When I play with the Wind Tube I quickly challenge myself to some type of goal, typically sustained flight in the Wind Tube. My four year old appreciates things shooting out of the top of the tube, with the exception of a long ribbon, which he has figured out how to hook to the base so it flutters in the tube.
We mucked around with our own designs and challenges this weekend. I was inspired by Todd Burleson's work with his students using ping pong balls and practice golf balls. While too heavy to achieve flight on their own, they can be incorporated into models to act as ballast.
Here is another bird design I quickly put together.
I added a second "leg" to increase the weight a bit to keep it flying in the wind tube.
I left the room and came back several minutes later and this bird was still happily circling in the wind tube! A successful design!