blanik L-13 glider, fowler flap

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Bille Floyd, Nov 5, 2019.

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  1. Nov 5, 2019 #1

    Bille Floyd

    Bille Floyd

    Bille Floyd

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    My project is gonna Need a different flap, than the one i have now.
    I used the Fowler flap on the L-13 glider , back in 1998 , and thought
    it was effective and very smooth to deploy.

    I did every search i could think of ; Had no luck finding out how, the
    thing worked. Anybody have an idea on how i could get that info ?

    The glider below, is the one i'm doing the Mods to ; it's going to look
    a lot like a BKB-1, when i'm done. The Fowler flap will add about
    25-sq ft when deployed, but 12 less squares than the stock glider
    when folded into the wing ; i might need All of those 12 extra squares
    if i ever need a full stop landing in the desert.

    Stock, my glider has 160 Sq-ft , and the stock flap has 12 squares . I can
    do a full stop landing , with no roll-out , on her now ; seated
    and and adding the weight for the fairings and motor , i will still be
    inside the parameters for the weight limit for current VNE and
    still be legal for a powered Ultralight. Those full stop landings, are
    gonna be problematic ; once i add the mods !


    Bille
     

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    Last edited: Nov 5, 2019
  2. Nov 5, 2019 #2

    BBerson

    BBerson

    BBerson

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    A fowler flap moves aft and down. The Blanik flap moves mostly aft, I don't recall if the Blanik flap went down much. That would be a problem for a tailless.
     
  3. Nov 5, 2019 #3

    dino

    dino

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    They got rid of them in the later L-21 Super Blanik to no detriment.
     
  4. Nov 5, 2019 #4

    crusty old aviator

    crusty old aviator

    crusty old aviator

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    You’re adding a lot a unnecessary weight and complexity to your “ultralight” by adding flaps. Why not choose a more appropriate airfoil and add a skid like Schweitzers use?
     
  5. Nov 5, 2019 #5

    Bille Floyd

    Bille Floyd

    Bille Floyd

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    @crusty
    I'm not changing the D-tubes ; just the flap.

    I already know a retractable flap works for this design. The
    Gostbuster had retractable flaps, and i could stay even with
    it, when his flaps were out ; when he retracted them , he
    just pulled away. Me and that other pilot, had near the same
    wing loading.
    https://www.google.com/search?q=gho...Nn0KHWTgBxkQ_AUICSgA&biw=828&bih=418&dpr=1.65

    Once again : "I already Know that it Will work" ; it's already bin done,
    but i liked the fowler flap on the L-13 better. Information on how
    it works , would be Great ; i really don't need people telling me
    their opinion on why i shouldn't do it.

    Bille
     
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  6. Nov 5, 2019 #6

    Bille Floyd

    Bille Floyd

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    Yes , the L-13 flap when out and down. Not that much added
    drag when coming out ; but my head went forward from the
    drag, when it went down. I used that Fowler flap a
    lot, when i thermaled in the glider; usually only 5 to 10-deg
    deflection , in the thermal, but it gave a LOT more
    feed-back from the wing, when deployed.

    The stock flap on my Exxtacy , is how i control the twist
    for the wing ; they recommend at least 5-deg flap , when
    flying at best L/D in turbulent air. I usually thermal with
    a 20-deg setting on the flap ; makes for a nice stable mush
    burger of a glider at low speeds , with Lots of feed-back
    from the wing. I know exactly where the spin entry is ,
    and use it for extra yaw rotation on the back-side of
    my 360's. What helped me a LOT in recognizing the point
    of stall for the inside wing ; i was # 4 in the world at ACRO
    on a Hg in the early 80's , and did it on a Manta Fledge-2
    rigid-wing.
    You wanna know what 4'th gets Ya ?
    That would be Nothing ; no money, no podium. What
    i did get from all that practice, was a good Feel, for
    stuff that can fly. I recognize UP, before the vario goes
    off.

    Bille
     
  7. Nov 5, 2019 #7

    ultralajt

    ultralajt

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    HI Bille! Are you the same one that I saw way ago on OZ report Hang Gliders Forum?
    If so, nice to meet you again!

    Regarding your question If I understand it right, you are wondering what the mechanics are hidden inside the wing to operate the L-13s fowler flaps in order to incorporate the idea in your rigid wing upgrade. I flew L-13 way back and as far I remember (as being a geek), it was made something like I show on my sketch, inside the wing. I will try to explain:
    - there is a bracket (a couple of them along flap semispan) that via pushrod push or pull the flap out from its closed position and vice verse. The flap has a couple of cantilevers attached to wing rear spar (reinforced ribs locations presumably). These metal levers had curved slots. The flap has brackets with two small bearing rollers and that bearings ride inside these slots. Slots are curved in such manner, that when flap travels aft, it also changes the angle of attack.. more aft, more downward flap trailing edge.
    Bytheway once making a preeflight check, I asked my instructor, if is normal for flaps do have so much lateral (spanwise) freplay, and he sad to me that in the flight there are no side forces (or minimal) in that direction... so I accepted that fact, even still now wondering if he was right.. :)
    So much from me about that fowler!
    Have a nice day!
    Mitja
    FLAP Mechanics.jpg
     
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  8. Nov 5, 2019 #8

    ultralajt

    ultralajt

    ultralajt

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    Wait! Maybe the slots were made different! Look at my sketch below. This is more like L13, as guide flaps most of the travel goes straight out little sloped down, and angled more down just at its very last portion of the movement.
    Another way.jpg
     
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  9. Nov 5, 2019 #9

    Bille Floyd

    Bille Floyd

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    YES -- That is Me !!
    And i Really REALLY thank you, for taking the time to
    answer my question !!!!!!!!! ... ...

