Transport. 

Some of the links we used:

How to make a balloon rocket.
https://www.youtube.com/watch?v=A7wrEWfV6TY
How to make a paper boat:
http://www.youtube.com/watch?v=hiAWx8odStA
How to make a paper helicopter
http://www.exploratorium.edu/science_explorer/roto-copter.html

Click on an image below for detail and caption.
To see the transport system we're building, click here.