Vortex Generator position VG

[WurlyBird]

If this has been discussed before I couldn't find it in the search function. I would like to call on everyone that has, or has had, VGs to give a report of their model, how far from the leading edge they positioned their VG, and what change they had. This may provide some empirical data to help others in the decision making process. I'm gonna do it, I just don't want to go through the flight testing process if it's already been done by others.

[Dusty]

One vg's supplier (stolspeed?)has a testimonial section,a kf flyer tried staggered installation which he seems to think works.

[jiott]

Try the search function again. Quite a lot of stuff comes up if you use the words: VG's or vortex generators in the keyword box and search Titles only (advanced search function). This subject has been rolled around a lot.

[WurlyBird]

At the risk of being an ass, I followed your suggestion and searched "titles only" for "VG", "VG's", and "Vortex generators" and only two threads came up. One about what material to make some DIY ones out of and this one. I know VGs are discussed, A LOT, but I can not find much info about KF specific placement. Some people report miracles and other a waste of money, it comes down placement and having a collection of placement on each model and the results could be very useful. Maybe even helping fix issues with those reporting the wasted money.

[WurlyBird]

As an admission of inaccuracy, I had searched for "vortex generator". I went back and searched for "vortex generatorS" and four more threads popped up. Only one made mention of measurements and it was for only one model.

[Cosmofly]

Do try Stolspeed, they are Australian based. Very reasonably priced and the website shows quite a lot of data on tests that they conducted.
Good luck.

[tx_swordguy]

I fly an avid flyer with a heavy hauler wing so my mileage may vary. I bought my VGs from land shorter.com due to price more than anything. I placed them 10% back from the leading edge and spaced roughly 2" I believe. Not saying it is a miracle but I am definitely a believer. I will state my performance changes and let you judge whether it is worth it to you. For me it was. My stall went from 40ish to 37ish no noted change in top end. prior to VGs my landings when approaching the flair my wings would rock back and forth as they were losing lift ( at least that is what they felt like) Now the wings are rock steady all the way to the ground and it has given me much more confidence in slipping over the power lines to land on my 1000' grass runway. That in and of itself is why I am so in favor of them for no other reason. To me the stall difference is not a big enough change to worry about but it did change. I also put VG on the underside of my horizontal stab approx 1" apart not sure I really noticed much more pitch authority but I do get a warm and fuzzy feeling and would probably do that again anyway. As far as cleaning the wing to me just wipe front to back with a wet rag and I don't have problems cleaning. Hope this helps a bit
Mark

[WurlyBird]

Thank you for the feedback. I had not read the STOLspeed site. I like their information. Vortex-generators.com also has good descriptions as well as the best prices and an option for rectangular VGs like the ones BigJohn used on his KF that he reported on so well. I would like to go with landshorter.com just because they are the only one made in the US, but as is always the case they are not only the most expensive but you also need to supply your own adhesive and I like the idea of laser cut adhesive strips. But that is all brand stuff, which is not what this thread is about.

STOLspeed describes the location as being the highest point in the airfoil at a stall AOA. All other math aside, I want my plane to stall with the tail wheel in contact with the ground and the mains just off. So the VGs should be just forward of the highest point as the plane sits in parking, right? Is there a flaw with this conclusion I'm not seeing? Can anyone verify with their plane if placement works out like this?

[trentp]

I spoke with a man at Oshkosh who essentially invented VGs as we know them today for increasing performance (prior to him they were used by the military as "engineering bandaids"), Jerry Burr. He has done tons of testing with VGs at every different location on his wing and he said he found the sweet spot to be at about 4% of the chord. He didn't seem to think there was any huge loss with mounting them too far forward however if you mount them too far back they can end up being blanketed by the separated boundary layer of air at high AOA (like at stall or during landing) and be rendered essentially ineffective. I asked him why most manufacturers suggest 10% of the chord for placement and he said he had no idea, and that he can let them do whatever they want and watch them scratch their heads as to how he lands so much slower than them.

I did have VGs on my standard wing that were about 10% back from the leading edge, they were on there when I bought it but the previous owner told me they didn't do much. On the STI wing I went ahead and placed them at about 4% and they seemed to have a pretty solid improvement. The plane is much more stable at slow speeds and it definitely stalls a little slower. It's insane the AOA that I can hang on the wing at. Overall I am happy with them and would definitely recommend them.

I used the STOLspeed VGs, they are nice because they are clear, are taped on instead of glued (you can remove them if you don't like them) and they are cheap :D

[tx_swordguy]

I am no engineer so take it for what its worth, but I don't think the a visual mark is going to be the proper place to use (highest point sitting) As Trent says too far back you will loose the boundry layer before the VGs have a chance to "stick the air to the wing" It may even disrupt the air even more and exagerate the stall but that is just me thinking here. Each airfoil is slightly different and the wing may have a different high point. I think in general the VGs are placed before the high point to ensure the air adheres to the wing to keep the lift. What ever you do I would not try to out think the VG engineers.

