Boeing B-47

Boeing B-47 Stratojet
A B-47A "Stratojet" of the US Air Force
Type:	Strategic bomber
Design country:	United States
Manufacturer:	Boeing
First flight:	December 17, 1947
Commissioning:	June 1951
Production time:	1948 to 1956
Number of pieces:	2032

The Boeing B-47 Stratojet was a six-engined strategic bomber of the Cold War era from US production.

development

The origins of the B-47 go back to 1943. At that time, the US Army Air Forces called for a bomber that could attack Germany from the American mainland if Britain were to fail as a base. Several manufacturers initially made suggestions, but obviously none could convince. After the turning point in the course of the war, which made a British defeat unlikely, the demand for a very high range initially faded into the background. Instead, the official tender for a bomber with a top speed of 800 km / h or more took place. Furthermore, an altitude of at least 12,200 meters and a range of 5600 km were required. Since the required performance values ​​could not be achieved with a conventional fan gun, General Electric was commissioned with the development of the TG-180 jet engines, later referred to as the J35.

When the development success of the J35 seemed realistic in April 1944, the USAAF asked companies to propose a jet-powered bomber. Boeing was one of four companies to initially come up with a number of fairly conventional designs. These ranged from the Model 345 with four J35 under B-29 wings through the Model 413 to the larger Model 424 . This design was also basically a slightly scaled-down B-29 with four jet engines. This was followed by the last Boeing design with straight wings, the Model 432 , with the four engines being housed in the fuselage. In late 1944, USAAF placed Phase I development contracts with all four companies. In the course of 1945, after the end of the war in Europe, the USA began to bring German scientists to the USA. George Schairer , then chief aerodynamicist at Boeing, evaluated German research results from wind tunnel tests. Here he saw studies on very thin swept wings and it quickly became clear to him that such a construction would produce significantly higher performance. He then convinced his superiors to incorporate this research into the new bomber.

From the Model 432 with straight wings, the Model 448 with swept wings was gradually developed up to September 1945 , with Schairer increasing the sweep angle even above the highest value found in the German data from 29 ° to 35 °. While the Model 448 received two additional engines in the stern, the arrangement of the engines was finally changed, which were now hung under the wings in the final concept, Model 450-1-1 . However, since these were made very thin, according to German research, there was a structural problem. Since it was clear that the machine would need six engines, but the wings could actually only have four, two engines were combined in the inner nacelles, while the outer nacelles were each given a single engine. The USAAF accepted the 450 model and commissioned Boeing to develop it. Now the problem with the landing gear had to be fixed. Although it was now possible to attach all six engines to the wings, the other total load-bearing capacity was exhausted, which is why the landing gear now had to be relocated completely into the fuselage. Since the new bomber should also be able to drop the atomic bombs, which were still very large at the time, a large internal weapon bay was required, which in turn reduced the space for the landing gear. It quickly became apparent that the conventional nose wheel landing gear was not sufficient. The new tandem chassis was developed in order to continue to guarantee stability . It consisted of two equally dimensioned landing gear legs, each provided with two wheels, which were arranged on the fuselage center line in front of and behind the bomb bay, as well as two additional stabilizing support wheels on the inner engine pods between the engines. Boeing presented this concept to USAAF in October 1945. A dummy inspection finally took place in April 1946.

USAAF ordered two prototypes ( Model 450-3-3 ) in April 1946 . These were given the designation XB-47 by the newly established US Air Force . The first XB-47 prototype was first flown on December 17, 1947 by test pilots Robert Robbins and Scott Osler. These reported very good flight characteristics after the 52-minute maiden flight, but complained about the insufficient thrust. In the following test flights, the realization that more powerful engines were needed was consolidated. So developed General Electric , the J47-GE-3 engines, which were designated initially as TG 190th The second XB-47 then took off for the first time with the new engines on July 21, 1948. The first prototype was also retrofitted with these.

Since the machine was a completely new design, the flight tests for this period were particularly intensive and lengthy. In the competition against the North American B-45 , Convair XB-46 and Martin XB-48 , the B-47 prevailed relatively quickly. All of these models still relied on conventional airframe designs , whose piston engines had only been replaced by jet engines. As a result, however, they achieved significantly poorer performance and were defeated in comparison. The XB-45 was temporarily in service as the B-45 Tornado , but only as a temporary solution until the B-47 were operational. On September 3, 1948, the US Air Force finally ordered the first B-47s.

