On Wednesday, July 9, 2014 3:34:25 PM UTC-6, Lee Davidson wrote:
has any one fitted turbulator tape to a kestrel or know where the best

position for it is, or if it's worth putting on at all.

I once asked Peter Masak and he suggested starting at 67% of chord but didn't think it would make a lot of difference, given the airfoil.

I later also discussed with Udo Rumpf more generally about the Wortmann FX67 airfoil series. His reply:

" The FX 67 airfoil can realise its potential.
It will fall short of any airfoil that came after, in one case before, as in the case of the ASW20.
I only know of one variant, the LS3 which performed reasonably well.
for a glider of that period. I do not know what the changes are on the LS3 airfoil, if any.

The sharp leading edge of the FX67/15 looks good for higher cruise.
but is detrimental in climb. combined with the high camber and the pronounced pressure drop in first 35% followed by a extreme pressure recovery make the airfoil very sensitive to all sort variables.
The bottom surface is very good and if all is right, the hinge line at 80% should act as a trigger for transition but a turbulator at 75% chord should do the trick

I recommend to place a turbulator on top at 40% chord only on the 40% outboard section of the wing. This turbulator is akin to small 3/16 cylinders (with sharp defined edges) about .040" high and spaced about an 1.25" apart.

The reason, the airfoil is Reynolds number sensitive.
this will help to keep the flow attach at slow speed and provide effective aileron control. This will not help regarding gust sensitivity in thermals, which it very pronounced with the thinner FX67 variant.

Udo"

With upper and lower mylar seals, the Kestrel 19 aileron control is already very good, the upper surface placement seemed moot. I considered zig-zag for the vertical as my rudder (the larger chord Glossop mod) seems to 'hunt', that is, suffer from flow separation on one side then the other when flying straight. Haven't done so. Tom Knauff suggested better sealing on the rudder was needed.

Still on my maybe do list.

Frank Whiteley