Profile – Boeing B-47 Stratojet

Under the direction of Lt General Curtis E LeMay, who took command in October, 1948, SAC underwent a programme of steady expansion for the next few years until the outbreak of the Korean War in 1950. As the Cold War suddenly became hotter seemingly inexhaustible funds were made available and with these, SAC was able to acquire a new generation of faster and potentially more capable jet powered aircraft.

USAF jet bomber designations began with the Douglas XB-43 which was created from the XB-42 Mixmaster basically by removing its piston engines and replacing them with turbojets. This design did not however go beyond the prototype stage. Next, Boeing’s 844 was actually the modified Superfortress which was re-numbered into the B-50 already mentioned. Towards the end of this sturdy plane’s lengthy service career it flew in the Vietnam War in its jet-boosted KB-50J tanker version. North American produced the B-45 Tornado and it was the second jet bomber to enter service in the world, the first being Germany’s Arado Ar234 Blitz.

Meanwhile, Convair’s XB-46 remained in prototype form. The huge Martin XB-48 first flew in June, 1947, and was an impressive machine powered by six wing-m·ounted Allison J35 turbojets but it was obsolescent at the outset and it too remained in prototype form. Last in the ‘forty’ range of bombers came Northrop’s graceful and unique YB-49 family of large flying wings. Although heaped with praise by its test pilots and showing excellent payload and performance figures, the design was too radical for conservative USAF chiefs who decided instead to order more B-36s.

The machine not mentioned in this list was the B-47 which came from Boeing. When the prototype was wheeled out of the company’s plant in Seattle in September, 1947, observers were introduced to a design far in advance of all of the other medium bomber contenders. It was large with a fuselage extending to more than 109 feet (33. 2m) but what caught the eye most was its slim but· striking swept back wings with six underslung jet engines. These 3,7501b (16. 68kNJ thrust General Electric J35s were housed in two twin inboard and two single outboard pods. The aircraft’s bicycle layout undercarriage consisted of tandem pairs of wheels which were housed in the underside of the fuselage plus small outrigger wheels under the inboard engine pods. Its high fin and tailplane was also swept back. At a gross weight of some 125,000lb (56,700kg) it was heavier than a B-29, WW2’s largest and heaviest bomber, yet it was still classified as a medium bomber.

The Stratojet, as it was named, represented the culmination of four years of effort. Initial design work had begun as early as 1943/4 and drawings of Boeing’s Model 424, the initial submission, depicted an aircraft which was actually a B-29 with a pair of jet engines underneath each wing. These were transferred into the fuselage of the next design, the Model 432, above its straight, mid-section wings. Meanwhile, by now the war in Europe had ended and this was to have a far reaching effect on the work then being done by the Boeing design team.

With the end of hostilities, the US Army sent a Scientific Advisory Group into Germany to find and evaluate technical and scientific data and records captured from the Germans. Of major concern was the fact that towards the end, the enemy had demonstrated a clear technical superiority especially in such fields as jet and rocket propulsion. The race to grab scientific secrets was on and one member of the American group was George Schairer, Chief Aerodynamicist at Boeing. Schairer was particularly impressed by the discovery that the 18. 5 degrees of sweep used for the wings of Messerschmitt’s impressive Me 262 jet fighter had resulted in significant improvements in the machine’s performance. He wrote back to his design team in Seattle with the result that the Model 432 was scrapped immediately and work commenced on a new design.

Their redirected efforts turned into the Model 448 which featured four jet engines mounted in two pods on each side of the fuselage together with laminar flow wings and tail, both swept back at an angle of 35°. Two more engines housed in a single pod towards the end of each wing tip were added later. A mockup of the aircraft was constructed out of timber and this was inspected by USAAF representatives in April, 1946. After some discussion, approval was given for the building of an improved version of the Model 448 and Boeing designated this modified machine as its Model 450.

