The Boeing B-47 Stratojet (Boeing company designation Model 450) is a retired American long-range, six-engined, turbojet-powered strategic bomber designed to fly at high subsonic speed and at high altitude to avoid enemy interceptor aircraft. The primary mission of the B-47 was as a nuclear bomber capable of striking targets within the Soviet Union.
Development of the B-47 can be traced back to a requirement expressed by the United States Army Air Forces (USAAF) in 1943 for a reconnaissance bomber that harnessed newly developed jet propulsion. Another key innovation adopted during the development process was the swept wing, drawing upon captured German research. With its engines carried in nacelles underneath the wing, the B-47 represented a major innovation in post–World War II combat jet design, and contributed to the development of modern jet airliners. Suitably impressed, in April 1946, the USAAF ordered two prototypes, designated "XB-47"; on 17 December 1947, the first prototype performed its maiden flight. Facing off competition such as the North American XB-45, Convair XB-46 and Martin XB-48, a formal contract for 10 B-47A bombers was signed on 3 September 1948. This would be soon followed by much larger contracts.
During 1951, the B-47 entered operational service with the United States Air Force's Strategic Air Command (SAC), becoming a mainstay of its bomber strength by the late 1950s. Over 2,000 were manufactured to meet the Air Force's demands, driven by the tensions of the Cold War. The B-47 was in service as a strategic bomber until 1965, at which point it had largely been supplanted by more capable aircraft, such as Boeing's own B-52 Stratofortress. The B-47 was also adapted to perform a number of other roles and functions, including photographic reconnaissance, electronic intelligence, and weather reconnaissance. While never seeing combat as a bomber, reconnaissance RB-47s would occasionally come under fire near or within Soviet air space. The type remained in service as a reconnaissance aircraft until 1969. A few served as flying testbeds up until 1977.
The B-47 arose from an informal 1943 requirement for a jet-powered reconnaissance bomber, drawn up by the United States Army Air Forces (USAAF) to prompt manufacturers to start research into jet bombers. Boeing was among several companies to respond to the request; one of its designs, the Model 424, was basically a scaled-down version of the piston-engined B-29 Superfortress equipped with four jet engines.[1] [2] In 1944, this initial concept evolved into a formal request-for-proposal to design a new bomber with a maximum speed of 550mph, a cruise speed of 450mph, a range of 3500miles, and a service ceiling of 45000feet.[3] [4]
In December 1944, North American Aviation, Convair, Boeing and the Glenn L. 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.[5] [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.[5]
In May 1945, the von Kármán mission of the Army Air Forces inspected the secret German aeronautics laboratory near Braunschweig. Von Kármán's team included the 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 German models of swept-wing aircraft and extensive supersonic wind-tunnel data, the concept was decisively confirmed. He wired his home office: "Stop the bomber design" and changed the wing design.[6] [7] Analysis by Boeing engineer Vic Ganzer suggested an optimum sweepback angle of about 35 degrees.[8] Boeing's aeronautical engineers modified the Model 432 with swept wings and tail to produce the "Model 448", which was presented to the USAAF in September 1945. It retained the 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 considered the engine installation within the fuselage to be a fire hazard.[5] [9] [10]
The engines were moved to streamlined pylon-mounted pods 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.[10] The Army Air Force liked this new configuration, so Boeing's engineers refined it, moving the outer engines further inboard to about of the wingspan. The thin wings provided no space for tricycle main gear to retract so it would have needed a considerable bulge in the fuselage aft of the bomb bay for lateral stability. The only way to get a bomb-bay long enough for an A-bomb was to use a "bicycle landing gear",[11] 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 impossible, it was designed so that the aircraft rested on the ground at the proper angle for takeoff.[5] [12] [13]
Pleased with the refined Model 450 design, in April 1946, the USAAF ordered two prototypes, to be designated "XB-47".[14] Assembly began in June 1947. The first XB-47 was rolled out on 12 September 1947,[12] a few days before the USAAF became a separate service, the United States Air Force (USAF), on 18 September 1947. According to aviation authors Bill Gunston and Peter Gilchrist, Boeing subjected the first prototype to "one of the most comprehensive ground-test programmes ever undertaken".
