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One can notice the forward fairing of pylon is very shiny and metallic. This is quite unique and I do not find it in other aircraft. Why is this?

Does it serve any specific aerodynamic purpose or does it house any anti-icing provisions?

a350 zoomed in

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    $\begingroup$ It is definitely the first panel of the engine pylon and is indeed left unpainted. Would be interesting to know why. $\endgroup$
    – sophit
    Commented Nov 15, 2022 at 22:45
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    $\begingroup$ It's not heated. It's probably made of a material that is difficult to obtain paint adhesion, say titanium or some grade of stainless, or doesn't need paint because it's a corrosion resistant material and they are saving a few ounces, or some other reason known only to insiders. $\endgroup$
    – John K
    Commented Nov 16, 2022 at 13:42
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    $\begingroup$ @JohnK: that's titanium, right. Is it really difficult to be painted? The Blackbird was definitely painted :) $\endgroup$
    – sophit
    Commented Nov 16, 2022 at 14:47
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    $\begingroup$ Titanium requires elaborate processes to get paint to stick, acid etching, sometimes sandblasting. They may just leave the paint off BECAUSE it's titanium or stainless (more likely) so they can leave it unpainted without worrying about corrosion. $\endgroup$
    – John K
    Commented Nov 16, 2022 at 17:55
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    $\begingroup$ It is also specifically covered during manufacturing: flickr.com/photos/131621852@N02/33312795343 $\endgroup$
    – ocirocir
    Commented Apr 18, 2023 at 7:19

2 Answers 2

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Not just the Rolls-Royce XWB, but also the R-R Trent 7000 on the newer A330neo:

Rolls-Royce Trent 7000
LMP 2001, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

Airbus made changes to the forward mounting of the engine by incorporating a "cradle" system under that metal part.

The cradle's main function is to reduce the inlet deformation encountered during e.g. take offs.

The specifics are hard to tease out of the patent legalese, but there's mention of impact resistance to that now more forward structural area (which would explain why the cover is now metal—the patent mentions the "Fan Blade Out", and the location of the new system is indeed inline with the trajectory of an ejected blade). Photos after flight testing also show this panel removed, which hints at a post-flight visual inspection of the structural integrity of the new system with respect to the aforementioned inlet deformation (a photo is linked at the end of the answer).

Note that item 31 in the drawing below is optional according to the patents; item 24 (in the first linked patent) not shown below is what you're asking about, but the drawing shows what is now under it. The routing of hydraulics and electrical also goes through the cradle, and there's no mention of an anti-ice system there.

As to why it's not painted, that could be:

  • If the panel's skin is load bearing, which is likely since the function of the new unit is absorbing the loads that lead to inlet deformation, i.e. under cyclical loads, the paint would crack—similar to this big unpainted joint on the A380 (Q&A); and/or:
  • Weight and manufacturing cost/time saving as paint for corrosion resistance is not needed for titanium parts (ref: Henriques, Vinicius AR. "Titanium production for aerospace applications." Journal of aerospace technology and management 1.1 (2009): 7-17.), which the A350 makes use of in the pylon and other systems.

patent showing what's below item 24
Public domain from one of the patents assigned to Airbus

showing the aforementioned panel removal
Photograph: H Gousse/Airbus/PA via theguardian.com; alternate link via aerospace-technology.com
Photo showing the aforementioned panel removal

Consider this a good-enough answer from what is publicly made available by Airbus. It should go without saying that patents don't spill all the beans.

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  • $\begingroup$ This doesn't explain why the panel needs to be unpainted. Metal can easily be painted without affecting impact resistance. In fact, you want to paint critical metal pieces to minimize possible weakening due to corrosion. $\endgroup$
    – user71659
    Commented Oct 3 at 19:11
  • $\begingroup$ @user71659: If it's subject to concentrated cyclical loads, the paint would crack. The A380 also has unpainted metal joints for that reason (see this older Q&A of mine), but keep your downvote. $\endgroup$
    – ymb1
    Commented Oct 3 at 19:58
  • $\begingroup$ Your answer doesn't say anything about concentrated cyclical load, you bold the words "impact resistance". The answer is incomplete, as evidenced by some further explanation you had to give in the comments. $\endgroup$
    – user71659
    Commented Oct 3 at 20:16
  • $\begingroup$ @user71659: "The cradle's main function is to reduce the inlet deformation encountered during e.g. take offs." // The panel's skin would be subject to the same. The question didn't ask why it's not painted; if it had, I would have remembered to make that remark; but instead of waiting for a response, you decided: "Nah, this answer isn't useful one bit" (see the help center, unless they changed it); so as I said, keep the DV. $\endgroup$
    – ymb1
    Commented Oct 3 at 20:21
  • $\begingroup$ The cradle does that, but it's not the "forward aerodynamic structure" in the patents. A easy method to prevent loading is to let it float over the rear structure or add compliance in the mounting hardware. This answer lacks an explanation of why the skin/forward aerodynamic structure is loaded (or even a mention that it is loaded), and only points out the cracking problem in the comments. $\endgroup$
    – user71659
    Commented Oct 3 at 20:26
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You figured it out when you wrote the question. It's because the engine nacelles are equipped with anti-icing heaters powered by air from a compressor port, and painting those areas would be counter-productive. Same with the inboard sections of the wings.

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    $\begingroup$ According to the ice and rain protection scheme for the A350-900, with respect to the engine and wing protection, the engine nacelles' air intake (lips of the nacelles) and slats 3, 4 and 5 (outboard of the engines) can be heated (for anti-ice) by bleed air. $\endgroup$
    – user22445
    Commented Nov 16, 2022 at 2:38
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    $\begingroup$ Can you update with relevant sources @JuanJimenez? I tried to look up and found what @757toga says is correct. I cannot find any pylon heaters but only nacelle heaters. smartcockpit.com/docs/… $\endgroup$
    – karthikeyan
    Commented Nov 16, 2022 at 5:48
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    $\begingroup$ You won't get ice accretion on areas like that unless it's runback ice and cowls are usually evaporative heating to prevent that. The A350 anti-ice system description doesn't mention a heated panel. $\endgroup$
    – John K
    Commented Nov 16, 2022 at 13:33
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    $\begingroup$ @JuanJimenez But the A350 is powered by RR Trent XWB, not GE engines. I haven't seen this part unpainted on other RR Trent engines, or any GE engines for that matter. $\endgroup$
    – Bianfable
    Commented Nov 16, 2022 at 16:31
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    $\begingroup$ The patent does NOT show the shiny metal plate on the pylon being heated. Fig 2 is a cross-section of the inlet cowl at the 12 o'clock position. I believe the drawing is being mistaken for a drawing of the forward end of the pylon. Accordingly, Item 16 is the outer wall of the inlet cowl, not the shiny plate of interest. $\endgroup$
    – Pete P.
    Commented Jan 23, 2023 at 17:30

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