Calls

The B-47 was subordinate to the US Air Force's Strategic Air Command , where it was in service from 1951 to 1965.

The early years

The first B-47 bombers entered service in 1951. Nevertheless, they were no longer used in the Korean War , as the crews first had to be trained on the new types. The new machines were a real change for them, as they had previously performed their duties on the comparatively sluggish B-29 Superfortress and B-36 Peacemaker bombers . Now they had a much faster machine at their disposal, with which completely new flight maneuvers were possible, but which had to be trained first. The basic approach maneuver for an atomic bomb was completely changed. With the B-47, the crews learned to first approach their destination at great heights. On the final approach they went low before they started a steep climb shortly before the target. In this case, the bomb was released, so that it should fly into its target in a trajectory parabola . The bomber continued the maneuver with an upswing in order to avoid the effects of the weapons against the original direction of attack . This type of bombing is also known as "toss bombing". Even if it is disputed whether such maneuvers could have brought the machine out of the danger zone in time, the crews trained them in this way. The loads for the crews were significantly higher; the crew was reduced to three men. This enabled a much higher number of machines with a reduced weapon load compared to the B-36. This was accompanied by new operational plans that the crews first had to familiarize themselves with. This in turn meant that the machine was not operational until 1953.

Overload start attempts at Edwards AFB with a B-47E-65 (USAF serial no. 51-5257), in which an externally attached drop- off RATO "belt" with 33 missiles was used. Earlier versions used 18 rockets built into the fuselage.

In daily use, further deficits first became apparent. Despite the more powerful engines, the machine was still underpowered during take-off, which increased the take-off distance. This has been corrected in the B version with JATO additional missiles. The landing characteristics were also not without problems. As a rule, the machines were too fast when landing, which resulted in a very hard landing. This increased the loads on the chassis, which is why maintenance had to be carried out more frequently than originally planned. Nevertheless, the machine was easy to maintain, as damaged parts could be replaced relatively easily. Despite problems with the avionics , the reliability of the machines was also quite good.

Late 1950s

USAF Boeing B-47E Stratojet

Cockpit of a Boeing B-47B

In the late 1950s, the B-47 bombers were the primary component of US nuclear deterrence, although the successor to the B-52 had already entered service. In addition, with the development of ICBMs, atomic bombers themselves were increasingly pushed into a secondary role.

A third of all B-47s were operational around the clock. The machines were stationed at bases in the USA, Great Britain, Morocco, Spain, Alaska, Greenland and Guam. There was always at least one squadron with atomic bombs in the air, which flew one of a total of 28 different routes. Due to the great importance of the bombers at this time, other maneuvers such as the interval start were practiced. Several machines start from the same runway at intervals of less than 15 seconds. This was particularly challenging because of the turbulence of the machines that had started earlier. The reason for the maneuver was to get as many machines into the air as quickly as possible in the event of an enemy nuclear strike. In order to further eliminate the B-47 itself from the list of a possible target, the plan was to “bog down” the aircraft at non-SAC airfields if there was increased readiness.

It was not possible for the Soviet airspace defense to determine whether the B-47-based aircraft penetrating into Soviet airspace were reconnaissance aircraft such as the RB-47 or bombers armed with nuclear weapons. This, also in connection with a possible Renegade case, caused extreme concern in the military and political leadership of the Soviet Union. In 1958, ahead of a conference, the Soviet Union expressed concern that the military command had acted unauthorized during these routine patrols. Secretary of State Gromyko said on April 19: “The Soviet government does not want to believe that these actions by the American Air Force have been personally sanctioned by the American government and by President Eisenhower; but no one has declared otherwise. ”His declaration was about those of the constantly patrolling bombers who had temporarily set course for the Soviet Union due to interference with the radar in arctic areas when the air situation was unclear. The NZZ criticized the wording of Khrushchev's and Gromyko's diplomatic maneuvers and remarked: “One wonders whether Khrushchev is still interested in a“ summit conference ”or whether he considers the successes achieved so far in the psychological warfare against the West to be sufficient. "

It is certain that RB-47 scouts flew over the Soviet Union to obtain information. Probably the first reconnaissance flight took place on October 15, 1952, when a B-47 flew a coastal route of around 1300 kilometers over easternmost Siberia to find out whether the Soviet Union had Tu-4 bombers on two airfields there, Mys Schmidta and Prowidenija , relocated. RB-47 were stationed around the world, in Europe on the RAF Brize Norton base in England . Weather scouts collected not only weather data, but also air samples after Soviet nuclear tests. The electronic reconnaissance aircraft of the type RB-47H were used to collect the radar data of the Soviet air defense. In the course of the flights from 1952 to 1956, one RB-47 was fired at over the Soviet Union and two more were shot down.

