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Question: if my stall velocity is 20m/s, then...

If the airplane is travelling at a velocity greater than or equal to the stall velocity, can one assume the plane will not stall?

Can one assume that for a take off distance of 750m, as long as the velocity is greater than 20, the plane won’t stall (assuming constant angle of attack when take off)

Is this correct, or am I wrong somewhere? I just want to know generally please, in relation to lift and stall.

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    $\begingroup$ Does this answer your question? How does stall depend on angle of attack but not speed? $\endgroup$
    – Bianfable
    Commented Mar 11, 2022 at 9:30
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    $\begingroup$ Is the first answer to this question useful? aviation.stackexchange.com/questions/27706/… $\endgroup$
    – Dave Gremlin
    Commented Mar 11, 2022 at 11:04
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    $\begingroup$ How can you not want to think about AOA, and still want a valid answer? It can't be yes, and you won't accept no because AOA will be involved... the two linked topics cover the topic pretty well, I recommend read them, and if something remains unclear, press edit to refine the scope. And of course, welcome to the site, and please take a moment to check the How do I ask a good question? help page. $\endgroup$
    – user14897
    Commented Mar 11, 2022 at 11:15
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    $\begingroup$ I disagree with the question being closed. The OP is under the (very common) misconception that stall follows directly from low speed, but that's hardly a reason to close the question. Correcting a misconception is the very reason to ask questions about it. $\endgroup$
    – HiddenWindshield
    Commented Mar 11, 2022 at 19:15
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    $\begingroup$ Your confusion isn't clear at all. What is it about the definition of the term "stall speed" that you don't understand? $\endgroup$
    – Michael Hall
    Commented Mar 12, 2022 at 17:15

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As the angle of attack of an airfoil increases, the lift it generates increases -- at least, up to a point. Once it reaches that point, called the critical angle of attack, the lift begins decreasing again. This reduction in lift is called a stall.

However, airspeed also affects the amount of lift generated. The slower the airplane goes, the less lift is produced. Thus, if the pilot wants to maintain altitude while going slower, they need to increase the AoA to compensate for the reduced speed.

If the speed continues to deteriorate while the pilot is trying to maintain level flight, then the plane will eventually reach its critical AoA. The speed where that happens is called the "stall speed". But the stall only happens at that particular speed because the pilot is trying to stay level. If the pilot is willing to go into a dive, it's possible to fly below the defined "stall speed" without stalling*. Conversely, if the pilot is pulling up, this temporarily increases the AoA, which may make the plane stall even if it's above its "stall speed".

So, to answer your question, no, your thinking is not correct. It is possible to stall the plane, even if it's traveling faster than 20 m/s. The length of the runway is completely irrelevant.

*At least temporarily. To maintain that speed without stalling, you'd need to keep the wings unloaded, which would imply an ever-increasing rate of descent, resulting in the plane accelerating due to gravity. But you could, for a few moments, fly below "stall speed" without actually stalling.

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  • $\begingroup$ I’d say instead: “If the pilot is willing to lose altitude, it’s possible to fly below the stall speed.” Some planes just “mush” at AoAs above critical. But I would not say without stalling; they are “in the stall…” $\endgroup$
    – Jim
    Commented Mar 11, 2022 at 17:55
  • $\begingroup$ @Jim A plane "mushes" when part of the wing has stalled, but part of it is still flying normally. And, yes, it's possible to fly indefinitely in that condition. But it is also possible, by pushing forward (increasing the rate of descent), to fly below stall speed without any part of the wing stalled (i.e. without "mushing"). Granted, you can't stay like that for very long since you'll start picking up speed from the dive, but it is physically possible. $\endgroup$
    – HiddenWindshield
    Commented Mar 11, 2022 at 19:06
  • $\begingroup$ Yes, that’s what’s happening during stall recovery. But it’s more of a brief transient condition. I just thought your sentence was misleading because I took it to imply that you could reach a steady state of “flight” in that diving condition. It’s also what’s happening on the runway as you are accelerating- you just have the ground to hold you up. $\endgroup$
    – Jim
    Commented Mar 11, 2022 at 19:20
  • $\begingroup$ @Jim Good point, I added a footnote (since I couldn't figure out a clean way to put it in the actual sentence). $\endgroup$
    – HiddenWindshield
    Commented Mar 11, 2022 at 19:32

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