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

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.

fixnflyguy said:

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.

Click to expand...

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

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!