To Whom it May Concern,

  I asked a Boeing engineer a few years ago
why winglets were being added to the -400
revision of the 747.  Her response was that they
were there to reduce turbulence at the end of the
wing, thereby increasing fuel efficiency.  

  However, I have noticed that some planes have
them (A-330, 747-400, MD11) and others do not
(777, A-380, etc.).

  If what she said was true, I would have expected
all new planes to have them.

  Can anybody shed any light on why some of these
new planes do not have winglets?

  Posts and email welcome.

  Thanks in advance.

  regards,

  Lars Ewell

737-600  143,000/1341=106 lbs/ft^2
777-200   545,000/4605=118 lbs/ft^2
A330       606,000/3890=155lbs/ft^2
777-300ER  760,000/4694=161lbs/ft^2
MD11      630,000/3688=170lbs/ft^2
747-400   875,000/5650=154lbs/ft^2
717          121,000/1001=120 lbs/ft^2

You can get them on the 737-700/800/900, but I don't think anyone is
talking about them for the -600, it just doesn't weight enough for it
to be attractive.

The A340-A330 wing have winglets for the best efficiency in "limited" span.
The 777 don't have span limit for designers, the wing don't have winglet.
The A380 N0001 don't have winglet.... I think heaviers futur versions will
be equiped with.

On other side:
See the D{*filter*} Falcon executive jets: no winglets for the best jets,
always a new wing for a new plane.

by
--
        Philippe Vessaire  ??

Because of the pressure differential between the upper and lower
surfaces of the wing the air under the wing at the end rolls you and
around towards the top.  This creates a vortice that is shed as the
aircraft flies forward through the air.  The vortice creates parsitic
drag on the aircraft.

Winglets help 'fence' off the airflow and reduce the vortice.  Thereby
reducing drag.  But they also add drag in that they're additional
aerodynamic surfaces cutting through the air.  So it isn't pure gain.

Depending on the type of airfoil used, the weight of the aircraft,
crusing speed, etc, the strength, and drag, of the vortice will vary.
So it may not be worth adding the winglets on some aircraft.

Winglets are also not the only solution.  The airfoil can be tailored,
other forms of fences can be used, etc.  Look at the wingtips of
several Airbus aircraft, including the A380 - there are small
'winglets' pointing both up and down from the wingtip, and these
reduce the vortice.

The 777 was originally designed with folding wingtips, at the request
of American Airlines (though none were ever ordered with the option,
and it is no longer offered), so that probably precluded using
winglets in the design.

Computers, and computational fluid dynamics, have also *vastly*
improved in the past decade.  And now we're seeing much more
integrated winglet designs - such as the Blended Winglets available on
some 737 models and the winglets that have been designed right into
the 787 design.

Doing it right takes more than just slapping some end-plates on an
existing wing design.  Any time you alter the airflow over a wing you
need to re-check everything.

-MZ
--
<URL:mailto:megazoneatmegazone.org> Gweep, Discordian, Author, Engineer, me.
"A little nonsense now and then, is relished by the wisest men" 508-755-4098
<URL:http://www.megazone.org/>  <URL:http://www.eyrie-productions.com/> Eris

If I remember correctly, winglets can improve the performance (Cl, Cd,
etc.) of a wing given a constraint on span, but that it is always
possible to design a wing with longer span that will outperform the one
with winglets.

I don't remember how a constraint on root-bending-moment would affect
things.

Cheers,

Geoff S.

Since no one else has answered your question, I'll give it a try.  I'm not a
professional aerodynamicist, so those more qualified are free to critique my
response.

Simply put:  If you're designing a new aircraft, its more efficient to
increase the wingspan than to use a shorter wing with winglets.

However, increasing the wingspan increases the bending loads at the wing
root.  Thus, you can't just upgrade a 737, for example, by increasing its
wingspan.  However, by adding winglets, you can get much of the same effect
as a longer span, but without significant additional bending loads.  A
secondary advantage is that using winglets doesn't appreciably change the
"footprint" of the aircraft, bypassing gate-usage problems.

The MD-11 and 747-400 were both upgrades of an existing aircraft.  Some
Airbus aircraft (including the A380) use small chevron-style winglets which
may have some positive effect, but which I suspect are more of a "signature"
item than a big efficiency booster.  The A330/340 use small vertical
winglets, but I'm not sure why that choice was made on a new aircraft.  Same
with the Bombardier RJ series.

FWIW, winglet design is non-trivial.  If not designed properly, winglets can
*reduce* the overall performance of the wing.

Frank

I see that you have an .edu email address. Therefore, you can reach
some good textbooks at the University of Arizona library. Please read
pages 215 - 221 from Aerodynamics, Aeronautics, and Flight Mechanics by
Barnes W. McCormick, regarding the winglets.

--
-Stephen H. Westin
Any information or opinions in this message are mine: they do not
represent the position of Cornell University or any of its sponsors.

--
-Stephen H. Westin
Any information or opinions in this message are mine: they do not
represent the position of Cornell University or any of its sponsors.