Vortex generators on Super STOL

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Vortex generators on Super STOL

Postby Jim Bair » Sat May 30, 2015 5:37 pm

i did some testing before and after the addition of VGs on my SS. I'm pleased with the results. I'm not pleased with my inability to get the audio to attach to the video so I had to put in title pages to read what is going on instead of me simply describing it while the video is running so you may have to pause an extra couple secs on each page to read what's going on. My apologies. If I get it fixed I'll repost the video. In the mean time, here is what I did and the bottom line is that achievable AOA increased by approximately 10% with the addition of VGs both power off and power on.
https://m.youtube.com/watch?v=vtMhWbubQ ... e=youtu.be
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Re: Vortex generators on Super STOL

Postby Just Aircraft NZ Ltd » Wed Jun 03, 2015 1:49 am

Great work Jim. It's great to actually see the difference that we feel with the VG's.

Where did you place them exactly ?

The factory built machines that we bought into NZ have them as far forward as possible on the wing just against the aft edge of the slats when closed.

Cheers,

Grant
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http://www.justaircraft.co.nz
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Re: Vortex generators on Super STOL

Postby Jim Bair » Wed Jun 03, 2015 10:15 am

There is a space just aft of the slats (when retracted) where there is no rivets. Sort of like a missing row of rivets in the perfect spot. It is pretty close to the correct MAC according to the directions and seems to be a pretty logical place to install them. I used Air Wave, but I suspect they're all probably about the same result. I can't really comment on that. My instructions said to put them about 1% of the wingspan apart which would be perfect for a box of 100. However, I wanted to put some on the underside of the HS and possibly the rudder, so I got 2 boxes and put them a little closer together because i read the directions of other manufacturers, too. Opinions on exact spacing varied, which led me to believe that probably most applications would work, within reason. I chose 2.5" on center on the wings, and 1.5" on center on the HS, because those numbers made the math easy. Yes, we should have joined the rest of the world in the metric system, but I digress.... The bottom line was I could see a difference in the airflow over the wing the difference. It was smoother after installation and the angle I could achieve relative to the horizon measuring on the computer monitor was significantly different. Obviously the slats make a huge difference. An interesting exercise I didn't think of doing would be to do it with the slats taped up in the retracted position and make it a conventional wing for one test run. --Jim
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Re: Vortex generators on Super STOL

Postby Jim Bair » Wed Jun 03, 2015 10:18 am

I also see that on my original post it says there was a 10% increase in AOA. I didn't mean to type %. Not sure how that happened. I meant 10 degrees. Big difference. Sorry about that, but I hope it was clear in the video I meant degrees. --Jim
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Re: Vortex generators on Super STOL

Postby kenryan » Wed Jun 03, 2015 11:27 am

Jim, when you tested "before and after" were you testing the effect of placement of VGs on both the wings and HS or just the wings? The Zenith STOL airplanes use VGs on the bottom of the elevator because they are greatly effective at increasing elevator authority at slow speeds, but not on their slatted wing.
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Re: Vortex generators on Super STOL

Postby Jim Bair » Fri Jun 05, 2015 9:44 am

What I was really interested in was the effect on the wings, but it would have been interesting to do the same test one variable at a time. I installed them on the HS before testing, so I didn't get the data on the difference between none and and HS only. In hindsight, I wish I had done that one extra step to see how much the AOA could be increased with the addition of VGs on the HS. --Jim
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Re: Vortex generators on Super STOL

Postby Allan » Sat Aug 01, 2015 9:20 pm

Jim, I really enjoyed your video. Just for interest I didn't put the VGs straight on and I found that my indicated air speeds for power off stalls at no flap and full flap reduced by around 3 knots for my airplane when I did. That was with a weight around 1250 lbs in both cases. At the speed we are talking about its quite significant. Allan
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