A typical phenomena on every wing is, that the high pressure air from the bottom is sucked up to the low pressure region on the top, around the wingtip
http://www.flysurfer.com/wp-content/gallery/research-and-development/zwischenablage11_3d.jpg
http://www.flysurfer.com/wp-content/gallery/research-and-development/zwischenablage11_3d.jpg
En daar ga je dan een gat voorzien- dus vermindering van drukverschil - dus minder performatie.