Technicalities: Something for Nothing

Peter Garrison

Tuesday, June 14, 2011 at 07:08 PM ET

Verified

To roll downwind faster than the wind, all you need is one of these. Flying

Key Takeaways:

The article explores methods of unconventional energy harvesting from air movement, such as recapturing lost rotational energy from wingtip vortices in aircraft.
It details how sailplanes and birds like albatrosses exploit atmospheric energy through techniques such as microlift gliding and dynamic soaring, which leverage differences in air movement and wind velocities.
The text discusses the counter-intuitive concept of a wind-powered vehicle moving directly downwind faster than the wind itself, explaining that this is achieved by exploiting velocity differences and not simply by being pushed by the wind.
Ultimately, all these examples demonstrate how seemingly "free" energy is harvested by exploiting differences in velocity between mediums and the force-multiplying ability of aerodynamic surfaces (wings).

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(June 2011) In the February issue, Robert Goyer reported on a project to convert Cessna Skyhawks to electric power. Many Skyhawks are used as trainers, and training flights seldom last more than 90 minutes; so batteries, though notoriously lacking in stamina, might be an adequate power source for this application.

Parenthetically, Robert mentioned that wingtip turbines — little windmills just behind the wingtips — could capture some of the energy of the tip vortices and return it to the batteries. I soon received an e-mail from a friend who objected that this sounded like some sort of harebrained perpetual-motion scheme. After all, your battery had to supply the energy that moved the airplane and created the tip vortex in the first place; wasn’t this something like charging the battery of an electric car with a rooftop windmill driven by the car’s own motion?