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 test pilots Robert Robbins and Scott Osler at the controls. It lasted 27 minutes, flying from Boeing Field in Seattle to Moses Lake Airfield in central Washington state.[15] [16] While not experiencing major problems, the emergency hot wire system was needed to raise the flaps and the engine fire warning indicators falsely illuminated. Robbins stated that it had good flight characteristics.[17]
Robbins had been skeptical about the XB-47, saying that before his first flight he had prayed, "Oh God, please help me through the next two hours." Robbins soon realized that he had an extraordinary aircraft.[17] Chuck Yeager also flew the XB-47, noting it was so aerodynamically clean that he had difficulty landing on the Edwards lakebed.[18] In February 1949, Russ Schleeh and Joe Howell "broke all coast-to-coast speed records" flying from Moses Lake AFB to Andrews AFB, averaging 607.8mph.[19] During an early test flight, the canopy came off at high speed, killing pilot Scott Osler; the aircraft was safely landed by the copilot.[20] The accident resulted in a canopy redesign and the hiring of pilot Tex Johnston as chief test pilot.[21]
The second XB-47 (46-066) prototype first flew on 21 July 1948 and, following its delivery to the USAF in December of that year, served as a flying test bed until 1954. Its final destination was Chanute AFB where it was used as a maintenance and familiarization aircraft.[22] The second prototype was equipped with more powerful General Electric J47-GE-3 turbojets with 5200abbr=onNaNabbr=on of static thrust each.[23] [24] The J47 or "TG-190" was a redesigned version of the TG-180/J35; the first prototype was later retrofitted with these engines.
Flight testing of the prototypes was careful and methodical since the design was new in so many ways. They initially suffered from "Dutch roll", an instability that caused it to weave in widening "S" turns, remedied by the addition of a "yaw damper" control system to automatically deflect the rudder to damp out the weaving motion. Wind tunnel tests had shown it would pitch up at maximum speed due to wing stall on the outboard section of the wing. This was confirmed during flight tests so small vanes called "vortex generators" were added to prevent airflow separation.[25]
Both XB-47 prototypes were test flown at Edwards AFB; the first XB-47 (46-065) was disassembled and scrapped in 1954, making the second 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, remaining there until the museum announced its closure due to financial difficulties in April 2015.[26] In late 2015, the Flight Test Historical Foundation[27] began fundraising 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 21 September 2016 the aircraft arrived at Edwards AFB for reassembly, restoration and eventual display at the Flight Test Museum.[28]
By mid-1948, the USAF'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 in the XB-47.[29] A formal contract for 10 aircraft was signed on 3 September 1948.[30] [31]
| Variant | XB-47 | B-47A | B-47B | B-47E | RB-47E | RB-47H | ERB-47H | RB-47K | |
|---|---|---|---|---|---|---|---|---|---|
| Built | 2 | 10 | 399 | 1341 | 240 | 32 | 3 | 15 |
The total number of B-47s built was 2,042.[32]
The XB-47, which looked nothing like contemporary bombers, was described by Boyne[33] as a "sleek, beautiful outcome that was highly advanced". The 35-degree swept wings were shoulder-mounted, the inboard turbojet engines mounted in twin pods, at about a third of the span, and the outboard engines singly near the wing tip. This arrangement reduced the bending moment at the wing roots, saving structural weight. The engines' mass acted as counter-flutter weights.[34]
The wing airfoil was identified by Boeing as the BAC 145, also known as the NACA 64A(.225)12 mod airfoil.[35] Wing flexibility was a concern, flexing as much as 17.5feet at the tip;[36] [34] major effort was expended to ensure that flight control could be maintained as the wing moved up and down; these worries proved to be mostly unfounded. Its maximum speed was limited to 425lk=onNaNlk=on IAS to avoid control reversal, where aileron deflections would cause the wings to twist and produce a roll in the opposite direction to that desired by the pilot.[37] The wings were fitted with a set of Fowler flaps that extended well behind the wing to enhance lift at slow speeds.[38] The flight control surfaces were powered, augmenting the pilot's inputs and reducing the exertion required to overcome the forces involved.[39]
The XB-47 was designed to carry a crew of three in a pressurized forward compartment: a pilot and copilot, in tandem, in a long fighter-style bubble canopy, and a navigator/bombardier in a compartment in the nose. The copilot doubled as tail gunner (using a remotely controlled, radar-directed tail gun), and the navigator as bombardier.[40] The bubble canopy, which provided a high level of visibility to the pilots, pitched up and slid backward; as the cockpit was high off the ground, the crew entered via a door and ladder on the underside of the nose.[41] The extreme front of the nose was initially glazed for visual navigation and bomb sighting, but this requirement was soon deleted together with the glazing. Most production versions had a metal nose with no windows. A K-series bombsight provided integrated radar navigation and visual navigation, the optical portion extending through the nose in a small dome. For greater comfort, both heaters and refrigeration systems were present in the cockpit to manage the cockpit environment. There was little vibration compared to prior bombers powered by reciprocating engines.[39]
