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CCI VG's on the Avid Flyer STOL

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CrownLJ(at)verizon.net
Guest

Posted: Wed Apr 11, 2007 2:46 pm Post subject: CCI VG's on the Avid Flyer STOL

CCI VG’s on the Avid  Flyer STOL 

 <?xml:namespace prefix  = o ns = "urn:schemas-microsoft-com:office:office" /> 

  

  

  

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 74x48 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(at)yahoo.com (My93Avid(at)yahoo.com) 

  

 

   [quote][b]

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Wed Apr 11, 2007 6:42 pm Post subject: CCI VG's on the Avid Flyer STOL

At 03:45 PM 4/11/2007, you wrote:

 	  Quote: 	
		  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.


	


Larry,

         Thank you for the great report. Where did you place the VG's 

on the stab?



Thanks,

Guy Buchanan

San Diego, CA

K-IV 1200 / 582-C / Warp / 100% done, thanks mostly to Bob Ducar.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

Clem Nichols

Joined: 10 Jan 2006
Posts: 88
Location: Munfordville, Ky

Posted: Thu Apr 12, 2007 5:11 am Post subject: CCI VG's on the Avid Flyer STOL

Top or bottom side?



Clem Nichols

Do Not Archive

---

CrownLJ(at)verizon.net
Guest

Posted: Thu Apr 12, 2007 6:21 am Post subject: CCI VG's on the Avid Flyer STOL

Guy, 

  

   I don't want to be uncooperative, and my only  stake in this is a set of free VGs for doing the experimenting.   Please understand that Art (CCI) is a business and desires to keep spacing  propitiatory.  His instructions has all the information needed.   

   I'm happy to report that it works very well and  is money well spent; especially in the tail improvements!

  

 Larry

  

 At 03:45 PM 4/11/2007, you wrote:

 	  Quote: 	
		  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.


	


Larry,

         Thank  you for the great report. Where did you place the VG's 

on the  stab?



Thanks,

Guy Buchanan



   [quote][b]

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Thu Apr 12, 2007 6:56 am Post subject: CCI VG's on the Avid Flyer STOL

At 07:19 AM 4/12/2007, you wrote:

  	  Quote: 	
		  I don't want to be uncooperative, and my only stake in this is a set of free VGs for doing the experimenting.  	


 Larry, you might want to clarify this with the list. It wasn't clear from your previous post that you were compensated for your efforts.



  	  Quote: 	
		  Please understand that Art (CCI) is a business and desires to keep spacing propitiatory.  His instructions has all the information needed.  	


 I understand. I was really asking whether they were on the bottom or top. And anyway, VG spacing can never be proprietary, unless you plan to only fly at night out of Area 51!  Anyone who sees your aircraft at a fly-in will be able to replicate your placing. The reason I would pay Art for his VG's are for his parts and service.



  	  Quote: 	
		    I'm happy to report that it works very well and is money well spent; especially in the tail improvements! 	


 I'm glad. Unfortunately my interest will have to wait further information on the wing, as I do not see the difficulties you had with your stab.



 

 Guy Buchanan

 San Diego, CA

 K-IV 1200 / 582-C / Warp / 100% done, thanks mostly to Bob Ducar.     [quote][b]

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

smokey_bear_40220(at)yaho
Guest

Posted: Thu Apr 12, 2007 7:31 am Post subject: CCI VG's on the Avid Flyer STOL

Hey Clem,



Your computer date is off again.  ha ha  You are way

back in May of '03.



Hope the Spring storms haven't been too bad for you,



Kurt

--- Clem Nichols <cnichols(at)scrtc.com> wrote:



 	  Quote: 	
		   Top or bottom side?

 

 Clem Nichols

 Do Not Archive


	




       

Looking for earth-friendly autos? 

Browse Top Cars by "Green Rating" at Yahoo! Autos' Green Center.

http://autos.yahoo.com/green_center/

Clem Nichols

Joined: 10 Jan 2006
Posts: 88
Location: Munfordville, Ky

Posted: Thu Apr 12, 2007 9:15 am Post subject: CCI VG's on the Avid Flyer STOL

Thanks, Kurt.  Another crash and another re-boot with the default values.  A 

local computer whiz is building me a new tower with all the bells and 

whistles including Windows Vista, and was supposed to deliver it one day 

this week, but it hasn't gotten here yet.  Hopefully I can finish this 

message and send it before I have to do another re-boot.  That process 

requires sitting here beside the computer and nursing it along past a couple 

of glitches.  Very frustrating.  We were fortunate in having no wind damage 

here, but much of the green which was appearing on the landscape has turned 

brown thanks to the freezing weather.  I'm just glad I don't have a bunch of 

money invested in an orchard as this years fruit crop in Kentucky is 

probably going to be a wipeout.



