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.

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The original tailwheel installation

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The tailwheel installation with the tail spring bent 1.5 inches


Mike Marker
Carbon Cub EX N77NM