This is a closer look at the winding mechanism. Two elastic bands go on either side, powering the larger gears. They, in turn, power a smaller gear to rotate the propeller. Unfortunately, unless new blocks are invented, this mechanism will never fully work the way I want it to. But it's an interesting alternative to electro motors.
Another idea behind this build was to make sure even younger children can build this glider. That is why I chose to keep it simple and to use common household objects, such as paper and Sellotape. Alternatively, it is also possible to substitute paper with Plastic wrap, making the glider lighter and easier to manoeuvre if turned into an RC plane. However, working with this material might be a bit tricky.
If you have any questions, please let me know.