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Pratt & Whitney R-4360 Wasp Major



Starting in 1940, and production begining in 1945, just too late for the Second World War, the engineers at P&W were tasked with developing a 3,000 h.p.-plus engine. At the beginning of the R-4360's development, state-of-the-art engines were struggling to achieve 2,000 h.p. P&W decided on air cooling and, after a number of variations and permutations of cylinder arrangement had been investigated, the final concept, which went into production, was four rows of seven cylinders, giving a total of 28.

Cooling high-performance air-cooled engines was always a challenge, for the R-4360. Each row of pistons was slightly offset from the previous, forming a semi-helical arrangement to facilitate efficient airflow cooling of the successive rows of cylinders, with the spiraled cylinder setup inspiring the engine's "corncob" nickname. Seven plenums, one between each cylinder bank, created the necessary cooling air path. A complex tight baffling system ensured that cooling air was forced through the cylinders in a quasi-cross-flow pattern. To ensure an unobstructed path, intake manifolds were routed over the top of the cylinders, terminating in a downdraught flow into the hemispherical combustion chamber.


Pratt & Whitney R-4360 Wasp Major


A mechanical supercharger geared at 6.374:1 ratio to engine speed provided forced induction, while the propeller was geared at 0.375:1 so that the tips did not reach inefficient supersonic speeds. General Electric (GE) had designed most previous P&W superchargers, but this time P&W decided to do it in-house. According to former R-4360 engineers, P&W's supercharger was more efficient than GE's. Most superchargers were single-stage, with variable speed or single speed. Additionally, most R-4360 applications were augmented by GE turbosuperchargers with intercooling, A two-stage gear-driven supercharger was also developed.

Inevitable teething problems arose when the R-4360 entered service, such as frying the ignition system, intake manifold problems and, perhaps most seriously, poor oil scavenging owing to aeration of the oil. The disarmingly simple solution for the last of these problems was to incorporate perforated sheet-metal plates in the rear housing, which took out much of the entrapped air.

Although reliable in flight, the Wasp Major was maintenance-intensive. Improper starting technique could foul all 56 spark plugs, which would require hours to clean or replace. As with most piston aircraft engines of the era, the time between overhauls of the Wasp Major was about 600 hours when used in commercial service.




Engine displacement was 4,362.50 (71.5 lt), hence the model designation. Initial models developed 3,000 hp (2,240 kW), and later models 3,500 hp, but one model delivered 4,300 hp (3200 kW) using two large turbochargers in addition to the supercharger. Engines weighed 3,482 to 3,870 lb (1,579 to 1,755 kg), giving a power-to-weight ratio of 1.11 hp/lb (1.83 kW/kg), which was matched or exceeded by very few contemporary engines.

Designed for military use, the R-4360 also saw commercial use as the "Wasp Major”. The R-4360 was used for a number of applications, including commercial aviation, military aircraft and air racing. The R-4360-8 powered the Douglas XTB2D-1 Skypirate, the contra-rotating propeller shafts each drove a Hamilton Standard four-bladed propeller. The Skypirate was cancelled after one prototype.

Wasp Majors were produced between 1944 and 1955; 18,697 were built.


Pratt & Whitney R-4360 Wasp Major


A derivative engine, the Pratt & Whitney R-2180-E Twin Wasp E, was essentially the R-4360 "cut in half". It had two rows of seven cylinders each, and was used on the postwar Saab 90 Scandia airliner.


The R-4360-33 powered the Boeing XB-44, essentially a B-29 converted to carry R-4360s. Note auxiliary gear driven supercharger on the rear of the engine. Some R-4360s utilised both contra-props and two-stage supercharging.


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Boeing 377 Stratocruiser
Boeing B-50 Superfortress
Boeing C-97 Stratofreighter
Boeing KC-97 Stratotanker
Boeing XF8B
Boeing XB-44 Superfortress
Convair B-36
Convair XC-99
Curtiss XBTC
Douglas C-74 Globemaster
Douglas C-124 Globemaster II
Douglas TB2D Skypirate
Fairchild C-119 Flying Boxcar
Fairchild C-120 Packplane
Goodyear F2G Corsair
Hughes H-4 Hercules ("Spruce Goose")
Hughes XF-11
Lockheed R6V Constitution
Martin AM Mauler
Martin JRM Mars
Martin P4M Mercator
Northrop B-35
Republic XP-72
Republic XF-12 Rainbow
SNCASE SE-2010 Armagnac
Vultee A-41


R-4360-4 - 2,650 hp (1,976 kW)
R-4360-20 - 3,500 hp (2,610 kW)
R-4360-25 - 3,000 hp (2,237 kW)
R-4360-41 - 3,500 hp (2,610 kW)
R-4360-51 VDT - "Variable Discharge Turbine" 4,300 hp (3,210 kW). Intended for B-36C. Used on Boeing YB-50C Superfortress. Turbo-supercharger exhaust used to augment thrust.
R-4360-53 - 3,800 hp (2,834 kW)
R-4360-B3 - 3,500 hp (2,610 kW)
R-4360-B6 - 3,500 hp (2,610 kW)


Type: 28-cylinder supercharged air-cooled four-row radial engine
Bore: 5.75 inches (146 mm).
Stroke: 6.00 inches (152 mm).
Displacement: 4,362.5 cubic inches (71.489 lt).
Length: 96.5 inches (2,450 mm).
Diameter: 55 inches (1,400 mm).
Dry weight: 3,870 pounds (1,760 kg).
Valvetrain: Poppet, two valves per cylinder
Supercharger: Gear-driven single stage variable speed centrifugal type supercharger
Turbocharger: General Electric CHM-2
Fuel system: Bendix-Stromberg PR-100E2 pressure carburetor
Fuel type: 115/145 Aviation gasoline
Cooling system: Air-cooled
Power output: 4,300 hp (3.2 MW)
Specific power: 0.99 hp/ (44.9 kW/lt)
Compression ratio: 6.7 : 1
Power-to-weight ratio: 1.11 hp/lb (1.83 kW/kg)








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