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06/09/95

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New, improved flying disc developed

STANFORD -- It has taken Alan Adler more than 20 years, but he finally has come up with an improvement on the flying disc.

The "Aerobie Superdisc," as he is calling his new design, has been in production by his small, family-owned company, Superflight, for almost a month, and is just beginning to appear in toy and sporting goods stores, Adler said.

This is the fourth flying toy that Adler, a lecturer in mechanical engineering at Stanford University, has developed and marketed. His aerobie flying ring set the Guinness world record for the farthest thrown object when it was hurled 1,257 feet in 1985. In 1987, he introduced a triangular boomerang, and, in 1993, he marketed a toy football with fins that allows almost anyone to throw a perfect bullet pass.

Many of the prototypes for these inventions were made in the mechanical engineering workshop on campus and first tested on Stanford's Roble athletic field.

"After years of building instrumentation systems for military aircraft and nuclear reactors, I wanted to make something that ordinary people could use and enjoy," says the electrical engineer-turned-inventor. He had taught himself basic aerodynamics in order to design sailboats. So, in the mid-1970s, he decided to turn his talents to designing innovative flying toys.

Adler's first unsuccessful effort, in fact, was an attempt to design a better flying disc. Every few years, he returned to the subject. But, until now, he had not been able to come up with an airfoil shape that was more stable than the traditional, convex Frisbee design.

"Stability is the most elusive goal of all in disc design," Adler says. "For a disc to fly straight, its center of aerodynamic lift must remain near its center of gravity over a wide range of airspeeds and angles of attack."

If the center of lift moves away from the center of the disc, then the disc will begin to roll and curve away from a straight path. The reason for this is gyroscopic precession, the same force that causes a boomerang to fly in a circular path. For example, if the disc is spinning clockwise and the center of lift moves ahead of the center of the disc, the upward force acts on the right side of the disc, causing it to tilt and curve to the left.

Adler finally solved the stability problem by designing a disc with a concave outer rim, with ridges both above and below the plane of the disk. These ridges act as "spoilers" that create turbulent airflow that confines the center of lift to the center of the disc. The rim is made out of a soft rubber that also makes the disc particularly easy to throw and catch.

"Actually, it shouldn't have taken me as long as it did to come up with this solution, because I used a similar spoiler on the flying ring. In fact, I did try basically the same approach several years ago but didn't have the proportions quite right," Adler says.

With properly proportioned spoilers, the "Aerobie Superdisc" has much less tendency to roll over in flight. An unanticipated benefit is the elimination of the conventional disc's tendency to wobble. That is because in the new design the thrower's hand naturally grasps the disc at the same level as the flat portion of the disc, where most of its mass is centered, the inventor says.

The net result is a disc that is easier to throw and that flies with greater stability. Consequently, many people will find that they can throw the superdisc farther and with more accuracy than ordinary discs, Adler says, but expert players will not notice much difference in its range.

Adler also has tried to make the new disc dog-proof. At one point, he thought he had found the right plastic to make the superdisc stand up to all kinds of abuse. But then a dog chomped down on one of his test models, and promptly cracked it. "As a result, I had to go back and reformulate the plastic to make it tougher," he says. "Now it even survives the dog test."

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