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I was looking how speed is distributed on this B747 airfoil:

enter image description here
Source.

Nearly all of the upper surface has air flowing above Mach 1. I'm wondering if this is frequent for commercial airliners to use supercritical airfoils? I'm particularly interested in the A330 case.

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    $\begingroup$ those are 2/3 different questions, which one do you want answered? What's the point of the image? $\endgroup$ – Federico Apr 10 '17 at 16:22
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Supercritical aerofoils are definitely widespread in modern airliners, including the A330. In fact, the A300 which is the predecessor to the A330 was one of the first airliners to fly with a supercritical wing.

The reason for this is that maintaining slightly supersonic flow over the majority of the upper surface keeps it at high speed, hence producing low pressure and lift for longer and it also shrinks the shock from flow decelerating back to subsonic, compared to a conventional foil. As well as these direct aerodynamic benefits their thicker t/c ratio compared to efficient conventional sections makes the wing structure easier to design, making them a no-brainer for pretty much all modern airliners.

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  • $\begingroup$ Can you expand t/c ratio for dummies? Thickness to chord? $\endgroup$ – hobbs Apr 10 '17 at 21:39
  • $\begingroup$ That's exactly it. Having a thicker wing means the spar(s) can be bigger in the vertical direction, so it is easier for them to resist bending. $\endgroup$ – Talisker Apr 11 '17 at 15:48
  • $\begingroup$ The wing is swept 37.5°. That means shock wave only forms when the stream exceeds M1.26 (1/cos 37.5°) and that only happens in the last quarter-or-so chord. $\endgroup$ – Jan Hudec Apr 11 '17 at 19:35

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