Boeing B-47 Stratojet

1st Flight 1947

The Boeing B-47 Stratojet (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.

Variants

XB-47

Two prototype aircraft, powered by six Allison J-35-GE-7 turbojet engines for the first flights.

The second and subsequent aircraft were built with the specified General Electric J-47-GE-3 engines, which were retrofitted to the first XB-47.

B-47A

The first 10 aircraft were designated “B-47A”, and were strictly evaluation aircraft, the first delivered in December 1950.

While the XB-47s had been built by at Boeing’s Seattle plant, all B-47s were built at a government-owned factory in Wichita, Kansas that had previously built B-29s.

Their configuration was close to the XB-47.

They were fitted with J47-GE-11 turbojets, offering the same 5,200 lbf (23 kN) thrust as the earlier J47-GE-3, and also featured the built-in rocket-assisted-take-off (RATO) bottles.

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.

B-47B

In November 1949, prior to the B-47A’s first flight, the USAF ordered 87 B-47Bs, the first operational model.

The first flew on 26 April 1951.

A total of 399 were built, including eight assembled by Lockheed and 10 assembled by Douglas using Boeing-built parts.

YRB-47B

The USAF considered building a specialized RB-47B reconnaissance variant, but schedule slips ensured that the RB-47E was the first such variant.

As an interim measure, 91 B-47B bombers were fitted with a heated pod stowed in the forward bomb bay that housed eight cameras.

These were designated YRB-47Bs and were capable of daylight reconnaissance only. Once the RB-47E arrived, they returned to the bomber role.

TB-47B

A total of 66 of the 87 non-combat B-47Bs were re-designated TB-47B in 1953 to alleviate logistics problems due to different engines and systems.

Most were used as trainers; some were modified for Air Training Command by Douglas at Tulsa under the Field Goal program, adding a fourth seat for an instructor and removing the tail turret.

They were upgraded to B-47E standard in 1956 under the Ebb Tide program, joined by 41 more early build aircraft, also designated TB-47B.

They provided training through the 1950s.

MB-47B

With the introduction of the hydrogen bomb, the USAF studied converting a few B-47Bs into MB-47B drones, essentially huge cruise missiles, under the “Brass Ring” program.

Found to be impractical, Brass Ring was cancelled on 1 April 1953.

YDB-47B / DB-47B

There were various flight tests through the 1950s for using the B-47B as a launcher for the 31 ft (9.5 m) GAM-63 Rascal missile, and one B-47B was modified into a YDB-47B Rascal launcher.

The Rascal program never became operational; a total of 74 B-47Bs were modified into DB-74B Rascal launchers before cancellation.

WB-47B

In 1956, a B-47B was converted into a WB-47B weather reconnaissance model and operated by the Military Air Transportation Service (MATS), one of a few B-47s not operated by SAC.

It was used by the Air Weather Service until the mid-1960s.

KB-47B

In 1953, two B-47Bs were modified to test the probe-and-drogue refueling system.

The tanker, fitted with a British built tanker kit, was given the designation KB-47G and was known as “Maw” by flight crews.

The receiver aircraft was designated YB-47F and was known as “Paw”, though other aircraft were also used as refueling targets.

The program was cancelled in 1954 as the KB-47G could not carry a practical fuel load.

The idea of fielding B-47 tanker conversions was re-examined, but unfavorable economics meant that it was again discarded in 1957.

In parallel to the KB-47, Boeing tested its aerial refueling system aboard its Dash 80, later evolving into the KC-135 Stratotanker, which had greater fuel capacity.

Canadair CL-52

An unusual conversion was the Canadair CL-52: a B-47B (USAF S/N 51-2059 RCAF S/N 059X) loaned in 1956 to the Royal Canadian Air Force to test the new, powerful Orenda Iroquois turbojet (rated at 19,250 lbf (85.6 kN) dry, 25,000 lbf (110 kN) afterburning) for the Avro Canada CF-105 Arrow interceptor.

Canadair attached the Iroquois engine to the right side of the rear fuselage; due to the large exterior diameter of the engine, no other location was feasible.

Flying the CL-52 was reportedly a nightmare.

After the Arrow was canceled in early 1959, the B-47B/CL-52, which saw 35 hours of engine flight tests, was returned.

The CL-52 was the only B-47 to be used by any foreign service.

YB-47C / RB-47C / B-47Z / B-56

B-56

A four engined variant of the B-47, the YB-47C, was proposed by Boeing in 1950 to be powered by four Allison J35-A-23 turbojet engines, providing 10,090 lbf (44.9 kN) thrust each, in place of the six GEs J47s.

