The design rules for counterrotating VGs are generally accepted to be:

• h = 0.95 * boundary layer height
• D = 10 * h (Distance between set of VGs)
• d = D / 4 (Center distance between a pair of VGs)
• l = 2.5 * h

Thus I designed the VGs for cooling to be:

• h = 2 inches
• l = 5 inches
• D = 20 inches
• d = 5 inches

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Once the templates are in position, it's simply a matter of roughening the paint at each VG location with a Scotchbrite pad (or a chisel in the case of the 310's wing-walkarea), and then gluing the VG tab in place using the provided two-part adhesive (Loctite 330).

Here's where proper placement of VGs is critical, Jay chimed in. If they're placed too far forward, they'll hasten the transition from laminar to turbulent flow and therefore increase drag. On the other hand, if they're placed too far aft, their effectiveness will be compromised. The trick is to mount the VGs right at the boundary layer's transition zone from laminar to turbulent flow.

How about icing, I asked? Won't the VGs pick up ice?

Not unless they're tall enough to poke up through the boundary layer, Bob replied.That's one reason why the VGs are sized to a height of about 80% of the boundary layer thickness. The VGs have been tested extensively in icing conditions during FAA certification, and do not pick up ice except possibly when flying in freezing rain or supercooled drizzle drops – conditions in which no portion of the airframe is completely immune from icing.

[1] https://www.kitplanes.com/vortex-generators-for-cooling/
[2] http://ntrs.nasa.gov/search.jsp?R=19930081705
[3] http://www.avweb.com/news/reviews/182564-1.html