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On commercial flights it often feels like the plane gets faster just before touching down. What creates that sensation?

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  • $\begingroup$ Are you sure it's not just subjective? It's been a while since I've flown commercial, but I don't remember any such feeling. And I don't notice a "feeling" in light airplanes, other than the visual sensation from being closer to the ground. $\endgroup$ – jamesqf Sep 7 at 1:14
  • $\begingroup$ @jamesqf I am not sure what a feeling could be, if not subjective. $\endgroup$ – Daniele Procida Sep 7 at 22:24
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The aircraft flares just before touching down. It descends with a constant velocity, and just before touching down pulls the nose up to reduce the descent. This results in a higher angle of attack, more lift, and a vertical deceleration of the airplane. A passenger perceives this vertical deceleration as a force. Direction of the force is straight down and the aircraft is nose up, you're leaning back, so there is a component of (gravity + vertical deceleration) that pushes you into the back of your seat.

This same effect is used in flight simulators with a motion base. Upon accelerating, the simulator pushes forward like the aircraft does, but also slowly rotates backwards so that the pilot feels sustained seat back pressure. He cannot see the leaning back angle inside the simulator because the horizon of the projected outside visual image does not move. As happens in the aircraft: look forward in the aircraft and your view of the inside of the aircraft is always the same, irrespective of aircraft angle.

enter image description here So for your eyes there is no apparent tilt, the inner ear senses rearwards force, and there is increased pressure from the seat backrest. The brain translates this into perceived forward acceleration.

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    $\begingroup$ In other words: you are being accelerated downwards into your seat by gravity as well as the seat being accelerated upwards into you by the flare, but you think that your seat is being accelerated forwards into you. $\endgroup$ – Jörg W Mittag May 25 '17 at 8:18
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    $\begingroup$ Gravity - yes. Additional upward acceleration from flare - yes. But your seat is tilted backwards, that is why the back feels some of the vertical acceleration. $\endgroup$ – Koyovis May 25 '17 at 8:23
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    $\begingroup$ @mins During rotation the flare action would contribute a small amount of reduction in the apparent "backwards" force due to the rotating gravity vector, but the movement is slow enough that the effect is minimal. The dominant force would be gravity. 6 degrees of flare produces about 1m/s^2 apparent acceleration force into the back of the seat - about the same as the acceleration you would feel in a normal car accelerating from a stop (driving conservatively). $\endgroup$ – J... May 25 '17 at 11:40
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    $\begingroup$ @mins Rotational acceleration is pretty small anyway. I'm assuming you're referring to rotational acceleration, not velocity, since you mentioned inertia. $\endgroup$ – Koyovis May 25 '17 at 12:41
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    $\begingroup$ @Koyovis: I don't think a leaning chair will help, it's not about the existence of a gravity component backwards in a static situation (nobody will challenge that), it's about how all forces combine during the flare. As for the rotation under elevator deflection being around a center above the passenger seats in a A320... I'm lost :-) $\endgroup$ – mins May 25 '17 at 16:50
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Aside from the sensory effects already mentioned, there are also occasions when the pilot does indeed add a bit of power shortly before touchdown. See, for example, comments #5, #16, and #17 from Adding Power Just Before Touchdown.

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    $\begingroup$ Yes, the sound of the engines spooling up will further add to the sensory inputs. $\endgroup$ – Koyovis May 26 '17 at 1:41
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Visual perception of your perspective; as the aircraft gets closer to the ground your field of view constricts and you are closer to terrain and other structures, making them appear to move faster past the jet than at altitude.

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    $\begingroup$ This is not only a visual sensation, because I recall this same feeling apart from looking out the window. It feels as if you are being pushed back in your seat. $\endgroup$ – PV22 May 25 '17 at 0:59
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I think what you're feeling is the brief float due to the ground effect. Within about 10 feet of the ground the air being forced down by the wing encounters the resistance of the ground. It actually arrests the downward motion unless the angle is pretty steep and that float gives a slight sinking feeling that feels like acceleration. Sometime too the pilot will add a little throttle to transition out of the ground effect a little less abruptly.

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  • $\begingroup$ Yes ground effect helps in arresting the downward velocity. But how does that transform into a sensation of forward acceleration? $\endgroup$ – Koyovis May 28 '17 at 7:23
  • $\begingroup$ You'd have to instrument it to see the small changes and there may be a small decrease in drag. What we feel in the air isn't what necessarily what is really happening which is why we fly by instruments and not feel in low visibility situations. Our senses fool us very readily. $\endgroup$ – MTCWBY Jun 5 '17 at 18:48
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As the plane descends into ground effect, it may actually accelerate if the engines are producing enough thrust, since in ground effect the plane requires much less power to keep "flying". Power from the engines will translate into speed, if not height.

I don't know if it happens often in real world landing configurations, but it's certainly possible. To make it happen for sure, set the power so that the plane is just barely descending, and when it gets into ground effect, it will certainly speed up measurably.

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when the flaps are lowered more power is applied to make up for the losses sometimes I fell a drop in speed and then a little surge in acceleration.

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    $\begingroup$ Welcome! Do you suggest the flaps are lowered just before touchdown? $\endgroup$ – mins May 27 '17 at 12:16
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It does accelerate just before touching down in case something goes wrong with the landing gear and the plane has to immediately take off again.

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  • $\begingroup$ DV - I'm sorry for any confusion, but this is not what I am referring to. I am asking about a phenomena felt during a routine and successful landing. $\endgroup$ – PV22 May 26 '17 at 15:12
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    $\begingroup$ Welcome to aviation.SE! Do you have any reference for this? It does happen during aircraft carrier landings, but that's a very special case and not really what this question is about. $\endgroup$ – Pondlife May 26 '17 at 15:12

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