The XB-47 (Model 450-3-3), No. 46-065, was prepared for its maiden flight on December 17, 1947. Takeoff was delayed until just after 1. 00pm because of unsuitable weather. Except for when test pilot Robert Robbins aborted the first takeoff attempt because of a blinking fire warning light (which proved to be a false alarm), everything went smoothly. The prototype Stratojet flew serenely from Boeing Field, Seattle, to Moses Lake AFB in Washington State, a distance of 145 miles (233km). Coincidentally, this day also marked the 44th anniversary of the Wright brothers’ first powered flight. The second prototype flew for the first time in July, 1948 and it was fitted with more powerful General Electric J47 engines.

Testing of the two prototypes revealed a couple of unanticipated and pleasant surprises. Thanks to its advanced swept wing design, drag proved to be 25% less than predicted and this in turn gave a bomb carrying range better than expected. Meanwhile, the thin structure of the wings caused them to flex during flight with the tips rising and falling as much as 5 feet (1. 52m) from their ‘normal’ position.

Problems did come to the surface but they were relatively minor. Owing to the slow ac_celeration characteristics of early jet engines and because of the aircraft’s high wing loading, eighteen Jet-Assisted Takeoff (JATO) solid fuel rockets had been built into the sides of the rear fuselage to give an emergency takeoff thrust of up to 20,000lb (88. 97kN). These fixed units were heavy and made higher landing speeds necessary with the result that severe braking ·problems were encountered. This was rectified by releasing a ribbon-type parachute from the tail as the wheels came into contact with the tarmac. Later, to save weight, the JATO rockets (also referred to more accurately as RATO for Rocket Assisted Takeoff) were mounted on an external rack which could be jettisoned after the plane had climbed to height. A takeoff using this equipment provided a spectacular sight. The parachute device was also modified on later models so that while the plane was in its landing pattern a small drogue chute was released and then just before landing its much larger braking parachute popped free.

Boeing received a contract for 10 8-47 A Stratojets (Model 450- 10-9) towards the end of 1948. These were required by the USAF for wider scale service testing and familiarisation trials. They were built at the government owned, Boeing operated plant in Wichita, Kansas, were similar to the second prototype and like it they had the more powerful General Electric J47-GE-11 turbojets of 5,200Ib (23. 1kN) thrust. The first of this pre-production batch had its maiden flight on June 25, 1950, coincidentally on the same day as the commencement of the Korean War. Evaluation of these machines was concentrated mainly on finding the best type of fire control and tail armament. They were fitted with remotely controlled . 50 inch (12. 7mm) machine guns which could be operated manually by the copilot or aimed and fired automatically by radar.

Meanwhile, on February 8, 1949, one of the XB-47s set an impressive speed record by flying coast-to-coast across the USA covering a distance of 2,289 miles (3,684km) in 3 hours 46 minutes giving it an average speed of 607. 8mph (978. 1km/h).

Meanwhile, the conflict in Korea had a profound effect on the production and development of the 8-47. SAC committed only a small number of its units to the war and these were equipped with 8-29 Superfortresses. When the Communists introduced the Russian built MiG-15 into hostilities the chances for survival in daylight of heavy, slower moving piston engined bombers were drastically reduced. The future clearly lay with new jet powered aircraft and, as East and West seemed more and more to be teetering towards the brink of wider spread hostilities, an expanded SAC with true intercontinental capabilities was clearly needed. As the 8-47 was close to entering service it became the subject of an accelerated programme of manufacture. In the space of just five years, SAC was to receive more than 1,500 of these machines. The first true production Stratojet was the 8-478 (Model 450- 11-10) which flew for the first time on April 26, 1951. It differed from the 8-47 A by having structural modifications for greater fuel carrying capacity in an effort to increase its range to better meet SAC’s. need to be able to stage intercontinental missions. This, incidentally, became the pattern of development for successive models. More fuel meant more weight and so the 125,000lb (56,700kg) gross weight of the prototypes became 160,000lb (72,575kg) for the B-47A; 200,000lb (90,718kg) for the 8-478; and a massive 230,000lb (104,326kg) for the B-47E, four times heavier than a Second World War B-17E Flying Fortress. Such weight increases necessitated greater power to maintain an increased performance and from the 88th production machine J47-GE-23 engines of 5,800lb (25. 8kN) thrust were introduced. By the end of the year B-47Bs were entering service and an overall total of 399 were built.