    One slot, guides and holds the flap, the other one controls
    the AOA of such ?

    Bille
     
  10. Nov 5, 2019 #10

    ultralajt

    ultralajt

    ultralajt

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    Yes! But I wonder how to attach such a system in the dacron wing... Probably couple of let says foldable "reinforced carbon ribs" could incorporate the "slotted studs", while flap could be made as carbon/foam sandwich to resist bending and torsion loads.
     
  11. Nov 5, 2019 #11

    Bille Floyd

    Bille Floyd

    Bille Floyd

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    All my battens are made from a near 1/2" square carbon, and
    cross-braced for stress . The bottom Dacron skin will be
    removed , to about where the fowler flap is the thickest ;
    probably 25% flap cord. The mechanics can be attached
    to each end of the flap. The flap is 100" long, and will be 18"
    in cord length. Only (2) center batten's will need to float ; i
    just need to keep the slot thickness the same, at those points.
    100 inch of flap, can be made strong and light ; just not
    very portable. Maybe stick them inside the fuse, for transport.

    Bille
     
  12. Nov 5, 2019 #12

    jedi

    jedi

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    Have a look at Cessna 150, 170 or 180 series aircraft or Glasair Sportsman or most any Boeing Airliner as examples. Post 7 and 8 are good examples. Cessna uses push rods to extend. Boeing uses a jack screw. The slot geometry with a manually actuated push rod can affect deployment forces and those forces can drive the desired extend retract path. Forces can be to high or cause the flaps to want to self deploy.

    You are right to be concerned with the attachment structure as you have no rear spar. You may need a support extending to the D Spar or you may allow the flap moment to change the washout.
     
  13. Nov 6, 2019 #13

    SMORGAN

    SMORGAN

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    Dug through some very old photos as I thought I had one of the Blanik flap unfortunately the photo only shows half of it but confirms it is a straight slot at least the forward section is.

    If your design is like the the BKB 1 will it have elevons like the Millenium or are is it going to it keep weight shift for pitch and use the spoilers for roll like a Kasper wing.

    Keep posting as Im interested in how it develops.

    By the way I flew Crestline once in 1979 a Phoenix 6B if I recall correctly when passing through the US on my way back to Oz CBD NO NAME  34.jpg
     
  14. Nov 6, 2019 #14

    Bille Floyd

    Bille Floyd

    Bille Floyd

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    Thanks for the reply !!!
    1979 i was being paid by Tut Woodruf , (the Coca-Cola heir)
    to travel around the western USA, and take movies of my
    HG flying . Awesome job ; but like selling HG rides over a
    nude beach in La jolla Ca for a decade , it didn't really do
    squat, for my work ethic !! LOL !!

    Phoenix 6-B was a Bill Bennett design ; also the first HG
    that i ever gained altitude with, in a thermal ; where did
    the Time go ??

    I'll be using elevator where they usually place the elevons
    on a flying wing ; stay with the stock spoilers for turning.
    the Exxtacy has a foot of dihedral at each tip , over a 40'
    wing span ; don't think ailerons would be effective for turning ?
    I thought of going with a tail ; don;t think it's needed on
    the Exxtacy, because it has a fair amount of sweep angle
    (16-deg) at the 1/4 cord is what i measure.

    That shot you took of the L-13 wing ; it helped a Lot . Thanks !!

    Bille
     
  15. Nov 6, 2019 #15

    ultralajt

    ultralajt

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    I just found a video from a factory where Blanik gliders are under repairs. There is a time in video (at 1:14) where these slots are visible. I made a screen shot and a small portion cut out enlarged and it seems to me that it is like on my second sketch of this thread:
    wing from video.jpg slots.jpg

     
  16. Nov 6, 2019 #16

    ultralajt

    ultralajt

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    And moments ago I stumbled at this video with even more detailed shot:
    slots 2.jpg



    and another photo where a flap is visible in relation to the rest of the wing:
    flap.jpg
     
    Last edited: Nov 6, 2019
  17. Nov 6, 2019 #17

    Victor Bravo

    Victor Bravo

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    You remember right, it moved 3X as much rearward as it did downward. Like the very first notch of flap on a Cessna. The flaps on the Blanik were likely meant only to give it a tighter circling radius and perhaps a steeper winch launch at low speeds. It already had good spoilers for drag and glidepath control, so the flaps did not need to make a lot of drag as part of their job description (like "normal" powerplane flaps).

    Using flaps on a flying wing is a delicate balancing act best left to trained experts. It is possible, but the flaps have to be out at a certain distance from the center at the neutral lifting point, at a location where the lift from the flap does not cause nose up or nose down pitch.
     
  18. Nov 6, 2019 #18

    BBerson

    BBerson

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    Yeah, that looks mostly area increasing for thermals. Maybe the last bit is for landing.
     
  19. Nov 7, 2019 #19

    Bille Floyd

    Bille Floyd

    Bille Floyd

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    @ ultralajt
    You did "My" homework , For me ; i really appreciate your
    efforts . Obviously, you are Better at research, than i am --
    thank-Goodness !!!!!!
    You gave me ALL the information needed ; to design
    a fowler track system , for my project.

    Bille
     
    Last edited: Nov 8, 2019
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  20. Nov 8, 2019 #20

    Aesquire

    Aesquire

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    I never placed as high as 4th.;)

    One thing to be careful about. On Fowler flaps the wing area and lift increase in a fairly linear fashion, along with drag, during the initial rearward deployment. Then when the flaps start rotating down more, the drag goes up quickly, as does the pitching moment.

    I'm very interested in the mechanical how you get the flaps to work, controls and deployment. I've long been a Fledgling fan, and keep telling myself to take the step beyond flex wings to rigid wings.
     
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