Franklin O-335

O-335/6AC

Type	Flat-6
National origin	United States
Manufacturer	Franklin Engine Company
Major applications	Bell 47

The Franklin O-335 (Company designations variations on 6A4) was a series of air-cooled aircraft engines of flat-six configuration.

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

Applications

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

Franklin O-335/6AC Engine.

Data from ^[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 cs) 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/in³ (20.35 kW/l)
Compression ratio: 7:1
Specific fuel consumption: 0.51 lb/hp/hr (0.311 kg/kW/hr, 229.5 US.gal/hp/hr) cruising
Oil consumption: 0.01 lb/hp/hr (0.006 kg/kW/hr, 4.5 US.gal/hp/hr) cruising
Power-to-weight ratio: 0.488hp/lb (0.8kW/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.

Franklin aircraft engines

Horizontally opposed engines

United States military piston aircraft engine designation system

H (four-bank H-configuration inline)	H-1640 XH-2240 H-2470 XH-2600 XH-3130 XH-3730 H-4070

I (inverted-V inline)	IV-1430 IV-2040 IV-2220

L (single-bank inline)	L-330 L-365 L-375 L-390 L-410 L-440 L-510 L-825

O (opposed)	O-15 O-40 O-45 O-90 O-100 O-145 O-150 O-170 O-175 O-180 O-190 O-200 (C) O-200 (F) O-205 O-235 O-290 O-300 O-335 O-360 (C) O-360 (L) O-405 O-425 O-435 O-470 O-480 O-520 O-540 (F) O-540 (L) O-550 O-580 O-805 O-1230

R (radial)	R-250 R-265 R-270 R-370 (LB) R-370 (K) R-420 R-440 R-500 R-540 (W) R-540 (K) R-545 R-550 R-600 R-670 R-680 R-720 R-755 R-760 R-790 R-830 R-915 R-975 DR-980 R-985 R-1044 R-1300 R-1340 R-1454 R-1510 R-1535 R-1640 R-1670 R-1690 R-1750 R-1820 R-1830 R-1860 R-2000 R-2060 R-2160 R-2180 R-2600 R-2800 R-3350 R-4090 R-4360 XR-7755

V (upright-V inline)	V-720 V-770 V-1150 V-1237 V-1400 V-1410 V-1440 V-1460 V-1510 V-1560 V-1570 V-1650 (L) V-1650 (P) V-1710 V-1950 V-3420

W (three-bank W-configuration inline)	W-2779

See also: X-1800 US military gas turbine aeroengines Piston engine configurations

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