Alongside the bomber variant ‘B’ series Stratojets (DB-478) were built as control aircraft for drones, reconnaissance planes (RB-478) and crew trainers (TB-478). A single . B-478 was transferred to the RCAF and loaned to Canadair Limited as a test bed for its large and powerful Orenda Iroquois turbojet engine which was mounted in a pod on the starboard side rear fuselage. Another·(WB-478) was especially converted for weather reconnaissance. One 8-478 was set aside to be the sole B-47C, and after being re-engined to become the prototype XB-56, but the project was abandoned before conversion. Finally, two of the ‘B’ series were re-engined and re-designated XB-47Ds to be used as testbeds for the Curtiss Wright 9,710eshp (7,241ekW) YT49-W-1 turboprop engines. These were at that time the most powerful turboprops built and they were installed in place of the inboard jet engine nacelles but the single outboard J47s were retained.

The Barents Sea Incident

On July 1, 1960, a Boeing RB-47H Strajet of the 55th Reconnaissance Wing, SAC, took off from Norton AFB, Eng- land, to carry out an electronic reconnaissance mission out Over the Barents Sea. At the controls was Major Willard G Palm Palm’s crew consisting of copilot Capt Bruce Olmstead navigator Capt John McKone and three electronics experts (Ravens) to operate the intricate radar monitoring equipment housed in the pressurized compartment in the bomb bay. Major Eugene E Posa and Captains Dean B Phaos and Oscar L Goforth.

The purpose of their mission was to attempt to pick up signals from any new Russian radar stations, measure their pulse rates and frequencies and pinpoint their locations. The method employed to do this could be extremely dangerous. Because of the likelihood that the Soviets would not use their top secret equipment unless there was a serious direct threat “errer planes, as these electronic reconnaissance ar were known, sometimes hurtled across the border in simulated attacks. Under such provocation not only would the Russian radar swing into action, so too would their interceptors and missile sites. Reactions had to be quick and once the American ferret planes detected what they wanted they swiftly turned for friendly territory and raced to safety. It was a new variation on the old game of Russian Roulette and the results could be just as deadly for over the previous ten years 75 American airmen had failed to return from similar fights.

Sometimes the Soviets did not wait for provocation. . .

At 2. 56pm navigator John McKone checked their position. According to his radarscope, they were over 50 miles (80km) from the Soviet coastline but to be absolutely sure he checked where they were in relation to Svatoi Nos (Holy Nose Cape), a prominent landmark. It was time to change course but before he could call for a turn to port he heard Bruce Olstead’s voice call a warning. There a Russian fighter at 3 o’clock flying on a parallel course.

For long moments the two planes flew side-by-side. . . The Americans checked their position. They were undoubtedly outside Soviet airspace. Then the MG turned off and disappeared.

Shortly afterwards Palm commenced a at almost the same time another MG, or perhaps it was the same one, appeared not 50 feet (15m) off his starboard course. The Strojet banked carefully, making sure not to bump the close flying Russian jet. Hallway through the turn, the MiG-15 veered off and circled, coming around onto the RB-47’s tail Palm was in the middle of warning his crew to be ready for anything when suddenly the MiG opened fire and the American plane took hits in the port wing. The man with his finger on the trigger was later identified as Captain Vasily Ambrosievitch Polyakov. Olmstead tried to return fire using his radar directed 20mm cannon in the tail but Polyakov had come in too close so he had to switch to manual. Before he could aim, the Boeing slewed around into a flat spin with fames issuing from two of its three engines under left wing.

Palm and lead struggled with the controls trying to pull the Strojet out of the spin but then they felt Russian cannon shells hudding home as Polyakov fired again. All they could do was continue with their desperate efforts to recover.

When McKone heard Palm call for the crew to standby he knew the plane was badly damaged. Seconds later he felt it level out but it was not flying normally. Flames from the engines were now blazing out of control and flaring back nearly to the tail Then he heard Palm’s order to bail out.

As they ejected McKone and Olmstead were both knocked unconscious by the force. Fortunately, their parachutes opened automatically at 14,000 feet (4,300m) and they floated down into the ice cold waters of the Barents Sea. They were both able to scramble aboard their survival rafts and were both picked up several hours later by a Russian trawler.

