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  #1  
Old January 7th 06, 12:20 AM
bagmaker bagmaker is offline
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First recorded activity by AviationBanter: Aug 2005
Location: Melbourne Australia
Posts: 167
Default winglets

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
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  #2  
Old January 7th 06, 01:22 AM
clipclip clipclip is offline
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First recorded activity by AviationBanter: Nov 2005
Posts: 16
Default

Quote:
Originally Posted by 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!, [...] 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
  #3  
Old January 7th 06, 07:50 AM posted to rec.aviation.soaring
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Default winglets

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.

  #4  
Old January 7th 06, 08:26 AM posted to rec.aviation.soaring
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Posts: n/a
Default winglets

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



  #5  
Old January 7th 06, 09:07 AM posted to rec.aviation.soaring
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Posts: n/a
Default winglets

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/Te...lets/Masak.htm
which explains the design and function of winglets.

Greetings, Erik.

  #6  
Old January 7th 06, 02:12 PM posted to rec.aviation.soaring
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Posts: n/a
Default winglets

"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/Te...lets/Masak.htm
which explains the design and function of winglets.

Greetings, Erik.


  #7  
Old January 7th 06, 02:12 PM posted to rec.aviation.soaring
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Posts: n/a
Default winglets

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/Te...ts/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/Te...lets/Masak.htm
which explains the design and function of winglets.

Greetings, Erik.



  #8  
Old January 8th 06, 09:44 AM posted to rec.aviation.soaring
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Posts: n/a
Default winglets

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

  #9  
Old January 8th 06, 09:48 AM posted to rec.aviation.soaring
external usenet poster
 
Posts: n/a
Default winglets

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

  #10  
Old January 8th 06, 09:49 AM posted to rec.aviation.soaring
external usenet poster
 
Posts: n/a
Default winglets


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/Te...lets/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

 




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