I'm still in the process of getting my little Rans S14 ready for an 

airworthiness inspection.  I can't remember whether I told you or not, but a 

mechanic for UPS who is a DAR and lives only about 25 miles from here (Mark 

Cottrell) is going to do the job for me.  I've spoken with him by phone a 

couple of times, and he sounds like a pretty reasonable ol' country boy.  I 

got the EAA packet which does a good job of guiding you through the process. 

Hopefully I'll get it right the first time.



Thanks for the heads-up on the time and date.  Stay in touch.



Clem

---

Fox5flyer
Guest

Posted: Fri Apr 13, 2007 7:49 am Post subject: CCI VG's on the Avid Flyer STOL

Larry, this is one some of the most well written  data that I've seen yet regarding VGs and is exactly what I've been waiting to  see before I make the move to installing some on my S5.  One thing, you  stated you had a ten mph increase in cruise with just the VGs on the HZ.   What happened when you installed them on the wings?  How, if any, did it  affect your cruise airspeed?

 Great report and one that I'm definitely  keeping.

 Deke

 

 

 [quote]      

CCI VG’s on the    Avid Flyer STOL   

    

    

    

    

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 74x48 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.   

 ...snip   

 

[b]

rjdaugh

Joined: 30 Aug 2006
Posts: 195

Posted: Fri Apr 13, 2007 3:10 pm Post subject: CCI VG's on the Avid Flyer STOL

Larry,  

Thanks for the good info.  I have been waiting on VG’s until I was pretty familiar with my plane.  Your great report has got me going.  

   

Randy  

   

Do not archive  

     

.             

  

         

  

From: owner-kitfox-list-server(at)matronics.com [mailto:owner-kitfox-list-server(at)matronics.com] On Behalf Of Larry Martin

 Sent: Friday, April 13, 2007 11:11 AM

 To: fox5flyer(at)idealwifi.net

 Subject: Re: CCI VG's on the Avid Flyer STOL  

  

     

Deke,  

    

   

    

  The cruise speed remained +10 with the vgs on the wing.  I usually cruise (stol wing - no where to go) at 5400 rpm (582/3:1 box)  and I always had a comfortable 74 ias.  Now, I can hold 74 with only 4900-5000 rpm.  Setting 5400 puts it at 85 ias, but with the stol wing, the drag is already starting to build at this speed.  The gain in speed comes from the tail now doing its job, and allowing the wing to do its.  

    

   

    

Larry  

   	  Quote: 	
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       [quote][b]

_________________
Randy
Kitfox 5/7 912S
Black Hills, South Dakota

smokey_bear_40220(at)yaho
Guest

Posted: Fri Apr 13, 2007 5:51 pm Post subject: CCI VG's on the Avid Flyer STOL

I am keeping a copy of your report too Larry.  Great

job!  You got the kind of gains VG's should provide,

though it seems most were gained from your tail

installation.



I think VG's can provide a significant drag reduction

on a lot of planes, homebuilts and store bought, if we

just experimented more with them.  Looking at a

friend's Aztec made me think those engine cowls have

to be draggy and could use VG's to gain some speed.



I might try some on my lower cowling to enhance

cooling too.



These little devices can have a lot of beneficial

applications.



Thanks for the report,



Kurt S.  S-5



--- Larry Martin <CrownLJ(at)verizon.net> wrote:



 	  Quote: 	
		   Deke,

 

   The cruise speed remained +10 with the vgs on the

 wing.  I usually cruise (stol wing - no where to go)

 at 5400 rpm (582/3:1 box)  and I always had a

 comfortable 74 ias.  Now, I can hold 74 with only

 4900-5000 rpm.  Setting 5400 puts it at 85 ias, but

 with the stol wing, the drag is already starting to

 build at this speed.  The gain in speed comes from

 the tail now doing its job, and allowing the wing to

 do its.

 

 Larry


	


__________________________________________________

smokey_bear_40220(at)yaho
Guest

Posted: Fri Apr 13, 2007 6:02 pm Post subject: CCI VG's on the Avid Flyer STOL

I figured as much Clem,



But it was an opportunity to write you again, if just

to bug you, ha ha.



My computer is screwing up lately too.  One of my

cleanup programs seems to be attacking my word

processor and a few other things it thinks are bad.  I

am trying to not to lose documents over it, but have

no time to fix it right now.



My cousin and her hubby just left after being here for

4 days.  I needed the entertainment break, but now I

am behind and have to catch up again.  The good news

is the house got cleaned and better organized.  The

bad news is I slept on the couch because the rest of

the house isn't furnished yet.  One day... I mean,

aaaa "I have a dream..." 



