Author Topic: Vortex Generator Test 1 & 2 (Read 3258 times)

Chris_Rud · « **on:** August 04, 2014, 07:12:38 AM »

Frank Williams challenged me to do this test. I think you can see some differences between having vortex generators and not but it is definitely hard to say. You will need to be the judge. Please let me know if there are any other experiments you would like me to take on. It was fun.

Monty Summach · « **Reply #1 on:** August 04, 2014, 07:30:32 AM »

Thanks for doing that test Chris. The video quality and the editing were excellent. I am not bold enough to say I can draw conclusions one way or the other but I am sure this will provide some good (documented) data for discussion.
Regards,

Dave_Trible · « **Reply #2 on:** August 04, 2014, 08:36:22 AM »

Yes Thanks Chris for the test and post. I'll admit I'm a little skeptical about these at our scale and speeds but open to learn. I noticed you put them on one wing only. I would think that if they were doing much they would have caused trim issues. Did you notice anything like maybe rolling motions or something else? I can see that would be complicated with the camera mounting.

Dave

Joe Yau · « **Reply #3 on:** August 04, 2014, 09:29:17 AM »

Quote from: Chris_Rud on August 04, 2014, 07:12:38 AM

I think you can see some differences between having vortex generators and not but it is definitely hard to say. You will need to be the judge. Please let me know if there are any other experiments you would like me to take on. It was fun.

Hi Chris, interesting experiment! Since this type of test is to plot when the wing starts to stall or to see when the boundary layer starts to separate.. I would think the power off glide prior to landing might shows a little more difference. or maybe slow the run down a little (5.60-5.8?) etc. without the VGs then compare with.. of course you would have to increase the speed slightly to the same lap time to compensate for the drag with the VGs.

sort of similar to this experiment...

Paul Walker · « **Reply #4 on:** August 04, 2014, 09:51:49 AM »

Nice test Chris. Thanks!

I would be tempted to do this test again with more tufts near ( and crossing) the flap hinge line. Focus the camera more in that area to get a close up look at those tufts.

Some times these things come down to a subjective feel for the pilot. That makes it harder for others to accept. That's OK with me though.

Chris_Rud · « **Reply #5 on:** August 04, 2014, 11:22:06 AM »

Quote from: Dave_Trible on August 04, 2014, 08:36:22 AM

Yes Thanks Chris for the test and post. I'll admit I'm a little skeptical about these at our scale and speeds but open to learn. I noticed you put them on one wing only. I would think that if they were doing much they would have caused trim issues. Did you notice anything like maybe rolling motions or something else? I can see that would be complicated with the camera mounting.

Dave

Dave, I agree that I would have noticed a major trim issue if the VGs did a lot. I don't think that they make a "major difference" but I don't think I'm testing for or looking for them to make a "major difference." The question I'm trying to answer is do they help? I'm not sure. Prior to the experiment I didn't honestly think they made a difference. But was open to being showed that they do.

I can say that the flight with the VGs on did seem to fly without as much noticeable wing flutter. I must confess that it was difficult to get the plane into perfect trim with the camera being on the fuse sideways (drag) and then the weight addition. Without the VGs the plane slug through corners and slightly dropped the outboard wing. After the addition of the VG's to the outboard wing the plane tracked and flew better. The outside wing didn't dip. It did help resolve the trim issue. Not a major difference but enough for me to start thinking they might actually do something.

Now regarding the strings. What I see is when you hit hard inside corners without the VGs the strings still flutter and do separate from the wing ever so slightly. They also turn upwind more often (showing stall) more frequently. You can see this in the squares. When the VGs are on the strings appear to not flutter as much and don't show a stall as much. I may be looking into it to much but that is my opinion.

I'm going to change somethings and do test 2 with the camera in a different position and more string on the trailing edge. I hope you take a minute and watch it when finished.

It was a fun experiment. And thanks for watching!!!!

-Chris

Chris_Rud · « **Reply #6 on:** August 04, 2014, 11:26:20 AM »

Quote from: Paul Walker on August 04, 2014, 09:51:49 AM

Nice test Chris. Thanks!

I would be tempted to do this test again with more tufts near ( and crossing) the flap hinge line. Focus the camera more in that area to get a close up look at those tufts.

Some times these things come down to a subjective feel for the pilot. That makes it harder for others to accept. That's OK with me though.

