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I watched The Insane Engineering of the 787 by Real Engineering. He just gave short detail about the HLFC(Hybrid Laminar Flow Control) panel and mentioned their purpose isn't available online. I found the following from flight global:

HLFC surfaces are designed to suck in the surface airflow, allowing the boundary layer to remain attached, moving the onset from laminar to turbulent flow further back along the surface, reducing overall drag.

So why they aren't mounted under the pressure side of the wing same as on the horizontal stabilizer? It would decrease the drag significantly. My other concern, the flow is more turbulent on the suction side. Isn't it reasonable to mount an HLFC panel on the suction side rather than the pressure side of control surfaces?

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  • $\begingroup$ You're talking about a technology which is currently tested, not a production solution. $\endgroup$
    – mins
    Commented Oct 3, 2021 at 17:42
  • $\begingroup$ @mins Aren't they already on 787? $\endgroup$
    – Auberron
    Commented Oct 3, 2021 at 17:49
  • $\begingroup$ Yes on the fin, not on the wing. There are studies to use HLFC on the wing, which may be in production near 2025-2030 to meet CO2 scheduled improvements requested by EU and other regulating bodies. The problem is to find a balance between additional weight from HLFC system and fuel consumption reduction, while at the same time adapting the new engines to come to the wing design. $\endgroup$
    – mins
    Commented Oct 3, 2021 at 18:21
  • $\begingroup$ "their purpose isn't available online": The principle of laminar flow is studied since a long time, this is not secret. See this article for more recent work. $\endgroup$
    – mins
    Commented Oct 3, 2021 at 18:35

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The underside of the horizontal stablizer is (generally) the suction side, as it is producing downwards lift to keep the plane stable.

The HLFC panels shown in the video (screeshot below) are too small to make any meaningful difference to the flow, so they are most likely some sort of access doors or measuring devices. These can be see, at least on vertical stabilizer on some pictures of tails of 787-10. screenshot from video

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    $\begingroup$ Each square is supposed to be the outlet door of the suction system. Air enters through holes around the leading edge, and is rejected by a pump with this door. Better image. $\endgroup$
    – mins
    Commented Oct 3, 2021 at 19:24
  • $\begingroup$ Thanks! So this is a "local" system, with no functional parts outside the fins. $\endgroup$
    – Jpe61
    Commented Oct 3, 2021 at 21:37

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