Pratt & Whitney R-1535 Twin Wasp Junior

The Pratt & Whitney R-1535 Twin Wasp Junior is an American aircraft engine developed in the 1930s. The engine was introduced in 1932 as a 14-cylinder version of the 9-cylinder R-985, and was a two-row, air-cooled radial design. Displacement was 1,535 cu in (25.2 L); bore and stroke were both 5+3⁄16 in (132 mm).^[1]

R-1535 Twin Wasp Junior
Pratt & Whitney Twin Wasp Junior, at the National Museum of Naval Aviation, Pensacola, Florida
Type	Radial engine
National origin	United States
Manufacturer	Pratt & Whitney
First run	1932
Major applications	Bristol Bolingbroke Curtiss SBC-3 Helldiver Hughes H-1 Racer Vought SB2U Vindicator
Developed from	Pratt & Whitney R-985 Wasp Junior

Variants

• R-1535-11 - 750 hp (560 kW)
• R-1535-13 - 750 hp (560 kW), 825 hp (615 kW)
• R-1535-44 - 625 hp (466 kW)
• R-1535-72 - 650 hp (480 kW)
• R-1535-94 - 825 hp (615 kW)
• R-1535-96 - 825 hp (615 kW)
• R-1535-98 - 700 hp (520 kW)
• R-1535-SB4-G - 825 hp (615 kW)

Applications

• Bellanca 28-70
• Boeing XF6B
• Breguet 695
• Bristol Fairchild Bolingbroke (Canadian licence-built version of the Blenheim)
• Canadian Car and Foundry FDB-1
• Consolidated XB2Y
• Curtiss SBC-3 Helldiver
• Douglas O-46
• Fokker G.I (G.I The Wasp)
• Fokker D.XXI (Finnish licence-built series 4 and 5)
• Great Lakes BG
• Grumman F2F
• Grumman F3F-1
• Grumman XJF-1 Duck (prototype only)
• Grumman XSBF
• Grumman XSF-2
• Hughes H-1 Racer
• Miles Master
• Northrop A-17
• Northrop BT
• Northrop XFT-2
• Vought SBU Corsair
• Vought SB2U Vindicator
• Vought V-141
• Vought XF3U
• Vought XO4U-2

Engines on display

• There is a R-1535-96 on display at the New England Air Museum, Bradley International Airport, Windsor Locks, CT.^[2]
• There is an R-1535 on display at the San Diego Air and Space Museum. It is now being installed in the museum's Hughes H-1 Racer reproduction project.^{[citation needed]}

Specifications (R-1535-SB4-G)

Data from ^[3]

General characteristics

• Type: Fourteen-cylinder two-row supercharged air-cooled radial engine
• Bore: 5+3⁄16 in (131.8 mm)
• Stroke: 5+3⁄16 in (131.8 mm)
• Displacement: 1,534.9 cu in (25.153 L)
• Length: 53.27 in (1,353 mm)
• Diameter: 44.13 in (1,121 mm)
• Dry weight: 1,087 lb (493 kg)

Components

• Valvetrain: Two overhead valves per cylinder
• Supercharger: Single-speed centrifugal type supercharger, 11:1 step-up
• Fuel system: Two-barrel Stromberg carburetor
• Fuel type: 87 octane rating gasoline
• Cooling system: Air-cooled
• Reduction gear: Epicyclic gearing, 0.75:1

Performance

• Power output: 825 hp (615 kW) at 2,625 rpm for takeoff
• Specific power: 0.54 hp/cu in (24.57 kW/L)
• Compression ratio: 6.75:1
• Specific fuel consumption: 0.49 lb/(hp•h) (295 g/(kW•h))
• Oil consumption: 0.39 oz/(hp•h) (15 g/(kW•h))
• Power-to-weight ratio: 0.76 hp/lb (1.25 kW/kg)

See also

• Pratt & Whitney Wasp series

Related development

• Pratt & Whitney R-985 Wasp Junior
• Pratt & Whitney R-1340 Wasp
• Pratt & Whitney R-1830 Twin Wasp
• Pratt & Whitney R-2800 Double Wasp
• Pratt & Whitney R-4360 Wasp Major

Comparable engines

• Bristol Taurus

Related lists

• List of aircraft engines