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Thread: Tail strakes

  1. #1

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    Tail strakes

    I. Have the patterns to fabricate some tail strakes to be used with BLR vortex generators but need to know the material thickness ? Hopefully someone can help me out.

  2. #2
    Darrel Starr's Avatar
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    Someone tried to sell strakes last week on eBay for $75, no takers. Should look up the seller and make a deal.
    Here they are relisted for a starting bid of $50:
    http://www.ebay.com/itm/Piper-Super-...949e0f&vxp=mtr

    Recommend you buy them -- cheaper than trying to make them!

    Only 7 hrs. left so I have a Bidnapper bid on them to hopefully get them so they won't get away. Will resell them for the price I pay plus all the shipping costs just to get them into the right hands.
    Last edited by Darrel Starr; 01-13-2015 at 10:48 PM.

  3. #3

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    Mine are 0.063

  4. #4
    Darrel Starr's Avatar
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    I bought the set on ebay for $69 + $15 = $84. Will send them along to you for that price plus shipping.
    Keep in mind that making identical ones is tough because they have a very tight bend but also are made of very hard aluminum. I believe they were bent soft then heat treated. Just contact me at darrelstarr@aol.com.
    If you don't want them, I'll place an AD in classified.

  5. #5
    Olibuilt's Avatar
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    Do they really do something? Is it worth putting them. I have a set and I dont want to cut my fabric to install them.

  6. #6

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    Quote Originally Posted by Olibuilt View Post
    Do they really do something? Is it worth putting them. I have a set and I dont want to cut my fabric to install them.
    Like VG's they help keep your arse in the air when going slow
    Remember, These are the Good old Days!

  7. #7
    aktango58's Avatar
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    My understanding is that VG's on the tail work just like the strakes. One or the other is helpful.
    I don't know where you've been me lad, but I see you won first Prize!

  8. #8
    Bill Rusk's Avatar
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    You do need them. The VG's on the wing are pretty useless if the tail can not develop enough downforce to drive the wing to a high AOA. Gap seals help too, to increase tail effectiveness.


    Bill
    Very Blessed.

  9. #9
    Jerry Burr's Avatar
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    Hi Bill. If you are flying along at a high AOA with the strakes adding to the area of the stabilizer trying to push the nose down so you don't stall ( that's what they do on a Lear Jet ) where is your additional down force coming from? Jerry B.

  10. #10
    Bill Rusk's Avatar
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    Jerry

    Not sure what you are saying. The tail strakes on a Lear are primarily for directional stability to reduce the dutch roll tendencies. (Reference here http://www.flightglobal.com/pdfarchi...h=learjet%2023) but they also "soften the stall". It is common on T tailed aircraft for the wingwash to disturb the horizontal tail/elevator airflow at high AOA, such that the tail abruptly looses its bite and the wing will pitch down abruptly at the stall. Not a good thing in transport category aircraft.
    My understanding is the strakes on a Cub add energy to the boundary layer flow (on the bottom) of the tail thus delaying the airflow separation at high AOA,( in the case of the tail that is downward lifting), thus making the tail more effective at driving the wing to a higher AOA. It has been my experience that at some CG positions the tail will stall before the wing, such that the tail effectiveness, or lack therein, does not allow for maximum wing lift. I thought that was on reason you often see square tail feathers and increased tail area on Cubs.

    My understanding is that you were heavily involved with the testing of the VG systems during implementation. What is your take on all this? I certainly don't have your background on this subject. I would love to learn more, I'm fascinated by aerodynamics.

    Bill
    Very Blessed.

  11. #11
    Jerry Burr's Avatar
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    Hi Bill. I think the key words in the Lear info. are "soften the stall". The test flight information that I had read was that with the delta fins they could eliminate the stick shaker or one of the other stall warning devices. Because the fins had the tendency to keep them from entering deep stalls. The original sales info on the BLR setup was that it was going to reduce moose spins. Mr Deroche ( not positive on spelling ) couldn't just copy Micro so they had to do something a little different. For the most part they used the same V.G. chord line as had been used on the twins and added (delta fins).So they had a new product. The idea was not to pull the tail down but to limit the down force. And therefore cure the moose spin. That's why it's short on span and long on chord. And effects a proportionally small area of the elevator. You are right about the square tail feathers increasing the down force. But the area of the elevator is increased not the stabilizer. It's easier to increase the elevator than decrease the area of the stabilizer. It they were to add a couple of inverted T strakes on the bottom leading edge of the stabilizer it would create more downforce but that was not the idea. On Micro the wing lift characteristics were improved to the point that V.G.'s had to be added under the stabilizer to re-balance the wing - tail dynamics. That's why they were placed clear across the whole elevator. Simple as that. That STC was flown on a stock Super Cub. If you look at an airplane with Mackey Slats on a high angle approach you will see that the stabilizer is one big delta fin. Imagine the problems if the stabilizer area were increased. It's a problem that many are dealing with in various ways. Survival gear in the trunk is one. Fertile minds are working on it. Take Care. Jerry B.

