Flying in Circles: Thermalling

Here is a video of an electric glider catching and riding a thermal. The glider is relatively heavy and draggy with the camera mounted on it, but it still thermals. The location is the same as that in last week’s quadcopter video, allowing a comparison of the two platforms. Besides the differences in flying characteristics, there also is the difference in energy consumption: the quadcopter takes a 4200mAh battery for a ten-minute flight, and the electric glider takes 1000mAh for about the same duration, with the motor on for a quarter or a third of it. The quadcopter drives its four propellers, while the glider relies on its wings for lift and uses servos to actuate control surfaces.

When thermalling, the glider takes advantage of raising air to stay aloft. The warm air creates a strong updraft that carries the glider. The updraft accellerates somewhat with distance from the ground, but it also becomes more narrow, as it rises to the cloud that it forms above. The glider has to fly relatively narrow circles to stay within the area of lift. Immediately outside the area of lift is turbulence and downdrafts, called “violent downsuck” by (some) glider pilots.

The challenge of a thermal flight lies in identifying the location of a thermal, and in keeping the glider in it as it moves, reading the behavior of the glider to interpret the air motion around it.

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