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View Full Version : Why doesnt the B777 use winglets?


Roxy_Chick_1989
12th Oct 2010, 17:02
I have done many searches on this topic, but all i can seem to find is 'the 777 uses a computer designed wing and bla bla bla...' Im not sure if this cuts the mustard, so a few other ideas i have come up with

-Supercritical wing (although i am not sure if there are other transport cat a/c with this)
-High aspect ratio (as above)
-Raked wingtips

Can anyone else add to the list? and perhaps explain this question.

Abbey Road
12th Oct 2010, 17:09
The 777 was the first airliner to be entirely designed on computers and thus the wing was as good as it could be got at the time the design was frozen for production. Look at the 787 - far more recent technology, designed on a compter, but still the wing does not have/need winglets!

As a general rule, winglets only seem to appear on designs that are being updated/improved i.e. tweaking older designs to improve them without going through the expense of a complete redesign and certification.

DDobinpilot
12th Oct 2010, 17:32
Another interesting point is that Air Southwest order all their 737's without winglets, because the 4% fuel efficiency to them isn't worth the extra weight to stick a few more PX on due to their fairly short routes..

Mad (Flt) Scientist
12th Oct 2010, 17:33
There are a fair number of new, clean-sheet designs which incorporated winglets from day 1, so it's not true to say that they are just a fix to improve things without a full recert.

Simply, they are one of the tools in the aircraft designers' toolbox. Sometimes they trade-off and buy their way on, sometimes they don't. Part of that trade-off can be tangibles (like weight and drag considerations), sometimes its intangibles ("all our aircraft have winglets, we aren't changing that" or "customers think winglets look nice" or whatever).

There's no technical justification for the winged lady on the bonnet of a Rolls Royce, but they still put one there.

Boeing CHOSE not to include winglets, based on a combination of engineering trade-off of the pros and cons, and that will have included things such as the corporate "look" of their aircraft (especially compared to AB), their comfort level with the technology, and so on.

To address the OP, supercritical (or pseudo-supercritical) wings and high aspect ratio wings have both been designed from the start with winglets, so those aren't reasons not to include them.

Mr Good Cat
12th Oct 2010, 17:34
Nearly all recent orders for the 777 are for the 300ER / 200LR and 200F.

These are fitted with raked wingtips.

juliet
12th Oct 2010, 21:40
Roxy,

Winglets are a little bit of 3 steps forward, 2 steps back. They arent a perfect solution that instantly improves performance. They have drawbacks, but as has been alluded to, if the pros outweigh their inherent cons then they are added.

If you can design a wing without winglets you will have a more efficient design. Look at the new wing designs out there, namely 788 and 748. Both have in effect a raked wingtip that gives the pros the designers are looking for without the extra weight/drag etc of a winglet.

The 777 family was I guess the first wing that could take the step away from winglets, providing that extra 5% or so of efficiency through good overall wing design, rather than using a compromise in the form of the winglet.

J

ZimmerFly
12th Oct 2010, 22:03
Would that be Air Southwest based in UK with 5 Dash 8 -300s, or Southwest Airlines based in USA with 544 737s? :confused:

Performance-enhancing Blended Winglets have been added to our fleet of 737-700s, and all new 737-700 aircraft arrive from Boeing with Blended Winglets installed. Additionally, Southwest began installation of Blended Winglets on some of our 737-300 aircraft in early 2007; installation of Blended Winglets on these aircraft was completed as of the end of second quarter 2010.

Southwest Airlines Factsheet

john_tullamarine
12th Oct 2010, 23:28
I don't think I saw this elsewhere in the thread - for the larger end of the market, winglets become a necessary evil for airport infrastructure limitations.

One can't extend the span so the slightly less effective option of tip work becomes the alternative. I have seen figures along the lines that a tip sail roughly equates to a span extension of about 3/4 the height of the sail.

grounded27
13th Oct 2010, 00:18
Why doesnt the B777 use winglets

The wing design "sweep and flexability" negates the advantage, the B787 took it 1 step further.

singleseater
13th Oct 2010, 07:25
When EK got the 300 ER's one of the test pilots gave us a brief on the aircraft and was asked this question.
Answer
The raked wing tips give the required performance increase with only limited additional wieght in the wing structure.
Also and I quote " To get the same performance increase, the wing-lets would have to be 21 Ft. High with a corresponding huge increase in the wing wieght to support".
Horse's for courses ??

bvcu
13th Oct 2010, 10:38
Another point with the original 777 was it was designed with a folding wingtip option to enable use of smaller gates . This was not taken up by any operators in the end and meant the wing tanks stopped further inboard. On the LR/300ER this space has been used again as part of fuel qty increase.

DDobinpilot
13th Oct 2010, 12:52
@Zimmer

I meant Southwest airlines based in the US :P

Roxy_Chick_1989
13th Oct 2010, 13:48
Thanks for the discussion, and many more questions have now popped up!!

Now onto another though, I notice alot of the modern airliners equipped for long range ops mainly utilise winglets, these aircraft obviously spend the majority of their time in the cruise. I believe winglets are used to reduce induced drag generated from the mainplane, however if these aircraft are spending the majority of time in CRZ (thence low AoA = low induced drag) how are winglets beneficial as all i see is a potential parasite drag increase. Im not out to reinvent the wheel, and i trust everything the engineers/designers have done. I am however very interested to know the reasoning behind this.

Spooky 2
13th Oct 2010, 13:56
I meant Southwest airlines based in the US :P

Somebody better go tell SWA (USA) that someone is gluing winglets on all of their airplanes when no one is looking. New, used...all of them unless they are scheduled for retirement. :oh:

DDobinpilot
31st Oct 2010, 19:11
Lol! Well it came up in my tech interview for an airline. The guy told me that Southwest airlines order all their aircraft without winglets, but yes looking at pics it seems they now have blended winglets, unless as you said someone is sneaking around sticking winglets on them..

Mad (Flt) Scientist
31st Oct 2010, 19:57
Thanks for the discussion, and many more questions have now popped up!!

Now onto another though, I notice alot of the modern airliners equipped for long range ops mainly utilise winglets, these aircraft obviously spend the majority of their time in the cruise. I believe winglets are used to reduce induced drag generated from the mainplane, however if these aircraft are spending the majority of time in CRZ (thence low AoA = low induced drag) how are winglets beneficial as all i see is a potential parasite drag increase. Im not out to reinvent the wheel, and i trust everything the engineers/designers have done. I am however very interested to know the reasoning behind this.

Not quite true in the reasoning there.

Low AOA means a low induced drag CD (i.e. drag coefficient). But there's also a low CL as well. That CL is able to support the weight of the aircraft thanks to a nice high airspeed multiplying up the CL to a good amount of Lift. That same kinetic pressure also multiplies the CD to give a fair amount of Drag. So while the saving in terms of induced CD may be small, the saving in terms of drag (hence fuel burn / range) is a fair amount, and often worth having.

olepilot
1st Nov 2010, 17:20
Because Boeing couldn't reach an agreement with the company supposed to supply the wing tips in time for production.

bearfoil
1st Nov 2010, 17:28
Retrofit requires a substantial increase in structure and weight at the wing root. (And the tip). Extrapolating from that would infer that the 777 is designed to be without the weight increase, and the formula for fuel specifics is not served by the inclusion of the feature.

bear

MISSED APCH
20th Nov 2010, 16:21
IMO, its like buying a new HD-TV.
they dont include the HDMI cable.
so after you setup your brand new HDTV at home, you notice something weird, then read the book and it says. Go buy that $100 cable to improve you SD-HD-TV to HD-TV.

a.k.a winglets !:ouch: