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Pratt & Whitney R-2800 Double Wasp

Pratt & Whitney · Aircraft Engine · USA · WWII (1939–1945)

Pratt & Whitney R-2800 Double Wasp — Aircraft Engine
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The Pratt & Whitney R-2800 Double Wasp is an American 18-cylinder, twin-row, air-cooled radial aero engine with a displacement of 2,800 cubic inches (46 L). First run in 1937 and certified in 1939, the Double Wasp became the highest-output U.S. radial of the Second World War, with marks rated from 2,000 hp on early B-series builds to 2,400 hp on water-injected late-war C-series units and 2,800 hp on post-war commercial variants. Around 125,334 examples were produced between 1939 and 1960 at Pratt & Whitney's East Hartford works and licence plants run by Ford, Nash-Kelvinator, and Chevrolet — placing the R-2800 among the most-built high-power piston engines in history.

The 18-cylinder twin-row layout gave the engine its Double Wasp name: two banks of nine cylinders arranged radially around a common crankshaft, fed by a single-stage two-speed supercharger on most marks. Designer Luke Hobbs and chief engineer Leonard Hobbs solved the cooling problem that had stopped earlier 18-cylinder designs by forging cylinder heads from aluminium and machining deep cooling fins between every cylinder pair, allowing each cylinder to breathe through its own valves without overheating the rear bank. Bore and stroke were both 5.75 inches; compression ratio 6.65:1 on B-series, 6.75:1 on C-series. The engine ran on 100/130 octane avgas, with anti-detonation water-methanol injection on later marks for war-emergency power.

Wartime airframe applications read as a roster of the most-iconic U.S. fighters and attack types. The Republic P-47 Thunderbolt used the R-2800 with a General Electric turbocharger to fly at 40,000 ft. The Vought F4U Corsair mounted the R-2800 on a gull wing that cleared a 13-foot Hamilton Standard propeller. The Grumman F6F Hellcat rode the same engine to a 19:1 kill ratio over the Pacific, and the Grumman F8F Bearcat matched the Hellcat's R-2800 to a lighter airframe for the fastest climb of any piston fighter in U.S. service. Twin-engined applications included the Martin B-26 Marauder medium bomber, the Douglas A-26 Invader light attack bomber, the Northrop P-61 Black Widow night fighter, and the Curtiss C-46 Commando transport.

Post-war the R-2800 powered the first generation of long-haul pressurised airliners, including the Douglas DC-6, the Martin 2-0-2, and the Convair CV-240/340/440 family. The DC-6's four 2,400 hp CB-series Double Wasps gave it transatlantic range, and Convair's twins flew U.S. domestic routes for two decades. Military post-war use included Lockheed P2V Neptune maritime patrollers and the Douglas AD Skyraider attack aircraft.

The R-2800's combat record drove a generation of derivative work. Pratt & Whitney scaled the same architecture up to the 28-cylinder R-4360 Wasp Major for the Convair B-36 Peacemaker, but the R-2800 itself remained in production until 1960 and on airline schedules into the 1970s. Surviving Double Wasps still fly on warbird Hellcats, Corsairs, and Bearcats at airshows, and many DC-6 freighters serving Alaskan bush routes flew with original-spec R-2800s into the 2010s. The engine's mix of brute power, mechanical reliability, and licence-production scale made it the workhorse U.S. radial of the piston era.

For Kids — a shorter, friendlier version

The Pratt & Whitney R-2800 Double Wasp is a powerful airplane engine made in America. It was first tested in 1937 and ready to fly by 1939. Engineers built over 125,000 of these engines between 1939 and 1960. That makes it one of the most-built powerful piston engines ever made.

The engine has 18 cylinders arranged in two rings of nine. That twin-ring design is why it got the name "Double Wasp." A supercharger helped push air into the engine so it could fly high in the sky. Smart engineers solved a tricky heating problem by using aluminium tops on each cylinder with deep cooling fins.

The Double Wasp could make between 2,000 and 2,400 horsepower during the war. Later versions made even more. That is heavier than a compact car in raw pushing power — truly incredible for a piston engine!

This engine powered some very famous planes. It flew inside the P-47 Thunderbolt, the F4U Corsair, and the F6F Hellcat. After the war, it even powered the DC-6 passenger plane. People all over the world flew in planes using this engine.

Fun Facts

  • The Double Wasp has 18 cylinders arranged in two rings — just like two necklaces of nine beads each.
  • Over 125,000 of these engines were built — that is more than enough to fill a small town!
  • The engine was first tested in 1937, before many of today's grandparents were even born.
  • It could produce up to 2,400 horsepower during the war — faster than almost any other piston engine at the time.
  • The engine is heavier than a compact car, yet planes carried it through the sky with ease.
  • Car companies like Ford and Chevrolet helped build this airplane engine during the war.
  • Special water injection on late-war engines gave them an extra boost of power when needed most.
  • The same engine that fought in wartime also carried passengers peacefully in the DC-6 airliner.

Kids’ Questions

Why is it called the 'Double Wasp'?

It is called the Double Wasp because it has two rings of cylinders. Each ring has nine cylinders, making 18 in total. Two rings together = double!

What famous planes used the Double Wasp engine?

The Double Wasp powered the P-47 Thunderbolt, the F4U Corsair, and the F6F Hellcat. After the war, it also powered the DC-6 passenger plane.

How did engineers stop the engine from getting too hot?

Engineers used aluminium tops on each cylinder. They also cut deep cooling fins between cylinders. This let cool air flow around every part of the engine.

How many of these engines were ever built?

More than 125,000 Double Wasp engines were built between 1939 and 1960. They were made at factories run by Pratt & Whitney, Ford, Chevrolet, and others.

Variants

R-2800-8 / -8W (B-series)
Early-war single-stage two-speed supercharged build rated at 2,000 hp military, 2,250 hp with water-injection (8W). Powered early F4U-1 Corsair and F6F-3 Hellcat production.
R-2800-21 / -59 (B-series, turbocharged)
Mated to a General Electric C-series turbocharger for high-altitude flight. Standard installation on the P-47 Thunderbolt; 2,000 hp military, 2,300 hp WEP.
R-2800-18W / -32W (C-series)
Late-war redesign with forged crankcase, two-stage supercharger and water-injection. 2,100 hp normal, 2,400 hp WEP. Used on F4U-4 Corsair, F6F-5N Hellcat, and F8F-1 Bearcat.
R-2800-CA / CB (commercial)
Post-war airline variants rated 2,400 hp continuous, certified for 1,500-hour TBO. Powered the DC-6, Martin 2-0-2/4-0-4, and Convair 240/340/440.
R-2800-44W / -52W (late military)
Korean War-era marks for the Douglas AD Skyraider and Lockheed P2V Neptune. Production continued at East Hartford until 1960.

Notable Operators

U.S. WWII fighter installations
P-47 Thunderbolt (turbocharged, 15,683 built), F4U Corsair (12,571 built), F6F Hellcat (12,275 built), F8F Bearcat (1,265 built), P-61 Black Widow (706 built). Together these airframes consumed the bulk of wartime R-2800 production.
U.S. WWII twin-engine applications
B-26 Marauder medium bomber (5,288 built), A-26 Invader attack bomber (2,503 built), C-46 Commando transport (3,181 built). The C-46 flew the Hump route over the Himalayas with R-2800 power.
Post-war airliners
Douglas DC-6 (704 built), Convair CV-240/340/440 family (1,000+ built combined), Martin 2-0-2/4-0-4. These types flew U.S. trunk and feeder routes from 1947 into the 1960s and freight routes into the 2010s.
Korean War and late military
Douglas AD/A-1 Skyraider attack aircraft (3,180 built, R-2800 on early marks; Wright R-3350 on later) and Lockheed P2V Neptune maritime patrol bomber. Skyraiders flew combat over Vietnam into 1972.

Frequently Asked Questions

What made the R-2800 the dominant U.S. radial of WWII?

The combination of power density and reliability. At 2,000-2,400 hp the Double Wasp matched or beat every contemporary liquid-cooled V-12, but with no coolant system to puncture in combat. The 18-cylinder twin-row layout fit the same frontal area as earlier 14-cylinder radials, so fighter designers could swap it into existing airframes without redesigning the fuselage. Pratt & Whitney shipped over 125,000 examples between 1939 and 1960, according to the National Museum of the U.S. Air Force fact sheet.

How did the R-2800 differ from the Rolls-Royce Merlin?

The R-2800 was an air-cooled radial; the Merlin was a liquid-cooled V-12. Each had trade-offs. The radial absorbed battle damage better (no coolant lines), ran cooler at low altitude, and was simpler to field-maintain. The Merlin offered a smaller frontal area for lower drag and better high-altitude breathing with its two-stage supercharger. U.S. doctrine paired the R-2800 with General Electric turbochargers on the P-47 to recover the high-altitude edge, while the British leaned on the Merlin's mechanical supercharger.

Why did the R-2800 stay in production until 1960?

Post-war airliners. The DC-6, Convair 240/340/440, and Martin 2-0-2/4-0-4 needed a 2,400 hp powerplant that could run 1,500 hours between overhauls, and the R-2800's CA/CB commercial marks delivered exactly that. Jet airliners did not displace these types on short-haul U.S. routes until the early 1960s. The Skyraider and P2V Neptune also held military demand into the Korean War period.

How many cylinders did the R-2800 have, and what is a twin-row radial?

18 cylinders in two rows of nine, arranged radially around the crankshaft. A single-row 9-cylinder radial is the simpler layout (used on the R-1830 Twin Wasp and earlier engines); the twin-row stacks a second bank of nine behind the first, doubling displacement while keeping frontal area nearly the same. The challenge was cooling the rear-bank cylinders, which Pratt & Whitney solved with forged aluminium heads and aggressive baffle design.

What power did the R-2800 produce?

Marks ranged from 2,000 hp (B-series military rating) to 2,400 hp (C-series with water-methanol injection) to 2,800 hp (post-war CB-series at full throttle). War-emergency power on the F4U-4 and F8F-1 Bearcat reached 2,400 hp briefly, enough to give the Bearcat the fastest piston-fighter climb rate ever measured in U.S. service.

Are R-2800s still flying today?

Yes. Warbird F4U Corsairs, F6F Hellcats, F8F Bearcats, and P-47 Thunderbolts on the airshow circuit fly with rebuilt R-2800s, and a handful of DC-6 freighters in Alaska operated R-2800s into the 2010s. Specialist shops in the U.S. and Europe still rebuild the engine to original 1944 specifications.

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