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Thread: Vortex Generator suggestions

  1. #1

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    Vortex Generator suggestions

    VGs come with recommended placement. We have all seen or had aircraft with variations from supplier recommended placement. Has anybody had experience or knowledge about deviation from suppliers recommended placement. These VGs will be on a standard 18 wing with original flaps and round tips. It will be flown by experienced cub pilots only.

    I would appreciate knowledgeable input and discussion. Thanks. Stu

  2. #2
    BC12D-4-85's Avatar
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    Their chordwise placement is a result of testing and ultimately is a compromise of several values like stall behavior, control response, and cruise speed. Another variable is their height into the boundary layer of flow above the wing for the same reasons. One thing I'd be cautious about is placing them too far back from the LE or made from too low a design without some tuft testing of the airflow during high AOA. If their vortices suddenly reduce or stop due disturbed flow above the stall can become abrupt. My opinion and experience FWIW.

    Some are mounted on a straight line along the LE and others are offset to the rear inboard to let that part of the wing go first. I've wondered how a tapered straight line further to the rear inboard would work.

    Here's some reading material: https://stolspeed.com and http://fly-fbi.com/html/vortex_generators.html

    Gary
    Last edited by BC12D-4-85; 04-12-2019 at 12:16 PM.
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  3. #3
    Eddie Foy's Avatar
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    Why would you not put them where the manufacturer dictates?
    "Put out my hand and touched the face of God!"
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    BC12D-4-85's Avatar
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    Another interesting factoid is Micro chose short height VG's for the PA-18 and then tall (like the tail VG's on some) for the PA-20-22. Same airfoil. What aerodynamic mystery created that?

    Gary
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    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by Eddie Foy View Post
    Why would you not put them where the manufacturer dictates?
    because the manufacturer used to send kits with double sided sticky tape so you could try them in different configurations and provide feedback as what worked best (micro, for 185 in the 1990's)

  6. #6

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    I'm fixing to put VGs on my Cub in a day or two. When considering VGs I consulted the best VG expert I could think of, and Jerry Burr told me to do what my supplier advised since they'd done the testing and already had the position figured out.

    I don't need to know how, I need to know who to ask!

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    Gordon Misch's Avatar
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    Quote Originally Posted by stewartb View Post
    I'm fixing to put VGs on my Cub in a day or two. When considering VGs I consulted the best VG expert I could think of, and Jerry Burr told me to do what my supplier advised since they'd done the testing and already had the position figured out.
    FWIW, I followed Jerry's advice for application with Crosswinds leading edge cuff, and am very happy with the result.
    Gordon

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    Next time down, tell me about that. I suspect the Crosswinds cuff needs VGs.

    As to experience with non-standard placement - yes. I flew a C-180 with Sportsman + Micro, where they used the stock wing placement template. Not dangerous, but I was not impressed at all. I was more comfortable at low speeds with the stock wing/Horton and no VGs.

    But that was gut feel - I did not experiment or take any data.

  9. #9
    BC12D-4-85's Avatar
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    VG's and Crosswinds cuff - Charly recommends them together on his webpage.

    I've flown the cuff on three planes. I owned his cuff w/o VG's on a 7GCBC and liked the improvement in slow flight. I also owned a PA-12 with his cuff and no VG's that had extended wings with Sullivan tips. After some years I had the cuff removed and enjoyed the difference both slow and fast. Gordon Mandell who was involved in the design when working for Crosswinds told me the cuff "reduced the LE pressure peak at the stall".

    I guess that's good. Maybe VG's make it even better.

    Gary
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  10. #10
    BC12D-4-85's Avatar
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    If you're interested in a summary of high lift wing devices including VG's get a copy of this older SAE Publication: https://www.sae.org/publications/tec...ontent/670245/

    Lots of good info there and easy to digest.

    Gary

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    BC12D-4-85's Avatar
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    "When we are at cruise speed the AOA is zero" Alex left me in his wake with that while me is looking for a snack. Maybe his is. Some aren't. Ask Boeing. Flying at +25 degrees AOA? Why?

    Gary

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    Jerry Burr is/was pretty much the authority from experience on VG's. There is some interesting tables and info if you search for it. Most interesting to me was the sweet spot was much further forward than I expected. If you find the thread(s) that this chart was saved from, you'll get some good explanations as well.

    1.1%, that's less than 1" back in a 63" chord... but I like that data profile.