Paul,

Thanks for the suggestions. I really want to try and see if I can create a noticeable difference. I hope that your suggestions can show that so I will do another test and move the camera behind the cockpit. I will post the video once completed.

-Chris

Dennis Toth · « **Reply #7 on:** August 04, 2014, 12:02:04 PM »

Chris,
Great test information. Have you tried putting them on both in board and out board wings yet? Also, could you give us some technical description of size, shape, spacing and angles. How did you attach them? It would also be interesting to see if moving them closer together would have any additional benefit or just make more work with no gain.

Best, DennisT

Chris_Rud · « **Reply #8 on:** August 04, 2014, 12:32:38 PM »

Quote from: Dennis Toth on August 04, 2014, 12:02:04 PM

Chris,
Great test information. Have you tried putting them on both in board and out board wings yet? Also, could you give us some technical description of size, shape, spacing and angles. How did you attach them? It would also be interesting to see if moving them closer together would have any additional benefit or just make more work with no gain.

Best, DennisT

Dennis,

Good suggestions. I don't have enough VGs to do both wings. Frank Williams only sent me enough for 1 wing panel. I don't know the specific on each VGs but Frank Williams can tell you. I spaced them out 3.5 inches apart and put them right across the spar. I didn't have a specific angle that I used cause I wasn't sure what angle I should use so I just said "that looks to be the same angle as Fitzgeralds." If anyone knows a "correct angle" let me know. I glued them on with medium CA to a piece of masking tape. I was flying a 5.4 lap time. I think that is a pretty common lap time for a high-level stunt ship.

Michael Palm · « **Reply #9 on:** August 04, 2014, 01:33:47 PM »

An interesting thing to see was that the wing covering was pushed in between the ribs in the sharp corners.

Derek Barry · « **Reply #10 on:** August 04, 2014, 01:49:02 PM »

Looks like they do nothing more than make pretty planes ugly.

Thanks for doing the tests Chris, I look forward to seeing more.

Derek

frank williams · « **Reply #11 on:** August 04, 2014, 01:49:40 PM »

Great Video Chris ...
It really worked .... I can't believe it .... been wanting to do this for years ...... amazing modern technology ....

OK ....... next time .... we need more tufts .......
.... we need , let's say three to four rows of tufts ..... with tugts spaced at about every inch......I make them up on a steel ruler by wrapping the string around the ruler at even increments, say 1 inch, and then taping them down to one edge, then cutting them to length desired, maybe about only an inch. The tufts I sent might have been a little bit too long.
Lets shorten them to 1in long spaced at 1 to 1 1/2 in increments on the strip (just tape down the whole strip of tufts at once rather than cutting them up into individual units. ....... run one row at about the 1/4 chord .... one about half way back on the wing .... one before the flaps (with the end of the tuft at the hinge gap line) ... and one row taped at the le of the flap. Make the strips of tufts cover from about 4 in from the fuse to about 2 in from the tips. Making up the tufts is the hardest part.

Your vg placement looked fine to me ..... the ones I sent are probably larger than the norm, but I think thats ok.

The inside triangle seems to be the best test .... square was good also ..... Don't worry yet about the other wing panel. Might also try just a full hard jammer of an inside pull .... not necessarly a manuever ... just a test point.

I saw one of the tufts on the triangle that seemed to be better with the vg's ..... Also the closest tuft seemed to be showing some spanwise flow, but it might just be the prespective.

Chris_Rud · « **Reply #12 on:** August 04, 2014, 05:03:07 PM »

Quote from: frank williams on August 04, 2014, 01:49:40 PM

Great Video Chris ...
It really worked .... I can't believe it .... been wanting to do this for years ...... amazing modern technology ....

OK ....... next time .... we need more tufts .......
.... we need , let's say three to four rows of tufts ..... with tugts spaced at about every inch......I make them up on a steel ruler by wrapping the string around the ruler at even increments, say 1 inch, and then taping them down to one edge, then cutting them to length desired, maybe about only an inch. The tufts I sent might have been a little bit too long.
Lets shorten them to 1in long spaced at 1 to 1 1/2 in increments on the strip (just tape down the whole strip of tufts at once rather than cutting them up into individual units. ....... run one row at about the 1/4 chord .... one about half way back on the wing .... one before the flaps (with the end of the tuft at the hinge gap line) ... and one row taped at the le of the flap. Make the strips of tufts cover from about 4 in from the fuse to about 2 in from the tips. Making up the tufts is the hardest part.

