On Friday, March 4, 2016 at 4:56:49 PM UTC-5, Bob Kuykendall wrote:
On Friday, March 4, 2016 at 1:14:43 PM UTC-8, Robert M wrote:

...if you are not flying absolutely in trim they will shed a vortex...

Robert raises some good points. The one thing that I'd add is that fences will probably shed a vortex even if you _are_ absolutely in trim. At issue is that airflow on the bottom surface will tend to have a slight outboard component, and that on the top a slight inboard component. These spanwise components will tend to be stronger nearer the tip.

Thanks, Bob K.

In engineering speak, "You fix one issue, you FUBAR another issue".
Question is, does the "fix" overwhelm the negative issue?

I can't/won't say, a lot depends on the speed ranges you run it as well as how coordinated you are (lots of side slip add's a lot of drag thus possibly negating any gains in the aileron sealing).....