Pratt & Whitney R-4360 Wasp Major

Pratt & Whitney R-4360 Wasp Major
Name	R-4360 Wasp Major
Type	Radial engine
National origin	United States
Manufacturer	Pratt & Whitney
First run	1944
Major applications	Boeing B-50 Superfortress Convair B-36 Peacemaker Boeing C-97 Stratofreighter
Number built	18,697
Developed from	Pratt & Whitney R-2800 Double Wasp

Pratt & Whitney R-4360 Wasp Major was a large aircraft piston engine and the most powerful radial engine produced in the United States. Developed during the final years of World War II by Pratt & Whitney, it powered a generation of massive strategic bombers, transport aircraft, and ambitious experimental planes. Its complex 28-cylinder design represented the pinnacle of piston engine technology before the widespread adoption of the jet engine.

Design and development

The engine's design originated from a United States Army Air Forces request for an engine exceeding 3,000 horsepower. Engineers at Pratt & Whitney in East Hartford, Connecticut, created a unique "corncob" configuration featuring four rows of seven cylinders each, arranged in a spiral for optimal cooling. This 28-cylinder layout was an evolution of the earlier 18-cylinder Pratt & Whitney R-2800 Double Wasp. The massive engine required advanced features like fuel injection and a sophisticated turbocharger system, developed in conjunction with General Electric. The immense power and mechanical complexity presented significant challenges in cooling and reliability during its development phase.

Operational history

The R-4360 entered service too late for combat in World War II, but it became a cornerstone of early Cold War United States Air Force and United States Navy aviation. It was the primary powerplant for the postwar Boeing B-50 Superfortress, an upgraded version of the Boeing B-29 Superfortress, and famously powered the ten-engine Convair B-36 Peacemaker, a key nuclear deterrent. Its service was marked by immense power output but also by demanding maintenance requirements and occasional reliability issues, particularly with its intricate propeller gearing and cylinder cooling in rear rows.

Variants

Numerous variants were produced to suit different airframes and roles. Key models included the R-4360-41 for the Boeing C-97 Stratofreighter and its commercial derivative, the Boeing 377 Stratocruiser. The R-4360-53 powered the Boeing B-50 Superfortress, while the R-4360-20W series, with water injection, was used on the Convair B-36 Peacemaker. The United States Navy utilized versions like the R-4360-4 in the Martin JRM Mars flying boat. Special high-performance variants were developed for racing aircraft like the Pratt & Whitney R-4360-powered Republic XP-72.

Applications

The engine was synonymous with large, multi-engine aircraft of the 1940s and 1950s. Its major military applications included the Boeing B-50 Superfortress, Convair B-36 Peacemaker, Boeing C-97 Stratofreighter, Fairchild C-119 Flying Boxcar, and the Douglas A-1 Skyraider. In commercial aviation, it powered the Boeing 377 Stratocruiser and the Hughes H-4 Hercules. It also found use in experimental projects like the Northrop YB-35 flying wing and the Republic XF-12 Rainbow, and even in land speed record cars like the Summers Brothers' "Goldenrod."

Specifications (R-4360-59B)

* **Type:** 28-cylinder, air-cooled, four-row radial piston engine * **Bore:** 5.75 in (146 mm) * **Stroke:** 6.00 in (152 mm) * **Displacement:** 4,362.5 cu in (71.5 L) * **Length:** 96.5 in (2.45 m) * **Diameter:** 55.1 in (1.40 m) * **Dry weight:** 3,870 lb (1,755 kg) * **Valvetrain:** Two poppet valves per cylinder * **Supercharger:** Gear-driven single-stage centrifugal type with General Electric turbocharger * **Fuel system:** Bendix-Stromberg fuel injection * **Cooling system:** Air-cooled * **Power output:** 3,500 hp (2,600 kW) at 2,800 rpm * **Specific power:** 0.80 hp/cu in (36.6 kW/L) * **Compression ratio:** 6.7:1 * **Power-to-weight ratio:** 0.90 hp/lb (1.48 kW/kg)

Survivors

Many surviving R-4360 engines are displayed in museums alongside the aircraft they powered. Complete engines can be seen at 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. Aircraft like the Boeing B-50 Superfortress "Lucky Lady II" at the National Museum of the United States Air Force and various Douglas A-1 Skyraider examples in collections such as the Yanks Air Museum preserve operational examples. Several engines are also held in private collections and by organizations like the New England Air Museum.

Category:Pratt & Whitney aircraft engines Category:Radial aircraft engines Category:Aircraft piston engines 1940–1949