November 15, 2019

Goodbye to Plastic Bushings

I really, really dislike the plastic bushings used for the elevator torque tubes, so I decided to design a better way to support the tube. I found a thin section (aka Thinex) ball bearing that fits perfectly over the 1” aluminum tube, and has a small overall diameter that will fit in the space without requiring mods to the ribs. The bearings I bought are flanged on one side. I plan to fabricate a small bearing plate to which I will press-fit the bearings, and then rivet the bearing plate into the floor ribs, just like the current bushing close-out plates do. I expect the smoothness of these bearings will improve elevator control feel in the control stick.

1” bore stainless steel flanged ball bearings
Just loosely test fitting the bearing. I can tell you already that the tube rotates much more smoothly on this bearing than on the bushing!
Another view of the bearing on the short elevator torque tube

2 thoughts on “Goodbye to Plastic Bushings

    1. That’s a good question. I had considered the static loads (hence why I went with stainless steel), but didn’t think too much about vibe. I researched bearing failures a bit today – there’s a failure mechanism called false brinelling that can occur when a bearing is subject to external vibration. I linked below to a guide that shows what this looks like. The bearings will be held in place by an aluminum shaft collar, so I don’t expect the bearings would just fall apart, but this brinelling could occur over time. I may do some testing with one of the bearings by applying some vibration on it (consistent with the prop frequency) and see how it holds up.. but I really don’t know what the vibration level/spectrum looks like at the locations where these bushings are used.

      A solution that comes to mind is to leave one or two of the vesconite bushings on the shaft, allowing them to absorb the vibration, and then use the ball bearings just at the end of the shafts.

      https://www.schaeffler.com/remotemedien/media/_shared_media/08_media_library/01_publications/barden/brochure_2/downloads_24/barden_bearing_failures_us_en.pdf

      https://en.m.wikipedia.org/wiki/False_brinelling

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