Starduster tail wheel spring

Discussion in 'Starduster' started by Jimmy, Oct 30, 2018.

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  1. Oct 30, 2018 #1

    Jimmy

    Jimmy

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    N34AJ came to me with just 2 leaves in the tail wheel spring, and from all the articles I've read, it seems the caster angle was in the wrong direction. I experienced shimmy problems on hard surface landings. I had the spring re-arched and a 3rd leaf added (there was apparently a 3rd leaf at one time). After doing this, the caster angle is now in the correct direction, but I fear perhaps too much. In a taxi turn, it now wants to accelerate the turn when significant rudder is applied, causing the tail to want to swing. I suspect I need to have some of that arch taken back out to get things more civil. Right now, with an eye-ball protractor, I seem to have about 6 degrees caster angle. Any advice on what the actual angle should be?
    Thanx!
     
  2. Oct 30, 2018 #2

    chicoduster

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    I have fought this on my Starduster Too for 8 years . I have had my springs re-arched twice. I put a little longer bolt thru the front mounting hole and put spacers under to get the correct angle. For my plane and tail weight ( about 86 lbs) it is about 2-3 degrees forward? As the springs flatten out I move the washers to the bottom side to keep the angle. It has worked well for me. BTW make sure you have the U-channel bracket at the tail post side facing downward with a 1/8" aluminum plate on the bottom. This will take the side stress off of the rear mounting bolt bolts and the bracket.
     
  3. Oct 30, 2018 #3

    Jimmy

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    Thanx Mike!
    I was thinking 2 degrees or so would be about right. I sure appreciate your reply!
     
  4. Oct 30, 2018 #4

    lakeracer69

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    IanJ just recently posted a study that may debunk the angle thing. It may have more to do with the amount of friction the wheel has against side to side movement that starts the shimmy. I feel it may be a combination of both the amount of friction, or lack thereof, and the rake and trail.

    For instance, the rake and trail is extremely important to the steering on a motorcycles front end. Poor handling and high speed wobble can be the result of improper rake and trail numbers.
     
  5. Oct 30, 2018 #5

    chicoduster

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    I missed on the bottom plate for the rear clampas mine is actually 1/4" thick not 1/8". I actually have a 4th leaf in my leaf spring set as when I got the plane ( and before I moved the gear back and lengthened the engine mount) it weighed 145 lbs at the tail horizontal. You can also adjust the angle by putting a spacer under the rear mounting bracket. Usually a heavier rubber like off of a conveyor belt.
     
  6. Nov 3, 2018 #6

    IanJ

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    The rake angle makes a big difference to how the wheel tracks in terms of its desire to return to center, independent of shimmy problems. As the pivot point moves forward from the wheel contact point (up to a point), centering force increases. As that point moves backwards (pivot axis tilting forward, toward the plane), centering force decreases, and it can get to feel like power steering, even feeling like the wheel is trying to run away, needing counter-force. This is all the same as on a bicycle or motorcycle, if it helps to think of in that context.
     
  7. Nov 3, 2018 #7

    taff

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    Ian, I am trying to understand, especially the connection of the motorcycle/bicycle.
    Anyway, can you can add a sketch to help me understand?

    A couple of photos to show the rake angle (pivot axis) of mine.

    DSCN8371.JPG DSCN8371 - Copy.JPG
     
  8. Nov 3, 2018 #8

    lakeracer69

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    Taff, You almost have it. Draw another vertical line down through the wheel axle center and perpendicular to the ground. Now measure between these two lines on the ground. That is the trail number.

    The tailwheel socket pivot angle can be likened to the fork angle on a motorcycle frame. Also google it, there are many illustrations out there. There is a range of rake and trail for motorcycles that works and outside of that range handling characteristics suffer. If one were to amass enough data, I believe a range might also be generated for tailwheels. I think one of the issues here may be that on a lot of airplane plans there are places where there is little or no guidance and the end result is up to the builder, or the designer didn't fully think about this. You can't know everything. I'd be willing to bet that most certified A/C designers put some thought here.
     
  9. Nov 3, 2018 #9

    Wpsullivan99

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  10. Nov 3, 2018 #10

    Wpsullivan99

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    Where did yo get the tapered tail wheel rod. I thinking of converting my Acroduster from leaf springs to your configuration. My alternative would be to resend my leafs and get them heat treated. Bending is not a problem but getting them heat treated is. And ideas? Thanks.
     
  11. Nov 3, 2018 #11

    Jimmy

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  12. Nov 3, 2018 #12

    taff

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    I got mine from Steen Aero.
    https://secure.steenaero.com/Store/...lt_tailwheel_assembly_chris_color_640x480.jpg
     
  13. Nov 3, 2018 #13

    Jimmy

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    Benz Spring Co. in Salem, Oregon can bend & heat treat. They're very reasonable.
     
  14. Nov 3, 2018 #14

    Wpsullivan99

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    Thanks for the info! I have the same tail wheel but set up for leaf springs. I think Ill try resending my springs and find some one on the East coast to heat treat them. What angle is your tail spring? I believe mine was at about 45 degrees. I would like to lower it to about 25 so the tail would sit lower on landing. Any thoughts. ?
     
  15. Nov 4, 2018 #15

    Larry Lyons

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    Rebend and reheat treat worked well for me. Two and a half years, a couple hundred landings, and well over 150 hours and it’s still exactly where it should be.
     
  16. Nov 5, 2018 #16

    Wpsullivan99

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    Hey Larry, that’s what I would like to do also. I can bend them but is there anywhere on the east coast the can heat treat them properly? Also what angle did you use for the springs.
    Thanks.
     
  17. Nov 5, 2018 #17

    Jimmy

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    Quick update on my original post... Test flight with about 5 degrees caster went well. Ground handling was OK and (so far!) no shimmy to speak of.
    To Wpsullivan99 - just a thought here - the caster angle of the pivot pin is probably more important than the angle of the spring. If you have a spring angle of 45 degrees now and flatten that out to 25, you may wind up with negative caster, which could lead to ground handling problems. Good luck with it - and thanx everyone for all the suggestions/comments.
     
  18. Nov 6, 2018 #18

    Larry Lyons

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    Yes the angle of the spring has to work for your installation. I found a heat treat place in Rockford, IL. I can get their name (don't remember right now) but there are probably many out there that are way closer to you. Google is your friend here.
     

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