The GoPro HD is a great little piece of kit, but has it's drawbacks.
For starters there is not - yet - a remote control for it. So, mounting it on the outside of the a/c, you have to switch it on before start and keep it running. Fine for a short little hop, but not too good for long x-country.
Second, it is sensitive to vibrations. You get what's called 'rolling shutter' or 'jello' effects; think of the image looking as if it was a wave.
There are some others out there that do have remote control. Do a bit of a Google search and you shall find!