The Delta was a 12-cylinder inverted-V aircraft engine built by Isotta Fraschini prior to and during World War II.
Design and development
The Delta 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.
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.
Isotta Fraschini Delta R.C.21/60
Isotta Fraschini Delta R.C.35
Isotta Fraschini Delta R.C.35I
Isotta Fraschini Delta R.C.35IS
Isotta Fraschini Delta III R.C.40
Isotta Fraschini Delta IV R.C.17/50
Ambrosini SAI.107
Ambrosini SAI.207 prototype
Ambrosini SAI.403 prototype
CANT Z.515
Caproni Ca.313
Caproni Ca.314
Caproni Ca.331
Caudron C.714 (C.760) prototype
Henschel Hs 129 prototype
Reggiane Re.2001 prototype
Savoia-Marchetti SM.86
Data from
Type: 12-cylinder air-cooled 60 degree inverted vee
Bore: 132 mm (5.197 in)
Stroke: 160/165 mm (6.299/6.496 in), with main and articulated rod
Displacement: 26.685 Litres (1,628.44 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)
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 petrol (aviation gasoline)
Oil system: dry sump, 2 scavenging, 1 pressure pump
Cooling system: Air-cooled
Power output: 770hp/2600rpm take off, 750hp/2600rpm/4000meters. Reduction gear ratio 0.64:1
Specific power: 21.5 kW/L (0.47 hp/in³)
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)
