Jacobs R-755
# Jacobs R-755

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.

## Variants

### R-755A1

    The base-line direct drive production version.

### R-755A2

    300 hp variant.

### R-755A3

    Similar to A1 but with Scintilla magnetoes.

### 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

* Anahuac Tauro
* Beechcraft Model 17 Staggerwing (B17L, C17L, E17L)
* Boeing-Stearman PT-18 Kaydet
* Cessna AT-17 Bobcat
* Cessna 195
* Funk F-23
* Grumman G-164 Ag Cat
* Kellett KD-1
* Lascurain Aura
* Morane-Saulnier MS.505 Criquet
* Waco F series (YMF, YPF)
* Waco Custom Cabin series (YOC, YQC)
* Waco Standard Cabin series (YKC, YKC-S, YKS-6)
* Waco PG-3 (twin-engined powered version of Waco CG-15 glider, prototype only)

## Engines on display

* A preserved Jacobs R-755 is on display at the Arkansas Air Museum.
* A Jacobs R-755 is on public display at the Aerospace Museum of California
* A preserved Jacobs R-755 is on display at Super T Aviation Academy in Medicine Hat, Canada.
* A restored Jacobs R-755A is on display at the House of Whitley.

## Specifications (R-755-A1)

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

### 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)

### 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: 225 hp (168 kW) at 2,000 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)
