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  #1  
Old 05-17-2021, 02:05 PM
ScottK ScottK is offline
 
Join Date: Feb 2007
Location: SLC, UT
Posts: 45
Question Trim tab horn trimming rationale

I have a nit-picky "why is the sky blue" kind of question. Looking at the elevator trim tab horn on drawing 4, it comes with two clevis attach points, and we're directed to trim away one of them depending if we have cabled or electric trim. On the electric side, we drive the upper point and shave off the lower one presumably for workmanlike neatness. On the cabled version, we drive the lower point and remove the upper one "to allow travel".

But...wait, doesn't an electrically-driven tab need the same travel as well? Are we actually trimming just for neatness in both cases? Is the cited reasoning specious? Will my airplane be unairworthy if I just skip the trimming step entirely? Do I worry too much?
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  #2  
Old 05-17-2021, 03:11 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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The manual cable has a longer travel range from stop to stop than the electric trim motor does, so that requires a different length horn dimension to get the same amount of travel of the trim tab.
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RV-6A (aka "Junkyard Special ")
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  #3  
Old 05-17-2021, 05:03 PM
ScottK ScottK is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
The manual cable has a longer travel range from stop to stop than the electric trim motor does, so that requires a different length horn dimension to get the same amount of travel of the trim tab.
I inferred that the cable would have greater excursion and possibly less force than the servo, ergo the difference in attach points. But that would not change the stop-to-stop angular range of the tab and horn itself. Unless - the upper attach lobe doesn't interfere with the bottom of the elevator at all in nose-up trim...but it might bump into the cable clevis in nose-down trim? That would make it make sense. And now that I'm thinking of it that way, it does look like that on the drawing. I might have just learned something!
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