Well, back to catching up some more.  I am no where

near working on my plane yet.  Poor thing.  And my

flying skills are not getting excercise either.  



Kurt



__________________________________________________

Bob

Joined: 24 Oct 2006
Posts: 89
Location: Damascus, Maryland, USA

Posted: Sat Apr 14, 2007 4:50 am Post subject: Re: CCI VG's on the Avid Flyer STOL

Great report Larry!

Guy - HStab VGs typically go on the lower surface, but knowing that doesn't really help you.  The height, angle, shape, %chord location, and spacing all play a part and those are the proprietary details.  VG's aren't that expensive to try and there are multiple suppliers who sell them in both plastic and metal.  From there, it gets into all sorts of claims about what is best and I'm glad Larry found what works for him.

Bob

_________________
Remember that internet advice may only be worth what you pay.

Clem Nichols

Joined: 10 Jan 2006
Posts: 88
Location: Munfordville, Ky

Posted: Sat Apr 14, 2007 4:56 am Post subject: CCI VG's on the Avid Flyer STOL

Ditto that message, Deke.  My EA81 powered  model IV is nose-heavy, and even with the gaps on the tail sealed and a 5 pound  lead ballast on the tail spring I still have difficulty doing soft 3-pointers  even with the stick all the way back.  I'm wondering if VG's on the bottom  of the horizontal stabilizer wouldn't help that as well as my cruise  speed..

  

 Clem Nichols

 Do Not Archive

 [quote]   ---

asq(at)roadrunner.com
Guest

Posted: Sat Apr 14, 2007 7:16 am Post subject: CCI VG's on the Avid Flyer STOL

Clem,

   My plane is pretty much the same bird w/ the same characteristics.  Where are you located

                                                                                                  Larry  Huntley,Dundee,NY

 [quote]   ---

Clem Nichols

Joined: 10 Jan 2006
Posts: 88
Location: Munfordville, Ky

Posted: Sat Apr 14, 2007 12:09 pm Post subject: CCI VG's on the Avid Flyer STOL

On I-65 in Central Kentucky, about 20 miles from  Mammoth Cave National Park, if that helps.

  

 

Do Not Archive

 [quote]   ---

dafox(at)ckt.net
Guest

Posted: Sun Apr 15, 2007 6:56 pm Post subject: CCI VG's on the Avid Flyer STOL

Larry,

  

         Getting the  best performance from our Kitfox is always a challenge,

 but for the most of  all our efforts its hard  to surpass whats already  been

 designed in the airplane.  Its been tried and  tested  to give the best it can 

 be. There are  add on's and upgrades that can  help, but some things can

 not be improved on.     The  Rotax 582 Engine was designed for the best

 performance, longevity, and longer life to cruise  at  5800 RPMs and any-

 thing below that was detrimental to the engine, and  shortened there lifespan.

  

                                                          David ,   Kitfox  4-1200  Rotax 912  UL.

                                                                                   Previous  582,   Good engine

                                                                                   243  hours and never failed

                                                                                   sold  it, got a    good price. and 

                                                                                   upgraded  to a 912

  

 [quote]   ---

skypics

Joined: 12 May 2008
Posts: 2

Posted: Fri May 03, 2013 2:27 pm Post subject: Re: CCI VG's on the Avid Flyer STOL

Larry:



I have 4,000 on my Avid B STOL and had tried two different brands of VGs and found no significant improvement.



Then my hangar mate installed them on his Pelican and it reduced his flaps up stall speed from 60 MPH to 46 MPH with 400 pounds of pilot and passenger.



So I decided to try the ones he used. They are Stolspeed VGs. They are flexible plastic and are very easy to attach and remove should the need arise.



It took me two hours to install them on the wing.



On the test flight I noticed the same as with the other two brands. With flaps full down (10 degrees on my Avid) there was only a very slight reduction in IAS which could be AOA error.



However, I kept the VGs on and soon noticed, after flying several more hours that, while my flaps down stall didn't change much, my flaps at neutral stall speed dropped from 46 MPH IAS to 41 MPH IAS so that there was little difference in flaps off and on stall speed.



Then I noticed that my typical climb rate increased by 200 FPM and my glide ratio improved.



I fly a lot of back country strips and the VGs will help in getting me into and out of the more challanging strips in Idaho.



Full power stall with a Jabiru 2200, Tennessee 64 x 36 2 blade prop and 10 degrees flap is 29 MPH IND.



Idle stall with flaps is 39 MPH IND.



These VGs were only $100 bucks and I consider the cost worth while.



John M

_________________
John

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