Trailing Edge Flaps

今日同大家討論Trailing Edge Flaps~

首先要了解 Extend Flaps 有咩影響~

1. Extend Flaps 之後Camber line 會更加curve，代表飛機係唔同Angle of Attack (AOA) 嘅 coefficient of lift 會增加; 而drag 同時會上升，因為more lift = more drag

2. 由於flaps down 之後升力多左，所以AOA 嘅角度會相應減少，反而亦之，下面個figure 顯示左唔同flaps setting 對CL 同AOA 嘅關係~

3. Flaps down 之後升力多左，Stall Speed 亦都會下降

***詳細原因可以睇關於Stall and Stall Speed 個discussion***

https://www.hkcockpit.com/forum/principles-of-flight/stall-and-stall-speed

4. Sinking effect & Balloon effect

5. Change in Pitching Moment

Trailing Edge Flaps 嘅種類~

1. Plain Flap

Plain Flap 唔會增加wing area，只會增加effective wing camber; 而center of pressure 會隨住flap 嘅角度增加往後移，因此會出現 nose down pitching moment。

2. Split Flap

Split Flap 係Plain Flap 嘅改良版，Lift 、drag、Stalling Angle 比Plain Flap 更多/大

當Split Flap Extended， Wing 嘅 Upper Surface 唔會出現變化，而 lower surface 就同平時嘅flap 一樣，形成開叉嘅情況。

3. Slotted Flap and Double Slotted Flap

Slotted Flap

Double Slotted Flap

Slotted Flap 嘅特點係Trailing Edge of the Wing 同 Leading Edge of the Flap 之間有gap 比機翼下面嘅high pressure air 透過venturi effect流向機翼上面。空氣會因為經過Venturi 而加速，額外嘅Kinetic Energy 因此而產生，所以upper surface 嘅airflow 會延伸，繼而separation point 會延後令CL 上升。

4. Fowler Flap

Fowler Flap 會令wing area 大左同埋camber line 長左，能夠做到咁嘅效果係因為fowler flap 唔用嘅時候可以收埋，需要嘅時候再extend， 加上結合埋slotted flap 嘅優點e.g. venturi effect ，令fowler flap 成為最 efficient 嘅flap system。

最後用一張Figure 總結一下唔同種類嘅Trailing Edge Flaps 係Coefficient of Lift 同 AOA 之間嘅關係啦~