and round they went…
Upon their return to Dayton in the
fall of 1902, the Wrights anticipated no problems at all in
designing propellers for their powered flying machine. All that
was needed was to calculate the proper thrust needed for lift, and
Samuel Langley had indicated there was "a very considerable
analogy between the best form of aerial and marine
propellers." Thus, the Wrights felt, all they needed to do
was apply the theory used to design marine screws, substituting
air pressures for water pressures.
The Wrights' Propeller
Blade Had A Completely New Pitch.
Unfortunately, they found there was
none. Marine screws were designed by varying size and pitch until
a propeller was produced that could supply the required
performance. What was more unsettling, ship screws operated
roughly at an efficiency of 50 percent, whereas Orville and Wilbur
calculated that a 66 percent efficiency rate was needed to thrust
their flyer into the skies. Thus, they set about to devise a
workable theory of propeller action - something that had never
"What at first seemed a simple
problem became more complex the longer we studied it,"
Orville recalled. "With the machine moving forward, the air
flying backward, the propellers turning sidewise, and nothing
standing still, it seemed impossible to find a starting point from
which to trace the various simultaneous reactions…After long
arguments, we found ourselves in the ludicrous position of each
having been converted to the other's side…"
Heated discussions on propellers
filled the Wrights' parlor for many evenings. What they finally
decided was that a propeller was actually a vertically moving wing
that provided the thrust of the flying machine through the air.
Thrust depended on the shape of the propeller blade; its pitch (or
angle it strikes the air); the speed at which it turns; the speed
at which the machine travels forward; and the speed of the air
advancing through the rotating blades.
How the Wrights designed their
propellers is still not completely known to this day. In December,
they began analyzing the thrust of a fan 28 inches in diameter,
driven by a one horsepower motor. By February of 1903, they were
working with a propeller 8 feet in diameter. By March they had
designed propeller blades with a predicated efficiency of 66
percent. Using two propellers instead of one, they decided, would
increase power, and running them in opposite directions would
eliminate any twisting effect on lateral control.
By June they were confident they
come up with propellers that were efficient enough to do the job.
Writing to George Spratt, Orville reflected that confidence.
"(We) soon discovered, as we usually do, that all the
propellers built heretofore are all wrong, and then built a pair…based
on our theory, which are all right! Isn't it astonishing that all
these secrets have been preserved for so many years just so that
we could discover them!!"
This "Kitty Hawk Moment" is brought to you by EAA, whose
Countdown to Kitty Hawk program, presented by Ford Motor Company,
includes an exact flying reproduction of the Wright Flyer. It is
the centerpiece of EAA's national tour during 2003, which will
conclude with a five-day celebration at Kitty Hawk, North
Carolina, where the Wright flyer will fly again at exactly 10:35
a.m. on Dec. 17, 2003, commemorating 100 years of powered flight.