"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 30, 2017 #41

    BJC

    BJC

    BJC

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    I've no doubt that he can feel even the most minute difference.


    BJC
     
  2. May 30, 2017 #42

    Little Scrapper

    Little Scrapper

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    After reading this twice I'm not sure what to say except that I'm certainly happy nobody got hurt.

    And it's great that you shared this and the honesty as well. If more people shared stories like this weekend could learn more because of it.
     
  3. May 30, 2017 #43

    Dana

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    Many Kolbs have mass balances forward of the hinge line but I've never heard of one needing spades. Makes me wonder if something's very wrong with the aileron linkage.

    Dana
     
  4. May 31, 2017 #44

    stevel

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    Those pictures are of other Kolbs, and Bill posted them to show the torque-tube arrangement. The plane in question does not have spades, and does have the straight balance weights out at the tips.
     
  5. May 31, 2017 #45

    Victor Bravo

    Victor Bravo

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    We lifted up directly on the trailing edge of both ailerons, and later placed weights on the trailing edges of the ailerons, to determine whether air loads were making this problem worse. There was a very large increase in the amount of friction/resistance in the system with the additional simulated air loads.

    We have not yet lifted upward on the wing tips themselves, to see whether the piano hinges were bowing. That will definitely be done as soon as the airplane goes back together. But we are stuck with the piano hinges unless we want to redesign the entire aileron system on the airplane. (knowing what I know now, if I were building a Kolb right now I would be putting ye olde tyme aileron bellcranks in the wings).

    Last night I finished the structural repairs to the outboard two wing ribs. Turned out pretty slick, I was able to splice new sections of aluminum tubing in to the upper rib trusses using fabricated internal sleeves. I was able to leave the undamaged portions of the rib structures in place without removing them from the spar.

    Kolb has an ever so slightly different interpretation of sheet metal fastener "minimum edge distance" than AC 43.13 has. The FAA expresses this minimum edge distance in terms of 1.5 to 2 rivet diameters, and Kolb believes the minimum is 1.5 to 2 sheet thicknesses :shock:

    Perhaps the anti-chafe tape I put over the rib edges will add some usable strength...
     
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  6. May 31, 2017 #46

    Dana

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    Remember the Kolb's aileron linkage is [at least partly] driven by the need to fold the wings.

    Might the hinges be misaligned? Or just needing lubrication?

    On the early models the piano hinges were full length, but that was changed to shorter segments back in the Ultrastar days.

    Dana
     
  7. Jun 1, 2017 #47

    Victor Bravo

    Victor Bravo

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    After studying the design for a while, I have come to understand many of the compromises or decisions that Homer made, and for what goal. I get a lot of the things that were once mysteries to me... the spar not being at the max thickness point, the elevator control mechanism doubling as the rear stabilizer attach bracket, the super short landing gear and the huge angle of incidence.

    But in my humble mind, there are very few compromises that can or should be made to the flying qualities or handling, and there better be an awfully big reward for it. Heavy control forces will ruin the experience of flying the airplane far more than easy wing folding or faster building time will enhance the experience of building or owning.

    So from where I am sitting now... with very very little Kolb flight experience and all of it disappointing... an extra 10 hours of build time for the bellcranks and an extra 2 minutes of control hookup during assembly... looks like a really good bargain to me.

    I don't think the hinges are misaligned because the ailerons moved more or less freely on the ground. Aileron torque tube twist under load, or aileron deformation under load, seems like a much more viable explanation.
     
  8. Jun 1, 2017 #48

    Dana

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    But, the extremely heavy control forces you experienced are not typical of other Kolbs, leading me to believe there's something wrong with this particular example, not the design in general.

    Dana
     
  9. Jun 1, 2017 #49

    pictsidhe

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    Is this a yellow Kolb? As in lemon yellow?
     
  10. Jun 1, 2017 #50

    pictsidhe

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    Get an assistant to wiggle the stick while you feel everything that should move. If you have the knack, you can feel a binding hinge bend. You could also try blasting hinges and pivots with wd40, waggle them and see if they leak rust.
     
  11. Jun 1, 2017 #51

    Victor Bravo

    Victor Bravo

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    No this Kolb is white and red.

    There was very little friction in the system with no loads on it. You could wiggle the stick easy enough and see the ailerons move. Not exactly a Bucker biplane, but not difficult to move because of hinge friction or binding.... little or none of that with no air loads.
     
  12. Jun 5, 2017 #52

    proppastie

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    When people asked me if I was sad I crashed my MM1, I say, no ....I did not get hurt. So look on the bright side.

    My second though is "rigging"..... I would guess it takes a mechanic or builder to study the plans and find the problem, perhaps another Kolb Builder of the same model. You have something very wrong here and if it is not evident on other of the same model, then you need to go back to the drawings.
     

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