"The Kolb Quit" bit me in the butt yesterday

Discussion in 'Hangar Flying' started by Victor Bravo, May 29, 2017.

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  1. May 29, 2017 #21

    FritzW

    FritzW

    FritzW

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    I'm sure your looking back at the ordeal and drawing up a list of things you should of or shouldn't of done. Not to be a Captain Obvious, but one thing's for sure: flight control problems are ALWAYS an in-flight emergency. Fly whatever pattern you need to to get the airplane safely on the ground as soon as possible, you'll be forgiven. ...taking off again, with two on board, without being absolutely sure you found the problem and fixed it??? ...I'm sure you've put that on your list;)


    NOTE: I'm not throwing stones, my glass house is full of list's of things I shouldn't have done:emb:
     
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  2. May 29, 2017 #22

    Rockiedog2

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    If I'm understanding things properly, I wonder if one(both?) of the wings has gotten out of trim from maybe some unmentioned incident...type thing. The difficulty and effort to roll makes it sound like fighting a large surface. I know of a plane that was grounndlooped with no apparent damage and there turned out to be a similar roll situation to what you're describing. I was told the fuse had gotten twisted and it threw the wings outa rig and it was barely controllable laterally.
    Or maybe that flap thing you're talking about VB?

    well just wondering out loud.
     
  3. May 29, 2017 #23

    Victor Bravo

    Victor Bravo

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    All makes sense of course. The airplane is a stock Kolb Mark 3 Classic with flaps. I believe the flap hinge system is OEM. It was also a factory quick build kit, for whatever that represents.

    The wing on a Kolb uses a massive 5 or 6 inch diameter aluminum tube spar, the ribs are riveted to a torque plate which is riveted to the spar. This large round spar carries the torsion loads as well as bending loads. There are inserts riveted into the tube at the highest bending load locations. So I would not immediately suspect a "soft" wing, although it is of course entirely possible

    Lost motion in the torque tube is one primary suspect, because this is proven to be an issue with many Kolb aircraft. It's a 1.25" diameter T6 aluminum tube that is about 12 feet long, driven from one end and having the aileron at the other end. Springiness and lost motion (inflight flex) of this tube is a commonly reported thing. But that would result in equally sloppy ailerons in both directions.

    The aircraft could have been operated from the main runway (N numbered aircraft), and this might have made a difference in the outcome.
     
    Last edited: May 29, 2017
  4. May 29, 2017 #24

    Dana

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    The Kolb flap hinge arrangement is a bit odd, but there are an awful lot of them flying with no problems. Might there have been a problem with the wing fold mechanism? Kolbs are fairly light on the controls, no way should you need two hands to roll.

    The early Kolbs, like my Ultrastar, had torsionally soft wings-- on mine you could actually see the wing twist and the ailerons got less effective as speed increased-- but the later designs had an improved wing spar root attachment to fix that.

    Dana
     
  5. May 29, 2017 #25

    lr27

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    People comment on the wing having no washout, but isn't it a constant chord wing? It's my understanding that untwisted, rectangular wings stall at the root first, not all at once.

    If there's some kind of rigging problem, a quick test for twist in flat bottom wings is to sight along the bottom. In this case, you'd probably want to look from the front, with the tail wheel elevated enough so that you can line your eye up with the plane of the bottom surface of the wing. Seems like you could see a fraction of an inch of twist. A quarter inch in a 4 foot chord would be 0.3 degrees. A little trick from the model airplane world. I also suggest grabbing the wing tip and twisting it by hand, or with a weight. If one tip twists more easily than the other, that might be a clue. Also testing the aileron force with only one aileron weighted, in case the problem is only on one side.

    I wonder if one of the torque tubes is bent a little?
     
  6. May 29, 2017 #26

    BBerson

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    Check all the rigging of wings, ailerons and rudder, as suggested. And aileron angles up and down. Aileron horn might be loose. Loose ribs on spar. Loose fabric.
    Check control design. If cables, the bell-crank length must be same on both ends of cables or it binds.
     
  7. May 29, 2017 #27

    bmcj

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    Glad you are OK Bill.

    Does the control stiffness present itself when flown solo? If not, then I would suggest either linkage binding under the seat or increased flexure of the torque tube due to the higher wing loading.
     
  8. May 30, 2017 #28

    jedi

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    The aircraft did have an N number didn't it?

    I am guessing the whole flight was with flaps up. Did you try different flap positions to see if that would lighten the loads?

    Check to see if aileron input moves the flaps too. Did you really have stiff flaperons or stiff ailerons with a lot of friction when loaded?
     
  9. May 30, 2017 #29

    FritzW

    FritzW

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    If that was on a bumper sticker I'd stick it on my Volksplane ;)
     
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  10. May 30, 2017 #30

    Victor Bravo

    Victor Bravo

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    Aircraft is N numbered.

    Entire flight flaps up, not used at any time.

    Kolb flap/aileron hinge design creates "movement" of the flaps whenever the ailerons are moved. But it is NOT the kind of movement you are thinking of.

    Aileron input moves the flaps, but NOT in the sense of angular flap deployment. Normal aileron movement results in the FLAP HINGE LINE moving up and down vertically 1/2 inch, with NO ANGULAR FLAP "DEPLOYMENT".

    This aircraft thus does not have "flaperons" in the sense of the flaps becoming full span ailerons, because even though the flap hinge line moves up and down the flaps never change their angle.

    However, all that said, I believe that the air loads from the flaps are affecting and worsening the Kolb's already heavy ailerons.
     
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  11. May 30, 2017 #31

    Victor Bravo

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    Here is one photo of a Kolb flap hinge system, showing the entire flap and flap torque tube behind the aileron torque tube.

    P2100035.jpg

    Here is another photo of aileron spades, which clearly shows the "double hinge" of the ailerons and flaps.

    Kolb Aileron Spades.jpg
     
  12. May 30, 2017 #32

    TFF

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    Spades puts it into a different range of problems. Were they there before? I can't think of the aerobatic/ Redbull pilot but supposedly he flew 1000 flights before he was happy with adjustments. Take the spades off as a baseline.
     
  13. May 30, 2017 #33

    MikePousson

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    Just from the look of the fabric above spade, it looks like user add on. Your buddy needs to talk to previous owner about it.
     
  14. May 30, 2017 #34

    bmcj

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    Again, was this the first flight for his plane (under the new rule that allows a second crew member), or had he flown it solo prior to this with or without binding?
     
  15. May 30, 2017 #35

    BJC

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    Has the airplane been flown without the flaps?


    BJC
     
  16. May 30, 2017 #36

    BBerson

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    Have someone lift up the wing tips and check for binding. Piano hinges can bind over long distance. Looks like the piano hinge is effectively full span.
     
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  17. May 30, 2017 #37

    TFF

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    Michael Goulian is the one who spent all the time tuning the spades to perfection.
     
  18. May 30, 2017 #38

    BJC

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    I don't doubt what you wrote, TFF, but if Mikie, or anyone else, actually spent 1,000 flights to get spades just right, he knows nothing about how to do it.


    BJC
     
  19. May 30, 2017 #39

    TFF

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    I think he was being picky, and I'm not saying he went and flew 1000 flights in a row before hitting the airshows. I think Goulian has the ability to feel the difference of that degree.
     
  20. May 30, 2017 #40

    TFF

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    I went looking for the 1000 number, but have not found it yet, but I did find reliable that Goulian spent two years tweaking the spades to where he thought they were perfect.
     

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