baldwin471
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Difference Between 330 And 744 Winglets

Sat Apr 06, 2013 8:33 pm

Hey,

So this has bugged me for a while. Is there any difference at all in the winglets used on the 744, and the Airbus 330+340 family? They look incredibly similar to me, both in design and size.

Anyone have any more info?

Cheers
 
ferpe
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RE: Difference Between 330 And 744 Winglets

Sun Apr 07, 2013 1:22 am

They both look like a straight implementation of the Whitcomb winglet upper part.

I have studied winglets quite a lot to come to some conclusion how to handle them in my airliner performance model, the best all-inclusive paper I found was this one from Doug McLean at Boeing:

http://www.google.fr/url?sa=t&rct=j&...s64Q&bvm=bv.44770516,d.ZG4&cad=rja


It shows that what is written at Wikipedia is a little wrong in it's conclusions (talks about what happens at the wingtip which is wrong, it is about what happen at the complete trailing edge of the wing). Essentially the McLean paper says (and many more advanced studies says the same, eg Ning and Kroo Stanford 2008):

- Winglets function to increase the equivalent span of the aircraft. It is not about what happens at the wingtip but what happens behind the complete wing. Therefore wingtip devices work by shifting the lift distribution outward.

- If one does it with a winglet, a tip extension or some other device like a fence, they all use the same mechanism of virtually extending the span, ie shift the lift distribution outward.

- For a classical winglet you can count the effective span increase as 45% of the physical size of the device, for a raked tip 80%, for an Airbus style fence as a 2% extension of the wing span.

- All other things being equal the raked tip gives a lower total weight increase as it does not induce the same wing torsion moment but it's has the negative it increases gate space requirements.


So the bottom line is they seem very similar and as they are rather small they are not to effective (their sharp bend might also cause transonic drag effects).

If you go to the bother of making a tip device, make it big to get a significant effect and make the transition smooth to avoid interference drag (the smoothest being the true Sharkfins of the A350  Wow!  ). If you have span to spear and are an owner of the patent (B), make a raked tip (the tip is raked due to tip-stall considerations, there is no slat out there so you better pass 60° rake to get a stable vortex at high alfa and thus a stable tip roll moment).

[Edited 2013-04-06 18:24:02]
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DocLightning
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RE: Difference Between 330 And 744 Winglets

Sun Apr 07, 2013 6:14 am

Quoting ferpe (Reply 1):
If you go to the bother of making a tip device, make it big to get a significant effect and make the transition smooth to avoid interference drag (the smoothest being the true Sharkfins of the A350  &nbsp Wink.

So why is the transition so abrupt in the first generation of winglets? Surely they were capable of manufacturing a blended device, no?
-Doc Lightning-

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ferpe
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RE: Difference Between 330 And 744 Winglets

Sun Apr 07, 2013 7:57 am

Quoting DocLightning (Reply 2):
So why is the transition so abrupt in the first generation of winglets? Surely they were capable of manufacturing a blended device, no?

I don't know, it might have been that Whitcomb concieved it this way and knowing that he was a transonic wiss kid (he invented area rule and the transonic wingshape) they didn't dare to question how the junction should be made.
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Starlionblue
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RE: Difference Between 330 And 744 Winglets

Sun Apr 07, 2013 9:21 am

Quoting DocLightning (Reply 2):
Quoting ferpe (Reply 1):
If you go to the bother of making a tip device, make it big to get a significant effect and make the transition smooth to avoid interference drag (the smoothest being the true Sharkfins of the A350  &nbsp .

So why is the transition so abrupt in the first generation of winglets? Surely they were capable of manufacturing a blended device, no

Apart from what ferpe said, I think there was an ease of manufacturing element. I saw a docu once about the 747 and they introduced a guy at Boeing who said most people just knew him as "The Winglet Guy". His job was to install the winglets. With a mallet.

Add to that the ease of simply removing a damaged winglet and despatching without.

As times have progressed, and wingtip devices have become more mainstream, you get a more blended element being acceptable.
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