trying to understand winglets

[jeanpascal]

we are making researches on winglets.
for the moment we try to show the vortices that are created by the wing of our model glider.
that's why we are trying to construct a wing that have a lot of drag and the problem is that we don't know what is the airfoil we should choose :)
we know people usually seek the contrary, but if someone could help us to find the good dimensons it would be fine.
after that we would bring our plane through a smoke and notice it's behavior.
thank you.

[Andy W]

Anything undercambered..
..a

[Sparky Paul]

I did some tests with winglets on a ZAGI™, using 1/4" cassette tape as streamers.
The streamers began about 4 feet long.
On the no-winglet plane they shortened in flight to less than 50% of the length.
On the winglet plane, they stayed the same length.

[Andy W]

Why?

[raptor22]

How bout a thick undercambered wing that needs with WAY too much reflex. Then put it on a wing.

--Alex

[raptor22]

Or, and I think this is ideal for draggy, you can use profili to thicken and sharpenbt he leading edge of a modern transonic airfoil. Forget the proper name right now, but they are flat on the top with curvature on the bottom. Except at the TE, where it is heavily cambered to make up for the wierd forward sections.

These foils can reach up to mach .99 without going transonic, but suck like verything at lower speeds.

--Alex

[Sparky Paul]

Why?
.
Because I could?
.
The tipless plane's vortex tears up the tape, as the lack of a tip surface concentrates the energy in a single vortex.
The tiplets spread out the vortex over the span of the tiplet.

[macr]

Next time put the tape in the same place and see the difference. Your test is not accurate, by putting the tape on top of the tiplets away from the wing

[Sparky Paul]

Do it yourself.
Post the results.

[Andy W]

Paul, I meant why did it do it, not why did YOU do it! :D
..a

[silentfly]

and a stupid question from me,
whats underchambered?

[Sparky Paul]

Paul, I meant why did it do it, not why did YOU do it! :D
..a
.
There is of course no difference in erosion of the tapes regardless of their position on the winglets.
I was actually looking to alleviate the bothersome head-shaking of the ZAGI™ type plane by experimenting with winglets or not.. the tape erosion was unexpected.

[Sparky Paul]

and a stupid question from me,
whats underchambered?
.
It's when the bottom of the profile is concave... this is the Selig 1223, an extreme example of such.. It's used a lot on the SAE Lifter airplanes..

[turbojoe]

Here is a simple winglet question....Is there a reason NOT to use them on a sport plane? I'm in progress on a scratch built (from plans) Eastwind Gemini Twin (http://www.eastwindmodels.com/). I'm starting on the outer wing panels and thought winglets would just look downright cool on this plane. I'll be using a variety of brushless motors as I plan to do some spirited high speed flying with this plane. Would the winglets be a huge detriment to aerobatic ability or high speed flight? Keep in mind I'm not looking for any benefits as they'll mainly be for looks. I just don't want them to render the plane a pig.


Joe

[raptor22]

On a sport plane that is not striving for absolute effeciency, it makes little difference either way in most cases. So unless you make them the size of the wing or something, they will not make it be a pig.

Theoretically, they will slightly increase high-speed drag whle improving you aerobatic ability (speed retention, turn radius, etc). Keep in mind that it will also tip stall surprisingly less, so if you want to do snaps or spins you do not want to have them.

--Alex

[jeanpascal]

Are the winglet interesting for airplanes in general?
I know Boeing use theme, but not Airbus.
Is there an explanation?

[natoquick]

Airbus actually does use winglets, but they're of a different style than the Boeing ones. In fact, I think Airbus was using winglets on aircraft before Boeing.

[Andy W]

I thought airbus had the ones that go up and down, vs. boeing's that just go up?

[natoquick]

Airbus has quite a range of winglet designs. The A300, A310, and A320 have winglets that go up and down (but the actual design varies between models). The A330/A340 has winglets that just go up; quite similar to what's on the Boeing 747-400. I believe that the A380 is going with a winglet that goes both up and down, similar to the A320 design.

[Spinner]

I recently wrote a book for NASA summarizing some of the contributions of the NASA Langley Research Center to aeronautics, and had the opportunity to put together a chapter on winglets with their inventor, Dick Whitcomb. You'll find a pretty complete review of NASA winglet activities beginning on page 35 at

http://techreports.larc.nasa.gov/ltrs/PDF/2003/spec/NASA-2003-sp4529.pdf

We tried to write it in non-technical language, and I hope you find it informative. :)

I think that Whitcomb's approach to designing winglets is one of the most misunderstood concepts around. For example, winglets are NOT the same as wingtip end plates (as posted by Sparky in his model tests), which have been around since the earliest days of aviation. Winglets are different--they are carefully designed for high subsonic cruise drag reduction, with wing bending moment constraints in mind.

We also have to be careful in our model applications, because for many aero design concepts (airfoils being one) full-scale flight conditions typically produce different results than our RC models. ;)

Thanks,
Joe

[Mat]

This might be off the subject alittle bit but in the book Model Aircraft Aerodynamics on p.69 it say a little about winglet and says that there is more drag on winglets below the wing.

[green66]

jeanpascal,

Not trying to discourage you, but this is a major technical challenge, especially if an aerodynamic benefit is sought over a wide speed range.

An effective winglet creates a flow field that destructively interacts with the tip vortex in order to reduce induced drag, without creating an offsetting increase in parasitic (profile + viscous + interference) drag. After evaluating smoke trails and deciding on your best winglet configuration, you'll have to quantify the reduction of induced drag versus the increase in parasitic drag.

Here is a good qualitative intro to winglet design (for full-scale gliders): Winglet design (http://www.mandhsoaring.com/articles/Winglet_Design.pdf)

[biber]

Some managers of airbus or boeing aswell want winglets because they are modern and because they themselves don't know how winglets work, nor do the customers. So they must have winglets. If they hadn't them it would be to old fashioned and nobody would want to fly with that old stuff. ;)