Your vg placement looked fine to me ..... the ones I sent are probably larger than the norm, but I think thats ok.

The inside triangle seems to be the best test .... square was good also ..... Don't worry yet about the other wing panel. Might also try just a full hard jammer of an inside pull .... not necessarly a manuever ... just a test point.

I saw one of the tufts on the triangle that seemed to be better with the vg's ..... Also the closest tuft seemed to be showing some spanwise flow, but it might just be the prespective.

That sounds good I will work on that and get another flight up soon.

-Chris

PJ Rowland · « **Reply #13 on:** August 04, 2014, 07:27:02 PM »

I love reading new experiments with Vortex Generators.

I first contacted a company called Mirco Aerodynamics in the Mid 90's who build these kits for full size use. We worked together to develop a system that would allow more consistent / repeatable turning of the aircraft for Control line aerobatics ,our speed, our wing loading / weight.

Since 1997 I've done hundreds of tests ( size, location, VG design ( I noticed yours are triangular ? Not as I would do it.. ) - and lets estimate over 17 years of installing them onto contest winning planes @ 400 + flights per year thats ALOT of flying with many back to back tests done.

My findings have been replicated by others of far more superior aeronautical experience and stunt acumen - and generally you will find those with superior technical understanding of the event ( Paul, Dave, Howard, Frank ) are supporters.

There seem to be 2 schools of thought on the subject :

1: They don't do enough to improve performance, but detract visually.
2: They do improve consistency.

Derek is a HUGE supporter of the 1st point - What everyone needs to understand is exactly what Derek and Doug Moon are showing with the results :

If you have a light well trimmed plane and are a GUN flier - you don't need these to win.

The question is not IF they work thats been answered plenty of times... but if its going to give YOU the individual flier that extra 1% improvement.

At this level 1% over your competitor could be the difference between Making Top 5 or not.. Or winning open Vs placing 2nd.

As subjective as this sport is - if there is an advantage there rest assured Id be looking into ANYTHING that could help me place higher.

My experience of the Nats was great - I saw everything from High performance Electrics flown by the best of the best - to a machine like performance by Dave to Win using IC and those inside the Top 5 share key elements.

Ultimately what you need to find to be a winner in this sport cannot be taped onto a wing or programmed into a Jeti Spin.

Its putting the plane in the RIGHT SPOTS consistently - Vortex Generators help with consistency of airflow over the wing and control surfaces, promote more reliable and consistent corners under a range of conditions.

Just like Electrics help promote consistency in engine run / power delivery and speed - none of these will make you win, but it will make the job more repeatable.

Its worth noting the last 2 years of Open Nats Champions used Vortex Generators on their Nats winning ship.

One was Electric .. One was IC

Doug Moon · « **Reply #14 on:** August 04, 2014, 11:42:59 PM »

Chris,

The video is awesome! It totally supports what PJ has been saying for years, and what I found when I tested them in 2011. Watch the little piece of yarn that is about half way out on the trailing edge of the wing. During the inside square several times when the flap came back to neutral the little piece of string was facing forward showing us the direction the air was flowing at that moment. PJ has stated before that he found they were most effective when placed top and bottom of the wing something like 6-8" off the fuse. Well, this would just be just outside the prop wash. This is about the same spot this little piece of string is placed.

After the VGs were added that piece pretty much stayed in place.

Are your hinge lines taped? I would think they would need to be taped so we can properly see the airflow without any interruption from air popping through the hinge gap. But even if they aren't taped the VG stopped that air popping through from snapping off that piece of string.

Plus, for the sake of experimentation, the model will need to be flying slow for that model. These things are in place to keep air on the wing and flaps in a slow speed situation. In our case the second of any square maneuver will be slower than the first and we will see more issues there, especially in calm air. If the model is traveling with enough airspeed to get through everything with ease there may not be much to see. But, for testing purposes, if the model is slow and you slow it down in a maneuver you may see real separation without the VGs and less separation with them. Just some thoughts about the tests.

