Jetrader - Summer 2018 - 49

WIKIMEDIA COMMONS

PETER BOWERS COLLECTION IN SDASM ARCHIVES

A nearly head-on shot showing the extremely thin, flexible wings
and the engine configuration of the Boeing B-47. The two pilots sat
in tandem under a bubble canopy while the bombardier/navigator's
position was down below, with a downward-firing ejection seat.

North American B-45 Tornado.

Convair XB-46 prototype.

with its XB-46. Both would have straight wings and four engines
in pairs of two, tightly faired into the underside of the wings.
Martin offered its six-engine XB-48, also with straight wings,
with the engines lined up in a row of three in the underside of
each wing.
At first Boeing proposed its in-house project number 424, which
resembled a straight-wing B-29 with four (or sometimes six) jet
engines under the wings like the Convair and North American models. After unpromising wind tunnel testing, the project morphed
to project number 432, with all the engines buried cleanly inside
the fuselage, but this didn't seem to be very promising either.

design team back in Seattle to redirect their work to investigate
wing sweepback. At this point, Boeing decided to "go rogue" -
aiming all-out for speed.
Unlike the other three competitors, Boeing had its own wind
tunnel, which had been put into service in 1944. At the time, it
was the largest and fastest privately owned wind tunnel, capable
of reaching up to Mach 0.975, or 97.5 percent of the speed of
sound, giving Boeing a competitive edge over the other entries.
A brand new project - now number 448 - was hatched, with
very thin wings swept back by 35 degrees, with four engines buried
inside the forward fuselage and two more in the rear. The Army
Air Forces (the U.S. Air Force did not become a separate branch of
the military until 1947) worried about safety problems with the
buried-engine configuration, so further iterations placed the six
engines under the wings; one pair at near mid-span and a single
engine at each wingtip. (Later, the wing tips were extended
beyond the outboard engines, improving range performance.) This
new project, designated number 450, began in October 1945. It
included a few more tweaks, moving the outboard engines slightly
inboard under the wings, and by April 1946 the Army Air Forces
ordered two prototypes to be built bearing the designation XB-47
and named "Stratojet."
The use of swept wings was almost a leap of faith. At that time
the rocket-propelled Bell X-1 was under development, and became

SDASM

The XB-47 prototype on the Boeing Field ramp. The aircraft's weight is
carried by "bicycle type" landing gears, with large dual wheels forward
and aft while small outriggers drop down from a space between the
two podded engines, acting like training wheels on a child's bicycle.
Also apparent is the tail-down, nose-up attitude that puts the aircraft
at the proper liftoff angle for taking off.

How About Sweeping the Wings?
Studies by scientist R.T. Jones of the National Advisory
Committee for Aeronautics (which later became NASA) suggested
that swept wings might be the way to transonic flight, a concept
that had earlier been explored by Dr. Adolf Busemann in Germany
but never taken up in the United States.
As the war was ending, Allied teams raced into Germany to seize
as much technological information and hardware as possible. On
7 May 1945, the morning of the German surrender, George Shairer,
then Boeing's chief aerodynamicist, entered Herman Goering's
Aeronautical Research Institute at Braunschweig. On seeing the
models and wind tunnel data there, Shairer urged the Boeing

Jetrader * Summer 2018 49

Jetrader - Summer 2018

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