The Long Reach of the Str

The B-47 first flew 50 years ago this month. Its influence
went far beyond its military role. A whole host of airliners followed its basic design characteristics.
The Long Reach
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AIR FORCE Magazine / December 1997
By Walter J. Boyne
of the Stratojet
Displaying the characteristics that
defined a half-century of aircraft, a
Lockheed–built Boeing B-47E Stratojet banks its swept wings as its pod
mounted jet engines pour out the
power. The aircraft markings are typical
for the later period of B-47 service.
AIR FORCE Magazine / December 1997
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Boeing photo
The future for both civilian and military jet aircraft takes shape in the form of swept
wings tested in December 1945 on this wind tunnel model. The smooth body and
tail, typical of a B-29, were incidental to the tests.
directly into the KC-135 tanker and the
Boeing 367-80 prototype. The latter led
to a series of epoch­-making 707 airliners,
which in turn spawned all of the followon aircraft from the 727 to the 777 that
have made Boeing an industry giant.
The B-47’s basic formula was also seen
in the designs of other US and foreign
manufacturers, including the Convair
880/990, the Douglas DC-8, and the
European Airbus Industrie series.
The B-47 was an enormously flexible
aircraft. Over the first decade of the Cold
War, as Soviet defenses improved, so did
B-47 tactics. The B-47 was created to be
a high altitude penetrator, but later its
pilots embraced low-level “oil burner”
tactics to slip in under radar. Low-level
tactics included the “pop-up,” which
featured a low-level run-in followed
he Air Force’s B-47 bomber was
radically new in design, a sleek,
swept-wing beauty built with all the
expertise that Boeing had acquired in
World War II and inspired by the latest and best in American and German
technology. Unlike previous aircraft,
the new bomber was powered by six jet
engines. The Stratojet, whose first flight
was made 50 years ago this month, was
the most influential multijet aircraft in
aviation history.
Gen. Curtis E. LeMay, commander
of Strategic Air Command, seized on
the B-47 to endow SAC with awesome
power, equipping no fewer than 28
bombardment and five strategic reconnaissance wings with the new long-range
aircraft. No one who has witnessed the
takeoff of a wing of 45 B-47s will ever
forget the sight of the powerful aircraft
rolling down the runway, one after the
other, separated only by seconds, seeming to take forever to lift off and then
vanishing swiftly in the distance.
At the time of their debut, and for
years afterward, the B-47s formed
the most powerful bomber fleet in the
world, each bomb bay packed with
explosive force equivalent to scores of
thousands of tons of TNT. Faster than
most fighters at operational altitude and
with global range provided by in-flight
refueling, the bomber confronted the
Soviet Union with a virtually insoluble
defensive problem.
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Boeing photo
T
The future unveiled. In this early press release photo, Boeing’s “radical” XB-47
Stratojet faces a partially completed B-50, the last propeller-driven bomber delivered to the Air Force.
The Progenitor
Had it done nothing more than serve
in its military deterrent role, the B-47’s
place in history would be secure, but the
aircraft’s basic design characteristics
were so fundamentally sound that they
dominated the aviation industry for
decades. Its combination of cylindrical fuselage, swept wings, and podded
engines would be adopted not only
by tankers and the next generation of
bombers but also by most of the world’s
commercial jet transports.
The basic B-47 design was translated
by a quick pull up to 18,000 feet. After
bomb release, the aircraft would turn
sharply and dive for the ground.
Pilots reached an extreme with what
was called the low altitude bombing
system maneuver. Like the pop-up, the
LABS also featured a low-level run-in,
but this time it was followed by a pull
up into a half loop, with the nuclear
bomb released at the quarter-loop point.
The aircraft would continue with the
half loop, rolling out in an Immelmann
turn, then dive away.
LeMay flaunted the B-47’s power as
AIR FORCE Magazine / December 1997
Steve Richards via Warren Thompson
A B-47 and F-94 fly into Ladd AFB, Alaska, in 1951. In 1958, SAC’s arsenal of of the
versatile B-47 peaked at 1,367 bombers in 28 wings and 176 reconnaissance models. In all, there were 38 variants.
Still, the B-47’s creation was filled
with uncertainty, and, in its early years,
its promise was almost overshadowed
by its problems.
Remarkable Requirements
In June 1943, alert to the strong possibilities of turbine power, US Army Air
Forces asked several manufacturers to
produce designs for a multijet aircraft.
On Nov. 17, 1944, a formal requirement
was issued for a jet-powered medium
bomber with a maximum speed of 550
mph, a range of 4,100 miles, and a
Fred Johnsen via Walter J. Boyne
a matter of policy, sending it on recordsetting missions, operating it from overseas bases, and taking every opportunity
to make clear to the Soviets that the
US possessed an unparalleled offensive
nuclear force and would use it if necessary.
Spurred by the Suez Crisis of 1956,
SAC demonstrated its ability to launch
a large strike force on short notice. In
a two-week period, more than 1,000
B-47s were flown on nonstop simulated
combat missions, averaging 8,000 miles
each, over North America and the Arctic.
