Jacobs R-915

R-915
R-915
Type	Radial engine
Manufacturer	Jacobs Aircraft Engine Company
Developed from	Jacobs R-755

The Jacobs R-915 or Jacobs L-6 is a seven-cylinder, air-cooled, radial engine for aircraft manufactured in the United States, production started in 1936.

Design and development

The R-915 was effectively an enlargement of the R-755 with strengthened stressed parts. With a bore and stroke of 5.5 in × 5.5 in (140 mm × 140 mm), for a displacement of 915 cu in (15 L). Take-off power was around 330 hp (250 kW). The engine features steel cylinders with aluminum-alloy cylinder heads.

Variants

L-6MB: Rated at 300 hp (220 kW) at 2,100 rpm.

R-915-7: Military version of the L-6MB.

R-915A1: Baseline variant; an enlarged R-755.^{[citation needed]} Equivalent to the L-6MB.
R-915A3: Similar to the A1 but with Scintilla magnetos.^{[citation needed]} Equivalent to the L-6M.
R-915A4: With a power take-off for autogyros.^{[citation needed]} Equivalent to the L-6MBA.

Applications

Engines on display

A preserved Jacobs R-915 is on display at the Nanton Lancaster Society.
A Jacobs L-6 is on display at the Canadian Museum of Flight

Specifications (R-915A1)

Data from Jane's

General characteristics

Type: 7-cylinder air-cooled radial piston engine
Bore: 5.5 in (140 mm)
Stroke: 5.5 in (140 mm)
Displacement: 915 cu in (15 L)
Length: 40 in (1,030 mm)
Diameter: 45.5 in (1,160 mm)
Dry weight: 555 lb (252 kg)

Components

Valvetrain: 2 valves per cylinder (pushrod-actuated); sodium cooled exhaust valves
Fuel system: Single Stromberg NA-R7A carburetor
Fuel type: 80 octane
Oil system: One pressure pump, two scavenge pumps
Cooling system: Air-cooled
Reduction gear: Direct drive, right hand tractor

Performance

Power output: 330 hp (246 kW) at 2,200 RPM at sea level
Specific power: 0.36 hp/cu-in (16.4 kW/L)
Compression ratio: 6:1
Power-to-weight ratio: 0.6 hp/lb (1 kW/kg)

References

Notes

↑ Gunston 1989, p.85.
↑ Wilkinson, Paul H. (1950). Aircraft engines of the World 1950 (8th ed.). London: Sir Isaac Pitman & Sons Ltd. p. 161.
1 2 3 4 Wilkinson, Paul H. (1945). Aircraft Engines of the World, 1945 (Revised ed.). New York: Paul H. Wilkinson. p. 103. Retrieved 13 October 2026.
↑ Mingos, Howard, ed. (1946). The Aircraft Year Book for 1946 (PDF). New York, New York: Lancair Publishers. p. 392. Retrieved 13 October 2026.
↑ Nanton Lancaster Society: Jacobs L-6 MB Archived 2015-09-23 at the Wayback Machine Retrieved: 23 July 2015
↑ The Canadian Museum of Flight - L-6 Retrieved: 31 January 2009
↑ Janes 1989, p.305.

Bibliography

Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9
Jane's Fighting Aircraft of World War II. London. Studio Editions Ltd, 1989. ISBN 0-517-67964-7

External links

Jacobs L-6 MB Archived 2015-09-23 at the Wayback Machine, Bomber Command Museum of Canada - Nanton Lancaster Society
FAA Type Data Certificate Sheet - R-915

[1] Gunston 1989, p.85.

[AEotW50-2] Wilkinson, Paul H. (1950). Aircraft engines of the World 1950 (8th ed.). London: Sir Isaac Pitman & Sons Ltd. p. 161.

[Wilkinson1945-3] 1 2 3 4 Wilkinson, Paul H. (1945). Aircraft Engines of the World, 1945 (Revised ed.). New York: Paul H. Wilkinson. p. 103. Retrieved 13 October 2026.

[4] Mingos, Howard, ed. (1946). The Aircraft Year Book for 1946 (PDF). New York, New York: Lancair Publishers. p. 392. Retrieved 13 October 2026.

[5] Nanton Lancaster Society: Jacobs L-6 MB Archived 2015-09-23 at the Wayback Machine Retrieved: 23 July 2015

[6] The Canadian Museum of Flight - L-6 Retrieved: 31 January 2009

[7] Janes 1989, p.305.

v t e United States military piston aircraft engine designation system
H (four-bank H-configuration inline)	H-1640 XH-2240 XH-2470 XH-2600 XH-3130 XH-3730 H-4070
IV (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-1740 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 R-7755
V (upright-V inline)	V-720 V-1150 V-1237 V-1400 V-1440 V-1460 V-1510 V-1560 V-1570 V-1650 (P) V-1710 V-1950 V-3420
V (inverted-V inline)	V-770 V-1650 (L)
VG (inverted-V inline)	VG-1410
W (three-bank W-configuration inline)	W-2779
See also: X-1800 US military gas turbine aeroengines Piston engine configurations