Wow, what a discussion!

It may be the OP's fault to put his question the way he did, but that "possible?" is still a perfectly valid question for me. Actually, it's a question about kinetic energy, its conversion and conservation. Why don't you just imagine an aerobatic glider trying that square loop as a pattern fixed to the ground, not to the moving air. Adding a decent wind shear, you might even invent a new DS pattern.