Winglets or Wing Fences??

[boeing boeing.. gone]

Hi

Just a quick question and probably a very straight forward answer... but. What is the difference between a wingtip and a wing fence?? do they do the same thing?? when would you choose one solution over the other..

Thanks in adavnce

Ross

[TheShadow]

Wing fence (normally at half-span) stops spanwise flow of the boundary layer. It's normally situate at half to 2/3rds span and extends no further rearwards than mid-chord. Its spanwise leak-stopper effect on the boundary layer can be reinforced by the endplate effect of a large tip-tank.

By contrast, a winglet extracts energy from the wingtip vortex and part converts the wing-tip's induced drag into a thrustworthy component. The winglet is normally optimized for cruise. In the future we may see variable incidence flow-modifying winglets.

[zerozero]

Good technical answers from The Shadow.

But I just want to address the very basics here.

Wing fences and winglets serve two very *different* functions.

Wing fences are used to inhibit the propagation of a stall--just as The Shadow described, they help to stop the burbling and airflow separation that begins at the wing root and spreads towards the wingtips during incipient stalls.

The basic idea here is to protect the effectiveness of the ailerons during very slow speed regimes.

Winglets, on the other hand, (again, credit to The Shadow) exploit *high speed* aerodynamics exactly as he described.

So just to be perfectly clear, one would never choose between wing fences or winglets. They each address very specific aerodynamic problems.

By the way, if you're interested in aerodynamics you might also be interested in other "fixes" like vortex generators and slotted leading edge devices.

Try a search first, but if you have any questions, fire away!

:8

B727 Wing Fence

http://tbn0.google.com/images?q=tbn:S9HwhXf8fyOymM:http://farm4.static.flickr.com/3229/2591675993_9ed2f9d067.jpg%3Fv%3D0

B738 Winglet

http://tbn0.google.com/images?q=tbn:UeFIQqehvBkDGM:http://upload.wikimedia.org/wikipedia/commons/5/5a/Winglet_B737-800.JPG

[mustafagander]

Take a close look at a B747, classic or 400 doesn't matter, and you will see that the inboard side of the outboard engine pylons actually is a fence. If you don't believe that it's meant to be a fence, take a peek at the inboard pylons.

A cunning way to almost get something for nothing. :ok:

[boeing boeing.. gone]

Thanks for all the help very interesting :ok:

[acunningham]

Mustafagander, what is the point of having a stall fence on the under side of the wing? After all, the boundary layer separation that causes stalls is on the upper surface, and the purpose of stall walls is to prevent the turbulent flow which starts at the wing root due to washout from flowing span-wise, especially on swept wings. Is my understanding incorrect?

[boeing boeing.. gone]

another question, sorry, what job does a wingtip fence do as opposed to a winglet??

thanks again

[FE Hoppy]

Next time you fly in moist conditions have a look for the votex coming from the pylon up and over the wing.


boeing boeing.. gone
Try doing a search as these subjects have been covered a number of times and the better contributers are less likely to print it all again.

[boeing boeing.. gone]

FE Hoppy

I did do a search!!:confused:

[redsnail]

acunningham,

The Hawker 800XP uses a vortilon, whereas the 800A uses a fence.

Explained here (http://www.aerospaceweb.org/question/aerodynamics/q0228.shtml)

[TeachMe]

I may be wrong here, but perhaps what the OP is refering to is the A380 which I seem to have read/heard had 'wing fences' that are on the end of the wing. Think this was on some post about one of them getting damaged or something and it flying without one side.

Or I might just be dead wrong about hearing that....

[FE Hoppy]

Try here to start. If you limit the search to tech log through the advanced search function you will get better results.

http://www.pprune.org/tech-log/320976-different-types-winglets.html