Prove that for a given angle of attack the drag force on an airfoil is the same for all altitudes. (For a given angle of attack, CD will not change with altitude.) A wing model of 3-ft span and 4"...

Prove that for a given angle of attack the drag force on an airfoil is the same for all altitudes. (For a given angle of attack, CD will not change with altitude.) A wing model of 3-ft span and 4" chord is tested at a fixed angle of attack in a wind tunnel. The air, at standard pressure and 80°F, has a velocity of 60 mph. The lift and drag are measured at 5.8 Ib and 0.50 Ib, respectively. Determine the lift and drag coefficients.