Franklin O 335

Design and development

These engines were commonly vertically mounted and used to power many early helicopters in the United States. They were closely related to the 2A4 and 4A4 2- and 4-cylinder engines. In various subtypes, the 6A4 remained in continuous production from 1945 to the time Franklin's United States operations ceased in 1975, with versions continuing in Polish production into the 1990s.

In 1947 this engine was modified into a water-cooled version by the Tucker Car Corporation for use in the 1948 Tucker Sedan. Tucker liked the engine so much that he purchased the Aircooled Motors/Franklin Engine Company, and it remained under the ownership of the Tucker family until 1961.

Variants

O-335-1

Military designation of vertical installation model for helicopters

O-335-3

Similar to -1 but changes in starter installation

6A-335

180 hp (134.2 kW) at 2,800rpm

6AL-335

150 hp (111.9 kW) at 2,600 rpm

6A4-125

125 hp (93.2 kW) at 2,200rpm

6A4-130

130 hp (96.9 kW) at 2,200rpm

6A4-135

135 hp (100.7 kW) at 2,450rpm

6A4-140

140 hp (104.4 kW) at 2,375rpm

6A4-145

145 hp (108.1 kW) at 2,600rpm

6A4-150

150 hp (111.9 kW) at 2,600rpm

6A4-165

165 hp (123.0 kW) at 2,800rpm

6A4-200

200 hp (149.1 kW) at 3,100rpm

6AG-335

220 hp (164.1 kW) at 3,400rpm

6AG4-185

185 hp (138.0 kW) at 3,100rpm

6AGS-335

260 hp (193.9 kW) at 3,400rpm

6AS-335

240 hp (179.0 kW) at 3,200rpm

6V-335-B

210 hp (156.6 kW) at 3,100rpm

6V-335-A1A

200 hp (149.1 kW) at 3,100rpm

6V-335-A1B

200 hp (149.1 kW) at 3,100rpm

6V4-165

165 hp (123.0 kW)

6V4-178

178 hp (132.7 kW) at 3,000rpm

6V4-200

200 hp (149.1 kW) at 3,100rpm

6VS-335

225 hp (167.8 kW) at 3,200rpm

Specifications (6AL-335 / 6A4-150-B3)

Data from

General characteristics

Type: 6-cylinder air-cooled horizontally opposed direct drive supercharged aircraft piston engine

Bore: 4.5 in (114.3 mm)

Stroke: 3.5 in (88.9 mm)

Displacement: 335 cu in (5.49 l)

Length: 37.4 in (950.0 mm)

Width: 30.8 in (782.3 mm)

Height: 21.6 in (548.6 mm)

Dry weight: 307 lb (139.3 kg)

Components

Valvetrain: OHV, 1x inlet valve, 1x exhaust valve operated by pushrods

Supercharger: mechanically driven supercharger

Fuel system: 1x Marvel-Schebler MA-3SPA updraught carburettor

Fuel type: 80 Octane gasoline

Oil system: 80 S.U. secs (15.6 cSt) grade pressure fed at 40 psi (275,790 Pa), wet sump

Cooling system: Air-cooled

Delco-Remy direct cranking electric starter motor

Performance

Power output:

(Take-off): 150 hp (111.9 kW) at 2,600 rpm for take-off

(Normal): 150 hp (111.9 kW) at 2,600 rpm at sea level

(Cruising): 112 hp (83.5 kW) at 2,350 rpm at sea level

Specific power: 0.45 hp/(cu in) (20.35 kW/l)

Compression ratio: 7:1

Specific fuel consumption: 0.51 lb/(hp h) (0.311 kg/(kW h), 229.5 US gal/(hp h)) cruising

Oil consumption: 0.01 lb/(hp h) (0.006 kg/(kW h), 4.5 US gal/(hp h)) cruising

Power-to-weight ratio: 0.488 hp/lb (0.8 kW/kg)

B.m.e.p.: 137 psi (945 kPa)