Wingtip Fence design ?

Tip fences put out two tip vortices instead of one, which can be quite draggy.
What about selecting a desired crossover altitude and designing a winglet to match it?

Mid-wing fences can work quite well in straight line flight. They can blank an aileron in a slip if too tall.

A snag or VG pair near the front of the wing just outboard of the aileron/flap juncture can serve a similar purpose and can be made active.

Jim,

Would you further explain the 3rd paragraph please.

Olibuilt said:

I've built a set of slatted (not yet) 17' wings, with the flap-aileron tunnel straight to the tip:
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I want to built a wing tip fence to finish the wing tip. Something like this wing:
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But I don't like the idea having something that ''hangs'' under the wing.
Would it be as efficient if the fence was only on top of the wing?? To force the airflow to stay on top of wing??

Any more design of fences??

I did my try with my paintbrush skills...
From small to big fence only on top.


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Thanks

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This thread is about all I was able to find on flat plate tips using the search function. Not a Cub but my RANS S-7S. What prompted this was my aluminum tube tip bow, used to be covered with kit supplied plastic tips, that did nothing but add a bit of weight, purely cosmetic, and I took mine off 1500 hours ago. But just the other day, walking by the plane, I noticed a couple 3/16" holes in the sides of the tip bow, and remembered that they were there for the assembly process: my wing jig spinner thing attached there, via nut plates. So, I spent about 20 minutes and bolted on some 7/16" OSB, taking a purely WAG on what size to make it, and went flying.

It stalled at the same number, but I only tested it with no flaps, but it seemed to reach a higher AOA, though at the same number. Then I shot a half dozen landings, all on slopes and holding it off as long as possible with lots of power, the last 2' above the snow, safe enough. These tips SEEMED to let me land even slower, hold it off longer, then I already do, which is really slow. Then I tried a high speed cruise, high speed for me anyway, 83 ind. at 7K, and if anything, it seemed to go maybe 1 to 1.5 mph faster WITH the OSB tips, this was a major surprise. It for sure was not slower anyway. For test purposes, the neat thing is I can jump out and take these off in a minute per side and throw them in the baggage. Out of pocket cost was zero, and I already had the means to secure them already there, seemed like a fun thing to try.

My next move, if I do anything, is to have a local composites guy make some carbon fiber ones, but if I do that I want to guesstimate the shape a bit better. These stick down about 1.5" below the bottom surface, not shown in the picture, I did that, just because, I guess. I for sure didn't want to block my side view so didn't consider going further. The top is also something I just intuited, WAG'd at. And the last rib is inboard a ways, like a Cub the tip bow is tapered down from the last full rib. I would also make them sexy looking, not like the squared off test ones, goes without saying! Any advice or info on this flat end plate fence concept, or whatever they are called, would be appreciated.

courierguy said:

It stalled at the same number, but I only tested it with no flaps, but it seemed to reach a higher AOA, though at the same number. Then I shot a half dozen landings, all on slopes and holding it off as long as possible with lots of power, the last 2' above the snow, safe enough. These tips SEEMED to let me land even slower, hold it off longer, then I already do, which is really slow. Then I tried a high speed cruise, high speed for me anyway, 83 ind. at 7K, and if anything, it seemed to go maybe 1 to 1.5 mph faster WITH the OSB tips, this was a major surprise. It for sure was not slower anyway. For test purposes, the neat thing is I can jump out and take these off in a minute per side and throw them in the baggage. Out of pocket cost was zero, and I already had the means to secure them already there, seemed like a fun thing to try.

... Any advice or info on this flat end plate fence concept, or whatever they are called, would be appreciated.

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Since your performance change was slight, take one of them off and go flying. Notice how heavy one wing is. That will give you some clues as too how much they help or hinder.

I thought that the flaps on my 185 could use some extra lift. So I put a fence on the outboard end of one of them to see what would happen. Nothing.

Fluid flow is from high pressure to low pressure. Having the tip plate below the rib outline helps meet the high pressure where it belongs, rather than letting spanwise flow to sill off the tip and go to the low pressure area above the wing. The whole idea is limit spanwise flow to the greatest amount possible.


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https://www.youtube.com/watch?v=FiOFtul8gu8 Steve's done all the work, I think I'll just more or less copy what he came up with! I know he does his homework on his numerous mods on his Highlander, obsessively so (and I mean that in a good way) and since mine flies so slow already, I don't think I can go too far wrong.

courierguy said:

https://www.youtube.com/watch?v=FiOFtul8gu8 Steve's done all the work, I think I'll just more or less copy what he came up with! I know he does his homework on his numerous mods on his Highlander, obsessively so (and I mean that in a good way) and since mine flies so slow already, I don't think I can go too far wrong.

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horsepower??

Me?? Strong 106.

courierguy said:

So, I spent about 20 minutes and bolted on some 7/16" OSB, taking a purely WAG on what size to make it, and went flying.

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OSB!? I want to hang out with you for a few days. I thought I was radical with marine plywood. LOL.

courierguy said:

https://www.youtube.com/watch?v=FiOFtul8gu8 Steve's done all the work, I think I'll just more or less copy what he came up with! I know he does his homework on his numerous mods on his Highlander, obsessively so (and I mean that in a good way) and since mine flies so slow already, I don't think I can go too far wrong.

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Thanks for that link. I hadn't looked at what he was doing the past few years. He's got hydraulic flaps, too.

RVBottomly said:

OSB!? I want to hang out with you for a few days. I thought I was radical with marine plywood. LOL.

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Free scraps no less. If I didn't have a composites whiz buddy, and fellow S-7 flier, I'd use some aircraft ply. CF ought to weigh about nothing.

courierguy said:

Me?? Strong 106.

