Vortex Generators

Strange small devices found in many places. Do they really give you 5 % fuel saving and / or reduction of drag?

http://www.youtube.com/watch?v=f80a9jssUFU

http://en.wikipedia.org/wiki/Vortex_generator

http://www.microaero.com/

http://www.buyairtab.com/

http://www.fuelsavers.com.au/

The following video is telling no fuel savings (or too small).

http://www.youtube.com/watch?v=We8LWkqjdX4

The following source is telling other benefits.

http://www.youtube.com/watch?v=L508itf3oy8