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Old Jan 21, 2012, 01:52 PM
G_T
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Kevin,

Interesting pictures at 160K. It appears he placed the turbulator about 20% chord in front of the start of the bubble. I wonder if it really needed to be that much in front of the bubble? Of course this is at a higher Reynolds number then we are dealing with.

Gerald
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Old Jan 21, 2012, 02:29 PM
the anthropocebo effect
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Originally Posted by G_T View Post
Kevin,

Interesting pictures at 160K. It appears he placed the turbulator about 20% chord in front of the start of the bubble. I wonder if it really needed to be that much in front of the bubble? Of course this is at a higher Reynolds number then we are dealing with.

Gerald
Unfortunately people never do their wind tunnel testing at exactly the Re I wanted! One decent wind tunnel test is worth about 362,584 XFLR5 plots to me though.

He did a test with the turbulator on a slope across the panel (photo there), and he must have decided that was as far back as he could go to get the results he wanted. The airfoil on that glider was very thick (scale?), with severe laminar separation issues though.

Kevin
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Old Jan 21, 2012, 02:37 PM
G_T
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Benjamin,

Yes, I read other people's posts and the references they link to. I may not have read all of them yet though. I did read Philip's post you reference, with interest.

Perhaps my goals with the turbulator are different than yours. I am not attempting to improve the performance of the foils at slower speeds AT ALL. I am not attempting to place a turbulator in a location that boosts optimal performance of any particular foil.

What I am attempting to do is two-fold:

First, have the turbulator be effective at improving the synchronization of the foils in the outer portion of the wing.

Second, at slower speeds, have the turbulator be masked by the thickened boundary layer just in front of the natural transition or even have the turbulator behind the natural transition. The reason for this is to do no damage to slow flying characteristics. Note this philosophy is for the majority of the span of the wing but will not hold for the region approaching the tip (due to the flow being fully laminar at the tip and nearly so somewhat in from the tip, neglecting tip vortex and leading edge sweep phenomenon).

I am not trying to place a turbulator at the position for any particular foil station such that it boosts the performance of that foil at its expected optimal alpha. That is a different goal.

What I have specified is the rear-most location for the transition to occur for each foil in this series, under the assumption that turbulation will be used to achieve this. You are quite correct that the location of the turbulator required to achieve this needs to be determined for each foil in the series.

As to where I came up with the half root chord starting point for a turbulator for a quick test, that falls out of my goal #1, as should be shown by the picture in this post.

I very much appreciate the posts, the references, the examples, and the experience of those contributing to this thread!

Gerald
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Last edited by G_T; Jan 21, 2012 at 04:22 PM. Reason: Removing stupid cut and paste error.
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Old Jan 21, 2012, 10:29 PM
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FYI, my tests today on an AG45.. wing, were inconclusive. I ran 2 layers of masking tape, no pinking shears, darn it, in the rearward location per GT suggested location. No apparent consistent difference. I removed one layer, still no consistent change. The strips were .003 each, about 1/8" wide.

This particular plane doesn't fly a consistent straight flight path, if disturbed at all, it will go into a wide circle in either direction. Rudder area probably needs tweaking.

Gary
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Old Jan 23, 2012, 01:57 AM
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Originally Posted by oakman7004 View Post
I did start to place the turbulators like Bas but ended up more forward since the turbulators behind 60-70% just affected the aileron efficiency.

I today say that the sweetspot is 55-60% of the cord. I have had them at 50%-73% and were I have then now they do the job well for me. I must thank Kevin (who is hell of a lot better in the aerodynamic theories than I am) who at least confirmed my findings with his some years back.

/Jonas
Jonas,

thanks for the information. Below a picture of the Salpeter of Andreas Herrig (turbulator is about the same position as on your Polaris).

Bas
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Old Jan 23, 2012, 03:54 PM
Father of Fr3aK, DLG Pilot
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The Salpeter airfoil appears to be quite unique at the tips... at least the one I played with was. Maybe it benefits from turbulation more than others?
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Old Jan 24, 2012, 07:51 AM
Chuck 'Em and Chase 'Em
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How clean does the wing need to be to see the effects of the turbulators?

