Franklin O-335

O-335/6A/6V
Type	Flat-6
National origin	United States
Manufacturer	Franklin Engine Company
Major applications	Bell 47, Hiller OH-23 Raven

The Franklin O-335 (company designations variations on 6A and 6V) was an American air-cooled aircraft engine of the 1940s. The engine was of six-cylinder, horizontally-opposed layout and displaced 335 cu in (5.5 L). The power output of later variants was 225 hp (168 kW).

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 :175 hp (130 kW)
O-335-3: Similar to -1 but changes in starter installation
O-335-5: 200 hp (149 kW)
O-335-5B: 200 hp (149 kW)
6A-335: 180 hp (134 kW) at 2,800 rpm
6AL-335: 150 hp (112 kW) at 2,600 rpm
6A4-125: 125 hp (93 kW) at 2,200 rpm
6A4-130: 130 hp (97 kW) at 2,200 rpm
6A4-135: 135 hp (101 kW) at 2,450 rpm
6A4-140: 140 hp (104 kW) at 2,375 rpm
6A4-145: 145 hp (108 kW) at 2,600 rpm
6A4-150: 150 hp (112 kW) at 2,600 rpm
6A4-165: 165 hp (123 kW) at 2,800 rpm
6A4-200: 200 hp (149 kW) at 3,100 rpm
6AG-335: 220 hp (164 kW) at 3,400 rpm
6AG4-185: 185 hp (138 kW) at 3,100 rpm
6AGS-335: 260 hp (194 kW) at 3,400 rpm
6AS-335: 240 hp (179 kW) at 3,200 rpm
6V-335-B: 210 hp (157 kW) at 3,100 rpm
6V-335-A1A: 200 hp (149 kW) at 3,100 rpm
6V-335-A1B: 200 hp (149 kW) at 3,100 rpm
6V4-165: 165 hp (123 kW)
6V4-178-B32: 178 hp (133 kW) at 3,000 rpm
6V4-200-C32: 200 hp (149 kW) at 3,100 rpm
6VS-O-335: 225 hp (168 kW) at 3,200 rpm

Applications

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

Franklin O-335/6AC Engine.

Data from Wilkinson ^[1]

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 mm)
Width: 30.8 in (780 mm)
Height: 21.6 in (550 mm)
Dry weight: 307 lb (139 kg)

Components

Valvetrain: OHV, 1 x inlet valve, 1 x 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 (3 bar), wet sump
Cooling system: Air-cooled
Delco-Remy direct cranking electric starter motor

Performance

Power output:
(Take-off): 150 hp (110 kW) at 2,600 rpm
(Normal): 150 hp (110 kW) at 2,600 rpm at sea level
(Cruising): 112 hp (84 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) cruising, 4.5 US gal/(hp h)) cruising
Oil consumption: 0.01 lb/(hp h) (0.006 kg/(kW h)
Power-to-weight ratio: 0.488 hp/lb (0.8 kW/kg)
B.m.e.p.: 137 psi (945 kPa)

Notes

^ Wilkinson, Paul H. (1945). Aircraft Engines of the world 1945. New York: Paul H. Wilkinson. pp. 80–81.

References

Gunston, Bill. (1986) World Encyclopedia of Aero Engines. Patrick Stephens: Wellingborough. p. 57
Erickson, Jack. Horizontally Opposed Piston Aero Engines
Wilkinson, Paul H. (1945). Aircraft Engines of the world 1945. New York: Paul H. Wilkinson. pp. 80–81.
US Department of Transportation Federal Aviation Administration Type Certificate Data Sheet E-238 Revision 12, December 8, 1994.

[Wilkinson-1] Wilkinson, Paul H. (1945). Aircraft Engines of the world 1945. New York: Paul H. Wilkinson. pp. 80–81.

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