The following is a posting on a Sportsman forum by an experienced pilot current on several types of aircraft::
I have to disagree with the advice given by some above. I approached the installation of vortexgenerators on the Sportsman to address specific performance characteristics; Lowering of the stall speed was not one of them although it did have that affect by only a knot or maybe two.
The main issues I sought to address were lack of low speed elevator authority in forward CG situations and stall characteristics (not speed) in the three point landing flare.
With a forward CG, full back stick (to the stops) had to be applied to achieve a three point landing. The other issue was that when the Sportsman stopped flying in the flare for a three point landing, you needed to be close to the ground because it really STOPPED flying.
"Stolspeed" VGs were installed first under the horizontal stabiliser as per the supplied instructions (100mm forward of the hinge line). During subsequent tests in a forward CG situation, three point and indeed tail first landings were then achievable with approximately three inches of remaining joystick travel; achieving a significant increase in low speed elevator authority!
Stolspeed VG's were then installed on the wing after flight tests were complete with the stabiliser installation. The VG's were again installed as per instructions, which included greater frequency (Smaller separation gap between inward facing pairs) along the outboard three feet of each wing from the tips to the large factory VGs. Outboard spacing is 60mm - inboard spacing is 90mm.
With subsequent flight testing, the noticeable drop when the aircraft stalled was significantly tamed with the capacity to reduce the rate of rapid sink still available by increasing the AOA with additional elevator input. This was not possible before the installation of the VGs.
The results were repeatable with multiple tests and tests were then extended to stall characteristics at altitude. The joystick can now be held at the rear stops in a fully developed stall (Well not quite if you read on) and a wing drop can be induced with rudder and then picked up with aileron input only after recentering the rudder. The outboard wings are obviously still flying and not stalled like the inboard sections and the ailerons are still therefore effective; A bit like the effects of fixed wing cuffs on a Cirrus or Cessna Corvalis (Columbia). I did the Australian agent's demonstration flying in the Columbias and this was a regularly demonstrated safety feature on my demo flights.
The Stolspeed VG's took about three hours to install in-situ under the horizontal stabiliser and about four to five hours to install on the wings. They are also inexpensive compared to other brands and come as a complete kit. I did have the supplier send me a few extras in his wing kit. He now advises that you should state a "Sportsman kit" if you order so he can include extra VGs. The VGs have remained tight despite being secured with only flexible acrylic adhesive supplied in die-cut sheet form. If one does work loose because you splash it with avgas (which dissolves the adhesive) they can be worked off and any adhesive residue rolled off with fingers before replacing.
In summary I am very pleased with the installation and say it is the cheapest modification I have made to our Sportsman tail dragger but one of the most effective. I recommend them.