The Jacobs R-755 (company designation L-4) was a seven-cylinder, air-cooled, radial engine for aircraft manufactured in the United States by the Jacobs Aircraft Engine Company.
Design and development
The R-755 was first run in 1933 and was still in production in the 1970s. With a bore and stroke of 5.25 in × 5 in (133 mm × 127 mm) the displacement was 757 cu in (12.4 L), power ranged from 200 hp to 350 hp (150 kW - 260 kW). The engine features steel cylinders with aluminum-alloy cylinder heads. An R-755E variant was developed for use in helicopters.
R-755A1
The base-line direct drive production version.
R-755A2
300 hp variant.
R-755B1
De-rated version of the R-755A to drive a fixed pitch airscrew.
R-755B2
De-rated version of the R-755A to drive a variable or controllable pitch airscrew.
R-755E
Up-rated engine with reduction gearing.
R-755EH
Developed to power the Jacobs Type 104 Gyrodyne.
Anahuac Tauro
Avro Cadet
Beechcraft Staggerwing
Boeing-Stearman Model 75
Cessna AT-17
Cessna 195
Funk F-23
Grumman Ag Cat
Kellett KD-1
Morane-Saulnier MS-505
Waco CG-15
Waco Custom Cabin series (YKC, YKC-S etc.)
Waco Standard Cabin series (YKS-6 etc.)
A preserved Jacobs R-755 is on display at the Arkansas Air Museum.
Data from Jane's
Type: 7-cylinder air-cooled radial piston engine
Bore: 5.25 in (133 mm)
Stroke: 5.0 in (127 mm)
Displacement: 757 cu in (12.4 L)
Length: 27.25 in (692 mm)
Diameter: 44 in (1,188 mm)
Dry weight: 505 lb (229 kg)
Valvetrain: 2 valves per cylinder, pushrod-actuated, Sodium cooled exhaust valves
Fuel system: Single Stromberg NA-R7A carburetor
Fuel type: 73 octane
Oil system: One pressure pump, two scavenge pumps
Cooling system: Air-cooled
Reduction gear: Direct drive, right hand tractor
Power output: 245 hp (183 kW) at 2,200 RPM at sea level
Specific power: 0.32 hp/cu-in (14.8 kW/L)
Power-to-weight ratio: 0.48 hp/lb (0.8 kW/kg)