What happened to Willard Palm and the others is less clea Monitoring equipment tracked the crippled Stratojet for another twenty minutes. It remained airborne but losing a tude in an erratic wide north-easterly turn out over the water. Apparently Palm had decided to remain with the plane, possibly to give the electronics experts time to bail out. It crashed, or crash landed, into the sea. Palm’s body was re-covered by the Russians and returned to US authorities for subsequent burial in Arlington Cemetery, Gene Posa, Dean Phillips and Oscar Goforth were never seen again.

Seven months later, on January 24, 1961, Bruce Olmstead and John McKone were released from a Soviet prison where they had been held on charges of espionage. They were returned to the USA as a friendly gesture towards the newly inaugurated American President, John F Kennedy.

However, the Stratojet, and SAC, still did not have a true intercontinental capability until the technique of inflight refuelling was introduced and perfected. Boeing developed its own method of using a rigid Flying Boom which extended down from a tanker aircraft and using aerodynamic controls was flown into a receptacle in the bomber. ‘B’ series Stratojets were soon outfitted for inflight refuelling and also had provision for extra underwing fuel tanks. On September 20, 1951, a Stratojet made the very first jet flight over the North Pole. On January 28, 1953, one crossed the Atlantic Ocean in 4 hours 45 minutes to average a speed of 617. 4mph (933. 6km/h) and then five months later shattered this record by crossing again at an average speed of 650. 5mph (1,046. 9km/h). From November 16-18, 1954, using inflight refuelling, a 8-47 flew non-stop a distance of 21,000 miles (33,795km).

The B-47E (Model 450-157-35) became the standard production version of the Stratojet and over 1,500 were produced by three separate companies. Such were the world’s tensions during and after the Korean War (particularly when the Soviets detonated their first A bomb) that when the first ‘E’ series machine was flown on January 30, 1953, urgent talks regenerated the WW2 production agreement between Boeing, Douglas and Lockheed for the accelerated building of Stratojets. Consequently, a total of 386 B-47Es were made at Douglas’s Tulsa plant and 247 were built by Lockheed at Marietta while the parent company produced 931.

Powered by six 7,200lb (32. 03kN) thrust (with water injection) J47-GE-25 engines, the B-47E incorporated numerous major changes. It featured a modified nose with an inflight refuelling receptacle, strengthened undercarriage for withstanding its increased gross weight, ejection· seats for the crew, a drag parachute and the tail armament was changed from . 50 inch machine guns to two 20mm cannon. The inbuilt JATO units were removed and replaced by the previously mentioned jettisonable external rack which carried up to thirty three 1,000Ib (4. 45kN) thrust rockets. Maximum speed at 16,300 feet (4,970m) was 606mph (975km/h) and it had a service ceiling of 40,500 feet (12,345m). Internally it could carry up to 20,000lb (9,071kg) of bombs.

As well as becoming SAC’s standard front line bomber, the ‘E’ series included the DB-47E drone director aircraft for launch and control testing of the Bell GAM-63 Rascal missile which turned into being the world’s first true stand-off bomb to achieve operational status – it was first delivered at the end of October 1957, had a range of around 100 miles (160km) and could carry a thermonuclear warhead. There were also fourteen QB-47Es constructed as radio-controlled drones, twenty four WB-47E weather reconnaissance aircraft for the Military Airlift Command’s (MAC) Air Weather Service and 240RB-47Es were used in the strategic photo reconnaissance role. According to a brochure put out by the US Information Service at the end of July 1955, an RB-47E flying at a height of 39,000 feet (12,000m) could photograph an area of 100,000 square miles (2,000,500sq km) in three hours. For this purpose it was equipped with between 7-11 large cameras for taking frontal, sideways, vertical, panoramic and overlapping photographs either by day or night.