During the late 1940s, the bomber was hailed as the fastest of its class in the world.[42] The first prototypes were fitted with General Electric J35 turbojets, the production version of the TG-180, with 3970lbf of thrust. Early jet engines did not develop good thrust at low speeds, so to assist take off when heavily loaded, the B-47 had provisions for fitting solid-fuel rocket-assisted takeoff (RATO) rockets, each generating roughly 1000lbf of static thrust.[43] Early aircraft had mounts for nine RATO units built into each side of the rear fuselage, arranged in three rows of three bottles. Most of the space within the upper fuselage was taken up by self-sealing fuel tanks, the wing having been deemed unsuitable for storing fuel.[44]
The performance of the Model 450 was projected to be so good that the bomber would be as fast as fighters then on the drawing board;[45] thus the only defensive armament was to be a tail turret with two .50 in (12.7 mm) AN/M2 Browning machine guns, which would in principle be directed by an automatic fire-control system.[46] The two XB-47s were neither fitted with combat equipment nor tail turrets as they were engineering and flight test aircraft only. The total bombload capacity was to be 25000lb. Production aircraft were to be equipped with modern electronics for navigation, bombing, countermeasures and turret fire control. Navigation was more difficult than on earlier aircraft due to the higher speed involved.[47]
One problem with the aircraft was that at higher altitudes, where the pure turbojet engines could produce good fuel economy, the wing was very compromised. At the top of the B-47's envelope, about 35000feet, it was in "coffin corner".[48] That means that at this level, which produced the most range at most weights due to fuel consumption, there was an envelope of 5kn between maximum mach and stall speed. For the B-47 to cross the Atlantic Ocean, it had to be flown this high. Due to its rudimentary autopilot, the pilot had to leave it turned off and spend up to eight hours diligently monitoring the airspeed and adjusting the throttles to avoid going into a stall. For perspective, a modern Boeing 757 has over 50kn of difference at even a very heavy weight at 41000feet. Fuel capacity was enormous, at 17000abbr=onNaNabbr=on, more than triple the 5000usgal on the B-29 Superfortress, and meant that maintaining fuel trim to ensure a stable center of gravity was a critical copilot duty.
The aircraft was so aerodynamically clean that rapid descent ("penetration") from high cruise altitude to the landing pattern required dragging the deployed rear landing gear. The relatively high wing loading (weight/wing area) required a high landing speed of 180kn. To shorten the landing roll, USAF test pilot Major Guy Townsend promoted the addition of a 32feet German-invented "ribbon" drag chute (thrust reversers had not then been developed).[43] For the same reason, the B-47 was the first mass-produced aircraft to be equipped with an anti-skid braking system.
A related problem was that the aircraft's engines would have to be throttled down on landing approach. Since it could take as long as 20 seconds to throttle them back up to full power, the bomber could not easily do a "touch and go" momentary landing. A 16-foot "approach chute" (drogue parachute) provided aerodynamic drag so that the aircraft could be flown at approach speeds with the engines throttled at ready-to-spool-up medium power. On the ground, the pilots used the 32-foot "brake chute". The brake chute could be deployed to stop the aircraft from "porpoising", or bouncing, after a hard landing on the front nose gear.[49] Training typically included an hour of dragging the approach chute around the landing pattern for multiple practice landings.
The USAF Strategic Air Command operated multiple B-47 models (B-47s, EB-47s, RB-47s and YRB-47s) from 1951 through 1965. Upon entry to service, its performance was closer to that of contemporary fighters than SAC's extant B-36 Peacemaker bomber, setting multiple records with ease. It handled well in flight, the controls having a fighter-like light touch. The large bubble canopy enhanced the flying crew's vision and gave a fighter-like feel, but also caused internal temperature variations for the crew. The three-man crew consisted of the commander, copilot and a navigator/bombardier or a crew chief.[50]
In 1953 the B-47 became operational. It was sluggish on takeoff and too fast on landings, an unpleasant combination. If 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 it to skid onto one wing and cartwheel. Because the wings and surfaces flexed in flight, low-altitude speed restrictions were necessary to ensure effective flight control. The B-47 was regarded as a maintenance "hog".[50] General reliability was good, the only major issuing relating to the avionics, typical of the vacuum tube technology used and the placement of equipment outside the pressurized crew compartment. Much work was done to improve avionics reliability, but avionics remained troublesome throughout the B-47's operational life.
Starting in 1950, several models of the B-47 included a fuel tank inerting system, in which dry ice was sublimed into carbon dioxide vapor while the fuel pumps operated or while the in-flight refueling system was in use. The carbon dioxide was pumped into both the fuel tanks and the fuel system to ensure low oxygen levels throughout. It was implemented largely to reduce the probability of an explosion from static electricity discharges.
Initial mission profiles included the loft bombing of nuclear weapons. As the training for this imposes repeated high stress on the aircraft, the airframe lifetime would have been severely limited by metal fatigue, and this maneuver was eliminated. Improved training led to a good safety record, and few crews felt the aircraft was unsafe or too demanding, but apparently there were some aircrews who had little affection for the B-47. Crew workload was high, having only three crew members to operate it.[51] Boeing's B-52 Stratofortress, in contrast, generally had six crewmen, five officers and one enlisted, with more internal cabin space.
