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Boeing-Wichita built 240 RB-47E reconnaissance variants, similar to the B-47E but with a nose stretched by 34 inches (0.86 meter), giving them an arguably more elegant appearance than the bomber variants of the B-47. The long nose was used to stow up to 11 cameras, which could include:
An O-15 radar camera for low-altitude work.
A forward oblique camera for low-altitude work.
A K-17 trimetrogon (three-angle) camera for panoramic shots.

K-36 telescopic cameras.
The RB-47E could carry photoflash flares for night reconnaissance. Although the RB-47E could be refueled in flight, its fuel capacity was increased, to a total of 70,000 liters (18,400 U.S. gal). The navigator controlled the cameras, becoming a "navigator-photographer" instead of a "navigator-bombardier".

A total of 32 RB-47H models were built for the electronic intelligence (ELINT) mission, as well as three more specialized "ERB-47Hs". These aircraft featured distinctive blunt, rounded nose and sported blisters and pods for intelligence-gathering antennas and gear. They were designed to probe adversary defenses and then collect data on radar and defense communications signals. The Boeing B-47 Stratojet jet bomber was a medium-range and -size bomber capable of flying at high subsonic speeds and primarily designed for penetrating the Soviet Union. A major innovation in post-World War II combat jet design, it helped lead to the development of modern jet airliners. While the B-47 never saw major combat use, it was the mainstay of U.S. Air Force Strategic Air Command in the 1950s.

Development
The B-47 arose from a 1943 U.S. Army Air Forces requirement for a jet bomber and reconnaissance aircraft that could reach Nazi Germany in the event that Great Britain fell. The next year, the requirement evolved into a formal request for a bomber with a specified speed of 500 mph (800 km/h) or more, a range of 3,500 mi (5,600 km), and a service ceiling of 40,000 ft (12,200 m). It envisioned using the General Electric TG-180 turbojet engine, then in development.
By this time, the war in Europe was obviously winding to a close. General Henry H. Hap Arnold, head of the USAAF, asked the prestigious expatriate Hungarian aerodynamicist Theodore von Kármán, of the California Institute of Technology, to form up a committee of American scientists to go to Europe and examine captured German technology. The result was the Scientific Advisory Group One of the members was Boeing's chief aerodynamicist, George Schairer. During his visit to Germany, Schairer examined data obtained by German aircraft manufacturers on the advantages of swept wings, and became so convinced of the merits of such a design that in May, 1945 he wrote a letter to Boeing management suggesting the matter be investigated.

[edit]Preliminary designs
North American, Convair, and Boeing submitted proposals. The first Boeing proposal, the Model 424, was a modification of a conventional propeller-driven bomber design, basically a scaled-down version of the Boeing B-29 fitted with four jet engines.

Meanwhile, the USAAF had awarded study contracts to all three aircraft manufacturers working on the jet bomber project, as well as to Martin, which had also decided to join the competition. All of the competing bombers, including the North American B-45, Convair XB-46 and Martin XB-48 would have conventional straight wings with four to six engines, and would lack the performance of the swept wing B-47.

The XB-47 looked unlike any contemporary bomber, described by some observers as a "sleek, beautiful outcome that was highly advanced".[2] The 35-degree swept wings were shoulder-mounted, with the twin inboard turbojet engines mounted in very neat pods, and the outboard engines tacked under the wings short of the wingtips. With the exception of a change from the shoulder-mounted wing configuration to being under the fuselage, most future airliners would use a similar configuration, with the engines mounted in under-wing pylons.

The airfoil was 11 times as wide as it was thick. This unusual thinness (dry, no fuel tanks) was believed to be necessary to attain high speed (.86 Mach), but the wing's flexibility was a concern. It could flex as much as five ft (1.5 m) up or down, and major effort was expended to ensure that flight control could be maintained as the wing moved up and down. As it turned out, most of the worries proved unfounded. (Wing "twist" limited tree-top speed to 425 knots to avoid control reversal) The wings were fitted with a set of Fowler flaps that extended well behind the wing, to enhance lift at slow speeds.
The bicycle landing gear dictated by the thin wing consisted of a pair of large wheels fore and aft of the bomb bay, with small outrigger wheels carried on the inboard twin-jet pods.

