Learning how to fly, reptile style - mechanical model of pterodactyl

Science News, Oct 19, 1985 by Stefi Weisburd

Next June, a strange and ancient shadow will pass over the tourists and congressional staff who crowd Washington, D.C.'s parklike Mall. The shadow, which last glided over the earth 65 million years ago, will belong to a mechanical model of the pterodactyl Quetzalcoatlus northropi, the largest flying reptile, distantly related to the dinosaurs. Last week, Paul MacCready, chair of AeroVironment Inc. in monrovia, Calif., announced that the model -- complete with an onboard computer, latex coverings, advanced aerodynamic material for bones, six pounds of nickel-cadmium batteries for powering five minutes of flight and even some neck hair--was finished and ready for its first flight test. The 35-pound replica has wings spanning 18 feet and is patterned after the few fossilized remains of a pterodactyl with a 36-foot wingspan found in 1971 in west Texad, as well as the more complete skeletons of some much smaller pterodactyls.

In designing the model, MacCready's group had to solve some rather tough engineering problems. Quetzalcoatlus, for example, didn't have a tail, which keeps modern-day birds and airplanes from heading into a nosedive. By progressively shortening the tail on preliminary models, the engineers learned how to compensate for the lack of a tail by changing the characteristics of the wings. Quetzalcoatlus alo didn't have a vertical stabilizer, as planes do, bit it did have a very narrow and movable head, which could be used as a front-end rudder for controlling yawing (the tendency to swing from side to side). "We've always supposed that this is what they did, but until we have a working model of it that will actually do that, we can't be sure that this is feasible," says Wann Langston Jr., a paleontologist at the University of Texas in Austin whose graduate student discovered the giant pterodactyl wing in Texas. The researchers will find out when testing begins next week. Movable fingers midway down the wings will also provide drag for the animal.

The mechanical model's public debut on the Mall in June will publicize its role in a new movie on flight, which will be just opening at the nearby Air and Space Museum. While the replica looks hauntingly lifelike for its movie role, it differs from the genuine article in two main ways. First, while the mechanical animal will propel itself by flapping its huge wings, paleontologists suspect that only the smaller flyers could generate a steady stream of energy necessary to lift their bodies and continuously flap their wings. Instead, scientists think that Quetzalcoatlus flew much like modern-day vultures, storks and cranes, which primarily soar and glide and are capable of only very feeble wing flapping, usually during takeoff.

Another difference between the model and the living beast are the brain and sensors that monitor and correct flight. "The computers and sensors that they're going to use in the model are quite sophisticated from out standpoint, but compared with what nature produced through the evolutionary process, it's still in the stone age," says Langston.

The design and capabilities of the real animal also impress MacCready, who has become well known for his Gossamer Condor and Gossamer Albatross crafts, which demonstrated sustained and controlled human-powered flight. Says he: "I've gotten to appreciate Mother Nature, the engineer."