gear gear gear

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Franklin 6V4
1946 - 1970



The Franklin 6V4 is an air cooled 6-cylinder boxer engine, built by Aircooled Motors Inc., in Syracuse in the state of New York. It It has been mainly used in the small helicopter Bell 47.

Technical specifications

ManufacturerAircooled Motors, Syracuse, New York, USA, from 1946 to 1970
Descriptionaircraft engine with 6-opposed cylinders (boxer-type), aluminium alloy crankcase composed of two parts with 5 main bearings, cylinders with integrated aluminium alloy head and internal hot-forced steel liners
Stroke89 mm
Bore114 mm
Displacement5.5 litri
Compression ratio8.5
Power200 hp at 3100 rpm
Valvetrain system2 overhead valves per cylinder, operated by pushrods and rocker arms
Fuel feeding systemwith one single-barrel Marvel Schebler MA4-5 gasoline carburetor
Ignition systemwith two spark plugs per cylinder fed by two magneto distributors Scintilla S6RN-23
Cooling systemair-fed
Lubrication systemforced by a gear pump
Weight135 kg (dry)
Mass-to-power ratio0.76 kg/hp
Specific power36.4 hp/litre
Propeller speed ratio9:1 by means of an epicyclic gear train


Augusta Bell 47 helicopter, model G, E, HTL-3 (millitary) and H1

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Testi e immagini di Giuseppe Genchi
Sito realizzato da Pasquale Pillitteri