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.^[1]

Design and development

The R-915 was effectively an enlargement of the R-755 with strengthened stressed parts.^[2] 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

R-915A1

Baseline variant; an enlarged R-755

R-915A3

Similar to the A1 but with Scintilla magnetoes

R-915A4

With a power take-off for autogyros

Applications

• Avro Anson Mk II and Mk III
• Beechcraft Model 18D
• Beechcraft F-17D Staggerwing
• Fleet 50
• Howard DGA-15J
• Kellett KD-1
• Waco AQC, AGC, ARE, AVN

Engines on display

• A preserved Jacobs R-915 is on display at the Nanton Lancaster Society.^[3]
• A Jacobs L-6 is on display at the Canadian Museum of Flight^[4]

Specifications (R-915A1)

Data from Jane's^[5]

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)