winglets

[bagmaker]

OK, I can get the theory (OR can I?) with winglets to reduce wingtip vortices.

Surely the best direction for the tip is DOWN!, I understand this may be difficult for actually making, especially with gliders and groundloops, aesthetics, etc, but can someone explain why they are pointing up?

Consider this..
The HIGH pressure area is UNDER the wing, we want to keep this from migrating to the LOW pressure area ABOVE the wing. Our current wingtip style will restrict the LOW pressure from bleeding sideways (and why would it anyway) yet the majority (?) of our lift is generated from the HIGH pressure BELOW the wing.

This high pressure is what we want to retain and utilise, yet it is still allowed to bleed out sideways. Sure the current shape of wingtip will reduce the vortices caused by the two pressures meeting, and thus the drag, but it wont increase the lift available by retaining the HIGH pressure UNDER the wing, where it is most useful.

I also note the return of the "plate" style winglet on latest jetliners, half above, half below the wingtip, instead of a large winglet.

Enlighten me, O knowledgable ones!

Wayne

[clipclip]

OK, I can get the theory (OR can I?) with winglets to reduce wingtip vortices.

Surely the best direction for the tip is DOWN!, [...] Enlighten me, O knowledgable ones!

Wayne

i'm certainly not that knowledgeable person, but i have heard people whom i would consider quite knowledgeable say that the orientation of the winglet really doesn't matter - it could be flat, or pointed down. either way it reduces induced drag. however, costly hangar space is costlier if the wingspan is wider, and i imagine crosswind landings could become more interesting with winglets pointed down.

:-)

frank

[[email protected]]

It does matter. The pressure on the top side of the wing I a lot lower
that the surrounding air, the overpressure on the downside only a bit
higher. That way it makes sense.
For avery angle of attack (Cl) there is an optimum configuration,
usually a double eliptical shape. (Bend up like a Discus-2, a bit the
shape of an ls-6/8)
Alhoewel real life deals with Reynolds and sideslip whick makes is a
lot more complicated.

For the jetliners, a very small "extra" inverted winglet clearly lowers
the vortices. Also dependant of cruise Cl, Reynolds, mach number.

Jarno Nieuwenhuize
The Netherlands.

[Andy Blackburn]

At 04:12 07 January 2006, Bagmaker wrote:
>
>OK, I can get the theory (OR can I?) with winglets
>to reduce wingti
>vortices.
>
>Surely the best direction for the tip is DOWN!, I understand
>this ma
>be difficult for actually making, especially with gliders
>an
>groundloops, aesthetics, etc, but can someone explain
>why they ar
>pointing up?
>
>Consider this..
>The HIGH pressure area is UNDER the wing, we want to
>keep this fro
>migrating to the LOW pressure area ABOVE the wing.
>Our current wingti
>style will restrict the LOW pressure from bleeding
>sideways (and wh
>would it anyway) yet the majority (?) of our lift is
>generated from th
>HIGH pressure BELOW the wing.
>
>This high pressure is what we want to retain and utilise,
>yet it i
>still allowed to bleed out sideways. Sure the current
>shape of wingti
>will reduce the vortices caused by the two pressures
>meeting, and thu
>the drag, but it wont increase the lift available by
>retaining the HIG
>pressure UNDER the wing, where it is most useful.
>
>I also note the return of the 'plate' style winglet
>on lates
>jetliners, half above, half below the wingtip, instead
>of a larg
>winglet.
>
>Enlighten me, O knowledgable ones!
>


It's not so much about blocking the flow since it's
all going to mix once it gets aft of the wing anyway.
The winglet actually reduces the vortex by creating
circulation off the vortex itself - this is why a winglet
is an airfoil and not just a plate. It flies in the
local flow field at the tip and creates a lift vector
that is inward and slightly forward (that's right forward
lift - thrust!).

I honestly don't know if pointing up versus down is
for practical or aerodynamic reasons - I can't think
of a reason why it would matter, you'd have to reverse
the airfoil and reoptimize for the underside flow field.