As Frank suggests you would want a row of pretty tightly spaced pieces along the TE. This is where the issue lies. If there is ay separation what so ever then the consistency can be lost flight to flight. Taped hinge lines produce a positive effect as there is no loss of air on the back of the flap due to air bleeding through. Oddly enough I have taped nearly every stunt plane I have built since 1999, except this last one, and only did I ever actually notice a difference on that one model in 1999. I have tried it on the others with no noticeable difference in feel or performance. I have always wondered why I am not noticing the sealed lines....

I did a test in 2011 on VGs and here is what I found.

http://stunthanger.com/smf/index.php/topic,23110.msg222103.html#msg222103

The next thing to do is to get a smoke bomb, the little round one we used to get on the 4th of July, and somehow place it on a stick or something out in front of the wing and watch the smoke go over the VG and see if the flow....

Chris_Rud · « **Reply #15 on:** August 05, 2014, 08:01:59 AM »

Here is the wing ready for test number 2. Next I will try Doug's smoke bomb idea?

Hopefully the rain lets up so I can give it a shot.

-Chris

Shug Emery · « **Reply #16 on:** August 05, 2014, 08:32:22 AM »

This was very interesting to see and read about. A bit beyond my scope but working to understand it.
Mighty fine Chris.
Shug

Paul Walker · « **Reply #17 on:** August 05, 2014, 08:43:28 AM »

Chris,
I am concerned about the length and thickness of the tape holding on the tufts. They could act as turbulator strips and "confuse" the results. I would remove the long strips and cut them so they were JUST big enough to hold the tuft on. Yes, it is more work, but should give more accurate results.

Am anxious to see your results.

frank williams · « **Reply #18 on:** August 05, 2014, 01:08:36 PM »

Paul
Pounding 75 should have everything shook loose.
PJ
I'm not doubting the vg's ... you can't fly in anything nowdays that doesn't have vg's somewhere on it ..... just a great opportunity to look out the window of the plane and see the flow.
Chris
.... ok if you're up to it .... Doug has a point ... the 3rd corner of the hourglass is the worst ..... you will have to do an inverted hourglass to stall the top of the wing with and inside turn .... start from inverted flight - outside, inside, inside, then bail to upright level ..... the third corner should have the total ac speed down a bit .....
The Strega you are using has one of the thickest wings available (more difficult to stall) .... we'll have to repeat all this with a Ringmaster you know

Frank

Chris_Rud · « **Reply #19 on:** August 07, 2014, 07:21:55 AM »

Here is test number 2.

I think you can see some differences now. The major change between test 1(previous video) and 2 (current video) was checking the flap line. I had taped it 9 years ago but when we checked it was pretty much all broken and the gap wide open. We re-taped it and you could see a difference in the second vertical turn in a square and triangle. Images below.

The silk is cracked close to the camera. I tried to tape it but it isn't really flat. I wouldn't rely on the tuffs directly behind the tape since the airfoil isn't perfect. Anyway the major changes happens further out in the wing anyway so it shouldn't flaw the experiment.

Let me know your thoughts and/or you think the experiment needs any changes.

-Chris

Dave_Trible · « **Reply #20 on:** August 07, 2014, 08:27:02 AM »

What's most interesting to me is what the tufts are doing right at the hinge line in both cases. It's obvious the VGs are aiding the airflow attachment. Kudos Chris !

Dave

frank williams · « **Reply #21 on:** August 07, 2014, 08:36:53 AM »

Great Videos Chris .....
The triangle pictures, w/ and wo/ are worth a thousand words.
Thanks so much for the tests ...... you are securing your place in the model aerodynamic testing hall of fame, and you didn't even have to take the windshield out of your car.

.... more later
Frank

Chris_Rud · « **Reply #22 on:** August 07, 2014, 03:29:23 PM »

Thanks Frank! It was a blast doing the experiment. Do you have any other ideas or have we completed your goal?

If you know of any other experiments you would like to try let me know. I really enjoyed the process!

Thanks,
Chris

PJ Rowland · « **Reply #23 on:** August 07, 2014, 05:32:31 PM »

Great work Chris.

Certainly this level of testing has a more precise visual explanation on its effects it was fairly clear cut. I've always been more interested in how it feels to me than how scientific it was ; your findings are great to see !!!

There are 2 tests I'd like to see done.

Test 1: Remove the VG's and use zigzag tape. Igor Burger is a proponent of this technology . I've not done this as yet but in theory the boundary layer thickness is in the ballpark of the tape. Which is why PW suggested you cut the tuffs smaller as to not affect the experiment.