If there is some texture from the cloth due to a dry layup, would the testing be inconclusive?

Do you need to seal the hinge gap before testing turbulators?

Can a dirty wing get in the way of the analysis?
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Old Jan 24, 2012, 09:14 AM
G_T
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The front ~third of the wing needs to be quite smooth or the air will (possibly at least) transition earlier. The leading edge area needs to be rather nice.

I would recommend gap seal, fly, then turbulate half a wing and fly. If you find your wing does not fly as well after gap seal is added, that is informative. For a moldie, I'd expect it to fly better. For bagged, I'd expect it to make little if any noticable difference. But you'd have to test.

The reasons are bagged wings are not going to be as smooth or as accurate, and the gap has a shape and size that makes triggering a transition a little less likely. Also, with 70% hingeline, it is far enough back that having the transition be tripped and therefore occur perhaps 75% back will make less observable difference. If a difference is noted, it should be when one is flying a little too fast.

In calm air (if any is available) trim for min sink. Then add enough clicks of down elevator to force the plane to be flying a couple meters per second too fast. Don't change the camber setting. See what your times are like. See if gap seal makes it better or worse. See if turbulation makes it better or worse.

See if roll control when just short of a stall is better or worse.

See what happens to launch height (not that timing flights doesn't already cover this if you lack an altimeter - any combination of higher or better glide is good).

Those are the flight conditions most likely to make observable differences.

You may have to re-trim for changes in gap seal or turbulation. That is also a sign that something is going on. So when trimming to fly too fast, keep track of the number of clicks of elevator setting being used so it can be duplicated.

Gerald
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Old Jan 26, 2012, 05:05 AM
Graham Kirkland
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Early days

This picture of yellow and black carbon niceness happens to be a wing set made with the new turbulated foils. Took the second half out of the bag this morning. They still need to be properly cleaned up. It will take a couple of weeks before they are flying, but I can't wait to start testing.

I have an issue to be sorted during the build. Gerald recommended that the aileron gap is sealed on these wings. What is the best/easiest way of achieving this ?

The wings have a kevlar live hinge on the bottom surface.

Graham
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Old Jan 26, 2012, 06:37 AM
Father of Fr3aK, DLG Pilot
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Celophane tape and your favorite artist from the 70s on cassette tape.
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Old Jan 26, 2012, 12:11 PM
G_T
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I still need to compute out where to actually put the turbulator. The foil names specify where the transition is to occur, and the turbulator needs to be at least a little bit in front of that point. I've been rather busy the last few days, but I'll try to get it done soon.

Gerald
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Old Jan 26, 2012, 02:20 PM
Graham Kirkland
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Ah!! I thought that I had heard of that method before. I was a bit concerned that the audio tape would be a little flimsy and flap in the airflow. I will try it.

Gerald - no rush as I am a couple of weeks away from actually flying, and the turbulators can easily be moved anyway.

Graham
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Old Jan 27, 2012, 06:38 AM
Chuck 'Em and Chase 'Em
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Couldn't you just lay one piece of tape off center onto another piece of tape (sticky side towards each other) and then cut in half? then each piece has a section where the sticky section is exposed for mounting.

No need to sacrifice a cassette. then again, what else are you going to do with them. I guess save them for mandrel wrapping.....
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Old Jan 27, 2012, 07:12 AM
Father of Fr3aK, DLG Pilot
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I sacrificed a John Schneider tape (yes, the one from Dukes of Hazard) and bit by bit I've been working through him. I still don't know how that tape ended up in my possession. My brother used to smuggle NOT COOL music into my stash so I'm blaming it on him.

Yes, you can do the back to back tape but I just find the cassette mylar much easier to work with. I did my wings for JEM in the hotel room with no tools in about 5 minutes a few weeks back.
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Old Jan 27, 2012, 09:44 AM
Graham Kirkland
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The two pieces of tape back to back has me confused. Just so that I understand the process properly with audio tape, please correct me if I am wrong. The audio tape lies across the hinge gap, flat on the surface of the wing. It overlaps the trailing edge of the wing a bit and also the leading edge of the aileron. Then the cellotape is used to stick the front edge of the audio tape to the trailing edge of the wing.

Graham
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