This article was taken from the October 2012 Issue of Wired magazine. Be the first to read Wired's articles in print before they're posted online, and get your hands on loads of additional content by <span class="s1">subscribing online.
Ever wondered how your car would hold up in a hurricane? In physics labs, scientists can test the force of air in giant wind tunnels on everything from Formula One cars to oil rigs. Life-sized tunnels are hard to build in your garage, but "the principles are the same for all wind tunnels -- it's just scale," says Clive Evans, founder of Scale Engineering, a company that makes models for testing.
1. Aim for a top speed
The main component is the fan. To be able to make any valid measurements of air force, you need an air speed of at least 30m/s, according to Durham University wind-tunnel scientist David Sims-Williams. "Find a fan with a performance datasheet."
2. Build from scratch At one end you need a broad, conical nozzle, which you can make from plywood. This funnels air into a Perspex tube.
The section then broadens out until it meets a diffuser, behind which is the fan. Stick the components together with masking tape.
3. Become an instant expert
Low-speed Wind Tunnel Testing by Barlow, Rae and Pope is "the wind-tunnel bible", according to Sims-Williams. It will help you determine the ratio of lengths and area that can improve your wind tunnel's shape for greater efficiency.
4. Scale it down
There's no point trying to test a real car in your wind tunnel.
Realistically, says Sims-Williams, a 300mm by 300mm model is the largest that would fit. "A six-per-cent scale model, such as a toy car, would work well for your experiment."
This article was originally published by WIRED UK
