Wright R-760 Whirlwind
|Female mechanic working on the R-760 engine of a U.S. Navy N3N trainer in October 1942|
|Type||Air-cooled 7-cylinder radial piston engine|
|National origin||United States|
|Manufacturer||Wright Aeronautical Corporation
Naval Aircraft Factory (under license)
|Major applications||N3N Canary U.S. Navy primary trainer
Other U.S. Navy trainers
Various civil utility aircraft
|Number built||around 1400|
The Wright R-760 Whirlwind was a series of seven-cylinder air-cooled radial aircraft engines built by the Wright Aeronautical division of Curtiss-Wright. These engines had a displacement of 756 in³ (12.4 L) and power ratings of 225-350 hp (168-261 kW).
Design and development
Wright introduced the J-6 Whirlwind family in 1928 to replace the nine-cylinder R-790 series. The J-6 family included varieties with five, seven, and nine cylinders. The seven-cylinder version was originally known as the J-6 Whirlwind Seven, or J-6-7 for short. The U.S. government designated it as the R-760; Wright later adopted this and dropped the J-6 nomenclature.
Like all the members of the J-6 Whirlwind family, the R-760 had larger cylinders than the R-790. The piston stroke of 5.5 in (14.0 cm) was unchanged, but the cylinder bore was expanded to 5.0 in (12.7 cm) from the R-790's bore of 4.5 in (11.4 cm). While the R-790 was naturally aspirated, the R-760, like the other J-6 engines, had a gear-driven supercharger to boost its power output.
Over time, Wright refined the R-760, using suffix letters to indicate successive versions. The original R-760 (or J-6-7) was rated for 225 hp (168 kW), while the R-760E of 1931 could do 250 hp (186 kW) thanks to an improved cylinder head design. Wright later added another suffix to show different power levels. The R-760E-1, introduced the same year as the R-760E, had a takeoff power rating of 300 hp (224 kW) thanks to higher-compression pistons and a greater RPM limit. The even more powerful R-760E-2 of 1935 could reach 350 hp (261 kW) for takeoff due to increased supercharging and an even higher RPM limit. On the other hand, the R-760E-T, designed for trainer aircraft, had the R-760E-1's high-compression pistons, but the supercharger was removed, thus giving just 235 hp (175 kW).
The R-760 was a direct replacement for the R-790, with similar displacement and power. The U.S. Navy used it as the powerplant for several biplane primary trainers, including the Consolidated NY, the Curtiss N2C Fledgling, and the Naval Aircraft Factory N3N Canary. The last of these was produced in large numbers, with most of the engines built under license by the Naval Aircraft Factory. Trainers usually had the unsupercharged R-760E-T engine.
A variety of civil utility aircraft also used the R-760, including models built by Beechcraft, Cessna, Curtiss-Wright, Howard DGA-8, Stearman, Stinson, and Waco. These aircraft generally used the various supercharged versions of the R-760.
- J-6-7 (R-760): 225 hp (168 kW) at 2,000 RPM.
- R-760E: 250 hp (186 kW) at 2,000 RPM. Higher power from improved cylinder head.
- R-760E-1: 285 hp (213 kW) at 2,100 RPM, 300 hp (224 kW) at 2,250 RPM for takeoff. Higher compression ratio.
- R-760E-2: 320 hp (239 kW) at 2,200 RPM, 350 hp (261 kW) at 2,400 RPM for takeoff. Increased supercharging, slightly higher compression ratio.
- R-760E-T: 235 hp (175 kW) at 2,000 RPM. Unsupercharged version of R-760E-1 for trainer aircraft.
- R-760-2, -4, -8: 235 hp (175 kW) at 2,000 RPM. U.S. Navy versions of R-760E-T.
