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I'm told that wing redesigns (edit: for tapered, swept wings) are difficult, so variants of a model often do with a common wing optimized for the middle member.

But then I read the following:

Based on Antonov's earlier An-124, the An-225 has fuselage barrel extensions added fore and aft of the wings. The wings also received root extensions to increase span.

That doesn't look so difficult. Of course, the wing root would be a new design, but we still get to keep the rest of the wing. Perhaps the flutter modes are less favorable......but wouldn't that be more or less inherent to higher spans?

So: Is/why isn't this method used to design variants or derivatives of large airliners?

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  • $\begingroup$ I think you may be underestimating the effort that went into the wing root extensions. Sure it was probably easier than designing a whole new wing, but I doubt is was as simple as "drawing longer lines". $\endgroup$
    – FreeMan
    Commented Jul 10, 2020 at 17:41
  • $\begingroup$ @FreeMan could be. I don't know, that's the point. $\endgroup$
    – Abdullah is not an Amalekite
    Commented Jul 10, 2020 at 17:54
  • $\begingroup$ The Antonows you mentioned are quite a specialty freighter compared to other planes. Other planes, think of the commonly available jets of Airbus and Boing, need to fit certain geometric size ranges to allow their use with jet-bridges and other airport infrastructure. The Antonows generally do not dock on Terminals, thus, the may have more wingspan than other planes. Boing designed folding wing tips to maintain maximum on-ground wingspan for this reason. If your plane always loads/unloads out on the tarmac, you can affort to increase wing span. $\endgroup$
    – Dohn Joe
    Commented Jul 13, 2020 at 8:09

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With straight wings the root extension method is very common. Airplanes that come to mind are

  • Me-109 H (high altitude version with increased span)
  • Beech Twin Bonanza and Model 65 Queen Air (used the Bonanza wing from the engines out)
  • SB-10 (uses SB-9 wings stuck to a new carbon-epoxy center wing).

This is impractical with swept wings because of the strong twist and airfoil changes which are needed at the wing root to keep the isobars straight on the swept wings. The only way to increase an existing wing's size was used for the A340-500/600 by inserting a triangular section at mid-chord into the A340-200/300 wing which also allowed to increase its wingspan.

triangular section
Source: Evolvability and design reuse in civil jet transport aircraft

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  • $\begingroup$ but the 225 was swept? that was what interested me $\endgroup$
    – Abdullah is not an Amalekite
    Commented Jul 11, 2020 at 7:06
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    $\begingroup$ @Abdullah: The An-124 doesn't have the wing twist and also not the increasing root chord of most other transport airplanes, also its maximum Mach number is only 0.77. Its wing allows to be added to a new center section. Note that the An-225 is not as thoroughly optimized as other heavy transports; for example it does not have leading edge devices on the new center section. I guess the Ukrainians simply allowed themselves a few shortcuts when the An-225 turned out to be good enough for its intended purpose (to transport Buran). $\endgroup$
    – Peter Kämpf
    Commented Jul 11, 2020 at 8:30
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    $\begingroup$ "stuck to"? Had to laugh at that though may be 100% true... I'm thinking of buying a pot of glue and opening my own modification center... $\endgroup$
    – quiet flyer
    Commented Jul 11, 2020 at 13:40
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    $\begingroup$ @quietflyer. The SB-10 wing is made of 5 parts which can be taken apart for road transport. When being prepared for flying, the parts are stuck together. Literally. Did it myself often enough to be sure about this. $\endgroup$
    – Peter Kämpf
    Commented Jul 11, 2020 at 13:56
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    $\begingroup$ @Abdullah I mean the reduced TE sweep which is used on many swept wings but not on the An-124. $\endgroup$
    – Peter Kämpf
    Commented Jul 11, 2020 at 13:59

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