9B

[Erik Braun]

Hi Wayne,

> yet the majority (?) of our lift is generated from the
> HIGH pressure BELOW the wing.

No, it only generates 1/3 of the lift. The rest is generated by lower
pressure on the upper side.

I recommend you read
http://www.soaridaho.com/Schreder/Technical/Winglets/Masak.htm
which explains the design and function of winglets.

Greetings, Erik.

[Ken Kochanski (KK)]

"The rest is generated by lower pressure on the upper side."

hmmmm ...

http://www.eskimo.com/%7Ebillb/wing/airfoil.html

http://www.aa.washington.edu/faculty/eberhardt/lift.htm


Erik Braun wrote:
> Hi Wayne,
>
> > yet the majority (?) of our lift is generated from the
> > HIGH pressure BELOW the wing.
>
> No, it only generates 1/3 of the lift. The rest is generated by lower
> pressure on the upper side.
>
> I recommend you read
> http://www.soaridaho.com/Schreder/Technical/Winglets/Masak.htm
> which explains the design and function of winglets.
>
> Greetings, Erik.

[Wayne Paul]

Wayne,

I have created a page containing links to various winglet articles. Most
are based on Mark Maughmer's research at Pennsylvania State University.
http://www.soaridaho.com/Schreder/Technical/Winglets/PSU_Ref.htm

Wayne
HP-14 N990 "6F"
http://www.soaridaho.com/



"Erik Braun" > wrote in message
...
> Hi Wayne,
>
> > yet the majority (?) of our lift is generated from the
> > HIGH pressure BELOW the wing.
>
> No, it only generates 1/3 of the lift. The rest is generated by lower
> pressure on the upper side.
>
> I recommend you read
> http://www.soaridaho.com/Schreder/Technical/Winglets/Masak.htm
> which explains the design and function of winglets.
>
> Greetings, Erik.
>

[[email protected]]

True.
But I`m teaching aerodynamics in my club and it is extremely hard to
explain this to people. I don`t want to confuse people with vorticity
fields so the explanation "pushing air down will result in an
underpressure on top and an overpressure on the lower side of the wing;
that`s lift" seems to be sufficient for the understanding of lift as
far as gliding is concerned.

http://www.navier-stokes.net/

Not too smart to post when you`re just woken up. For those who wanna
know why, just take a look at my last post ;-)

Jarno Nieuwenhuize.
The Netherlands

[[email protected]]

True.
But I`m teaching aerodynamics in my club and it is extremely hard to
explain this to people. I don`t want to confuse people with vorticity
fields so the explanation "pushing air down will result in an
underpressure on top and an overpressure on the lower side of the wing;
that`s lift" seems to be sufficient for the understanding of lift as
far as gliding is concerned.

http://www.navier-stokes.net/

Not too smart to post when you`re just woken up. For those who wanna
know why, just take a look at my last post ;-)

Jarno Nieuwenhuize.
The Netherlands

[[email protected]]

Ken Kochanski (KK) schreef:

> "The rest is generated by lower pressure on the upper side."
>
> hmmmm ...
>
> http://www.eskimo.com/%7Ebillb/wing/airfoil.html
>
> http://www.aa.washington.edu/faculty/eberhardt/lift.htm
>
>
> Erik Braun wrote:
> > Hi Wayne,
> >
> > > yet the majority (?) of our lift is generated from the
> > > HIGH pressure BELOW the wing.
> >
> > No, it only generates 1/3 of the lift. The rest is generated by lower
> > pressure on the upper side.
> >
> > I recommend you read
> > http://www.soaridaho.com/Schreder/Technical/Winglets/Masak.htm
> > which explains the design and function of winglets.
> >
> > Greetings, Erik.

