Vortex Generators on the wing

[wypaul 448]

John Miller I know you posted some good info on vg's on the Yahoo site and it would be nice to have that posted here if you get a chance.

Like John found my results were that it did not reduce the stall speed with flaps but lowered the no flaps stall to about the same as the full flaps stall. There is a difference that I did not notice at first but realized it the other day and that is with no flaps the angle of attack is much greater than with the full flaps stall which stands to reason. So wheel landings are easier and slower with the full flaps in my plane, maybe I am just a little slow to pickup the obvious.

I used the StolSpeed VG's at about 8%.

Edited 15 Nov 2013 by Paul S

[C5Engineer 1170]

Here's a little bit about the theory of VG's on the bottom of the wing and a few pics of Johns Wing

 

http://www.avidfoxflyers.com/index.php?/topic/611-vortex-generators-on-bottom-of-wing/?hl=vortex

 

Here's some info from an old thread I dug up as well.

 

CCI VG’s on the Avid Flyer STOL by Larry Martin
This is a report of my findings using CCI VG’s on the Avid Flyer STOL wing aircraft.
Background:
The aircraft is an Avid Flyer TD STOL wing with a Rotax 582, 3:1 gearbox, Culver 74×48 prop. Built according to the kit/plans with no modifications except for "Grove" landing gear. (heavier) Published allowable center of gravity is 11.185 to 16.5. This aircraft was at 13.5". Designed stall speed at approximately 900lbs in flight weight is 32.5 mph.
The landing characteristics of this airplane were such that in order to affect a comfortable flare, power and additional speed was required beyond what I consider to be normal. In addition, there was insufficient nose up trim available on approach. On take-off, it was evident that the wings could fly sooner, but the airplane would not lift off. The tail could not be brought up before lift off speed, and would take off quicker from the 3-point attitude. The stall characteristics were such that when the airplane was gradually slowed to minimum speed, the airplane would sink, well above the designed wing stall speed. (Not with standing of course that indicated airspeed is most inaccurate at high angle of attack) The wing would not "break" at the stall, as most wings will. When the nose of the aircraft was "lobed" up and speed was allowed to bleed rapidly, the wing would exhibit traditional stall characteristics. It was determined that the elevator was not working sufficiently.
After discussion with the designer of the aircraft, the center of gravity was moved to the published aft limit of 16.5" with the assurance that the aircraft was tested well beyond the published limit. For reasons of liability at that time, the published limit was set very conservatively. The aircraft was tested beyond 19.0", which can be safely used. (37% mac) The change in center of gravity helped considerably, but still not sufficient. Further to the designer’s recommendation, the elevator area was increased approximately 15% by extending the elevator aft. There is no room physically to change the horizontal stabilizer angle of incidence. Short of making a new one, modifications were complete.
The flying characteristics at this point were much improved as measured by the following: A much shorter take off ground roll, the tail could be raised on take off with full flaps; almost sufficient elevator trim was available on approach with full flaps; and power off, full flap approaches could be safely made at normal speeds. The stall characteristics were similar, but at a slower indicated airspeed. Almost content with the airplane, but still not to the standard of performance that I thought it was capable of. I followed the studies of vortex generators.
In the pursuit of finding the truth of if and how VGs would enhance performance, I read many studies and opinions. Some say that they help, others called it snake oil, etc. Art at CCI (http://www.vortexgenerator.net) was not in a hurry to sell me anything, but offered me aerodynamic and physics proofs and rebuttals. To say that he was patient is a huge understatement. Finally, he managed to overcome my skepticism, and I ordered a set with a money back guarantee. Art was first concerned about getting more lift from the tail, and we placed the VGs per his instructions on the flat surfaced (non airfoil) horizontal stab.
The results of the VGs on the stab were nothing short of incredible and better result than the sum of what was done before this point. The tail was now producing more lift at all angles of attach. Subjectively, the tail felt more "alive". The take off run was even shorter, with the tail coming off the ground with the application of power. The increase of lift was objectively measured by comparing the neutral trim, hands off, level altitude minimum speed with and without the VG’s on the tail surface. A 10mph slower speed could hold level altitude with the VGs on. This was a dramatic increase in tail effectiveness. So much so, that I was able to remove 5# of ballast and move the CG .80" forward and have the same control feel. The stick position was physically further forward at all speeds, thus proving the elevators were working more effectively. The trim was effective at approach speed even with the cg further forward. (.5" cg change affects a considerable difference in this aircraft) The stall characteristics were such that the wing would stall at a higher angle, a noticeably slower IAS, and much more aft stick movement remained during the stall. Art then wanted to test the effectiveness of stabilizer end plates. There was a small subjective gain in effectiveness, but no objective, measurable results could be recorded. Most likely this was due to installation error inherent in the airspeed system. In addition to the enhanced low speed qualities, an unexpected gain in normal cruise speed of approximately 11% was attained. The top speed was approximately the same, but this is due to the large drag caused by the undercamber of the STOL wing. The airplane reaches a drag point similar to mach drag, in which the airplane will not accelerate above, or in the case of the Avid Stol, a disproportional increase in power only yields a minute increase in speed. It is not practical to fly at this speed. However; in the normal cruise range with a cruise rpm of 5400 yielded 84 mph with the vg’s on the tail. Without the vgs, the same rpm yielded 74mph. This is explained by the efficiencies of the tail.
The next step was to install VG’s on the wing. Research shows that there is a wide range of "ideal" or "sweet spot" placement with respect to percentage of wing cord. Experience gained from others suggest that in a range from 4% to 12%, one would find that spot. CCI suggested 10% as a starting point. I initially placed them as per the supplied directions except I started at 7% and planned to move forward to 4% then aft to 10% to test the effectiveness. The results of the VG’s at 7% were immediately noticeable. The take-off roll was shorter. In slow flight, the stall occurred at a much higher angle of attach and the IAS was 5 mph slower. Again, I caution putting much emphasis in IAS, especially at high AOA due to position error. There is no argument that the AOA was much higher than ever before, and the airspeed needle was slower than previous witnessed. At 75+% power the nose attitude was extremely high and could remain this way flying at the verge of the stall. The Avid has "flaperons" which trail the wing. They are always flying, even in a stall. Therefore a subjective opinion of aileron control cannot be rendered. The Avid does not spin well and enters into a spiral instantly, so fast that I choose not to spin. I did fly a spin series, hoping that due to the higher AOA that was possible, it may spin. Unfortunately the spin qualities did not change, and with rudder application and a pivot of the wings, it becomes unstalled and spirals picking up speed very rapidly. Thus I still don’t spin.
There was a gain in airspeed at the high end. It appears that the "stol wing drag point" was been changed to a higher speed. The old "aerodynamic drag point" is now easily overcome. I also noticed by way of control feel, and wing attitude that the center of pressure is moved forward on the wing. I replaced 5# in the tail to the original CG.
The airplane was designed to be flown STOL. Dean Wilson designed the flaperons to enhance this ability. I use full flaperons for all take off and landings. I have landed with complete control in 20+ mph direct crosswinds with no problems. (grass strip) The VG’s do not detract from landing control nor do they negatively affect any of the flight characteristics. I am completely satisfied with the VG’s and help from CCI. Due to the satisfaction with the results, and my too busy schedule, I have not changed the VG placement from 7%. I would still like to, but it has to take a lower priority for the time being.
Please feel free to contact me for further information. I heartily endorse CCI VG’s (http://www.vortexgenerator.net) if you want to fly the Avid the way it was made to fly!
Larry Martin My93Avid@yahoo.com         

