Pratt & Whitney R-2800 Double Wasp

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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 Template:Cvt, 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,<ref name=P&W>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> near the time that the larger Template:Cvt competing 18-cylinder Wright Duplex-Cyclone's development had been started in May of that year, the Template:Cvt 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 Template:Cvt.<ref group="nb">The American Wright Duplex-Cyclone radial of Template:Cvt was also under development at the time,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and promised to be more powerful than either the P&W or Gnome-Rhone radials.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref></ref>

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.<ref name=avhist>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Cutaway of a Pratt & Whitney R-2800 Double Wasp

The twin distributors<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }} Note the "outboard" wire exits from the distributor cases.</ref>

When the R-2800 was introduced in 1939, it was capable of producing Template:Cvt, for a specific power value of Template:Cvt. 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 Template:Cvt, and to Template:Cvt late in the war. Even more was coaxed from experimental models, with fan-cooled subtypes like the R-2800-57 producing Template:Cvt, but in general the R-2800 was a rather highly developed powerplant right from the beginning.<ref name=avhist/>

WWII

The first prototype F4U Corsair, the earliest aircraft specifically designed to use the Double Wasp

The R-2800 powered several types of fighters and medium bombers during the war, including the US Navy's Vought F4U Corsair, with the XF4U-1 first prototype Corsair becoming the first airframe to fly (as originally designed) with the Double Wasp<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> in its XR-2800-4 prototype version on May 29, 1940,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and the first single-engine American fighter plane to exceed Template:Cvt 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), 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 Template:Cvt on 115-grade fuel with water injection.<ref name=avhist/>

After World War II, the engine was used in the Korean War, and surplus World War II aircraft powered by the Double Wasp served with other countries well past the Korean War, some being retired as late as the latter part of the 1960s when the aircraft were replaced.<ref name=utc>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

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.<ref name=avhist/>

The Double Wasp still flies in restored vintage warbird aircraft displayed at air shows, and sees service worldwide on aircraft such as the Canadair CL-215 water-bomber. In addition, R-2800s continue to power Douglas DC-6 cargo and fuel-carrying aircraft in locations such as Alaska. A total of 125,334 R-2800 engines were produced between 1939 and 1960.<ref name=P&W/>

Variants

This is a list of representative R-2800 variants, describing some of the mechanical changes made during development of the Double Wasp. Power ratings quoted are usually maximum "military" power that the engine could generate on takeoff and at altitude; 100 Octane fuel was used, unless otherwise noted.

The R-2800 was developed and modified into a basic sequence of subtypes, "A" through "E" series, each of which indicated major internal and external modifications and improvements, such that the "E" series engines had very few parts in common with the "A".Template:Citation needed. Pratt & Whitney's internal variant identification incorporated the series letter as part of the designation, for example Double Wasp S1A4-G ("A" series) and Double Wasp CB17 ("C" series).

Note
Suffixes such as -S14A-G denote engines developed for export to other countries.

Data from White (Airlife)Template:Sfn unless otherwise noted:

Military

The dash number for each military type (e.g.: -21) was allocated to identify the complete engine model in accordance with the specification under which the engine was manufactured. Thus dash numbers did not necessarily indicate the sequence in which the engines were manufactured. For example: the -18W was a "C" series engine, built from 1945, whereas the -21 was a "B" series engine, built from 1943.

Until 1940 the armed forces adhered strictly to the convention that engines built for the Army Air Forces used engine model numbers with odd numeric suffixes (e.g.: -5), while those built for the US Navy used even (e.g.: -8). After 1940, however, in the interests of standardization, engines were sometimes built to a joint Army-Navy contract, in which case the engines used a common numeric suffix (e.g. the -10 was used by both Army and Navy aircraft.)

The suffix W e.g.: -10W denotes a sub-series modified to use water injection. The "Anti-Detonant Injection" (ADI) system injected a mixture of water and methanol into the carburetor to increase power for short periods. Several models of the R-2800s were fitted with ADI as standard equipment and were not given the W suffix.<ref group="nb">P&W authorised the use of: 50% methanol, 50% water; 60% methanol, 40% water; 25% methanol, 25% ethanol, 50% water; or 60% methanol, 39% water, 1% anti-corrosive oil.Template:Sfn</ref> Few commercial aircraft used water injection.