In 1958, SAC’s B-47 strength peaked
with 1,367 bombers (in 28 wings) and
176 RB-47s in service. These two aircraft
fleets were reinforced by 380 jet-powered
B-52s, 22 aging Convair B-36s, and a
mixed fleet of 780 KC-97 and 182 KC135 tankers. The mix changed as newer
aircraft and missiles entered service, but
the basic premise remained the same:
The US would use SAC’s strength and
proficiency to contain the Soviet Union
and blunt its policy of expansion.
As the fleet grew, the Air Force’s
requirements expanded. Fortunately,
the basic design was versatile, lending itself to no fewer than 38 variants,
ranging from the XB-47A prototype
through the “standard” B-47E bomber
to tankers, electronic and photographic
reconnaissance models, missile carriers, drones, and weather birds. It even
served in Vietnam as a communications
relay aircraft.
Even with landing gear and flaps down, the B-47 was so clean that it required a
parachute to provide additional drag on approach. The pilot maintained power on
the slow-to-accelerate jet so that a go-around could be made quickly if needed.
AIR FORCE Magazine / December 1997
service ceiling of 45,000 feet. These
were remarkable requirements; the
respective figures for the B-29, which
was just being proven in service, were
358 mph, 3,500 miles, and 31,850 feet.
Boeing went through a long series of
design studies, but the critical breakthrough came when George Schairer,
Boeing’s chief aerodynamicist, analyzed German research on the swept
wing and asked that it be applied to
the XB-47. The resulting tests showed
such promise that a nearly $10 million
contract for two prototypes was issued.
More than two years of design and
production effort followed, with the prototype aircraft emerging from the factory
on Sept. 12, 1947. It was unlike anything ever seen before and represented
a total departure from Boeing practice.
Its slender, flexible, laminar-flow wing
was swept back 35 degrees and drooped
under the weight of its structure and six
engines. The 3,750-pound–thrust General
Electric J35 engines were installed three
on a side, two inboard engines suspended
in a streamlined pod, with the outer engine faired tight beneath the wing. The
wing was too thin to contain either fuel
or landing gear. The streamlined fuselage was marred by only a few bumps
and was large enough to house a series
of longitudinally placed tanks, which
meant that fuel use had to be carefully
managed to maintain the center of gravity
within limits.
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Fred Johnsen via Walter J. Boyne
Any B-47 takeoff was interesting, but when ATO bottles were used, it was spectacular. Early B-47s had 18 bottles mounted internally. Later versions had an external
33-bottle unit.
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Osler would become the first man to
lose his life in a B-47, killed when a
cockpit canopy came off in flight.)
From Skepticism to Belief
The two pilots were impressed by the
performance of the new bomber, but, like
everyone else, they had no idea of just
how much it would shape the future of
the company, the industry, the Air Force,
and the country. The crucial test flight
came when Col. Pete Warden persuaded
Maj. Gen. K.B. Wolfe, the patron saint of
the B-29 program, to take a short flight
Photo by Ray Shewfelt via Warren Thompson
The bicycle-style landing gear—two
sets of two wheels in tandem, supplemented by a pair of small outrigger
wheels that retracted into the inboard
engine nacelles—derived from the
Martin Aircraft Co. experiments. This
arrangement dictated some of the aircraft’s flying characteristics, for the
gear placement meant that the aircraft
could not be rotated for takeoff or flared
for landing. For descents, the aft gear
was extended to double the drag of the
entire aircraft.
The three-man crew was grouped in
a small pressurized compartment. The
radar observer/navigator/bombardier
sat in a dark cubbyhole forward, while
the two pilots sat in tandem with an
unrestricted view from the fighter-like
canopy. Early planning called for all
three crew members to be “triple rated,”
and thus able to do each other’s job, but
this proved to be impossible to sustain
as the B-47 program expanded.
Boeing and the Air Force committed
to the XB-47 program some of their
top pilots, including Capt. Jack Ridley,
Capt. Chuck Yeager (who flew a P-84
chase aircraft), Maj. Guy Townsend,
Bob Robbins, and Scott Osler.
On Dec. 17, 1947, the anniversary
date of the historic first flight at Kitty
Hawk in 1903, Boeing test pilots Robbins and Osler made the short flight
from Boeing Field in Seattle to company
facilities at Moses Lake, Wash. (Later,
with Townsend. After a 20-minute ride,
Wolfe had become a firm believer in the
B-47, and promised large-scale production, with the first production order for
10 B-­47As coming on Sept. 3, 1948.
Later, the B-47 became the first airplane to receive a weapon-system designation, the bomber becoming WS-100A
and the reconnaissance version WS-100L.
The second prototype and all subsequent production B-47s were fitted
with General Electric J47 engines,
whose thrust was increased over time
to a maximum of 7,200 pounds (with
water injection) in the B-47E series. Additional thrust was provided by ATO—
assisted takeoff—bottles. The early
aircraft had 18 ATO bottles mounted
internally, but this system was replaced
on the E model by a jettisonable rack
of 33 of the 1,000-pound thrust units.
