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The top picture is from Buccaneer and rest are from F4 FGR2. There's not any sealing mechanism between the joints, so these can’t be fuel or hydraulic related. They might have something to do with the blown air slaps/flaps systems, I'm not sure.

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4 Answers 4

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Yes they are engine bleed ducts, either for anti-icing purposes, or for blowing along the flap leading edge to improve the efficiency of the flap.

High temp ducts often depend on just a smooth metal flange that mates with its connecting duct to provide an adequate seal, with possibly some compression preload provided by the springyness of the duct when they are butted together. They don't have to be 100% air tight, just tight enough.

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  • $\begingroup$ Thanks for confirming my assumption, did some further research on bleed air application on F4, turned out it did have such system. The diagram also shows 3 sub pipelines around the folding mechanism, from main on the leading edge. $\endgroup$ May 12, 2023 at 16:03
  • $\begingroup$ The Phantom has blown flaps? $\endgroup$
    – John K
    May 12, 2023 at 16:27
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    $\begingroup$ according to this arc.aiaa.org/doi/pdf/10.2514/6.2018-0561 $\endgroup$ May 12, 2023 at 16:31
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According to the following cutaway of the Buccaneer, 53 and 67 seem to be good candidates for your answer i.e. ducts for the leading edge, aileron and flaps blowing system.

 Buccaneer cutaway

According to this other cutaway, the only system located in the outer wings of the F-4 is 78 and 123 i.e. the slat actuators.

 F-4 cutaway

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  • $\begingroup$ Did some further research, on F4 the bleed air system was implemented for boundary layer control, on lead slats and flaps $\endgroup$ May 12, 2023 at 15:56
  • $\begingroup$ @DanielYang: Very interesting discovery 👍 So the F-4 did have a boundary layer control like the Buccaneer $\endgroup$
    – sophit
    May 12, 2023 at 16:44
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Manage to find this document, unfortunately don't have the full access. https://arc.aiaa.org/doi/pdf/10.2514/6.2018-0561

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From Dowgwillo on boundary layer control, cited elsewhere:

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