Modify rudder control horn?

[ScottS97385]

Has anyone modified the rudder control horn by widening it out a bit or changed the cable attachment point on the pedals?

I am looking to lighten pedal force and reduce the sensitivity of the rudder.

IMG_6613.jpg

[airlina]

Scott, I have a Series 5 as well and also think that our rudder control horns are too short as well . They are so short that I had to add SS sheet protection over the fabric of the leading edge of my rudder where the control cable will rub at large deflections. Apparently Kitfox agreed because somewhere along the line after the Series 5 , they lengthened the horns on later models . Looks like from your picture yours might have already been lengthened? Without removing fabric and welding a longer horn in place I never saw a way to safely simply mechanically attach an extention, so I just live with it . Be interested to see what some others may have done . Bruce N199CL

[airlina]

Here are the stock rudder horns on my Series 5 , yours look like they were already modified. Bruce N199CL

[Eric Page]

The horns on my Series 5 rudder are stubby like the photos @airlina posted above. I'd be interested to hear some more background on this issue. My rudder hasn't been covered yet, so I could still make this modification.

Does anyone know how far outboard the cable attachment holes would need to move to achieve the Series 7 configuration?

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@ScottS97385: What's the distance between the bolt/rivet head on your rudder horn and the new cable attachment hole, center-to-center? With that configuration, what is the problem you're having with the rudder that you'd like to solve?

It looks like the extension that was added to your horn is a single piece that passes all the way through the rudder, and is bolted/riveted to the factory horn, through the original cable attachment holes. If that's the case then you might be able to remove the fasteners, slide it out and replace it with a longer piece, without having to remove fabric.

[Dave S]

Scott,

Bruce's comment is spot on that your rudder horns have already been extended. If you look at the rivet near the rudder, the rivet is going through the hole that would have been used for connecting the rudder cable without the addition of the of the extended horn you have.

If you are thinking about reduced effort to move the rudder - that is exactly what happens when the rudder horn (arm) sticks out further. Without the extension, more effort would be needed to move the rudder. Short horns=more effort, long horns= less effort.

Also, as with Bruce's plane with the short horns, our early (meaning pre John Mc Bean) S7 also has the short rudder horns like yours would have had if the the existing extension had not been installed. I believe the current Kitfox design has longer rudder horns.

As with Bruce's rudder with the short, unmodified horns, I fabricated a wear shield on the rudder on both sides to prevent fabric wear. That has worked perfectly since the build - no wear on the fabric at all.

Given the development of the kitfox over time, the short horns provided no interference on earlier planes which had the slab, non-airfoiled rudder/vert stab. One of the early skystar S7s (now owned by another member of this list) was equipped with a slab rudder/stab rather than the now common airfoiled rudder/stab so the short horns hold the cable well away from the fabric. The increased thickness of the rudder due to the airfoiled design causes the cable to ride directly the sides of the rudder with the short rudder horns.

[airlina]

The horns on my Series 5 rudder are stubby like the photos @airlina posted above. I'd be interested to hear some more background on this issue. My rudder hasn't been covered yet, so I could still make this modification.

Does anyone know how far outboard the cable attachment holes would need to move to achieve the Series 7 configuration?

---

@ScottS97385: What's the distance between the bolt/rivet head on your rudder horn and the new cable attachment hole, center-to-center? With that configuration, what is the problem you're having with the rudder that you'd like to solve?

It looks like the extension that was added to your horn is a single piece that passes all the way through the rudder, and is bolted/riveted to the factory horn, through the original cable attachment holes. If that's the case then you might be able to remove the fasteners, slide it out and replace it with a longer piece, without having to remove fabric.

Eric , one of my " to do's " at OSH this past summer was to check the factory airplanes at the kitfox display for this measurement. I found the fabric to the center of the horn hole was 1 3/16" and about
1 1/2" from fabric to end of horn. If I was in the build stage I would make the mod with a single piece welded or bolted to the existing horn to lengthen both sides . I'm not able to do this without major surgery so I live with it. A longer arm would dampen the rudder control some and eliminate the cable rub described above.

[Eric Page]

...fabric to the center of the horn hole was 1 3/16" and about 1 1/2" from fabric to end of horn.

Thanks very much for the measurements; that's exactly what the folks building older kits need.

If I was in the build stage I would make the mod with a single piece welded or bolted to the existing horn to lengthen both sides.

I was thinking just the same thing. I don't really want to remove ribs or fiberglass for welding, so the bolted modification sounds like the way to go. I might dummy up something in wood first as a template and see what the hive mind here thinks...

[Eric Page]

Well, that didn't go well. Ten minutes into the effort, my rudder fell over and shattered the Hysol/SuperFil cap. So, I get to re-live that couple of days' worth of work.

Rudder Cap Damage.jpg

Here's what I came up with for extending the rudder horn -- just a cardboard template at this point. It's 6-1/2" x 1-1/2" with a ~5/8" radius notch to clear the vertical tube and its weld bead. The holes for bolting it to the existing horn can be match drilled from underneath, and the new holes are marked 1-3/16" from the fabric surface, as @airlina measured on a factory Series 7 at OSH.

Rudder Horn Template 1.jpg Rudder Horn Template 2.jpg

The existing horn measures 0.115" thick including powder coat, so I presume it's made from 0.100" material. Spruce sells 0.100" x 1-1/2" x 36" strips of 4130 for $6.50.

[n85ae]

Looking at your pic, I see that you have the old Aluminum Spring. Grove told me to not use that kind of spring and
remove it since a number of them had broken. So you might want to make tailspring replacement a todo item, just a
suggestion.

Regards,
Jeff hays

Has anyone modified the rudder control horn by widening it out a bit or changed the cable attachment point on the pedals?

I am looking to lighten pedal force and reduce the sensitivity of the rudder.

IMG_6613.jpg

[airlina]

Well, that didn't go well. Ten minutes into the effort, my rudder fell over and shattered the Hysol/SuperFil cap. So, I get to re-live that couple of days' worth of work.

Rudder Cap Damage.jpg

Here's what I came up with for extending the rudder horn -- just a cardboard template at this point. It's 6-1/2" x 1-1/2" with a ~5/8" radius notch to clear the vertical tube and its weld bead. The holes for bolting it to the existing horn can be match drilled from underneath, and the new holes are marked 1-3/16" from the fabric surface, as @airlina measured on a factory Series 7 at OSH.

Rudder Horn Template 1.jpg Rudder Horn Template 2.jpg

The existing horn measures 0.115" thick including powder coat, so I presume it's made from 0.100" material. Spruce sells 0.100" x 1-1/2" x 36" strips of 4130 for $6.50.

Eric , the mockup looks great, should work well to get your cables clear of the rudder leading edge and rudder authority will be dampened some. sorry bout the rudder crash and burn, better notify the NTSB. Bruce N199CL