winglets

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

"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.

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