A battery powered paper airplane launcher, easy to build by children from about 6 years on, with a little preparation beforehand (some soldering and hot melt gluing). It will give ordinary folded paper planes some serious battery powered speed.
In the last step I added a template to help children fold a plane that works great with the launcher. The template also shows how decorations are affected by the folding (two pilots becoming one).
See how it works in the following videos (I did not select the fastest launches as this way you get to see something):
The device can launch a large range of models. As long as there is vertical and longitudinal bottom section at least about 1 cm height, it should work. You can find the principle in a number of other applications. As a kid I had toy accelerating matchbox cars on a track in a similar way. The Science Museum in London carries kits to make either a paper plane launcher or a Ping-Pong ball canon. In this instructable I explain how to build a battery powered paper plane launcher for less than 5 euro. If someone with a little experience (or willing to learn) does the soldering and hot melt gluing in advance, the construction and use makes a great childrens activity. It involves cutting and folding paper, nailing, some ordinary gluing and decorating. The high speed is not the best way to reach distance records, although it does allow children with less tossing skills to reach new personal records. Most importantly it is quite spectacular and great fun. Putting fingers between the fast turning wheels will be painful. But if you keep to the power of two AA batteries, there is no real danger of injury. Do avoid launching towards people, animals ore anything fragile. Of course, I can not accept any liability.
I first published this instructable arround the time of the "Toss it! Speed contest". Of course it did not compete in that contest as it involves battery powered launching instead of tossing. It still was a good time because of all those inspiring entries in the "Toss it! Speed contest", which made this launching device did come in handy.