StolSpeed Vortex Generators on the Rans S7

The Rans S7 is well-proven with vortex generators.

I owned a Rans S7 for about 100 hours. When I bought it, it wasn’t equipped with VGs, and I had to fly it home, a 15-hour trip, without them. I was trained on taildraggers, and the S7 is well-behaved, so it felt familiar. But several of those landings along the way were abrupt!

I wanted to do slow three-pointers, but if I was just a little high when the stall happened, it really tested the durability of the landing gear, just as it will in any aircraft. When I got home, I didn’t install the VGs right away, because I wanted to get a better “feel” for it first. Eventually, I could land it smoothly, but the margin for getting the speed and height exactly right was very small.

After adding the VGs, that margin improved considerably. The stall became a gentle, progressive mush that would settle the aircraft down softly even if I didn’t get everything perfect. It became very forgiving and far more relaxing to land.

Now it’s easy to drag the tailwheel on first and let the mains sit down gently, really slow, and with great control. The ASI shows less than 30 knots. It’s easy to see why so many S7 pilots have installed VGs.

I also added VGs under the horizontal stabilizer for firmer pitch control. The S7 originally had just enough authority there, but the VGs gave it extra margin and stability. I also sealed the hinge-line gap with household weather stripping , the kind with a soft fabric pile. I removed the elevator to stick the self-adhesive strip to the back of the horizontal stabilizer.

Video tuft testing showed tufts being sucked down through that hinge gap, not a good sign for clean airflow. After sealing it, airflow improved significantly.

Very pleased with the results all around!
John G

I recently installed StolSpeed VGs. The stall, as near as I can figure, believe it or not, is at about 21 KIAS with either three or four notches of flaps. There’s no break, no wing drop, you just go into a falling leaf, and that’s it. Not that I’ve ever tried a landing at Vs × 1.3 = 27 KIAS, but you’ve got a huge safety margin.

The manufacturer specifies 9 cm spacing on the inner wing, 6 cm toward the tips, and 3 cm on the underside of the stabilizer. I found that last part surprising, but only until I flew it. Those tightly spaced VGs on the tail gave me tremendous elevator authority that I didn’t realize I was missing. Landings are now much easier.”

Griff

I installed the VGs on my Rans S7. While I haven’t completed full testing yet, I’ve done enough to be convinced they’ve made quite a difference.

Before VGs:

• AUW: about 410 kg

• Clean stall (power off): 38 kt IAS, clean break, slight left wing drop

• With 2 stages of flap: about 35 kt IAS

After VGs:

• Same weight, no definite break

• Aircraft simply starts to descend at a high nose attitude with wings level, stick full aft

• IAS so low as to be meaningless

• At AUW of 480 kg: slight nose drop below 25 kt IAS

The aircraft now has full control at 35 kt IAS and feels more stable in turbulence. It’s also much more forgiving during three-point landings, with no sudden drop at the stall like before, especially with flaps.

Another interesting observation: the airflow at the wingtips. Previously, there was a “dead” area beyond the outboard rib, with no dust streaks or signs of flow. After fitting VGs (right to the tips), moisture traces now show attached airflow all the way to the tip.

Thanks again for your help.
Dean, Australia