Boeing B-47’s in volume production

The Boeing B-47B

Following a series of preliminary contracts for production B-47s, in November 1949, even before the first flight of the B-47A, the Air Force had ordered 87 "B-47Bs", the first operational variant. The first B-47B flew on 26 April 1951. A total of 399 were built, including eight that were assembled by Lockheed and ten that were assembled by Douglas, using Boeing-built parts. The USAF was impatient to get their hands on as many B-47s as they could as quickly as possible, and signed up Lockheed and Douglas for the additional production. Lockheed-built aircraft were designated by a "-LM (Lockheed Marietta)" suffix and Douglas-built aircraft were given a "-DT (Douglas Tulsa)" suffix. Boeing production was designated by a "-BW (Boeing Wichita)" suffix, except for the Seattle-built XB-47s and B-47As, which had a "-BO" suffix.

The initial batch of 87 B-47Bs featured the same J47-GE-11 engines as the B-47As, but all subsequent production featured substantially uprated J47-GE-23 turbojets with 25.8 kN (2,630 kgp / 5,800 lbf) thrust each. Early production was retrofitted with the improved engines. They all featured the built-in JATO system used on the XB-47 and B-47A.

All were fitted with full combat systems. Early production retained the K-2 BNS installed on some of the B-47As, but most production featured the K-4A BNS, which featured an AN/APS-54 warning radar and an AN/APT-5 electronic countermeasures (ECM) system.

The K-4A used a periscopic bombsight fitted into the tip of the nose of the aircraft, with the transparent plexiglas nose cone of the XB-47 and B-47A replaced by a metal nose cone. There were four small windows on the left side of the nose and two on the right. Another visible change from the earlier models was that the B-47B had a tailfin with a squared-off top, instead of a rounded top as with its predecessors.

The bombbay of the B-47B was shorter than that of the XB-47 and B-47A, since nuclear weapons had shrunk in the meantime. However, the B-47B could carry a much larger bombload, of up to 8,165 kilograms (18,000 pounds). All B-47Bs featured the tail turret with twin 12.7 millimeter guns and the B-4 radar-guided FCS. The B-4 FCS proved troublesome, in fact so troublesome that some in some B-47Bs it was replaced with an N-6 optical sight. The copilot could swivel his seat around to face backward and sight the guns.

In practice, the enormous fuel capacity of the B-47 was still not enough to give it the range the Air Force wanted, and in fact there had been substantial prejudice against the type among senior Air Force brass because of the limited range of the initial design. Solution of this problem was a high priority, and so an "in-flight refueling (IFR)" receptacle was fitted in the right side of the nose for "boom"-style refueling. This was the main reason for getting rid of the plexiglas nose cone.

The B-47B was also fitted with a pair of jettisonable external tanks, carried between the inboard and outboard engine assemblies. These were really big drop tanks, with a capacity of 6,750 liters (1,780 US gallons).

The B-47B suffered a considerable gain in weight compared to the B-47A, and so as a weight-reduction measure the ejection seats were deleted, and a windbreak panel was fitted to the aircraft's main door to make escapes easier. Some sources also claim that a fatal ejection-seat accident in a B-47A contributed to this decision. Whatever the case, this was not a very popular change with the aircrews, since getting out of the aircraft even at altitude was troublesome. Bob Robbins recalled that George Martin, the B-47 program manager, showed him the letter from the Air Force ordering Boeing to remove the seats. Martin told Robbins: "Bob, put that letter in a safe place. The day is going to come when the Air Force is going to regret this decision, and we want to be able to make it very clear where the decision came from to do away with the ejection seats."

The Boeing B-47E

The designations "B-47C" and "B-47D" were applied to special variants that never went into production (described later), and so the next production version of the B-47 was the definitive "B-47E".

The first B-47E flew on 30 January 1953. Four "blocks" or "phases" of the B-47E were built, each incorporating refinements over the previous block, and also sometimes featuring production changes within a block. Older blocks were generally brought up to the specifications of later blocks as they were introduced.

Early production "B-47E-Is" featured J47-GE-25 turbojets with 26.59 kN (2,710 kgp / 5,970 lbf) thrust each, but they were quickly changed to J47-GE-25A engines, which featured a significant improvement in the form of water-methanol injection. This was a scheme in which a water-methanol mix was dumped into the engines at takeoff, increasing mass flow and so temporarily kicking the thrust up to 32.03 kN (3,265 kgp / 7,200 lbf). The methanol was apparently just added to the water as anti-freeze. Water injection caused the engines to pour out black smoke, no doubt due to incomplete combustion of fuel, and produce a thunderous roar.

The introduction of water-methanol injection reduced the need for JATO. JATO was expensive and had its hazards, and it would now be reserved for emergency alerts, when bombers had to get off the runway as fast as possible. It was otherwise only done once a year or so as a training measure. Early B-47E-Is had provisions the 18 built-in JATO bottles, but there were worries about having the JATO bottles so close to full fuel tanks, and in any case once the rocket bottles were exhausted they were just dead weight. Since JATO launches were rarely performed, the built-in JATO system was deleted, to be replaced by an external, jettisonable "split vee" or "horse collar" rack fitted under the rear fuselage. The rack carried 33 JATO bottles, in three rows of 11 bottles. The racks were expendable, and were dropped over specific range areas after takeoff.