[saskavid 47]

One of the things having the largest effect on the performance of vg's on the wing is this  squared velocity physics rule, so the force or power of these vortexes being generated at these slow thirtyish landing speeds is very puny compared to planes at landing speeds in the 50/60ish range.Double or triple the vg count on the wing and you will probably double or triple the efect they are currently having.May still not be enough, could also produce a detremental drag condition, or screw up the planes handllling in other areas of flight performance.(Speculation)  

[wypaul 448]

Thanks Joey that was a good write-up and a good reference for anyone still thinking about VG's.

[EDMO 1078]

Thanks Joey that was a good write-up and a good reference for anyone still thinking about VG's.

Paul,

     If you have not read it, there is something in files and forms on the Riblett rib conversions and VGs on bottom of wings by Nate and DHolly.

If I remember right, the letter said the owner did a homemade VG attachment and gained 10 mph cruise with the undercambered ribs.

EDMO

[EDMO 1078]

Joey / WyPaul,  I just read the instructions online for the STOLSpeed VG's and he says that the polycarbonate VG's can deteriorate over time because of UV light, and to paint them before installing.    What kind of paint would you safely use on Polycarb?  I would think that only Stewarts water-thinned paints would be the only paint thinner that would not harm Polycarb.      Has anyone painted theirs?   Do you think that they need painting?  EDMO 

Edited 19 Feb 2016 by EDMO

[wypaul 448]

I did not paint mine.  I have some on my Q bird (different brand same material) been on there for over 10 years and doing fine.

[Knuckledragger 135]

 The Avid does not spin well and enters into a spiral instantly, so fast that I choose not to spin. I did fly a spin series, hoping that due to the higher AOA that was possible, it may spin. Unfortunately the spin qualities did not change, and with rudder application and a pivot of the wings, it becomes unstalled and spirals picking up speed very rapidly. Thus I still don’t spin.

^^True dat!

Several planes around the field where I hang out have unpainted VGs.  These are in open T-hangars in the florida sun.  They seem to hold up very well.  Paint with care, the polycarb seems a bit sensitive to solvent based paints.  Spray light coats and allow to dry completely before handling.

