What is that "wing fence" for?
 

Hi!

I was just wondering what is the purpose of that thing in the picture below:

http://www.fotosik.pl/pokaz_obrazek/...37d77d157.html

wingfence.jpg | | Fotki, Zdj?cia, Obrazki Fotosik.pl

I've seen that in Pipers (Seneca V in the picture), Beech (King Air) and couple others.

Can somebody explain me what is that for?

Reduces lateral movement of air toward the wingtip hence reduces vortex (lift induced) drag.

What is efficiency of such small device? Why it's installed only in GA aircraft? Here you can see it even with King Air BLR winglet:

Winglet Systems - BLR Aerospace

(Enlarge pics on the right side)

Google is your friend

Google doesen't say a lot about that particular device. And of course we're not talking here about winglets or proper wing tip fence (like Airbus or PZL-101A).

Google so far gives me a tip that it can be connected with shielding pilot from the lights (landing or strobe). So as you can see it differs a bit from your theory and thats why I'm asking about some evidence of your statement.

To reduce span-wise flow.

Wing fence - Wikipedia, the free encyclopedia

hardly a light twin
http://farm3.staticflickr.com/2505/3...13c933e5_z.jpg

From wikipedia link above:

"Wing fences, also known as boundary layer fences and potential fences are fixed aerodynamic devices attached to aircraft wings. Not to be confused with wingtip fences, wing fences are flat plates fixed to the upper surfaces (and often wrapping around the leading edge) parallel to the airflow. They are often seen on swept-wing aircraft. They obstruct span-wise airflow along the wing, and prevent the entire wing from stalling at once."



This is not a device which I mean. Especially the dimensions, purpose, place of installation and size...

Of course you have to know that Seneca I II and III doesn't have such "wingtip device" from my first post. It's only fitted to Seneca V.

All of them are there for the same reason. Design details dictate the size and position; determined by either modeling or flight test.

Think you might find that these " fences" on the PA's are to help prevent glare from the tip lamps entering the nearby cockpit i.e. not an aerodynamic device at all :ok:

What rubbish.

Aerodynamically - poor to nil. They don't do much harm either.

Su-25s have it too.

Glareshield.

PPRuNe at its best.

Also sometimes referred to a stall fences, these devices tend to delay aerodynamic stall on the outboard portion of the wing by creating an impediment to spanwise flow along the upper wing surface. Several 1960s and '70s swept wing bizjet types used this aerodynamic "tweak" to improve low speed characteristics including the HS125 and Falcon 20. Dassault eliminated the need for them in later wing designs. Hawker/Beech replaced stall fences with vortilons for the HS125 -1000 and 800XP models.

westhawk

I think the fence referred to in the first pic is to reduce glare for the pilot.

That's nothing to do with aero dynamics.

Its the gauge that you use to find out when to trigger the de-icing boots.

And as reds says to stop the lights blinding you

Dak Man post #7 shows you EXACTLY what the fences are for.

Fences on the upper surface of a wing are used to help reduce reverse span wise airflow which in turn, help reduce the chances of wing tip stall to occur.

For it to work as an aerodynamic fence.
It needs to be thicker than the boundary layer and extend past the point of lowest pressure.

It would have to be a bit more beefy than 2 mm plate

It is simply to reduce the glare from the aircraft lighting. If you were able to get a close look, you would see a small hole in it, which helps you see if the lights are working.:ok:

Well I read the headline in the OP and didn't look at the image. I thought we were talking about FENCES! :uhoh:

westhawk

Sure about that are we??:ok:

OK, let us agree to differ.

On big aircraft (see Falcon 20, if I remember) the fence is to reduce span-wise flow. There is no doubt.

If, on little aircraft, there is a hole to see if the light is on of not, or protect the pilots' vision, fair enuff.

It has little to do with aerodynamix, however.

Well the a/c in the original photo is a G/A Piper twin with non-swept wings, indeed if you look at the "fence" in question it measures just a few cm of chord so is no aero value whatsoever!! Not to confused with genuine wing fences especially on 1st/2nd generation swept wing jets which do indeed help to reduce span wise flow. Another solution used was the "dogtooth" or "sawtooth" leading edge. :ok:

I flew the Hunter; I know about that also.

Ha! This thread is hilarious

Most people didn't bother to click the link the OP has posted, so are talking about actual wing fences, when the OP is in fact asking about the very small piece of metal at the very edge of the wingtip on a typical light piper.

They are clearly not for any aerodynamic purpose, but to stop the glare from the Nav Lights and wingtip strobe, which would be blinding at night otherwise.

How lucky you were! So your deep, extensive knowledge and experience should tell you that the devices,in the original photo has the square root of sod all to do with span wise flow or any other aero phenomena :rolleyes:

A nav light is so designed as to be visible only from certain directions.

Specifically, you can see the problem should that green, starboard nav light be visible from left of the aircraft!

Nav lights are arranged so that when they can be seen from another aircraft, they convey certain positional info on the aircraft showing them.

From memory is it 140 degrees from parallel to the centreline?

That wee 'fence like' thing is to make sure you can't see the nav light from the 'wrong' side.

a wing fence keeps the wing demons from getting on the wing and ripping it apart...please see the Twilight Zone episode known as "Nightmare at 20,000 feet"...note that there is no WING FENCE on this plane...we learned from that one!