Last years of service and retirement

Production of the B-47 ended in 1956, but it continued to be modernized and modified. From 1959, the B-52 Stratofortress replaced the B-47 as the most important bomber in the US Air Force .

When Gary Powers was shot down in a U-2 over the Soviet Union, the SAC's favored operational doctrine became obsolete, as it was now clear that the previous operational plans were outdated. Until then, it was believed that they could operate at great heights deep in Soviet airspace and attack targets with nuclear weapons unhindered. This strategy, for which the B-47 was primarily designed, was now obsolete. So the B-47 itself was no longer up to date. They responded with low-level maneuvers, for which the B-47 was only suitable to a limited extent. The use of long-range missiles and cruise missiles like the B-52 was not possible here because the load-bearing capacity was too low. When the modernization costs then rose sharply, as material fatigue slowly set in as a result of the significantly increased flight performance, the B-47 began to be retired in 1963. The SAC put the last machine out of service in 1965.

The accident rate of the threshold type B-47 was unimaginably high compared to modern conditions; 203 aircraft, about 10% of total production, were lost. There were 464 dead; most of the accidents occurred in 1957 and 1958 (49 machines and 122 deaths).

The Tactical Air Command used the B-47 as an RB-47 reconnaissance aircraft and as an EB-47 fighter for electronic warfare until 1977. Both versions were also increasingly used over Vietnam. Several TAC machines were lost during the Vietnam War , the exact number of which is unknown. The RB-47s proved to be quite unsuccessful in the Vietnam War, as in the dense jungle only low-level reconnaissance that they could not provide was effective. As a result, they were sent back to Europe, where they resumed their original reconnaissance routes across Scandinavia and the Baltic States. In Vietnam, however, the EB-47 was more successful. Together with the F-4G Wild Weasel, it fought the North Vietnamese air defense relatively effectively . With the introduction of the EF-111 Raven in 1977, the TAC also put the last variant of the B-47 out of service.

A special feature was the landing of the reconnaissance aircraft in England with the braking parachute open; Since the engines did not develop the power for a go-around quickly enough , the aircraft landed with a slight thrust - and the brake parachute open.

production

The B-47 was built in series by three companies (Boeing in Wichita, Douglas in Tulsa and Lockheed in Marietta).

Approval of the B-47 by the USAF:

Manufacturer	version	1948	1949	1950	1951	1952	1953	1954	1955	1956	1957	total	price
Boeing	XB-47	1	1									2	4,720,704 USD
	B-47A			1	9							10	$ 2,800,000
	B-47B				47	302	30th					379	$ 2,449,456
Douglas							10					10	$ 2,449,456
Lockheed							7th	1				8th	$ 2,449,456
Boeing	YB-47E						1					1
	B-47E						278	157	132	124		691	$ 1,869,667
Douglas							31	107	73	53		264	$ 1,869,667
Lockheed							30th	143	120	86	7th	386	$ 1,869,667
Boeing	RB-47E						15th	167	73			255	$ 2,056,913
	RB-47H								30th	3	2	35	$ 2,126,917
total		1	1	1	56	302	402	575	428	266	9	2041

Conversion of the B-47:

version	out	FY 1953	FY 1954	FY 1955	FY 1956	FY 1957	FY 1958	FY 1959	FY 1963	FY 1964	FY 1965	total
YRB-47B	B-47B	36	55									91
YDB-47E	B-47E		2									2
TB-47B	B-47B, YRB-47B	70	1		37	6th	4th	2				120
XB-47D	B-47B			2								2
RB-47K	B-47E				15th							15th
WB-47B	B-47B						1					1
WB-47E	B-47E								3	30th	1	34
EB-47E									95	1		96
EB-47H	RB-47H								3			3
EB-47L	B-47E								18th	2	16	36
total		106	58	2	52	6th	5	2	119	33	17th	400

(FY = Fiscal Year. The FY 1953 ran from July 1, 1952 to June 30, 1953. In the years FY 1960–1962, no modifications took place.)