Edited 19 Feb 2016 by Knuckledragger

[EDMO 1078]

 The Avid does not spin well and enters into a spiral instantly, so fast that I choose not to spin. I did fly a spin series, hoping that due to the higher AOA that was possible, it may spin. Unfortunately the spin qualities did not change, and with rudder application and a pivot of the wings, it becomes unstalled and spirals picking up speed very rapidly. Thus I still don’t spin.

^^True dat!

Several planes around the field where I hang out have unpainted VGs.  These are in open T-hangars in the florida sun.  They seem to hold up very well.  Paint with care, the polycarb seems a bit sensitive to solvent based paints.  Spray light coats and allow to dry completely before handling.

I will leave my VGs unpainted - they will probably last longer than I will...Got to get the plane flying before adding them.   EDMO

Edited 19 Feb 2016 by EDMO

[TJay 1041]

 The Avid does not spin well and enters into a spiral instantly, so fast that I choose not to spin. I did fly a spin series, hoping that due to the higher AOA that was possible, it may spin. Unfortunately the spin qualities did not change, and with rudder application and a pivot of the wings, it becomes unstalled and spirals picking up speed very rapidly. Thus I still don’t spin.

^^True dat!

Several planes around the field where I hang out have unpainted VGs.  These are in open T-hangars in the florida sun.  They seem to hold up very well.  Paint with care, the polycarb seems a bit sensitive to solvent based paints.  Spray light coats and allow to dry completely before handling.

I will leave my VGs unpainted - they will probably last longer than I will...Got to get the plane flying before adding them.   EDMO

How close are you to flying?

[lostman 198]

I had plastic VG's on my Teenie Two. After two years in a hangar and one outside they started to discolor slightly. The big issue I had was actually the glue holding them on got brittle. Kids and people passing by would go, "hey what are those" and touch them. They'd just fracture off. I'm pretty sure kids would take them home. After a few disappeared that way I built my own from .020 aluminum and replaced them. They worked wonders on that plane.

After I had Pursang at home I build another set and installed those. This time with a different glue. It stuck well to the fabric and paint but sadly I didn't see much difference after the install. I can concur that the stall speed with no flaps was slightly less so wheel landings were easier. Otherwise I didn't have them on there long enough to do too much testing. Most of you know "the rest of the story" with the plane.

[EDMO 1078]

Lostman,   What kind of glue did you use, and can it be used on polycarb?  

TJay,  Hopefully before I turn 80!   EDMO

Edited 20 Feb 2016 by EDMO

[lostman 198]

Lostman,   What kind of glue did you use, and can it be used on polycarb?  

 

Which time? The first time I actually used a quick set epoxy. That was mistake even on the aluminum skins. On the avid I used an exterior grade adhesive from Home Depot. I'm trying to remember the name of it but it was basically a silicone type flexible glue. It held very well but also would release if you turned the VG 90 degrees with no damage. That way they could be removed without hurting anything. Even in the 'incident', I only lost a couple. That's saying something. I also had them on the top of the skylight with the same adhesive. It was poly carbonate and worked just fine. 

Edit: It was bugging me so I went and found what I used. Here it is, it really is just called stick and seal exterior adhesive.  http://www.homedepot.com/p/Loctite-1-fl-oz-Stick-n-Seal-Outdoor-Waterproof-Adhesive-230461/100371831 

Edited 20 Feb 2016 by lostman
left something out.

[C5Engineer 1170]

Stolspeed use a flexible 3M double sided tape. They've stayed on awesome on my stab and you can peel them off with no damage if you are careful.

[wypaul 448]

Ed just for the record I have removed most of the VG's from my wings on the Avid but leaving them on the underside of the HS.    They increased the angle of attack but did not reduce the stall speed for me, making the plane want to land tail low.  One of these days I may try placing them back a ways (10 or 12%) on the wing to see if it will move the center of lift to the rear and reduce the stall also.  I used the Stolspeed suggested placement the first time.

On the Quickie 2 they are there to correct a problem with the laminar flow and are placed behind fifty percent of the chord.  I used silicone to attach them on the Q and double sided tape supplied for the Avid.  The silicone maybe a problem if I repaint in the future causing fish-eyes I have been told. 

[TJay 1041]

Lostman,   What kind of glue did you use, and can it be used on polycarb?  

TJay,  Hopefully before I turn 80!   EDMO

Ha Alright I will hope to have mine flying by the time I hit 35 then, I have till next June 15

[EDMO 1078]

Lostman,   What kind of glue did you use, and can it be used on polycarb?  

TJay,  Hopefully before I turn 80!   EDMO

Ha Alright I will hope to have mine flying by the time I hit 35 then, I have till next June 15

It really hurts to say 80 - my body says so, but my brain is still at about 30 - I guess someday my brain will grow up too!     EDMO

Edited 21 Feb 2016 by EDMO