Isotta Fraschini Delta

The Delta was a 12-cylinder inverted-V aircraft engine built by Isotta-Fraschini prior to and during World War II. It is a fairly rare example of a large air-cooled inline engine, which normally have cooling problems with the rearmost cylinders. It produced about 750 hp in common versions, although others were rated up to 900 hp. The Delta was not widely used, although it could be found on a number of production aircraft and some advanced prototypes.

Although the air-cooling might be considered an anachronism even during the 1930s, the engine included a number of otherwise advanced features. For instance, the valves were powered by dual overhead cams driven by power shafts at the rear of the engine. Exhaust ports were arranged to exit toward the middle of the engine, one cylinder bank being the mirror of the other, allowing the piping to be ganged below the engine nacelle.

Specifications (Isotta Fraschini Delta R.C.35 IS)

General characteristics

Type: 12-cylinder air-cooled 60 degree inverted vee
Bore: 132mm (5.2 in)
Stroke: 160 mm (6.4 in)
Displacement: 26.685 Litres (1,628 in³)
Length: 2000 mm (78.8 in.)
Width: 840 mm (33.07 in.)
Height: 883 mm (34.76 in.)
Dry weight: 510 kg (1,111 lb)

Components

Valvetrain: 2 Poppet valves per cylinder, sodium cooled exhaust valves, double overhead camshafts.
Supercharger: single stage single speed centrifugal type supercharger, gear ratio 9.8:1
Fuel system: 4*Isotta Fraschini downdraft carburetors
Fuel type: 80/87 octane gasoline
Oil system: dry sump, 2 scavenging, 1 pressure pump
Cooling system: Air-cooled

Performance

Power output: 770hp/2600rpm take off, 750hp/2600rpm/4000meters. Reduction gear ratio 0.64:1
Specific power: 0.75 hp/in³ (34.1 kW/L)
Compression ratio: 6.4:1
Specific fuel consumption: 270 grams/hp*hour maximum, 250 grams/hp*hour cruise (70%)
Power-to-weight ratio: 1.485 hp/kg (0.67 hp/lb)

Uses

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