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  14. #14
    Gordon Misch's Avatar
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    Yep, that's what I based my installation on. Jerry is an interesting guy to chat with about this stuff.
    Gordon

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  15. #15
    BC12D-4-85's Avatar
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    Determining the best position for VG's that yields the lowest TAS stall is interesting but is it a practical application in normal flight? By practical I mean what angle relative to earth can be used for takeoff or landing especially on floats or skis? For 3-point there's a limit unless we're willing to roll the tail on takeoff or land tail first and drop like Storch. For slow flight it has more application.

    For Jerry's chart adding that deck angle versus TAS for all configurations would be a bonus. I'd guess the lowest airspeeds with flaps were determined in a nose high AOA at altitude.

    My Micro AeroDynamics prints for the PA-12 and 18 indicate the forward edge of the small VG's are located 0.75" behind the wing leading edge, or about 1.1% chord #4 in the chart.

    Gary

  16. #16
    Gordon Misch's Avatar
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    Yep, and furthermore that 3/4" remains valid with the Crosswinds leading edge cuff.

    In my opinion the value isn't so much being able to use a high AOA for touchdown. It's the "safety margin" that's provided in situations such as gusty conditions or landing in a turn (or my sloppy flying). I don't have any knowledge of how cruise speed is affected by the combination, but overall I'm happy with the arrangement.
    Gordon

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  17. #17
    BC12D-4-85's Avatar
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    Yes Gordon safety margin for sure especially on a sharp LE wing Taylorcraft that's prone to an abrupt loss of lift and nose down stall.

    For my Cubs and 12 the benefit was mainly on floats and somewhat skis in deep snow. In any wind the float planes with power would fly directly from plowing mode to takeoff (in the 30's mph GPS) via wave bounce and prop blast on the flapped portion of the inboard wing with little planing and then maintain flight just above the water while speed built. On landing I could touch the rear of the floats easy (same 30's mph with power) then plop down in a very short arrival. The 12 had a Crosswinds cuff and I never added VG's but now wished I had retained it and put them on. The cuff without VG's stalled like the Taylorcraft when it was pushed at altitude and was all done flying, the stock wing not as much. On normal landing (less than ~15*) it never let go unexpectedly.

    Gary

  18. #18
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    Vortex Generator suggestions

    Quote Originally Posted by BC12D-4-85 View Post
    Determining the best position for VG's that yields the lowest TAS stall is interesting but is it a practical application in normal flight? By practical I mean what angle relative to earth can be used for takeoff or landing especially on floats or skis? For 3-point there's a limit unless we're willing to roll the tail on takeoff or land tail first and drop like Storch. For slow flight it has more application.

    For Jerry's chart adding that deck angle versus TAS for all configurations would be a bonus. I'd guess the lowest airspeeds with flaps were determined in a nose high AOA at altitude.

    My Micro AeroDynamics prints for the PA-12 and 18 indicate the forward edge of the small VG's are located 0.75" behind the wing leading edge, or about 1.1% chord #4 in the chart.

    Gary
    Quote Originally Posted by Gordon Misch View Post
    In my opinion the value isn't so much being able to use a high AOA for touchdown. It's the "safety margin" that's provided in situations such as gusty conditions or landing in a turn (or my sloppy flying). I don't have any knowledge of how cruise speed is affected by the combination, but overall I'm happy with the arrangement.
    I agree 100% with Gordon on this. If theres no meaningful effect to cruise speed, I dont know why Id consciously turn down a slower stall speed.

    Ive never landed in a full stall. And I dont think Id ever start to do that just because my airplane could fly slower after a mod.

    Safety margin is where its at. Still land within the limits of your landing gear, regardless of stall speed.
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  19. #19
    BC12D-4-85's Avatar
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    I've thought about these VG's off and on over the years. They are fun to play with at odd AOA and control can be improved during slow flight. For the Cubs, Cessnas, Aeroncas, and Beaver I've flown without them I never felt the absolute need as I never unintentionally stalled or spun those planes. I've done lots of slow flight and same in turbulence apparently safely but perhaps marginally so. As mentioned in #17 there were certain ops that they outperformed a standard wing for me. If they save a life then of course that's good.

    To quote Stu the thread's originator "Has anybody had experience or knowledge about deviation from suppliers recommended placement. These VG’s will be on a standard 18 wing with original flaps and round tips. It will be flown by experienced cub pilots only". I guess #13 and #!5 answers that for short height Micro-style VG's. I wondered in #4 why the PA-20/22 has the higher units installed from Micro. And Cub Crafters further chooses a different method of placement and style to compound the questions.

