Hi,
I happen to agree with Jester on this one. This reminds me of a high school experience:

Grayle (fellow RCU poster) and I went to high school together in the area and took a class called aviation/aerospace. This was about 14 years ago, we both chose to build and fly a glider, we chose the Gentle Lady. Neither of us had flown before, but we were interested in it, so why not. We spent most of the school year building it at his house and near the end of school we decied to fly it in the football field, using a surgical rubber upstart. we pulled it back a fair distance and let it go, it promptly went skyward, then back to the ground in about 6 seconds. Terribly embarrasing.

Well, I guess the good thing is that we never gave up, he is a successful machinist and I am a Mechanical Engineer. BTW, please tell me you aren't teaching them about the Reynolds number, ugh!

These students are lucky to have a teacher that wants to challenge them like you want to, but I would pick something easier, or maybe something with more iterations where they can refine their designs. Maybe the small balsa planes would be a good start. I used to build the Guillows brand planes out of balsa, and covered them with tissue and shrunk it with water mist. The kits are very inexpensive and they are die cut. These can be modified and they have a great cheap starting point, and are driven by rubber bands. Maybe your payload on these planes could be stacks of coins. Using a standard regulation rubber band and you can control the environment by flying them in your gymnasium.

Have fun,
Curtis