WING FENCES

Airacobra · February 24, 2026, 12:01:28 PM

I just read an article that was provided to me that Dave Trible wrote and he seems to like wing fences and their effects on the plane. I was curious with the amount of expertise on this forum if anybody else has used them and what are the positives and negatives of these?

Dave_Trible · February 25, 2026, 07:40:30 AM

While wing fences surely aren't anything new, Mig aircraft has had them since the Mig 15 of the Korean war, they are pretty much untried in our sport-yet. From some of the questions and interest I have received I'm pretty sure others will be trying them out and I'd bet more than a few airplanes will sport them soon. However since the article came out there hasn't been much time and it's still winter in most the world so it is too soon to get much take on them. There has been more interest in the fences than the main points of the article if that is any indication.

Dave

david eyskens · February 25, 2026, 07:57:25 AM

Quote from: Dave_Trible on February 25, 2026, 07:40:30 AMWhile wing fences surely aren't anything new, Mig aircraft has had them since the Mig 15 of the Korean war, they are pretty much untried in our sport-yet. From some of the questions and interest I have received I'm pretty sure others will be trying them out and I'd bet more than a few airplanes will sport them soon. However since the article came out there hasn't been much time and it's still winter in most the world so it is too soon to get much take on them. There has been more interest in the fences than the main points of the article if that is any indication.

Dave

Hi Dave, can you post photo of the fences discussed here? Same as Gurney strips?

Dave_Trible · February 25, 2026, 09:45:43 AM

Yes I'll post a photo in a bit. Fences are entirely different than Gurney strips and a different purpose. Gurneys are vertical 'dams' stuck on the trailing edge of elevators (could also be flaps) that to my estimation, are control 'neutralizers' where the airflow over them cause the elevator to snap back to neutral after control pressure is let off. You might call it self centering as if the surface was spring loaded at neutral.
Fences are dams of another sort. As airflows over the wing the boundary layer naturally starts to curve outwards toward the tips which is aggravated by the air being pushed aside by the penetrating fuselage. Once the boundary layer starts to detach and go turbulent this layer rapidly grows thicker and simply lifts off the wing and is gone. I do not know what the prop wash might be doing here but it probably isn't helping. The fences stop the boundary layer from moving sideways, growing and lifting off the surface at that point. Then the whole process starts over cleanly on the other side of the fence without the influence from the fuselage and most of the prop wash. The gain is pretty significant in overall lift. It's like having larger wings without the added weight or drag.
I hadn't mention it before but my son in law is a pilot of many years. He teaches flying the 737 nowadays but has flown everything from WWII fighters to DC 3s to crop dusting for a while. He says there is a huge difference flying like Ag Cats with and without fences. Those without fences will shutter and hang on the edge of a stall during their tight turns. Those with fences turn tighter without the shutter. We approximate that with our stunt planes.

Dave

Dave_Trible · February 25, 2026, 09:55:40 AM

Well I don't how to post photos on this new site.......I am out of time right now. Maybe I'll try to figure it out later.

Dave

Dan McEntee · February 25, 2026, 12:49:29 PM

Quote from: Dave_Trible on February 25, 2026, 09:55:40 AMWell I don't how to post photos on this new site.......I am out of time right now. Maybe I'll try to figure it out later.

Dave

Hey, if I can post pictures now, ANYONE can post pictures now!! I mentioned on the other thread that this new format is a lot like the one that the Penton Owners groups site that I am a member of went to in the last year. I could post pics there just fine, just a few clicks and it's there. I just could never get a grasp of doing the resizing bit. So HEY!! LOOK AT ME!! I"M POSTING A PICTURE!! Maybe this new software does all the resizing for you?? As I'm typing this and adding the photo, it says it's .1MB or 108KB, but I don't know what that means. Is that what was required before?
Type at you later,
Dan McEntee

Dave_Trible · February 25, 2026, 01:40:17 PM

Ok so give me a clue? I find no icon that I understand as to photos.

Dave

Steve Helmick · February 25, 2026, 02:00:06 PM

Good job, Dan, you da MAN for posting a picture! As for file size, SSW used to have a 50 kb limit, and SH previously had a 1,000 kb limit. IDK what the limit is now, but for SH, I usually cropped and compressed pictures to just under 100 kb. With that done, I could post 10 pictures in one post. A lot of guys would post multiple pictures in multiple posts, which costs Sparky "bandwidth"...which rather resembles GVW or gas tank capacity. Some care in framing the picture can help tremendously. Avoid complex foregrounds and backgrounds. Clouds are fine, but leafy trees, grass, or exposed aggregate concrete makes the file size bigger, and that's not what we want to see in detail.

On the subject of Wing Fences, I have no idea what the reasoning might be, except to stop spanwise flow on a sweptback wing. They'd create more drag, make finishing more difficult and increase the eternal problem of hangar rash. I remember Duke Fox kitting a 1/2A stunter with an offset fence on the outboard tip. I don't think it was a great idea. Steve

Steve Helmick · February 25, 2026, 02:05:33 PM

"Click or drag files here to attach them." Too big, I reckon! Steve

Dave_Trible · February 25, 2026, 02:21:11 PM

I saw the drag and drop thing on the laptop. Actually I don't know how to that with relation to photos. In any case I am on my phone now and the drag and drop bar isn't on the mobile app.

Dave

Dan McEntee · February 25, 2026, 03:22:47 PM

Quote from: Dave_Trible on February 25, 2026, 02:21:11 PMI saw the drag and drop thing on the laptop. Actually I don't know how to that with relation to photos. In any case I am on my phone now and the drag and drop bar isn't on the mobile app.

