Wing fences

[RickH]

Have been doing some reading on wing fences and am wondering if anybody out there has any experience with fitting these to air craft, what type of aircraft , location and type of fence etc, also results.

 

Are there any simple designs that you may be aware of. Also thoughts on vortex generators.

 

Regards

 

RickH

 

 

[Kyle Communications]

www.stolspeed.com

 

for vg info and awesome videos on vg testing

 

 

[Guest Maj Millard]

Wing fences work. They basically 'straighten' the airflow across the wing, and make the wing more efficient. Air, much againt common belief, does not flow straight across a wing from front to back. It wants to 'flow' at an angle toward the tip where there is lower pressure . A wing fence located about a third of span from the root will have a major effect on the whole wing.

 

When I started testing my Biplane years ago, with a wing based on the one in my avatar (Easy riser), I just thought it should be getting off the ground quicker than it was, with all that wing area. By way of experimentation I fitted wing-fences about a third of the span out, and I reckon it took 1/4 to 1/3 off my take-off roll distance. The fences are fitted parallel to direction of flight, and were approximatly 1/2 as high as the max thickness of the airfoil (this may vary with different wings).I recall removing the fences and doing some more runs just to confirm that they did work.

 

They are not just a low-speed thing either, the Mirage 111 supersonic jet had wing fences on it's highly swept delta wing. They were in the form of leading edge 'saw cuts' which directed a flow of air above the wing to form 'air fences'.

 

Some wing types may find the application of wingfences more effective than others. One of our DHC-2 Beavers has an improved 'high-lift' wing fitted, and there are wing-fences fitted at the junction of flap and aileron. There are aslo two 'lift-producing' devices fitted close to the wing root, one about a foot out and another 18' further out....Vgs of course also work very well, especially at very low speed where they improve the wings capability to 'hang-on' just above the stall.

 

Because of their small profile they produce almost no drag at higher speeds.The turbulance-producing design of VGs produce lines of turbulance along the whole span of the wing and are in fact a series of little wing-fences which also 'straighten' the airflow. Also because of the 'disturbed' air they also delay the separation of airflow from the top wing surface, which delays the stall..................................................................................Maj...

 

 

[djpacro]

A fence may also be useful to prevent spanwise spread of separation. Fences, VGs, strakes etc are some of the fixes that often appear during a flight test programme. They are my thoughts, Rick, and I have had successful experience with them on GA aeroplanes.

 

 

[Guest GraemeM]

I parked my gyro into a barbed wire fence once, did not help much at all. Although it did take chunks of hide off me in various places.

 

Graeme.

 

 

[Guest Maj Millard]

GraemeM, those are called lift decreasing devices !!!!!!

 

 

[RickH]

Thanks heaps guys for the input I think you have confirmed my thoughts and also settled the question for me.

 

I think I will probably look at attaching a set to my machine. I am limited to having to position them at about two thirds span out from the root and seem to recall reading somewhere that this was the preferred position although I note Major that you mention it as being one third. What are your thoughts on the differences between these two positions.

 

Regards

 

RickH

 

P.S. Not sure I want anything to do with fitting the barbed wire kind Graeme. Not good for fabric coverings.

 

 

[Guest Maj Millard]

Mine on the bipe were 1/3 span out from root and worked well there, (10 deg swept wings) I didn't try any other position. I looked again today at the Beaver, and they are 2/3 out from root. I would guess that there would be more benifit derived inboard of the fence so maybe 2/3 out is the place to be ?.........................................................Maj...

 

 

[RickH]

Thanks Major

 

I really appreciate your input.

 

Regards

 

Rick

 

 

[djpacro]

Spanwise location for the fence depends on the spanwise stall pattern. eg if the wing stalls at mid semi-span then putting a fence inboard of that is fairly useless.

 

The way things normally happen is that a problem is identified and then an appropriate fix is considered.

 

 

[eightyknots]

Now, if only they had some solid wing fences at the Paris Airshow, the Airbus A380 wouldn't have caused so much damage to the building:

 

http://www.airlinereporter.com/2011/06/airbus-a380-wing-hits-building-at-paris-airshow/

 

 

[eightyknots]

Have been doing some reading on wing fences and am wondering if anybody out there has any experience with fitting these to air craft, what type of aircraft , location and type of fence etc, also results.Are there any simple designs that you may be aware of. Also thoughts on vortex generators.

Regards

 

RickH

Seriously though, a wing fence article I read which explained it pretty well is here: http://www.b2streamlines.com/WingFences.pdf . To sum up, they're usually mounted between 40% and 60% from the wing root. I read elsewhere that winglets are really a form of wing fence as well.

 

I wonder how many RA Aus planes actually have them and, if so, does the extra weight make it worthwhile in improved fuel savings, range or stall speed?

 

 

[Sapphire]

Have been doing some reading on wing fences and am wondering if anybody out there has any experience with fitting these to air craft, what type of aircraft , location and type of fence etc, also results.Are there any simple designs that you may be aware of. Also thoughts on vortex generators.

Regards

 

RickH

I previously had a Varieze which required these devices. The downwash from the front cunard would stall the outer wing area at low speed [ie short final] causing uncontrolled roll. Modifying the shape of the wings leading edge was another method to solve the problem by Rutan

 

 

[Guest ozzie]

There is also a leading edge addition fitted to Piper Warriors that is a short length of triangle extrusion that is about 6 inches or so long about 3 ft from the wing root, this was an AD about 20 or so years ago. It causes the inboard section to break earlier than the outer wing at the stall.

 

added

 

i also fitted some VGs as part of some performance kits. One such VG application was fittted in front of the ailerons of some high performance twins and singles that suffered from stiff aileron input at speed. The VGs softened up the control input as well as improving low speed roll control. Some kits also included them for rudder and elevator.

 

Ozzie