June 1986 R/C Modeler
 Vol. 23 No. 6 Pg. 10
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Feature Article

The Largest Ornithopter To Ever Fly

Dick Tichenor

A lifelike, radio controlled flying replica of the giant prehistoric pterodactyl Quetzalcoatlus northropi was demonstrated for the press at a special briefing and demonstration at the Greater Los Angeles Press Club.

The fully articulated flapping wing replica is the largest ornithopter to ever fly successfully and was created by Aero Vironment, Inc., under the direction of noted aviation pioneer Dr. Paul MacCready. The creature has an 18-foot wingspan, weighs 44 pounds, and is controlled by a complex onboard autopilot system under the command of a ground based operator using a model airplane radio control system.

The replica, called On The Time Traveler® was developed for a major role in the "On The Wing," a new large screen IMAX© film now in post production for the Smithsonian Institution's National Air and Space Museum in Washington, D.C.

The greatest problem the team faced was to develop the means to give the creature stability and control.

"Very little is known about how natural fliers such as birds combine their sensing devices, brains and muscles to fly effectively," MacCready said. "The challenge is especially difficult with this pterodactyl replica: The original creature did not even have a tail to help with stability and control."

To overcome these problems, the Aero Vironment engineers had to develop and program a special onboard autopilot system. "In response to the computer, the QN replica maintains stable flight by moving its head from side to side, extending its fingers midway out on the wings, twisting its wings and swinging them forward and backward. All this occurs while the battery powered muscles flap the wings to provide propulsion."

Development of the pterodactyl replica began in December, 1984. The original plan was to create a 36-foot wingspan replica, patterned after fossilized remains of the largest known pterodactyl that were discovered in West Texas in the 1970s. According to MacCready, however, the half-scale 18-foot version has achieved virtually all of the goals outlined in the original project report released in December, 1984. Those goals included the following:

That the replica fly realistically, propelling itself by wing flapping.

That it be fully controllable in normal flying conditions.

That it use an electric power system that would allow for several minutes of powered flight.

Quite a few materials were considered for the pterodactyl's structure including aluminum, spruce, and plywood. The ultimate selection included a widespread usage of carbon fiber. Various shapes (tubes, angles, etc.) were precisely made in the Aero Vironment shop by their craftsmen, This material provided the strength of steel at one-fifth the weight

Primary power comes from two powerful samarium cobalt electric motors. The motors draw energy from nickel cadmium battery packs to produce a full horsepower each. These motors drive the jack shaft that flaps the wings. A third, smaller, motor mounted toward the rear of the body controls the fore and aft sweep needed as the wings flap.

Aero Vironment crew transport the pterodactyl to launch position.

To reduce stress on the motors, the pterodactyl specialists designed an ingenious counter tension system basically a set of 66 rubber band "muscles" running from the jack shaft up through the lizard's neck.

When the wings flap up or down, a cord winds onto a spindle and stretches the bands. That provides a counter tension on the motor so that the wings always return in the opposite direction of where they are.

The Cobalt 60 and 05 electric motors were provided by Astro Flight, Inc., renowned leaders in the RIG electric flight activity.

Getting the reptile replica airborne was only one more of the many challenges to solve. A two-wheeled dolly containing a tail boom with conventional vertical and horizontal surfaces was devised. When towed behind a van, the machine lifts off and is guided to altitude. When the desired height has been reached, the dolly is released and the normal flight operations take over.

Last minute launch preparations with cameraman and director on the ready.

So sophisticated are the computer controlled autopilots that a standard model aircraft radio system is used unmodified - to control the pterodactyl's flight. The ground controller uses the system to initiate turns and altitude changes and during take-offs and landings. To land, the creature slides onto its reinforced chest and belly, which serve as a skid.

(Left) The wing-flapping mechanism consists of 2 one horsepower samarium-colbalt DC motors which drive the flapping through a gear box and ball screw drive. The mechanism is normally powered by six lbs. of nickel cadium batteries. (Right) The finger motions of the hand halfway out the wing acts as spoilers and drag breaks and operate on only one wing at a time to provide yawing moments. Each finger is driven by a small model airplane servo.

Sequences involving the creature were filmed at The Racetrack Dry Lake and Ubehebe Crater in Death Valley, California.

The film, produced by Francis Thompson, Inc., explores the dynamic relationship between natural and mechanical flight, contrasting the biological evolution of winged creatures with the technological innovation of man. "On The Wing" will premiere at the Museum's Samuel P. Langley Theater on June 20, 1986 and will open subsequently in IMAX© and OMNIMAX© theaters worldwide.

The first public flight of the pterodactyl replica is scheduled to take place in Washington, D.C., in mid-June to coincide with the premiere.

All Contents Copyright © 1986. R/C Modeler Corporation. All Rights Reserved.

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