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Vortex Generators on bottom of wing

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Posted

I'm really not sure where I found these; it may have been the Yahoo site but I couldn't re-locate them there. Anyway, I know most people look into VGs for slow speed handling & stall speed reduction but I thought that this was interesting.

-Nate

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Posted

Here are the missing 2 pages:

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Posted

John Miller has been having good results with this set up on his STOL wing

 

 

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Posted

I believe John, has a very large data base that we could all benefit if published in the right way,

He has also experimented with drag reduction, in few places on the AVID.

he was skeptic about the VG´s under the wing when I first published this report on the yahoo group long time ago, but I can see he really pay attention to the fact that this little tiny THINGS, help keeping the airflow attached to a surface and or oriented in our benefit!

 

I´m trying to get the old messages with his reports and findings, but that freaking new format is driving me mad, it always comes the AD screen and won´t let me go further!!!

 

ANY chance we can get the exact locations of the VG on the wing tip, and what does this means for the performance!!

 

Regards

Dimi3

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Posted

Joey,

 

I realize this was posted last year but is there any way for you to find out where the VG's were located on John Miller's wing tips? I'd like to know at least an approximate starting point. I'm going to do some testing with them on the long cross country bringing Pursang to the mid-west next month.

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Posted

Just my opinion, but I would get good and used to the plane before I changed a whole lot of things that aren't currently broke.  :-)  Jim

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Posted (edited)

Just my opinion, but I would get good and used to the plane before I changed a whole lot of things that aren't currently broke.  :-)  Jim

 

 

Amen!  +1

 

If it ain't broke, don't fix it.

Edited by Av8r3400

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Posted

Believe me I understand and appreciate the "if it ain't broke don't fix it" attitude. However to me, an experimental airplane is meant to be experimented with! I love toying with getting better performance on both ends of the spectrum, both high and low speeds. If that means a few small VG's, possibly some fairings to clean things up and then maybe lightening up the aircraft, then I don't see a problem with it. I'm not "fixing", simply experimenting, as I believe the FAA intended when the experimental class was created. Remember that the reason this class exists is for the learning and knowledge that it leads to, and that is very loosely paraphrased from the FAA's statement.

 

With my current plane I gained almost 10 knots cruise speed doing various modifications to it, I also was able to decrease the stall speed by 5-6MPH. It represented a net gain of almost 20% between cruise and stall than it sat before. It wasn't broken, but all these modifications helped me better understand the aerodynamics and such, as well as creating a safer plane because now it will land at 60 MPH instead of 65, it uses less runway and since there is no restarting the engine in flight, that equals safety in my mind by giving much better survivability if such an engine loss should occur.

 

By nature I am a builder, tinkerer and love to learn. As such I enjoy owning an experimental because of the ability to learn through change, the fact that I can fly it just adds to my happiness. Hopefully you all understand that.

 

Just my .02 worth.

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Posted

Ken,

        I think I understand where both of you are coming from, and both are correct.  I believe that you have every right to try to improve your bird as you see fit.  However, flying an unfamiliar bird across the country should give you enough to worry about, without doing any experimenting until you get to know it better.  I would like to hear the results of any mods as you do them.

Hoping you have a safe and enjoyable flight to bring it home.

EDMO

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Posted

Ed,  you said just what I meant.  Once it's home and you are accustomed to it, then fire away.  One other thing to consider as well is the plane wasn't just built by someone with very little experience in the field of aircraft.  Might not be easy to improve on it much.  As I understand it, it wasn't John's first rodeo.  :-)  I would definatly listen though if he says things like "I should have done this" and the like.  Nothing is perfect and could always be improved upon and maybe John has some ideas after having been there and done that.  Jim Chuk

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Posted (edited)

I guess I am saying that - which is sort of hypocritical of me - I have made so many changes in my design and build that I really don't know how it is going to fly - wonder if I will be able to handle it on test flight, but not willing to risk someone else doing it either.

If I survive the test flights, and get comfortable with it, then I will see if there are ways to improve it.

