There are some booklets to help you below. Unfortunately I do not have some on all the topics or competitions. If you find neat websites, put them in the comments section.
You will need to choose from one of the three topics. From that you need to select a competition you wish to enter. Here are the choices; (More information is in the attachment at the bottom)Flippers - Catapults not Slingshots
Fliers - Paper Airplanes