- Abrams P-1 Explorer
- Beechcraft Staggerwing
- Cessna DC-6B Scout
- Consolidated NY-3
- Curtiss N2C-2 Fledgling
- Fairchild Model 45
- Howard DGA-8 and DGA-15W
- Naval Aircraft Factory N3N Canary
- St. Louis YPT-15
- Stearman C3R Business Speedster
- Stinson Junior
- Stinson Reliant
- Waco CSO and CTO
- Waco CJC, CJC-S, DJC, DJC-S, and DJS
- Waco CUC, DQC-6, EQC-6, DGC-7 & 8, EGC-7 & 8
- Waco CRG
Engines on display
- Type: 7-cylinder supercharged air-cooled radial piston engine
- Bore: 5.0 in (127 mm)
- Stroke: 5.5 in (140 mm)
- Displacement: 756 in³ (12.4 L)
- Length: 42.44 in (107.8 cm)
- Diameter: 45.0 in (114.3 cm)
- Dry weight: 570 lb (259 kg)
- Valvetrain: 2 valves per cylinder, pushrod-actuated
- Supercharger: gear-driven, 9.17:1 impeller gear ratio
- Fuel type: 80 octane
- Reduction gear: Direct drive
- Power output: 320 hp (239 kW) at 2,200 RPM at sea level; 350 hp (261 kW) at 2,400 RPM for takeoff
- Specific power: 0.42 hp/cu-in (19.3 kW/L)
- Compression ratio: 6.3:1
- Power-to-weight ratio: 0.56 hp/lb (0.92 kW/kg)
|Engine||Power, continuous||Power, takeoff||Compression ratio||Supercharger gear ratio||Octane rating||Dry weight|
|R-760E||250 hp (186 kW) at 2,000 RPM||5.1:1||7.05:1||73||530 lb (240 kg)|
|R-760E-1||285 hp (213 kW) at 2,100 RPM||300 hp (224 kW) at 2,250 RPM||6.1:1||7.05:1||73||565 lb (256 kg)|
|R-760E-2||320 hp (239 kW) at 2,200 RPM||350 hp (261 kW) at 2,400 RPM||6.3:1||9.17:1||80||570 lb (259 kg)|
|R-760E-T||235 hp (175 kW) at 2,000 RPM||6.1:1||none||73||540 lb (245 kg)|
- Related development
- Comparable engines
- Related lists
- Gunston 1989, p.181.
- Curtiss-Wright (1940), p. 11
- Curtiss-Wright (1983), p. 1
- Curtiss-Wright (1940), p. 13
- FAA Type Certificate Data Sheet ATC 26
- Curtiss-Wright (1940), p. 14
- FAA Type Certificate Data Sheet TC 94
- Curtiss-Wright (1940), p. 17
- FAA Type Certificate Data Sheet TC 155
- Curtiss-Wright (1940), p. 16
- FAA Type Certificate Data Sheet TC 126
- Summary of Wright Engine Shipments: 1920 to 1963 (PDF), retrieved December 10, 2009. Transcribed from Wright Aeronautical documents by Robert J. Neal T; available from the Aircraft Engine Historical Society's reference page.
- FAA Type Certificate Data Sheet 5E-6
- AEHS List: Engines in Museums Worldwide, retrieved 2009-12-13.
- Aircraft Engines, retrieved 2009-12-13. This personal collection of museum aircraft engine photos includes a photo of the museum's R-760E-2 under the section for the Evergreen Aviation Museum.
- 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
- Curtiss-Wright (1940), Wright Engines - Past and Present (PDF), pp. 11, 13, 14, 16, 17, retrieved December 12, 2009. Available from the Aircraft Engine Historical Society's reference page.
- Curtiss-Wright (1983), Historical Engine Summary (Beginning 1930) (PDF), p. 1, retrieved December 12, 2009. Available from the Aircraft Engine Historical Society's reference page.
- R-760E: Type Certificate Data Sheet ATC 26, retrieved December 12, 2009.
- R-760E-1: Type Certificate Data Sheet TC 94, retrieved December 12, 2009.
- R-760E-2: Type Certificate Data Sheet TC 155, retrieved December 12, 2009.
- R-760E-T: Type Certificate Data Sheet TC 126, retrieved December 12, 2009.
- R-760-2, -4, -8: Type Certificate Data Sheet 5E-6, retrieved December 12, 2009.
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