  12. #12
    Bill Rusk's Avatar
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    Excellent info, Jerry. I sometimes forget that the designer may be trying to limit performance Vs increase it.

    Bill
    Very Blessed.

  13. #13
    mvivion's Avatar
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    A number of years ago, I visited BLR....not long after they certified their VG Kit. The owner discussed his kit with me, including the strakes, and their purpose.

    He showed me video and photos of the tail of his wife's cub (the test airplane) taken in flight at high AOA. His purpose for installing the strakes was to reorganize the flow of air coming off the inboard end of the flaps at high AOA. In the stock configuration, with the horizontal tufted, the tufts closest to the fuselage were in very disturbed flow. In fact many of them were actually pointed forward at least part of the time.

    He then experimented with blocking off that gap between the inboard end of the flap and the fuselage, by installing a (temporary) flap extension, which extended the flap to the fuselage. He flew that configuration with the tail tufted, and the disturbance to flow in that area was worse.

    hence the strakes, which were intended to (and do) re-organize and smooth the disturbed air flow coming off the inboard end of the flaps as it flows over the inboard end of the horizontal stab, at high Alpha with flaps deployed.

    Its been quite a few years, so my memory of the details is probably not great, but those images of the tufted tail in action were pretty dramatic.

    MTV

  14. #14

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    Mike, so your saying on non flapped cubs the strake serves no purpose?

  15. #15

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    The strake serves a purpose with or without flaps.

  16. #16

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    So a related....perhaps stupid..but related question: I get the idea of smooth/organized air vs. disturbed air and the idea of keeping airflow against the airfoil vs. burbling off..

    ...but what are the physics of what makes the horizontal stabilizer/elevators "fly"? There is no airfoil (i.e. like a wing rib) to the tail surfaces unless it's such a small airfoil that it looks flat......and it seems to me that the control effect comes from the impingement of air on the surfaces of stab/elevators rather than from any "venturi" or "bernoulli" effect like there (allegedly) is on a curved wing airfoil.

    If the control effect is from the air "hitting" the surfaces, do strakes and VG's help with that effect?

    FWIW, I have underside tail VG's on the 12 and have never run out of control authority at the tail, whether slow mushing no-flap flight, stalled, or otherwise.
    Back In Alaska

  17. #17
    algonquin's Avatar
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    PA12 drvr, do you have the flaps extended to the fuselage? Also wondering about the square tail feathers in this situation. I'm just getting to assembly and my head is spinning with all the mods for the 12.seems everytime I'm set I read a blog like this,lol , the research starts again.

  18. #18
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by algonquin View Post
    PA12 drvr, do you have the flaps extended to the fuselage? Also wondering about the square tail feathers in this situation...
    yes extended into fuselage, as much as possible, -12 fuselage shape/sides PREVENT extending flap into side like a -18 (fuselage tapers)... (wind blows flap down from rear, WILL break windows..)

    on His I got a deviation field approval to STC just continue to use the -18 round tail feathers, and not use the square tail feathers STC called out in the long flap(cub aileron as a flap STC, Day & Night) (Day & Night kinda tried to bundle/tie this STC to their other 2 STC's they sold for wing tips & tail feathers...)

  19. #19

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    What Mike said.....there's like 1 - 2" or so of space between the edge of the flap and the window/fuselage. .....and as Mike said, it's "just" the standard 18 tail feathers.