In 1959, the aircraft had a lifespan of 3300 flight hours. Until the introduction of the B-52, the B-47 was the aircraft with the highest fuel consumption. In 1953 it needed 1513 gallons (5727 liters) per flight hour, 40% more than the much larger B-36. Under the designation Boeing XB-56 , a version of the B-47 was planned, which instead of the six engines should have four more powerful engines in identical engine nacelles. This would have simplified maintenance and optimized thrust, range and fuel consumption. However, the project was ended before an already designated B-47 was converted into an XB-56. Between 1952 and 1967, 184 B-47s, 21 RB-47s and 9 TB-47s were lost in accidents. The year with the highest accident rate was 1958 with losses of 28 B-47s, two RB-47s and four TB-47s.

Incidents

• On April 17, 1955, near the Kamchatka Peninsula, an RB-47E reconnaissance aircraft of the USAF ( Air Force No. 51-2054 ), which had penetrated Soviet airspace to photograph military installations, was used by Soviet MiG-15 fighter planes shot down and fell into the sea 13 km west of Nikolskoye. The three crew members are considered missing.
• On March 10, 1956, a B-47 vanished from MacDill Air Force Base on a non-stop transfer flight to the Moroccan air base at Ben Guerir Airbase in the Mediterranean near the Algerian border. A refueling maneuver with a tanker aircraft at an altitude of around 4,200 meters had failed because the two aircraft had no contact with each other. The bomber had nuclear weapons on board, but no nuclear bombs; the machine could not be found until today.
• On July 27, 1956, an American B-47 crashed while approaching the RAF Lakenheath military base in England and hit a concrete nuclear weapon bunker in which three US Mark-6 atomic bombs, similar to the Nagasaki bomb, were housed. Three crew members died in the collision and all three atomic bombs were damaged. The incident was kept secret until 1979.
• On October 10, 1957, an American B-47 with a bomb and a non-installed nuclear capsule crashed shortly after takeoff from Homestead Air Force Base in Florida , USA and burned out. The explosive charge exploded, but no nuclear explosion.
• On January 31, 1958, a USAF B-47 with an atomic bomb on board crashed near Rabat in Morocco shortly after take-off at the Sidi Slimane military base about 90 km northeast of Rabat and burned out for about 7 hours. There was no nuclear explosion, but the area was widely contaminated, so that the population in the area had to be evacuated.
• On February 5, 1958, after a collision of a B-47 (pilot: Howard Richardson) with an F-86 fighter aircraft on the coast of Georgia, a Mk.15 hydrogen bomb was dropped from an altitude of 2200 meters into the Atlantic Ocean Savannah and Tybee Island in Georgia. The B-47 was able to make an emergency landing on Hunter Air Force Base, the pilot of the F-86 saved himself with the ejector seat. In 2001 the search for the bomb was started again, but it was unsuccessful (see Tybee bomb ).
• A B-47 had a serious accident on February 28, 1958 at the US Air Force Base Greenham Common (near Newbury), Great Britain. Scientists who worked for the Atomic Weapons Research Establishment in Aldermaston discovered a high level of radioactive contamination on the base in 1960. In their conclusion, they pointed out that a nuclear weapon must have been involved in the accident. The US government never confirmed this assumption.
• On March 11, 1958, a B-47E from Hunter Air Force Base, Georgia, accidentally lost an atomic bomb without a detonator at an altitude of 4,200 meters. On the ground she demolished a house in Florence, South Carolina. One resident was injured.
• On November 4, 1958, a B-47 with a nuclear weapon on board caught fire shortly after takeoff and crashed from 450 meters near Dyess Air Force Base , Texas . The explosive charge exploded and the nuclear material could be safely recovered.
• On November 26, 1958, a fire on the ground at Chennault Air Force Base , Louisiana, with a nuclear weapon on board, caused low levels of radiation.
• On July 1, 1960 a USAF reconnaissance aircraft of the type RB-47H (S / N 53-4281) of the 343th Strategic Reconnaissance Squadron, 55th Strategic Reconnaissance Wing was defeated over the Barents Sea by a Soviet MiG-19 (pilot: Vasily Polyakov) of the 206 Air division shot down. Of the six crew members, only two survived, rescued by a Soviet trawler after six hours. US soldiers John R. McKone and Freeman Bruce Olmstead remained in custody in Lubyanka prison in Moscow until January 25, 1961 . Willard Palm, Eugene Posa, Dean Phillips and Oscar Goforth died.