[edit]Performance and engines
The performance of the Model 450 design was projected to be so good that the bomber would be as fast as fighters then on the drawing board, and so the only defensive armament was to be a tail turret with two .50-cal Browning machine guns, which would in principle be directed by an automatic fire-control system. The two XB-47s were not fitted with the tail turret as they were engineering and flight test aircraft, and in fact the prototypes were not fitted with any combat equipment at all.
Fuel capacity was an enormous 17,000 U.S. gal (64,400 liters), compared to 5,000 U.S. gal (19,000 L) on the B-29. That meant that maintaining fuel trim to ensure a stable center of gravity in flight would be very critical co-pilot duty.
The first prototypes were fitted with General Electric J35 turbojets, the production version of the TG-180, with 3,970 lbf (17.7 kN) of thrust. Early jet engines did not develop good thrust at low speeds, so to assist in takeoffs in heavily loaded condition, the XB-47 prototype had provisions for fitting 18 solid-fuel rocket-assisted takeoff (RATO) rockets with 1,000 lbf (4.4 kN) thrust each. Fittings for nine such units were built into each side of the rear fuselage, arranged in three rows of three bottles.

Early years
When B-47s began to be delivered to the Air Force, most crews were excited about getting their hands on the hot new bomber. The bomber was so fast that in the early days, the B-47 set records everywhere it flew without even trying. The aircraft handled well and comfortably in flight, with a fighter-like light touch to the controls. The big bubble canopy enhanced the fighter-like feel of the big aircraft with improved all around vision, but the inherent design would cause variations in internal temperatures for the 3-man crew.

However, it took the Air Force until 1953 to turn the B-47 into an operational aircraft. The big aircraft was sluggish on takeoff and too fast on landings, a very unpleasant combination of circumstances. Furthermore, if the pilot put the machine down at the wrong angle on the bicycle landing gear, the aircraft would "porpoise", bouncing fore-and-aft. If the pilot didn't lift off for another go-round, instability would quickly cause the bomber to skid onto one wing and cartwheel to its destruction. Because the wings and surfaces were flexible and bent in flight, low altitude speed restrictions were necessary to ensure that basic flight control surfaces remained effective.

Improved training led to a good safety record, and few crews felt the aircraft was inherently unsafe or too demanding, but apparently there were aircrews who had little affection for or were even afraid of the B-47. Crew workload was also high, with only three crew members to keep the B-47 flying right. The B-52 Stratofortress, in contrast, generally had six crew, with much less cramped accommodations. While the original XB-52 used a fighter-style canopy, production versions used a conventional flight deck.

[edit]Training and problems
The B-47's reliability and serviceability were also regarded as good. The only major problem was that the avionics were not very reliable, unsurprising given the vacuum tube technology available at the time, and the need to locate some equipment outside the pressurized crew compartment. Much work was done to improve the reliability of the avionics, but they remained something of a maintenance headache all through the B-47's operational life.
Several models of the B-47 starting in 1950 included a fuel tank inerting system, in which dry ice was sublimated into carbon dioxide vapor while the fuel pumps operated or while the in-flight refueling system was in use. The carbon dioxide was then pumped into the fuel tanks and the rest of the fuel system, ensuring that the amount of oxygen in the fuel system was low, and thereby reducing the probability of an explosion in flight. Ten carbon dioxide tanks and heaters were involved. The system was implemented largely to reduce risks from static electricity discharges occurring during in-flight refueling.
Strategic Air Command B-47 Stratojet bombers. The world's first swept-wing bomber.

]Prime years
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 at forward bases in the UK, Morocco, Spain, Alaska, and Guam. B-47 bombers were often set up on "one-third" alert, with a third of the operational aircraft available sitting on the runway, loaded with fuel and nuclear weapons, crews on standby, ready to take off for no-holds-barred attack against the USSR at short notice.

