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  1. ski-bum added a post in a topic Looking into VG's   


    Here is an article written by Larry Martin, a friend of mine, on his experience with CCI VGs.


    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.
    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 ( 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 ( if you want to fly the Avid the way it was made to fly!
    Larry Martin
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  2. C5Engineer added a topic in Avidfoxflyers General Hangar   

    Looking into VG's
    Who's got em? Worth it on a short chord wing like ours? The Rans S-7 guys swear by them. Thoughts?
    • 3 replies
  3. dholly added a post in a topic Kitfox News Letters   

    Kitfox Owner Newsletter 1989

    Jan -

    Feb - Kitfox_O_News_Feb1989.pdf

    Mar - Kitfox_O_News_March1989.pdf

    Apr -

    May -

    Jun - Kitfox_O_News_June1989.pdf

    Jul -

    Aug -

    Sept - Kitfox_O_News_Sept1989.pdf

    Oct -

    Nov -

    Dec -

    Kitfox Optional Equipment List 1989


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  4. akflyer added a post in a topic Kitfox News Letters   

    a couple more.. I am having problems uploading on my aircard so I will finish the rest tonight
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  5. akflyer added a topic in KitFox General Forum   

    Kitfox News Letters
    I have some newsletters that you may find useful. If you have additional letters post them up so we can get a complete collection of them!

    • 4 replies
  6. dholly added a post in a topic History of KITFOX structural changes   

    As a new M-III owner I've been snooping around for info and history, and thought this one was worth sharing. Something that has become clear is there does not appear to be a compilation of old Kitfox newsletters on CD as there is for the Avid.
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  7. Av8r3400 added a post in a topic History of KITFOX structural changes   

    Great find, Doug! Lots of good information.

    (Pages 2 and 3 are reversed, in case anyone is confused by this...)
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  8. dholly added a topic in KitFox General Forum   

    History of KITFOX structural changes
    A good record of structural changes between Model I - IV
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  9. dholly added a topic in Kitfox III   

    KITFOX Model III turns 20 years old this month!
    A bit of Birthday nostalgia to celebrate your Independence Day:

    Copy of July 1990 Kitfox Pack News by Denney Aerocraft - Introducing new KITFOX Model III, ROTAX 912 and Aerocet 1100 Floats.
    Aerocet Kitfox_Pack_News_July1990.pdf
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  10. Russ. added a post in a topic Prop. Spinner   

    It has two bulkheads, one behind the prop, and the other infront of the prop. The spinner is attached to the rear bulkhead with screws and lock nuts.
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  11. akflyer added a post in a topic Prop. Spinner   

    how is the spinner attached? My ivo has one screw in the center. the brolga has about 8 or 10 screws around the perimeter. just trying to figure out how it mounts to give a suggestion for making it spin true.

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  12. Russ. added a post in a topic Prop. Spinner   

    I am running a Culver 74" x 49 pitch. The prop runs true, just the spinner has a wobble. Running on a MK IV HH 582. Russ.
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  13. akflyer added a post in a topic Prop. Spinner   

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    Hey Russ,

    What prop are you running? I know the brolga on akflyerbobs plane will wobble a bit unless you have it lined up PERFECTLY. The last time I put it on I just barely snugged the screws down, gave the prop a spin and then bumped it here and there till I had it running true, then tightened it down all the way. Any pics of you spinner so we can see how it mounts?
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  14. Russ. added a topic in Avid Flyer General Hangar   

    Prop. Spinner
    Hi All,
    I noticed my prop. spinner is not running true, has a little wobble. I could paint a spiral on it, just kidding. I noticed a MK IV HH for sale on Barnstormers, and it has no spinner. I talked with owner and he had same problem with wobble. He claims the spinner is not needed. What are the thoughts on this?
    Thanks Russ.

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  15. C5Engineer added a post in a topic Idaho Backcountry Trip Report   

    Thanks guys it was by far the best flying trip I've ever been on. Flying around home is going to be soooo boring now after landing those insane strips. I can't wait to go back.
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  16. akflyerbob added a post in a topic rotary pinking shears   

    Our local JoAnn Fabrics store has them.
    Its a chain store, maybe you have one near you.
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  17. horsepower added a post in a topic Idaho Backcountry Trip Report   

    Nice job Joey,Thats a trip we all would like to take.Someday when my bird is done and I have a little more tailwheel and mountain flying experience I am doing a trip like that.It was pretty cool with the SPOT tracking you, looks like something we all should have especially up here in the NW and the Alaska boys should all have one.Me and a buddy were suppose to fly down to Johnson Creek Sunday morning but it didnt work out.Nice pics,might even use some for my screen saver.Glad to see your 582 purrred like a kitten,goes to show you that if you maintain them and treat them right they will treat you right.Good job man. Randy
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  18. dholly added a post in a topic 2 Stroke Oil   

    Old owner of my M-III was using Amsoil black gold, damn expensive compared to S'nS or even the new Aeroshell. I'll be switching oils and was curious if y'all just topped off with the new stuff or drained the reservoir and lines when changing products like recommended in the attached article?
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  19. akflyer added a post in a topic rotary pinking shears

    may work for you. Not exactly the rotary shears, but will work if you have a good table and mark the fabric. I didn't have any issues just using normal pinking shears when I did mine.

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  20. Russ. added a post in a topic rotary pinking shears   

    Try Stewarts Systems , or go to ebay. I found a pair on ebay 2yrs ago.
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  21. akflyer added a post in a topic Idaho Backcountry Trip Report   

    Nice write up! sounds like an AWESOME time. Will have to put that one on my bucket list. I was following some of the JC on the supercub forum. I see some faces from there in the pics you took!

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  22. C5Engineer added a post in a topic Idaho Backcountry Trip Report   

    Short video to give you an idea of the terrain we were flying around up there

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  23. egp8111 added a topic in Avidfoxflyers General Hangar   

    rotary pinking shears
    I'm about to start the recovering processs on my KF III. I'm looking for a pair of rotary pinking shears but I understand they are not being made anymore. Anyone have any suggestions on a source ?

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  24. dholly added a post in a topic Idaho Backcountry Trip Report   

    A very enjoyable read, thanks. What an incredible adventure that must be, can't wait for the vids!
    Oh, and welcome to the [other] Mile-Hi Club haha...
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  25. C5Engineer added a post in a topic Idaho Backcountry Trip Report   

    This is what it looks like pretty much all the time

    Indian Creek

    Lower Loon

    Atop of Soldiers Bar

    Cabin Creek... Another beautiful strip.. fairly long but no go around once your committed.

    Another Avid post card shot

    Vines...looks good from here but it's short with trees on both ends and it's really narrow with huge rocks on either side. This is known as one of the Big Creek drainage "Big Four"

    This is Steve the Dead Stick Take guy showing us how it's done on Mile Hi. The normal way is known as one of the craziest places up there and he landed it with four different variations.

    Dewey Moore

    We were done flying on Saturday by 11am so I hiked up to the hotsprings.

    Gotta be the coolest Hot bath I've ever taken..check out that view..the perfect end to a perfect flying day.

    These dudes were from Florida

    The town of Yellow Pine. It's only 5 miles down a gravel road. Not much but they had gas and beer.

    The Potluck on Saturday night

    That is the moon not the sun..awaiting daylight on Sunday morning

    Headed back towards the desert

    Some of the trip home coming across the Oregon desert

    I was packed pretty tight

    Flying low out across the desert..had to make it interesting somehow.

    In the climb for 10,500...

    One final shot coming across the Sierra's before descending into the Sac Valley.

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