Fiat AS.6
The Italian aircraft engine Fiat AS.6 was a piston engine with 24 cylinders.
history
The engine was designed by Fiat under the direction of the engineer Tranquillo Zerbi for the Macchi-Castoldi MC72 racing aircraft that was to take part in the Schneider Trophy in Calshot Spit (Great Britain) in September 1931 . The first test run took place on April 20, 1931. The first flight on June 22, 1931 ended due to misfiring and damage to the new engine. Due to technical problems and a fatal accident involving pilot Giovanni Monti on August 2, 1931, Italy canceled participation.
As a result of the extensive further development, the first speed record was set on April 10, 1933 with 682.078 km / h; the last record followed on October 23, 1934 and is still unbeaten in its class at 709.209 km / h.
construction
Development goals
The design of the engine by the engineer Tranquillo Serbi followed three development goals:
- small frontal area to reduce air resistance
- Compensation of all mass moments in every load condition
- maximum power output
Minimizing the frontal area
The auxiliary units such as the ignition system, downdraft carburetor and charger were arranged behind the engine so as not to impair the slim silhouette of the V-engine .
The oil and water coolers on the aircraft were designed as surface coolers.
Minimizing the free moments
The two uncoupled crankshafts turned in opposite directions, as did the propeller shafts and propellers. This firstly eliminated the moments of inertia when accelerating the engine and secondly neutralized the propeller torques.
With only one propeller, the torque of the propeller would be critical for take-off: the moment would have to be absorbed by one of the two swimmers, which would change the immersion depth and thus the resistance of this float - the aircraft could hardly be kept on course during the take-off phase.
Maximizing the power output
The power unit was based on the Fiat AS.5 racing engine with around 1000 hp and 12 cylinders, which already had two inlet and two outlet valves per cylinder, but was not yet charged. With the mechanical supercharger, the AS.6, with doubled displacement, was supposed to achieve outputs of 2500 hp for racing and 3000 hp for record flights.
Technical design
Engine block
The basic concept of the motor consisted of two AS.5 motors, which were mounted face to face. The two counter-rotating crankshafts ran in a common crankcase, but each had its own oil pump, two cooling water pumps and its own output in the middle of the 24-cylinder engine with 48 spark plugs and 96 valves. The two propeller shafts were designed as coaxial shafts and ran between the cylinder banks of the front 12 cylinders at a speed reduced by the reduction factor of 0.6 compared to the respective crankshaft.
Ignition system
Two magneto ignition systems for the rear 12 cylinders were arranged below the carburetor, they were driven by the crankshaft. The two magneto ignition systems for the front 12 cylinders were mounted exceptionally high in front of the front cylinder heads, and they were driven by the outer propeller shaft.
The spark plugs were supplied by the British manufacturer KLG , the magneto ignition systems by the Italian manufacturer Magneti Marelli .
Carburetor and charger
The carburetor was designed as a downdraft carburetor with eight mixing chambers.
The British expert Francis Rodwell Rod Banks was hired for the formulation of the fuel . The composition was 55% gasoline, 23% alcohol, 22% benzene and 0.15% tetraethyl lead . The rear crankshaft drove the single-stage centrifugal compressor ; to the dissipated power of about 200 bhp at 19,000 to 20,000 rpm -1 compensate for the angle of attack of the front propeller has been reduced accordingly.
Technical problems of the engine
The technical problems of the engine could not be solved satisfactorily despite great efforts.
- After the first engine run on April 20, 1931, which ended with a disappointing 2200 HP and two burned valves, twelve valve combinations and 1000 valves made of ten different steels were tested.
- On June 22, 1931, severe misfires during the first flight forced the pilot Giovanni Monti to abort. The loader was destroyed.
- A test stand with two 400 HP and 700 HP engines was set up in a hall in order to get to grips with the problems with the carburettor and the mixture formation at speeds of up to 750 km / h. The cause of the mixture preparation problems were, on the one hand, unwanted charging effects due to the high speeds in flight, and, on the other hand, segregation processes in the intake ducts, which are almost four meters long.
