In the age of computer design, why do engineers still send airplane models to the wind tunnel?
- By Peter Garrison
- Air & Space magazine, March 2007
(Page 3 of 3)
Long’s model ship—delicately detailed, down to each railing, antenna, and hatch—came into being in Valencia, California. Valencia’s industrial parks contain several firms engaged in the futuristic business of stereolithography (SL), a way to manufacture single examples of complex objects by a completely robotic photochemical process.
SL creates solid objects of extreme complexity by selectively hardening an epoxy-like liquid with laser light. The process begins with a computer file, a cloud of numbers defining the shape of an object as a series of cross-sections at intervals of a few thousandths of an inch. Inside the SL machine, a simple metal cabinet with an angled window—think of it as a three-dimensional printer—an ultraviolet laser dances across the surface of several gallons of liquid photopolymer, a clear plastic liquid that hardens when the laser contacts it. A perforated floor immersed in the polymer drops by a few thousandths of an inch and the tremulous blue-violet light, directed by the computer file, sketches anew. Over and over and over—there is no sound, no one watches, no waste results. When the process, which advances at a rate of inches per hour, is finished, the perforated floor rises to the surface and the newborn object—a gear, a turbine, a wing, a ship, anything you like—emerges from the liquid like Aphrodite: perfect, virginal, and untouched by human hands.
Stereolithography and numerically controlled machining represent the final stage in the withdrawal of the human touch from the making of wind tunnel models. The craftsmen who carved mahogany for Douglas and Northrop and Lockheed are mostly gone; likewise the sheet metal men who built up countless impeccable wing sections for NACA, and the artisans whose files and sanders sculpted massive steel to the precision of a clockwork. Their skill was impressive, and no doubt their satisfaction was great. But technology moves forward, toward pilotless airplanes built by pilotless machines, and the art and science of wind tunnel testing moves with it.