J71-A-5 A contract was signed in January 1950 for the rework of one B-47B.

The first flight was projected for April 1951.

A combination of delays and less-than-expected performance of the J35 led to the consideration of other engines.

The Allison J71 was proposed, however engine problems meant that this was not feasible for the by-then redesignated B-56A.

The Pratt & Whitney J57, eventually rated at 17,000 lbf (76 kN) thrust, was also considered, but was still in development.

The Boeing B-52 Stratofortress, which was being concurrently developed, had priority for this engine.

Thus, the B-56 was cancelled in December 1952 before conversion of the prototype was started.

The donor fuselage intended for the XB-56 was reused as a ground instructional airframe.

XB-47D

Starting in 1951, two XB-47Ds were modified from B-47Bs as experimental platforms, replacing each inboard two-jet pod with a Wright YT49-W-1 turboprop engine spinning a huge four-bladed prop.

Engine development issues delayed the XB-47D’s first flight until 26 August 1955.

Performance was comparable to a conventional B-47, and its reversible propellers shortened the landing roll, but the idea was not pursued.

B-47E

The designations B-47C and B-47D applied to variants that were never produced, thus the next production model was the definitive B-47E, first flying on 30 January 1953.

Four “blocks” or “phases” were built, each incorporating refinements on the previous block; changes sometimes occurred mid-block.

The B-47 incorporated the radar-controlled rear tail turret.

A total of 1,341 B-47Es were produced; 691 built by Boeing, 386 built by Lockheed, and 264 built by Douglas.

Most B-47Bs were rebuilt to B-47E standards and given the designation of B-47B-II, though they were often called B-47Es.

EB-47E

The Tee Town B-47s led to a specialized ECM conversion of the B-47E, designated EB-47E.

Initial conversions involved a set of 16 jammers in a removable cradle stored in the bomb bay, plus radar warning receivers and chaff dispensers, known as “Phase IV” or “Blue Cradle” EB-47Es.

A more advanced “Phase V” EB-47E used a pressurized module stowed in the bomb bay housing 13 jammers controlled by two Electronic Warfare Officers (EWOs), also known as “Crows” or “Ravens”.

While the Phase IV jammer was “broadband”, blanketing a wide frequency range to jam radars operating within that range, the Phase V jammer could be selectively tuned by EWOs to specific radar frequencies, enabling higher jammer power on the most effective frequencies.

About 40 B-47Es were converted to EB-47Es; they could not carry bombs but retained tail turrets.

EB-47E(TT)

Three B-47Es were converted to the specialized EB-47E(TT) “Tell Two” configuration to be used for “telemetry intelligence”, picking up radio signals from Soviet missile tests and space launches, being a precursor to the RC-135S Rivet Ball and Cobra Ball.

It featured two ECM operators, a “Crow capsule” in the bomb bay loaded with gear, and distinctive antennas below each side of the cockpit.

All three aircraft were operated out of Turkey until 1967.

Crews often made up stories about their purpose, such as a “return to fighter” defensive system that made air-to-air missiles loop back and attack their own launch fighters.

ETB-47E

As with the B-47B, a few B-47Es were converted to trainers, with a fourth seat for an instructor, and designated ETB-47E.

They replaced older TB-47Bs, serving into the early 1960s.

DB-47E / YDB-47E

Two B-47Es were converted to YDB-47Es to support the GAM-63 RASCAL stand-off missile program; two more B-47Es were converted to DB-47Es in preparation for the missile’s introduction before it was axed and were reused as drone controller aircraft.

JB-47E

Several B-47Es were assigned to other specialized test duties and given the blanket designation of JB-47E.

One was used in the late 1960s to test “fly by wire” control system concepts.

JTB-47E

Two B-47Es were also used for secret flight experiments in the early 1960s and given the designation JTB-47E, and a third modified B-47E was given the designation JRB-47E.

NB-47E

A B-47E was loaned to the US Navy to test the GE TF34-2 turbofan for the Lockheed S-3 Viking.

It was given the designation NB-47E and performed test flights from 1969 through 1975.

QB-47E

A total of 14 RB-47Es were converted to QB-47E target drones in 1959 and 1960.

These aircraft were radio-controlled and included self-destruct charges, arresting gear to assist landings, and carried pods on the external tank pylons to help in scoring weapons tests.

RB-47E

A typical reconnaissance route from Thule AB (Greenland) to Soviet Union flown by RB-47H crews

The B-47E was the basis for several reconnaissance models, the only B-47s to see anything resembling combat.

