Aeronautical Engineering/Airfoil Lift-to-Drag Ratio
I have a question about the lift-to-drag ratio of an airplane wing. Say the l/d ratio of an airfoil is 120:1. Is the drag factored on the leading edge of the airfoil? Meaning for every 1lb of force pushing back against the leading edge of the wing, it would generate 120lbs of lift pushing up from the bottom of that wing?
Lift and drag are integrated forces that are the result of pressures acting over the entire aircraft. The total force opposite to the flight direction is drag, and the total force perpendicular to the flight direction is lift. L/D is the ratio of lift to drag. Aerodynamicists often consider wing aerodynamic forces to be acting through the aerodynamic center or wing quarter chord, which is where the pitching moment does not change with angle of attack.
Another way to think of it is that the integrated aerodynamic forces act through the center of pressure. In other words, the vector sum of all the pressures act through one point. On a wing, the center of pressure moves with angle of attack.
For a schematic of these concepts see https://www.google.com/search?q=aerodynamic+center&client=firefox-a&hs=ahK&rls=org.mozilla:en-US:official&channel=sb&tbm=isch&tbo=u&source=univ&sa=X&ei=3ydVVL3iE5WcygT-nYKoDg&ved=0CDQQsAQ&biw=1384&bih=710