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the plane in the video.

Something insane, around 300 hp, maybe more!

just curious, with that much power how do you tell what wing candy works and what dosent, with 50 hosepower and loaded up then wing stuff would tell the tale of the tape.

Agreed, the tips are such a simple mod, that requires no downtime of the aircraft, and so minimally labor intensive, to install in my case, and I'm not even building them, I figured what the heck I'll give them a shot. I'm more a simple and light as possible guy. I think those appearance is kinda cool also.

Tom, Copied the Super Stols after doing my research also. As has been sed , Would’ve been best to extend below the wing but didn’t want one more thing to hit my head on!

When I get them done, I'll fly over to Joe Clark's strip, he's Mr.Winglet, and he can tell me what I did wrong. Already have spades hanging down, so used to ducking, think I will stick with just a bit of plate below the wing. Half the fun of mods like these is BSing other pilots on your performance gains! Plus, like you, I'll have a nice flat area to put a sign of some kind on, or artwork.

Here's what I have settled on. Aluminum for now, carbon fiber ones on the way. Tuft testing and video camera documentation were considered, as was fluid flow dynamics calculations. I could bore you with my thoughts on span wise flow over a tapered (from the full rib) tip, but it'd just be all BS! I pretty much just pulled this out of my posterior. I realized Chrysler had it figured out long ago, google "1958 Dodge", and you'll see what I mean.

Again, this is no lose proposition for me, no mods to the plane, the attach points already there, so, what the heck? To my surprise, the results are "slat like." VERY low approach speeds, feel like 2-4 mph less then the already real slow approach my light bird can make. No loss in speed at all though, still as slow as ever.... but no slower. I would never be so casual about adapting this shape if it meant a major mod, adding weight and taking a lot of time, but I think I stumbled upon a trick tip for my particular bird. Nothing to lose, and I for sure seemed to have gained a bit of even lower approach speed at least when landing upslope like I almost always do, and with some power, sub 20 MPH touchdowns.

That is pretty neat, courierguy. I think I'll plan on leaving mounting holes on my wingtips for experimentation.

Sort of an aside, I was watching some geese land on the Snake River today. I've always admired their final approach in calm winds--wing tips bent down and stable.

So I was wondering if anyone has ever tried retractable fold-down tips?

The XB-70 for sure, but for different reasons.

ive been studying franks wing end plates for some time now.https://www.youtube.com/watch?v=5Nj-Q7VA_xE

RVBottomly said:

That is pretty neat, courierguy. I think I'll plan on leaving mounting holes on my wingtips for experimentation.

Sort of an aside, I was watching some geese land on the Snake River today. I've always admired their final approach in calm winds--wing tips bent down and stable.

So I was wondering if anyone has ever tried retractable fold-down tips?

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Off topic but couldn't help but remember how I loved to see the geese with wings locked and set for landing...and a splash down...when I was goose hunting! Sorry, it just slipped out.

courierguy, did you notice any change in your aileron response? If not, try extending that fence further aft to reduce swirling around the outboard end of the aileron.

Interesting question Sky! I think you may have suggested the tip fence when we decided to go with the droop ailerons on my LSA. Any idea on how far back beyond the aileron?

I didn't specifically test for that, but I've always seemed to have adequate control before , no change was noted either way. I set the end length of the tip based purely on where the aft tip nut plates were located. How far I could extend them past that attach point, without messing with additional attach points, may change when I get the carbon fiber ones, if they come longer then needed. I will getting CF blanks in effect, that a friend is laying up for me the next time he is working with the stuff, that I will cut to the final shape, Based on their stiffness I may extend them a bit further. The whole project was half ass from the start, and I just wanted to keep it simple as possible, if I was building up an entire new wing I'd do more testing as to the optimum tip length and placement, but for such a simple mod, it seems to be paying off. I landed about 20 or 30 times in an hour yesterday on the slopes across the valley from my place, just playing, leaving tracks I can see from my place later (with binoculars) when I get home! All gain and no losses near as I can tell.

I noticed that courierguy's ailerons extend to the wing tips with nothing else outboard. The lower side of the wing has a higher air pressure than the upper. Therefore the air has a tendency to flow out around the tip creating a swirling motion. This results in the outboard few inches in this case of the aileron, to have dirty air. With a fence the flow will be smooth and flowing straight aft. This will have the effect of increasing the area of the aileron, thus improving the response. Perhaps you have more than enough now, in which case the fence improvement would not be noticed.

There ought to be no need to extend beyond the trailing edge.

If you do decide to experiment by extending the fence further aft, consider adding a stiffener to prevent any flutter action. This could be just a simple angle stiffener in line with the air flow.

Another 2 + hours today of mucho slow flying and lots of ski landings.

I think I'm good with the fence stopping where it does. Unless I do a major wing mod and move the aileron outboard to the tip, and then enlarge the flap, (a mod other S-7 fliers have done) extending the fence will still leave a gap due to the aileron ending where it does. AFTER an extended aileron mod.....I would for sure extend the fence. All I need to really do is wreck a bit, easy enough to do, just enough to justify tearing into a really well flying wing, but I can't seem to do that. And I can't bring myself to mess with a done deal, especially as I fly slow/land plenty short already. It kind of bugs me that RANS seems to have gotten things as well thought out as they have, it leaves me with nothing to do but fly.

courierguy said:

It kind of bugs me that RANS seems to have gotten things as well thought out as they have, it leaves me with nothing to do but fly.

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Looking from the other end of a project spectrum, that doesn't sound too bad!