They operated from most airfields that gave access to the USSR and often probed Soviet airspace.

Boeing built 240 RB-47Es, similar to the B-47E but with a nose stretched by 34 in (0.86 m), giving an arguably more elegant appearance.

The long nose accommodated up to 11 cameras, possibly including 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 and K-36 telescopic cameras.

Cameras were controlled by the “navigator-photographer”.

Photoflash flares were carried for night photography. While it could be refueled in flight, fuel capacity was increased to a total of 18,400 US gal (70,000 l).

WB-47E

Following the single WB-47B conversion, in the early 1960s, 34 B-47Es were converted by Lockheed into WB-47Es for weather reconnaissance to replace 44 WB-50D Superfortresses that had suffered several fatal crashes between 1956 and 1960.

Stripped of combat gear, they were fitted with nose cameras to photograph cloud formations and a meteorological instrument pod in the bomb bay.

Initially assigned to the Air Weather Service of the Military Air Transport Service (MATS), they became part of the Military Airlift Command (MAC) upon its establishment.

The WB-47Es, the last B-47s in USAF service, were retired in October 1969.

RB-47H/ERB-47H

A total of 32 RB-47H models were built for electronic intelligence (ELINT) missions, as well as three more specialized “ERB-47Hs”.

Featuring a distinctive blunt, rounded nose and sported blisters and pods for intelligence-gathering antennas and gear, they were designed to probe defenses and collect data on radar and communications signals.

The bomb bay was replaced by a pressurized compartment, which accommodated “Crows”, or Electronic Warfare Officers (EWOs).

There were three Crows on board the RB-47H and two on the ERB-47H.

A distinctive bulged radome fairing replaced the bomb bay doors.

They retained the tail turret and were fitted with jammers and chaff dispensers.

A recognizable difference between the RB-47H and ERB-47H was the latter’s distinctive antenna fairing under the rounded nose.

YB-47J

A single B-47E was modified to test the MA-2 BNS for the B-52, and given the designation YB-47J.

RB-47K

The RB-47K was a photo and weather reconnaissance variant based on the RB-47E generally used for weather reconnaissance missions, carrying eight dropsonde weather sensors that were released at various checkpoints along its flight path.

Data radioed from the dropsondes was logged by the navigator. Fifteen RB-47Ks were built, the variant was in service until 1963.

EB-47L

Between 1961 and 1963, 36 B-47Es were modified to carry a communications relay system and were designated EB-47L.

Used to support US flying command post aircraft in case of a nuclear attack on the US, the EB-47Ls were only briefly in service as improved communications technologies made them redundant by 1965.

Specifications

Crew

3

Length

107 ft 1 in (32.64 m)

Wingspan

116 ft 0 in (35.36 m)

Height

28 ft 0 in (8.53 m)

Wing area

1,428 sq ft (132.7 m2)

Aspect ratio

9.42

Airfoil

NACA 64A(.225)12 mod (BAC145)

Empty weight

80,000 lb (36,287 kg)

Gross weight

133,030 lb (60,341 kg)

Max take-off weight

221,000lb (100,244 kg)

Zero-lift drag coefficient

0.0148 (estimated)

Zero-lift drag coefficient area

21.13 ft2 (1.96 m2)

Powerplant

6 × General Electric J47-GE-25 turbojet engines, 7,200 lbf (32 kN) thrust each

Performance

Maximum speed

607 mph (977 km/h, 527 kn)

Cruise speed

557 mph (896 km/h, 484 kn)

Combat range

2,013 mi (3,240 km, 1,749 nmi) with 20,000 lb (9,100 kg) bomb load

Ferry range

4,647 mi (7,479 km, 4,038 nmi) with underwing tanks

Service ceiling

40,500 ft (12,300 m)

Rate of climb

4,660 ft/min (23.7 m/s)

Wing loading

93.16 lb/sq ft (454.8 kg/m2)

Thrust/weight

0.22

Armament

Guns

2 × 20 mm (0.787 in) M24A1 auto cannon in a remote controlled tail turret with

Bombs

25,000 lb (11,340 kg) of ordnance, including:

2 × Mk15 nuclear bombs (3.8 megaton yield each),

or

4 × B28 nuclear bombs (1.1–1.45 megaton yield each),

or

1 × B41 nuclear bomb (25 megaton yield),

or

1 × B53 nuclear bomb (9 megaton yield),

or

28 × 500 lb (227 kg) conventional bombs.

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