In summer 2007, Alexander Miller and Jan Lehmann, aerospace-engineering students at Stuttgart University in Germany, took on an unusual task: building a wind-powered vehicle that could race directly into the wind. A year later, their team unveiled its creation, the Ventomobile, which handily defeated the field at North Holland's Racing Aeolus, the first-ever track race between vehicles powered solely by wind.
Needing a lightweight material for the frame, the team settled on carbon fiber, which was available in abundance at the university's Institute for Aircraft Design. A huge rotor mounted on top captures the wind and powers gears connected to a bicycle-style transmission to propel the vehicle forward. A pulley system the driver can operate with one hand keeps the rotor turned into the wind, which is necessary to reach maximum speed.
At the race in North Holland, the vehicle won with a top speed of 15 mph -- about 65 percent of the wind speed over the 5.5-mile course. It was also honored as the most innovative design. Now the students are tweaking it with an eye toward running at 100 percent of the wind speed at this year's race, a feat that would win them a $1,400 prize from the Energy Research Center of the Netherlands.
Build: 10 months
For maximum strength with low mass, the team constructed the rotor from plastic reinforced with carbon fiber and tested it in the university’s wind tunnel. Although the rotor generates the power that propels the Ventomobile, it also produces an opposite force of thrust that slows the vehicle down. So instead of going for maximum power, the team shaped the blades to strike a balance —between harvesting power and minimizing countervailing thrust—that achieves the highest possible speed.
The driver steers the vehicle with foot pedals, leaving his hands free to adjust the angle of the blades and the direction of the rotor. With one hand, he keeps the rotor tower turned into the wind, using a sailboat-style block-and-tackle system. A hand crank adjusts the angle of the rotor blades. The driver can tell by the electric-fan-like humming noise of the blades whether the cranking is helping or hurting the vehicle’s efficiency, allowing him to (literally) play it by ear.
A display in the cockpit shows the driver the rotor speed, which he can adjust to increase the vehicle’s speed by switching gears. The transmission uses mountain-bike components: a chainring in front and an eight-gear cassette in the back. The driver shifts the back gears using a bicycle-style derailleur to move the chain from one sprocket to another. The team hopes to replace this system with a new, expandable bicycle gear wheel. Instead of shifting from one gear to another, the chain will remain in place around a tooth wheel that can expand or contract as needed.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.