winglets

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.

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 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?
--

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 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