Jacobs R-755

R-755 / L-4
Jacobs R-755 on display at the Evergreen Aviation & Space Museum
TypeRadial engine
ManufacturerJacobs Aircraft Engine Company
First run1933

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.

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.

It was the first modern radial engine to use a battery ignition.

Variants

L-4
Produced 225 horsepower (168 kW) at 2,000 rpm, dual battery
L-4M
Dual magneto
L-4MA
Dual magneto, for use in autogyros
L-4MA7
Similar to R-755A3, for use in autogyros
L-4MB
Rated at 225 hp (168 kW) at 2,000 rpm.
L-4MBB
Rated at 225 hp (168 kW) at 2,000 rpm.
R-755-7
Rated at 225 hp (168 kW) at 2,000 rpm.
R-755-9
Rated at 225 hp (168 kW) at 2,000 rpm. Military version of the L-4MB.
R-755-A
Replaced the R-755-9. Rated at 300 hp (220 kW) at 2,200 rpm. Increased compression ratio to 6:1.
R-755A1
The base-line direct drive production version. Equivalent to the L-4MB.
R-755A2
300 hp variant.[citation needed]
R-755A3
Similar to A1 but with Scintilla magnetoes.[citation needed] Equivalent to the L-4M.
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.

Applications

Waco YQC-6

Engines on display

Specifications (R-755-A1)

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

General characteristics

Components

Performance

See also

Comparable engines

Related lists

References

  1. ↑ Gunston, Bill (1989). World Encyclopedia of Aero Engines (2nd ed.). Cambridge: Patrick Stephens Limited. p. 85. ISBN 1-85260-163-9.
  2. ↑ The Aircraft Year Book for 1935 (PDF). New York: Aeronautical Chamber of Commerce of America. 1935. p. 268. Retrieved 9 October 2026.
  3. ↑ "225 Horsepower Jacobs L-4 Engine". Aero Digest. Vol. 24, no. 3. Aeronautical Digest Publishing Corporation. March 1934. p. 42. Retrieved 9 October 2026.
  4. 1 2 3 "Jacobs L-4". Aero Digest. Vol. 26, no. 4. Aeronautical Digest Publishing Corporation. April 1935. p. 110. Retrieved 9 October 2026.
  5. 1 2 3 4 Wilkinson, Paul H. (1945). Aircraft Engines of the World, 1945 (Revised ed.). New York: Paul H. Wilkinson. p. 101. Retrieved 13 October 2026.
  6. ↑ Mingos, Howard, ed. (1942). The Aircraft Year Book for 1942 (PDF). New York, New York: Aeronautical Chamber of Commerce of America. pp. 362–364. Retrieved 13 October 2026.
  7. 1 2 Aircraft Engine Listing. Washington, D.C.: Civil Aeronautics Administration, U.S. Department of Commerce. 15 May 1950. pp. 11, 13. Retrieved 13 October 2026.
  8. 1 2 Mingos, Howard, ed. (1946). The Aircraft Year Book for 1946 (PDF). New York, New York: Lancair Publishers. p. 392. Retrieved 13 October 2026.
  9. ↑ "Announcing the New Jacobs R-755-A". Aviation. Vol. 44, no. 11. McGraw-Hill Publishing Company. November 1945. p. 56. Retrieved 13 October 2026.
  10. 1 2 3 4 5 Bridgman, Leonard (1955). Jane's All the World's Aircraft, 1955-56. New York: McGraw-Hill Book Company. pp. 396–397. Retrieved 16 October 2026.
  11. ↑ "Jacobs R-755-9". Arkansas Air Museum. Archived from the original on 3 December 2010. Retrieved 9 October 2026.
  12. ↑ 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.
  13. ↑ Grey, C.G.; Bridgman, Leonard, eds. (1938). Jane's All the World's Aircraft, 1938. London: Sampson Low, Marston & Company Limited. pp. 86d–87d.