[efwd]

I thought we agreed that the engineers didnt get the carb synch cross tube right?

[WurlyBird]

The "engineers" also agree that somewhere between 4-12% of chord SHOULD improve flight characteristics. In this case of course, the "engineers" are any people that want to shape pieces of Lexan and be panacea salesmen. Here is a quote from the STOLspeed website,

"So, with the wing positioned at the stall angle of attack, the VGs should be slightly forward of the highest point of the airfoil."

So if my KF3 stalled in a 3 point attitude (I wish) that would mean it stalls in the same position as when taxiing or parked. I'm not trying to "out think" the engineers, just rephrase. That's also why I asked if anyone could look at their VG and confirm or deny.

And furthermore, if the "engineers" are so spot on why don't we just fly Cessnas that we could buy for less than our KF? For that matter why are all the KF so different from one another?

And if you're wondering why "engineers" is in quotes so much, it's because anyone that manufactures a solution to a problem is an engineer and level of schooling or a title is not necessarily indicative of capability. I know old school, blue collar machinists running on a GED that are far superior engineers to most Ph.D. recipients.

Now if you'll excuse me, I need to take my soap box over by my plane so I can look at the top of the wing.

[tx_swordguy]

Ok point taken. Call them basket salesmen for all I care. My vgs are ahead of the highest point of the wing when sitting 3pt. I have no idea if it stalls in that attitude or not, I believe it is much more tail down when it stalls. I followed the instructions from the site I got mine from and it worked out well for me. Your mileage my vary so do what you want

[GMKman]

You can use double sided tape to temporarily experiment with various placements ( which is what I did). I lost one or every once in a while but was worth the data. I found that the more forward/ the more effective however it came with a cost of more drag. I inevitably didn't like the look or the drag of them and didn't feel like they made much difference so off they came with no harm to the wing from the sticky tape.
I did put some on the bottom of the elevator which made a difference in authority ( I still have the small elevator with a continental engine up front).
I "glued" them on permanently now. I'm happy with them.

[redbowen]

Here is a video I put together showing a VG installation. Hopefully it is helpful.

https://www.youtube.com/watch?v=vGzHZKRZi7s

I also started a new thread for it here.

http://www.teamkitfox.com/Forums/showthread.php?p=71255#post71255

[DesertFox4]

Great video Bryan.

The larger elevator would be a good mod to increase elevator authority in the flair.

[jrthomas]

I installed Stolspeed vg's yesterday and thought some of you might be interested. I installed mine about 2 and a half inches from the leading edge. I used the 90mm spacing except for the 24 inches from the wingtip where I used the 60mm spacing. My flight testing was not under ideal conditions since it was mid day, well into the 90's and thermals making things pretty bumpy but the results seem to be pretty impressive so far. Stall with zero flaperons went from 45 mph to 40. There was a tremendous increase in angle of attack before stall with the vg's, especially with flaperons, so obviously they're working. I don't have any exact stall numbers with flaperons down because of the thermals and the wind changing directions. I was into the mid to upper 30's but I'd like to try it again in more calm air before giving any exact numbers. It's just amazing how it hangs in the air at that speed and AOA. Oh, I'm flying a Model 4/1200, 912ul, long wing but with all the Speedster options so it's a little heavier than some. James Thomas

[Hockeystud87]

Great info! I was thinking about VG's at some point as well... Lowering your stall is never a bad thing!

Any issues on the top end? Speed decrease?

[jrthomas]

I plan on flying tomorrow so we'll see how it does and maybe post my results tomorrow night.

[David47]

Did you put any vg’s on the stab. Lower surface as well ?. This should increase overall tailplane effectiveness ...

[jrthomas]

Not yet and not really planning to at this point though that was my plan before I flew it. Slow flight AOA is so extreme that I can't imagine needing more elevator. A full stall landing, stick all the way back would cause the tailwheel to touch long before the mains as is.

[skyguy04]

Just chiming in here with another report on the Stolspeed VGs. jrthomas helped me install the Stolspeed VGs on my Model 4 Speedster. We installed them at the same location (about 2" back from leading edge). Basically we just put the nose of the VG on the leading edge tape line. We did not stagger them, and we used the 60mm spacing. My Speedster has the short wing and it worked out to exactly 60 vg's per side.

First flight test showed very noticeable difference. No flaps p/off stall went from 47 to 43, full flaps from 41 to 37-38ish. Also the stall characterics improved. It used to buffet/shake when it stalled and now it just hangs. Very smooth/solid feel as the nose just bobs. P/on stall is ridiculous. The AoA feels like i'm standing on the tail and it stalls in the low 20's. If I am ever in that situation on takeoff, i've got much more to worry about than stalling.

