LIGHT FLIGHT. These are not the folded-paper darts you threw crookedly across third-period study hall

THE sensei (master) of paper airplanes can't recall anything unexpected happening while flying one. ``Always, something expected happens,'' Yasuaki Ninomiya explains. But the question prompts a reminiscence from Dr. Ninomiya, a retired Japanese engineer whose books on paper-airplane design are best sellers in Japan. It's the story of the roots of his fame. On Christmas Eve 1966, his wife spotted a tiny newspaper item: The First Great International Paper Airplane Contest, sponsored by Scientific American magazine, was to be held in America the next month. Any Japanese who wanted to enter a plane could bring it to the Pan American Airlines office and Pan Am would fly it to the United States for free.

``Since I had been making [paper] airplanes from childhood,'' says Ninomiya, ``I made racing planes and put eight of them in a box so as not to be broken, and asked Pan Am to send them.'' His planes - among the nearly 12,000 entries from 28 countries - arrived in good time to compete in the Pacific Basin division of the contest, held in San Francisco.

The rest is paper-aviation history.

``I won the grand prize in both duration and distance flights,'' reports Ninomiya (who requested written questions, and responded enthusiastically in kind - and in Japanese). ``Since then, I've been living with paper airplanes. The small article was the beginning. I am thankful to my wife.'' A recent photo shows a delighted Ninomiya posing in a room of his Yokohama home. The ceiling is thick with parked airplanes, hanging like sleek, white bats from their paper noses. He's been making kami hikohki for more than half a century now.

``I am one of those airplane fans who think an airplane is the most beautiful work of art a human has ever created,'' he says. ``I like everything that relates to airplanes - from a real plane, to a model airplane, to movies in which an airplane appears.'' He has built rubber-band-powered planes, gas-powered models, and radio-controlled craft. He pilots a real one.

For 30 years, Ninomiya worked to develop microwave communications for Nippon Telegraph & Telephone. But the prizes he won in 1967 inspired him to bend his research skills toward another development project: the paper airplane. Not surprisingly, he couldn't find a job doing that. But he concluded that ``it is a suitable theme for one person to pursue.'' So he did. ``Making a paper airplane became a job from just a mere hobby.''

Today, he has the closest thing to a job perfecting paper airplanes. In 1976, the president of AG Industries in Osaka, Japan, met with Ninomiya after seeing his seven-volume ``Collection of High Performance Paper Planes,'' 3 million copies of which have been sold in Japan in the last 15 years. Ninomiya became exclusive designer for AG Industries' Whitewings gliders, paper airplane kits distributed in the United States by the company's subsidiary in Redmond, Wash.

In 1985, Ninomiya served as one of five judges at the Second Great International Paper Airplane Contest, held in Seattle. Since he retired in 1984, paper planes have been Ninomiya's career. He spends more than 10 hours a day building, flying, and photographing them.

These are not the folded-paper darts you threw crookedly across third-period study hall. Carefully built, Ninomiya's laminated-paper models can be launched with a rubber-band catapult to soar for half a minute or more. Given just the right conditions of wind and launch, a flight of more than 10 minutes is possible.

``If you really want to experience, first hand, the joy of flight,'' he says, ``I believe the most exciting opportunity available to most of us is to fly a miniature plane that you've made by your own efforts. That is why I highly recommend that you make and fly your own paper airplanes.''

Such advice has certainly been heeded in his native country: Japanese swept eight of the 10 first prizes in the Second Great International Paper Airplane Contest three years ago. The Kinura Cup paper-airplane competition is held twice yearly in Tokyo, sponsored by a famous Japanese aircraft designer, Hidemasa Kinura. Hundreds of paper-flight enthusiasts gather every other month or so in several Japanese cities. Ninomiya is host to a monthly outing in Tokyo to fly planes and instruct beginners.

According to a newspaper survey this spring, flying paper airplanes ranks fourth among Japanese boys as an outdoor activity, and seventh among Japanese children overall. Ninomiya traces this popularity in part to the good showing made by Japanese entrants in the 1967 contest. Many books on paper flight were published in Japan in the ensuing years, and more sophisticated laminated-paper designs evolved from folded-paper models. Japan's origami (paper folding) tradition also plays a part. Far from being an activity only for children, adults also participate in this hobby in Japan.

The science that a knowledgeable adult can apply to a simple delight can be seen in Dr. Ninomiya's response to the question ``What are the keys to designing a paper airplane that performs well?'' (Non-aerophysicists may want to skip the next paragraph.)

``A real high-performance glider has a glide ratio of about 50 and a sinking speed around 0.5 meter a second,'' he says. ``On the other hand, since the Reynolds number of a paper airplane is smaller than that of a real aircraft by more than double figures, the gliding ratio of a paper plane is expected to reach only 6 or 7 due to heavy air drag. But as far as the sinking speed is concerned, a lightweight paper airplane can have the speed of about 0.5 to 1 meter a second, almost the same as that of a real high-performance glider.''

The simpler answer: ``The most important things in designing a real or a model aircraft are making the air drag as low as possible and making the airplane lightweight and solid.''

To anyone interested in designing paper planes, he recommends the study of basic aerodynamics.

BOOKS

Paper Flight: 48 Models Ready to Take Off, by Jack Botermans. New York: Holt, Rinehart & Winston. $9.95.

The Great International Paper Airplane Book, by Howard Gossage et al. New York: Simon & Schuster. $8.95.

The Ultimate Paper Airplane, by Richard Kline and Floyd Fogelman. New York: Simon & Schuster. $6.95.

The Best Paper Aircraft, by Campbell Morris. New York: Putnam Publishing Group. 64 pp. $6.95.

Thirty Planes for the Paper Pilot, by Peter Vollheim. New York: Pocket Books. $8.95.

Wings & Things: Origami That Flies, by Stephen Weiss. New York: St. Martin's Press. 128 pp. $8.95.

The Paper Airplane Book, edited by Allen L. Hammond and Allson Fujino. New York: Vintage Books. 100 pp. Out of print.

KITS

Whitewings Excellent Paper Airplanes: Original Series, Collection Series, designed by Dr. Yasuaki Ninomiya. Set of 15 cutout paper models, $15; individual plane kits of precut balsa/paper or styrene, under $3. Distributed by AG Industries, Inc., 3832 148th Ave., N.E., Redmond, WA 98052.

INFORMATION

Paper Airplanes International has hundreds of paper airplane kits and books from around the world for sale by mail. Catalog costs $7.50, deductible from the first order over $20. 1521 Morningside Drive, Burbank, CA 91506.