John would be the best source for improvements, since he has flown it for years, and designed it too.

EDMO

Edited by Ed In Missouri

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Posted

Both good points. I do plan on doing quite a few touch n go's with the plane before doing anything to it. But I am still going to do that before I start the long cross country. I have the luxury of taking this to my parents place out in Utah before heading back this way with it. I'll be there for several days installing a new transponder and a few other misc. things, as well as going over almost every inch of it that I don't have time to do in Boise (even though I will do a very thorough inspection).

 

It appears with the weather that I should have Tuesday afternoon/evening to pick John's brain on things that he would do differently or change if he were to keep the plane. I know enough to respect his opinion, as well as those with a lot of experience.

I also ferry aircraft for a living and adjust to a new plane very quickly, having flown almost 60 different makes and models I'm comfortable flying the way the plane wants to be flown versus the way I was "taught" all aircraft fly.

 

Thanks for chiming in. One thing I've learned in my life is that I ask questions to see other peoples opinions, and then respect them for it. It doesn't mean I'll do anything differently, but it might change my opinion too if there is new information or a point I hadn't considered before.

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Posted (edited)

Guys; I apologize if I´m stealing some one else´s work and stepping in some else´s toes, but I think John  is member of this forum and wouldn´t mind me polsting here some of his findings.

He Quote

...........................

Avideers:

Over the 3980 hours I have flown my Avid I have tried adding three different brands of VGs on my STOL wing only to find that there was no significant improvement in stall speed with flaperons on.

Lately I have been experimenting with the 3rd brand of VGs, namely STOLSPEED VGs. I like their design and ease of attachment and the response of the manufacturer. They are plastic and shaped like the fletching on an arrow.

It took about two hours by myself to attach them and I only placed them on the wings, not the under surface of the horiz stab.

As before there was no reduction of stall speed with full (10 degrees on my bird) flaperon. However, by leaving them on for a while instead of removing them I discovered other performance improvements that I hadn't even considered or checked before.

When you have flown an aircraft of close to 4,000 hours you are intimately familiar with its characteristics. I began to notice these improvements over a two week period.

The first improvement was noticed when I was doing stall tests. NOTE: When I refer to stall I'm not referring to wing stall, but horizontal stab stall.

I noticed that even though my flaperon on "stall" was still about 38 MPH IND, the flaperon off stall had been reduced from 46 MPH IND to 41 MPH IND. This is at 3000 MSL solo with 10 gallons of fuel at idle RPM.

Slow speed aileron control with no flaperons was my crisper. At cruise RPM 2700 RPM I could slow it to 40 MPH and make 30 degree banking turns while climbing with a better aileron authority.

Secondly, I noticed a better climb rate. Again, this is with no flaperons. As a minimum I am seeing 100 FPM better and typically average 200 FPM better over several tests. 

To confirm this improvement I matched my climb against my friend's Kitfox 5 powered by a 100 HP Rotax. 

In the past I could out climb him when we were both lightly loaded, but when we both had full fuel and camping gear he would out climb me.

On a recent camping trip when we were both loaded I can now out climb him.

Finally, I believe I am noticing a better glide rate. This is harder to quantify and I use the glide ratio on my Garmin pilot 3 to measure this. 

Over two week of comparing the GR as compared to before the VGs and at 65-70 MPH IND, I see a definate increase in GR compared to what I am used to seeing.

The under cambered wing with flaperons is a great design allowing us to get in and out of short, unimproved fields with ease, but I feel the VGs have , in my case, made the Avid an even better short field flier.

Why do I not put VGs on the horiz stab? I typically touch down at 40 MPH and do not have the tail first, then main plop that I used to have, since I lowered the tail wheel and went to larger 21 inch tires on the mains. 

I'm sure VGs on the tail surface would get me a higher AOL and land a bit slower, but then I would have the tail/mains plop syndrom back again. I consider the horizontal stall before the wing stall a safety feature.

New test in progress: I have placed 6 VGs at 60 MM spacing on the bottom of the wing tips at mid chord running from the tip inboard. 

