The Rans S7 is well-proven with vortex generators.
I owned a Rans S7 for 100 hrs. When I bought it, it wasn't equipt with VGs, and I had to fly it home (15 hrs) without them. I was trained on tail-dragger aircraft, and the S7 is well-behaved, so it was familiar, but several of those landings on the way were 'abrupt'. I was wanting to do slow three-pointers, and found that if I was a bit high when the stall happened, it would test the durability of the landing gear, just as it will in any aircraft...... When we got home I didn't put VGs on straight away because I wanted to get more of a 'feel' for it first. Eventually I could sit it down OK, but it was a fine margin to get the speed and height just right.
After adding the VGs that margin improved considerably. Now the the stall became a progressively increasing 'mush' that would sit me down gently even if I didn't get it just right. It became very forgiving, and far more relaxing. Now it's easy to drag the tail wheel on first and sit the mains down gently - really slow, and good control. ASI showing less than 30 kts! It's really easy to see why so many S7 fliers have gone to VGs.
I also put VGs under the horizontal stabilizer to get firmer pitch control. The S7 had just enough authority in that regard, but the VGs now give it more margin for security. I also sealed the hinge-line gap with the household weather stripping that has a fabric pile like carpet. Removed the elevator enough to stick the self-adhesive weather stripping to the back of the horiz stab. I had done video tuft testing and noticed the tufts being sucked down through that gap - not a good sign for good airflow..... Very pleased with the results all round!
Found on the Yahoo Rans S7 forum:
I also recently installed the Stolspeed VGs. The stall, as near as I can figure it -- believe it or don't -- is at about 21 KIAS with either 3 or 4 notches of flaps. There is no break; there is no wing drop. You go into "falling leaf", and that's it.
Not that I've ever tried a landing at Vs x 1.3 = 27 KIAS -- but you've got lots of safety margin.
The manufacturer specifies 9cm spacing on the inner part of the wing, 6cm spacing towards the wingtips -- and 3 CM SPACING on the underside of the stab. I found that last bit surprising, but only until I flew the plane. Those ridiculously close VGs on the tail gave me tremendous, precise elevator authority that I never knew I was missing. Landings are a bunch easier.
Hope this helps.
As discussed in our recent telephone conversation I installed the VGs on my Rans S7 and while I have not done a full test on the aircraft I have done enough to convince me that they have made quite a difference.
Pre VG's at an AUW of about 410 kg the clean stall speed (power off) was 38kt IAS with a clean break and usually a slight left wing drop. With 2 stages of flap this would reduce to about 35 kt IAS.
With the VG's installed, and at the same weight, the aircraft does not exhibit any definite break, but simply starts to descend at a very high nose attitude with wings level and the stick on the aft stop. IAS is so low as to be meaningless.
If the AUW is increased to about 480 kg there is a slight nose drop as the IAS drops below 25Kt.
The aircraft can be flown with full control at 35 Kt IAS and now seems to be more stable in turbulent conditions. It is also much more forgiving when doing 3-pointers as it does not have the sudden drop at the point of stall that it had before, especially when using flap.
Another interesting aspect is the behaviour of the airflow at the wingtips. I have always been interested in the patterns left by accumulated dust on the upper surface of the wing when the aircraft has been flown in drizzly or dewy conditions. The airflow lines are clearly visible as dirty streaks over the wing. At the wingtip however, there was an area outside of a line from the outboard end of the wing leading edge to the rear of the most outboard rib where there was no apparent air movement at all. The dust layer in this area was untouched. After fitting the VG's (which go right to the tip) the lines left by the moisture flowing over the dust now show that the airflow is most certainly attached right over the whole of the tip.
Anyway those are a few of my observations.
Thanks again for your help.
Opening Windows on the S7
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