The R-2800 saw widespread use in many important American aircraft during and afterWorld War II. During the war years,Pratt & Whitney continued to develop new ideas to upgrade the engine, includingwater injection for takeoff in cargo and passenger planes and to give emergency power in combat.
First run in 1937,[1] near the time that the larger 3,347.9 cu in (54.862 L) competing 18-cylinderWright Duplex-Cyclone's development had been started in May of that year, the 2,804.5 cu in (45.958 L) 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, theGnome-Rhône 18L of 3,442 cu in (56.40 L).[nb 1]
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.[4]
Cutaway of a Pratt & Whitney R-2800 Double Wasp
Thetwindistributors[5] 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.[6]
When the R-2800 was introduced in 1939, it was capable of producing 2,000 hp (1,500 kW), for aspecific power value of 0.71 hp/cu in (32 kW/L). 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 2,100 hp (1,600 kW), and to 2,400 hp (1,800 kW) late in the war. Even more was coaxed from experimental models, with fan-cooled subtypes like the R-2800-57 producing 2,800 hp (2,100 kW), but in general the R-2800 was a rather highly developed powerplant right from the beginning.[4]
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 theUS Navy'sVought F4U Corsair, with the XF4U-1 first prototype Corsair becoming the first airframe to fly (as originally designed) with the Double Wasp[7] in its XR-2800-4 prototype version on May 29, 1940,[8] and the first single-engine American fighter plane to exceed 400 mph (640 km/h) in level flight during October 1940. The R-2800 also powered the Corsair's naval rival, theGrumman F6F Hellcat, theUS Army Air Forces'Republic P-47 Thunderbolt (which unusually, for single-engined aircraft, used a General Electricturbocharger), the twin-engineMartin B-26 Marauder andDouglas A-26 Invader, as well as the first purpose-built twin-engine radar-equipped night fighter, theNorthrop 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 higheroctane 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 2,800 hp (2,100 kW) on 115-grade fuel with water injection.[4]
After World War II, the engine was used in theKorean 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.[9]
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 theDouglas DC-6,Martin 4-0-4, andConvair 240 transports. The last two were twin-engine aircraft of size, passenger capacity, and high wing loading comparable to theDC-4 - itself usually powered by theR-2000 bored-out version of the Twin Wasp - and the firstConstellations, which mostly used Wright Aeronautical's large Duplex-Cyclones.[4]
The Double Wasp still flies in restored vintagewarbird aircraft displayed atair shows, and sees service worldwide on aircraft such as theCanadair CL-215 water-bomber. In addition, R-2800s continue to powerDouglas DC-6 cargo and fuel-carrying aircraft in locations such asAlaska. A total of 125,334 R-2800 engines were produced between 1939 and 1960.[1]
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".[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)[10] unless otherwise noted:
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 suffixW e.g.:-10W denotes a sub-series modified to usewater injection. The "Anti-Detonant Injection" (ADI) system injected a mixture of water andmethanol 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 theW suffix.[nb 2] Few commercial aircraft used water injection.
"A" Series:
R-2800-1
1,500 hp (1,100 kW) at 2,400 rpm at 7,500 ft (2,300 m). Production prototype of "A" series engines with the first flight test July 29, 1939.[12] Single-speed two-stage supercharger. Production = 2 (P&W). Tested inVultee YA-19B.[13]
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 tubularignition harness fitted to some R-2800 subtypes.[nb 3]
R-2800-8
2,000 hp (1,500 kW) at 2,700 rpm at 1,000 ft (300 m); 1,800 hp (1,300 kW) at 2,700 rpm at 15,500 ft (4,700 m). First series production "B" Series engine using a two-stage, two-speed supercharger and with internal engineering changes resulting in increased power and reliability. UpdraftBendix-Stromberg PT-13D-4 pressure carburetor. First production engines delivered toUSN November 11, 1941. Used inBrewster F3A-1, Goodyear FG-1, Vought F4U-1 and F4U-2. Production = 3,903 (P&W 2,194; Nash 1,709.)[15]
