Question

An airfoil with symmetric profile has pitching moment about aerodynamic centre as 13 Nm at 4° AOA. Determine Pitching moment at same point if AOA is increased by 8°.

(a) 13Nm

(b) 8Nm

(c) 5Nm

(d) 13Ncm

The question was posed to me by my college director while I was bunking the class.

The query is from Airfoil Selection-2 topic in portion Airfoil and Geometry Selection of Aircraft Design

Answer 1

Right option is (a) 13Nm

To elaborate: Given, a symmetric airfoil

Pitching moment PM1 = 13Nm at AOA = 4°.

Now AOA is increased by 8°. Hence new AOA = 4+8 = 12°.

Now PM1 is acting through aerodynamic centre. PM will be independent of AOA at aerodynamic centre. Hence, at 12° pitching moment will not change.

Hence, at same point at 12° PM2 = PM1 = 13Nm.