I kept getting jealous of Suo and Jok and their small scripts, rather than my huge, lumbering ones. So here's one under 70 lines.

How to Fly:
In general, when your hands are gripped, you will generate force in the direction opposite that your hands are moving. So if you raise your arms, set grip, and lower them, you will generate lift on your body. In a similar fashion, you can generate downward thrust, and forward, backwards, and lateral movements.

If you keep your hands held for longer than 50 frames you'll start to glide, picking up lateral speed.

Unfortunately, modeling it so that you can perform tight aerial maneuvers makes it very difficult to move as you'd want otherwise. If I find a little more time, and people seem interested, I'll make an advanced wing script.

Enjoy.

Edit: I took out that debug info (oops), and modified gliding to work more naturally (there was kind of an annoying speed lag before).

Edit again: Modified the behavior again. After 30 frames held, you start to swoop (for 50 frames) to pick up lateral speed, and then you glide as normal. You can dive bomb Uke with a couple of flaps from 2000 engage distance, done right.