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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. $\endgroup$
    – user14897
    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 $\endgroup$
    – user14897
    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
  • $\begingroup$ Mmh, I'm not that sure that lower swept angle and/or higher aspect ratio are mainly due to a switch toward supercritical airfoils. For a jetliner, OEI climb at takeoff normally drives the choice of the AR, while CG location, weight and pitch and lateral stability drive the choice of the sweep angle. $\endgroup$
    – sophit
    Nov 8 at 19:16

2 Answers 2

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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, in the 1960s), 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 (roughly in the 1970s).

On the more recent designs (1980s and 90s) 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 little to do with supercritical airfoils but results from more efficient engines.

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Note, I found what I believe to be a pretty good answer to my question. As a bit of context, the basic supercritical airfoil design was created in the early 1970s by Richard Whitcomb. I was curious whether the airfoils of ~1990 and beyond, because they were designed using much more advanced CFD tools than Whitcomb's sections were designed with, had improved performance, despite embodying the basic supercritical ideas (which were, generate a region of supersonic lift, weaken the shock wave, move it to the rear, generate lift from the aft using increased camber).

The following image is taken from a lecture given by Frank Ogilvie, the Chief Aerodynamicist on the Airbus A380, at Cranfield University on transonic wing design. He goes through the evolution of HSA (Hawker Siddeley Aviation) and BAC (British Aerospace Corporation) outboard airfoils found on various Airbus aircraft in the 1970s and 80s. The lecture can be found on Scribd, but you need an account to access it.
enter image description here

enter image description here

You can clearly see how, in tandem with increasing complexity of CFD codes (from no transonic CFD methods on the A300 to transonic small perturbation methods for the A310 to 3D viscous-coupled full potential codes + inverse design methodologies for the A330/340) the pressure distributions associated with the outboard sections of the wings became more aggressive. The shocks became weaker and they were pushed from 40% of chord to around 55% of chord. This translates to greater lifting performance for a given drag.

Also, note - the reason the A320 airfoils are less aggressive is because they had less space to incorporate the high-lift system on a smaller wing. That's why I have focused on the wide-bodies.

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    $\begingroup$ Basic work on transsonic airfoils was performed as early as 1940 by K. A. Kawalki in Germany when it was found that inverted airfoils performed better at transsonic speed. Also, the A310 wing is based on a design by Airbus Bremen which was proposed after the Hawker Siddeley design for the A310 wing proved to be mediocre. To save face, Hawker Siddeley used the Bremen design and sold it as their own. Next, the US sued Airbus for patent infringement when the A310 came out with its supercritical wing, only to lose the case because of the earlier work by Kawalki. $\endgroup$ Nov 9 at 14:30
  • $\begingroup$ Do you have a source for this? I'm pretty sure J.A. Jupp and Dykins would disagree with this. See this lecture on their A310 design efforts - they depict the airfoil as a natural development of Pearcey's "Peaky" airfoils that were used on the A300: jstor.org/stable/2398246?seq=11#metadata_info_tab_contents $\endgroup$ Nov 19 at 4:31
  • $\begingroup$ Though I will say, I don't disagree that there have been some conflicts between Bremen and the UK teams in the past. I interviewed an aerodynamicist from Airbus currently and he talked about the big fight over including variable-camber on the A340 wing (eventually it was not included). The A340 wing was also a competition between Bremen and the HSA team. $\endgroup$ Nov 19 at 4:32
  • $\begingroup$ Nothing in the linked article contradicts what I said. It is only selective in what is reported. Also revealing it its way: The achievement by Vickers with their VC-10 wing is not credited, although it was the best of its time. BTW, Figure 8 demonstrates a lack of understanding what drives maximum subsonic lift. I'm not impressed. $\endgroup$ Nov 19 at 9:11

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