So, the point of a turbulator* is to cause a little bit of turbulence that hugs the wing surface, which then prevents getting a big wodge of turbulence that separates from the wing and causes an outright stall.  This is as opposed to the stall strips that you sometimes see right at the leading edge of a wing at the wing root, which are intentionally designed to cause a Real Live Stall during high angle of attack maneuvers, but predictably and close to the center of gravity of the plane to avoid lots of roll moment and thus embarrassing things like the plane doing a tip stall half a wingspan above the ground.

I suspect that they're just having too great an effect, more like a stall strip instead of a turbulator.  That's causing the big stall that they're supposed to be preventing.  Either you just shouldn't use them on that plane at all, or you should use more and smaller ones** -- or if those are the only ones you have, line them up more with the airstream instead of angling them so severely.

If I had the courage I'd either just use the bottoms without the vanes, or align the vanes with the direction of flight.  Then I'd set the bottoms of my maneuvers about 15' off the ground, clench my buttocks, and try, try again.  Assuming I still had a plane at the end of that, I'd try them a bit forward of where you have them, to see if that makes things better (or bad enough that I had an opportunity to build a nice new plane!)

It could just be that your particular plane won't benefit from them.

* I could maybe bring myself to call them "trip strips" if they were continuous across the wing -- dunno why that name is setting me off.

** Those do look pretty big -- are they, or is it just the angle of the picture?

Ken is right, the vortex generators have been on the airplane since it was new. The electric tape behind it was the new addition that made for an interesting day

My guess is that the tape is lifting somewhere.  Did you remove wax from the wing before you put the tape on. If there's just one layer of tape, .006" or so thick,  it shouldn't do much at 24-26% chord.  I thought I saw some degradation--nothing awful-- when I put the trip strip behind the VGs, but I can't find mention of it in my log. 

Your trip strips are ugly. Gimme your postal address.

My guess is that the tape is lifting somewhere.  Did you remove wax from the wing before you put the tape on. If there's just one layer of tape, .006" or so thick,  it shouldn't do much at 24-26% chord.  I thought I saw some degradation--nothing awful-- when I put the trip strip behind the VGs, but I can't find mention of it in my log. 

Your trip strips are ugly. Gimme your postal address.

  Those are my “cut them with pinking sheers at the field, slap them on and see what happens” version. My NATS plane has .007” packing tape on at 25% cord and you can hardly see it

Sending you an email!

Interesting thought. It’s possible. I’m open to ideas on the cause as I’m at a complete loss. I only removed the wing strips and it returned to normal. The ones on the stab I can’t tell a bit of difference in how the plane flies.

As far as your thoughts on the VG’s and trip strips placed together, I saw Dave Fitzgerald have his VG’s placed on top of his trip strips. Naturally I had to ask and he said there was a benefit to having both of them. And naturally I had to try them on my NATS plane. Dave was correct, there was a distinct benefit having them installed on top of the trip tape. Since installing them, I’ve been able to fly the plane a tenth slower with ease (5.5) and no issues. Here’s a pic of them

Here are the things I know about trip strip turbulators. In general they haven't much impact on thin low chambered airfoils, (Michael Selig's test show some) and often but not necessarily improve the duration of gliders using highly chambered airfoils with them. Duration is the bottom of the power required to fly bucket so any benefit to drag reduction is measurable with a stopwatch. The thick symmetrical sections would fit in the high curvature and I would anticipate some benefit empirically, maybe. In order for the strip to have an impact they must be of the right thickness, on model gliders I normal use monofilament because it is easy to change thickness but thick tape works too. Making them thicker can and generally does make improvements, to a point. They have a sweet spot and further aft they are placed of that the less likely they will have an impact, my previous explanation. If they are behind the laminar to turbulent transition or laminar separation point they won't do much of anything except maybe trigger the stall separation (above speculation).  Trip strips don't increase the Cl max and generally reduce Cl max, they mainly reduce the drag of laminar separation which generally is a very low Reynolds number phenomenon <300,000, a small chord of 9 inches or less at 50 mph.

I used 0.060" and 0.090" string trimmer line on my 4/4  Laser aft of the max chamber to see if they would improve aileron effectiveness, they didn't. Someplace I have video of them installed in flight with tufts. Basically the boundary layer was already turbulent by that point.

Your experience with the stall characteristics being sudden and violent is consistent with a separation trigger. Usually, or I should say desirably, a stall progresses from the TE forward in a more or less steady progression with AOA. This causes a smooth bend in the Cl curve. When the stall begins at the leading edge from turbulence, the separation is rapid and causes the discontinuity in the Cl curve. This type of stall creates the perfect driving conditions for the "snap roll ona string", visualize Jeff Dunam's Jose saying it.  With such a discontinuity of the stall curve one wing can easily loose 40% of it's lift in just 1 degree of AOA difference which can be created with a little bit of yaw especially with a swept wing or one having a bit of dihedral.

That one airplane does and other doesn't probably lies within the airfoil, thickness and location of the trip strip. The evidence is that one strip is thicker, photo comparison and is triggering separation on the other airfoil, test result. A minor difference in LE radius can also make a significant difference in behavior. This means, even though your airplane could be the same design with the same basic airfoil it is still different. The Learjet model 60 is so susceptible to this that there is an Airworthiness Directive which requires a Learjet test pilot to test fly any LJ60 that has had LE work performed during field maintenance before release to service.   

Here's a question regarding the observation of flight quality. The statement that the airplane can be flown slower through the flight with trip strips and VGs is kind of open ended. In what maneuver(s) does that come from? I find that I can fly my airplane much slower than I do by three or four tenths primarily because of line tension.

I think the bottom line to this is take them off and leave them off. At least on this one airplane.