R-2800-8W
2,250 hp (1,680 kW)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.)[15]
R-2800-10 andR-2800-10W
2,000 hp (1,500 kW) at 2,700 rpm at 1,000 ft (300 m); 1,800 hp (1,300 kW) at 2,700 rpm at 15,500 ft (4,700 m); up to 2,250 hp (1,680 kW) WEP with water injection. Similar to -8 series apart from downdraft PT-13G2-10 and PT-13G6-10 (-10W) carburetor. Used inCurtiss XP-60E,Grumman F6F-3 (-10; late production -10W) and F6F-5 (-10W) series andNorthrop 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.[15]
2,000 hp (1,500 kW) at 2,700 rpm at 2,500 ft (760 m); 2,000 hp (1,500 kW) at 2,500 rpm at 25,000 ft (7,600 m); 2,300 hp (1,700 kW) WEP with water injection. Main production variant used in P-47 series, fed by an improved C-23 turbosupercharger.[19] 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).[20][nb 5]
R-2800-59W - 2,500 hp (1,900 kW)
R-2800-65 - 2,000 hp (1,500 kW)
R-2800-65W - 2,250 hp (1,680 kW)
R-2800-71 - 2,000 hp (1,500 kW)
R-2800-75 - 2,200 hp (1,600 kW)
R-2800-79 - 2,100 hp (1,600 kW)
Double Wasp 2SB-G - 1,850 hp (1,380 kW)
"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
2,100 hp (1,600 kW) at 2,800 rpm at 1,000 ft (300 m); 1,800 hp (1,300 kW) at 2,800 rpm at 25,500 ft (7,800 m).[21][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 thancast 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 operatedtorque-monitoring equipment and an automatic vacuum-operatedspark-advance unit.[22] The supercharger usedfluid coupling for the second stage.[23] Updraft Bendix-Stromberg PT-13G2-10 carburetor. Used inVought F4U-4 and variants of the -4.[nb 6] Production = 3,257 (P&W).[25]
R-2800-22W - 2,400 hp (1,800 kW)
R-2800-34 - 2,100 hp (1,600 kW)
R-2800-34W - 2,100 hp (1,600 kW),[26] 2,400 hp (1,800 kW) with water-methanol injection
R-2800-44 - 2,300 hp (1,700 kW)
R-2800-44W - 2,400 hp (1,800 kW)
R-2800-48 - 2,500 hp (1,900 kW)
R-2800-48W - 2,400 hp (1,800 kW)
R-2800-52W - 2,500 hp (1,900 kW)
R-2800-54 - 2,100 hp (1,600 kW)
R-2800-57 - 2,800 hp (2,100 kW)
R-2800-57C - 2,800 hp (2,100 kW)
R-2800-73 - 2,800 hp (2,100 kW) — with General Electric CH-5-A3 turbocharger[27] for P-61C Black Widow
R-2800-77 - 2,800 hp (2,100 kW)
R-2800-83 - 2,100 hp (1,600 kW)
R-2800-83AM - 2,100 hp (1,600 kW)
R-2800-99W - 2,300 hp (1,700 kW)
R-2800-103W - 2,500 hp (1,900 kW)
Double Wasp CB16 - 2,400 hp (1,800 kW), 2,500 hp (1,900 kW)
Double Wasp CB17 - 2,500 hp (1,900 kW)
Double Wasp S1C3-G - 2,100 hp (1,600 kW)
"D" Series:
R-2800-23 - 2,200 hp (1,600 kW)
R-2800-29 - 2,000 hp (1,500 kW)
"E" Series:
R-2800-30W - 2,250 hp (1,680 kW), 2,500 hp (1,900 kW) with water-methanol injection — with variable speed single-stage supercharger forGrumman F8F-2 Bearcat[28]
R-2800-32W - 2,450 hp (1,830 kW), 2,850 hp (2,130 kW) with water-methanol injection — with variable speed two-stage supercharger forVought F4U-5 Corsair
^The AmericanWright Duplex-Cyclone radial of 3,347 cu in (54.85 L) was also under development at the time,[2] and promised to be more powerful than either the P&W or Gnome-Rhone radials.[3]
^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.[11]
^The placard on this R-2800, photographed in theNational 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.
^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.[17]
^R-2800-63 with small manufacturing differences was interchangeable with -21 or -59 . Production =2,092 (P&W 1,262; Ford 767).[20]
^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.[24]
Bodie, Warren M. (1994).Republic's P-47 Thunderbolt: From Seversky to Victory. Hayesville, North Carolina: Widewing Publications.ISBN0-9629359-1-3.
Gunston, Bill (2006).World Encyclopedia of Aero Engines: From the Pioneers to the Present Day (5th ed.). Stroud, UK: Sutton.ISBN0-7509-4479-X.
Bridgman, Leonard, ed.Jane's All The World's Aircraft 1951–1952. London: Samson Low, Marston & Company, Ltd 1951.
White, Graham (1995).Allied Aircraft Piston Engines of World War II: History and Development of Frontline Aircraft Piston Engines Produced by Great Britain and the United States During World War II. Warrendale, Pennsylvania: SAE International.ISBN1-56091-655-9.
