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Thermal Gliders, and how to find the invisible thermal

Dedicated thermal gliders are usually launched from a flat field, using a winch or a "high-start". The goal is generally to stay in the area as long as possible, by riding invisible bubbles of air known as thermals.

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You have most likely seen hawks or other larger birds circling over areas while hunting, not flapping their wings but somehow staying aloft.

An advanced six servo glider, spanning 110 inches

Thermals are created by uneven heating of the ground.

The air over the warmer portions of ground gets heated up more than neighboring air. The hot air rises over the warm spot, and cooler air moves in from nearby to take its place. The bubble of warm air sometimes breaks free and drifts skyward.

If a bird or thermal glider catches a ride, the fun begins! The bird or rc pilot circles with the area of the bubble. The art form comes in knowing how big a circle to turn.

The wind is also pushing the bubble across the field, adding to the challenge. Find out how to "see" these invisible thermals here.

The high-start is like a gentle slingshot. A length of latex rubber tubing is tied to a length of nylon line, which is attached to a ring.

The ring goes over a hook on the bottom of the sailplane. The other end of the line is attached to a peg driven firmly into the ground.

When ready to launch, the pilot stretches the line downwind, away from the peg, then releases with a gentle, slightly upward through. The glider carves out a curving path upward, while the pilot steers with the transmitter.

At the top of the flight path, the pilot noses down the aircraft slightly, and the ring slides off the hook on the glider, which can then be flown around the field in search of thermals.

A winch is slightly more complicated and expensive launch system. (Thermal glider clubs generally have one or more of these for club members). The winch is powerful motor run by a 12V battery.

The motor pulls on the launch line, as the pilot increases or decreases motor speed with a foot switch.

Winch launches are generally more powerful than a high-start, yet with more control.

Some options for beginners' thermal gliders are the Thunder Tiger "Whisper" and "Windstar", the Great Planes "Spirit" and the Goldberg "Gentle Lady". All of these are readily available from major hobby retailers.