Elevator Horn/Shackle Interference

[Dpearson]

Hi all,
I'm seeing interference between the AN115-21 shackle and the flange at the top of the elevator horn, when the elevator is deflected down below the neutral position. At the "full down" elevator position, the shackle is about 35 degrees off line from the cable:
thumb_18966.jpg

The previous builder fabricated some "horseshoe" parts, presumable to address this issue:
thumb_18967.jpg

So here's my questions:
1. Is some interference at the shackle/elevator horn joint, as seen here, typical? It seem it would increase cable tension and add stress to the system.
2. Has anyone seen these "horseshoe" parts as a workaround?

Thanks,
David

[U2fletch]

Did you try doing it this way?

20250424_161213_resized.jpg

[Battson]

Is that how the Bearhawk 5 is supposed to do it? I would not be comfortable with that construction on a Bearhawk 4-place, it would increase bending stresses on the bolts considerably, and upset the alignment. This thread is about a 4-place model.

[Jhankins]

See my comment below, that is the way it is depicted on the plans for a 5. I am building a 4 and a buddy is building a 5 we compared plans after he talked about needing the 1/4” spacers between the horns. His plans call for it, mine do not. I am curious as to why Bob made this change on the 5.

[jaredyates]

(Edited to remove my misunderstanding that the BH5 uses a different type of horn configuration as pictured by u2fletch above)

Below are some pictures of our plane.

David, Bob and the plans are the definitive source for structural information. I would take a look at the plans and see if it shows any detail about the flange on the elevator horn, and whether yours is conforming. Perhaps the flange extends too far towards the top. If the plans are not conclusive, call Bob and see what he says.

Not related to your post but since we are here, note also that the bolt orientation of the trim horn is important. On our last plane I had a case where the elevator cable got caught on the trim horn bolt, because I had the nut on the right instead of the left.

Screenshot_20251028-091216.jpg
Screenshot_20251028-091226.jpg
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[alaskabearhawk]

You should be able to trim back the flange to allow for full movement of the shackle, it won't take much. File a smooth stress relief notch at the bend.

Elevator horn 1.jpg Elevator horn 2.jpg

[Battson]

This is what I did, it's an easy fix.
Just be sure not to leave any large file marks or other scratches which could serve as crack initiation points.

[U2fletch]

Here is a picture from the Bearhawk Website for the QB kits showing the elevator horn configuration. There are bushings in between the left and right elevator horns to cinch down the bolts.

photo 215_s.jpg

[Jhankins]

This configuration is for the model 5 only to my knowledge, it is shown on the plans. My 4 place plans do not show the spacers

[jaredyates]

That is good to know!

[svyolo]

I also had to remove a small amount of material like Alaskabearhawk. I also wanted to use a threaded fork. But the threaded fork had far worse clearance issues. I did mine per the plans, with a small amount of material removal which I also had to do at the stick and rudder pedals. Very little.

[Dpearson]

Thanks all for the great feedback!
Fletch, I can't do bushings as shown on in your photos. That configuration looks like a nice improvement. The kit I'm working with is an OLD A-model 4-place quick build, circa 2006. Looks like that design improvement (and many others) came after my kit was manufactured. Shifting the elevators outboard would misalign the hinges and probably cause other problems.

Jared, thanks for the pictures! I've checked the plans and while the flanges aren't dimensioned, they are 1:1 scaled so comparing was easy. My flanges are a bit (maybe 1/16"?) longer top and bottom vs. what's shown in the plans. I think if I trim back the top flange to match the plans I should be fine. Thanks also for the tip on the trim horn bolts - I'll watch out for that!

Alaskabearhawk, thanks for the tip on the stress relief notch - I'll do that.

[U2fletch]

Had a feeling that was the case. Looks like you are on the right track to a solution.

[Dpearson]

Hi all - I called Bob late last week and he said to just trim the flange so that a AN115-21 shackle will fit without binding. He suggested using a 3/16" round file to round out the inside corners and avoid stress risers.

[svyolo]

Worked for me. I had to do it in a few other places also. The control stick IIRC.