The internal fuel capacity of initial production B-47Es was cut to 55,371 liters (14,610 gallons) as a weight-saving measure. This was considered acceptable because of the big external tanks and the fact that the USAF had refined mid-air refueling to the point where it could be relied upon as a standard practice.

One particularly welcome change in the B-47E relative to the B-47B was the return of the ejection seats. Air Force brass had reconsidered the decision to delete them and realized it didn't make sense. In addition, the twin 12.7 millimeter guns in the tail turret were replaced with twin 20 millimeter cannon to provide more punch, backed up by an A-5 FCS in early production and an MD-4 FCS in later production.

A final change in the B-47E was that most of the windows in the nose were deleted, with only one left on each side. However, many pictures of B-47Es show them with the full set of windows used on the B-47B. Whether the number of windows varied through B-47E production or whether these were B-47Bs updated to B-47E specification is unclear.

The "B-47E-II" featured only minor changes from late production 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 much more substantial update, featuring stronger landing gear, airframe reinforcement, greater fuel capacity, and a bombload uprated to 11,340 kilograms (25,000 pounds), though the bombbay was once again shortened because of the introduction of more compact nuclear weapons.

Another improvement was the introduction of the MA-7A BNS, a major step up from its predecessors. The MA-7A included the AN/APS-64 radar, with a range of up to 385 kilometers (240 miles). The AN/APS-64 could be used as a long range "identification friend or foe (IFF) transponder" interrogator to allow a B-47E-IV to find a tanker or other B-47, or it could be used as a high-resolution ground-targeting radar. The B-47E-IV retained the optical bombsight, though this was rarely used.

A total of 1,341 B-47Es was produced. 691 were built by Boeing, 386 were built by Lockheed, and 264 were built by Douglas. Most B-47Bs were rebuilt up to B-47E standards under two consecutive programs, designated HIGH NOON and then EBB TIDE. They were given the designation of "B-47B-II", though it appears that in practice they were simply called B-47Es.

Boeing RB-47E, RB-47H, ERB-47H and RB-47K

The B-47E was also the basis for a number of important long-range reconnaissance variants.

Boeing-Wichita built 240 "RB-47E" reconnaissance variants, similar to the B-47E but with a nose stretched by 86 centimeters (34 inches), 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 US gallons). The navigator controlled the cameras, becoming a "navigator-photographer" instead of a "navigator-bombardier".

A total of 32 "RB-47H" models was built for the electronic intelligence (ELINT) mission, along with 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 bombbay was replaced by a pressurized compartment, which accommodated "electronic warfare officers (EWOs)", also known as "crows" or "ravens". There were three crows on board the RB-47H, but only two on the ERB-47H. A distinctive bulged fairing replaced the bombbay doors. The RB-47H / ERB-47H retained the tail turret, and were also fitted with jammers and chaff dispensers. The only easily recognizable difference in appearance between the RB-47H and ERB-47H was that the ERB-47H had a small but distinctive antenna fairing under the rounded nose.

The first RB-47H was delivered in August 1955. The ELINT B-47s proved so valuable that they were put through a "Mod 44" or "Silverking" update program in 1961 to provide them with updated electronics systems. Silverking aircraft could be easily recognized by a large teardrop pod for ELINT antennas attached to a pylon, mounted under the belly and offset to the right side of the aircraft, as well as an pylon-style antenna attached under each wing beyond the outboard engine. It is unclear if all RB-47Hs and ERB-47Hs were updated to the Silverking specification.

The RB-47H and ERB-47H were highly capable aircraft, but the EWO compartment was cramped, with sitting room only, and had both poor noise insulation and climate control. This made long missions very uncomfortable and tiring, and some sources say that the crows even had to deal with fuel leaks on occasion. Getting out in an emergency was also a problem. The crows had ejection seats that would cut a hole through the compartment floor when fired, but nobody regarded such a scheme as very credible, and the scuttlebutt was that test firings with dummies had often resulted in decapitations.

Operations of the RB-47H and ERB-47H were top secret, with the missions generally flown at night and even base commanders often not knowing what they were all about. When crews were asked what they were doing, they always answered that such information was classified. On inquiries on what the blunt black nose was for, they would sometimes reply that it was a bumper, used in in-flight refueling in case they nosed into the tanker. This reply was often believed.

While a few of these aircraft performed special duties during the Vietnam war, such as relaying ELINT data from drones, they were eventually replaced by much more comfortable and capable Boeing RC-135 platforms. The last RB-47H was retired on 29 December 1967.

The final 15 RB-47Es built were fitted with additional equipment for the weather reconnaissance mission, and were given the designation of "RB-47K". Initial deliveries were in December 1955. The RB-47Ks were generally used for weather reconnaissance missions, carrying a load of eight "dropsonde" weather sensors that were released at various checkpoints along the aircraft's flight path. Data radioed back from the dropsondes was logged using equipment operated by the navigator. The RB-47Ks stayed in service until 1963.

Incidentally, there were "F", "G", and "J" B-47 variants, but these were all one-shot conversions of B-47Bs or B-47Es, to be discussed later. There never was a "B-47I" variant. The Air Force didn't use the "I" suffix because it was too easily confused with "1".

Author: Greg Goebel