P.XII
The Piaggio P.XII displayed at Museo dell'Aria e dello Spazio in San Pelagio, Due Carrare, Province of Padua
Type	Radial engine
National origin	Italy
Manufacturer	Piaggio
Major applications	Piaggio P.108 CANT Z.1018

The Piaggio P.XII is an Italian 18-cylinder radial aircraft engine developed in the 1930s by Rinaldo Piaggio S.p.A. The P.XII was two Piaggio P.X engines in tandem, which were versions of the French Gnome-Rhône 9K Mistral made under license, themselves being much modified Gnome-Rhône 9A - a license-built Bristol Jupiter.

The engine was used in some Italian aircraft from 1940 until the end of World War II, especially the Piaggio P.108. An up-rated version was tested as the Piaggio P.XXII.

Variants

Variants of the Piaggio P.XII include: (R - Riduttore - reduction gearing and C - Compressore - supercharged)

P.XII R.C.35

(geared, rated altitude 3,500 m (11,500 ft))

P.XII R.C.40

(geared, rated altitude 4,000 m (13,000 ft))

P.XII R.C.l00/2v

(geared, rated altitude 10,000 m (33,000 ft))

P.XV R.C.60/2v

(geared, rated altitude 6,000 m (20,000 ft))

P.XXII R.C.35D

Higher rating with slightly higher displacement than the P.XII series engines. (geared, rated altitude 3,500 m (11,500 ft))

P.XXII R.C.35R

Same as P.XXII R.C.35D, but propeller rotates in opposite direction

P.XXII R.C.60

(geared, rated altitude 6,000 m (20,000 ft))

Applications

• CANT Z.1015
• CANT Z.1018
• CANT Z.511
• Caproni Ca.169
• Piaggio P.108
• Savoia-Marchetti SM.84ter
• Savoia-Marchetti SM.89

Specifications (P.XII R.C.35)

Data from Aircraft Engines of the World 1945.^[1]

General characteristics

• Type: 18-cylinder air-cooled radial engine
• Bore: 146 mm (5.75 in)
• Stroke: 176 mm (6.93 in)
• Displacement: 53 L (3,200 cu in)
• Length: 1,700 mm (66.93 in)
• Diameter: 1,410 mm (55.51 in)
• Dry weight: 850 kg (1,874 lb)
• Frontal Area: 1.56 m² (16.8 sq ft)

Components

• Valvetrain: 2 x overhead valves per cylinder operated by rockers and pushrods
• Supercharger: Centrifugal compressor, geared to 7.81:1
• Fuel system: Single Piaggio downdraught carburettor with automatic boost and mixture control
• Fuel type: 87 octane
• Oil system: Pressure fed at 482.6 kPa (70 psi), dry sump
• Cooling system: Air
• Reduction gear: Epicyclic reduction gear, gear ratio: 0.62:1
• Starter: Garelli compressed air starter
• Ignition: 2x Marelli AQ18 magnetos, 2 x spark plugs per cylinder fed by a shielded ignition harness.

Performance

• Power output: Take-off: 1,500 hp (1,100 kW) at 2,100rpm
• Military: 1,350 hp (1,010 kW) at 2,100rpm at 3,500 m (11,500 ft)
• Cruising: 1,000 hp (750 kW) at 1,700rpm at 3,500 m (11,500 ft)
• Specific power: 22.29 kW/L (0.49 hp/cu in)
• Compression ratio: 6.5:1
• Specific fuel consumption: 0.2795 kg/kW/hr (0.46 lb/hp/hr)
• Oil consumption: 0.0134 kg/k/w/hr (0.022 lb/hp/hr)
• Power-to-weight ratio: 1.324 kW/kg (0.8 hp/lb)