"A" Series:

  • R-2800-1
Template:Cvt at 2,400 rpm at Template:Cvt. Production prototype of "A" series engines with the first flight test July 29, 1939.Template:Sfn Single-speed two-stage supercharger. Production = 2 (P&W). Tested in Vultee YA-19B.Template:Sfn
  • R-2800-5
Template:Cvt at 2,600 rpm at Template:Cvt. Main production "A" series engine used in Martin B-26A, early B series and XB-26D and Curtiss C-55/XC-46. Production = 1,429 (P&W 475, Ford 954.)Template:Sfn

"B" Series:

A preserved "B Series" R-2800-21 or -59. The A and B series can be most readily identified by their smooth, single piece nose casings. This photo shows the simplified tubular ignition harness fitted to some R-2800 subtypes.<ref group="nb">The placard on this R-2800, photographed in the National Museum of the United States Air Force says that this is a -21, built by Ford in 1943: components such as ignition harnesses were interchangeable between the likes of -21 and -59 series engines.</ref>
  • R-2800-8
Template:Cvt at 2,700 rpm at Template:Cvt; Template:Cvt at 2,700 rpm at Template:Cvt. First series production "B" Series engine using a two-stage, two-speed supercharger and with internal engineering changes resulting in increased power and reliability. Updraft Bendix-Stromberg PT-13D-4 pressure carburetor. First production engines delivered to USN November 11, 1941. Used in Brewster F3A-1, Goodyear FG-1, Vought F4U-1 and F4U-2. Production = 3,903 (P&W 2,194; Nash 1,709.)Template:Sfn
  • R-2800-8W
Template:Cvt WEP with water injection. First production engine using ADI equipment, major production version of -8 and used in some versions of F4U Corsair. Production = 8,668 (P&W 5,574; Nash 3,094.)Template:Sfn
  • R-2800-10 and R-2800-10W
Template:Cvt at 2,700 rpm at Template:Cvt; Template:Cvt at 2,700 rpm at Template:Cvt; up to Template:Cvt WEP with water injection. Similar to -8 series apart from downdraft PT-13G2-10 and PT-13G6-10 (-10W) carburetor. Used in Curtiss XP-60E, Grumman F6F-3 (-10; late production -10W) and F6F-5 (-10W) series and Northrop XP-61, YP-61, and P-61A-1. Production = 4,621 -10 (P&W 2,931; Nash 1,690) and 12,940 -10W (P&W 3,040; Nash 9,900); Total = 17,561.Template:Sfn
  • R-2800-21
Template:Cvt at 2,700 rpm at Template:Cvt; Template:Cvt at 2,700 rpm at Template:Cvt. First production variant fed by a General Electric C-1 turbosupercharger.Template:Sfn<ref group="nb">Prototype and production prototypes were the "A" series R-2800-17 (one built) and R-2800-35 (11 built), fitted to the XP-47B and early P-47Bs respectively.Template:Sfn</ref> Designed for use in the Republic P-47B, C, D, G and XP-47F and K. Production = 5,720 (P&W 1,049; Ford 4,671.)Template:Sfn
Template:Cvt at 2,700 rpm at Template:Cvt; Template:Cvt at 2,500 rpm at Template:Cvt; Template:Cvt WEP with water injection. Main production variant used in P-47 series, fed by an improved C-23 turbosupercharger.Template:Sfn Differed from -21 in being fitted with ADI and a General Electric ignition system with a simplified tubular ignition harness developed by the Scintilla company in partnership with Bendix. Used in P-47C and D, XP-47L. Production = 11,391 (P&W 592; Ford 10,799).Template:Sfn<ref group="nb">R-2800-63 with small manufacturing differences was interchangeable with -21 or -59 . Production =2,092 (P&W 1,262; Ford 767).Template:Sfn</ref>

"C" Series

A "C Series" R-2800, with the two section nose casing incorporating torque-monitoring equipment and a Spark Advance unit, with the "outboard" sparkplug wiring conduit location for each of the twin enclosed distributors.
  • R-2800-18W
Template:Cvt at 2,800 rpm at Template:Cvt; Template:Cvt at 2,800 rpm at Template:Cvt.<ref>USN history 1986, p. 8.</ref>Template:Full citation needed 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.Template:Sfn The supercharger used fluid coupling for the second stage.Template:Sfn Updraft Bendix-Stromberg PT-13G2-10 carburetor. Used in Vought F4U-4 and variants of the -4.<ref group="nb">Because the "C" series engines ran more smoothly than previous R-2800s the F4U-4 was able to use simplified, solid engine mountings rather than needing mountings incorporating shock absorbers.Template:Sfn</ref> Production = 3,257 (P&W).Template:Sfn

|CitationClass=web }}</ref> Template:Cvt with water-methanol injection

"D" Series:

"E" Series:

Applications

Martin B-26 Marauder

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):

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Engines on display

R-2800 on display at Museum of Aviation, Robins AFB

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Specifications (R-2800-54)

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See also

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References

Footnotes

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Citations

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Bibliography

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