16.885J/ESD. 35J-Sept 2003 Pressure coefficient Lift proportional Due to geometry of airfoil, the to area under velocity, and therefore the curve pressure, vary Manifestation of lift It is convenient to express this as a pressure coefficient (p-p) · From bernoulli eg and assuming density is constant (ok for M<0.3) Pick out some features on Pressure coefficient for a figure at left conventional airfoil: NACA 0012 airfoil at a= 3016.885J/ESD.35J - Sept 2003 Pressure Coefficient • Due to geometry of airfoil, the velocity, and therefore the pressure, vary. – Manifestation of lift • It is convenient to express this as a pressure coefficient Cp = (p - pf)/ qf • From Bernoulli Eq and assuming density is constant (ok for M < 0.3), Cp = 1 - (V/ Vf)2 • Pick out some features on figure at left Lift proportional to area under curve Pressure coefficient for a conventional airfoil: NACA 0012 airfoil at D = 30. Lower surface Upper surface Cp x/c 1 0 -1 -2 +1