An XB-47 was flown in the 1951 Operation Greenhouse nuclear weapons test. This was followed by a B-47B being flown in the 1952 test, Operation Ivy and the 1954 test, Operation Castle. A B-47E was then flown in the 1956 test, Operation Redwing.[52] "Reflex" missions proved the long-endurance (eighteen hours) and long range capability of the B-47 and aircrews. These were "simulated strike missions against the then Soviet enemy".[53]
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 601.187mph.[54] [55] [56]
By 1956, the USAF had 28 wings of B-47 bombers and five wings of RB-47 reconnaissance aircraft. The B-47 was 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 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 trained to perform "Minimum Interval Take Offs (MITO)",[57] one bomber following another into the air at intervals of as little as 15 seconds to launch as fast as possible. MITO could be hazardous, as the bombers left wingtip vortices and general turbulence behind them; the first generation turbojet engines, fitted with water-injection systems, also created dense black smoke.[58]
The B-47 was the backbone of SAC into 1959, when the B-52 began to assume nuclear alert duties and the number of B-47 bomber wings started to be reduced. B-47 production ceased in 1957, though modifications and rebuilds continued. Operational practice for B-47 bomber operations during this time went from high-altitude bombing to low-altitude strike, which was judged more likely to penetrate Soviet defenses. Crews were trained in "pop-up" attacks, coming in at low level at 425kn and then climbing abruptly near the target before releasing a nuclear weapon.[59]
Stress and fatigue incurred in low-altitude operations led to a number of wing failures and crashes, and an extensive refit program was begun in 1958 to strengthen the wing mountings. The program was known as "Milk Bottle", named after the big connecting pins that were replaced in the wing roots.
One of the more notable mishaps involving a B-47 occurred on 5 February 1958 near Savannah, Georgia, in the so-called 1958 Tybee Island B-47 crash. A B-47 based at Homestead AFB, Florida, was engaged in a simulated combat exercise against an F-86 fighter. As was the practice at the time, the B-47 was carrying a single 7600lb Mark 15 nuclear bomb, without its core.[60] During this exercise, the two aircraft collided. The F-86 crashed after the pilot ejected, while the B-47 suffered substantial damage, including loss of power in one outboard engine. After three unsuccessful landing attempts at Hunter Air Force Base, the bomber pilot had to "safe" soft drop the Mark 15 weapon off the coast of Savannah, Georgia near Tybee Island, after which the B-47 landed safely. Despite an extensive nine-month search, the unarmed bomb was never found.[61] [62] [63]
In 1963, the Kennedy administration offered 24 B-47E bombers as an interim Canberra Mk 20 replacement for the Royal Australian Air Force (RAAF), pending delivery of the much delayed F-111C aircraft. Three B-47E aircraft flew to Australia for demonstration purposes, but RAAF declined the B-47E as technically outdated and too resource-intensive.[64]
During 1963, final phaseout of B-47 bomber wings began; the last were out of SAC service by 1966. The last USAF operational aircraft, WB-47Es assigned to the Air Weather Service, were withdrawn from use in September 1969. Shortly before, a B-47E, USAF Serial Number 53-2280, was used as a testbed for a newly developed fly-by-wire system.[65] The U.S. Navy kept specialized EB-47E test aircraft from USAF inventory in occasional use to support the Fleet Electronic Warfare Systems Group (FEWSG) until December 1977, being replaced by government owned/contractor operated (GOCO) NKC-135 modified Stratotankers also loaned from the USAF.[66]
The final recorded flight of a B-47 was on 17 June 1986, when a B-47E was restored to flightworthy condition for a one-time ferry flight. This aircraft was flown from Naval Air Weapons Station China Lake, California, to Castle Air Force Base, California, for static display at the Castle Air Museum, where it presently resides.[67]
See main article: United States aerial reconnaissance of the Soviet Union. The only B-47s to see anything close to combat were the aerial reconnaissance variants. The first overflight of Soviet territory with a B-47B, fitted with special radar and cameras in the bomb bay, occurred on 15 October 1952, overflying Soviet airfields in Northeastern Siberia.[68] RB-47s operated from almost every airfield that gave them access to the USSR and routinely probed Soviet airspace. Occasionally, they would avoid confrontations with speed and evasion. At least five aircraft were fired upon and three were shot down. The RB-47s returned fire with their tail turrets, although it is uncertain if they scored any kills; these were the only shots fired in anger by any B-47.
