Question

What is the thickness in NACA 747A315 airfoil?

(a) 15%

(b) 25%

(c) 30%

(d) 7%

I got this question during an internship interview.

I'd like to ask this question from Airfoil Nomenclature topic in portion Incompressible Flow over Airfoils of Aerodynamics

Answer 1

The correct option is (a) 15%

Easy explanation: In NACA 747A315 airfoil. The  7 denotes the series, 4  provides the location of minimum pressure on the upper surface in a tenth of chord, 7 provides the location of the minimum pressure on the lower surface in tenth of chord, the 4^th character i.e. A indicates the thickness distribution and mean line form used. Again 5^th digit 3 indicates the design lift coefficient in the tenth and the final two digits indicate the thickness of the chord 15%.