This is a test to see if I can reduce the wing tip vortex formed by the spillover of air from the bottom surface to the lower pressure top surface. 

I'll publish the results when they are finalized.

John M
Avid B STOL 3980 hours
Jabiru 2200 680 hours
Tennessee 2 blade wood prop 64 x 36

 

-----------------------------------------------------------------------------

 

I just read this old post on the VGs on my Avid STOL and the last part says I placed the VGs under the wing tip and I would publish the results. I forgot to do that so here are the results.

 
I had place the under tip VGs only on the left wing and before doing the right wing.  I took a friend up to show him the straight forward stall characteristics of the Avid.
 
However, when I did the stall the Avid fell off on the right wing. I tried it two more times with he same results. This had never happened before.
 
So I landed and put the VGs on the right wing and BINGO...the Avid stalled straight ahead as it used to.
 
My theory...and everyone has one...the VGs under the tip help to keep the wind stream flowing back to the trailing edge instead of allowing it to flow over the tips from the high to low pressure areas and causing the infamous wing tip vortices.  
 
Whatever they are doing...the are staying put.
 
John M 

 

-----------------------------------------------------------------------------------------

 

Three inches from leading edge of spar to leading edge pf vg.

Your results may vary.

John M

Edited by Wolverine
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Posted

That is exactly the information I was looking for. Thank you very much for posting that up. It confirms my findings with my current plane and reassures me that I will be putting VG's on the Pursang in the not too distant future. I already have about half of them made up (I make my own simple aluminum ones).

 

I know that the Pursang has the horizontal stabilizer down lower than the typical Avid so I will likely not see as much turbulent air over the tail that the Avid seems to exhibit so I may do some testing on them on the bottom of the HS in the future but not right away.

 

I do think that the under cambered wing is great for the STOL capabilities from my understanding and research, but I also realize that with VG's placed under the wing it won't hinder that ability but should decrease drag slightly and that should increase cruise speed slightly. I figure even a 2MPH increase is worth a change. I really just like to experiment and see how to push the limits both directions.

 

Again, thanks for posting that up!

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Posted

Thanks for that post; I might try the underside VG's, on the tips first

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Posted

One person reported a 10 mph increase in cruise when he added the VGs to the underside of his leading edge.

EDMO

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Posted

One person reported a 10 mph increase in cruise when he added the VGs to the underside of his leading edge.

EDMO

Any idea the spacing ?

Believe me I understand and appreciate the "if it ain't broke don't fix it" attitude. However to me, an experimental airplane is meant to be experimented with! I love toying with getting better performance on both ends of the spectrum, both high and low speeds. If that means a few small VG's, possibly some fairings to clean things up and then maybe lightening up the aircraft, then I don't see a problem with it. I'm not "fixing", simply experimenting, as I believe the FAA intended when the experimental class was created. Remember that the reason this class exists is for the learning and knowledge that it leads to, and that is very loosely paraphrased from the FAA's statement.

 

With my current plane I gained almost 10 knots cruise speed doing various modifications to it, I also was able to decrease the stall speed by 5-6MPH. It represented a net gain of almost 20% between cruise and stall than it sat before. It wasn't broken, but all these modifications helped me better understand the aerodynamics and such, as well as creating a safer plane because now it will land at 60 MPH instead of 65, it uses less runway and since there is no restarting the engine in flight, that equals safety in my mind by giving much better survivability if such an engine loss should occur.

 

By nature I am a builder, tinkerer and love to learn. As such I enjoy owning an experimental because of the ability to learn through change, the fact that I can fly it just adds to my happiness. Hopefully you all understand that.

 

Just my .02 worth.

what modifications did you do to increase the cruise ? 

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Posted

I modified my wing ribs to be like the Kitfox 4 Riblett and extended and sharpened my leading edges about 4" - mine hasn't been completed or flown yet.  I don't know anything about the guy who put the homemade VGs on the bottom of his wings - I think his letter is in Files and Forms or somewhere under VGs.   EDMO

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