    Hopefully when Stu tests them he'll take this to another level we'll get feedback on their experience with and without.

    Gary
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  20. #20

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    Vortex Generator suggestions

    I recall a comment Jerry Burr made in a thread about Micro and BLR's different VG placements about 14 years ago. He said BLR was better for power off landings and Micros were better for power on. I assumed that meant Micros were better at a higher AOA. I haven't kept up with BLR/Cubcrafters/VG STOL and have no idea what their locations are these days. When I think VGs I think Micro.

    Any comments about VGs with slats? I'm a few minutes from sticking mine on. Here's a pic of BCSC's VG template. CNC milled aluminum. That's different!

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  21. #21
    mvivion's Avatar
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    Yes, Boundary Layer Research applied larger VGs to the Piper wing, and in a somewhat different location and they’re staggered, in an attempt to keep flow energized over the ailerons at high Alpha. That design and STC is now owned by Cub Crafters, and installed on the Top Cub and perhaps others?

    Years ago, I discussed this kit with Bob DeRuesh (and I’m sure I butchered his name) the owner of BLR. Bob worked for Robertson STOL back when. He now has a number of mods for various aircraft involving VGs, including some spray planes.

    With regard to the different height of the VGs between the BLR and Micro kits for the Cub, I have to wonder......why Micro uses the same taller VGs that BLR/CC uses on the Cub in its kits for the Cessnas? Intuitively, I would think that the boundary layer on a Cub wing would be thicker than that of a Cessna, not the other way around. So why does Micro use shorter, smaller VGs on there Cub kits and taller, larger VGs on their Cessna kits?

    MTV
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    BC12D-4-85's Avatar
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    MTV: "So why does Micro use shorter, smaller VGs on there Cub kits and taller, larger VGs on their Cessna kits?" And tall VG's on PA-20/22's? I confirmed that today.

    Also short on my Taylorcraft. I feel puny and insecure with my small VG's but I'd never leave Earth now without them. Oh, and run them across the upper windshield to keep the fuselage flying.

    Gary
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  23. #23
    hotrod180's Avatar
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    Quote Originally Posted by mvivion View Post
    ...With regard to the different height of the VGs between the BLR and Micro kits for the Cub, I have to wonder......why Micro uses the same taller VGs that BLR/CC uses on the Cub in its kits for the Cessnas? Intuitively, I would think that the boundary layer on a Cub wing would be thicker than that of a Cessna, not the other way around. So why does Micro use shorter, smaller VGs on there Cub kits and taller, larger VGs on their Cessna kits?
    Charlie White at Micro would be the one to ask.
    Cessna Skywagon-- accept no substitute!
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  24. #24

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    Quote Originally Posted by BC12D-4-85 View Post
    Yes Gordon safety margin for sure especially on a sharp LE wing Taylorcraft that's prone to an abrupt loss of lift and nose down stall.

    For my Cubs and 12 the benefit was mainly on floats and somewhat skis in deep snow. In any wind the float planes with power would fly directly from plowing mode to takeoff (in the 30's mph GPS) via wave bounce and prop blast on the flapped portion of the inboard wing with little planing and then maintain flight just above the water while speed built. On landing I could touch the rear of the floats easy (same 30's mph with power) then plop down in a very short arrival. The 12 had a Crosswinds cuff and I never added VG's but now wished I had retained it and put them on. The cuff without VG's stalled like the Taylorcraft when it was pushed at altitude and was all done flying, the stock wing not as much. On normal landing (less than ~15*) it never let go unexpectedly.

    Gary
    As a past T-Craft flier, I still find any comments on it's flight characteristics interesting. Mine didn't have VG's though, and I didn't do any off airport with it. It wasn't until I bought my first RANS S-7 25 years ago that I got interested in all that, and I started noticing Micro's ads for certified aircraft VG's. I remember Chuck White referencing Jerry Burr when we talked about where to put them on my 7, ( the same as on a Champ it turned out, wing and the hor stab) and after 3 different placements (with double sided tape) I settled on the first, which is quite far forward. I set my second 7 up the exact same way, if it was good enough for Jerry Burr, it's good enough for me! It's when landing steeper slopes that I get my slowest landing, the slope kinda matching the high AOA on touchdown.

    I can safely venture much closer to the "all done flying, ain't no more" area on landings and even low level maneuvering, and often do. BUT, when I really push it right to the edge, it can bite. Like a friendly dog, friendly, right up until it snaps at you! But it is nothing I worry about doing accidental, as the stick pressure and AOA gives me plenty of warning, in fact I have played with it, at 6" height.....just to get more familiar with it. I like to keep some power in on very short landings, and the vg;s placement seems to really help this be safe and keep it flying.

