飛行最美--輕航機世界

常常聽到人說地面效應~~地面效應,倒底什麼是地面效應呢?他跟我們在飛行的時候又有何關聯?簡單的說好了大家會比較容易了解 Ground Effect ..地面效應何時會發生,先看一下你飛機的機翼翼展長度,對~~就是這個長度把它想像成高度,對^ ^ 就是這個高度,當你飛機接近地面這個高度的時候就會發生地面效應,

那麼地面效應有何特色呢?簡單的說就是一樣在空中,如果你拿1000FT的高度跟你飛到距離地面翼展高度來做比較,靠近地面翼展長度的高度可以保持更低的空速,也就是說你再1000FT做失速測試可能50浬就失速了,但是因為有地面效應的協助,你貼近地面時失速速度可能會降到40,這就是地面效應的特色,此外另一個解釋如果你再1000FT飛70浬的空速所需要的推力是4500rpm..那你降到有地面效應高度的時候,一樣是70浬的空速,但是所需的推力只需要4200rpm.這也是地面效應給你的協助,這是地面效應的現象。

地面效應是如何產生的呢?這就要跟機翼與氣流有關聯了,怎麼說呢?當氣流受到翼剖面形狀的影響,氣流會順著翼面順勢流動!流體的特性即是順勢,當氣流受到翼剖面形狀的影響,上機翼前緣會產生所謂的上洗氣流(upwash),機翼後緣會產生下洗氣流(downwash),而翼端也會產生所謂的翼尖渦流(wingtip vortices)來參考一下圖片,當機翼接近地面的時候地面會限制不好的氣流或阻力的組成,也就是說地面會修改下洗流的角度,讓它會變小變陡峭,減少了在原本在機翼附近所剝離的平均氣流,換言之就是會把誘導阻力(induced drag)跟寄生阻力(parasite drag)降到最低,減少了這些阻力機翼自然而然會恢復更佳的升力~~這就是大家所謂的地面效應

a result of the extra lift (from the increased lifting ability of the wing) because of less drag.

An airplan’s flight characteristics change when it is very close to the ground or any other surface,because 1:it can fly at a slower speed than when it is at altitude 2:it

Can fly at the same speed using less thrust than when it is at altitude.

This increased performance of an airplane flying just above a surface is known as ground effect.Ground effect is greatest when the aircraft is just airborne and least

When the aircraft is at an altitude above the ground approximately one wingspan’s

Distance in part one.we considered the airplane to be flying well away from the ground . There was no restriction to the downwash of the airflow behind the wings.nor to the upwash ahead of the wings.There was also no restriction to the formation of wingtip vortices.

When the wing is just above the ground,the ground modifies the downwash and the angle is reduce,thus reducing the effect on the local average relative wind.In other words,the relative wind angle about the wing will be closer to the remote free stream.This keeps drag at a minimum and increase it’s altitude above the ground.the downwash angle steepens and increase the induce drag,all without an aircraft altitude change the downwash or wingtip vortices and induced drag is at it’s maximum.