Results 1 to 7 of 7

Thread: Tailwheel Shimmy

  1. #1
    Junior Member
    Join Date
    Nov 2012
    Location
    lOS lUNAS, nm
    Posts
    1

    Default Tailwheel Shimmy

    I have recently completed the Phase I test period on my Carbon Cub EX. One problem encountered was occasional tailwheel shimmy occurring on maybe one out of four landings. Video of landings showed that the tail wheel would sometimes do a rapid 360 immediately on touchdown followed by left and right oscillations on some of the landings.

    My tail wheel is the 3200 type installed on the Pawnee tail spring using three leafs of the spring. I tried making adjustments to the spring tension, checked the mounting hardware and tire inflation to no avail. Talking to people and web searches revealed all sorts of conflicting reasons for the cause of tailwheel shimmy (too much or too little tire inflation…too much or too little tail spring tension…too much or not enough caster, etc.).

    This is what I did to solve shimmy. I changed the caster angle of the tailwheel spindle by bending tail springs with a hydraulic press. The top of the spindle axis now leans more forward. The original spring bend was traced on a poster board. Then it was bent and compared to the original bend traced on poster board. The modified spring was bent 1.5 inches more (down) at the tailwheel end. I have tested the modified tailwheel spring with several loadings (solo and 220 lb passenger) and 3 point/wheel landings and have not experienced a re-occurrence of shimmy.

    10-5-2015 Carbon Cub Tailwheel Spacers 026532.jpg

    The original tailwheel installation

    P1030849.jpg

    The tailwheel installation with the tail spring bent 1.5 inches


    Mike Marker
    Carbon Cub EX N77NM

  2. #2
    Senior Member N867SP's Avatar
    Join Date
    Oct 2013
    Location
    Severna Park, MD
    Posts
    328

    Default Re: Tailwheel Shimmy

    I've noticed that I've had a few landings with shimmy as well. I am running the same spring by the 3400 BabyBush...on my list of things to look at during next maintenance cycle.


    Pete
    CCK-1865-0078
    ️N9PW
    Severna Park, MD
    Sent from my iPad using Tapatalk
    Pete
    ✈️CCK-1865-0078 N9PW
    Severna Park, MD W18

  3. #3
    Senior Member chipallen's Avatar
    Join Date
    Jan 2010
    Location
    Marietta, GA
    Posts
    738

    Default Re: Tailwheel Shimmy

    I have found that running the 2-leaf Heavy Duty PA-18 Tail Spring (available from Jeff Glab at CubCrafters) completely solves the shimmy problem; even when I am flying demos with a guy in front and my heavy "self" in the back.
    Chip Allen
    SWT Aviation, Inc.
    Cubcrafters Southeast Sales Center
    Marietta, GA
    www.swtaviation.com

  4. #4
    Senior Member Clay Hammond's Avatar
    Join Date
    Feb 2010
    Location
    Hudson Valley, NY
    Posts
    264

    Default Re: Tailwheel Shimmy

    You did exactly the right thing. Re-arching the spring.

  5. #5
    Senior Member Jon Delamarter's Avatar
    Join Date
    Feb 2013
    Location
    Yakima, WA
    Posts
    205

    Default Re: Tailwheel Shimmy

    Sounds like you essentially made a three leaf version of our two leaf Chip mentioned.


    Sent from my iPhone using Tapatalk
    Jon Delamarter
    Customer Support Manager
    Cub Crafters, Inc.
    jond@cubcrafters.com
    Office (509)367-5200
    Cell (509)833-6993

  6. #6
    Member Tahoe Cub's Avatar
    Join Date
    Feb 2013
    Location
    Zephyr Cove, NV
    Posts
    46

    Default Re: Tailwheel Shimmy

    I used the Alaskan Bush Wheel 2 leaf spring set up. I don't know what the "heavy duty" PA-18 spring from Jeff is, but I suspect it is the same set up. The stock three leaf spring is not nearly as stout. My stock spring sagged and became too flat to keep the tail adequately high. This allows the caster angle to decrease contributing to increase shimmy. I still have some shimmy on pavement, but not as much. It is definitely worth getting the beefy two leaf spring arrangement. Finally, it the three leaf spring fails I am told the damage to the rudder is not pretty. Mike

  7. #7
    Senior Member Jon Delamarter's Avatar
    Join Date
    Feb 2013
    Location
    Yakima, WA
    Posts
    205

    Default Re: Tailwheel Shimmy

    Our two leaf spring Chip referred to is indeed made by Alaskan Bushwheel (now Airframes of Alaska). It's identical to their three leaf PA18 spring, but with the top leaf removed.


    Sent from my iPhone using Tapatalk
    Jon Delamarter
    Customer Support Manager
    Cub Crafters, Inc.
    jond@cubcrafters.com
    Office (509)367-5200
    Cell (509)833-6993

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •