This is what I know:

  • $V_1$ is the takeoff airspeed after which the aircraft must take off, no matter what happens after $V_1$ has been reached. That's the easy part (I think).
  • $V_R$ is the rotation airspeed

Are there any other $V$-speeds?

What I'm specifically curious about:

  • Is $V_1$ related to runway length?
  • Is there an absolute maximum $V_1$ for each aircraft type? If so, can it vary based on conditions (takeoff weight, density altitude, etc.)
  • Are there circumstances where $V_1$ is higher than $V_R$? If so, does that mean that $V_1$ is never called on a normal takeoff? (this is the case for most light aircraft, but I guess the whole concept is not applicable in that case)
  • What exactly is $V_2$?
  • Is there a $V_3$? (and so on)

Anything else worth knowing about $V$-speeds?

up vote 4 down vote accepted

$V_1$ is takeoff decision speed. It is based upon:

  • Runway length
  • Temperature
  • Reduced thrust takeoff
  • Takeoff weight
  • Takeoff flap setting

If $V_1$ is higher than $V_R$, then (as far as I am aware), $V_1$ will be adjusted to be the same as $V_R$. You have to make the decision to takeoff by the time you rotate, so it does not make much sense to have $V_1$ higher than $V_R$.

$V_2$ is takeoff safety speed. During a one engine inop takeoff we would accelerate to and climb at this airspeed to our acceleration height (a height we could level off at and be safe from obstacles while we further accelerate). We also referenced certain flap transitions on takeoff to $V_2$ (e.g. $V_2+15$ - flaps 0)

To address the rest of the question, $V_1$ and $V_2$ are primarily used in large aircraft. In light twins you also need to be aware of $V_{MC}$. $V_{MC}$ is the minimum controllable airspeed with an engine inop. In particular you do not want to be slower than this airspeed during climbout in case of engine failure.

  • 4
    A single engine takeoff is pretty scary in a 747! (You might want to use "one engine inop"). :-) – Lnafziger Jan 23 '14 at 2:42

Stretching my memory, but I'll try, and others can correct what I get wrong. Think 'balanced field length'. Given an engine failure, $V_1$ is that speed at which if you abort you will be able to stop at the very end of the runway. $V_1$ is that speed at which if you choose to fly you will lift off at the very end of the runway. $V_1$ is that speed which if you are above and you abort you will go off the end of the runway (Kalitta 747 freighter a few years back tried to abort at $V_1+30$).

The longer the runway, the higher your $V_1$. Enough runway and $V_1$ can exceed $V_2$, but that doesn't mean anything because you're going to rotate at $V_2$. If you choose to stay on the runway after $V_2$, you begin moving into an area limited by max tire heating. Maybe you can say that max $V_1$ is the max tire speed? I don't know.

Can't remember a $V_3$.

VMO and VMC are both important

VMO = Maximum Operating Speed, a structurally safe maximum speed which varies with altitude. For example with an emergency descent in a B777 the VMO is 310kt IAS, but in level flight it is 330 KIAS. As you climb the air thins so the true airspeed increases.

VMC = Minimum Controllable Speed with one engine inoperative, gear retracted with CG at most rearward limit, bad engine at idle but not feathered (if propellor)

  • 2
    How is the VMO relevant to the question? – Thunderstrike Jun 20 '14 at 0:27

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