Establishing fuselage longitudinal centerline to set trim horn position

[Jskyking]

I’m trying to establish fuselage centerline in order to set the trim horns 5/8 inch to the left of the centerline. I’m trying to mis- drilling the horns to the trim torque tube/rod that runs horizontal thru the horizontal stabilizer. I’ve shot a laser plumb line thru the aft section of the fuselage using the vertices of the fuse tube at STA K-L and the vertical tail post,and it doesn’t seem to give the acneeded accuracy. Is there a better way to establish the centerline in order to set the trim horns? Thanks// jt IMG_2451.jpg

[geraldmorrissey]

I may be missing somthing here but couldn't you stretch a string from firewall cross tube to the tailpost to establish Buttock Line 0.00 line. Add a plumb line you have a BL 0.00 plane.
Gerry
Patrol #30

[Jskyking]

Thanks Gerry. I’ll give that a go. That helps. Hopefully, I can establish the required 5/8 left offset from CL offset in order to drill the trim torque tube to its permanent mount position.

[Jskyking]

I’ll add- when I shot the laser down the fuselage from the firewall top engine mount a few days ago it didn’t give me the desired accuracy on the tail post. This deviation could have easily been caused by beam parallax. Tomorrow I’ll install the elevator and the elevator horns should help validate the positioning of the centerline- I’m hoping.