Isotta Fraschini Zeta

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. In 1939, the Italian air ministry, looking for an appropriate power plant for their next generation of fighter aircraft, approached Germany to license the Daimler-Benz DB 605. 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, 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 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 company also developed the Caproni Vizzola F.6 derived from this design, powered by the more powerful Daimler-Benz DB 605. 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, also owned by Caproni, was also tasked by the Air Ministry to develop a version of their Reggiane Re.2005 with the new engine. Seven examples of the proposed Reggiane Re.2004 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. 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. The sole F.6Z remained the only aircraft flown with the Zeta. ==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 supercharger, rated at and , for the Reggiane Re.2004 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 • Reggiane Re.2004 • Savoia-Marchetti SM.79 (mock-up only for development) ==Specifications (R.C.35)==