Soaring: Difference between revisions

=== Influence of lift and sink ===

The vertical motion of air has likewise a pronounced influence on the effective glide ratio. Assume we're in an airmass rising at 0.5 m/s flying again at 110 km/h. This increases the glide ratio by 1/0.5 to 1:80 because we're actually sinking only 0.5 m/s. However, we can do better - suppose we reduce the airspeed to 70 km/h to get the sinkrate to 0.7 m/s. In still air, this would correspond to a glide ratio of 1:36, i.e. not worth doing. But since the air rises, efectively we sink only 0.2 m/s now, and so the glide ratio goes to about 1:125. The opposite is true in sinking air.

The rules derived from these examples are: Fly slower than optimum speed in rising air, faster than optimum speed in sinking air. If your minimum sinkrate is equal to the lift, you do not lose any energy at all. Consequently, in any airmass providing net lift, the glider is flown at the velocity of minimum sinkrate (which is always lower than the optimum speed) to maximize the altitude gain. This makes it also easier to fly tight turns in small thermals.