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Watching this short stall test video for the MD-11, one can notice obvious buffeting (starting at about 0:04) of the tail section, while at the same time – at least apparently – there doesn't seem to be any major buffeting of the wings.

I've also read Why are aircraft designed so that the wing stalls before the tail?

Considering that vision (especially in a degraded old video) isn't a great gauge for what's happening, I thought to ask this question with two related components:

  1. Are we really watching the horizontal stabilizer stalling first?
  2. Either due to a bad design, CG issues, or trim errors, is it possible to have the tail start buffeting before the wing, but not stall before it?

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    $\begingroup$ I have a question for the composer: WHY? $\endgroup$ – Todd Wilcox Apr 20 at 4:56
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    $\begingroup$ That's the 80s/90s for you ;) $\endgroup$ – Digital Dracula Apr 20 at 5:41
  • $\begingroup$ Ah, the past: when the present was still future. $\endgroup$ – Dohn Joe Apr 20 at 7:49
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The entire tail is shaking (not just the horizontal stabilizer) not because it's stalling but because it is in the turbulent wake of the main wing. The tail is generating downforce as you can see from the up elevator. The main wing's nose down pitching moment increases when the center of pressure shifts aft at stall, as well as the change in the overall center of lift outboard and aft due to wing sweep as the root stalls with the outer end still flying.

The increase in pitching moment exceeds the downforce that the tail is able to produce, and the wing wins the force balance tug-of-war with the tail, and the airplane pitches over.

If the tail itself stalled, the nose would pitch over radically from the near complete removal of downforce, as if the pilot suddenly shoved the stick forward. That's not what is happening in the video. When this happens the tail's local AOA can increase further due to the pitch over and and a partially stalled tail can stall completely as if you sawed it off, and the airplane ends up pointed at the ground, as demonstrated in this testing in a Twin Otter.

I recall another incident in in a Twin Otter in the Canadian Arctic where tail stall was induced by the pilot pitching over hard after a zoom climb right after takeoff. Extreme pitch rotation at low speed means very high local AOA at the tail's leading edge. The pitch over rotation cause the horizontal tail's stall AOA to be exceeded when the pilot re-applied up elevator, and once exceeded it just got worse, and the Twin Otter just pitched over straight into the ground.

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What you see here is not the actual stall of the horizontal stabilizer but the "rudder rattle" that indicates that the stall of the main wings is just about to happen. Airplanes are designed to have this "rudder rattle" as a mechanical way to warn the pilot.

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    $\begingroup$ I am not sure if "designed to have" is the best description. Stabilizer simply ends up in the massively turbulent airflow produced by high AoA main wings . Even if this is a convenient stall warning indicator, I do not think there was any primary design effort towards just this behavior, it is more of a consequence. $\endgroup$ – Martin Apr 19 at 12:49
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    $\begingroup$ @Martin When I started my career as a glider pilot I was thought so. And I'm pretty sure that it could be easily avoided by placing the horizontal stabilizers somewhere else or making them stiffer. $\endgroup$ – Timothy Truckle Apr 19 at 13:05
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    $\begingroup$ Martins answer makes sense to me. The flow separation on the main wing would cause a very turbulent stream crossing the horizontal stabilizer. $\endgroup$ – seattle272SP Apr 19 at 14:43
  • $\begingroup$ I decided to eventually accept John's answer, as the more elaborate, providing detailed analysis. $\endgroup$ – Digital Dracula Apr 20 at 3:01
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    $\begingroup$ @DigitalDracula never mind. I'm a big boy and I can deal with that. ;o) $\endgroup$ – Timothy Truckle Apr 20 at 6:27

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