Pratt & Whitney R-2800 Double Wasp  

 

The Pratt & Whitney R-2800 Double Wasp is a twin-row, 18-cylinder, air-cooled radial aircraft engine with a displacement of 2800 in³ (46 L), and is part of the long-lived Wasp family.

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The R-2800 is considered one of the premier radial piston engines ever designed and is notable for its 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 this already powerful workhorse, most notably water injection for takeoff in cargo and passenger planes and to give emergency power in combat.

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Design and development

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First run in 1937, the R-2800 was America's first 18-cylinder radial engine design. The Double Wasp was more powerful than the world's only other modern eighteen, the Gnome-Rhône 18L of 3,442 in³ (56.4 L). (The American Wright Duplex-Cyclone radial of 3347 in³ (54.86 L) was also under development at the time and promised to be more powerful than either the P&W or Gnome-Rhone radials.

 

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 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.

 

The twin distributors on the Double Wasp were prominently mounted on the upper surface of the forward gear reduction housing 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 2000 hp (1500 kW), for a specific power value of 0.71 hp/in³ (32.6 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 2100 hp (1600 kW), and to 2400 hp (1800 kW) late in the war. Even more was coaxed from experimental models, with fan-cooled subtypes producing ,800 hp (2100 kW), but in general the R-2800 was a rather highly developed powerplant right from the beginning.

 

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 in its XR-2800-4 prototype version on May 29, 1940 and the first single-engine US fighter plane to exceed 640 km/h in level flight during October 1940.

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The Vought F4U-1,F4U-2 and the GoodyearFG-1 and the Brewster F3A-1 Corsair were powered by a Pratt & Whitney R-2800-8 with 2000 horsepower (1491 kW) at 2700 RPM at 305 m; 1800 horsepower (1342 kW) at 2700 rpm at 4724 m, first series production "B" Series engine using a two-stage, two-speed auxiliary supercharger. The engine's power was transmitted through the use of a three bladed constant speed Hamilton Standard Hydromatic propeller.  

Three different settings were possible, high, low and neutral.

When in high or low, all of the intake air is compressed in two stages. The intake air is compressed by the auxiliary blower, then cooled by the intercooler, then sent through the main stage blower before entering the cylinders.

In neutral, the Pratt & Whitney R-2800-8 performed like a single-stage engine.

High gear was used for high altitudes, low gear for medium altitudes and finally neutral is used for low altitudes.

Later on the Vought F4U-1A, F4U-1D and the F4U-1C were installed with a Pratt & Whitney R-2800-8W with water injection and with 2250 horsepower (1677 kW) WEP, the W stand for water injection, used for an additional burst of power for a limited time , descripted as war emergency power with designation WEP.

The water injection system was permitted for higher manifold pressures, giving the engine a maximum of 2700 RPM.

Engaging the water injection system was rather simple, a safety wire stopped the throttle handle from advancing completely, in stage of an emergency, the throttle handle was advanced completely to full open, breaking the wire and so engaging the water injection system.

A green warning light in the cockpit would flash after two minutes and remain on while the throttle was in the full open position.

A safety measure was introduced, If the throttle was in any other position other than full throttle, the water injection system would automatically turn off.

The Vought F4U-4, F4U-4B, F4U-4P and F4U-7 used a Pratt & Whitney R-2800-18W with 2100 horsepower (1566 kW) at 2800 RPM at 305 m; 1800 horsepower (1342 kW) at 2800 RPM at 7772 m. The engine's power was transmitted through the use of a four bladed constant speed Hamilton Standard Hydromatic propeller. Some Vought F4U-4 and F4U-4B used a Pratt & Whitney R-2800-42W engine.

The Vought F4U-5, F4U-5N and F4U-5NL used a Pratt & Whitney R-2800-32W with 2450 horsepower (1827 kW), 850 horsepower (2125 kW) with water-methanol injection. The engine's power was transmitted through the use of a four bladed constant speed Hamilton Standard Hydromatic propeller.

Finally, the AU-1 corsair used a Pratt & Whitney R-2700-83W engine generated 2300 horsepower, slightly down on the power available in the F4U-5, its top speed also dropped, partly because of an increase in armor. The engine's power was transmitted through the use of a four bladed constant speed Hamilton Standard Hydromatic propeller.

 

The R-2800 also powered the Corsair's naval rival, the Grumman F6F Hellcat, the US Army Air Forces' Republic P-47 Thunderbolt, 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 2800 hp (2100 kW) on 115-grade fuel with water injection.

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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.

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Variants

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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.

