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Boeing - Pratt & Whitney
 

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The XB-44

The XB-44 was a modification of a Boeing B-29A-5-BN (S/N 42-93845) done by Pratt & Whitney to adapt the aircraft for R-4360 supercharged radial engines. The larger and more powerful engines required a complete redesign of the engine nacelles which featured a distinctive scoop air inlet on the underside. The XB-44 was never intended to be anything except an engine test-bed, but it carried minimal defensive armament--two .50-cal. machine guns in the tail.

The XB-44 program was initiated in mid-1943 when Pratt & Whitney offered to modify a B-29 with larger engines, a contract was awarded in July 1944, and the first flight of the aircraft occurred in May 1945. The XB-44 was capable of cruising speeds about 50-60 mph. faster than a production B-29.

Although the XB-44 was superior to the B-29, the entire program was near cancellation because of the approaching end of World War II and rapid demobilization. The Army Air Forces needed a very heavy bomber and lobbied for continuation of the program. Initially, a production version design was designated B-29D, but because Boeing engineers had modified the basic B-29 design extensively, the aircraft was re-designated B-50. The first production versions were produced as B-50A. Ironically, the aircraft initially classified as a very heavy bomber in the mid-1940s was, by the end of its service life, classified as a medium bomber. Aircraft like the B-36 and B-52 dwarfed the last of the USAF's propeller driven bombers.

TYPE XB-44

Number Built/Converted 1 (cv)

Remarks B-50 prototype, a.k.a. XB-29D

Notes:

• Serial number: 42-93845, originally B-29A-5-BN

SPECIFICATIONS
Span: 141 ft. 3 in.
Length: 99 ft. 0 in.
Height: 29 ft. 7 in.
Weight: 140,000 lbs. (max. gross weight)
Armament: Two .50-cal. machine guns in the tail
Engines: Four Pratt & Whitney R-4360-33 Wasp Major supercharged radials of 3,000 each (takeoff power)
Crew: 11 maximum, although it usually flew with a smaller test crew.

PERFORMANCE
Maximum speed: 392 mph. at 25,000 ft.
Cruising speed: 282 mph.
Range: 2,400 miles
Service Ceiling: 39,000 ft.
 

 

Boeing B-29D/XB-44 Superfortress

 

Joe Baugher

The Wright-powered B-29 had always been somewhat underpowered for its weight, and it became clear that the aircraft could take substantially more engine power if it were available. In pursuit of this objective, one B-29A (42-93845) was handed over to Pratt & Whitney for conversion as a testbed for the new four-row 28-cylinder Pratt & Whitney R-4360 Wasp Major air-cooled radial engine, which was rated at 3500 hp. The aircraft was later redesignated XB-44, and was readily recognizable by the new engine installation, with the oil cooler intake pulled further back on the lower part of the nacelle.

An order for 200 production examples under the designation B-29D was placed in July of 1945, but was reduced to only 50 after V-J Day. In December of 1945, the designation of the B-29D was changed to B-50A. This was a ruse to win appropriations for the procurement of an airplane that appeared by its designation to be merely a later version of an existing model that was already being cancelled wholesale, with many existing models being put into storage. Officially, the justification for the new B-50 designation was made on the basis that the changes introduced by the B-29D were so major that it was essentially a completely new aircraft. The ruse worked, and the B-50 survived to become an important component of the postwar Air Force.

By Joe Baugher

Sources:

1. Warbird History--B-29 Superfortress, Chester Marshall, Motorbooks International, 1993.
    

2. The Boeing B-29 Superfortress, Mich Mayborn, Aircraft in Profile, Doubleday, 1969.
    

3. B-29 Superfortress, John Pimlott, Gallery Books, 1980.
    

4. Famous Bombers of the Second World War, William Green, Doubleday, 1960.
    

5. Jane's Fighting Aircraft of World War II, Bill Gunston, Military Press, 1989.
    

6. Boeing Aircraft Since 1916, Peter M. Bowers, Naval Institute Press, 1989.
    

7. United States Military Aircraft Since 1909, Gordon Swanborough and Peter M. Bowers, Smithsonian Institution Press, 1989.
    

8. Jane's Fighting Aircraft of World War II, Bill Gunston, Military Press, 1989.
    

9. American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 1982.

 

Boeing XB-44 Superfortress

 

XB-44 Superfortress
Boeing XB-44
Role	Test Plane
Manufacturer	Boeing

The Boeing XB-44 Superfortress was a United States B-29 Superfortress bomber aircraft upgraded with Pratt & Whitney R-4360-33 Wasp Major radial engines of 3,000 horsepower (2,200 kW) takeoff rating, in place of the production engines rated at 2,200 hp (1,600 kW) takeoff rating.

 

Development

The program began in mid-1943, when Pratt & Whitney proposed to the United States Army Air Forces (USAAF) that the B-29 be modified with larger engines. In July 1944, a contract was signed and one B-29A-5-BN (s/n 42-93845) was made available to P & W for developmental work. Modification involved complete redesign of the four engine nacelles, including the addition of a large airscoop below each cowling.

Because the aircraft was intended to be only a testbed for the engine installation, most of its defensive equipment was removed before testing. Two machine guns in the rear fuselage were left in place.

Only the one aircraft was used in the B-44 flight test program.^]

First flying in May 1945, the XB-44 proved 50-60 mph faster than the B-29 (available sources do not indicate how much of this increased speed was due to differing aircraft weight or to deleted armament).

Production of the re-engined bomber was initially planned as the B-29D, but it was decided to change the aircraft designation in military inventory because of the extensive airframe changes that would be required (this design work would have to be performed by the aircraft manufacturer, Boeing; it was not performed on the B-44 prototype except for the engine nacelle rework). The upgrade program became the B-50 Superfortress in December 1945. Officially, the aircraft's new designation was justified by the changes separating the proposed B-29D from its predecessors:

• New engines

• New engine nacelles and engine mounts

• Larger vertical tail required for engine-out stability

• Wing reinforcing due to greater engine weight

• Revised routing for combustion and exhaust gases

• Upgraded armament-control equipment

• Increases in landing gear capability

• Added fuel capacity

However, according to Peter M. Bowers, a long-time Boeing employee and small aircraft designer, and a well-known authority on Boeing aircraft, "the redesignation was an outright military ruse to win appropriations for the procurement of an aeroplane that by its designation appeared to be merely a later version of an existing model that was being canceled wholesale, with many existing examples being put into dead storage."

 

Engine Power

 

When the R-4360 was first developed, its takeoff power rating was 3000 horsepower. By the time it was incorporated into the B-50, its MTO rating was 3,500 horsepower (2,600 kW), and even higher when used in other aircraft (e.g., 3800 in the Convair B-36). Much of the difference is due to differing turbochargers installed in the different aircraft (the engine also contains a supercharger, gear-driven by the crankshaft).

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