On 8 May 1954, after a top secret reconnaissance mission near the Kola Peninsula, a 4th Air Division / 91st Strategic Reconnaissance Wing RB-47E, flown by then-Capt (later Col) Harold "Hal" Austin, overflew the Soviet Union at high altitude, out of reach of MiG-15s. Unknown to USAF intelligence, capable of intercepting it had been stationed nearby. The RB-47E was chased by several MiG-17s, firing upon it with their guns over Soviet and Finnish airspace. While taking damage, the RB-47E escaped over Sweden to its home base at RAF Fairford, Gloucestershire. Its top speed and combat radius superiority to the fighter jets were decisive factors. The mission marked the first time a jet aircraft equipped with modern aerial photography equipment, K-17 and K-38 cameras, was used for USAF reconnaissance over the Soviet Union. The incident was kept secret by all parties.[69]
Other interceptions resulted in losses. An RB-47 flying from Alaska was scouting the Kamchatka Peninsula on 17 April 1955, when it was intercepted by Soviet MiG-15s in international airspace before disappearing. Between 21 March and 10 May 1956, 16 RB-47Es and five RB-47Hs operating from Thule performed overflights the length of Siberia 156 times under Project HOMERUN. The Soviets filed a complaint with the US government, which attributed the overflights to "navigational difficulties". MiGs intercepted RB-47s on three separate occasions in late 1958: over the Black Sea on 31 October, over the Baltic on 7 November, and over the Sea of Japan on 17 November.
On 1 July 1960, a PVO Strany MiG-19 shot down an RB-47H (AF Serial No. 53-4281) in international airspace over the Barents Sea,[70] killing four of the crew while two were captured by the Soviets and released in 1961. The co-pilot reported that the MiG-19 jammed his MD-4 FCS (that aimed the tail guns), rendering it defenseless.[71] [72] The last known confrontation between MiGs and RB-47s occurred on 28 April 1965, when an ERB-47H was intercepted by two North Korean MiG-17s over the Sea of Japan. While hit by the MiGs, it returned to Yokota Air Base in Japan with three engines out.[73] A few operated during the Vietnam War on missions such as relaying ELINT data, but were replaced by more efficient and capable Boeing RC-135s. The last RB-47H was retired on 29 December 1967.
The final 15 RB-47s, built from December 1955, were fitted with additional equipment, including the AN/APD "side looking airborne radar" (SLAR) system, and gear to sample the air for fallout from nuclear tests. These were given the designation RB-47K and generally used for weather reconnaissance missions, carrying a load of eight "dropsonde" weather sensors that were released at various checkpoints along the flight path. Data radioed back from the dropsondes was logged by the navigator. The RB-47Ks were in service until 1963.[74] The type was succeeded by dedicated reconnaissance aircraft such as the Lockheed U-2.[75]
Section source: Baugher.[76]
The first 10 aircraft were designated B-47A and were evaluation aircraft, the first delivered in December 1950. While the XB-47s had been built at Boeing's Seattle plant, all B-47s were built at a government-owned factory in Wichita, Kansas that had previously built B-29s.[78] Their configuration was akin to the XB-47. All were powered by J47-GE-11 turbojets, offering the same 5200lbf thrust as the earlier J47-GE-3, and had built-in rocket-assisted-take-off (RATO) bottles.[77] Four were fitted with the K-2 bombing and navigation system (BNS), HD-21D autopilot, an analog computer, APS-23 radar, and a Y-4 or Y-4A bombsight. Two were fitted with the tail turret mounting two 20mm cannons; one of them used an Emerson A-2 fire control system (FCS), another a General Electric A-5 FCS. The eight other B-47As lacked defensive armament.
The B-47As were fitted with ejection seats. The pilot and copilot ejected upward, while the navigator had a downward ejection seat built by Stanley Aviation.[79] Minimum safe ejection altitude was about 500 ft (150 m). In the 1950s, there were no suitable "dummies" to test ejection seats, thus live people were used. Several volunteers were injured testing the downward ejection seat. The first person to successfully use it was USAF Colonel Arthur M. Henderson who ejected over Choctawhatchee Bay, near Eglin Air Force Base, Florida, on 7 October 1953.[80] Most B-47As were retired by 1952, though one performed flight tests for NACA for a few more years.
The initial 87 B-47Bs used the same J47-GE-11 engines as the B-47A, subsequent deliveries had uprated J47-GE-23 units with 5800lbf thrust; early aircraft were later retrofitted. It had a built-in RATO system, as used on the B-47A, along with full combat systems. Early aircraft retained the K-2 BNS installed on some B-47As, but most featured the K-4A BNS, incorporating an AN/APS-54 warning radar and an AN/APT-5 electronic countermeasures (ECM) system. The K-4A used a nose-mounted periscopic bombsight. Ejection seats were deleted as a weight reduction measure; a windbreak panel on the main door made for a difficult escape.
The bomb bay was shorter than the B-47A's as nuclear weapons had shrunk in the interim; the B-47B could carry a larger bombload of up to 18000lb. All B-47Bs had a tail turret with twin 20 mm (0.79 in) guns and the B-4 radar-guided FCS. Due to issues, this FCS was often replaced with an N-6 optical sight; the copilot could swivel his seat to face backward and sight the guns directly. A nose-mounted in-flight refueling (IFR) receptacle enabled flying boom refueling from KB-50 and KC-97 tankers, requiring the plexiglas nose cone's replacement by a metal nose cone with four small windows, two on either side of the nose. The B-47B was also fitted with a pair of jettisonable external tanks, carried between the inboard and outboard engine assemblies, with a capacity of 1780usgal. Another visible change was the vertical tailplane's squared-off top instead of a rounded top.