Dave

Wait until you get home on a real computer. The right tool for the job!! I click on that prompt at the bottom, and my files window pops up. Then I can navigate to where the photo is, right click it and then choose "Select." If you have a quote in your post, you have to hit "preview" to see the link for adding a photo. Dan Winship took this ohoito I think at Oshkosh, or maybe was Mike Schmidt?? I always seemed to run into those two each year among hundreds of thousands of strangers!!
Type at you later,
Dan McEntee

Jim Hoffman · February 25, 2026, 03:47:55 PM

Here's Dave Trible's 2024 Nats plane w/ wing fences.

Dave_Trible · February 25, 2026, 04:20:57 PM

As always, thank you very much Jim.

Dave

If you take an airplane you are familiar with flying then put on the fences the first thing you may notice is how much longer the glide is on landing. You might wonder if it will ever come down. If the airplane is on the heavy side and sometimes stalls in overheads that will probably stop happening. Lastly, and I can't explain it at all- with the fences I have had to remove quite a bit of tip weight from airplanes I had in pretty good trim. Someday I will figure that one out.

Dave_Trible · March 01, 2026, 09:01:33 AM

Quote from: Steve Helmick on February 25, 2026, 02:00:06 PMGood job, Dan, you da MAN for posting a picture! As for file size, SSW used to have a 50 kb limit, and SH previously had a 1,000 kb limit. IDK what the limit is now, but for SH, I usually cropped and compressed pictures to just under 100 kb. With that done, I could post 10 pictures in one post. A lot of guys would post multiple pictures in multiple posts, which costs Sparky "bandwidth"...which rather resembles GVW or gas tank capacity. Some care in framing the picture can help tremendously. Avoid complex foregrounds and backgrounds. Clouds are fine, but leafy trees, grass, or exposed aggregate concrete makes the file size bigger, and that's not what we want to see in detail.

On the subject of Wing Fences, I have no idea what the reasoning might be, except to stop spanwise flow on a sweptback wing. They'd create more drag, make finishing more difficult and increase the eternal problem of hangar rash. I remember Duke Fox kitting a 1/2A stunter with an offset fence on the outboard tip. I don't think it was a great idea. Steve

Hi Steve. Duke came out with the 'Stunt Runt' for the Fox .07. I had one as a kid. It had what he called a skyhook on the outboard wing near the tip. I sort of remember we left it off ours back then. I actually have a another kit of it and an .07 here which I may get built one day. The airplane really did fly well though-full pattern capable I think on about 42' lines. The skyhook was a fairly large plate angled outward a few degrees to 'hook' air and pull the airplane outwards for added line tension. It probably worked but more likely in just adding a bunch of drag to keep the nose directed outward because of being angled away from the airflow. Something similar, there were a few fliers in the 70s who mounted a drag tab to the outboard wing tip to accomplish the same thing. The fences however are mounted perfectly straight ahead and should add nill in anything more than parasitic drag. These are 1/32" plywood about 3/8" tall so that can't amount to much. Yeah finishing with them is a bit more complicated but not too great. I don't put them on until after the wing is covered so no issue up to painting and sanding. It is kinda hard to control dope blisters at the joint-and it must remain square without a fillet. I believe the gain much exceeds the added effort.

Dave

Dave Harmon · March 02, 2026, 03:30:17 PM

Just to see if I could do it.

Dave_Trible · March 02, 2026, 04:43:57 PM

Quote from: Dave Harmon on March 02, 2026, 03:30:17 PMJust to see if I could do it.

There you go Dave! I'd sort of forgotten what it looked like. Wish I could remember what happened to the one I had about '66 or '67. Probably wasn't good. The kit I have now is incomplete but I'll figure it out. Also the Fox .07 I have now is RC. I'll just tie it open. I flew mine in the front yard where I grew up. Those longer lines-maybe flew it into an evergreen tree...I also have a kit of the Fox Falcon 35 which looks like it could just be a big brother of the Stunt Runt (without skyhook). Duke said he tested most of his engines flying the Falcon. The one my dad built for me in about '65 had a Johnson on it, it was the first .35 we had, and he put working wing flaps on it-couldn't know better. He bought the kit at a local hobby shop and it had no plans in the kit. Most all the other airplanes being flown in KC at the time had wing flaps so.....Can't decide about when (if) I build the kit I have to go with a Johnson or Fox as was intended. Maybe I can have it fit both.

Dave

Luke N. · March 03, 2026, 01:36:34 AM

Are the fences on the top only or both sides of the wing ?

Luke

Dave_Trible · March 03, 2026, 06:33:14 AM

Quote from: Luke N. on March 03, 2026, 01:36:34 AMAre the fences on the top only or both sides of the wing ?

Luke

They are on both sides to function equally on inside and outside maneuvers.

Dave

Ken Culbertson · March 03, 2026, 09:14:26 AM

I don't think that wing fences are any more effective than turbulators. I tried them once in the mid 60's and they seemed to work but at that stage in my flying career I just seemed to know what I was doing. (not sure that has improved). They helped on a plane that was most likely poorly trimmed by today's standards. It appears that those using them today have them just outside of the prop arc. I am wondering if they are simply blocking or channeling the prop blast. Most of the articles I read were describing their effect on swept wings, mostly jets, which have no forward propulsion. I would suspect that tip shape has more to do with controlling vortices, but I have no proof and that is a different question.

Ken

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WING FENCES