Cross Section of a Wing

翼剖面

Mean Camber Line

Slice the wing exactly in half, the mean camber line is the precise center of the wing thickness.

Any point on the mean camber line, the top slice equals to the button slice.

Leading Edge

The point on the front-end of the mean camber line of the wing.

Trailing edge

The point on the rear-end of the mean camber line of the wing.

Chord Line

When you join the trailing edge and leading edge. You will get the chord line.

Relative Airflow

The direction of the air movement relative to the wing.

AoA(Angle of Attack)

The angle between the chord line and the relative airflow.

Airspeed（TAS）

The aircraft speed relative to the airflow.

因為實際的大氣密度難以測量，所以難以使用TAS計算升力。忽略位置誤差（Position Error），低速飛機使用IAS計算升力時所采用的密度也應是所在飛行高度于國際标準大氣表中的密度。

Wing Surface Area

Air density

More molecules equal higher density.

Lift formula

Lift equals to half of the coefficient of lift multiplying air density, square of airspeed and wing surface area.

密度取決于當前飛行高度/溫度/壓強（計算多用ISA），機翼面積取決于飛機類型。因此，飛行員控制飛機升力本質上是在控制飛機的空速（Airspeed）和迎角（AoA）。

飛機平飛時（升力恒定），若要低速飛行（Slow Flight）就需要增加飛機的迎角，補償速度對升力的減少量。

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