飛行最美--輕航機世界

側風修正
 

側風修正,這個大家耳熟能詳的名詞,我們來回顧一下國內的大部分輕航機場,有許多跑道的風向並不是常年固定與跑道平行的,有的時候風向的改變甚至於可達到90度的正側風,飛行員必須隨時準備應付這些風向的改變,正常的落地階段與側風落地階段是截然不同的程序,側風落地要考慮的因素會比較複雜些,所以在這裡是有必要來跟大家一起討論的,一起來教學相長,在側風落地與側風起飛階段會多了一點點的困難性,主要是在於除了要保持準確的操控飛機起飛或落地之外,同時也要兼顧做側風修正的程序。

我來介紹通常最常用到兩種側風修正的方法,一種是『蟹行法』,另一種是『 側滑法』。首先先來看『蟹行法』的操作方式,參考一下圖片一

 

(圖片一)

 

這個蟹行方式在五邊操作時是一種比較容易的操作方式,但使用這種修正方式的條件是=>必須五邊進場高度要比正常較高一些,還有五邊的距離拉得也要比正常來的遠一些,這樣才會有充分的時間使用蟹行法來修側風所造成的偏流效應.

 

在實施蟹行法修正側風的時候,首先必須先建立好一個正確的航向,這個航向不是對正跑道的方向,而是與跑道產生適當的夾角,也就是說機頭面向迎風處,取出一個適當的夾角,請參考一下(圖片一)會比較容易了解,使用蟹行法時,一但建立好取出的航向後,是要一直保持這樣的飛行軌跡持續進場,雖然他的航向並不是在正確的跑道航向上,但是因為面對的是迎風面,它會抵消風所造成的飛行軌跡偏航問題,也就是說這樣的操作方式,事實上從空照圖看下去,你的飛行軌跡是會正確的在跑道延伸線上,而不會產生偏航,保持這樣的方式一直到飛機準備觸地之前,當距離地面非常接近的時候,(要準備仰轉之前),就必須將飛行的航向修正回與跑道同一個方向來準備降落,這是避免因蟹行法所取出的角度,在飛機觸地的時候起落架遭受不平衡的力距而產生扭轉,造成起落架損壞,如果五邊的進場距離還很遠,飛行員就有充分的時間可以選擇使用蟹行法來調整側風修正。

 

另外一項『側滑法』又是如何來使用呢?側滑法是一般比較常用到的方式,它的操作方式也會比蟹行法來的簡單些,它可以同時讓你修正側風,又可以同時維持在下滑道與跑道的延伸線上,軌跡比較不會偏離也好掌握,這種操作方式很簡單,簡單的說就是對迎風面建立坡度抵擋側風的效應,請參考(圖片二)。

 

(圖片二)

 

建立坡度的大小就要看當時側風的大小跟角度來決定,大家先看一下圖片二,可以很明顯的可以看的出來這種操作方式,增加坡度的大小是依據當時飛機受側風影響的橫移量來決定之,不過使用『側滑法』修正側風會有一個問題產生,就是建立坡度會讓飛機產生滾轉效應,您要注意到是建立坡度的同時必須配合使用一點反舵來使飛機維持平衡,抵銷滾轉效應,這樣就不會因為壓坡度所產生的滾轉效應而發生掉高度的問題,假如您是使用『側滑法』側風修正一直要持續到飛機快觸地的時候,就必須提前把機翼改平,避免單輪先著地,單輪著陸有可能會發生危險,要特別注意~請參考圖片三操作說明。

 

 

 

圖片三

 

此外~當遇到強大的正側風時,側滑法的修正方試,就要將迎風面的坡度加大許多,要注意到此刻飛機本身滾轉的慣性會跟著加大變遽,這樣的操作方式會造成不好的效果,建議這時候就要考慮減少坡度的使用,改換增加反舵的操縱量來一起配合協調,一樣可以達到修正更大的側風問題,而飛機滾轉的效應會大幅降低許多,不論是選擇哪一種側風修正的方式,最重要的就是你要學習如何能將一架飛機維持在跑道的延伸線上,也就是下滑道與跑道在同一條延伸線上,越早修正側風問題,就能越穩定的在這條線上安全的進場直到落地。

