Today, the sound barrier. The University of
Houston's College of Engineering presents this
series about the machines that make our
civilization run, and the people whose ingenuity
created them.
In 1935 a British
aerodynamicist showed reporters a graph of
wind-tunnel results. They showed how the drag on a
wing depended on the Mach Number. As the speed
approached Mach One, the drag rose dramatically. He
told them, "See how the resistance of a wing shoots
up like a barrier against ... the speed of sound."
It was an innocent enough bit of hyperbole, but it
stuck. As a boy, in love with flight through the
'30s and '40s, I watched top airplane speeds go
from around 350 miles an hour to more than 500. All
the while we talked about the sound barrier -- that
brick wall you'd run into if you tried to trespass
into supersonic flight.
Chuck Yeager finally did fly the Bell X-1 past the
would-be barrier in 1947. He reached 670 miles an
hour and lived to tell about it. But he took a big
chance, because our knowledge was still very thin.
Consider what happens when air moves over an
airfoil:
We shape subsonic airfoils so the air speeds up
over the top. In near-sonic flight, air passes over
the wing at supersonic speed. And those mixed
subsonic and supersonic flows are complex. The
equations for mixed flows defied solution in the
1940s.
To make matters worse, the proper shape for a
lifting wing differs for subsonic and supersonic
flows. Designers had a pretty good idea how to
design for one region or the other. But supersonic
airplanes must pass through the mixed flow region
-- the region where nothing was predictable in the
'40s. There was a barrier even if Chuck Yeager had
bridged it. It was a knowledge barrier.
Stanford aerodynamicist and historian Walter
Vincenti worked on the problem, and now he writes
the story for a history journal. It's a tale of
high-level engineers focused on a terribly
important problem. He tells about a joyful
convergence of freedom of the mind with real
purpose -- a time when everything was new. That
mood lingered. It still spilled into the classroom
at Berkeley where I studied fluid-flow in the late
'50s. It was infectious.
Those engineers had created a method for solving
the transonic flow problem as early as 1953. But
transonic calculations were a terrible task on the
old hand calculators. So the problem shifted to
making calculation tractable.
Not 'til the early '70s were computers fast enough
to bring the problem within grasp. After that,
repeated calculations let engineers optimize their
airplanes and create the best design possible --
not just one that would work. No longer did test
pilots have to gamble their lives on each new
airplane.
And the magic was now gone from the old movies: a
pilot bravely pushing the airplane until it
trembles, then shakes violently. The needle
reaching Mach One. The airplane slamming into the
sonic barrier and breaking apart. Another problem
had, alas, been put to bed. But never fear. There
are more problems out there. More dangers, more
challenges and -- a lot more fun.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
