Zig zag turbulators ...last thoughts

[Dave_Trible]

As I am evaluating my performance at this Nats one thing I am doing away with are the turbulators.  Do they work?  Absolutely but to a fault.  I'll explain.  I just never got the weather I needed to really fly and trim the plane well at home so I left early hoping for better winds in Muncie.  Those first few days we got very light wind early and just before dark but hefty winds during the day.  When qualifying began the air went near still.  This provided a good spread of conditions to test the turbs.  These really did generate enough extra lift in the dead air that my 75 ounce, 660 square airplane never dropped a bottom all week.  What they also did was change the standard trim on the airplane.  Early on I noticed the outboard tip whipping around which I didn't get during my few flights at home.  I methodically pulled out tip weight until I removed 10-12 grams which stopped the tip whipping in the steady air.  I did notice, but kind of blew off, the tip dropping at times when the wind came up.  Then came qualifying.  Day one I flew and bud Stan Powell told me the outboard tip was riding high.  I added
back three grams then three grams more and the wings were level again and the plane feeling pretty good for flight three.  My last flight the wind came up again.  Without changing anything now the tip was dropping badly on several down wind maneuvers.  Only then did it become clear what the issue was.  During a manuever dead down wind-in the wind the breeze is side slipping down the inboard panel with the turbulators working on steroids but blocking or blanking out a fair portion of the outboard panel causing a net imbalance between the two wings which is always there but not so exaggerated, causing that panel to drop and giving the look of way too much tip weight.  Again this goes away in better air.  Maddening!  
My verdict is that these are gone .  I have no idea whether the experience with VGs would be the same but I wouldn't know why not.  Some are trying these on the stab LE for other reasons  and may be satisfied.  For me,  full span turbulation of the wings is out.

Dave

[Howard Rush]

I wouldn't think that the effect of trip strips would change with sideslip.   I think VGs do something different, although maybe the zig zags act as VGs instead of (or maybe in addition to) tripping the boundary layer.  From what I've read about VGs, the effect of  / \ / \  VGs peters out as sideslip angle increases.   I haven't noticed any petering out.  So what we observe is the opposite of what I would have guessed, which shows how much I have to learn about how this stuff works. 

[Dave_Trible]

You and me too Howard, for sure.

[Peter Germann]

Trying to improve tracking in both level- and inverted flight, while bearing in mind the hypothesis after which boundary layer behavior may be be influenced by motor vibrations (or the lack of it), I have recently installed zig zag turbolators spanwise at 35% chord of the wing. I have chosen to put the turbulators at 35% chord in order to trigger layer separation at a defined point in level flight, rather then trying to influence separation at high AoA situations in manoeuvres.

Relevant airplane data is:  693 sq in. 65 oz  electric pusher  5.35 sec/lap  19% trivial pursuit airfoil with smaller nose radius, flat plate flaps with round TE. Turbulator is 0.3 in wide and 20 thou thick, 20 in long,  self adhesive.

With no trim change whatsoever, some 10 flights at zero wind conditions seem to indicate slightly better tracking without any side effect. Power consumption and behavior in manoeuvres remain unchanged. Inasmuch the effect observed is real or perhaps some kind of wishful thinking (placebo effect, perhaps) I do not know yet...

rgds, Peter Germann

[Dave_Trible]

Peter my thought would be you are sensing a real improvement under your described conditions if only that the turbulators are causing transition evenly along the span in one defined chord rather than a constant flux naturally. I would like your thoughts after you've flown this set up in some wind.  I'd suspect you are right that you won't notice much added lift in maneuvers due to placement of the turbs.  My experimenting has shown me the benefit of turbs may not be so much a net gain at one given transition but rather the sum of a consistent line of transition across the span without variance.  That also could be its problem with my particular application.  Regards,

Dave

[PJ Rowland]

If your trim changes with the addition of VG's or Turbulators - guess what ?

You model wasnt in trim to start with...

[Wolfgang Nieuwkamp]

Peter, after seeing the videos on http://www.stolspeed.com/id/4 I would suggest applying small vortex generators.
If a small camera could be mounted on your plane, we could see the effect during flight…
I know that our Reynolds numbers are much lower, but who knows.