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Date:  3-30-2011
Number of Hours:  1.00
Manual Reference:  
Brief Description:  Tailwheel Shimmy

Once I began flying on asphalt, it became apparent that the Tundra tailwheel shimmied badly. The main culprit is supposed to be kingpin angle, which should have the bottom of the kingpin tilted forward. Check - not a problem. Bob Barrows solujtion is to lift the tailwheel off the ground and keep it there until you run out of elevator. Unfortunately, that doesn't always fix solve the problem, as maximal forward elevator doesn't always make the tailwheel not shimmy when it drops to the asphalt. However, learning to do that procedure definitely enhances your pilot skills, particularly in crosswinds. Watching the tailwheel revealed that the shimmy was taking its toll. The flanges that grip the tailwheel spring were bending, and the attach washer started wallowing out. Not apparent without raising the tailwheel off the ground was loosening of all the attachment bolts, which were tightened. I decided to remove the 11.5 inch diameter Tundra and replace it with a 10 inch diameter standard Bob wheel made by Iron-Design while Iron-Design try to figure out the problem.

I talked with Alaskan bushwheels and they felt that the spring may be reversing the kingpin angle during landing, and want me to try a heavier Husky spring which looks to be a good fit. Several landings on asphalt after switching the tailwheel, revealed only one episode of brief shimmy resolved by briefly lightening the tailwheel load. Unfortunately, relatively narrow standard tailwheel will probably be problematic on mud, which happens around here from time to time, so I'd like to get a wider tailwheel back on. The bent flange on the Tundra looks fixable by heating it with a torch and nudging it back in place. I went with -7 fender washers to give more metal to avoid wallowing. More to follow.
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Bent flange.

Bent flange.

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Wallowed out washer.

Wallowed out washer.

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Bob tailwheel.

Bob tailwheel.

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