The Cessna 120-140 Association Forum

As anyone got some experience setting trim tab adjustment. Or a procedure to do so?
We rebuilt my left elevator (new skins and repaint). When we reinstalled to elevator we are not able to get as per TCDS A768 the published: Elevator tab Up 6deg, Down 33deg.

Aside from the cubic blocks installed on the trim cable within the fuselage, the only limiting factor we can see is the trim tab rod coming out from the stab that does have forward and aft limits within the mechanism.
But even having discovered that and turning it in or out, we have no way getting to the down 33 deg. We even loose the cable limiters to make sure they would not interfere.

Any input or experience is welcome

The travel changes depending on where the elevator is in its travel. The spec is with the elevator fared to the contour of the horizontal stabilizer. If you're having trouble getting the down angle, I'd wind the control to the full down position, (nose up,) then, disconnect the actuator from the chain and wind it all the way in, less a tooth on the sprocket, then fit it into the chain. You should then be able to get the 33 degree spec by adjusting the length of the pushrod between the actuator and the tab. Finally, check the up limit and adjust, if necessary by moving one of the stop blocks (I think; it's been a long time...)

Thank you John,
We'll check you procedure and see if we make it work. Weird that suddenly it doesn't make it anymore. We removed the elevators for reskin and paint, put them back and doesn't work.
That is what happen when you don't take pictures of the before.....it is hard to argue after if it wasn't like that all the time.

Just did ours too. Seems a lot depends on where the trim screw cylinder is set. we disconnected the rod and changed that several times .

I just added the words "nose up" to my previous post to clarify "full down position" (of the tab.)

Also, there should be a dot on the trim control housing. (Maybe a rivet.) When the pointer aligns with the dot and the elevator is fared with the stabilizer the trim tab should be fared with the elevator. (Again, from memory).

Thank you John for clarifying. I was asking myself the question following your original post, but wanted to go to the hangar first and play with whole thing before coming back with questions. This is great information.