Gary said,
Without - 134to 136kts, with 132/133 kts.

Thanks Gary,
I'm curious if you have numbers at higher MAP and higher IAS where the drag would tend to kick in more.?

re: why they work.  I'm not an aerodynamacist.   but one observation is that at high angles of attack, the bottom of the vstab may be in cleaner air than the top.

Colyn