Pratt & Whitney R-1860

The Pratt & Whitney R-1860 Hornet B was a relatively uncommon aircraft engine. It was a development of Pratt & Whitney's earlier R-1690 Hornet and was basically similar, but enlarged in capacity from 1,690 to 1860 cuin. Bore was increased by 1/8" and the stroke by 3/8". Both engines were air-cooled radial engines, with a single row of nine cylinders.

Design and development
The cylinder and valve design was typical for Pratt & Whitney, a simple design with two large valves driven by pushrods. The enlarged engine was designed by George Willgoos and was first available in 1929.

The Hornet series of engines was similar to the Wasp, but larger. In both series a nine-cylinder single-row engine was later supplemented by an enlarged fourteen cylinder engine, with two rows of the same cylinders, but reduced in number to seven.

Two of these engines, the enlarged single-row Hornet B described here and the R-1830 Twin Wasp, were of near-identical capacity (1860 vs. 1830), although the fourteen-cylinder Twin Wasp was more complex and costly than the nine-cylinder, single-row Hornet B. The Twin Wasp was by far the more powerful engine though, even in its early versions it produced 800 hp to the Hornet B's 575 bhp. A further advantage was the reduced diameter of the Wasp: 48 inches compared to 57. This reduced drag, and the very large diameter of the Hornet would also have been a serious drawback for visibility if used in a small single-engined aircraft.

Although a technically competent design, the enlarged Hornet B engine was not a commercial success. Customers preferred to buy the R-1830 Twin Wasp instead, which in time became the most numerous aircraft engine ever produced.

Applications

 * Sikorsky S-40
 * Sikorsky S-41B
 * Keystone XLB-12 (evaluation only)
 * Keystone B-4A
 * Consolidated Fleetster