Aerodynamic coefficients plays an important role in performance analysis as well as  design of aeroplanes.Coefficient of lift is defined as Lift divided by dynamic pressure, \(L/{q_\infty }S\) where as drag coefficient is defined as Drag divided by dynamic pressure, \(D/{q_\infty }S\) .

Coefficient of lift,maximum or \({C_{L,\max }}\) is the determining factor for stalling velocity of aircraft.The higher is the \({C_{L,\max }}\) the lower is the stalling velocity.\[{V_{stall}} = \sqrt {\frac{{2W}}{{{\rho _\infty }S{C_{L,\max }}}}} \]However,\({C_{L,\max }}\) can be increased by the use of mechanical devices like high-lift devices.High lift devices include flaps,slats and slots on the wing.Air plane flying at given altitude with maximum thrust \({T_{\max }}\), the maximum value of \({V_\infty }\) ,corresponds to flight at \({C_{D,\min }}\).\[{V_{\max }} = \sqrt {\frac{{2{T_{\max }}}}{{{\rho _\infty }S{C_{D,\min }}}}} \]The actual value of \({C_L}\) and \({C_D}\) for a given body shape just depend on the orientation of body in the flow,that is angle of attack.

Therefore,aerodynamic coefficients are important engineering quantities for determining the stalling velocity by \({C_{L,\max }}\) and maximum velocity by \({C_{D,\min }}\) .

Lift to drag ratio is the measure of aerodynamic efficiency of aircraft .It is given as \[\frac{L}{D} = \frac{{{q_\infty }S{C_L}}}{{{q_\infty }S{C_D}}} = \frac{{{C_L}}}{{{C_D}}}\]The importance of aerodynamic efficiency \(L/D\) is that at a given velocity ,\(L/D\) should be as high as possible,the higher \(L/D\) is more efficient is the body.