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B-47 Stratojet 376th Bomb Wing Model


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B-47 Stratojet 376th Bomb Wing Model

Fly with SAC and the 376th Bomb Wing in this handcrafted B-47 model. Each piece is carved from wood and hand painted to provide a piece you’ll love. 18 inches

The B-47 arose from an informal 1943 requirement for a jet-powered reconnaissance bomber, drawn up by the U.S. Army Air Forces (USAAF) to prompt manufacturers to start research into jet bombers. Boeing was among several companies that responded to this request; its initial design, the Model 424, was basically a scaled-down version of the piston-engined B-29 Superfortress equipped with four jet engines.[2]

In 1944 this initial concept evolved into a formal request-for-proposal to design a new bomber with a maximum speed of 550 mph (890 km/h), a cruise speed of 450 mph (720 km/h), a range of 3,500 mi (5,600 km) and a service ceiling of 45,000 ft (13,700 m).[3] In December 1944, North American Aviation, the Convair Corp., Boeing and the Glenn Martin Company submitted proposals for the new long-range jet bomber. Wind tunnel testing had shown that the drag from the engine installation of the Model 424 was too high, so Boeing’s entry was a revised design, the Model 432, with the four engines buried in the forward fuselage.[4]

The USAAF awarded study contracts to all four companies, requiring that North American and Convair concentrate on four-engined designs (to become B-45 and XB-46), while Boeing and Martin were to build six-engined aircraft (the B-47 and XB-48). The powerplant was to be General Electric’s new TG-180 turbojet engine.[4]

Swept wings
In May 1945, the von Kármán mission of the Army Air Forces inspected the secret German aeronautics laboratory near Braunschweig. On von Kármán’s team was the eminent chief of the technical staff at Boeing, George S. Schairer. He had heard about the controversial swept-wing theory of R. T. Jones at Langley, but seeing models of swept-wing aircraft and extensive supersonic wind-tunnel data generated by the Germans, the concept was decisively confirmed. He wired his home office: “Stop the bomber design”, and changed the design of the B-47 wing.[5]

Analysis work by Boeing engineer Vic Ganzer suggested an optimum sweepback angle of about 35 degrees.[6] Boeing’s aeronautical engineers modified their Model 432 design to include swept wings and tail, resulting in the “Model 448”, which was presented to the USAAF in September 1945. The Model 448 retained its four TG-180 jet engines in its forward fuselage, with two more TG-180s in the rear fuselage. The flush-mounted air intakes for the rear engines were inadequate, while the USAAF disliked the installation of engines within the fuselage, considering it a fire hazard.[4][7]

The engines were moved out to streamlined pods (pylon mounted) under the wings, leading to the next iteration, the Model 450, which featured two TG-180s in a twin pod mounted on a pylon about a third of the way outboard on each wing, plus another engine at each wingtip. The Army Air Force liked this new configuration, and so Boeing’s team of engineers continued to refine it, with the outer engines being moved further inboard, to about 3/4 of the wingspan. The thin wings provided no room into which wheels could be retracted, so a “bicycle landing gear” was chosen, with the two main gear assemblies arranged in a tandem configuration and outrigger struts fitted to the inboard engine pods. As the landing gear arrangement made rotation (i.e., lifting the nose during takeoff) impossible, the landing gear was designed so that the aircraft rested on the ground at the proper angle for takeoff.[4][8]

USAAF selects Boeing
The USAAF was very pleased with the refined Model 450 design, and in April 1946, the service ordered two prototypes, to be designated “XB-47”.[9] Assembly began in June 1947.

The first XB-47 was rolled out on 12 September 1947,[8] a few days before the USAAF became a separate service, the U.S. Air Force, on 18 September 1947. The XB-47 prototype flew its first flight on 17 December 1947 (the anniversary of the Wright Brothers’ first four flights on 17 December 1903), with the test pilots Robert Robbins and Scott Osler at the controls of the aircraft. It flew from Boeing Field in Seattle to the Moses Lake Airfield in central Washington state, in a flight that lasted just 27 minutes,[10][11] with no major problems. Robbins had to pull up the flaps with the “emergency hot wire system”, and the “engine fire” warning indicators were falsely lit. Robbins reported that the flight characteristics of the aircraft were good.[12]

In Feb. 1949, Russ Schleeh and Joe Howell “broke all coast-to-coast speed records” flying from Moses Lake Air Force Base to Andrews Air Force Base. They averaged 607.8 miles per hour.[12]:34–36

During early tests of the XB-47 prototype, the canopy came off at high speed, killing pilot Scott Osler.[13] The copilot safely landed the aircraft. This resulted in a canopy redesign, and the hiring of pilot Tex Johnston as chief test pilot.[14]

Second X-model
The second XB-47 (46-066) prototype first took to the air on 21 July 1948 and following its delivery to the USAF in December of that year, it served as a flying test bed until its retirement in 1954. Its final destination was Chanute AFB where it was used as a maintenance and familiarization aircraft.[15]

This second prototype was equipped with much more powerful General Electric J47-GE-3 turbojets with 5,200 lbf (23 kN) of static thrust each.[16] The J47 or “TG-190” was a redesigned version of the TG-180/J35. The first XB-47 prototype was later retrofitted with these engines.

Flight testing of the prototypes was particularly careful and methodical, since the design was new in so many ways. The prototypes initially suffered from “Dutch roll”, an instability that caused the aircraft to weave in widening “S” turns. This problem was remedied by the addition of a “yaw damper” control system that applied rudder automatically to damp out the weaving motion. The prototypes also had a tendency to pitch up. This problem was solved by adding small vanes called “vortex generators” onto the wings that caused turbulence to prevent airflow separation.

Boeing test pilot Rob Robbins had originally been skeptical about the XB-47, saying that before the initial flight he had prayed, “Oh God, please help me through the next two hours.” The aircraft was “considered to be a radical airplane”. Robbins soon realized that he had an extraordinary aircraft.[12]

Chuck Yeager flew the XB-47 later in its development cycle and years later noted that the aircraft was so aerodynamically clean that he had difficulty putting it down on the Edwards lakebed.[17]

Both XB-47 prototypes were test flown at Edwards AFB, however the number one XB-47 (46-065) was disassembled and eventually scrapped by the Air Force in 1954, thus making the number two prototype (46-066) the sole surviving XB-47.

Upon retirement, XB-47 (46-066) was restored and placed on display at the Octave Chanute Aerospace Museum in Rantoul, Illinois where it remained on display until the museum announced it was closing its doors due to financial difficulties in April 2015.[18] In late 2015, the Flight Test Historical Foundation began fundraising efforts to purchase XB-47 (46-066) for relocation to the Flight Test Museum at Edwards AFB. The purchase was completed in August 2016 and on September 21, 2016 the aircraft arrived at Edwards AFB for reassembly, restoration and eventual display at the Flight Test Museum.[19]

X-model competitions
By mid-1948, the Air Force’s bomber competition had already been through one iteration, pitting the North American XB-45 against the Convair XB-46. The North American design won that round of the competition; as an interim measure, the USAF decided to put the North American bomber into production on a limited basis as the B-45 Tornado. The expectation was that B-45 production would be terminated if either of the remaining two designs in the competition, the Boeing XB-47 and the Martin XB-48, proved superior. It is sometimes claimed that the final production decision was made as a result of Boeing president Bill Allen inviting USAF General K.B. Wolfe, in charge of bomber production, for a ride on the XB-47.[20] A formal contract for 10 aircraft was signed on 3 September 1948.[21] Wiki