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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".

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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 it 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.

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Until 1940 the armed forces adhered strictly to the convention that engines built for the Army Air Forces used 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 Naval aircraft.)

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The suffix W e.g.: -10W denotes a sub-series modified to use A.D.I Anti-Detonant Injection or water injection equipment, using various mixes of water and methyl alcohol (CH3OH) injected into the carburetor to increase power for short periods, several models of R-2800s were fitted as standard with A.D.I and did not use the W suffix.

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"A" Series:

• R-2800-1

1500 hp (1 118 kW) at 2400 rpm at 7500 ft (2286 m). Production prototype of "A" series engines with the first flight test July 29, 1939. Single-speed two-stage supercharger. Production = 2 (P&W). Tested in Vultee YA-19B.

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• R-2800-5

1850 hp (1379 kW) at 2,600 rpm at 2,00 ft (823 m). 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.)

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"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.[nb 2]

• R-2800-8  installed in F4U-1/F4U-2//FG-1/F3A-1

2000 hp (1491 kW) at 2,700 rpm at 1000 ft (305 m); 1800 (1342 kW) at 2700 rpm at 15,500 ft (4724 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. Updraft Bendix-Stromberg PT-13D-4 pressure carburetor. First production engines delivered to U.S.N November 11, 1941. Used in Brewster F3A-1, Goodyear FG-1, Vought F4U-1 and F4U-2. Production = 3903 (P&W 2,194; Nash 1,709.)

• R-2800-8W  installed in F4U-1A/F4U-1D/F4U-1C

2,250 hp (1,677 kW) WEP with water injection. First production engine using ADI equipment, major production version of -8 and used in same versions of F4U Corsair. Production = 8,668 (P&W 5,574; Nash 3,094.)

• R-2800-10 and R-2800-10W

2000 hp (1491 kW) at 2700 rpm at 1000 ft (305 m); 1800 (1342 kW) at 2700 rpm at 15500 ft (4724 m); up to 2250 hp (1677 kW) 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.

• R-2800-21

2000 hp (1491 kW) at 2700 rpm at 2500 ft (762 m); 2000 hp (1491 kW) at 2700 rpm at 25000 ft (7620 m). First production variant fed by a General Electric C-1 turbosupercharger. Designed for use in the Republic P-47B, C, D, G and XP-47F and K. Production = 5,720 (P&W 1049; Ford 4671.)

• R-2800-59

2000 hp (1491 kW) at 2700 rpm at 2500 ft (762 m); 2000 hp (1491 kW) at 2500 rpm at 25000 ft (7620 m); 2300 hp (1700 kW) WEP with water injection. Main production variant used in P-47 series, fed by an improved C-23 turbosupercharger. Differed from -21 in being fitted with A.D.I and a General Electric ignition system with a simplified, tubular ignition harness developed by the Scinitilla company in partnership with Bendix. Used in P-47C and D, XP-47L. Production = 11,391 (P&W 592; Ford 10799).

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"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 installed in F4U-4/F4U-4B/F4U-4P/F4U-7

2100 hp (1566 kW) at 2800 rpm at 1,000 ft (305 m); 1800 hp (1342 kW) at 2800 rpm at 25500 ft (7772 m).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, and 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 -4 variants. Production = 3257 (P&W).

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R-2800-22W - 2400 hp (1,789 kW)

R-2800-25 - 2000 hp (1,490 kW) — for Northrop P-61 Black Widow

R-2800-27 - 2000 hp (1,491 kW)

R-2800-30W ("E" Series) - 2250 hp (1,677 kW)

R-2800-31 - 2000 hp (1,491 kW)

R-2800-32W ("E" Series) - 2,450 hp (1,827 kW), 2,850 hp (2,125 kW) with water-methanol injection was installed on the F4U-5/F4U-5N/F4U-5NL/F4U-5P.

R-2800-34 - 2100 hp (1,567 kW)

R-2800-34W - 2100 hp (1,567 kW), 2,400 hp (1,789 kW) with water-methanol injection

R-2800-39 - 2000 hp (1,491 kW)

R-2800-41 - 2000 hp (1,491 kW)

R-2800-43 - 2000 hp (1,491 kW)

R-2800-44 - 2300 hp (1,700 kW)

R-2800-44W - 2400 hp (1,789 kW)

R-2800-48 - 2500 hp (1,890 kW)

R-2800-48W - 2400 hp (1,789 kW)

R-2800-51 - 2000 hp (1,491 kW)

R-2800-54 - 2100 hp (1,567 kW)

