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  #1  
Old 01-28-2019, 06:53 PM
FinnFlyer FinnFlyer is offline
 
Join Date: Aug 2018
Location: Bell, FL
Posts: 156
Default Elevator electric trim tab horn (arm) length

The manual specifies 25 degrees up and 35 degrees down for elevator trim tab. 60 degree total travel.

Manual trim
Dwg 5a specifies 1 7/8" from piano hinge pin to horn clevis pin (arm) distance.
That would seem to indicate a maximum of 1 7/8" inch travel of trim cable.
(sin(25) + sin(35) =~ 1)
Is that what you have with your manual trim?

Electric trim
EEF-1 drawing for electric trim does not have an exact dimension for the arm, but looks like 1.6".

The T3-12A servo has 1.2" travel.

It would appear to only give 45 degree total travel -- only 75% of manual trim range.
Is that enough? Has anyone encountered lack of trim range with electric trim?

Finn
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Old 01-29-2019, 05:01 AM
fixnflyguy fixnflyguy is offline
 
Join Date: Jan 2006
Location: Winston-Salem, N.C.
Posts: 1,003
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I have electric trim on my -4, and if I recall, I used same arm as would be used for manual trim. I have no shortage of trim, and never use full travel. I find that my "nose down trim" is far more important than "nose up". I am almost always with a rear PAX, but when solo, I can pretty much leave my trim at neutral for the entire flight.
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RV-4/N76WE
8A7 / Advance NC
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Old 02-09-2019, 07:14 PM
FinnFlyer FinnFlyer is offline
 
Join Date: Aug 2018
Location: Bell, FL
Posts: 156
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Quote:
Originally Posted by fixnflyguy View Post
I have electric trim on my -4, and if I recall, I used same arm as would be used for manual trim. I have no shortage of trim, and never use full travel. I find that my "nose down trim" is far more important than "nose up". I am almost always with a rear PAX, but when solo, I can pretty much leave my trim at neutral for the entire flight.
Thanks. I ended up with a 1.25" arm, which gives about 20 up and 30 down with the T2-10A servo (1" travel). Sounds like that should be sufficient.

Finn

Last edited by FinnFlyer : 02-10-2019 at 07:44 AM. Reason: Reversed up and down
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Old 02-09-2019, 07:37 PM
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N804RV N804RV is offline
 
Join Date: May 2013
Location: Mount Vernon, Wa
Posts: 469
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When I ordered electric pitch trim, long after purchasing the empennage kit, it looked to me like neither of the 2 different control arms (1 for manual trim, and one that came with the trim kit) were correct for the RV-8. I emailed Van's with pictures. It took a couple of days. But, they emailed back to say that neither of those were correct for electric trim for an RV-8. And, they shipped me the correct one, free of charge!
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