What is hinge moment? Why in the process of calculating it we must calculate the coefficient of hinge in 2D? Why the distribution of airfoil thickness at 90%, 95%, and 99% of the line should be considered? Why is the line used for his (cf= line form hinge line to trailing edge) (cb = line from hinge line to leading edge) using a perpendicular line with Λ_(1/4) wings?
The hinge moment is the moment acting about the hinge line of a control surface. Simply put, it is the force that must be overcome to move a particular control surface. At any given dynamic pressure and airspeed, the hinge moment will vary with angle of attack, the amount of control surface deflection, and trim tab deflection. Not an easy concept and not one which is generally taught to pilots, however becomes critical for engineers who design control systems for aircraft.