R-2800-57 - 2800 hp (2,090 kW)

R-2800-57C - 2800 hp (2,090 kW)

R-2800-59W - 2500 hp (1,890 kW)

R-2800-65 - 2000 hp (1,491 kW)

R-2800-65W - 2250 hp (1,677 kW)

R-2800-71 - 2000 hp (1,491 kW)

R-2800-73 - 2800 hp (2,090 kW) — with General Electric CH-5 turbocharger for P-61C Black Widow

R-2800-75 - 2200 hp (1,640 kW)

R-2800-77 - 2800 hp (2,090 kW)

R-2800-79 - 2000 hp (,1491 kW)

R-2800-83 - 2100 hp (1,567 kW)

R-2800-83WA - 2300 HP

installed on the AU-1 Corsair

R-2800-99W - 2300 hp (1,700 kW)

R-2800-103W - 2500 hp (1,890 kW)

R-2800-2SB-G - 1850 hp (1,379 kW)

R-2800-CB16 - 2400 hp (1,789 kW), 2,500 hp (1,890 kW)

R-2800-CB17 - 2500 hp (1,890 kW)

R-2800-S1A4-G - 1850 hp (1,379 kW)

R-2800-S1C3-G - 2100 hp (1,567 kW

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TABLE OF SPECIFICATIONS

 

Models      R-2800-8, -8W, -10, -10W, -63

Type   Two row, radial, air coole

 

Numbers of cylinders  18

Bore   5.75 in.

Stroke 6.00 in.

Piston Displacement 2804 cu. in.

Compression Ratio 6.65:1

Impeller Diameter (Main) 11 in.

Impeller Diameter (Auxiliary) 13 in.

Impeller Gear Ratio (Main)  .7.80:1

Impeller Gear Ratio (Auxiliary): 

Low Speed 6.46:1

High Speed 7.93:1

Propeller Reduction Gear Ratio 5:01

Propeller Shaft Spline Size No. 50

Diameter of Mounting Bolt Circle 33. 7 5 in.

Number of Mounting Bolts 6

Dry Weight of Engine: 

R-2800-8. -8W, -10, -10W  2480 lb.

R-2800-65   2508 lb.

Overall Diameter of Engine 52.5 in.

Overall Length of Engine 90 in.

Valve Timing Check Clearance.143 in.

  

Cold Valve Adjusting Clearance 060 in.

Center of Gravity: 

Forward of Centerline of Mounting Pads 11.0 in.

 

FUEL SYSTEM 

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Carburetor Type: 

R-2800-8, -8W .PT13D4

R-2800-10, -10W, and -65PT13G6 

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Fuel Required in Flight AN-F-48 Grade 100/130

Fuel Inlet Connection 3/4-14 NPT

Fuel Drain Connection 3/4-18 NPT

Priming System Inlet Connection  5/16-32 NF-3

  

LUBRICATION SYSTEM.

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Grade of Oil Required AN-O-8

Grade 1100 or 1120

Oil Pump Drive Shaft Direction of Rotation Clockwise

Oil Pump Inlet Connection 5/16-32 NF-3

Oil Pump Outlet Connection 5/16-32 NF-3

Oil Tank Vent Connection 3/4-14 NPT

  

IGNITION 

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Magneto Type: 

R_2800-8 and -8WDF18RU

R-2800-10 and -10WDF18RN

R-2800-65 two S18LG-Pl

  

Rotation of Magneto Drive: 

R-2800-8, -8W, -10, -10WCounterclockwise

R-2800-65 Clockwise

Ratio of Magneto Drive Speed to Crankshaft. 1.125:11.125:1

Spark Plug Types   RC-34S, LS-86, C-345

Spark Plug Gap .011-.014 in.

Normal Spark Advance  20 degrees

  

VALVES AND TIMING

 

Inlet Opens Before Top Center 20 degrees

Inlet Closes After Bottom Center 76 degrees

Exhaust Opens Before Bottom Center 76 degrees

 

Exhaust Closes After Top Center 20 degrees

Inlet Remains Open 276 degrees

Exhaust Remains Open 276 degrees

  

Accessory with Dimensions 

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Starter 5.75 in. bolt circle

Generator 5.00 in. bolt circle

Vacuum Pump (without adapter; rear and side)  5.00 in. bolt circle

Vacuum Pump (with adapter;rear and side)  1.875 in. x 1.875 in.

Fuel Pump 2 in. x 2 in.

Tachometers 1.875 in. x 1.875 in.

Propeller Governor 2.125 in. x 2.125 in.

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