    On this recent video Jonas shot (he of landing in the snow on tires/getting stuck fame/infamy, his idea, don't drag me into his decision making process) I finally got visual affirmation of how slow I can land the thing when it all comes together, damn slow. Upslope, about 6500' about 35-40 degrees, no wind. Cut to the good part= 10:32 in. https://www.youtube.com/watch?v=nmTK-fdqe_M&t=16s
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    Tony flyrite's Avatar
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    Quote Originally Posted by stewartb View Post
    Any comments about VGs with slats? I'm a few minutes from sticking mine on. Here's a pic of BCSC's VG template. CNC milled aluminum. That's different!

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    Quote Originally Posted by courierguy View Post
    On this recent video Jonas shot (he of landing in the snow on tires/getting stuck fame/infamy, his idea, don't drag me into his decision making process) I finally got visual affirmation of how slow I can land the thing when it all comes together, damn slow. Upslope, about 6500' about 35-40 degrees, no wind. Cut to the good part= 10:32 in. https://www.youtube.com/watch?v=nmTK-fdqe_M&t=16s
    I have no need to comment on his decision to land there and not to simply fly off the side hill as he eventually did.
    BUT how can someone be so damn stupid to wear his seatbelts as he does. Why does he even put them on? It is clear he has never work belts in a car or truck.
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    mvivion's Avatar
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    Quote Originally Posted by hotrod180 View Post
    Charlie White at Micro would be the one to ask.
    Actually, Bob would be the one to answer that question. He explained the strake on the tail to me, complete with video of a tufted tail, and made me a believer in those devices on a Cub.

    MTV

  28. #28

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    Quote Originally Posted by CharlieN View Post
    I have no need to comment on his decision to land there and not to simply fly off the side hill as he eventually did.
    BUT how can someone be so damn stupid to wear his seatbelts as he does. Why does he even put them on? It is clear he has never work belts in a car or truck.
    I think he got distracted a bit, (!) next time I see him I will for sure point it out, and jam him on it. The other errors made are self evident. To be fair: seatbelts in cars/trucks auto adjust for proper position, so someone used to that feature would maybe still not have a habit of using plane type harnesses correctly, I know my passengers always need to be taught, and it's something I remind them on before landing. Least of his problems on that day, but good catch.
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  29. #29
    hotrod180's Avatar
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    Quote Originally Posted by mvivion View Post
    Actually, Bob would be the one to answer that question. He explained the strake on the tail to me, complete with video of a tufted tail, and made me a believer in those devices on a Cub.MTV
    If you had posed a question about BLR VG's, I'd agree -- ask Bob.
    But y
    ou posed a question about Micro's choice of VGs, that's why I suggested asking Charlie.
    Cessna Skywagon-- accept no substitute!

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    Does Micro include VGs on the fin of a Cub? I can't remember. They do on my Cessna. No fin VGs in my exp VG kit.


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  31. #31
    BC12D-4-85's Avatar
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    There's at least four Micro VG's. Small that's 1" long x 1/4" tall and a larger one that's 1.5" x 3/8" tall. They come in flat and curved to match the underlying surface. There's none provided for the vertical fin of a Cub just the underlying VG's in front of the elevator gap. But if better rudder control is needed during slow flight then adding some to the fin would be a good test. Same for sealing the elevator and fin gaps like CC does.

    Gary
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    Vortex Generator suggestions

    I never paid attention before but a 206 has large VGs on the wing and stabilizers and two sizes on the fin. My 180 has large on the wing and stab and small on the fin. The Wildcat has all large on wing and under the stabilizers. Nada on the fin.

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  33. #33
    hotrod180's Avatar
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    Micro kits have different placements for different models.
    They all place VG's on the wing.
    The kit that I put on my C150TD also placed VGs on the vertical.
    Some kits (172 & 180) also place them on the bottom of the horizontal.
    The MicroAero website used to have a page for each model airplane, showing VG quantity & placement--
    I don't see them there now, but I did find some location-only images though.
    https://microaero.com/image-gallery/?smfg=Cessna&smfgid=389
    Interesting that there's a considerable price difference on Micro's VG kits--
    ragwing Pipers & 2-place Cessnas @ $695 vs 4 seat Cessna singles @ $1450.
    https://microaero.com/category/vg-kits/
    Cessna Skywagon-- accept no substitute!

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