- In 1932 bench tests were mainly carried out to improve the engine. On February 26, 1932, a record flight of 3 km was simulated with 2400 hp.
In the end, the engine could only be used for a few flights; after the world record in 1934, it was no longer used.
Two pilots died while testing the MC.72 in accidents caused by the engine.
- on August 2, 1931, the pilot Giovanni Monti died in a takeoff accident
- on September 10, 1931 Bellini MC.72 exploded during a record attempt in Desenzano del Garda in the air
Technical specifications
| Parameter | Data of the AS.6 |
|---|---|
| design type | 24-cylinder V-engine (60 °), four valves per cylinder |
| drilling | 138 mm |
| Hub | 140 mm |
| Displacement | 50.25 L. |
| compression | 7: 1 |
| Loader | single-stage Zentrifugallader, 20,000 min -1 , boost pressure to 1.82 bar |
| power | 3,000 hp (2,200 kW ) at 3,200 min -1 |
| Dry matter | 930 kg |
Preserved engines
A complete Fiat AS.6 is on display in the Italian Aviation Museum Vigna di Valle . The Centro Storico Fiat in Turin is showing another complete engine.
See also
literature
- Edward Eves: The Schneider Trophy Story . Airlife Publishing Ltd., Shrewsbury 2001, ISBN 0-7603-1118-8 .
- Bill Gunston: World Encyclopedia of Aero Engines . Patrick Stephens Ltd., Cambridge 1989, ISBN 1-85260-163-9 .
Web links
- Macchi-Castoli MC 72. In: History of Air Racing. Century of Flight, accessed March 23, 2019 (English, article with pictures).
- Macchi MC 72. YouTube , accessed June 15, 2011 (original footage with sound).
Individual evidence
- ↑ a b The Speed Record Raised. (PDF) In: Flight. Flightglobal, November 1, 1934, p. 1152 , accessed on January 16, 2015 (English): "British equipment figured in the success, for Castrol oil and KLG plugs were used."
- ↑ a b The 5th VOLTA Congress in Rome in 1935, a breakthrough in high-speed aerodynamics. (PDF; 2.7 MB) Deutsche Gesellschaft für Luft- und Raumfahrt, p. 7 , accessed on January 17, 2015 (With a cross-sectional drawing of the Fiat engine of the record MC. 72 compared to the pilot's height.): “A solution of violence about the drive that made it possible to overcome the great aerodynamic resistance. "
- ^ A b Major GP Bulman: Engine Features from the Paris Show. (PDF) In: FLIGHT. Flightglobal.com, December 15, 1932, pp. 1188-1189 , accessed June 15, 2011 (with a side view of the engine).
- ^ William Pearce: FIAT AS.6 Aircraft Engine (for the MC.72). Old Machine Press, October 14, 2012, accessed October 1, 2017 .
- ↑ a b CF Bona: Italian High Speed Airplane Engines . In: National Advisory Committee for Aeronautics (Ed.): Technical Memorandums . No. 944 . Washington June 1940 ( ntrs.nasa.gov [PDF; accessed on January 17, 2015] Italian: I motori italiani per gli apparecchi di alta velocita. Rome 1935. Translated by S. Reiss, contemporary report, 39 pages with tables and pictures) .
- ↑ Editorial Comment. (PDF) Schneider Tragedies and Prospects. In: FLIGHT, AUGUST 7, 1931. Flight International , August 7, 1931, p. 777 , accessed on May 6, 2018 (English): “On Sunday […], Capt. Giovanni Monti, of the Italian tailor team, crashed with his seaplane into waters of Lake Garda and was killed. "
- ↑ Airisms from the Four Winds. (PDF) Italian Schneider Pilot Killed. In: FLIGHT, SEPTEMBER 18, 1931. Flight International , September 18, 1931, p. 960 , accessed on May 6, 2018 (English).