Pratt & Whitney Wasp

Wasp was the civilian name given to a family of air-cooled radial piston engines designed by Pratt & Whitney, and used in numerous American aircraft in the 1930s and 1940s.

Wasp series

*R-1340 Wasp
*R-985 Wasp Junior
*R-1830 Twin Wasp
*R-1535 Twin Wasp Junior
*R-2800 Double Wasp
*R-4360 Wasp Major

Note: the designations refer to the engine configurations as follows 'R' = Radial, followed by the displacement in cubic inches.

Background

At the end of the First World War, Pratt and Whitney (P&W) was a successful manufacturer of machine tools. The Aeronautical Division was founded in 1925 by Frederick Rentschler, who had previously been the President of Wright Aeronautical. He brought with him some of Wright’s best designers and the new team quickly came up with their first design, the immortal Wasp.

R-1340 Wasp

The military designation for this, the first version of the Wasp, was R-1340. The engine was built to a US Navy (USN) specification for a 400 hp engine weighing less than 650 lb. It had a conventional layout but introduced a significant innovation in the form of a forged aluminium crankcase. (Other US engines of this era used cast aluminium crankcases, although in the UK, Roy Fedden of Bristol Engines had used a forged design earlier in the Jupiter.) The R-1340 Wasp first ran in late 1925 and immediately developed 380 hp, rising to 425 hp by the third run. The USN ordered 200. By the beginning of World War 2, the R-1340 was rated at 600 hp take-off power at 2250 rpm for a weight of 684 lb. This version was widely used in the T-6 Texan/Harvard training aircraft, which was capable of 205 mph and a ceiling of 21,500 ft.

R-1830 Twin Wasp

Design of a more powerful twin-row engine started in May 1931 and this engine, designated the R-1830, was on test by the end of that year. This engine was known as the Twin Wasp. With two rows of seven cylinders, the design made use of large amounts of magnesium to save weight. Production was started in 1934. Early models were rated at 750 hp at 2300 rpm. This power was achieved with 80-octane fuel, but the introduction of 87-octane fuel raised the output to 800 hp at 2400 rpm. By the end of 1939, the –13 version was rated at 900 hp at 2700 rpm.

Through most of World War II, the P&W R-1830 Twin Wasp was rated at 1200 hp at 2800 rpm like the competing model of the Wright Cyclone series, the R-1820. Both these engine types powered Douglas DC-3 airliners but military versions of the DC-3 used R-1830s. Whereas the Cyclone was the engine of the Boeing B-17 Flying Fortress, the P&W R-1830 Twin Wasp powered America's other four-engine heavy bomber of the war, the Consolidated B-24 Liberator. The Liberator was the most produced U.S. airplane of that conflict. By war's end and during the postwar era, the R-1830 was typically rated at 1350 hp at 2800 rpm.

Approximately 178,000 examples of this legendary engine were eventually built, many under license. Although most examples had single-stage supercharging, some models had two-stage superchargers.

R-2800 Double Wasp

Developed from the Twin Wasp, the R-2800 Double Wasp was probably the most significant engine built by P&W during the Second World War. The Double Wasp had two rows of nine cylinders with a displacement of 2804 cu in (46L). Production started in 1940, rated at 1850 hp. (This was the first P&W engine to achieve 100 hp per cylinder.) Cylinders were manufactured from steel alloy forgings with aluminium cooling muffs shrunk on to the barrel. The engine was developed to the –C Series, rated at 2500 hp at 2800 rpm. This was boosted to 2800 hp with water/methanol injection, called Anti-Detonation Injection (ADI) in the US. This was the engine that powered dozens of aircraft, including the F4U Corsair, P-47 Thunderbolt, and the Grumman F6F Hellcat.

ee also

*Wright Cyclone - a comparable competing line of engines
* [http://www.pratt-whitney.com/pratt/web/indexbdcf.html] Pratt & Whitney -Classic Engines