众所周知,不可压缩理想流体绕翼型的定常流动的升力及力矩具有如下性质:(1)升力和绝对迎角的正弦成正比;(2)翼型上存在一个焦点(Focus)F,当来流迎角变化时,对焦点的力矩保持不变;(3)在不同迎角下升力作用线的包络线是一条以F为焦点的抛物线,称之为定倾抛物线(Metacentric Parabola)。经典的证明方法是将翼型外部保角变换为圆的外部区域,然后在圆的平面上很容易写出流动的复势,并代入著名的求升力及力矩的Blasius公式,便可证明上述升力和力矩的特性,如见文献[1]和[2]。然而这种基于保角变换的关系证明上述特性的方法虽然十分简单明了,但却很难应用于 It is well-known that the steady-state flow and torque of an incompressible ideal fluid around an airfoil have the following properties: (1) the lift is directly proportional to the sine of the absolute angle of attack; (2) there is a Focus F on the airfoil, (3) The envelope of the line of action of the lift at different angles of attack is a parabola centered at F, which is called the Metacentric Parabola. The classic method of proof is to transform the outer conic of the airfoil into a circular outer region and then to easily write the flow complex on the plane of the circle and to insert the famous Blasius formula for lift and moment to prove that the above mentioned lift And torque characteristics, see literature [1] and [2]. However, this method based on the conformal transformation proved that the above characteristics are very simple and straightforward, but hard to apply to