At the NATS, I was having problems with the hourglass, specifically the second corner. I worked with Dave Fitzgerald, Brett, Paul and Howard. It was a simple fix, keep adding tip weight until I didn’t have issues. I did have to pitch the prop up some to keep the speed up because it is a bit heavy at 70oz. I never got super comfortable with the hourglass by top 20 day and all the wind.

Since the NATS, I worked on the airplane on trying to improve the overhead tension, all the while continuing to fly around 5.4-5.5. The VG installation provided some of that improvement. I could fly at 5.5 and not worry much about overhead tension anymore. I continued to work on it, and ended up adding a 2 square inch area tab to the outboard flap and that provided a dramatic increase in overhead tension. The airplane was the best plane I had ever had at the NATS, now it’s way, way better!!

Okay that clarifies things quite well. In this case the VGs are within the realm or closely in realm of helping. It would be good to have a look at my AOA video and any of the other videos. The device on the wing tip was originally conceived as a reference device for doing things like evaluating the trim of the airplane and how much I suck at getting my angles set. The device is a box with two 60 degree supports. On squares the vertical posts should line up and the triangles and hourglass the 60's should line up. Look at pictures of 4/4 aerobatic airplanes and you'll see those funny looking triangular things on the wing tip, they are a reference sighting device.

Any hinging shows up as motion of the wing tip and therefore motion of me within the frame. My first "selfie" video you can see this fairly clearly as the wing tip exposing more view of me and less. To me, I thought I had the roll induced hinging fixed, I definitely was in the cross over zone weight wise. After seeing this, and knowing if I took weight out or added weight it would go backwards. I then calculated the area difference between inboard and out board and added a tab to equalize the flap areas to the outboard wing. All of the subsequent videos and I think the ones posted on SH are in the later configuration. I now have about thirty videos of the tufted wing in various configurations and wind conditions. Unfortunately I am a crappy note taker, I just learn lessons and move on.

My jury on VGs remains in deliberation. Certainly in aggressive maneuvering they will come in to play but I have to get very aggressive to get my airplane to go there, much more than required to fly the sequence. This can be a wing loading thing. A heavier airplane is going to approach the stall AOA much more frequently than a light one will and consequently will show more benefit of the addition of VGs. The only real thing I noticed moving to them was actually a reduction on line tension which I contribute to a likely asymmetric installation of the VGs. Most likely being that the inboard VGs are set ever so slightly different than the outboard ones. I'll remove them at some point in back to back flights to get a gooder B-A test than the A-B test. The initial test was a couple days between and perception is tough with such a long delay. Otherwise, I truly didn't get much perceived benefit on my airplane.

I have an overweight model that I have not flown very much at our 6,000+ foot altitude.  It mushes/stalls badly in the corners.  At the recommendation of a member from the West Coast Cabal, I placed the zig-zag trip strips cut from electrician tape place at 15% of the chord.  The mush/stall went away.  Moved the strips to 10%, got even smoother turns and some semblance of a sharp turn with no mush.

I am certainly no expert on these things with very limited experience using them, but I would suggest moving your strips forward, away from the high point of your airfoil.

Keith

I have an overweight model that I have not flown very much at our 6,000+ foot altitude.  It mushes/stalls badly in the corners.  At the recommendation of a member from the West Coast Cabal, I placed the zig-zag trip strips cut from electrician tape place at 15% of the chord.  The mush/stall went away.  Moved the strips to 10%, got even smoother turns and some semblance of a sharp turn with no mush.

I am certainly no expert on these things with very limited experience using them, but I would suggest moving your strips forward, away from the high point of your airfoil.

Keith

That's consistent with what I know as well as wind tunnel testing done by Michael Selig. At higher altitudes the Reynolds number is lower resulting in a higher likelihood of seeing laminar separation occurring. Your test result shows you're seeing that laminar separation. The most reliable position for turbulators is in the first few percent of the airfoil, around 5%. The impact of being too far forward is a slight increase in drag due to the greater turbulent / laminar boundary layer ratio. In CLPA that part doesn't matter much as it is measurably small. BTW the zig zag doesn't seem to have much performance advantage over a plain strip. What the test and empirical data shows is much stronger correlation to thickness and location than the other parameters, width and shape. About right on a 5 inch chord A2 airplane is around 0.010" and likely more like 0.015" on the larger CLPA airplane. As little as 0.002" can make an impact as well so the plastic films used for covering can be a trip.

From my limited experience with trip strips I gained very little benefit but I can see they could be trouble if placed too far back.  Howard’s VGs I found pretty effective on heavier airplanes when placed at 10% behind the leading edge as Frank Williams suggested to me.  Not much noticed further back or on lighter airplanes.  I do have trip strips just aft the leading edge of the stab on several airplanes to get turbulence started consistently on those surfaces.  I think that helps tracking at least.

Dave

Matt if you are willing to try it again (with caution)  move your zig zags forward to around 10% and see what happens.  Mine I cut from aluminum foil duct tape, cut both sides and 3/16" to 1/4" wide.  This tape is thinner that what you used by about half and stays down pretty well.  When you want them off douse them with rubbing alcohol to soften the gum and peal them up.  Being thinner the effect will be more subtle I'd think and shouldn't cause panic...the VGs are doing something different but not sure they are very effective where you have them.  When you dump those flaps the transition rolls well forward as the AoA increases.  I might guess as you have it configured, the transition rolled right across your strips and did something weird.

Dave

zizzag

You gotta excuse Frank's spelling.  Could be the influence of fellow Houstonians ZZ Top.

Here's where natural transition happens on an Impact MAC airfoil without an engine shaking it.  I figure from this that strips at 25% chord or so would affect round maneuvers, and 15% or so would affect everything.  I've been putting them in different places. Now I have them at about 20% chord.  They look cool.