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Pitch trim friction

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15 Oct 2017 08:23 #1248 by Chris Carlisle
Chris Carlisle replied the topic: Pitch trim friction
As it turns out, the fulcrum bolt on which the trim lever pivots is secured with a castellated nut and cotter pin so there's plenty of potential for wear and loosening. In my case, there was no friction at all at that point although the trim cable itself requires considerable force to move in either direction. Nonetheless, it still crept at cruise airspeed. I just replaced the castellated nut with an AN nylon friction nut equivalent. After setting the friction about where I thought it should be I threaded another thinner nylon nut on top of the first as a safety. Haven't flown it yet but I'm thinking it'll do the trick.

Chris
Sioux Falls, SD
415C, Ser# 508

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11 Oct 2017 10:55 #1246 by Chris Carlisle
Chris Carlisle replied the topic: Pitch trim friction
Thanks Warren. I figured some combination of compression and 'slip' washers would be the best solution.

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11 Oct 2017 01:59 #1245 by Warren D. Hampton
Warren D. Hampton replied the topic: Pitch trim friction
When you start to work on the trim control you will see that there is not a tight fit between the lever and the pivoting point( the bolt) which has no way to turn while moving the lever. My was setup flat washer(spacer) in front of the lever and a spring washer and flat washer (another spacer) behind it. by tightening the bolt you put pressure on the spring washer hence causing drag on the lever. The lever float between two sides of the bracket. They are being pulled together by the bolt being tighten...

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10 Oct 2017 17:33 #1244 by Chris Carlisle
Chris Carlisle replied the topic: Pitch trim friction
Thanks. I figured there probably weren't any more elegant solutions although I like the idea of a nylon (or fiber?) washer under the nut that the trim lever pivots on. That would help prevent the nut from de-torquing after multiple excursions of the lever.

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09 Oct 2017 18:59 #1241 by Ronald Raty
Ronald Raty replied the topic: Pitch trim friction
A spring washer and nylon washer under the nut might also be beneficial, the torque of the nut won't be quite so critical.

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09 Oct 2017 00:53 #1235 by Warren D. Hampton
Warren D. Hampton replied the topic: Pitch trim friction
try to tighten the bolt the control pivot on...

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