Assertion: airfoil's pressure | /r/Causes | air
Facets:
value: at each wingtip
type: LOCATION
value: to flow along the lower surface
type: PURPOSE
Source sentences:
text: Unequal pressure, however, also causes air at each wingtip to flow outward along the lower surface, around the tip, and inboard along the upper surface producing a whirlwind of air called a wingtip vortex.