Franklin O-335

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).

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

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 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
178 hp (133 kW) at 3,000 rpm
6V4-200
200 hp (149 kW) at 3,100 rpm
6VS-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 (950.0 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) 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)

See also

Comparable engines

Related lists

Notes
  1. 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.
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