Crews were also trained to perform "minimum interval takeoffs (MITO)", with one bomber following the other into the air at intervals of as little as 15 seconds, to get all the bombers on the way as fast as possible. MITO could be very hazardous, as the bombers left turbulence and, with water injection, dense black smoke that blinded pilots in the following aircraft.
B-47 bombers apparently performed training missions in which they penetrated Soviet airspace in numbers. The facts behind these missions remain controversial, with some claiming that Curtis LeMay ordered them without presidential knowledge or approval.

The B-47 would be the backbone of SAC into 1959, when the B-52 began to take over and the B-47 wings started to be cut back. Actual B-47 production had ceased in 1957, though modifications and rebuilds continued after that.
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. Bomber crews were trained in "pop-up" attacks, coming in at low level (425 knots) and then climbing abruptly on nearing the target before releasing a nuclear weapon, and the similar "toss bombing" procedure, in which the aircraft released the weapon while climbing and then rolled away to depart the target area before the bomb fell back down and detonated.

Later years
Stress and fatigue incurred in low altitude operations led to a number of wing failures and fatal crashes, and an extensive refit program was initiated 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.

A B-47 and a F-86 Sabre collided in 1958. The F-86 crashed and the B-47 losing one of its single jet engines catching fire after just leaving Homestead Air Force Base. The pilot had to "safe" soft drop a nuclear H-bomb off the coast of Savannah, Georgia (where it remains) and safely returned to base.

The only B-47s to see anything that resembled combat were the reconnaissance variants. They operated from almost every airfield that gave them access to the USSR, and they often probed Soviet airspace, and on occasion, B-47 pilots were caught in situations from which mostly speed and evasion in retreat saved them. At least five of these aircraft were fired on, and three of these were shot down. The B-47s fired back with their tail turrets, though it is uncertain if they scored any kills, but in any case these were the only shots fired in anger by any B-47. These missions became impractical upon the introduction by the Russians of the trans-sonic MiG-19. (Similar to the performance of USAF F-100)

Final phaseout of B-47 bomber wings began in 1963, and the last bombers were out of service by 1965. The very last USAF operational aircraft was grounded in 1969. The U.S. Navy kept specialized test aircraft in occasional use up to 1976. The final recorded flight of a B-47 was on 17 June 1986, when a B-47E was flown from the Naval Air Weapons Station China Lake, California, to Castle Air Force Base, California, to be put in the air museum there. There are at least 15 B-47s that survive on static display, but none are still flying.

Specifications (B-47E)
Data from Quest for Performance[7]
General characteristics
Crew: 3
Length: 107 ft 1 in (32.6 m)
Wingspan: 116 ft 0 in (35.4 m)
Height: 28 ft 0 in (8.5 m)
Wing area: 1,428 ft² (132.7 m²)
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)
Powerplant: 6× General Electric J47-GE-25 turbojets, 7,200 lbf (32 kN) each
* Zero-lift drag coefficient: 0.0148 (estimated)
Drag area: 21.13 ft² (1.96 m²)
Aspect ratio: 9.42

Performance
Maximum speed: 607 mph (527 kn, 977 km/h)
Cruise speed: 557 mph (484 kn, 896 km/h)
Combat radius: 1,749 NM (2,013 mi, 3,240 km) with 20,000 lb (9,000 kg) bombload
Ferry range: 4,037 NM (4,647 mi, 6,494 km)
Service ceiling 33,100 ft (10,100 m)
Rate of climb: 4,660 ft/min (23.7 m/s)
Wing loading: 93.16 lb/ft² (454.8 kg/m²)
Thrust/weight: 0.22
Lift-to-drag ratio: 20.0 (estimated)
Armament
Guns: 2× 20 mm M24A1 cannons
Bombs: 25,000 lb (11,000 kg) of ordnance, including:
2× nuclear bombs, or
28× 500 lb (230 kg) conventional bombs. 

