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ORIGINAL: abelard

Correct: slope soaring and dynamic soaring are two totally different animals. Dynamic soaring extracts energy from a property of the air flow called curl, which is, unfortunately, a vector calculus concept.

But there is a fairly simple way to describe it. Visualize a creek with some lily pads floating in it that have broken loose from their roots and are moving along with the current. If the pads are rotating, the flow has curl. In general, the curl will vary from one value near the left bank, to zero at the centerline, to an opposite-sign value near the right bank which is another way of saying that the pads on the left rotate counterclockwise and those on the right, clockwise.

Air flow can be curled just as water flow can, and a sailplane can extract lift from that, even without any vertical air motion. If you analyze the process deeply enough, you'll come to a remarkably elegant conclusion: you will get the maximum climb rate by circling in a 55-degree bank, regardless of your wingspan, your airspeed, the value of the curl, or pretty much anything else!

In practice, the airflow is rarely either "curled without vertical motion" or "with vertical motion but no curl"; what you actually encounter is almost always a combination. Soaring birds do an impressive job of using slope and dynamic lift at the same time.