Test 2: I'd like the see conducted is having them on the Stab. All of testing I've done I just couldn't see a difference - I've challenged others who have run it on the stab to explain the reasons and improvements - the consensus is its difficult to tell with any authority the effects on and off on the Stab. I think if its so subtle its difficult to tell one way or another then chances are the placebo effect is working more than anything else.

Great work Chris.

Gerald Arana · « **Reply #24 on:** August 07, 2014, 07:35:00 PM »

The Zig-Zag tape was put on gliders several years ago.....Supposed to increase performance..

But I couldn't tell anything. My glider didn't thermal for "Bleeep". Found out after I sold it that I was supposed to fly with the flaps down about 20 degrees, which I didn't. The guy I sold it to used it in a slope race and came in second. He was a very happy camper.

Oh well, live and learn.

The ZZ's were back by the TE on that particular airfoil.

Interesting thread, Jerry

PJ Rowland · « **Reply #25 on:** August 07, 2014, 09:09:57 PM »

"The Zig-Zag tape was put on gliders several years ago.....Supposed to increase performance But I couldn't tell anything"

Gerald - Igor Burger the CURRENT (for now) World Champion in Aerobatics uses Zig Zag tape to increase performance - perhaps that is something worth considering ?

We aren't talking about gliders in the 70's we are talking about high performance modern stunt ships specific to Control line aerobatics in 2014 ,I'm not sure what relevance mentioning that fact was.

In actual fact the height of the ZIGZAG tape is alot closer to the boundary layer thickness we require than using the VG's are. However during the development being told that I'd need to make my Vortex Generators 1/64th " in height proved to be beyond my steady hand. I choose the smallest height I could whilst still being able to hold them in tweezers to apply to the wing.

Doug Moon · « **Reply #26 on:** August 08, 2014, 08:09:32 AM »

It is very interesting to see the tuffs aft the hinge line in both pics.

It would be an interesting thing to see the following.

Leave the current VGs right where they are.

Add another row of them about 1" ahead of the trailing edge of the wing.

One experirment with them in line with the front VGs and one expiriment with them staggard/offset from the forward VGs.

Gerald Arana · « **Reply #27 on:** August 08, 2014, 10:16:32 AM »

PJ

Maybe I misunderstood...........but I thought this thread was about enhanced performance with the use of "vortex generators". So my mention of gliders and ZIGZAG tabulators was also about enhanced performance......
I also found that the video of the full scale airplane with vortex generators to be very interesting in as much as they lower the stall speed.

Full scale; nothing to do with "Precision Control Line Aerobatics", right? Darn, you'd think with 65 years of building and flying experience I'd have lernt sumptin.
Actually I learn something new almost every day.....

Have a G'day mate, Jerry

Chris_Rud · « **Reply #28 on:** August 08, 2014, 09:57:29 PM »

Quote from: Doug Moon on August 08, 2014, 08:09:32 AM

It is very interesting to see the tuffs aft the hinge line in both pics.

It would be an interesting thing to see the following.

Leave the current VGs right where they are.

Add another row of them about 1" ahead of the trailing edge of the wing.

One experirment with them in line with the front VGs and one expiriment with them staggard/offset from the forward VGs.

Doug,

Sounds like a good idea. I will give it a shot and post the results. Might be a bit my wife is ready to pop... Flying may take a back seat for a bit

-Chris

Sean McEntee · « **Reply #29 on:** August 09, 2014, 12:34:21 PM »

Chris,

The "zig-zag" tap is worth a try.

The MQ-1C has a strip of it running the entire lengh of the wing on the TE, right before the aileron/flap hinge. Although the exact reason or design problem that the tape is correcting is unknown, our instructors preached to us in flight school, "VERY important that ALL of it is there"

YOLO....

PJ Rowland · « **Reply #30 on:** August 09, 2014, 07:37:41 PM »

the Zig zag tape do exactly the same as Vortex Generators.

The height of the tape - is closer to the working boundary layer thickness than using actual cut out VG's like we use today. The problem has been applying something that small is difficult without an electron microscope !!!!!!!

I personally just didnt find the Zig Zag tape to be as effective in making the corners more repeatable when compared to the VG's. Thats just my personal observation in testing. However I did only test it on ONE plane. ( Cant test for everything ! )