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Below are some pictures of various fixed wing aircraft with winglets. It is widely accepted that these winglets will improve an airplane's performance by reducing drag and therefore improving fuel efficiency.

Here is an official video from Boeing showing the folding wing of B777x. According to Wikipedia, the wing's ratio increases from 9:1 to 10:1 which, in turn will improve efficiency up to 7%.

Here is also an official video of Boeing 737 Max that is being tested in Boeing's trans-sonic wind tunnel. In the video, it is claimed that the addition of the split winglet will reduce drag and improve fuel efficiency.

Airbus also said the claimed the same in regards to their A380. It has a claimed 4% efficiency improvement from the addition of a winglet.

But now, Boeing is developing a new airplane which with "foldable" wing, the 777x. The wing is "foldable" to accommodate taxiway width limitation of some airports. Clearly, it is not because of aerodynamics. But at the same time, Boeing claims that it will improve efficiency up to 7%.

Then my question is, if using a traditional winglet will increase the aerodynamic as well as fuel efficiency, why does Boeing not implement this for the B777x?

  • Picture 1: Boeing 777x with folded wings.
  • Picture 2: Boeing 777x with straight wing.
  • Picture 3: Boeing 737 Max with Y-shape winglet.
  • Picture 4: Boeing 747-400 with bent-up winglet.
  • Picture 5: Airbus A380 with Y-shape winglet (like Boeing 737 Max).

Boeing 777x' wings are folded Boeing 777x' wing's is expanded Boeing 737 Max' Y-shape winglet Boeing 747-400's bent-up winglet Airbus A380 Y-shape winglet

Noah
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AirCraft Lover
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    This question and answer from Peter Kämpf may potentially be your answer: https://aviation.stackexchange.com/questions/8556/is-a-winglet-better-than-an-equal-span-extension – aerobot Oct 23 '19 at 03:41
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    "Clearly, it is not because of aerodynamics" – what makes you think so? Of course the wider span improves aerodynamic efficiency. – Peter Kämpf Oct 23 '19 at 05:26
  • @PeterKämpf, sorry for my unclear sentence. But to fold the wing is not due to the aerodynamic reason, but due to possibility the airport is not wide enough. Mean, it is not mandatory to fold the wing, or if possible, the wing must be extended so it can take off shorter and landing slower. Just after takeoff, the wing is extended or just before landing the wing is folded, if necessary. But the answer in your question have a good explanation. – AirCraft Lover Oct 23 '19 at 06:08
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    Can we just auto-close questions with "really" in the title? – Christian Oct 23 '19 at 06:38
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    The wing is never folded or unfolded in the air! This is only possible on the ground, before take-off or after landing. – Peter Kämpf Oct 23 '19 at 11:59
  • Yes @PeterKämpf, you are correct, I was wrong. There is explanation here in 3:25. BUt however, it is not official video and explanation. Sorry for the mistake and thank you for have corrected my mistake. – AirCraft Lover Oct 24 '19 at 05:20
  • @PeterKämpf, but then, if it is not due to airport runway's limitation, then what it need to accommodate? – AirCraft Lover Oct 24 '19 at 05:21
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    @AirCraftLover: It's about the taxiways and mostly the width of the terminal parking positions. On a 98 ft runway with lots of clearance left and right there is no reason not to unfold the wings. Span brings most benefits at low speed. – Peter Kämpf Oct 24 '19 at 05:43
  • Thank you for the nice info. – AirCraft Lover Oct 24 '19 at 07:19

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