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 was unchanged, but the cylinder bore was expanded to 5.0 in from the R-790's bore of 4.5 in. 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 was rated for 225 hp, while the R-760E of 1931 could do 250 hp 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 thanks to higher-compression pistons and a greater RPM limit. The even more powerful R-760E-2 of 1935 could reach 350 hp 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.
Operational history
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. Production of the R-760 continued until 1945, with about 1400 examples being built by Wright, and more under licence by foreign manufacturers such as Fábrica Nacional de Motores in Brazil.
Variants
J-6-7 : 225 hp at 2,000 RPM.
R-760E: 250 hp at 2,000 RPM. Higher power from improved cylinder head.
R-760E-1: 285 hp at 2,100 RPM, 300 hp at 2,250 RPM for takeoff. Higher compression ratio.
R-760E-2: 320 hp at 2,200 RPM, 350 hp at 2,400 RPM for takeoff. Increased supercharging, slightly higher compression ratio.
R-760E-T: 235 hp at 2,000 RPM. Naturally aspirated version of R-760E-1 for trainer aircraft.
R-760-2, -4, -8: 235 hp at 2,000 RPM. U.S. Navy versions of R-760E-T.
