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Blended Wing Tips Vs Winglets  
User currently offlineKamboi From United States of America, joined Sep 2000, 143 posts, RR: 0
Posted (9 years 5 months 2 weeks 4 days 11 hours ago) and read 5069 times:

I am no aerospace engineer nor a pilot, but for those of you out there, why is it that some planes are now being fitted with "blended wind tips" as opposed to "winglest" on the original production. I know it's a fuels cost issue. But why don't the manufacturer just produce them with the winglets. I was surprised the B777 did not have winglets instead of raked tips, and neither does the new 787. Why is that?

8 replies: All unread, jump to last
 
User currently offlineFriendlySkies From United States of America, joined Aug 2004, 4106 posts, RR: 5
Reply 1, posted (9 years 5 months 2 weeks 4 days 11 hours ago) and read 5057 times:

The 777s wing is so efficient that winglets would most likely hurt it's performance, or provide any benefits worth mentioning. The raked wingtips do not disrupt airflow as much as a winglet (most noteably the airflowing off the end of the wing), but rather add minimal lift and thus slightly lower fuel burn on very long flights. You won't see raked wingtips on shorter range aircraft, such as the 787-3, as they don't do much of anything for flights under about 9 hours or so.

User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1609 posts, RR: 52
Reply 2, posted (9 years 5 months 2 weeks 4 days 5 hours ago) and read 4930 times:
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FriendlySkies:

I think you are speaking without much real knowledge. Raked tip and winglets do not "disrupt the airflow" or "add lift".

We've thrashed this subject in quite a number of other threads, both here and in Tech/Ops. I'd suggest that you go look there.


User currently offlineFriendlySkies From United States of America, joined Aug 2004, 4106 posts, RR: 5
Reply 3, posted (9 years 5 months 2 weeks 4 days 4 hours ago) and read 4917 times:

I meant that they disrupt the vorticies coming off the ends of the wings...I'm not sure how much, but I'm fairly certain they have some effect. They do add a small amount of lift because they add area to the wing. If they don't add lift, then their effect is null, because they would just be added weight.

User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1609 posts, RR: 52
Reply 4, posted (9 years 5 months 2 weeks 4 days 2 hours ago) and read 4844 times:
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On all aircraft lift = weight in cruise. You can't "add more lift". Wing tip extensions, raked wing tips, winglets, etc. all have the effect of decreasing the drag induced by creating lift.

I'd suggest Googling "induced drag" and reading some of the texts you find.


User currently offlineDfwRevolution From United States of America, joined Jan 2010, 977 posts, RR: 51
Reply 5, posted (9 years 5 months 2 weeks 4 days 1 hour ago) and read 4833 times:

Quoting FriendlySkies (Reply 1):
You won't see raked wingtips on shorter range aircraft, such as the 787-3, as they don't do much of anything for flights under about 9 hours or so.

That isn't true at all... the blended vertical winglet is simply more space efficent, which matters big for short-haul aircraft. Already some 737NG customers, FL comes to mind, have not opted for winglets because of gate access.

Quoting Kamboi (Thread starter):
I was surprised the B777 did not have winglets instead of raked tips, and neither does the new 787. Why is that?

Boeing found that adding several more feet to the 777's wingspan had the same effect of adding winglets, and that stretching the wing did not require the reinforcement necessary for winglets. In otherwords: stretching the wing was more structurally efficet.

Next, the winglet is hardly the epitome of aerodynamics. The 787 features a new generation of winglets known as "super-shark winglets." FD tried something simmilar before going belly-up.

Quoting FriendlySkies (Reply 1):
The 777s wing is so efficient that winglets would most likely hurt it's performance, or provide any benefits worth mentioning.

No... Boeing just found alternative ways to optimize the 777's wing


User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1609 posts, RR: 52
Reply 6, posted (9 years 5 months 2 weeks 4 days ago) and read 4802 times:
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> Boeing found that adding several more feet to the 777's wingspan had the
> same effect of adding winglets, and that stretching the wing did not require
> the reinforcement necessary for winglets. In otherwords: stretching the wing
> was more structurally efficient.

Not true. For the same span extension (measured with the winglet laid down flat), winglets produce the same drag reduction or slightly more than wing tip extensions. Wing tip extensions also produce more bending moment than winglets. Hence, the wingtip extension would require more structural reinforcement than required for winglets.

The problem with the 777 wing is that Boeing designed it with relatively high lift coefficients near the tip. They figured that if the wing wasn't carrying much lift there, they would minimize the chord, which drives up the lift coefficients. This makes it difficult to put a winglet on this wing.

> Next, the winglet is hardly the epitome of aerodynamics.

Ahem...

> The 787 features a new generation of winglets known as "super-shark
> winglets." FD tried something simmilar before going belly-up.

The design concepts that have been released and public comments show the 787-3 to have winglets and the 787-8 and 787-9 to have non-planar raked tips.


User currently offlineCO737800 From Canada, joined Dec 2003, 545 posts, RR: 1
Reply 7, posted (9 years 5 months 2 weeks 4 days ago) and read 4793 times:

I have a question why would Airbus not make so efficient wings like on the 777 and 787

User currently onlineStarlionblue From Greenland, joined Feb 2004, 17040 posts, RR: 66
Reply 8, posted (9 years 5 months 2 weeks 3 days 23 hours ago) and read 4780 times:

Quoting CO737800 (Reply 7):
I have a question why would Airbus not make so efficient wings like on the 777 and 787

The are making more efficient wings, on the 380! the 777 and 787 are simply newer and make use of slightly more modern aerodynamics than the 330/340... It's a constant "arms race".

As for winglets vs blended winglets, there are many ways to skin a cat, all leading to more or less the same result.

Winglets can be more appropriate sometimes because the increase in wingspan is less, and the plane can get into the same gates as before. Also, for the 380, any increase in wingspan is verboten due to the 80m box.



"There are no stupid questions, but there are a lot of inquisitive idiots."
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