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The B-47C was the initial designation for a design project initiated in January 1950 to redesign the aircraft for four Allison J35-A-23 turbojets in place of the six General Electric J47s. The C model configuration was nearly identical to the B-47B with the exception of the inboard engine nacelles -- one J35 was to be mounted in place of the two J47s on the production B model. One B-47B-20-BW (S/N 50-082) was scheduled for modification and the first flight was estimated for April 1951.
Because of delays and problems with the engines, a number of alternatives were proposed. The original Allison J35-A-23s turbojets had estimated performance of 9,700 pounds thrust each at maximum power (with afterburners) and a normal power rating of 8,200 pounds thrust each. The actual J35 performance was no where near the estimates (about 7,400 pounds maximum power and 5,600 pounds normal) so alternative engines were proposed.
The Allison J71-A-5 was the first engine considered for replacing the J35. The J71 had maximum thrust above 10,000 pounds at military power but other problems and delays forced it to be dropped from the B-47C project as well. By this time, the B-47C project designation was dropped and redesignated B-56. The Pratt & Whitney J57 was evaluated for the B-56 project, but it was still in development and delivery delays were unacceptable. The Boeing B-52 project was well underway by this time and had higher priority for the J57s when they became available.
The initial prototype conversion of the B-47B was first designated YB-47C then YB-56. A production version of the aircraft was designated B-56A and a photo reconnaissance version was designated RB-56A. The entire B-47C/B-56 project was canceled in December 1952 before conversion of the B-47B began.
Features incorporated in the B-56A preliminary design included cabin pressurization, thermal anti-icing, bombing-navigation radar, gun laying radar, anti-skid brakes, bail-out spoiler door, internal fuel purging, camera provisions, braking parachute, single point refueling, air refueling provisions and a maximum fuel capacity of 17,350 gallons.
||Four-engine version of B-47B
TECHNICAL NOTES (estimated as of March 1, 1950, as B-56A with J35 engines):
Armament: Two radar-directed .50-cal. machine guns with 1,200 rounds ammunition in a tail turret and up to 25,000 lbs. of conventional or nuclear bombs (maximum bomb load was one 25,000-lb. bomb)
Engines: Four Allison J35-A-23 axial flow turbojet engines of 9,700 lbs. thrust each (estimated)
or four Allison J71-A-5 axial flow turbojet engines of 10,700 lbs. thrust each or four Pratt & Whitney J57 dual-rotor axial flow turbojets of 10,000+ lbs. thrust
Rocket Assisted Take Off engines: One Aerojet YLR-45-AJ-1 or one M.W. Kellogg YLR-47-K-1; each with four rocket chambers of 5,000 lbs. thrust each; 20,000 lbs. total thrust with 60-second duration.
Cruising speed: 426 knots at approx. 35,000 ft.
Combat radius: 2,175 nautical miles with 10,000-lb. payload at 426 knots average in 10.4 hours
Combat range: 4,225 nautical miles with 10,000-lb. payload at 426 knots average in 10.0 hours
Service ceiling: Approx. 42,200 ft.
Span: 116 ft. 0 in.
Length: 106 ft. 7 in.
Height: 27 ft. 9 in.
Crew: Three (pilot, copilot-radio operator-gunner, bombardier-navigator)
Serial number: B-47B 50-082 was to be converted to YB-47C before project cancellation
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