 

 

The Boeing RB-47E "Stratojet"

The RB-47E differed outwardly from the B-47E in that its nose was 34 inches longer. An air conditioned compartment in the aircraft's redesigned nose housed cameras and other sensitive equipment. Included were an optical viewfinder, photocell operated shutters actuated by flash lighting for night photography, and interval meters for photographs of large areas at regularly spaced intervals. The RB-47E had no bombing equipment, but the 20 millimeter tail armament and A-5 fire control system of the B-47E were retained. A photographer/navigator replaced the bombardier in the aircraft's 3 man crew. The RB-47E also featured the internal jet assisted take off system of the earliest B-47Es.

The RB-47E flew sooner than expected. Nonetheless, the problems and delays anticipated by the Air Force in March 1952 (when many B-47Bs were modified for reconnaissance) did occur. It took almost another 2 years for the RB 47E to become a real asset.

An initial RB-47E was assigned to an operational unit in November 1953. This plane featured an interim camera control system that was also due to equip temporarily the next 134 RB-47Es. The sophisticated Universal Camera Control System designed by the Air Force's Photographic Reconnaissance Laboratory, already tested on the RB-47B, and earmarked for the entire RB-47E contingent, would first appear on the 136th RB-47E. Problems with the interim camera control system soon altered the USAF plans. Because of the system's repeated failures, the Air Proving Ground Command recommended early in 1954 that further operational suitability tests of the available RB-47Es be canceled. No meaningful testing could be conducted, Air Proving Ground Command stated, without a RB-47E equipped with the universal system. This fell in line with General LeMay's thinking. The SAC Commander had already advised Maj. Gen. Clarence S. Irvine, AMC Deputy Commander for Production, that the day and night photo capability of the reconnaissance B-47E was unsatisfactory, be it at low or high altitude. General Irvine was quick to point out that minor improvements had been made to the interim camera control system. He willingly admitted, however, that the RB-47E's problems would not be entirely solved prior to the October delivery of the first Universal Camera Control System equipped RB-47E production. Further discussion of the matter ended in May 1954, when the Air Staff decided that the first 135 RB-47Es would receive a simplified camera control system. This seemed to indicate that the aircraft would not undergo retrofit as originally planned and that SAC would be saddled with 2 RB-7E configurations. Although the Air Staff reversed its decision later in the month, this did not mean that all difficulties were over. Shortages of government furnished equipment, chiefly of Universal Camera Control Systems, continued to hinder the program. The Air Force nearly reached its production total of RB-47Es by mid 1955, but many of the aircraft were not fully equipped. Yet phaseout of the 91st Strategic Reconnaissance Wing recipient of the earliest RB-47Es was only 2 years away.

The Air Force took delivery of the 4 last RB-47Es in August 1955.

The Air Force accepted 97 RB-47Es in FY 54, 139 in FY 55, and 19 in FY 56

The Flyaway Cost Per Production Model was $2.05 million. Airframe, $1,409,441; engines (installed), $258,159; electronics, $49,163; ordnance, $6,303; armament and special equipment, $333,847.

On 5 November 1954, the Air Force officially agreed that 15 of SAC's RB-47Es would be fitted with special equipment for both weather and photo reconnaissance operations at low and high altitudes. These new configurations, featuring high resolution and side looking radars, were designated RB-47Ks. The first RB-47K was delivered in December 1955, as scheduled. In essence, the aircraft was an airborne weather information gathering system. SAC wanted the RB-47K to sense, compile, record, and make inflight radio transmissions of weather data. All these tasks were to be done automatically. The RB-47K was also expected to determine the size of clouds as well as to wind speed and direction. This was a large order, and severe equipment problems remained after mid 1956, when the 55th Strategic Reconnaissance Wing reached an initial operational capability. The 55th Wing's 15 RB-47Ks were flown all over the world to provide weather data for SAC and to sample fallouts from foreign nuclear blasts. They were phased out in the early sixties, when some of the last and more efficient B-47Es were modified to assume the weather role.

255 RB-47Es were accepted in 1955 and 1956. Phaseout began initially in 1957, although some remained in service as late as 1967.

The RB-47E phaseout followed the B-47E's pattern, and the first RB-47E (Serial No. 51 5272) was sent to storage at Davis Monthan AFB on 14 October 1957. Nevertheless, a number of reconnaissance B-47s (mostly RB-47Hs) kept on serving SAC for another decade.

 

 

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