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

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

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

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

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

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

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.

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

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

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.