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Thread: Need help

  1. #1
    bigbluvic's Avatar
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    Need help

    I recently purchased a use Maxair Drifter XP503. During the takeoff run, just before rotation has a very nasty yaw to the right. Do I need to rig the vertical stabilizer to counter this? Are Drifters on of those planes that need left rudder input instead of right. I have a private certificate and tailwheel endorsement. I am a low time pilot about 100 hrs.
    Any help or advice would very much appreciated.

  2. #2
    Dana's Avatar
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    If the plane has a LH prop (top of prop moves to the left when viewed from behind), then it will need left rudder, not right.

  3. #3
    rwanttaja's Avatar
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    What you might be looking at is a mismatch in the tailwheel yaw control compared to the rudder.

    Say your plane wants to yaw left under power. In the early part of the takeoff run, you're taking care of it by pushing the rudder pedal to turn the tail wheel. As the plane goes faster, the tailwheel has less and less effect until the tail itself leaves the ground.

    At that point, all the yaw correction is being provided by the rudder. Depending on the match in effectiveness, you'll have to either push the pedal harder, or back off a bit.

    I had exactly this problem when I first started flying N500F, the original Fly Baby. When the tail came off the ground, the nose started heading left.

    N500F had, way back in the past, been put on floats, with the tailwheel control system being connected to the water rudder. It didn't give enough command authority, so Pete Bowers welded on extension tabs to the tailwheel control horn:

    The springs in this illustration show where the tailwheel control springs normally attached. When on the floats, the holes at the end of the extensions were used, instead.

    At some point during its 1982 restoration, the tailwheel springs were connected to the holes on the extensions. When I started flying N500F a few years later, I noticed it would dart off to the right as the tail came up. I switched the tailwheel springs to the "normal" position, and the problem went away.

    Here's some steps for you to try:

    1. First, establish which rudder pedal do you need to press to keep the plane going straight on takeoff roll with full power.
    2. Note whether, when the tail comes up, whether it yaws in the direction of the pedal (you suddenly need less rudder pressure) or opposite to the direction of the pedal (you need more rudder pressure).

    If you need LESS rudder pressure, you need to either increase the tailwheel control effectiveness (preferred) or decrease the rudder effectiveness. You'll need to move the tailwheel control springs/rod further outboard on the control horn, or the rudder cables closer to the rudder on the rudder horn.

    If you need more rudder pedal, the opposite is the case.

    Can you post some pictures of the rudder horn and the tailwheel and tailwheel horn?

    Ron Wanttaja

  4. #4
    rwanttaja's Avatar
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    OK, found a picture of my own Fly Baby's tail. This should illustrate what I mentioned in the last post.


    Note that the tailwheel is pointed backwards because I'd just rolled the plane backwards into the hangar (through a pile of kitty litter, ew).

    See if your airplane has similar adjustment holes.

    Ron "Gonna have to wash it, one of these days" Wanttaja

  5. #5
    bigbluvic's Avatar
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    Name:  20200409_112321.jpg
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Size:  84.2 KB Yes it has the adjustment holes, but they are already as far out as is possible. Would stiffer springs do the same job?

  6. #6
    rwanttaja's Avatar
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    Quote Originally Posted by bigbluvic View Post
    Yes it has the adjustment holes, but they are already as far out as is possible. Would stiffer springs do the same job?
    No, the problem isn't the effectiveness of either the rudder or tailwheel controls, but their mismatch in effectiveness at rotation speeds.

    Again, this boils down to exactly how the problem manifests itself. If you're holding right rudder to keep running straight during the takeoff roll, and have to push MORE right rudder as the tail leaves the ground, the rudder is less effective than the tailwheel. You can decrease the tailwheel control effectiveness by moving the upper end of the spring to the open hole in the rudder horn (on both sides, naturally).

    The same is true if you're holding left rudder, of course.

    If the problem is the opposite (you suddenly need less rudder pedal when the tail comes up) you'll need to attach the spring further in on the TAILWHEEL horn (again, on both sides). There isn't a hole for it, so you'd need to drill your own. The center of the new hole should be AT LEAST three times the diameter of the hole from the center of the existing hole, and, of course, centered between the two sides of the horn. So if it's a 1/4" hole, its center should be 3/4" from the center of the existing one.


    I see Lockwood Aviation took over production of the Drifter. You might contact them.

    https://lockwood.aero/

    Ron Wanttaja

  7. #7
    bigbluvic's Avatar
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    Thank you Ron, I will check into tailwheel connection this week end. I will also give Lockwood a call
    Bill

  8. #8
    bigbluvic's Avatar
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    Name:  20200412_124436.jpg
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Size:  92.4 KBName:  20200412_124436.jpg
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Size:  92.4 KB
    I think I have found the problem. The tailwheel control horn is broken.

  9. #9

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    Hmmm...Looks like its actually 2pc construction?

  10. #10
    Norman Langlois's Avatar
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    You are pointing out that there is moment. Assuming breakage If that is enough to give you control fits .
    Then In my opinion ,it is 2 pieces . That is an attempt to resolve an extreme wear . The axle shaft hole is so worn it allowed the tail wheel to caster adversely. The previous owners must have added that second piece as a stop gap measure. The obvious wear from the washer indent shows that The part was made after and it is also noticeable hand made and not symmetrical. I bet if you clean it up between parts you will find red paint under all that grease,On the edge of the control horn. Unless that horn,had originally been made with a symmetrically located second point rivet, to the rear where there are now 2 rivets. If you want it resolved bore and sleeve the axle hole through all components.to tighten up the tolerance. Then if you wish replace that bump up piece tight against the horn.
    As long as those axle holes are allowed to remain over sized and indifferent to each other , you will have movement and they will continue to work against your efforts.

    Then trim up your plane as the others describe.
    Last edited by Norman Langlois; 04-30-2020 at 10:10 AM.

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