The Mechanical Principles of the Aeroplane #228102

Let us suppose that the moving body possesses a plane of symmetry, and that this plane is vertical during the motion, the direction of motion lying in the plane. The centre of gravity is of course in the plane of symmetry, and by the fact of the exist ence of the symmetry it follows that the resultant air pressure must be some system of forces in this plane. The applied forces must also be in this plane; and SO we have a problem in two-dimensional statics of a rigid body.