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I originally asked a question (Comparisons between the A340 and 747-200 wing: sweep angle and span) about the technological developments which allowed the Airbus A340 to have a wing with greater aspect ratio and lower sweep than the Boeing 747-200 wing, despite being designed to carry roughly the same number of passengers. @Koyovis graciously replied that a lot of the ability to design a lower-sweep and higher AR wing was a result of supercritical airfoil development. However, I had a follow-up question that I was encouraged by other commentators to post directly.

As far as I'm aware, the first supercritical sections were introduced on the generation of aircraft launched in the late 70s - early 80s (767, 757, A300, A310). The Airbus A340, along with the 330 and 777 however were launched a decade later, in the late-80s - early 90s.

I am curious whether the airfoils on these latter aircraft incorporated any improvements to their supercritical sections over the late-70s - early-80s generation of aircraft? If so, I'm curious as to what specific improvements were made?

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  • $\begingroup$ I can't provide any data, but my understanding is the main effort has been to improve stall behaviour. SC airfoils suffered from laminar bubbles at the LE with LE initiated flow separation at stall = holy cow when it goes. This is why some airplanes like the CRJs have stick pushers. Newer designs have tamed that behaviour somewhat. $\endgroup$
    – John K
    Apr 18 at 20:55
  • $\begingroup$ As you may already be aware, it's a lot more than just the airfoil. Have a look at Why does the wing root of the A330 have a pronounced twist? (also that's one of my all-time favorite answers on this site). So, in case you're interested in the whole wing, feel free to edit the question. $\endgroup$
    – ymb1
    Apr 19 at 10:32
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    $\begingroup$ also you may want to check this help center page: aviation.stackexchange.com/help/someone-answers consider accepting (✔) the answers you found most helpful to your previous questions $\endgroup$
    – ymb1
    Apr 19 at 10:51
  • $\begingroup$ Some formatting always helps. What is now the first paragraph could simply be reduced to "As a follow up to [this question]..." Anyone who clicks the link can read through the Q, the As, and comments to see how you got to this one if they're interested. $\endgroup$
    – FreeMan
    Apr 19 at 16:12

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What you are looking for are called Phase 3 airfoils.

While initial research focused on avoiding a shock completely at one specific operating point of the airfoil (Phase 1), Phase 2 airfoils accepted weak shocks for the benefit of a wider angle of attack range in which that shock could be kept weak, so the result could tolerate small deviations from the ideal operating point.

On the most recent designs another small lift contribution results from a slower pressure drop on the forward edge of the lower side pressure distribution (the forward lower-surface undercutting of Phase 3 airfoils). This gives slightly more lift at the same angle of attack and also lowers the pitching moment of supercritical airfoils.

Effect of forward lower surface undercutting

Effect of forward lower surface undercutting, from NASA Technical Paper 2969.

The reason for the higher aspect ratio of the A340 has nothing to do with supercritical airfoils but results from more efficient engines.

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