While the dimensions and the external appearance remained remarkably
stable over the life of the aircraft,
maximum gross weight in­creased over
time from the 125,000 pounds of the
prototypes to 230,000 pounds for the
E bomber model. At higher gross
weights, the aircraft was sluggish and
slow to accelerate, particularly at high
temperatures and high density altitudes.
Despite teething problems, production orders increased, and both Douglas
and Lockheed were tasked to build the
aircraft. Ultimately, Boeing would build
1,373, Douglas 274, and Lockheed 385
In 1955, pilot Ray Shewfelt took this self portrait showing off the superb visibility
afforded by the B-47’s fighter-like canopy. Created as a high altitude penetrator, its
pilots later embraced low-level “oil burner” tactics.
AIR FORCE Magazine / December 1997
Ankle-Biters
For all of the B-47’s technical marvels, a variety of mechanical problems
cropped up during its early development, and there were frequent groundings. Fuel leaks plagued maintenance
crews, and there were many difficulties
with the early K-2 and K-4A bombing
systems. The tail armament (originally
two .50-inch machine guns and later
two 20 mm cannons) was operated by
the copilot, whose seat could be turned
Boeing photo
for a total of 2,032. No bomber since
World War II has been produced in
such quantity.
Problems stemming from the developmental nature of the jet engine
and the very clean design of the B-47
combined to create difficulties in flying
the aircraft. The jet engines required 12
to 20 seconds to spool up from idle to
full power, which meant that approaches
had to be planned very carefully. The
problem was eased by the introduction
of a 16-foot drogue parachute, which
was deployed in the landing pattern. The
parachute created enough drag to permit
the pilot to maintain the engine rpm in
a range permitting quick acceleration
in case of a go-around, at which point
the drogue chute would be jettisoned.
Braking was also a problem, leading to
the incorporation of an antiskid device. On
Townsend’s suggestion, a 32-foot-diameter ribbon-style brake chute, developed
by Theodore Kan­ake, was fitted to the
airplane to reduce landing roll. Usually,
the pilot did not apply the brakes after
the brake chute had caused the bomber to
decelerate below 100 knots. (The brake
chute could also salvage a bad landing,
if deployed at just the right moment at
the top of the bounce.)
Despite the two parachutes, the B-47
was so clean that excess speed on the
approach caused an exceedingly long
landing run, so approach speeds were
carefully calculated and maintained. It
was not difficult to do so; the merest
touch of the throttle served to adjust
the speed in single knot increments.
The slightly longer nose of the RB-47E, shown here (foreground) with the bomber
version, added elegance to the sleek jet. A few recon­naissance Strat­o­­jets continued in service after all bombers had gone to the boneyard.
180 degrees. However, the guns were
often rendered useless by difficulties
with the fire-control system.
The aircraft was pleasant to fly,
although it exhibited Dutch roll, a
name for the tendency of the airplane
to make a series of S turns, each of
slightly greater amplitude. This was
corrected by the invention of the yaw
damper, a device which automatically
supplied just enough rudder motion to
offset the Dutch roll. There were other
aerodynamic problems. Early B-47s
exhibited a tendency to pitch up. This
problem was solved by the introduction of vortex generators—small lifting
vanes which diffused the airflow and
which can be seen today on almost
every high speed aircraft.
A problem which was simply accepted rather than solved was the fact
that, at speeds of 456 knots and higher,
the ailerons became ineffective because
the flexible wing twisted. The aircraft
was placarded at 425 knots to provide
an ample safety margin.
The greatest hazard to the B-47 was
corrosion and metal fatigue. Between
March 13 and April 16, 1958, no fewer
than six B-47s crashed. The investiga-
Walter J. Boyne, former director of the National Air and Space Museum in Washington, is a retired Air Force colonel and author. He has written more than 400
articles about aviation topics and 28 books, the most recent of which is Beyond
the Wild Blue: A History of the United States Air Force, 1947–1997. His most
recent article for Air Force Magazine, “Linebacker II,” appeared in the November
1997 issue.
AIR FORCE Magazine / December 1997
tion revealed widespread problems
ranging from fatigue in the lower wing
skin to failure due to stress corrosion of
the “milk bottle pin,” the main fitting
holding the wing to the fuselage. The
solution was Project Milk Bottle, an
expensive, time-consuming modification that nonetheless gave the B-47
fleet an additional six years of service.
As the Cold War deepened, the requirement for aircraft on alert increased
from one-third of the fleet to 50 percent,
and this put such a strain on manpower
that it was decided to phase out some
B-47 wings to make the personnel
available to other units. The phaseout
was accelerated as more B-52s and
ICBMs came on line, but two world
crises—Berlin in 1961 and Cuba in
1962—temporarily delayed the process.
By February 1966, all B-47 bombers had been retired to the boneyard at
Davis–Monthan AFB, Ariz. A handful
of reconnaissance versions continued
to operate. The last Air Force Stratojet,
an RB-47H, was retired in December
1969. The Navy had a specialized test
version that it kept in use until 1976.
Now, though the B-47 has flown
its last, at least 15 examples are preserved and on display in museums
or at airfields, and the B-47 Stratojet
Association is growing in numbers.
These artifacts are all that remain of
the beautiful aircraft that burst onto
■
the scene a half-century ago.
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