Development of the B-47 can be traced back to June 1943, when an informal Army Air Forces (AAF) request led several aircraft manufacturers to begin design studies of multi jet aircraft that could be used for fast photographic reconnaissance or medium bomber missions. Requirements had to be readied and money had to be found before a formal announcement could be made. Yet the procedure followed in June 1943 was not unusual and could only benefit the AAF. In this case, it might also have had the distinct advantage of keeping Boeing engineers busy and preventing them from drifting to Navy projects upon completion of their work on the development of along range bomber. The AAF already knew that Convair had pretty well clinched the long range bomber program (a B-36 production order had just been issued) and that the concurrent procurement of a similar bomber was out of the question. (Boeing did not receive a study contract for its "long range" XB-52 until mid 1946.)
General Electric's successful development of an axial flow jet engine, easier to install in wing nacelles than previous jet types, came at the same time as the manufacturers began design studies. This undoubtedly was important. Boeing and several other companies quickly included the new engine in their planning. But more crucial to the aircraft's development was Boeing's use at war's end of captured : German research data on the design of swept back wings. This led in 1947 to the sensational XB-47.
The informal requirements of 1943 became official on 17 November 1944. The AAF issued military characteristics for a jet propelled medium bomber with a range of 3,500 miles, a service ceiling of 45,000 feet, an average speed of 450 miles per hour, and a top speed of 550. Besides the Boeing Airplane Company of Seattle, Washington, the other firms North American Aviation, Incorporated, Convair, and the Glenn L. Martin Company entered the design competition prompted by these requirements. The Boeing entry (Model-432), designated the XB-47 by the AAF, was a straight wing design resembling a B-29 with much thinner wings and carrying 4 of the new General Electric axial flow jet engines. To overcome problems experienced with the engine pod nacelles of a previous design, Boeing had buried the new engines inside the fuselage of Model 432. All designs submitted by the other companies featured wing nacelles for housing the jet engines. Letter contracts for development and mockups of the 3 designs were awarded in the fall of 1944, resulting in the North American XB-45, Convair XB-46, and Martin XB-48. Of these, only the North American XB-45 went into production.
The letter contract came on 1 February 1945. This letter contract authorized Boeing to spend up to $150,000 (against an estimated $1.5 million set aside for development) in a Phase I (wind tunnel) study of Model 432, Boeing's first entry in the recently opened medium bomber competition. The model nevertheless was rejected on the grounds that the location of the engines could be unsafe. The AAF actually thought that Boeing engineers should do more research in the basic jet problems associated with high speed bombers. To achieve superiority in the air would require a new concept superior to any of the current bomber designs. Early in September, Boeing revised the original configuration of Model 432 and proposed its first swept wing bomber design. Labeled Model 448 (the AAF designation remained XB-47), the new aircraft featured a thin wing swept back and 2 more engines--a total of 6 engines. The AAF liked the wing configuration of Model 448, but still insisted that housing engines inside a fuselage created a fire hazard. Besides, externally mounted engines were easier to maintain and replace, which could add years to the service life of an aircraft. Boeing's hasty return to the drawing board resulted in Model 450, which carried 6 jet engines hung under the wings in pods--2 pairs in strut mounted inboard nacelles and single units attached directly under the wing, at a distance of 8 feet from the wing tip. The AAF promptly approved Model 450 in October 1945.
In December, a technical instruction authorized contractual negotiations for the development of 2 experimental aircraft. The AAF endorsed Boeing's proposal to build and test 2 flyable XB-47's for $9,357,800, counting the $1.5 million that had been set aside for development of the straight wing design (Model 432) initially submitted by Boeing. The proposed planes would be bare of any tactical equipment, but necessary space would be provided. The subsequent discovery that more equipment space was needed and that some structural changes had to be made raised Boeing's original quotation to $9,441,407. This figure also was approved, after the Wright Field price control experts concluded that the XB-47's cost of $95 per airframe pound was reasonable and considerably lower than the corresponding costs of the XB-45 and XB-48 bombers. Nonetheless, the letter contract of February 1945 was not officially amended until 17 April 1946 (after completion of the XB-47 mockup).
The XB-47 mockup was completed, inspected, and approved in the spring of 1946. Army Air Forces personnel attending the XB-47 mockup seemed impressed. Just the same, the Mockup Committee suggested major changes in the nose compartment, pilot and co pilot seating, and landing gear arrangement. The Chief of the AAF Requirements Division cautioned that any additional weight would cut down the speed of the XB-47, thus defeating the purpose for which the plane was designed.
Even though the XB-47 mockup had been well received, development of the experimental plane took longer than expected. Actual work began in June 1946, but progress was hampered by problems with the aircraft landing gear (The XB-47's thin swept wing eliminated any possibility of suspending a landing gear or retracting one into it. The problem was solved, however, with the installation of a tandem gear, fairly similar to the type previously tested on a Martin B-26. The new arrangement had an additional advantage: reducing the XB-47's weight by 1,500 pounds), control surfaces, as well as bottlenecks in power plant installations. The initial lack of overtime pay for the Boeing personnel did not help. All told, a 6 month slippage occurred.
It took a year and a half to complete the contractual negotiations initiated by the technical instruction of December 1945. The definitive fixed price contract (W33-038-ac-8429) of July 1947 called for 2 stripped XB-47s, spare parts, mockups of the completed airplane and fuselage, wing tunnel tests, and research data at a total cost of almost $9.7 million--about $25,000 more than the cost of the amended letter contract of April 1946, which the fixed price contract superseded. Moreover, the AAF estimated that post test flight changes most likely would raise the aggregate cost of the contract to more than $10.5 million--a prediction that did materialize. By February 1950, numerous change orders had brought total costs near the $12 million mark.
The first XB-47 rolled out of the Seattle factory in the same month that the United States Air Force was established. The plane was even more startling than the spectacular B-17 Flying Fortress had been 12 years before. The swept wing had already been used experimentally by the Bell Aircraft Corporation on 2 modified P-63 Kingcobras and by North American on the XP-86, first flown in October 1947, but this was the first time the design appeared on a large American jet.
The experimental B-47 was flown from Seattle to nearby Moses Lake AFB, Washington, to begin a series of extensive flight tests. Bad weather delayed the flight until 17 December 1947. 44 years to the day after the Wright brothers' first manned flight at Kitty Hawk, North Carolina.
The Air Force flew the first XB-47 (Serial No. 46-065) for about 83 hours, including nearly 38 hours of Phase II flight tests that were accomplished between 8 July and 15 August 1948. The contractor tested the XB-47 during most of the aircraft's 6 years of life, accumulating more than 330 hours of test flights in the process. In 1954, having been stripped of wings and engines, the experimental B-47 was cut in 2 and exhibited at Palm Beach AFB, Florida.
The Boeing pilots that first flew the XB-47 liked it. After completion of the first phase of testing, a Boeing pilot remarked, "The plane still is doing much better than anyone had a right to expect. We're still exploring one thing at a time, but every door we've kicked open so far has had good things inside." Just the same, the XB-47's overall performance proved disappointing. Its maximum altitude was 2,500 feet below the 40,000 foot ceiling proposed by Boeing and 7,500 feet lower than originally required by the AAF. Its speed was also slower than expected. In fact, in mid 1949 the XB-47 exchanged its six J35-GE-7/9 engines for the larger 5,200 pound thrust J47-GE-3s that equipped the second XB-47 from the start.
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