True.
But I`m teaching aerodynamics in my club and it is extremely hard to
explain this to people. I don`t want to confuse people with vorticity
fields so the explanation "pushing air down will result in an
underpressure on top and an overpressure on the lower side of the wing;
that`s lift" seems to be sufficient for the understanding of lift as
far as gliding is concerned.

http://www.navier-stokes.net/

Not too smart to post when you`re just woken up. For those who wanna
know why, just take a look at my last post ;-)

Jarno Nieuwenhuize.
The Netherlands

[[email protected]]

Ken Kochanski (KK) schreef:

> "The rest is generated by lower pressure on the upper side."
>
> hmmmm ...
>
> http://www.eskimo.com/%7Ebillb/wing/airfoil.html
>
> http://www.aa.washington.edu/faculty/eberhardt/lift.htm
>
>
> Erik Braun wrote:
> > Hi Wayne,
> >
> > > yet the majority (?) of our lift is generated from the
> > > HIGH pressure BELOW the wing.
> >
> > No, it only generates 1/3 of the lift. The rest is generated by lower
> > pressure on the upper side.
> >
> > I recommend you read
> > http://www.soaridaho.com/Schreder/Technical/Winglets/Masak.htm
> > which explains the design and function of winglets.
> >
> > Greetings, Erik.

True.
But I`m teaching aerodynamics in my club and it is extremely hard to
explain this to people. I don`t want to confuse people with vorticity
fields so the explanation "pushing air down will result in an
underpressure on top and an overpressure on the lower side of the wing;
that`s lift" seems to be sufficient for the understanding of lift as
far as gliding is concerned.

http://www.navier-stokes.net/

Not too smart to post when you`re just woken up. For those who wanna
know why, just take a look at my last post ;-)

Jarno Nieuwenhuize.
The Netherlands

[[email protected]]

True.
But I`m teaching aerodynamics in my club and it is extremely hard to
explain this to people. I don`t want to confuse people with vorticity
fields so the explanation "pushing air down will result in an
underpressure on top and an overpressure on the lower side of the wing;
that`s lift" seems to be sufficient for the understanding of lift as
far as gliding is concerned.

http://www.navier-stokes.net/

Not too smart to post when you`re just woken up. For those who wanna
know why, just take a look at my last post ;-)

Jarno Nieuwenhuize.
The Netherlands

[J. N.]

True.
But I`m teaching aerodynamics in my club and it is extremely hard to
explain this to people. I don`t want to confuse people with vorticity
fields so the explanation "pushing air down will result in an
underpressure on top and an overpressure on the lower side of the wing;
that`s lift" seems to be sufficient for the understanding of lift as
far as gliding is concerned.

http://www.navier-stokes.net/

Not too smart to post when you`re just woken up. For those who wanna
know why, just take a look at my last post ;-)

Jarno Nieuwenhuize.
The Netherlands

[J. N.]

True.
But I`m teaching aerodynamics in my club and it is extremely hard to
explain this to people. I don`t want to confuse people with vorticity
fields so the explanation "pushing air down will result in an
underpressure on top and an overpressure on the lower side of the wing;
that`s lift" seems to be sufficient for the understanding of lift as
far as gliding is concerned.

http://www.navier-stokes.net/

Not too smart to post when you`re just woken up. For those who wanna
know why, just take a look at my last post ;-)

Jarno Nieuwenhuize.
The Netherlands

[Eric Greenwell]

Ken Kochanski (KK) wrote:
> "The rest is generated by lower pressure on the upper side."
>
> hmmmm ...
>
> http://www.eskimo.com/%7Ebillb/wing/airfoil.html
>
> http://www.aa.washington.edu/faculty/eberhardt/lift.htm

Can you point out where these articles compare the pressures on the top
and bottom surface, or some reference that gives the relative
magnitudes? I was unable to find it.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

[jphoenix]

bagmaker wrote:

>
> I also note the return of the "plate" style winglet on latest
> jetliners, half above, half below the wingtip, instead of a large
> winglet.
>
The latest jetliners (not including Airbus) have gone to the eagle tip
configuration (swept up and back slightly like Nimbus 4's), dumping the
classic style winglet. The 787 and new 747 stretch have this config, I
think a couple of others.

