The basic structure and photos have already been explained on this site and on Wikipedia:

Looking at it, I understood that the pin and pivot that make up the axis of rotation and the link bar provided in front of that axis form the basic mechanical structure.

However, it is not clear why the structure produces traces of contact only in front of the axis on the undersurface skin of the wing.

swing arc on the underside of a wing
Modified from an answer here

My guess is that it is equipped with a guide contact. However, such a policy stresses thin skins. I also speculate that the skin is not an accurate plane. That seems absurd.

I also considered the deformation of the pylon as a candidate, but from the viewpoint of the aerodynamics of the payload, I thought that the upward aerodynamics would not be applied to the front because it moves downward from the head when falling.

Please tell me why the structure has an arc mark in front.

  • $\begingroup$ 1) maybe it produces an arc on the trailing edge too, but you can't see it in these images because of the angle. 2) The skin is thin, but maybe it's reinforced in these areas to accept the stress of the contact/motion. Also, use @ to address a user by name, it will actually send them a notification. $\endgroup$
    – FreeMan
    Apr 29 at 12:53
  • 3
    $\begingroup$ Are you sure that’s not a painted arc to show the sweep limits of the pylon? $\endgroup$
    – Jim
    Apr 29 at 13:23
  • $\begingroup$ Maybe making the geometry close-fitting enough that the pylon rubs in front as it rotates, creates a more rigid structure? $\endgroup$ Apr 29 at 13:29
  • 2
    $\begingroup$ “My guess is that it is equipped with a guide contact. However, such a policy stresses thin skins.”—it's OK to stress the skin where you know about it and can strengthen it appropriately. In fact it's better than random stress somewhere you don't expect it as would happen if it wasn't supposed to touch, but occasionally did as it flexes in flight. $\endgroup$
    – Jan Hudec
    Apr 29 at 13:31

2 Answers 2


Having put on probably hundreds of pivot pylons on an F-111E back in the late '70's, the pylon is NOT attached to the skin.

There is one large attachment collar. Teeth on the pylon meshes with teeth on the wing hardpoint, to manage the rotation.

All the wiring for the pylon and weapons features feed through that hollow collar. It is actually a real PITA to install these. IIRC there are 7-9 cables that feed through here, some of them reasonably large.

Illustrated F-111 pivot pylon, courtesy ResearchGate.com


The F-111 has 4 hardpoints on each wing, but only the inner two on each wing pivot.

To address the original question:

Just a supposition on my part for the Tornado and that black stripe, but I would surmise that is is an extra paint layer, to wear away as the pylon pivots back and forth, being rubbed by the flex material at the front. An indicator of how much paint has worn away...once you see grey, repaint the black arc.

To address a comment...

If there is contact between the wing skin/paint and the flex material at the front of the pylon, the pain is going to get rubbed off over time as the pylon rotates back and forth. Again, supposition because I never worked on the Tornado, but maybe a rough wear indicator.

  • $\begingroup$ This does not actually answer the question? $\endgroup$ Apr 29 at 16:38
  • $\begingroup$ "being rubbed by the flex material at the front."-- can you expand your answer to say a little bit more about this? What is the "flex material"? $\endgroup$ Apr 29 at 16:52
  • $\begingroup$ Thank you for your wonderful answers. I understand that the fact that the operating range is marked is also the case in the photo. I also found that the application of a structure that allows contact is sufficient for the skin to withstand. I also understood that it could actually be scratched for some reason. I've never heard of the existence of a stretchable sleeve. Providing many detailed photos was very helpful to me. Thank you everyone. $\endgroup$ Apr 30 at 0:07

enter image description here
Source: primeportal.net: 1, 2

On the Tornado, there is a sleeve mechanism (annotated above) to maintain the gap as it pivots due to the changing wing curvature as it does so; compare left and right.

Also, not all paint schemes have the arc marking, which is possibly for checking the alignment/position. Below is the marking with a hardpoint removed, and a closer look at the sleeve:

enter image description here
Sources: primeportal.net; britmodeller.com


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