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Thread: Baby Bushwheel tire pressure

  1. #1
    Bearhawk Builder's Avatar
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    Baby Bushwheel tire pressure

    What tire pressure do you run the baby bushwheel? I picked up wicked shimmy going to the wide fork and tire, never had it before. Maybe too much pressure?

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    Colorguns's Avatar
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    My rubber spacer between the spring and the frame died. and this made a very loose spring and also the bolt for the wheel bracket to the spring was also loose. Replaced and tightened and all good now.

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    Any play in the tail wheel mechanism will show up more with a larger tail wheel. I would check it all over for the possibility of a need for some new parts. I think that will be the bigger factor on the 'play' which you are experiencing.

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    I run whatever it says on the side of the tire. No shimmy. Maybe ya put the fork on too loose?

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    PerryB's Avatar
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    The leading cause of shimmy is excessive caster angle, usually caused by a fatigued tail spring. Your caster angle was effectively increased slightly by the larger diameter and the wider tire probably contributes as well. The swivel plate should be higher at the front than than at the rear. Level or less is a prime candidate for shimmy.
    After Monday and Tuesday, even the calendar says WTF !

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    Bearhawk Builder's Avatar
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    All good suggestions, but I just put the wide fork kit on my existing head. Cleaned, inspected, greased, nice and tight. Caster angle is if anything improved due to the addition of 31's at the same time which is why this has me baffled. I thought I'd start with tire pressure and go from there but there's no pressure recommendation on the tire.

  7. #7
    JPachl's Avatar
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    Airframes Alaska 907-331-4480 ask them. I run 6 to 8lbs.
    "If you want to be successful,it's just this simple. Know what you are doing. Love what you are doing. And beleive in what you are doing." Will Rogers

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    PerryB's Avatar
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    That is pretty strange. I cant remember what I ran in mine. I think it was about 10 or 12. I went back to a standard wheel during my rebuild last year. Never had a shimmy though. What pressure are you using now?
    After Monday and Tuesday, even the calendar says WTF !

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    Aussie Scout's Avatar
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    Bearhawk Builder's Avatar
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    I've got it up around 40 lbs now, which sounds like way too much. 3 years ago I re - arched my spring and all my shimmy issues went away, been flying since then with not a hint of shimmy until the BB upgrade. I really don't think it's a geometry problem. I'll lower the pressure and take a look to make sure everything is tight.
    Thanks Guys,
    Dave

  11. #11
    RaisedByWolves's Avatar
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    I think I set mine at 11 or so. 40 seems way high, that's what I use on a standard Scott 3200. Mine shimmys when loaded and on pavement but I know it's the spring. Stock old spring.

  12. #12
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    I've had mine at 10-12lbs for the last couple of years. Last week I upped it to 24 just because it's easier to push around. I liked the way it handled the rough stuff in the pasture at 10 though.

    .....Mike
    Last edited by tophand; 05-23-2014 at 09:39 AM.

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    Have a few friends sit in the plane than look at how the caster angle sits. I get some shimmy when I am heavy and my wheel landing is tail first (happens more than I like). Pick up the wheel and set it down real soft and it go's away.
    DENNY

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    PerryB's Avatar
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    If you've already had to re-arch the tail spring once, I am suspecting that it may be your culprit again. A leaf spring is just a big flat wire and every time you bend it, it loses some strength. Even when kept within its elastic range, routine flexing takes it toll and it gets soft. I think a new spring would fix the problem. ABW makes a good one. I was having the same problem about 4-5 years ago and their spring resolved it. If the attachment hardware is tight and the head is in good order, this is about all it can be.
    After Monday and Tuesday, even the calendar says WTF !

  15. #15
    Mauleguy's Avatar
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    Running 40 psi?, that pretty much defeats the purpose of a baby bushwheel, I am guessing it was also not designed to be at that much. I run around 10 in Bushwacker (Maule) and I would run 8 with a cub.

    I would get a new spring with the correct angle if you know that the tailwheel assembly is good.

  16. #16

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    Tailwheel shimmy with a Cub type airplane? Landing too fast. I can make any tailwheel shimmy if you give me a long paved runway and somebody else's Bushwheels.

    Check cable tension. Re-torque the head. Grease it. Study the exploded diagrams to see if you assembled it properly. Best advice? Keep the tail up until you can't. At that point you'll be so slow it won't matter.

  17. #17
    skukum12's Avatar
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    Baby says 25 max psi on sidewall
    "Always looking up"

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