Jim

[J. N.]

http://www.hsa.lr.tudelft.nl/~frits/fig8.jpg

Highly dependant of angle of attack (incidence?), but during cruise (5
degrees) typically only a fraction of the force is generated by the
lower side of the airfoil.

[Ken Kochanski (KK)]

Eric,

I just wanted to point out that Newton and Bernoulli based explanations
for lift exist. I did reread the articles and as you note neither
discusses top/bottom air pressure in any relative/absolute magnitudes.

KK

[[email protected]]

Eric Greenwell wrote:
> Ken Kochanski (KK) wrote:
> > "The rest is generated by lower pressure on the upper side."
> >
> > hmmmm ...
> >
> > http://www.eskimo.com/%7Ebillb/wing/airfoil.html
> >
> > http://www.aa.washington.edu/faculty/eberhardt/lift.htm
>
> Can you point out where these articles compare the pressures on the top
> and bottom surface, or some reference that gives the relative
> magnitudes? I was unable to find it.
>
> --
> Change "netto" to "net" to email me directly
>
> Eric Greenwell
> Washington State
> USA

[309]

Eric Greenwell wrote:
> Can you point out where these articles compare the pressures on the top
> and bottom surface, or some reference that gives the relative
> magnitudes? I was unable to find it.

For "classic" airfoils, try the book Theory of Wing Sections, by Abbott
& VonDoenhoff, THE reference for us old aero types.

You'll see section pressure distributions that clearly show far more
suction on the top (area under the curve of pressure coefficient vs.
chord), than high pressure on the bottom.

People are forgetting that there are other factors affecting the impact
of winglets, including the height of the winglet and more importantly,
the toe in -- which some have claimed generates "thrust."

I won't pretend to be a winglet expert (flying a non-wingletted 1-26),
but it has been pointed out to me that winglets tend to be point design
items (e.g., Global Flyer, Voyager), or compromises that provide
different benefit at different angle of attack (or C-L).

In some bathroom stall (at Boeing, Douglas or Northrop -- I've worked
for all 3), there was posted a truism:
"There is no substitute for span."

However, more span means more wing root bending (trying to pull the
wing tips up until they touch...), and some other problems (e.g., stall
characteristics, tail power required...). The complaint about hangar
space is in there, too, but look at the span of the 777 and the A380...
If you build it, they'll make room. Or maybe the Eta?

Winglets have competition from their more contemporary cousin, the
raked tip (fashionable on aircraft such as the 767-400). The raked
tips begin to lose thier effectiveness at higher angles of attack
(e.g., near stall), and thus mitigate some of the downsides of winglets
or added span.

You'll still have vortices and wake. One day I flew through the wake
of the late Mark Navarre (OD), and told him he "thumped" me. He
complained that his glider (ASW-20?) wasn't supposed to have a wake.
If you're heavier than air and you're flying, you ARE going to generate
a wake.

[Charles Yeates]

> You'll still have vortices and wake. One day I flew through the wake
> of the late Mark Navarre (OD), and told him he "thumped" me. He
> complained that his glider (ASW-20?) wasn't supposed to have a wake.
> If you're heavier than air and you're flying, you ARE going to generate
> a wake.
>
Back in the sixties, during a contest at Grand Prairie, TX, I was in the
reurn part of an O&R task -- approaching Fort Worth. Ahead, crossing my
path and well below was a B-36 taking off with all ten engines working
mightely. About two minutes later, wake turbulence threw my Schweizer
1-23 almost inverted. Luckily, after recovery enough height remained to
enable a "good finish".
--
Charles Yeates

ZS Jezow PW-6U & PW-5
http://www3.ns.sympatico.ca/yeatesc/world.html

[Charles Yeates]

Charles Yeates wrote:

> Back in the sixties, during a contest at Grand Prairie, TX, I was in the
> reurn part of an O&R task -- approaching Fort Worth. Ahead, crossing my
> path and well below was a B-36 taking off with all ten engines working
> mightely. About two minutes later, wake turbulence threw my Schweizer
> 1-23 almost inverted. Luckily, after recovery enough height remained to
> enable a "good finish".