Technical specifications

Three-sided tear

Play media file

NASA video of the B-47 captured at Edwards AFB

Parameter	B-47E data
crew	3
length	33.48 m
span	35.36 m
height	8.50 m
Wing area	132.66 m²
Wing extension	9.43
Wing loading	minimum (empty weight): 270 kg / m² nominal (normal take-off weight): 455 kg / m² maximum (max. take-off weight): 707 kg / m²
Empty mass	35,867 kg
normal takeoff mass	60,340 kg
Max. Takeoff mass	93,759 kg
Top speed	977 km / h (at optimal altitude)
Marching speed	896 km / h (at optimal altitude)
Service ceiling	12,345 m
Use radius	3240 km
Range	6494 km
Engines	6 × General Electric J47-GE-25 jet engines with 26.7 kN thrust each

Armament

Pipe armament for self-defense

• 1 × rear stand unit with a double mount in a rotating dome with 2 × 20 mm M24A1 automatic cannons with 400 rounds of ammunition each. The stern stand unit was remote-controlled from the cabin by a crew member. The AN / APG-39 fire control radar was installed as a target aid.

Explosive ordnance up to 11,000 kg in the internal bomb bay

Unguided bombs

• 2 × Mk.15 (nuclear free-fall bomb with 3.7 MT explosive device)
• 4 × B28 (nuclear free-fall bomb with 1.45 MT explosive device)
• 1 × B41 (nuclear free-fall bomb with 25 MT explosive device)
• 4 × B43 (nuclear free-fall bomb with 1 MT explosive device)
• 1 × B53 (nuclear free-fall bomb with 9 MT explosive device)
• 28 × Mark 82 LDGP (227 kg / 500 lb free fall bomb)

Self defense

Active measures

• 1 × decoys launcher with heat flare decoys
• 1 × electronic jammer AN / APT-5

Passive action

• AN / APS-54 radar warning sensor

literature

• Bill Yenne: Boeing B-47 Stratojet - Variant file. In: International Air Power Review, Volume 6, 2002, pp. 156-171.

Web links

Commons : B-47 Stratojet  - album with pictures, videos and audio files

Individual evidence

1. ↑ Boeing B-47 Stratojet (Low Altitude Bombing System) LABS Maneuver.
2. ^ Das goldene Telephon , Neue Zürcher Zeitung of February 3, 1962, page a23, title of the report on page a22
3. ↑ ^{a b} Yefim Gordon, Dimitriy Komissarov: Soviet Air Defense Aviation 1945–1991. Hikoki Publications, 2012, ISBN 978-1-902109-25-1 , pp. 136-138.
4. ↑ Gromykos' declaration on the threat to Russia and the inclusion of the Eastern bloc states in the discussions Gromykos , NZZ , April 21, 1958, page b2; Another quote on the wording of Gromykos: "The government statement issued by Gromyko was peppered with formulations and idioms that are well known from the high stage of the Cold War"
5. ^ Nuclear Weapons Test and Peaceful Nuclear Explosions by the Soviet Union 1949 to 1990 , Natural Resource Defense Council, October 1996
6. ↑ National Museum of the US Air Force: Boeing RB-47H Stratojet ( Memento from June 19, 2017 in the Internet Archive )
7. ↑ Boeing: Historical Snapshot B-47 (English) , accessed on June 8, 2015
8. ^ Air Force Magazine, February 2013
9. ↑ Statistical Digest of the USAF 1948. p. 16; 1949, p. 164 f .; 1951, p. 158; 1952, p. 158; 1953, p. 185 f .; 1954, pp. 70 f .; 1955, p. 80 f .; 1956, p. 91 f .; 1957, p. 97 f.
10. ^ ^{A b} Marcelle Size Knaack: Encyclopedia of US Air Force Aircraft and Missile Systems. Volume 2, Washington DC, 1978, p. 99 ff.
11. ↑ Statistical Digest of the USAF 1953-1965 , table "Gains and Losses"
12. ↑ Statistical Digest of the USAF 1953, p. 16
13. ↑ Statistical Digest of the USAF 1952–1970 , table "USAF Aircraft Gains and Losses".
14. ^ Joachim Bashin, Ulrich Stulle: Hot Heaven in the Cold War. In: Flieger Revue Extra. No. 4, p. 47.
15. ↑ Accident Report B-47 52-0534 , Aviation Safety Network WikiBase (English), accessed on 15 July 2016th
16. ↑ www.nationalmuseum.af.mil