Working on my Elevator Balance Horn and the Lower Horn.  Both of them have a Gap caused by the Center Channel Strap.  I was thinking of inserting a .040 shim in both to eliminate the gap (see pictures in the other post.  Still haven't quite figured out getting them in the same post).  What do y'all think?

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Comment by Gary Reed on March 30, 2017 at 10:52pm

Hello Rob;

Adding the shims raises the forward end of the horns to match the aft end.  This slight rotation causes the predrilled holes in the upper horn to move slightly aft; just enough to make C75T3-8 come close to rubbing the edge of the cutout.  I widened it to maintain clearance so it wouldn't rub when flexing while under load.

Comment by Rob A on March 30, 2017 at 6:35am

You had to widen it? Wouldn't adding the shims just very slightly raise the horns and not effect this cutout?

Comment by Gary Reed on March 29, 2017 at 11:02pm

Just an update if anyone is interested.

I went ahead and finished clecoing all parts together with the shims in place and everything looks great.  The only other modification I had to make was to slightly widen the lateral cutout (about 1 or 2 mm) in the upper and lower skins to accept the new geometry of C75T3-8.

Comment by Rob A on March 9, 2017 at 8:32pm

Looks good.

Comment by Gary Reed on March 8, 2017 at 3:26pm

So, I went ahead and made 2 shims; for the upper and lower horn.  They fill the little gap very nicely.  I'll cleco them in and see if all the other parts will fit together. 

Comment by Rob A on March 7, 2017 at 6:50am

I think Mark Pensenstadler added a shim also.

I can't see it being a problem either adding a shim. There certainly is a gap in the middle of the top horn and the whole side of the bottom one and a shim would fix that.

Comment by Gary Reed on March 6, 2017 at 11:58pm

It good to know that someone else has at least contemplated it.  I know that it was designed that way and I haven't heard of any issues with it, but the amateur engineer in me is worried about stress risers there at the edge of the center strap and the pinching action of the rivets. Because this is a high stress part, I have thought about eventual fatigue in the skin of the elevator there.  The shims should eliminate the pinch and the stress risers and will only increase the radius of the cable connect points by a hair more than 1mm.

Like I said, I haven't heard of any issues, and I'm sure that Chris and the Zenith team have conducted fatigue analysis of all major parts (like that hingeless aileron on the 601). 

Oh, the things that run through a builder's mind.  :)

Comment by Rob A on March 6, 2017 at 6:57am

I believe the balance horn will be brought up on the front by the elevator hinge thickness which is the same as the center channel strap (I think). I'm at the same point and was thinking of adding a shim between the strap and the hinge and also on the bottom horn too. I think it would have made more sense to have the center strap go over the top and bottom horns...just a thought.

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