This is a weird little side project I got involved in trying to determine whether a machine rolling on the ground could travel directly downwind faster than the wind. I first read about it on BoingBoing on 1 Dec 2008. Apparently the debate about whether these things are real or hoaxes has been going on since before Jan 2006.

It turns out they're real.

A number of people have proven to themselves that it really works. This document is an attempt to prove it to others. If you're not familiar with the device at all, hopefully you can read this and understand how it works well enough to get that it isn't a hoax and that they can actually go downwind faster than the wind.

There are a bunch of different ways to build one of these vehicles. The most common way is to have a little cart with a propeller on the back. They're all based in some way or another off of a gear that leverages the air and ground. I call the gear the “tumbleweed”. You can make a tumbleweed work, but it isn't as efficient as a prop-cart. But the tumbleweed is definitely easier to understand.

The entire document is about a thirty pages in a .pdf file and is completely self-contained. You don't have to read anything else to understand the concept or how it works. It includes a link at the and to a nice one-page set of plans that explains how to build an actual working prop cart.

You can read it here:

http://www.greglondon.com/tumbleweed/tumbleweed.pdf