnetos. The cylinder barrels had to be stronger to withstand the greater combustion pressures (2-300 atmospheres) required by the compression ignition Diesel. The swept volume of the Diesel engine was reduced by 23.4 % as the cylinders had a bore of 140 mm (5.51 in), compared with the A.12’s 160 mm (6.30 in). Two camshafts were fitted to operate the four valves per cylinder, though they were driven via the same tall vertical rod used for the single camshaft of the A.12, at its top, and the water pump of both models at its bottom.

The AN.1 was test flown in at least two aircraft, easily replacing the standard Fiat A.12bis in an Ansaldo A.300/4 reconnaissance and attack aircraft and also mounted in a specially designed biplane, the Fiat AN.1.

The first public performance of the AN.1 engine was at the Aerial Pageant held at Rome in June 1930 in the AN.1 biplane. This was flown by Renato Donati from the Fiat works at Turin to Rome, a distance of about 510 km (315 mi), on the first morning of the Pageant then displayed over Littorio Airport.

Applications
Ansaldo A.300/4
Fiat AN.1

Specifications
Type: Six cylinder inline, four stroke Diesel
Bore: 140 mm (5.51 in)
Stroke: 180 mm (7.09 in)
Displacement: 16.63 L (1,015 cu in)
Length: 1.78 m (70 in)
Width: 0.59 m (22 in)
Height: 1.14 m (45 in)
Dry weight: 390 kg (860 lb)
Valvetrain: Inlet and exhaust valves are driven directly from two parallel camshafts. The inlet valves draw in ambient air.
Fuel system: Each cylinder has its own fuel pump, arranged into two transverse banks of three at the rear of the engine. These meter, time and deliver fuel to an atomiser nozzle in the cylinder head which opens under fuel pressure.
Fuel type: Diesel (heavy-oil, naptha)
Cooling system: Water.
Cylinders: Steel barrels with two inlet and two exhaust valves formed in each cylinder head and with a central seating for the fuel injector. Water jackets and valve chambers welded on.
Pistons: Aluminium, with shaped heads to provide optimum compression ignition.
Power output: normal 180 hp (134 kW) at 1,600 rpm; maximum 220 hp (164 kW) at 1,700 rpm
Fuel consumption: 27 kg/(kW hr) (42 lb/(hp hr))