The Isotta Fraschini Zeta was an

air cooled Air-cooled engines rely on the circulation of air directly over heat dissipation fins or hot areas of the engine to cool them in order to keep the engine within operating temperatures. In all combustion engines, a great percentage of the heat ge ...

X engine An X engine is a piston engine with four banks of cylinders around a common crankshaft, such that the cylinders form an "X" shape when viewed from front-on. The advantage of an X engine is that it is shorter than a V engine of the same number o ...

with 24 cylinders developed by the Italian engineering company

Isotta Fraschini Isotta Fraschini () was an Italian luxury car manufacturer, also producing trucks, as well as engines for marine and aviation use. Founded in Milan, Italy, in 1900 by Cesare Isotta and the brothers Vincenzo, Antonio, and Oreste Fraschini, in 19 ...

in the 1940s. It was developed as an indigenous alternative to the imported

Daimler-Benz DB 605 The Daimler-Benz DB 605 is a German aircraft engine built during World War II. Developed from the DB 601, the DB 605 was used from 1942 to 1945 in the Messerschmitt Bf 109 fighter, and the Bf 110 and Me 210C heavy fighters. The DB 610, a pa ...

that was being built under licence as the Fiat RA.1050 R.C.58 Tifone. The engine was essentially two Gamma V12 engines on a single crankshaft, but proved troublesome to develop and never entered production.

Background

During the 1930s, Isotta Fraschini had developed a line of air cooled inverted V12 aircraft engines including the Gamma. These proved moderately successful at a time when most Italian aircraft engines were radials, including Isotta Fraschini’s own K.14.Gunston, 2006, p.107 In 1939, the Italian air ministry, looking for an appropriate power plant for their next generation of fighter aircraft, approached Germany to license the

. An inverted V12 like the Isotta Fraschini designs, it differed in its liquid cooling but also in its capability, being over twice as powerful as the Italian engines. To compete with this, and other foreign designs like the

Rolls-Royce Merlin The Rolls-Royce Merlin is a British liquid-cooled V-12 piston aero engine of 27-litres (1,650 cu in) capacity. Rolls-Royce designed the engine and first ran it in 1933 as a private venture. Initially known as the PV-12, it was late ...

, Isotta Fraschini developed the Zeta.

Design and development

Design

The Zeta was, in essence, two Gamma R.C.15 V-12 engines coupled to a single crankshaft. The engine consisted of an aluminium crankcase with four cylinder banks, each mounted at 90 degrees, with six cylinders. Each cylinder had a single intake and exhaust valve, driven by dual camshafts, and two spark plugs.Pearce, 2017 The whole engine was designed to be fitted as a replaceable power pack.

Development

Isotta Fraschini was owned by Caproni, who also produced aircraft, including the Caproni Vizzola F.4 which was originally planned to have an Isotta Fraschini V-12 engine but flew with a

Daimler-Benz DB 601 The Daimler-Benz DB 601 was a German aircraft engine built during World War II. It was a liquid-cooled inverted V12, and powered the Messerschmitt Bf 109, Messerschmitt Bf 110, and many others. Approximately 19,000 601's were produced befo ...

. The company also developed the Caproni Vizzola F.6 derived from this design, powered by the more powerful

. On 7 October 1941, the design of a version of the F.6, named F.6Z, to be powered by the new Zeta was instigated, the first aircraft being ordered on 16 June 1942. In October 1942,

Reggiane Officine Meccaniche Reggiane SpA (commonly referred to as ''Reggiane'') was an Italian industrial manufacturer and aviation company. Reggiane was founded during 1904 by its parent company Caproni, which was in turn owned by the aeronautical eng ...

, also owned by Caproni, was also tasked by the Air Ministry to develop a version of their

Reggiane Re.2005 The Reggiane Re.2005 ' ( en, Archer, Sagittarius) was an Italian monoplane fighter and fighter-bomber produced for the ''Regia Aeronautica'' during the later years of World War II. Along with the Macchi C.202/ C.205 and Fiat G.55, the Reggiane ...

with the new engine. Seven examples of the proposed

Reggiane Re.2004 The Reggiane Re.2004 was an Italian single-engined monoplane made by Reggiane and designed by Roberto Longhi. The aircraft never passed the preliminary stages. Design and development The Re.2004 had identical fuselage The fuselage (; from ...

were ordered. However, engine development was proving difficult; the first Zeta R.C.45 was run on 28 February 1941,rated at , but would only develop , as well as having many other issues. Resolving these took time and when the more powerful Zeta RC24/60 was run in May 1943, it still failed its type test. Reggiane tested a mock-up in a wind tunnel and mounted it in the nose of a Savoia-Marchetti SM.79 but cooling problems continued to hold development back. It was not until 14 August 1943 that the first engine took to the air in a Caproni Vizzola F.6Z, nearly two years after the Daimler-Benz-powered F.6M. Further development ceased following the armistice on 8 September 1943. By this time, Reggiane was still waiting for their first engine. As a consequence, the company had already started developing their own engine, the 18 cylinder Reggiane Re 103. The sole F.6Z remained the only aircraft flown with the Zeta.Green and Swanborough, p. 110

Variants

;Zeta R.C.15/45 : Project with two-speed supercharger, rated at and . ;Zeta R.C.21/60 : Project with two-speed supercharger, rated at and . ;Zeta R.C.22/50 : Project with two-speed supercharger, rated at and . ;Zeta R.C.24/60 : version with a two-speed

Wright Wright is an occupational surname originating in England. The term 'Wright' comes from the circa 700 AD Old English word 'wryhta' or 'wyrhta', meaning worker or shaper of wood. Later it became any occupational worker (for example, a shipwright i ...

supercharger, rated at and , for the

and Caproni-Vizzola F.6Z. ;Zeta R.C.35 : Initial design, , rated at . ;Zeta R.C.40 : Project, rated at . ;Zeta R.C.42 : project, rated at . ;Zeta R.C.45 : Version for Caproni-Vizzola F.6Z, rated at . ;Zeta R.C.50SD : Project with Isotta Fraschini supercharger, rated at .

Applications

* Ambrosini SAI.403 (unbuilt, Zeta R.C.21/60) * Breda Ba.201 (trial) * Caproni Ca.331 C.N. Raffica (unbuilt) * Caproni Ca.350 (unbuilt, Zeta R.C.42) * Caproni Vizzola F.6Z *

* Savoia-Marchetti SM.79 (mock-up only for development)

Specifications (R.C.35)

References

Notes

Bibliography

* * * * * * * * Air-cooled aircraft piston engines 1940s aircraft piston engines

Zeta Zeta (, ; uppercase Ζ, lowercase ζ; grc, ζῆτα, el, ζήτα, label= Demotic Greek, classical or ''zē̂ta''; ''zíta'') is the sixth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 7. It was derived f ...

X engines {{Isotta Fraschini aeroengines