R
Preserved Pobjoy R at the Shuttleworth Collection
Type	Piston radial aero-engine
Manufacturer	Pobjoy Airmotors
First run	1926
Major applications	BA Swallow Comper Swift

The Pobjoy R is a British seven-cylinder air-cooled radial aircraft engine designed and built by Pobjoy Airmotors.^[1] Introduced in 1926, it was a popular engine for ultralight and small aircraft in the 1930s. A notable feature of the Pobjoy R was the propeller reduction gear which allowed the small engine to operate at more desirable higher speeds.

The engine was license produced in Czechoslovakia by Walter Aircraft Engines as the Walter Mira.^[2]

Variants

Walter Mira R

License produced version of Pobjoy R.

Walter Mira I-R

Renaming of Mira R.

Walter Mira II-R

Developed version of the Mira R producing 95 hp (70 kW).

Applications

Walter Mira

• Letov Š-39
• Letov Š-139

Engines on display

A preserved Pobjoy R engine is on display at the Shuttleworth Collection, Old Warden, Bedfordshire.^{[citation needed]}

Two Pobjoy R engines, one installed in the remains of Comper Swift (R222 / LV-FBA) will be soon on display at the National Aviation Museum in Buenos Aires Province, Argentina.^{[citation needed]}

Specifications (Pobjoy R)

Data from Lumsden.

General characteristics

• Type: 7-cylinder air-cooled, radial, left-hand tractor
• Bore: 3.03 in (77 mm)
• Stroke: 3.43 in (87 mm)
• Displacement: 173.05 cu in (2.84 L)
• Diameter: 25.5 in (647.7 mm)
• Dry weight: 135 lb

Components

• Oil system: Dry sump
• Cooling system: Air-cooled

Performance

• Power output: 85 hp
• Specific power: 0.5 hp/cu in
• Fuel consumption: 4.9 imp. gallons per hour
• Power-to-weight ratio: 0.63 hp/lb