Originally Posted by HazelNuts39
As a student I piloted gliders. These routinely fly tight circles to stay in thermals. In a strong wind there is no airspeed loss turning downwind, nor gain turning upwind. I've never quite figured that out, may be as a physicist you can.
The same way a tacking sailboat can go faster than the wind. If you hit the wind at the right angle with an airfoil you can acquire energy from the wind. Of course, the sailboat has its keel to make this effect more pronounced. That allows its crumby airfoil called a sail to work. The sailplane has only its mass to provide the effect.