B-49 Flying Wing
The YB-49 evolved from the unconventional XB-35 "flying wing; its development being prompted by a 1944 study of the possibilities of converting the propeller driven XB-35 to turbojet engines. Actually, the YB-49 project and its reconnaissance counterpart represented the continuing effort of the Army Air Forces (AAF) and Northrop to establish a tactical use for the original "flying wing;' yet to be flown but already plagued by virtually insurmountable problems.
On 1 June 1945, Change Order 11 to Contract W535-ac-33920, a December 1942 document calling for 13 B-35 prototypes, confirmed earlier verbal decisions and authorized Northrop to convert 2 future YB-35s to the YB-49 configuration.
Conversion of the YB-35 to the YB-49 configuration, due to be completed by June 1946, slipped more than a year. The delay was caused by unforeseen problems, encountered in adding fins to the wings to provide the stabilizing effect that the propellers and propeller shaft housings gave to the basic XB-35.
The YB-49 featured eight 4,000 pound thrust J35 engines, 2 more than planned; 4 small trailing edge fins, to replace the XB-35's yaw dampening prop shaft housings; 4 large wing fences; and a reconfigured leading edge ahead of and between each pair of fences that provided a low drag intake slot for each of the 2 sets of jet engines. In most other respects, since the all metal XB-35 airframe was used for the conversion, the YB-49 was identical to the YB-35.
The initial flight of the first YB-49 occurred on 21 October 1947, from the contractor's plant in Hawthorne to Muroc Army Airfield, both in California. The new prototype's first flight lasted 34 minutes without incident. The second YB-49 was first flown on 13 January 1948, from and to the same places and also without special difficulties.
Testing of the first YB-49 was extensive. Northrop test flew it for almost 200 hours, accumulated in some 120 flights; the Air Force completed about 70 hours, totaled in some 20 flights (Conflicting information did not allow the computation of absolute figures. However, extensive research by various Air Force historians confirmed the stated estimates). Early in 1948, Northrop began test flying the second YB-49. Some 24 flights were made by the contractor's pilots for a near total of 50 hours. The Air Force test flew the second YB-49 5 times, for perhaps 13 hours. In the YB-49's case, early test results acquired special significance. Magically, just after being officially accepted by the Air Force, the second YB-49 crashed, killing its entire 5 man crew. Capt. Glen Edwards, from the Air Materiel Command Flight Test Division, was co pilot on this fatal trip. Muroc Army Air Base, after becoming Muroc AFB on 12 February 1948, was renamed Edwards AFB on 5 December 1949, in honor of Captain Edwards.
Investigations of the second YB-49's crash could assign no specific cause for the accident, but determined that a major structural failure had taken place in flight. An eyewitness described the plane as tumbling uncontrollably about its lateral axis just before hitting the ground. Project officers later verified that under certain conditions a "flying wing" would indeed "somersault" through the air. The loss of the aircraft and further wind tunnel work perpetuated doubts concerning the flying wing's aerodynamic stability and revealed the need for additional flight testing.
By 1948, progress in range extension had relegated the YB-49 to the status of a medium bomber. Actually, the YB-49 was the largest of the medium bombers under consideration, but it faced stiff competition from the B-45 (already in production), and from the XB-46, XB-47, and XB-48 (all in flight test). Soon afterward, and although the project would not be firmed up for another year or so, the Aircraft and Weapons Board decided to use flight test results to evaluate the B-47 and B-49 as possible "special piloted atomic" carriers. The YB-49 program also profited from the Air Materiel Command's decision to de-emphasize turboprop propulsion and push turbojet development. Yet, other aspects of the program were not so favorable.
The first YB-49 made a significant flight on 26 April 1948, a test of the aircraft's range which proved quite successful. The aircraft was aloft 9 hours, of which 6 hours were flown at an altitude of 40,000 feet. Both accomplishments were believed to set records for that period. Only 1 engine and 1 auxiliary power unit failure marred the otherwise excellent performance. But the second YB-49's fatal crash in June prompted the contractor and the Air Force to decide that the remaining prototype would be flight tested an extra 125 hours, and the testing that ensued gave mixed results.
Meanwhile, Lt. Gen. Benjamin W. Chidlaw, Deputy Commander of the Air Materiel Command, had ordered that determination of the YB-49's stability as a bombing platform be given first priority. Evaluated against a B-29 on comparable mission tests, the YB-49 (without an autopilot) performed poorly. Pilots concluded that the jet equipped "flying wing" was "extremely unstable" and found it "impossible to hold a steady course or a constant airspeed and altitude." The YB-49's circular average error and range error were twice those of the B-29. Finally, the B-29 invariably acquired bomb run stability in under 45 seconds, while the YB-49's best time was over 4 minutes. Clearly, the B-49 program was doomed unless sweeping improvements were made to correct the performance defects demonstrated by the prototype.
A total of 2 YB-49s were accepted. The first YB-49 was not accepted by the Air Force until 15 March 1950 (after being extensively tested by the contractor). The second, ill fated B-49 prototype was transferred to the Air Force on 28 May 1948. Northrop considered the airplane officially accepted on 5 June, when it crashed.
The October 1948 conclusion of the primary evaluation tests comparing the YB-49 and the B-29, and the YB-49's poor showing most likely determined the outcome of the B-49 program. Just the same, the YB-49 testing was extended, and even though remote, the possibility remained that the program might survive its initial calamities. This did not prove to be the case. Between May 1948 and the spring of 1949, the B-49 prototype was involved in 5 incidents, most of them due or related to engine problems. On 26 April 1949, a fire occurred in 1 of the aircraft's engine bays, necessitating $19,000 worth of repairs. Cancellation of the B-49 program became official on 15 March 1950 the day the sole XB-49 crashed and testing came to an abrupt end. There were no fatalities, but crewmen were injured and the airplane was completely destroyed. Failure of the nose gear was the accident's basic cause. Contributing factors were excessive shimmy of the nose wheel and final collapse of the gear, resulting from the unsatisfactory center of gravity.
After 1948, the additions and withdrawals of funds made a separate appraisal of any one aircraft's cost impractical, especially since the Air Force found it difficult to secure anything but an overall "flying wing" program cost estimate from Northrop.
The second YB-49 was totally destroyed on 5 June 1948; the first, on 15 March 1950.
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