Columbia 400 nose wheel shimmy

Discussion in 'Maintenance Bay' started by Jason Jennings, Sep 15, 2021.

  1. Jason Jennings

    Jason Jennings Filing Flight Plan

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    Have a Columbia 400 with a nose wheel shimmy. It is very light below 20kts and increases to moderate between 25 and 28kts. After 30kts it stops. Tire is balanced, bearings are good, strut is serviced and I'm out of ideas on what to do to stop this shimmy.

    Any thoughts are much appreciated! Thanks!
     
  2. Dan Thomas

    Dan Thomas Final Approach

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    There's static balancing and dynamic balancing. Yours is statically balanced. 99% probable. It won't cure shimmy. It can even make it worse.

    Besides that, IIRC the 400 has an adjustable friction clutch on the nosegear to discourage shimmy. There was a spec in the manual to set it to get a certain stiffness as measured by a scale attached to the aft end of the nosewheel fairing. Last did one four years ago. Don't remember the details anymore.
     
  3. FORANE

    FORANE En-Route

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    Does the Columbia share the same Esco nose strut that is in Lancairs?
     

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  4. Scott MacMoyle

    Scott MacMoyle Pre-takeoff checklist

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    if its like the Grummans the fork needs tightening
     
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  5. donjohnston

    donjohnston Pattern Altitude

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    Does the 400 have belleville washers to set fork tension? If so, check the breakaway tension.

    Other than that, dynamic balance the nose wheel.
     
  6. Gary Ward

    Gary Ward Cleared for Takeoff

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    Sometimes a new tire is required to stop the shimmy.
     
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  7. Jason Jennings

    Jason Jennings Filing Flight Plan

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    Two options. ESCO strut or Lancair strut. This one currently has the Lancair strut.
     
  8. a572mike

    a572mike Cleared for Takeoff

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    Once a nose tire gets a shimmy wear pattern (even just a little in my experience) no amount of balancing will stop it.
     
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  9. FORANE

    FORANE En-Route

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    Hmmm, I didn't know Lancair made struts. Or perhaps they have a rebranded strut made by an outside company?
    Did you notice the bearing preload and deadband tests in the checklist I posted above?
    Also, you might consider asking on the Lancair forum. There are some folks over there more familiar.
    https://lancairtalk.net/
     
  10. Rock714

    Rock714 Filing Flight Plan

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    Next step should be replacing the tire.
     
  11. Dan Thomas

    Dan Thomas Final Approach

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    Next step should be dynamically balancing the wheel assembly, just like they do when you get new tires on your car.

    Honestly, I really don't understand why people don't get this. Are they all so young they don't remember steering wheel shake in the car after the service station statically balanced the wheel? I guess so. For almost 50 years tire shops have had dynamic balancers that spin the wheel with the tire on it and show where to put the weights, and those weights will go in totally different places than a simple static balancer would tell you.

    Motorcycle shops have dynamic balancers that can handle small wheels. I converted an old dynamic balancer, and later built my own, and cured nosewheel shimmy problems with them all the time.

    But, most guys will persist in using static balancers, spend obscene amounts of money on shimmy damper and torque link repairs and new tires, or keep tightening the shimmy brake until the airplane will barely steer, and then they'll just resign themselves to the shimmy. They're not "following the science."

    Google the difference between static and dynamic balancing and learn something.
     
  12. pmanton

    pmanton En-Route PoA Supporter

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    Has it been apart?
    I found this tube in a wheel that had been on the plane for quite a while. The shimmy went away with the tube. IMG_0194.jpg
     
  13. Rock714

    Rock714 Filing Flight Plan

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    I agree, dynamic balancing is the key. How many shops have DB as opposed to static bubble balancers?
     
  14. Rock714

    Rock714 Filing Flight Plan

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    So....if all else fails start with a new tire & tube.
     
  15. Busflyer

    Busflyer Pre-takeoff checklist

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    It’s a Cessna. It’s supposed to shimmy
     
  16. Dan Thomas

    Dan Thomas Final Approach

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    I stopped numerous Cessnas from shimmying, by dynamically balancing that wheel. They're not supposed to shimmy. That's just another dumb aviation myth.

    Shimmy damages so much stuff. Besides wearing the tire, it beats up the nosegear torque links, steering collar, steering bungees, rudder bars, rudder system, and shimmy damper. It can loosen rivets in the firewall and forward fuselage. It shakes the daylights out of the instruments and radios. It can crack some engine mounts.

    No, they're not supposed to shimmy.
     
  17. Dan Thomas

    Dan Thomas Final Approach

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    Never seen any other shop than two I worked in. And then only because in the first, I modified an ancient dynamic balancer to fit nosewheels, and In the second I built my own from scratch. Like I said, motorcycle shops often have them to fit smaller wheels. You sure don't want violent shimmy on a bike.

    upload_2022-2-25_21-14-42.png

    A static balancer cannot find dynamic imbalance. It's impossible. The wheel must be spun to find it.
     
  18. Busflyer

    Busflyer Pre-takeoff checklist

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    Uhmm, that was a joke.
     
  19. Dan Thomas

    Dan Thomas Final Approach

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    I guess I missed the sarcasm. I tend to rely on emojis for that.

    Nevertheless, I get tired of people who have no maintenance experience, or who never read the service manuals, trying to tell owners how to fix intractable problems. They're simply parroting the misinformation, shall we call it, spread by other people who also don't have any frame of reference. So the owners go on to spend needless sums of money, trying to fix the problem as per SGOTI instead of manufacturer's manuals and troubleshooting guides and standard aircraft practices.

    One of the few things I detested about aircraft maintenance was the high cost of it. I tried to minimize that wherever possible by fixing stuff right the first time, and doing the preventive maintenance so that things worked and stayed working and didn't fail in inconvenient places or at critical moments. I didn't like to see owners have to give up flying due to poor maintenance ending up costing them too much. We all know it's too expensive, and yet we often fail to recognize why it's too expensive. Often it's because we just start replacing stuff in a futile attempt to fix something instead of intelligently analyzing the problem. For example, mechanics will chase fuel system stuff for a week instead of first checking to make sure the spark is as strong as it should be and is delivered to the right place at the right time, especially if those mags haven't been off for a long time. Ignition is way more troublesome than fuel. It's one reason why we have two magnetos but only one carb or fuel servo.

    Anyway. Sorry for that misinterpretation and the rant. I get too passionate about maintenance.
     
  20. Busflyer

    Busflyer Pre-takeoff checklist

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    No problem. Hard to reflect tone in written words. Guess that’s what the emojis are for!