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Reading this article (on the Boeing 737 MAX saga; irrelevant), I found the following excerpt:

Boeing ultimately accepted Davies recommendation and, we understand, halted production of the 707 for 10-11 months, whilst a new fin was designed and installed. All existing 707s were then retrospectively modified. A ventral fin was also installed on some variants to prevent ‘fully stalled take-offs’ which the Comet was also susceptible to.

I tried to search, but I found nothing on "fully stalled take-offs", whether about the Comet or any other aircraft.

So, what is a "fully-stalled take-off"? Are some aerodynamic designs (or aircraft models) more susceptible to it?

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    $\begingroup$ Related: skybrary.aero/index.php/Take_Off_Stall $\endgroup$
    – quiet flyer
    Nov 1, 2019 at 15:05
  • $\begingroup$ I understand the concept of stalling during (i.e. right after) take-off, but I'm having a hard time conceiving what a "fully stalled take-off" really is – in the context, I fail to see how "fully stalled" is different to "stalled", for instance. $\endgroup$
    – user12873
    Nov 1, 2019 at 15:33
  • $\begingroup$ The ventral fin was added to improve yaw stability. It's implausible that it could inhibit stalling, of any kind, on the 707 or Comet or anything else. $\endgroup$
    – Camille Goudeseune
    Nov 1, 2019 at 15:53

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A "fully-stalled take-off" is an attempted takeoff where the elevator has too much authority. This can cause the aircraft to rotate to an excessive nose up attitude, which can exceed the stall angle of attack, before takeoff speed is attained.

Ventral fins were added to some B707s to improve yaw control, and prevent over-rotation. Over rotation which could lead to a "full stall at takeoff".

https://en.wikipedia.org/wiki/Boeing_707

The British Air Registration Board refused to give the aircraft a certificate of airworthiness, citing insufficient yaw control, excessive rudder forces, and the ability to over-rotate on takeoff, stalling the wing on the ground (a fault of the de Havilland Comet 1). Boeing responded by adding 40 inches to the vertical stabilizer, applying full instead of partial rudder boost, and fitting an underfin to prevent over-rotation.

enter image description here

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    $\begingroup$ How does the ventral prevent over-rotation? Is it meant to serve as a geometric tail strike barrier? $\endgroup$
    – JZYL
    Nov 1, 2019 at 17:27
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    $\begingroup$ Yes, it would be a physical barrier to over rotation. $\endgroup$
    – Mike Sowsun
    Nov 1, 2019 at 17:56
  • $\begingroup$ So the idea is that FULL aft stick input (or however much it takes to strike the tail) may be allowed to result in a tail strike but must not result not a stalled attitude, as long the main wheels are still on the ground? So the problem may be prevented either by a physical barrier or by limiting elevator authority? $\endgroup$
    – quiet flyer
    Nov 1, 2019 at 20:19
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    $\begingroup$ @quietflyer It's referred to as Vmu, minimum unstick speed, and is now required to be demonstrated for certification. In the case of early rotation the speed at which the last main gear leaves the ground. The aircraft must then climb out without stall. Here's a video of the A380 Vmu test. $\endgroup$
    – Gerry
    Nov 1, 2019 at 22:17
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    $\begingroup$ @Sean You are correct andI have edited my answer. $\endgroup$
    – Mike Sowsun
    Sep 12, 2020 at 16:35

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