DERIVATION OF LIFT, DRAG AND THE KUTTA--JOUKOWSKI THEOREM FOR AIRCRAFTS ¹⁾

Several fundamental concepts and laws in aerodynamics are introduced and summarized in the article. Lift and drag are the two components of the air's force on the object respectively. They are caused by the relative motion of the object and the air, and proportional to the square of the speed of the motion. The Kutta-Joukowski theorem gives the relationship between the airfoil lift and the airfoil flow, and sparked the study of airfoil performance in the early 20th century. Furthermore, the contradiction between the calculation conclution of the inviscid flow around a cylinder and the experimental observations inspired the study of the viscous flow motion, therefore the Navier--Stokes equation was born. Then Prandt proposed the concept of boundary layer and skillfully solved the relationship between local flow and overall flow. For the wings with large aspect ratio, Prandt proposed a lift surface model based on the lift line assumption, which can obtain the aerodynamic performance of the wing based on the performance of the airfoil.