Originally Posted by jrs14855
Paul Dye wrote a recent article on gear mount failure on RV6 in Kitplane's. In that case I have issues with the positioning of the bushings at the lower firewall as well as the positioning of the lower truss crossmember and the vertical tubes from the lower gear socket to the upper firewall mount. i feel that these all have less than optimal positioning to properly transfer landing loads.
The round spring gear was designed and patented in the early 50's by Steve Wittman. The RV gear mount is a derivative of his mount design of that era. I am now leaning toward the idea that tire manufacturing process that creates out of round tires is a likely cause of shimmy. Also the shimmy that I am currently fighting is much more violent that what I experienced starting in the mid 60's. I am doing a visual inspection of the gear mount at intervals between 5 and 10 hours.
Some time ago I flew a Baron that had a violent nose wheel shimmy. Installed the most expensive Goodyear tire and the shimmy went away. No tire balance, just changed the tire.
My 7 got a rare shimmy after sitting for a cold period. And recently got an odd vibration from my Michelin auto tires. Although I am thoroughly familiar with the phenomenon with cars, it was never a consideration for my 7 until this recent event.
Has this been considered as a contributor/cause of shimmy? I know it happens just from rolling force from the hangar.
It would seem tire belt cord and "rubber formulations should be selected specifically to avoid this due to the operating cycles, physical and thermal.