Wasp Major

Wasp Major
Name	Wasp Major
Type	Radial engine
Manufacturer	Pratt & Whitney
First run	1944
Major applications	Boeing B-50 Superfortress Boeing C-97 Stratofreighter Convair B-36 Peacemaker
Number built	18,697
Developed from	Pratt & Whitney R-2800 Double Wasp

Wasp Major. The Pratt & Whitney R-4360 Wasp Major was an American 28-cylinder, four-row radial engine developed during World War II and representing the pinnacle of large-displacement piston engine technology. It was the largest-displacement air-cooled engine ever mass-produced in the United States, powering a generation of massive post-war bombers, transports, and experimental aircraft. Its complex design and immense power output cemented its legacy as a remarkable, if demanding, feat of aeronautical engineering.

Design and development

The engine's genesis lay in the need for greater power to propel increasingly heavy aircraft envisioned by the United States Army Air Forces during the war. Engineers at Pratt & Whitney in East Hartford, Connecticut, essentially stacked two 7-cylinder rows from the successful Pratt & Whitney R-2800 Double Wasp atop one another, creating a 28-cylinder powerhouse. To manage the intense heat generated by its 4,360 cubic inch displacement, the Wasp Major employed a sophisticated forced induction system with a single-stage, variable-speed supercharger and intricate cowling for airflow. The crankshaft and master-and-articulating-rod assembly represented a monumental challenge in precision manufacturing and durability under extreme stress.

Operational history

The Wasp Major entered service too late for significant combat use in World War II, with the first operational aircraft being the Boeing B-50 Superfortress, an upgraded version of the Boeing B-29. It became the definitive powerplant for the early Cold War Convair B-36 Peacemaker, where six of these engines, later supplemented by four General Electric J47 turbojets in the "Featherweight" configuration, provided intercontinental range. The engine also proved vital for large transports like the Boeing C-97 Stratofreighter and its commercial derivative, the Boeing 377 Stratocruiser. Its power was crucial for specialized aircraft like the Fairchild C-119 Flying Boxcar and the Hughes H-4 Hercules "Spruce Goose."

Variants

Numerous models were produced, differing primarily in supercharger configuration and power rating for specific airframes. Key military designations included the R-4360-4 for the Northrop XB-35, the R-4360-20W series with water injection for the Boeing B-50, and the R-4360-53, optimized for the Boeing C-97. The most powerful versions, such as the R-4360-51 (Variant) used in the Boeing 377, could produce up to 3,500 horsepower. Experimental variants explored turbo-compounding, where exhaust gases drove power-recovery turbines connected to the crankshaft, as seen in later models for the Lockheed R6V Constitution and the Republic XF-12 Rainbow.

Specifications (R-4360)

* **Type:** 28-cylinder, four-row, air-cooled radial engine with fuel injection * **Bore:** 5.75 in (146 mm) * **Stroke:** 6.0 in (152 mm) * **Displacement:** 4,362.5 cu in (71.5 L) * **Length:** 96.5 in (2,451 mm) * **Diameter:** 55 in (1,397 mm) * **Dry weight:** 3,482–3,870 lb (1,580–1,755 kg) depending on model * **Supercharger:** Single-stage, two-speed or variable-speed centrifugal type * **Power output:** 2,500 to 3,800 hp (1,860 to 2,830 kW) across variants * **Specific fuel consumption:** Approximately 0.39 lb/(hp⋅h) (0.24 kg/kWh)

Applications

The Wasp Major was the prime mover for several iconic American aircraft. Beyond the Boeing B-50 and Convair B-36, it powered the Boeing C-97 and its Boeing 377 civilian airliner counterpart. It was used in the Fairchild C-119, the Martin JRM Mars flying boat, and the Douglas A-1 Skyraider. It also found use in experimental and racing aircraft, most notably the Republic XF-12 and the Hawker Sea Fury-based F2G Corsair. The engine's tremendous power made it a candidate for many proposed designs that never reached production.

Survivors and displays

Numerous Wasp Major engines are preserved in aviation museums worldwide, often installed in surviving airframes. Complete engines are displayed at institutions like the National Museum of the United States Air Force near Dayton, Ohio, the Steven F. Udvar-Hazy Center of the Smithsonian Institution in Chantilly, Virginia, and the Museum of Flight in Seattle, Washington. Notable aircraft on display with their original engines include the Boeing B-50 "Lucky Lady II" at the Pima Air & Space Museum and several Convair B-36 airframes, such as those at the Strategic Air Command & Aerospace Museum and the National Museum of the United States Air Force.

Category:Aircraft piston engines Category:Pratt & Whitney aircraft engines Category:Radial aircraft engines