As well as producing aircraft and building Hispano-Suiza and Lorraine aero-engines under licence, Avia also designed and built their own radial engines. One of Avia's own designs, the 1930s Avia Rk.12 was a 7-cylinder supercharged radial engine with a rated output of 150 kW (200 hp), built in Czechoslovakia.
It was a conventional air-cooled radial: nitrided steel barrels with integral fins were screwed into heat treated Y alloy heads. The pistons were also of heat treated Y alloy. The crankcase was cast from aluminium alloy, with some minor parts using magnesium alloy. The single throw two piece crankshaft was linked to the pistons with an I-section Y alloy master rod, with a single piece big end, which carried the other six piston rods.
The Rk.12 was used in the Avia 51.
Type: 7-cylinder air-cooled radial
Bore: 130 mm (5.12 in)
Stroke: 130 mm (5.12 in)
Displacement: 12.08 L (737 cu in)
Length: 1,047.5 mm (41.24 in)
Diameter: 1,110 mm (43.7 in
Dry weight: dry, with ancillaries, without propeller hub 215.5 kg (475 lb)
Valvetrain: one inlet and one exhaust valve per cylinder, operated by push rods via rocker gear. Six cam push rod disc drive.
Supercharger: impeller drive ratio 10.7:1
Fuel system: single barrel Zenith 70P or Stromberg NAR68 carburettor
Ignition system: Scintilla magnetos, automatic advance
Fuel type: petrol, 74 Octane
Oil system: dry sump, with one pressure and one scavenging pump
Cooling system: air-cooled
Reduction gear: direct drive
Power output: rated, maintained to 3,000 m (9,840 ft), at 2,200 rpm: 150 kW (200 hp)
Power output: maximum continuous 195 kW (260 hp)
Power output: take-off 210 kW (280 hp)
Compression ratio: 5.3:1
Fuel consumption: 62 L/hr (13.64 Imp gal/h, 16.4 US gal/h)
Oil consumption: at cruising speed, 2 kg/h (4.4 lbs/h)