A couple of weeks ago I attended Skyfest 2008, a large skydiving convention ('boogie') which had attendees from all over the country. They also had a number of unconventional aircraft, namely helicopters and hot air balloons. I decided to make a hot air balloon jump, my second, but this time I got video of the jump, which appears after the fold!
This jump was quite successful, not only for the video but for the painlessness of the process: we managed to land right at the drop-zone. Though the balloon pilots try and account for the wind conditions and take off from a location which will pass near the DZ, just as likely as not a skydiver will have to find an improvised landing zone in some farmer's field, wait for the chase vehicle to find him, and possibly drive around looking for the balloon to help pack it back up! After my first jump, several years ago, my fellow jumpers and I were stuck in the back of a pick-up truck for about 1 1/2 hours while the driver tried to figure out exactly where the balloon had landed.
So why bother with a balloon jump at all? Because falling out of a hot air balloon is a completely different experience than jumping out of any other aircraft, and it is the only skydive one can do in which one truly feels weightless. (I'm not referring to 'base jumping' as 'skydiving'; we'll come back to that in another post.) I've never heard this explained by anyone before, but I thought I'd give it a try using some rough physics.
Keep in mind that an ordinary airplane is moving at probably 90-100 mph when the jumper exits. The skydiver experiences wind resistance at every part of the skydive. This is illustrated below; the red arrows indicate the direction of wind resistance at each point of the jump:
True 'weightlessness' is only experienced in what a general relativity expert would call a free-float frame, in which one's entire body is accelerating freely with gravity. To put it somewhat grotesquely, you only truly feel weightless when your insides are accelerating at the same rate as the exterior of your body, and are free to 'float around' inside you. When a skydiver leaves an airplane, he/she immediately experiences a 'breaking' force in the form of wind resistance: the exterior of his/her body is being slowed by the wind while his/her interior is attempting to keep moving according to inertia. Once the skydiver has reached terminal velocity, he feels his full weight and the sensation is no different than laying on one's belly on top of a very big fan!
The sensation is completely different upon leaving a hot air balloon. Because the balloon is essentially a stationary object in the air, there is no wind resistance. The jumper is very nearly in a true free-float, weightless motion, and the experience can be quite shocking. On my first balloon jump, I shouted, "Holy crap!" as I left; unfortunately, everyone on the balloon heard me and mocked me later!