Elevator Trim tab deflection spec question ?

[Larry DeCamp]

R4 plans specify UP AND DOWN RANGE .
Does this mean the center of the trailing edge referenced to the elevator surface ( top and bottom) 0r the centerline of the elevator ?
Does up and down spec refer to the direction of deflection, or the resulting response of the airplane nose ?
Example: moving the tab Up from neutral results in a NOSE DOWN RESPONSE AND THE OPPOSITE IS TRUE FOR TAB DOWN RESULTS IN NOSE UP RESPONSE.

Also these specs appear to conflict with the most probable RV4 condition. depending on your interpretation above, a heavy passenger or baggage could benefit from more NOSE DOWN TRIM CAPABILITY THAN NOSE UP. Of course this assumes neutral balanced empty weight.
your input is appreciated.

 

[Jetmart]

When rigging airplanes I have always used the centreline of the control surface measured from the centreline of the fixed surface being used as the reference.

 

[Kyle Boatright]

R4 plans specify UP AND DOWN RANGE .
Does this mean the center of the trailing edge referenced to the elevator surface ( top and bottom) 0r the centerline of the elevator ?
Does up and down spec refer to the direction of deflection, or the resulting response of the airplane nose ?
Example: moving the tab Up from neutral results in a NOSE DOWN RESPONSE AND THE OPPOSITE IS TRUE FOR TAB DOWN RESULTS IN NOSE UP RESPONSE.

Also these specs appear to conflict with the most probable RV4 condition. depending on your interpretation above, a heavy passenger or baggage could benefit from more NOSE DOWN TRIM CAPABILITY THAN NOSE UP. Of course this assumes neutral balanced empty weight.
your input is appreciated.

Larry, what I do is clamp the elevator in trail and run the trim tab to an in-trail position too. Then I use a digital level on top of the tab to determine the angle (relative to level) of the trim tab at neutral. From there, I run the tab all the way up, measure again using the digital level, run the tab all the way down, and measure again. Then I take the differences of the angle from full up to neutral and full down to neutral and see if those differences meet spec. Adjust from there.

For what it is worth, there are digital level app's for smartphones. I find that approach more convenient than dragging out my 30 year old 4' smart level.

As far as needing more nose down trim than nose up trim. That hasn't been my experience in either the RV-6 or the RV-10, even loaded to the aft CG limit.

 

[Roadjunkie1]

Larry, what I do is clamp the elevator in trail and run the trim tab to an in-trail position too. Then I use a digital level on top of the tab to determine the angle (relative to level) of the trim tab at neutral. From there, I run the tab all the way up, measure again using the digital level, run the tab all the way down, and measure again. Then I take the differences of the angle from full up to neutral and full down to neutral and see if those differences meet spec. Adjust from there.

Exactly (or near to it) what I did. Your trim lever (if you are in an RV-4 with manual trim) should be at the center of its travel when the trim tab is neutral on the elevator. Then measure the up and down angle and compare to specs.

For what it is worth, there are digital level app's for smartphones. I find that approach more convenient than dragging out my 30 year old 4' smart level.

As far as needing more nose down trim than nose up trim. That hasn't been my experience in either the RV-6 or the RV-10, even loaded to the aft CG limit.

Agreed. It depends on how straight your airplane is built and how well-rigged the horizontal (and likely wings) is/are. I have never come close to running out of nose-down trim even with passenger and baggage near aft CG limits. (Definitely flies differently with aft loading! With the tail not flying as much, she goes faster! Landing takes a little more attention than 'normal' loading!) I have, however, seen -4's that run out of nose-down trim with just a passenger. Build 'em light and build 'em straight!