Jacobs R-755

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

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.^[1]

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.

Variants

R-755A1: The base-line direct drive production version.^[2]
R-755A2: 300hp variant.
R-755B1: De-rated version of the R-755A to drive a fixed pitch airscrew.^[2]
R-755B2: De-rated version of the R-755A to drive a variable or controllable pitch airscrew.^[2]
R-755E: Up-rated engine with reduction gearing.^[2]
R-755EH: Developed to power the Jacobs Type 104 Gyrodyne.^[2]

Applications

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.)

Engines on display

A preserved Jacobs R-755 is on display at the Arkansas Air Museum.^[3]

Specifications (R-755-A1)

Data from Jane's^[4]

General characteristics

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)

Components

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

Performance

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)

References

Notes

↑ Gunston 1989, p.85.
↑ 2.0 2.1 2.2 2.3 2.4 Bridgman, Leonard (1955). Jane's all the World's Aircraft 1955-56. London: Jane's all the World's Aircraft Publishing Co. Ltd.
↑ Arkansas Air Museum - Jacobs R-755 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

Wikimedia Commons has media related to Jacobs R-755.

Jacobs aircraft engines

Radial engines	R-755/L-4 R-830/L-5 R-915/L-6

United States military piston aircraft engine designation system

H (four-bank H-configuration inline)	H-1640 XH-2240 H-2470 XH-2600 XH-3130 XH-3730 H-4070

I (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-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 XR-7755

V (upright-V inline)	V-720 V-770 V-1150 V-1237 V-1400 V-1410 V-1440 V-1460 V-1510 V-1560 V-1570 V-1650 (L) V-1650 (P) V-1710 V-1950 V-3420

W (three-bank W-configuration inline)	W-2779

See also: X-1800 US military gas turbine aeroengines Piston engine configurations

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