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Subject: Boeing B-47 Stratojet
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https://en.wikipedia.org/wiki/Boeing_B-47_Stratojet
The Boeing B-47 Stratojet (company Model 450) was an American long range,
six-engine, turbojet-powered strategic bomber 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. With its engines
carried in nacelles under the swept wing, the B-47 was a major innovation in
post-World War II combat jet design, and contributed to the development of
modern jet airliners.
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, remaining in service as a reconnaissance aircraft until 1969 and
as a testbed until 1977.
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.
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). 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
Analysis work by Boeing engineer Vic Ganzer suggested an optimum sweepback angle
of about 35 degrees. 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.
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.
Role
Strategic bomber/Aerial reconnaissance
National origin
United States
Manufacturer
Boeing
First flight
17 December 1947
Introduction
June 1951
Retired
1969, B-47E
1977, EB-47E
Primary user
U.S. Air Force
Number built
2,032
Unit cost
US$1.9 million (B-47E) equivalent to $20.1 million in current value
When B-47s began to be delivered to the Air Force, most crews were excited about
getting their hands on the hot new bomber, an aircraft whose performance was
closer to that of jet fighters of the period than SAC's extant B-36 Peacemaker
bomber. The B-47 was so fast that in the early days the aircraft set records
with ease. The aircraft handled well in flight, with a fighter-like light touch
to the controls. The large bubble canopy for the pilot and co-pilot enhanced the
fighter-like feel of the aircraft with improved vision, but the design would
also cause variations in internal temperatures for the three-man crew.
The three man crew consisted of the aircraft commander, copilot, and a
navigator/bombardier or a crew chief. The B-47 was a maintenance "hog", so as a
"valuable member of the ground crews, the crew chief was eligible for $50.00 per
month flight pay if they flew the customary 4 hours a month required by
regulations."
It took the Air Force until 1953 to turn the B-47 into an operational aircraft.
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.
Because the wings and surfaces were flexible and bent in flight, low altitude
speed restrictions were necessary to ensure effective flight control.
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
after that.
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.
Final phaseout of B-47 bomber wings began in 1963, and the last bombers were out
of service with SAC by 1966. The last USAF operational aircraft, WB-47Es
assigned to the Air Weather Service, were grounded in September 1969. Shortly
before, a B-47E number 53-2280 was used as a testbed for crucial early test of
the newly developed fly-by-wire system.
Specifications (B-47E)
General characteristics
Crew: 3
Length: 107 ft 1 in (32.65 m)
Wingspan: 116 ft 0 in (35.37 m)
Height: 28 ft 0 in (8.54 m)
Airfoil: NACA 64A(0.225)12 mod root and tip
Empty weight: 79,074 lb (35,867 kg)
Loaded weight: 133,030 lb (60,340 kg)
Max. takeoff weight: 230,000 lb (100,000 kg)
Zero-lift drag coefficient: 0.0148 (estimated)
Aspect ratio: 9.42
Performance
Maximum speed: 607 mph (528 kn, 977 km/h)
Cruise speed: 557 mph (484 kn, 896 km/h)
Combat radius: 2,013 mi (1,749 nmi, 3,240 km) with 20,000 lb (9,000 kg) bombload
Ferry range: 4,647 mi (4,037 nmi, 7,478 km)
Service ceiling: 33,100 ft (10,100 m)
Rate of climb: 4,660 ft/min (23.7 m/s)
Thrust/weight: 0.22
Lift-to-drag ratio: 20.0 (estimated)
Armament
with AN/APG-39 Gun-laying radar
megaton yield each), or
*
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