The Jacobs R-755 (company designation L-4) is a seven-cylinder, air-cooled, radial engine for aircraft manufactured in the United States by the Jacobs Aircraft Engine Company.[1]

R-755 / L-4
Jacobs R-755 installed in a Boeing-Stearman Model 75
Type Radial engine
Manufacturer Jacobs Aircraft Engine Company
First run 1933

Design and development edit

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.

Variants edit

The base-line direct drive production version.[2]
300 hp variant.
Similar to A1 but with Scintilla magnetoes.
De-rated version of the R-755A to drive a fixed pitch airscrew.[2]
De-rated version of the R-755A to drive a variable or controllable pitch airscrew.[2]
Up-rated engine with reduction gearing.[2]
Developed to power the Jacobs Type 104 Gyrodyne.[2]

Applications edit

Engines on display edit

Specifications (R-755-A1) edit

Data from Jane's fighting aircraft of World War II,[4] Jane's all the World's Aircraft 1938[5]

General characteristics

  • Type: 7-cylinder air-cooled radial piston engine
  • Bore: 5.25 in (133 mm)
  • Stroke: 5 in (130 mm)
  • Displacement: 757 cu in (12.4 L)
  • Length: 37 in (940 mm) overall
  • Diameter: 43.5 in (1,100 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


See also edit

Comparable engines

Related lists

References edit

  1. ^ Gunston, Bill (1989). World encyclopaedia of aero engines (Fully rev. 2nd ed.). Wellingborough: P. Stephens. p. 85. ISBN 1-85260-163-9.
  2. ^ a b c d e Bridgman, Leonard (1955). Jane's all the World's Aircraft 1955-56. London: Jane's all the World's Aircraft Publishing Co. Ltd. p. 305.
  3. ^ Arkansas Air Museum - Jacobs R-755 Archived 2010-12-03 at the Wayback Machine Retrieved: 31 January 2009
  4. ^ Bridgman, Leonard, ed. (1989). Jane's fighting aircraft of World War II (1995 ed.). New York: Military Press. p. 305. ISBN 0-517-67964-7.
  5. ^ Grey, C.G.; Bridgman, Leonard, eds. (1938). Jane's all the World's Aircraft 1938. London: Sampson Low, Marston & company, ltd. pp. 86d–87d.

External links edit