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Inspired from this question about the loss of a flap track fairing.

In the answer by Thunderstrike, a part of the configuration deviation list of an Airbus A320 is linked. In it, it says:

One fairing may be partly or completely missing.

Performance

  • Fuel consumption is increased by 3.14%

That really is a lot!

I found a post on Airliners.net citing the CDL of a B757:

Straight out of the MEL/CDL manual for the 757, The item falls under CDL 27-51-1 which states there are 6 installed [Flap Track Fairings, Remark] on the aircraft and up to one per side may be missing. No fuel burn penalty but there are a few small weight penalties, no speed penalty. Our A-300's with the same CDL item does have a 1% fuel burn penalty and only one can be missing out of the 10 installed. I see this item come up 3 or 4 times a year, no biggie.


  • What causes this very high increase in fuel consumption on Airbus planes?
  • What are the differences between the fairings of a Boeing and an Airbus (because Boeing has no increased fuel consumption, Airbus has)?
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  • $\begingroup$ I'd say that a weight penalty could be reinterpreted as a fuel penalty (i.e., the reduced payload translates in a shorter range, if you ignore the lower payload limitation), so I don't really think it is a special "feature" of Airbus. $\endgroup$ – Federico May 29 '17 at 13:55
  • $\begingroup$ and the reason why they allow for such fuel conservation is explained here: aviation.stackexchange.com/q/7955/1467 $\endgroup$ – Federico May 29 '17 at 14:04
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    $\begingroup$ I used to compete in aircraft recognition and one of the obvious differences comparing the two aircraft is the prominence of flap track fairings. At a distance it was always easy to ID an Airbus because of large and many flap track fairings compared to Boeing. Interesting. $\endgroup$ – STWilson Jun 9 '17 at 14:52
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The fairings double as anti-shock bodies (or Küchemann carrots) and help to reduce shocks on the lower side of the wing. Below you see a wind tunnel test from the Vickers VC10 development where flow visualization using oil was used at Mach 0.9:

Wing without (left) and with (right) anti-shock bodies

Wing without (left) and with (right) anti-shock bodies at Mach 0.9 (picture source). The light line on the left side indicates a strong shock which increases drag substantially over the situation pictured on the right where the flap track fairings have been used to smooth out the sudden reduction in cross sectional area from the rear-loaded wing airfoil.

Please read this answer if you are unsure why aircraft experience more drag as they approach the speed of sound. By stretching the aircraft body over a larger length, the gradients in the cross sectional area distribution can be made more shallow such that the air has more opportunity to make way for the aircraft.

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    $\begingroup$ In image A) there is a bright, sharp, narrow white line about half-way along the wing. This, as I understand it is the shock line. In image B) there are equally bright (to my eye), but very broad/spread out white areas. AIUI, the fact that they're spread out, and not in a thin, crisp line is what makes them not shock lines and therefore significantly lower contributors to drag. Is this a correct assumption? $\endgroup$ – FreeMan Jan 11 at 15:28
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    $\begingroup$ @FreeMan: The more interesting lines in the left picture are the very thin, parallel ones which show that past the shock line flow travels only towards the wing tip and slightly forward. This looks like fully separated flow to me. The right side picture does also show shocks, but they are weaker and do not cause separation. $\endgroup$ – Peter Kämpf Jan 11 at 15:39
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    $\begingroup$ Thanks for the interpretation. For those of us not versed in the black arts of aerodynamics, that's quite helpful! ;) $\endgroup$ – FreeMan Jan 11 at 16:15

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