The Pratt & Whitney Hornet was a 9 cylinder, single-row, air-cooled radial engine. Horsepower ranged from 525 hp to 1,050 hp depending on the model and configuration. It was produced in two ranges:

• The R-1690 Hornet A.
• The R-1860 Hornet B.

The series began with the R-1690 Hornet A in 1926 following production of the air-cooled R-1340 Wasp. It was enlarged in 1929 as the R-1860 Hornet B, but it was not a commercial success. The Hornet competed with its own Pratt & Whitney R-1830 Twin Wasp and the Wright Cyclone R-1820. Even though the Hornet was cheaper and simpler than the Twin Wasp, the Twin Wasp was a much more powerful engine and the Hornet's larger diameter was its main drawback. In the end, the Twin Wasp became preferred, and the Hornet was dropped from production. ¹

Production was a modest 2,944 engines produced from 1926 to 1942 and it was used in a range of aircraft that included the Boeing B-9 and Boeing Model 299. By 1934, the Sikorsky S-42 was using four Hornets rated at 750 hp each.² The Hornet was also built under license in Italy as the Fiat A.59 and in Germany as the BMW 132 which powered the Junkers Ju-52.³