BTW, the 1-23 and I earned a Gold C and two diamonds in ten days at
Grand Prairie --EVERYTHING IS BIG IN TEXAS, eh?
--

[bagmaker]

Thanks to all for the information on winglets and lift production in general.
It seems there is still a lot to be learned in design of airfoils, even NASA cant give a defintive, simple explanation of what produces lift, in what amount the sucking or deflecting proportions are.
The hours of research available from some of your suggested links has left me with bleeding eyes and a sore back, for those who want the simple version, my reading of it is-

Wings produce lift by diverting air down. The reactive force is up, the balance is drag.
Winglets enhance the lift produced from the wing by minimising vortices (drag) produced where the upper and lower airflow mixes at the wing end. The balance again is drag, it wouldnt matter if they were up or down facing, for the purpose of aerodynamics.

I particularly liked the spoon-in-waterflow demonstration (so did my kids) and recommend everyone tries it.

Boom time here in oz, 1000k flights, competitions, sun, sun, sun.

Wayne

[chipsoars]

bagmaker wrote:
> Thanks to all for the information on winglets and lift production in
> general.
> It seems there is still a lot to be learned in design of airfoils, even
> NASA cant give a defintive, simple explanation of what produces lift, in
> what amount the sucking or deflecting proportions are.
> The hours of research available from some of your suggested links has
> left me with bleeding eyes and a sore back, for those who want the
> simple version, my reading of it is-
>
> Wings produce lift by diverting air down. The reactive force is up, the
> balance is drag.
> Winglets enhance the lift produced from the wing by minimising vortices
> (drag) produced where the upper and lower airflow mixes at the wing end.
> The balance again is drag, it wouldnt matter if they were up or down
> facing, for the purpose of aerodynamics.
>
> I particularly liked the spoon-in-waterflow demonstration (so did my
> kids) and recommend everyone tries it.
>
> Boom time here in oz, 1000k flights, competitions, sun, sun, sun.
>
> Wayne
>
>
> --
> bagmaker

Probably one of the best lectures I've ever heard on any subject, was
given by Mark Maughmer of PSU on the subject of winglets. I highly
recommend it if you ever get the opportunity.

Chip F

[Martin Harvey]

"bagmaker" > wrote in message
...
>
> OK, I can get the theory (OR can I?) with winglets to reduce wingtip
> vortices.
>
> Surely the best direction for the tip is DOWN!, I understand this may
> be difficult for actually making, especially with gliders and
> groundloops, aesthetics, etc, but can someone explain why they are
> pointing up?
>
> Consider this..
> The HIGH pressure area is UNDER the wing, we want to keep this from
> migrating to the LOW pressure area ABOVE the wing.

:-)

Look at it the other way: 2/3 of the lift is generated by the low presure
over the wing, and 1/3 by the high pressure under it ... so what you want to
do is to "seal" in the partial vacuum above the wing.

Anyways, according to the 2/3 1/3 explanation you'd expect a winglet to have
about 2/3 of its area above the chord line, and 1/3 below, which is rougly
what you see on modern winglets on commercial aircraft.

MH.

[Bob Caldwell]

http://www.mandhsoaring.com/winglets.html

Here is a link to the M & H web site with a bunch of tech lit on the subject. Great reading for insomniacs.

My understanding is the winglet is an airfoil creating lift directed inboard to counteract the span wise flow that exists due the fact that the airfoil is finite in length. An infinite span would have no span wise flow and therefore no tip vortices (induced drag). It is not just fence to stop the span wise flow as that fence would have to be much larger and create as much or more drag than it reduces. As one of these papers indicates it is much easier to design a bad winglet and get a reduction in performance than it is to design one that actually works. Dr. Mark Maughmer (sp) at Penn State is the wizard (and the author of some of the tech lit referenced above). His designs are still evolving even after much study and experimentation so the idea that the average pilot can slap some board on his wing tip and actually get a performance advantage is a pipe dream.

Fly safely.

BC