PJ's VG's

[frank williams]

I've always wondered why PJ Roland's vortex generator arrangement seemed to be able to work with only as few as two vg's per wing panel.  Typically on full scale you see a whole row of numerous vg's strung out along the surface.  The following article,    http://www.stolspeed.com/id/8 describes a "rip stop" effect by vg's.  It seems that as a stall starts and begins to spread, if it runs into the vortex it can be "killed" or deterred.  The vortex acts like a "rip stop" thread in cloth.  As PJ has said that he can feel no benefit from extra vg's.  (I think that's a correct statement).  So ... more may not be better.  Interesting.

[Howard Rush]

That's interesting.  It shows again that trial and error is the way to go, especially on fancy stuff like boundary layer physics.

I started with an inboard pair , then added two more pairs per side (on both top and bottom, both left and right) when I thought I could feel a little improvement with each.  I guess I should try just an outboard pair, then work my way inboard.  I'd reckon that our wings start stalling near the tips. 

[PJ Rowland]

I just went with what I could feel.

I could certainly feel effects with them closer.. than further out.

When using the Tips only approach - say 12" from Tip inwards, the effect I was looking for seemed elusive.

Switching to the current configuration - out of the prop wash but closer toward the Fuse than the outter tips seemed to give me the results I was looking for.

As little as 2 did the trick.. but since then, and under the suggestions of Dave Fitzgerald and Howard Rush, I did add an additional 1 Pair ( for a total of 4 on each surface. ) Still spaced even.

I could notice improvement - but only in marginal circumstances over many flights. I confessed that if your looking to expand the envelope of performance the extra pair do help.


As for the Stab - I'm not convinced they help in ANY WAY AT ALL !!!

but thats just me..