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-755A1The base-line direct drive production version.
R-755A2300 hp variant.
R-755B1De-rated version of the R-755A to drive a fixed pitch airscrew.
R-755B2De-rated version of the R-755A to drive a variable or controllable pitch airscrew.
R-755EUp-rated engine with reduction gearing.
R-755EHDeveloped to power the Jacobs Type 104 Gyrodyne.
Anahuac TauroAvro CadetBeechcraft StaggerwingBoeing-Stearman Model 75Cessna AT-17Cessna 195Funk F-23Grumman Ag CatKellett KD-1Morane-Saulnier MS-505Waco CG-15Waco 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 engineBore: 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 valvesFuel system: Single Stromberg NA-R7A carburetorFuel type: 73 octaneOil system: One pressure pump, two scavenge pumpsCooling system: Air-cooledReduction gear: Direct drive, right hand tractorPower output: 245 hp (183 kW) at 2,200 RPM at sea levelSpecific power: 0.32 hp/cu-in (14.8 kW/L)Power-to-weight ratio: 0.48 hp/lb (0.8 kW/kg)