Hello All,

Can someone tell me what is meant by the term 9% airfoil, or 18% airfoil etc.

Thanks

Joseph

Most often, that number will be describing the maximum thickness of the airfoil. In other words, at the thickest point, the depth of the airfoil might be 9% of the chord (distance from the leading edge to the trailing edge).

-David

Sure, this refers to the ratio of thickness to chord, or if an airfoil is 10% it's thickness is 10% of the chord, or measurement from the front to back.
A wing that is 500 mm from the leading edge to the trailing edge, and it's a 10% airfoil, it would be 50 mm thick. Airfoils of the same section (or shape) with a greater thickness will stall at a slower speed, give more lift and drag, generally.

The amount of camber (curvature of the airfoil) is also often defined as a percentage of the chord... so you may need to be careful.

Yes, it depends on whether it's % thickness, or % camber. Usually % is given as airfoil thickness.