    When one goes to full deployment with those flaps, one knows that something is going on. I went from no flaps (albeit with the -18 tailfeathers) to flaps extended to the fuselage....BIG difference...my prior PIC time with flaps had been in a spam can with the electric actuated and even though I had 8 - 10 hours of Supercub dual to get familiar with the flap idea, the first time I pulled full with those big, long flaps, it felt like the -12 just sort of stopped in the air. Kinda cool.
    Back In Alaska

  20. #20
    algonquin's Avatar
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    I found out about the tie in of the other stc's when I bought the standard flap stc and square tail stc. From Ron. Now I'm trying to sort this out, bought a set of flaps which are extended five inches inboard. I need stabs and elevators so I bought the square tail stc and thinking I would just make them but didn't get any drawings with the STC. Ron told me he didn't have the drawings and atlee said they wouldn't sell me a copy but there tail is from the drawings. That means everybody else makeing them are illegal for certified planes as they have no way to doc. There work. Sometimes it feels like if I run a little faster, a little longer I'll catch my tail,lol. Thanks guys sorry to hi jack this thread.

  21. #21

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    Tail strakes

    PA-12 driver thanks for the reply, I have not extended my flaps to fus, thought about. It but when I posted my thoughts I had replies not do it, because I causes problems with airflow over the tail. I have no idea how this mod would work with the strakes and VG's installed. Maybe some good soul has tried it I would be interested in their results. Thanks again for the reply. Cliff

  22. #22

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    Quote Originally Posted by Clifford View Post
    PA-12 driver thanks for the reply, I have not extended my flaps to fus, thought about. It but when I posted my thoughts I had replies not do it, because I causes problems with airflow over the tail. I have no idea how this mod would work with the strakes and VG's installed. Maybe some good soul has tried it I would be interested in their results. Thanks again for the reply. Cliff
    Clifford...as noted, I can't help with the tail strakes, but I can tell you that (in my limited experience), there is not enough interference with the tail to cause control problems (either rudder or elevator) with the long flaps and VG's on the underside. Put another way, I've never experienced airflow interference with the tail. That being said, I've not worked terribly hard to find opportunities for interference: I've done power on stalls in level flight and in MAYBE up to 30deg bank and have done "power off" stalls in both those configs as well....to get any kind of stall break in power off "level flight" I've had to do whip stalls otherwise one learns what "falling leaf" means. Most of the "aggressive" stall experience has been with an instructor along...so the -12 might act differently being loaded a bit lighter if I was to undertake that same evaluation.

    ...but bottom line is that other than the pilot's grim look of concentration and state of mental anguish, I can't say I've seen any negative effects of the big flaps so far, even when mildly stretching the envelope.

    While I will admit that I don't have the skills to fly up to the capability of even a fat and heavy -12, it would still take some fast talking to convince me that the big flaps are not a benefit.

    All FWIW.
    Back In Alaska

  23. #23
    this would be a title NimpoCub's Avatar
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    I extended my flaps inboard, did nothing to the tail, and haven't noticed anything "different" in any of my playing. I do take off & land slower, usually only 2 notches, but 3 works just fine too, no loss of tail control. I took the VGs off the wing (no help) but left them under the elevator.

  24. #24

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    Nimpo, were your wing vg's submerged?

  25. #25
    this would be a title NimpoCub's Avatar
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    Nope, I've kept 'er right side up.
    I felt no noticeable diff in slow speed handling, and they cost me a few MPH in cruise. They are for high AOA handling, which I don't do on floats.

  26. #26

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    Are you sure they weren't submerged?
    (has nothing to do with water).
    In other words, were they located too far aft?
    That will have the effect you describe.

  27. #27
    this would be a title NimpoCub's Avatar
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    OK I'm with ya. Never heard that term before.
    I put 'em on close to the LE, as per Jerry B. I did some gap seals to prevent the geyser of air from the bottom. That did help.

  28. #28
    skywagon8a's Avatar
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    Quote Originally Posted by NimpoCub View Post
    ..I did some gap seals to prevent the geyser of air from the bottom. That did help.
    What do you mean by this?
    N1PA

  29. #29
    this would be a title NimpoCub's Avatar
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    Hi pressure air under the wing gushing up through the gap between the aileron & wing causes disturbance over the aileron. Flaps have gap seals, so I gap sealed the ailerons as well.

  30. #30
    skywagon8a's Avatar
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    I've never seen a flap seal on a Cub. Fairings to close the gap when the flaps are up, yes. When the flaps are down you want a gap of 1/2" or so to accelerate the air over the top. This increases the lift of the flap at low speeds and high angles of attack. By the same token a small slot ahead of the aileron improves airflow making the aileron more effective.
    N1PA

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