This weekend I was on a Airbus A319, and I noticed that the flaps have small extensions at the location of the shockbodies (indicated in the picture with the red circles)

I was wondering what the reason is for these extensions?

My guess is that it could be to compensate for the lower local lift generation caused by the presence of the shock bodies, but I'm not sure. I'm also interested in knowing why they have different sizes at different locations.

enter image description here

  • 2
    $\begingroup$ My guess is that the top of the fairing has to be open allow room for the actuator hardware to move, so the flaps have those extensions to cover the section that is open. $\endgroup$
    – fooot
    Oct 5, 2015 at 17:28
  • $\begingroup$ .. and the lengths are the same when taken from the hinge. $\endgroup$
    – amI
    Nov 2, 2015 at 18:01
  • 1
    $\begingroup$ @fooot pictures of flaps retracted support your guess. When retracted, thoses flaps extensions cover the shockbodies (almost) perfectly. $\endgroup$
    – Manu H
    Nov 5, 2015 at 16:32

2 Answers 2


The anti-shock bodies also serve as fairings for the flap actuators. When the flaps are extended, the anti-shock bodies move down as the flap mechanisms extend. The upper surfaces of the anti-shock bodies are open to allow room for these mechanisms to extend.

The extensions to the flaps are to cover the openings of the anti-shock bodies when the flaps are retracted to provide a more aerodynamic surface. Evidently the outer locations have larger openings to cover.

Below is an image of a different aircraft and flap track design, but the principle is the same. You can see some of the hardware that sits in the fairings, and the covers that allow the hardware to extend out of the fairings.

Anti-shock bodies showing flap mechanisms

When the flaps are retracted, you can see that the flaps close out the top of the anti-shock bodies, and the outer position is closed out further aft.

A320 wing, flaps retracted

  • $\begingroup$ Great answer, perhaps you could add the picture from Manu H's comment to the question as well? I think it helps to illustrate your point. $\endgroup$
    – ROIMaison
    Nov 5, 2015 at 16:36

I'm not sure, but I think that those are trim tabs.

  • $\begingroup$ Trim tabs on flaps? They seem to be pretty solidly connected to the rest of the flaps. $\endgroup$
    – fooot
    Nov 5, 2015 at 16:08
  • $\begingroup$ Trim tabs are usually located on ailerons, rudders and elevators and rarely extend further the flight control surface, as highlight by those pictures $\endgroup$
    – Manu H
    Nov 5, 2015 at 16:27
  • $\begingroup$ Trim is used on control surfaces in order to keep the pilot from having to put constant pressure on the stick. Flaps don't have trim. $\endgroup$
    – reirab
    Nov 5, 2015 at 17:00
  • $\begingroup$ Aren't those flaperons, though? Airliners have mid-span ailerons that I think are also flaps. $\endgroup$
    – ptgflyer
    Nov 13, 2015 at 21:17

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