Between 1955 and 1956, Boeing modified surviving B-47Bs from line numbers 235 to 399 to the B-47E standard under program High Noon; this included fitting ejection seats. It was followed by the Ebb Tide program covering early line numbers from 1 to 234; this included 66 aircraft from the 135 to 234 batch to the same standard as the High Noon aircraft. Another 30 in the same range had additional modification as drone directors DB-47Bs, and the 1 to 134 range which had the same High Noon modification, but lacked some non-combat changes. Following these programs, they were sometimes referred to as B-47B-II.
Due to the J35's less-than-expected performance and delays, other engines were considered, such as the proposed Allison J71,[83] however engine problems meant that it was not feasible for the by-then redesignated B-56A. The Pratt & Whitney J57, eventually rated at 17000lbf thrust, was also considered, but was still in development. The Boeing B-52 Stratofortress, which was being concurrently developed, had priority for this engine.[77] Thus, the B-56 was cancelled in December 1952 before the prototype's conversion had started.[77] The donor fuselage intended for the XB-56 was reused as a ground instructional airframe.
Early B-47E-Is had J47-GE-25 turbojets with 5970lbf thrust, these were changed to J47-GE-25A engines with water-methanol injection, which increased mass flow to temporarily raise thrust to 7200lbf and produce much black smoke when engaged. Jet-Assisted Take Off (JATO) was installed on early B-47E-Is, integrating 18 JATO bottles, but was removed due to its proximity to fuel tanks. A later JATO system used an external jettisonable "split V" or "horse collar" rack fitted under the rear fuselage, carrying 33 JATO bottles in three rows of 11 bottles;[87] the expendable racks were dropped over specific range areas after takeoff. Early B-47Es had a lower internal fuel capacity of 14627usgal to save weight, which was considered acceptable due to large external tanks and mid-air refueling becoming common practice. A welcome change was the return of ejection seats. The twin .50 in guns (12.7 mm) in the tail turret were replaced with twin 20 mm (0.79 in) cannon for more firepower, backed up by an A-5 FCS in early production and an MD-4 FCS in later production.[88]
The B-47E-II had only minor changes from later-built B-47E-Is. The B-47E-III featured an ECM suite, consisting of a radar jammer in a bulge under the fuselage plus a chaff dispenser, as well as improved electrical alternators. The B-47E-IV was a major update, featuring stronger landing gear, airframe reinforcement, greater fuel capacity, and an uprated bombload of 25000lb while the bomb bay was again shortened as nuclear weapons became more compact. Another addition was the MA-7A BNS, which included the AN/APS-64 radar, having a range of up to 240miles and could be used as a long range "identification friend or foe (IFF) transponder" interrogator to locate other B-47s or tankers, or as a high-resolution ground-targeting radar. The B-47E-IV retained the rarely-used optical bombsight. Most nose windows were deleted; only one remained on each side.
B-47E 52-0410 and 52-0412 were converted to EB-47Es in the mid-1960s for the U.S. Navy's Fleet Electronic Warfare Support Group (FEWSG). Considered to be on indefinite loan, they differed from USAF EB-47Es in that some podded ECM gear was mounted on the external fuel tank pylons. Used as "electronic aggressors" to test ECM systems, they were the last B-47s in service, 52-0410 performed its last flight on 20 December 1977.
The 53d Weather Reconnaissance Squadron, of the 9th Weather Reconnaissance Wing, operated WB-47Es from Hunter Air Force Base and Ramey Air Force Base. These assets were transferred to the 57th Weather Reconnaissance Squadron for Operation Arc Light, operating from Clark Air Base.[90]
The first RB-47H was delivered in August 1955 to Forbes AFB, Kansas. They received a "Mod 44" or "Silver King" program in 1961 to update electronics systems and was recognizable by a large teardrop pod for ELINT antennas upon a pylon under the belly and offset to one side, as well as a pylon-style antenna under each wing beyond the outboard engine. The EWO compartment was cramped with sitting room only and had both poor noise insulation and climate control, making 12-hour missions uncomfortable and tiring. Successful ejection downward through the belly radome was impossible near the ground. Crews sat bobsled-like on the pilot compartment's floor for takeoff and landing. They then crawled encumbered with Arctic clothing and parachute to and from their compartment along an unpressurized maintenance shelf during a temporary level-off at 10000feet.
Operations were generally flown at night and classified Top Secret.[91] The final RB-47H to be retired from service, 53-4296, was reactivated and fitted with an F-111-style nose to test avionics for the General Dynamics FB-111 in the early 1970s. It was not given any special designation. It is now on display at the Air Force Armament Museum at Eglin Air Force Base, fitted with a bomber nose.
See also: List of B-47 units of the United States Air Force.
See main article: List of surviving Boeing B-47 Stratojets. Twenty-three surviving airframes exist in museum collections; all are located in the United States.
