For a given set of free-stream conditions and angle of attack, the lift per unit span for a given airfoil is 200 pounds per foot (lb/ft). The location of the center of pressure is at 0.3c, where c is the chord length; c = 5 ft.
For a given set of free-stream conditions and angle of attack, the lift per unit span for a given airfoil is 200 pounds per foot (lb/ft). The location of the center of pressure is at 0.3c, where c is the chord length; c = 5 ft. The force and moment system on the airfoil, namely, the aerodynamic force of 200 lb acting through the center of pressure, which is located at 0.3c, with no moment about the center of pressure. What would the equivalent force and moment system be if the lift were placed at the quarter chord point? At the leading edge? (Assume that the line of action of the drag D is close enough to the quarter-chord and leading-edge points that any moment about these points due to drag is negligible.)
Moment arm =\( 0.3c – 0.25c = 0.05c\)
\[M_{c/4} = -(0.05c)(200) = -10c = -10(5) = -50 ft-lb\, \textrm {per unit span}\]
The moment about the leading edge point is given by the lift acting through the center of pressure, with a moment arm \(0.3c\),
\[M_{LE} = -(0.3)(200) = -60c = -60(5) = -300 ft-lb\, \textrm{per unit span}\]
