Nice!
I loved the video! The music worked well with it!
Technically free 'flight' is possible! If you get a much... well MUCH more powerful trebuchet or maybe a cannon and shoot yourself at just the right angle you can enter low earth orbit, and thus, flying endlessly. On the plus side, you could say that you can fly. On the downside, you would be in the low areas of the thermosphere (the ionosphere) in which there is little breathable air, and the temperatures can exceed 2000 degrees celcius. Not to mention that you would have to be traveling at 17,000 mph and you would be vaporized long before attaining that speed. So, in reality, you wouldn't be able to say 'I can fly' but rather utter a short 'Urk' before dying of asphyxiation.
Sorry to ruin your hopes and dreams. I think I take things to literally. Anyways, I love your animation style! It's very 'clean' i guess.