See also: List of military nuclear accidents.
Over its operating life, 203 B-47s were lost in crashes, with 464 deaths. This represents approximately 10% of the total number produced.[93]
On 8 February 1954, a B-47 of the 22nd Bomber Wing, March AFB, California, crashed in Stoke Wood, a mile and a half short of the runway at RAF Upper Heyford, England, while on a training run. All three crew were killed.[94]
On 28 February 1955, a crippled B-47 crashed into a trailer park in Lake Charles, Louisiana, killing the three crewmen and two people on the ground.[95] [96]
On 10 March 1956, four B-47s left MacDill Air Force Base in Florida for a non-stop flight to Ben Guerir Air Base in Morocco. After descending through clouds to begin their second round of aerial refueling over the Mediterranean Sea at 14,000 feet, one of the four aircraft, serial number 52-0534, failed to make contact with the tanker; neither the aircraft, its two nuclear weapon cores, nor its personnel were ever found.[97]
On 28 March 1956, a B-47 exploded near Wichita, Kansas, with an instructor and two student pilots on board.[98] It crashed four miles northeast of the city, killing its crew of three. The office of information services at McConnell Air Force Base said the explosion occurred after takeoff, probably at about 2,000 feet altitude. Wreckage was strewn along the countryside for several miles as the wings sheared off and the fuselage tumbled to earth.[99]
On 27 July 1956, a B-47 of the 307th Bombardment Wing crashed at RAF Lakenheath killing its crew and causing a near radioactive incident when it hit a storage igloo containing three MK-6 nuclear weapons. Although the bombs involved lacked their fissile cores, each carried about of high explosives for their trigger mechanism. The crash and ensuing fire did not ignite the high explosives and no detonation occurred.[100]
In November 1956, B-47E serial number 51-2421 of the 96th Bombardment Wing, flying from Altus AFB, crashed on a farm near Hobart, Oklahoma, following engine problems.[101] Four crewmen were killed in the incident.[102]
On 9 October 1957, B-47 serial number 51-2177A, of the 447th Bomb Squadron, 321st Bomb Wing at Pinecastle Air Force Base suffered wing failure and crashed northwest of Orlando, Florida, and west of Winter Park, Florida, while conducting a practice demonstration for the annual Strategic Air Command Bombing Navigation and Reconnaissance Competition at Pinecastle AFB. The wing commander, Colonel Michael Norman Wright McCoy, was killed in the crash; Pinecastle AFB was later renamed McCoy AFB in his honor.
On 4 December 1957, a MacDill Air Force Base B-47 exploded in mid-air over Choctawhatchee Bay, Okaloosa County, Florida. Parts were scattered over a wide underwater area that varied in depth from 20 to 30 feet. Assistance from US Navy divers from the Mine Detection Laboratory, Panama City, Florida, the Underwater Demolition Team No. 21 from Little Creek, Va., the 3201st Boat Squadron, APGC, recovered most of the plane. The three crew were killed.[103] [104]
On 5 February 1958, a B-47 was involved in a mid-air collision with an F-86 fighter over Georgia, known as 1958 Tybee Island mid-air collision.[105]
On 26 February 1958, RB-47E serial number 52-0720 crashed six miles south of Lancaster, OH on approach to Lockbourne AFB, OH, hitting the ground at an angle of 50 degrees. It was determined that the aircraft attained an unusual attitude and/or high speed through disorientation, from which there was no recovery. In actuality, a wheel door had broken away and prevented the control surfaces being fully active.
On 13 March 1958, two B-47s crashed on the same date in separate incidents when the lower wing skin failed at the same structural location.[106] One exploded over southeast Tulsa, Oklahoma, killing one crewman and raining debris over at least 8 square miles, witnessed by thousands of people on the ground. Two of the three men on a training mission from McConnell Air Force Base in Wichita, Kansas, parachuted to safety. The third was trapped in the nose of the plane and died.[107]
On 10 April 1958, a B-47 from Lockbourne Air Force Base, Ohio, exploded mid-flight behind the KC-97G tanker that was to refuel it. The KC-97 was unharmed, but the wreckage fell within a half-mile of a highway and none of the crew survived.[108]
On 15 April 1958, a B-47 from Walker Air Force Base in New Mexico, serial number 52–0562, crashed on takeoff at Pease Air Force Base in New Hampshire; all four crewmen were killed.[109] [110]
On 22 November 1958, a B-47B crashed while taking off from Loring Air Force Base in Maine, killing all four crew members on board. The plane belonged to a unit at McCoy Air Force Base in Orlando, Florida. The plane was described as having veered sharply to the right while two-thirds of the way down the runway, eventually crashing 400 feet north of the runway.[111] On 25 November 1958, a KC-135 of the 42d Air Refueling Squadron crashed on takeoff roughly in the same area as the B-47 three days before.
