《知識》了解飛機起飛速度（V1、VR 及 V2） Understanding Aircraft Takeoff Speeds: V1, VR and V2

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當飛機在跑道上加速起飛時，不論是正駕駛還是副駕駛操作，都會確認 V1、VR 及 V2 這幾個速度。這篇文章就要來快速帶你認識這三個速度代表的意思。

這三個速度都是飛機起飛過程中的關鍵速度。它們並不是固定的數值，而是會根據每次飛行的實際條件計算，例如：跑道長度、飛機重量、風速與風向、機場氣壓、氣溫及襟翼設定等。

飛行員會將相關資料輸入飛行電腦，系統再依照當時的飛行條件計算出適合這次起飛的 V1、VR 和 V2。

V1｜起飛決斷速度（Takeoff Decision Speed）─ 決定是否繼續起飛的速度

在 V1 之前，如果發生引擎故障或其它需要中止起飛的狀況，飛行員通常可以選擇中止起飛，因為此時剩餘跑道長度仍然可以讓飛機減速並停下。

但當飛機超過 V1 後，即使發生引擎故障等異常狀況，飛行員原則上會繼續起飛。這是因為此時飛機速度已經太快，剩餘跑道無法讓飛機安全停下，而衝出跑道（煞不住）。此時先飛到空中再做處理反而比較安全。

VR｜抬輪速度（Rotation Speed）─ 飛行員開始拉起機頭的速度

當飛機加速到 VR 時，飛行員會開始向後拉駕駛桿，使機頭抬起離開地面。

V2｜安全起飛速度（Takeoff Safety Speed）─ 確保飛機能安全爬升的速度

V2 是起飛後非常重要的安全速度，主要用於確保飛機在起飛階段，即使發生一具引擎失效，仍能維持規定的爬升性能。

在雙發或多發飛機的起飛過程中，即使其中一具引擎失效，飛機仍必須具備足夠的性能維持安全爬升。因此，V2 會根據飛機重量、襟翼設定及其他起飛條件等因素計算。

簡單來說：

• V1：決定要不要繼續起飛
• VR：開始拉起機頭
• V2：起飛後維持安全爬升

接下來就一起來看看 747-400 的實際起飛影片，實際來應用一下吧！✈

補充：影片 0:33 秒時，飛行員喊出的「80 knots」，是確認速度表數值與加速狀況是否正常的指標速度。

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Understanding Aircraft Takeoff Speeds: V1, VR and V2

As an aircraft accelerates down the runway for takeoff, the pilots will monitor and call out three important speeds: V1, VR, and V2. In this article, let's take a quick look at what these three speeds mean.

These are all key speeds during takeoff. They are not fixed numbers. Instead, they are calculated for each flight based on the actual conditions, such as runway length, aircraft weight, wind speed and direction, air pressure, temperature, and flap settings.

The pilots use this information along with the aircraft's performance data to calculate the appropriate V1, VR, and V2 for the takeoff.

V1｜Takeoff Decision Speed ─ The speed that determines whether to continue the takeoff

Before reaching V1, if an engine failure or another serious problem occurs, the pilots can usually choose to reject the takeoff. At this point, there should still be enough runway available for the aircraft to slow down and stop safely.

Once the aircraft reaches V1, the pilots will normally continue the takeoff, even if an engine failure occurs.

This is because the aircraft is already traveling at a high speed, and there may not be enough runway remaining to stop safely. In this situation, continuing the takeoff and dealing with the problem in the air can be safer than trying to stop on the runway.

VR｜Rotation Speed ─ The speed at which the pilots start raising the nose

When the aircraft reaches VR, the pilot begins to pull back on the controls, raising the nose of the aircraft and starting the rotation for takeoff.

V2｜Takeoff Safety Speed ─ The speed that helps ensure a safe climb

V2 is a very important safety speed after takeoff. It is mainly used to ensure that the aircraft can maintain the required climb performance even if one engine fails during the takeoff phase.

For twin-engine and multi-engine aircraft, the aircraft must still have enough performance to maintain a safe climb even after losing one engine.

Therefore, V2 is calculated based on factors such as aircraft weight, flap settings, and other takeoff conditions.

In simple terms:

• V1: Decide whether to continue the takeoff
• VR: Start raising the nose
• V2: Maintain a safe climb after takeoff

At around 0:33 in the 747-400 cockpit takeoff video above, the pilot calls out “80 knots.” This is an important check to confirm that the airspeed indication and aircraft acceleration are normal.