Today, we build with balsa wood. 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.
Model airplanes were the
great dream-factory of my early years. Those
wonderfully tough frameworks of feather-light balsa
wood captured my mind. Slender balsa stringers,
carefully bent about thin sections of balsa, gave
the plane its shape. That frame was covered with a
drum-tight skin of impregnated tissue paper. The
result was a half-ounce wing or body -- powerfully
strong and beautifully streamlined. The
strength-to-weight ratio of one of those gossamer
airplanes was astonishing.
South American Indians have long used balsa boats
on the great Brazilian rivers, but modern boat and
airplane makers were slow to adopt it. It's very
soft -- you can easily crush it. You can score it
with your thumbnail. But it's almost impossible to
break it by pulling on it, and it's shockproof.
You can see more clearly how to use balsa when you
know how a structural I-beam works. That's a steel
beam with a cross section that looks like the
capital letter I. The flat parts on the top and
bottom of an I-beam carry the load. All the middle
part of the beam has to do is to separate the top
and bottom. It doesn't have to be very strong. So
the trick is to use balsa to make the middle of a
sandwich with a tough skin outside -- rather like
we used to make model airplanes.
During WW-II, airplane builders used this kind of
construction in a light attack bomber called the
Mosquito. It was viciously effective in Europe.
When enemy shells passed through it, they didn't
start cracks or even weaken the structure very
much. The Mosquito's worst enemies were
micro-organisms in the South Pacific that ate the
casein glue holding it together.
But that was easy to remedy, because the
cell-structure of balsa wood makes it very easy to
glue. Today, large, light, high-speed boats are
being made of one-inch balsa with a hardwood
veneer. Their hulls are tough, resilient, and
light. They're very good under the wave-pounding
inflicted on a high-speed boat.
The important outgrowth of this is a new class of
materials called composites. They work the way
those balsa boats and airplanes do. A composite is
made of strong fibers embedded in a plastic matrix.
By spacing the fibers out with plastic, engineers
can create light materials stronger than steel. The
first non-stop round-the-world airplane was made of
composites, and so too will be the next generation
of aerospace equipment.
It has to be more than coincidence that these new
materials were given us by the generation whose
minds were most engaged in model-airplane building
-- whose minds were touched by the tactile
experience of building with that remarkable wood,
balsa.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