On 4 April 1959, B-47 serial number 52-0320 crashed in the Santa Rita mountains, south of Tucson, Arizona, while attempting to land at Davis-Monthan AFB. All three crew were killed. Investigators noted that a faulty altimeter was a contributing factor.[112]
On 24 April 1959, Captain John S. Lappo, operating from Lockbourne AFB flew a B-47 with two crewmen on board under the Mackinac Bridge in Michigan. Following a general court-martial, he was grounded for life.[113]
On 30 December 1959, a B-47B crashed at Torrejón Air Base, Spain one minute after takeoff. All four crew members were killed.[114]
On 31 March 1960, B-47E serial number 52-1414, of the 384th Bomb Wing (SAC), 545th Bombardment Squadron, Little Rock AFB, exploded inflight over Little Rock, Arkansas. Three of the four crew and two civilians on the ground were killed.[115] [116]
On 4 January 1961, B-47 serial number 53-4244, based at Pease Air Force Base, crashed on takeoff; all four crewmen were killed.[117]
On 24 February 1961, a B-47 crashed 10 miles southwest of Hurley, Wisconsin, while on a practice bombing mission from the 40th Bomb Wing at Forbes Air Force Base, Topeka, Kansas. Its four crew were killed. An engine was found 600 yards from the point of impact, indicating it detached prior to the crash.[118]
On 2 May 1961, a B-47 crashed eight miles southwest of Hurley, Wisconsin, only a few miles from the scene of a prior B-47 crash on 24 February 1961. Two of four crew survived. Evidence showed that it was steeply diving when the crash occurred.[119]
In January 1962, a B-47 based at Plattsburgh Air Force Base on a training mission crashed into the side of Wright Peak in the High Peaks in the Adirondacks of New York. All four crew were killed. It had veered about 30 miles east due to inclement weather. Wreckage can still be found at the summit, including a landing gear strut and a partial engine.[120] [121]
On 23 July 1962, a B-47 based at Dyess Air Force Base near Abilene, Texas, departed on a training mission through Montana. After crossing into Paradise Valley, it crashed into Emigrant Peak and exploded while turning toward the northwest. All four crew were killed.[122]
On 3 August 1962, B-47 serial number 52-0526, based at Pease Air Force Base, crashed on takeoff; all three crew were killed.[123]
On 22 August 1962, B-47 serial number 52-0553, based at Davis–Monthan Air Force Base near Tucson, Arizona, crashed on a training mission shortly before midnight in the Idaho mountains south of Smiths Ferry; controlled flight into terrain started a forest fire, and all three crew were killed.[124] [125] [126]
On 20 February 1963, a B-47 of the 98th Bomb Wing based at Lincoln AFB, Nebraska, crashed in Bashaw Township, approximately three miles north of the town of Comfrey, Minnesota. All four crew were killed. It had just completed a low-altitude simulated bombing run near Heron Lake when the sixth engine failed, causing it to crash in a field, resulting in a 25-foot deep by 50-foot wide crater.[127] [128] [129]
On 3 May 1963, B-47E serial number 52-0051, based at Mountain Home AFB, Idaho, crashed in Yellowstone National Park in Wyoming following a collision with a KC-135 during midair refueling. The co-pilot ejected safely, but the other three crewmen were killed; the tanker landed safely with no casualties.[130] [131] [132]
On 19 August 1963, two B-47E aircraft, serial numbers 53-2365 and 53-6206, both based at Schilling AFB near Salina, Kansas, collided over western Iowa and crashed several miles apart near Irwin. All six crewman ejected, but three were killed.[133]
On 20 August 1963, a QB-47 veered off course on its landing approach at Eglin AFB and crash landed on a road parallel to the runway. It was used for Bomarc Missile Program tests, normally operated from Eglin AFB Auxiliary Field Number Three (Duke Field), approximately 15miles north of the main base. Two cars were crushed, killing two occupants and injuring a third.[134]
On 6 February 1964, B-47E serial number 52-0366, based at Mountain Home AFB, Idaho, crashed in fog on takeoff; all four crewmen were killed.[135] [136]
On 27 March 1964, B-47E serial number 52-0321, based at Little Rock AFB, Arkansas, crashed shortly after takeoff, killing all four crewmen and two boys on the ground.[137] [138]
On 27 July 1964, B-47E serial number 53-2366, based at Lincoln AFB, Nebraska, crashed shortly after takeoff; all four crewmen were killed.[139] [140]
On 8 December 1964, B-47E serial number 52-0339, based at Pease AFB, crashed in Newington, New Hampshire, shortly after takeoff; all four crewmen were killed.[141] [142]
On 26 February 1965, B-47E serial number 52-0171, based at Pease AFB, collided during mid-air refueling with a KC-135 over the Atlantic Ocean, east of Maine. Both aircraft, with four crew members each, crashed into the water with no survivors. The bomber was one of three returning to Pease after a training mission in Spain.[143] [144]
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