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Mounting vertical stabilizer

Blake

Well Known Member
I have my tail mounted and about to install rudder hopefully for the last time. I ran a plum bob through all hinge holes. And top and middle are centered. Bottom is not centered. I adjusted the rod end two turns in on bottom to make it fit. Seems to not bind but I haven?t tightened the bolts yet. Any suggestions? This is for a rv-7a and I cut 5/8 inch off the front spar
 
VS

I have my tail mounted and about to install rudder hopefully for the last time. I ran a plum bob through all hinge holes. And top and middle are centered. Bottom is not centered. I adjusted the rod end two turns in on bottom to make it fit. Seems to not bind but I haven?t tightened the bolts yet. Any suggestions? This is for a rv-7a and I cut 5/8 inch off the front spar

Ideally you want the rear spar of the VS perfectly flat and perpendicular to the longerons with no stresses both fore/aft and starboard/port. A fishing line suspended should drop through the center of all three hinge brackets. Took me forever and 5/8" was too much. I had to fabricate a new mount plate.

That said, the bearings are adjustable for a reason and maybe that's ok. I'm not an engineer.
 
Haven't mounted mine to the airplane yet, but did a lot of messing about with alignment when making the VS top fairing fiberglass closeout. I agree with Larry, VS rear spar must be flat and perpendicular with the longerons. If a taut line through the rear spar hinge brackets does not touch all three brackets, then you've made a mistake. I found on my mockup, that the rear spar will bend a considerable amount, so I think if you have mounted the forward spar to the spar to fuselage bracket and the taut doesn't touch all three holes you have preloaded the rear spar and it has a bend in it. You should only adjust the rod ends on the rudder to fit the hinge brackets when the taut line touches all three hinge brackets.
 
The fishing line trick works good but to get it 100% true I would run a long steel straight edge along the back edges of the vertical hinge brackets. I made sure the bottom bolts were snug and then I was able to get the washer in for the left 1/4? offset for the prop wash. Then you can clamp, cut and drill the front spar. After the rudder was on and snug I fit and drilled the stainless vertical stab brackets from antisplat seen here. https://antisplataero.com/products/vertical-stabilizer-bracket-mod I just like the added measure of beef. I?m no aero-engineer but honestly that front vertical spar looks a little less than robust to me. JMO. Now with everything torqued the rudder swings free with no binding. Also check out this builders site. He has a detailed step by step of how he did it. http://www.rvplane.com/?categoryid=4&dayid=563
 
I did run a straight edge on the end of the hinge line and it was good. The plum bob was we?re I was seeing a problem. Installed all three bolts and torqued. Seems to move freely with no binding. Going to call Van?s tomorrow but I?m planning on moving along with the build
 
A straight hinge line is important.

If it is not, you may not feel any binding if it is not excessive but the rudder has to flex to compensate for any misalignment.

This is just one of the things that can have an influence on skin cracks that people are always looking for an explanation for.

The simplest way to check for alignment to to place a known straight edge against the back of the hinge brackets. If the hinge center line is properly aligned, the straight edge should touch the aft edge of the same three brackets (all top or all bottom, can't remember which is typical). If yours was straight but then a string showed it wasn't doesn't make sense to me.
All the brackets have the same edge distance to the holes so the result should be the same suing either method.

I would consider 2 turns of adjustment to make it work to be far more than just a slight misalignment, if the hole center line actually is not aligned.
 
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