Method producing a lift considered up to date

　　The shape of the wing producing a lift ;
　　　　　The characteristics of the wing shape can be represented by the chord,
　　　the thickness, the curve, the angle of attack and the span.
　　　　　The thickness/the chord and the chord/the span must be small and
　　　the rear edge must be shape.
　　　　　The angle of attack and the curve are restricted within small range.

　　When the wing is moved with an angle of attack, the circulation flow
　should occur around the wing.

　　The incident air toward the wing meets to the circulation air, and then
　the flow velocity increases on the upper side but it decreases on the
　down side. Since the Bernoulli's theorem may be valid if the flow is
　close to steady, the pressure decreases on the upper side but it increases
　on the down side. Thus the upward force, that is the lift, appears.

　　We can explain the above mention as the special case in general method;
　When the wing with circulation moves horizontally, the surrounding air
　is pushed down almost vertically. As the reaction, there appears the
　uoward force, that is the lift, and there is almost no load to the moving
　direction of the wing.

　　So as to move the wing horizontally, we must keep down the wing by the
　force against the lift. The bird keeps down the wing by its weight, and
　It is able to fly at a constant altitude. Then，the load to support the
　weight is required for the wing.

　　(Even if the span is short) the generation of a circulation is the conclusive
　evidence to a lift. It is same as that the rotation of the ball thrown by a
　pitcher is the conclusive factor to curve the boll ( to produce the force
　perpendicular to the advance direction).

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