The final Stratojets consisted of aircraft which were basically ‘E’ series conversions. Two were made into the one each of YB-47F and KB-47G respectively for probe and drogue inflight

Fortunately quite a few B-47s remain preserved in various museums around the USA. This E model is at the Pima Air Museum, Tucson. (Jim Thorn) refuelling experiments. There were over thirty RB-47H electronic reconnaissance conversions and it was one of these variants which was involved in the infamous Barents Sea incident of July 1960. (Refer to insert. ) One YB-47J was made into a testbed for the new MA-2 radar bombing system. Fifteen additional new RB-47Es were constructed under the designation RB-47K for use in photographic reconnaissance at all altitudes and finally, thirty five ‘E’s were converted for electronic communications.

The SAC’s Stratojet expansion programme began slowly in 1951 when the 306th Bomb Wing stationed at MacDill AFB, Florida, took delivery of its first 8-478 in October. By the end of the following year there were still only 62 on strength. Then, with the lessons of the Cold War and the Korean conflict being digested, delivery picked up in 1953-4 so that by December 1954, there were 1,060 in service. At its peak of operational strength early in 1957, no less than thirty three wings of 45 aircraft each were equipped with the type. Of these, 28 were bomber wings and the remaining 5 were strategic reconnaissance wings.

The concept of flying intercontinental bombing missions in conjunction with Boeing KC-97 inflight refuelling tankers was first tried in ‘Operation Leap Frog’ in mid 1954. Taking off from Hunter AFB, Georgia, the two 8-47 wings of the 38th Air Division carried out a simulated bombing attack and afterwards went on to land at one of the USAF’s air bases in North Africa. This successful operation demonstrated that response time to a full-scale nuclear attack could be significantly reduced. Meanwhile, Stratojet units were trained for maximum mobility by carrying out wing strength 90 day rotation operations to overseas bases in England, Morocco, Alaska and Guam in the Pacific. A 8-47 of the 321st Bomb Wing showed how easily SAC could extend the range of its bombers on August 14, 1957, when it made a nonstop flight from Andersen AFB on Guam to Sidi Slimane AFB in Morocco covering a distance of 11,450 miles (18,426km) in 22 hours 50 minutes using four refuellings from KC-97 tankers.

Initially, it had been envisaged that the Stratojet would be replaced by more advanced designs by 1957 and the last 8-47 to be built came off Lockheed’s assembly line at Marietta on February 5, of that year. Indeed, Boeing’s new heavy jet bomber the huge eight engined 8-52 Stratofortress, which had such a wide range that it did not need to be deployed overseas in order to reach its targets, had already begun to arrive in June 1956, when the 93rd Bomb Wing at Castle AFB, California, took By now improved Soviet air defenses, especially with surface to-air missiles (SAMs) and high altitude interceptors, meant that

the life expectancy of a B-47, with a service ceiling of only about 40,500 feet (12,345m), flying over Russian air space was considerably reduced. A change of tactics was needed and a fast, low-level ‘under the radar’ penetration of hostile air space was deemed necessary. When nearing his target the B-47 pilot was to pull his plane up into a steep half loop, release the bomb just before reaching vertical and then roll off at the top of the loop

in a classic Lmmelmann turn so that the Stratojet would be speeding off in the opposite direction away from the blast when the

bomb exploded. Unfortunately, these fighter-like manoeuvres and tight turns did not suit B-47 wings and airframes which had not been designed to withstand such forces. During one thirty day period in 1958 no less than six Stratojets crashed because of structural failure. Although production had stopped, an extensive (and expensive) programme of upgrading existing aircraft by reinforcing their airframes and wing structures was instituted. Modified B-47Es were re-designated B-47E-II while B-47Bs which had been upgraded to B-47E standard and further to the new requirements were designated B-478-I1.

Equipment revision, upgrading arid strengthening gave the Stratojet a front line service career of fifteen years. By 1962, its

numbers had declined from its peak of over 1,800 in 1957, down to 880. In 1966, it was completely withdrawn from SAC at last and, except tor the WB-47Es used by the MAC for weather reconnaissance which continued on until late 1969 and a few experimental aircraft, the last 114 were sold for scrap or mothballed.

Boeing’s B-47 Stratojet was indeed the world’s first swept wing jet bomber to go into mass production and it won for itself a well deserved place in the history of American military aviation.