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The Pratt & Whitney R-2800 Double Wasp is an American twin-row, 18-cylinder, air-cooled radial aircraft engine with a displacement of , and is part of the long-lived Wasp family of engines.

The R-2800 saw widespread use in many important American aircraft during and after World War II. During the war years, Pratt & Whitney continued to develop new ideas to upgrade the engine, including water injection for takeoff in cargo and passenger planes and to give emergency power in combat.

Design and development

First run in 1937, near the time that the larger competing 18-cylinder Wright Duplex-Cyclone's development had been started in May of that year, the displacement R-2800 was first flown by 1940, one year before the Duplex-Cyclone. The Double Wasp was more powerful than the world's only other modern 18-cylinder engine, the Gnome-Rhône 18L of .

The Double Wasp was much smaller in displacement than either of the other 18-cylinder designs, and heat dissipation was a greater problem. To enable more efficient cooling, the usual practice of casting or forging the cylinder head cooling fins that had been effective enough for other engine designs was discarded, and instead, much thinner and closer-pitched cooling fins were machined from the solid metal of the cylinder-head forging. The fins were all cut at the same time by a gang of milling saws, automatically guided as it fed across the head in such a way that the bottom of the grooves rose and fell to make the roots of the fins follow the contour of the head, with the elaborate process substantially increasing the surface area of the fins.

thumb|Cutaway of a Pratt & Whitney R-2800 Double Wasp

The twin distributors on the Double Wasp were prominently mounted on the upper surface of the forward gear reduction housing - with one of the pair of magnetos mounted between them on most models - and almost always prominently visible within a cowling, with the conduits for the spark plug wires emerging from the distributors' cases either directly forward or directly behind them, or on the later C-series R-2800s with the two-piece gear reduction housings, on the "outboard" sides of the distributor casings.

When the R-2800 was introduced in 1939, it was capable of producing , for a specific power value of . The design of conventional air-cooled radial engines had become so scientific and systematic by then that the Double Wasp was introduced with a smaller incremental power increase than was typical of earlier engines. Nevertheless, in 1941 the power output of production models increased to , and to late in the war. Even more was coaxed from experimental models, with fan-cooled subtypes like the R-2800-57 producing , but in general the R-2800 was a rather highly developed powerplant right from the beginning. in its XR-2800-4 prototype version on May 29, 1940, and the first single-engine American fighter plane to exceed in level flight during October 1940. The R-2800 also powered the Corsair's naval rival, the Grumman F6F Hellcat, the US Army Air Forces' Republic P-47 Thunderbolt (which unusually, for single-engined aircraft, used a General Electric turbocharger<!--some Fw 190 variants used Turbochargers as well-->), the twin-engine Martin B-26 Marauder and Douglas A-26 Invader, as well as the first purpose-built twin-engine radar-equipped night fighter, the Northrop P-61 Black Widow.

When the US entered the war in December 1941, designs advanced rapidly, and long-established engines such as the Wright Cyclone and Double Wasp were re-rated on fuel of much higher octane rating (anti-knock value) to give considerably more power. By 1944, versions of the R-2800 powering late-model P-47s (and other aircraft) had a rating (experimental) of on 115-grade fuel with water injection.

Peacetime

Engines grow in power with development, but a major war demands the utmost performance from engines fitted to aircraft whose life in front-line service was unlikely to exceed 50 hours flying, over a period of only a month or two. In peacetime however, the call was for reliability over a period of perhaps a dozen years, and the R-2800's reliability commended its use for long-range patrol aircraft and for the Douglas DC-6, Martin 4-0-4, and Convair 240 transports. The last two were twin-engine aircraft of size, passenger capacity, and high wing loading comparable to the DC-4 - itself usually powered by the R-2000 bored-out version of the Twin Wasp - and the first Constellations, which mostly used Wright Aeronautical's large Duplex-Cyclones. First series production variant of the "C" Series, which was a complete redesign of the R-2800. Some of the main changes were: forged rather than cast cylinders, allowing an increased compression ratio (from 6.65:1 to 6.75:1); a redesigned crankshaft; a single piece (rather than split) crankcase center section; a two section nose casing, incorporating hydraulically operated torque-monitoring equipment and an automatic vacuum-operated spark-advance unit. The supercharger used fluid coupling for the second stage. Updraft Bendix-Stromberg PT-13G2-10 carburetor. Used in Vought F4U-4 and variants of the -4. Production = 3,257 (P&W).

  • R-2800-22W -
  • R-2800-34 -
  • R-2800-34W - , with water-methanol injection
  • R-2800-44 -
  • R-2800-44W -
  • R-2800-48 -
  • R-2800-48W -
  • R-2800-52W -
  • R-2800-54 -
  • R-2800-57 -
  • R-2800-57C -
  • R-2800-73 - — with General Electric CH-5-A3 turbocharger for P-61C Black Widow
  • R-2800-77 -
  • R-2800-83 -
  • R-2800-83AM -
  • R-2800-99W -
  • R-2800-103W -
  • Double Wasp CB16 - ,
  • Double Wasp CB17 -
  • Double Wasp S1C3-G -

"D" Series:

  • R-2800-23 -
  • R-2800-29 -

"E" Series:

  • R-2800-30W - , with water-methanol injection — with variable speed single-stage supercharger for Grumman F8F-2 Bearcat
  • R-2800-32W - , with water-methanol injection — with variable speed two-stage supercharger for Vought F4U-5 Corsair

Applications

Martin B-26 Marauder|thumb

The following is a partial list of aircraft that were powered by the R-2800 (and a few prototypes that utilized it at one point):

Engines on display

thumb|R-2800 on display at [[Museum of Aviation (Warner Robins)|Museum of Aviation, Robins AFB]]

  • There is an R-2800-39 on display at the New England Air Museum, Bradley International Airport, Windsor Locks, CT.
  • An R-2800 used on Finnair Convair Metropolitan is on public display at Helsinki Airport.
  • An R-2800 Double Wasp is on display at the Aerospace Discovery at the Florida Air Museum.
  • An R-2800 Double Wasp Cutout is on display at Texas State Technical College in Waco Texas.
  • An R-2800 Double Wasp manufactured by Ford Motor Company is on display at the Yankee Air Museum Belleville, Michigan
  • An R-2800-8W Double Wasp is on display at the Flying Leatherneck Aviation Museum at MCAS Miramar, California.
  • An R-2800 Double Wasp moving cut-away is on display at the USS Midway Museum at San Diego, California.
  • An R-2800 Double Wasp is on display at (The National Museum of WWII Aviation) located in (Colorado Springs, Colorado).
  • An R-2800-34 Double Wasp is on public at the Aerospace Museum of California.
  • Two R-2800 Double Wasps are displayed alongside a B-25 at the Girua Airport, Popondetta, Oro Province, Papua New Guinea.

Specifications (R-2800-54)

thumb|right|

See also

References

Footnotes

Citations

Bibliography

  • Pratt & Whitney's R-2800 page