Boeing B-47 Stratojet
The Boeing B-47 Stratojet long range, six-engine, turbojet-powered strategic bomber made its Maiden flight 17 December 1946. It was designed to fly at high subsonic speed and at high altitude to avoid enemy interceptor aircraft. The B-47’s primary mission was to drop nuclear bombs on the Soviet Union. The B-47 entered service with the United States Air Force’s Strategic Air Command (SAC) in 1951. It never saw combat as a bomber, but was a mainstay of SAC’s bomber strength during the late 1950s and early 1960s, and remained in use as a bomber until 1965. It was also adapted to a number of other missions, including photographic reconnaissance, electronic intelligence and weather reconnaissance. The B-47 arose from a requirement for a jet-powered reconnaissance bomber, drawn up by the U.S. Army Air Forces (USAAF). Boeing was among several companies who responded its initial design, the Model 424, was basically a scaled-down version of the piston-engined B-29 Superfortress equipped with four jet engines.
In 1944 this initial concept evolved into 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). 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. The USAAF awarded contracts to four companies – North American and Convair concentrate on four-engined designs (to become B-45 and XB-46), while Boeing and Martin built six-engined aircraft (the B-47 and XB-48) powered by General Electric’s new TG-180 turbojet engine.
In May 1945, the von Kármán mission of the Army Air Forces inspected the secret German aeronautics laboratory near Braunschweig. The chief of the technical staff at Boeing, George S. Schairer had heard about the swept-wing theory of R. T. Jones at Langley, and after seeing models of swept-wing aircraft and extensive supersonic wind-tunnel data generated by the Germans, changed the design of the B-47 wing.Analysis work by Boeing engineer Vic Ganzer suggested an optimum sweepback angle of about 35 degrees. So Boeing’s aeronautical engineers modified their Model 432 to create 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. However 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 on each wing, plus another engine at each wingtip. Boeing’s team of engineers continued to refine it, with the outer engines being moved further inboard. In 1946 The USAAF ordered two prototypes, designated “XB-47”.
The first XB-47 was rolled out on 12 September 1947, and 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 Flying from Boeing Field in Seattle to the Moses Lake Airfield in central Washington state.In 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 averaging 607.8 miles per hour. During early tests of the XB-47 prototype, the canopy came off at high speed, killing pilot Scott Osler resulting in a canopy redesign. The second XB-47 (46-066) prototype flew on 21 July 1948 Serving as a flying test bed until retiring in 1954. This had more powerful General Electric J47-GE-3 turbojets with 5,200 lbf (23 kN) of static thrust each. Chuck Yeager also flew a test of the XB-47.
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 until it closed in 2015. Whereupon 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 21st, 2016 the aircraft arrived at Edwards AFB for reassembly, restoration and eventual and it is currently on display at the Flight Test Museum.
In 1948 USAF decided to put the North American bomber into production on a limited basis as the B-45 Tornado. the Boeing XB-47 and the Martin XB-48, proved superior and A formal contract for 10 aircraft was signed on 3 September 1948. The USAF Strategic Air Command operated B-47 Stratojets (B-47s, EB-47s, RB-47s and YRB-47s) from 1951 through 1965. The B-47 had a three man crew – the aircraft commander, copilot, and a navigator/bombardier or a crew chief
Unfortunately the B-47 initially had a few problems The aircraft was sluggish on takeoff and too fast on landings, a very unpleasant combination. If the pilot landed at the wrong angle, the B-47 would “porpoise”, bouncing fore-and-aft. If the pilot did not lift off for another go-around, instability would quickly cause the bomber to skid onto one wing and cartwheel. However by 1953 it was redesigned and performance was closer to that of jet fighters of the period and it was so fast and agile the aircraft set records with ease. Improved training led to a good safety record.The B-47’s reliability and serviceability were regarded as good although avionics reliability remained problematic throughout the B-47’s operational life.
From 1950, several models of the B-47 included a fuel tank inerting system in which
carbon dioxide vapor was used while fuel pumps operated or during in flight refueling to reduce the amount of Oxygen and minimize the risk of an explosion caused by static electricity discharge. An XB-47 was flown in the 1951 Operation Greenhouse nuclear weapons testing. This was followed by a B-47B being flown in the 1954 Operation Ivy and the 1955 Operation Castle. A B-47E was then flown in the 1956 Operation Redwing. Three B-47s flew cross country from March Air Force Base to the Philadelphia International Airport as participants in the 1955 Labor Day race. In the 1956 event, three B-47s participated in the G.E. Trophy race for Jet Bombers, flying from Kindley Field, Bermuda, to Oklahoma City. One of these set a course speed record of 601.187 MPH. By 1956, the U.S. Air Force had 28 wings of B-47 bombers and five wings of RB-47 reconnaissance aircraft. The bombers were the first line of America’s strategic nuclear deterrent, often operating from forward bases in the UK, Morocco, Spain, Alaska, Greenland and Guam. B-47s were often set up on “one-third” alert, with a third of the operational aircraft available sitting on hardstands or an alert ramp adjacent to the runway, loaded with fuel and nuclear weapons, crews on standby, ready to attack the USSR at short notice. Crews were also trained to perform “Minimum Interval Take Offs (MITO)”, with one bomber following the other into the air at intervals of as little as 15 seconds, to launch all bombers as fast as possible.
In 1959 the B-52 began to assume nuclear alert duties and the number of B-47 bomber wings was reduced. B-47 production ceased in 1957, though modifications and rebuilds continued after that.