[Norm]

This is something I have been considering for some time as my Model IV at 700Lbs empty has the 47 mph stall.
2 inches sounds very close to the leading edge as 10% of the chord is what the instructions say, however you are not the first to say this. I just want to confirm, if I take a carpenters square, place it on the leading edge (including the vinyl cuff) I can place the VGs two inches back. A five mile/hour drop in stall is a huge drop. I am always envious of my friend in his Savage cub landing so slowly. Seems like his stall is just above 30 or so.
I hope I am reading this right.

[skyguy04]

I'll measure exactly today as i'm out at the hangar. I used the leading edge tape line as a straight line and put the nose of the VG on it. See the attached pic.

https://photos.app.goo.gl/CMspYPCzbWQ8rL5R8

[efwd]

how long before those turn to urine yellow color and become brittle? Maybe they are built better than that? Can anyone speak to this?

[jrthomas]

how long before those turn to urine yellow color and become brittle? Maybe they are built better than that? Can anyone speak to this?

I can. One of my friends put the StolSpeed vg's on his "Swick T" Taylorcraft 7 or 8 years ago. They're all still there and look just like the day they were put on. I did some research before installing mine. If I remember right, the wings are about 43 inches wide and 4% worked out to something like 1.72 inches. I just used the finishing tape as a line to follow which was 2 inches or so back from the leading edge. I remember reading that people that put the vg's farther back saw very little if any improvement. Brian's improvements pretty much match mine so I think we're onto something. What's even more impressive than the much lower stalling speed is the way it will hang in the air at an AOA that I never came close to before. "Standing on its tail" is the way Brian put it. I went out for a while this morning and as I was on final I heard myself say out loud "how slow can you go". I'm much more confident coming in slow and it even seems to touch down softer doing a full stall 3 point. Oh, one more thing. SlolSpeed calls it 120 vg's but we put 120 on Brian's and I think we still had 9 left. Nice of them to put in extras I thought. Another thing. I didn't loose any speed and I don't think Brian did either. I'm a believer!

[skyguy04]

Not sure. But they were only $97 shipped for 120 of them. And they just stick on with 3M sticky tape. I would imagine they would be easily replaceable. It took us about 45 minutes to install them.

[efwd]

$97?! Thats a good buy for the results your showing. Ill probably do it later.

[GMKman]

You can use double sided tape to temporarily experiment with various placements ( which is what I did). I lost one or every once in a while but was worth the data. I found that the more forward/ the more effective however it came with a cost of more drag. I inevitably didn't like the look or the drag of them and didn't feel like they made much difference so off they came with no harm to the wing from the sticky tape.
I did put some on the bottom of the elevator which made a difference in authority ( I still have the small elevator with a continental engine up front).
I "glued" them on permanently now. I'm happy with them.

I need to retract some of this statement. I installed Stolspeed vg's on my wing now in pretty much the same place Bryan did in his video and DEFINITELY like the improvements in lower stall speeds, low speed stability, and no real drag increase. Not sure why the other vg's I tried didn't work as well but I'm glad I have these on my wing now.

[NinerBikes]

Ed, did you end up yet with these being installed?

I don't remember looking for them on Saturday.

Or will you fly first, get some measurements, and then install at a later date, so you can note and log the stall speed difference between clean and Stohlspeed installed a few inches back?

[efwd]

You know what, I enjoyed this build a bit too much I think. I am certainly not demonstrating the same drive to get it flying as you all well have noticed. I am not yet ready in my piloting skills now that I have not flown since April. Winter may delay me from flying with Paul so Im not rushing. I may need to get a check out in a Citabria down here in Southern CA where the weather is great for flying year round except winds. I have left a few things on my plane that will be done in the future. I like the thought of having the set up I have and will add Vortex generators, T3 tailwheel, in flight adjustable prop for some fun tinkering at a later date. I need to get my but flying so I am comfortable with the first flight.

[NinerBikes]

You know, Ed, it's such a beautiful build, with the fuel injection, 3 blade prop, and that G3X... IMHO, it would be a shame if you couldn't at least get 40 hours on it before Ohio. Or at least fly solo logging some hours to Copper State, in Feb. But, what do I know.... your plane, your schedule. It's a beautiful build. So good, your boy is asking for it already in your will / trust fund!!!! LOL!

[jmodguy]

After watching Bryan’s vid I will be putting them on before 1st flight!
Thanks Bryan for validating their worth!

[efwd]

Sorry, Lost track of what thread this was back there. Shouldn't of hi-jacked it.

[NinerBikes]

Stolspeed and Vortex Generator vanes for the leading edge, 2" back to lower your stall speed of plane under prop power. Not quite as effective dead sticking, so I have read.