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Inboard aileron of a jetliner

The picture I took here is left wing of a jetliner and it shows how the flap works during take off and landing.

In that video is the inboard aileron, and it shows that the inboard aileron is not firmly controlled. It is like it is swinging up and down.

My question is, why does it look like it swings? Is it intended to be so? If yes, why?

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    $\begingroup$ All I see is the aileron being actuated as the pilot (or autopilot) flies the approach. $\endgroup$
    – Jim
    Commented Mar 16, 2022 at 2:44
  • $\begingroup$ @Jim, in 4:04, it is still swing even just exactly before touch the ground, which in that situation should no more rolling control. $\endgroup$ Commented Mar 16, 2022 at 3:07
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    $\begingroup$ Why not? The pilot flies the aircraft all the way onto the ground and beyond. $\endgroup$
    – Jim
    Commented Mar 16, 2022 at 3:08
  • $\begingroup$ Also, at 4:04 the plane is still in the air. It doesn’t land until closer to 4:16. $\endgroup$
    – Jim
    Commented Mar 16, 2022 at 3:15
  • $\begingroup$ If you look carefully, you can also see the ailerons swing up and down in a seemingly "unfirmly controlled" manner. $\endgroup$
    – Jpe61
    Commented Mar 16, 2022 at 6:00

1 Answer 1

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The flaperon points downwards to function as a flap, and moves up/down to induce rolling moments, which may be necessary to keep the wings horizontal when for instance wind gusts or turbulence are attempting to roll the plane.

So what you see is the roll control to maintain level flight, the outboard ailerons move together with the corresponding flaperons at lower airspeeds, which can be seen in the video as well.

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  • $\begingroup$ First, is its official name flaperon? I searched over the net before I posted this, I got [here] (history.nasa.gov/SP-367/chapt2.htm) that its name is inboard aileron. Sorry if I was wrong. $\endgroup$ Commented Mar 16, 2022 at 21:10
  • $\begingroup$ If we see in 0:54, it began to "swings", just one or two second after it left the ground. Is rolling performed so immediately after it left the ground? $\endgroup$ Commented Mar 16, 2022 at 21:13
  • $\begingroup$ Maybe it is good to see 0:54 just a second after it left the ground it is already "swings", and 4:14, less than a second before it touch the ground it is still "swings". $\endgroup$ Commented Mar 16, 2022 at 21:22
  • $\begingroup$ @AirCraftLover A flaperon is an aileron whose "neutral" position is lowered below the normal chord line for low speed flight to provide double duty for roll control and additional lift, so it's accurate to call it a flaperon. They are also called drooping ailerons. But as far as I know, Boeing just calls them inboard ailerons whether they droop with the flaps or not, although in that case flaperon is a more accurate term. $\endgroup$
    – John K
    Commented Mar 16, 2022 at 22:46
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    $\begingroup$ @AirCraftLover They are used for high speed roll control when fully up but moving differentially. Low speed control when drooped and moving differentially. They are used as ailerons in all flight regimes, whereas the outboard ailerons may be idled at high speeds. It's just that when flaps come out, they still work as ailerons, but also droop with the flaps. $\endgroup$
    – John K
    Commented Mar 17, 2022 at 4:23

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