 

此外還是要重覆以前所提及的觀念問題,越早發現問題就能越早處理,越早處理問題就不會讓問題越演越烈,側風修正的問題也是相同的飛行觀念,先前不修正,等待快接近跑道時才大幅的修正,瞬間大幅度的改變飛行姿態,是非常危險的一件事,『莫非定律』必須隨時勞記在心,它會幫助你安全的完成每一趟愉悅的飛行~

 

全世界最大的飛機都要做側風修正了  那輕航機呢?

 

 

Many runways or landing areas are such that landings must be made while the wind is blowing across rather than parallel to the landing direction. All pilots should be prepared to cope with these situations when they arise.The same basic principles and factors involved in a normal approach and landing apply to a crosswind approach and landing; therefore,only the additional procedures required for correcting for wind drift are discussed here.Crosswind landings are a little more difficult to perform than crosswind takeoffs, mainly due to different problems involved in maintaining accurate control of the airplane while its speed is decreasing rather than increasing as on takeoff.

 

There are two usual methods of accomplishing a crosswind approach and landing—the crab method and the wing-low (sideslip) method.Although the crab method may be easier for the pilot to maintain during final approach, it requires a high degree of judgment and timing in removing the crab immediately prior to touchdown.

The wing-low method is recommended in most cases, although a combination of both methods may be used.

 

CROSSWIND FINAL APPROACH

The crab method is executed by establishing a heading (crab) toward the wind with the wings level so that the airplane’s ground track remains aligned with the centerline of the runway. [Figure 1]

This crab angle is maintained until just prior to touchdown, when the longitudinal axis of the airplane must be aligned with the  runway to avoid sideward contact of the wheels with the runway. If a long final approach is being flown, the pilot may use the crab method until just before the roundout is started and then smoothly change to the wing-low method for the remainder of the landing.

 

Crabbed approach.

The wing-low (sideslip) method will compensate for a crosswind from any angle, but more important, it enables the pilot to simultaneously keep the airplane’s ground track and longitudinal axis aligned with the runway centerline throughout the final approach,roundout, touchdown, and after-landing roll. This prevents the airplane from touching down in a sideward motion and imposing damaging side loads on the landing gear.

To use the wing-low method, the pilot aligns the airplane’s heading with the centerline of the runway,notes the rate and direction of drift, and then promptly applies drift correction by lowering the upwind wing.

 

[Figure 2] The amount the wing must be lowered depends on the rate of drift. When the wing is lowered,the airplane will tend to turn in that direction. It is then necessary to simultaneously apply sufficient opposite rudder pressure to prevent the turn and keep the airplane’s longitudinal axis aligned with the runway. In other words, the drift is controlled with aileron, and the heading with rudder.The airplane will now be sideslipping into the wind just enough that both the resultant flightpath and the ground track are aligned with the runway.

 

 If the crosswind diminishes, this crosswind correction is reduced accordingly, or the airplane will begin slipping away from the desired approach path. [Figure 3]To correct for strong crosswind, the slip into the wind is increased by lowering the upwind wing a considerable amount. As a consequence, this will result in a greater tendency of the airplane to turn. Since turning is not desired, considerable opposite rudder must be applied to keep the airplane’s longitudinal axis aligned with the runway.

 

In some airplanes, there may not be sufficient rudder travel available to compensate for the strong turning tendency caused by the steep bank. If the required bank is such that full opposite rudder will not prevent a turn, the wind is too strong to safely land the airplane on that particular runway with those wind conditions. Since the airplane’s capability will be exceeded, it is imperative that the landing be made on

 

Sideslip approach.

 

a more favorable runway either at that airport or at an alternate airport.Flaps can and should be used during most approaches since they tend to have a stabilizing effect on the airplane.

The degree to which flaps should be extended will vary with the airplane’s handling characteristics,as well as the wind velocity.