Elevator horn misalignment

[carlrai]

Followed the drilling instructions to the letter yet still managed to misalign. Ended up with about 3/16" difference in deflection of the counterweight arm. (left one flush, right one 3/16 off.) Welded the hole, re-drilled and now about .100 out.
question is, can I Iive with the slight misalignment and move on or weld again and redrill? Maybe use a round file on one side of the hole in the horn and rely on the clamping of the washers and nut?

Very frustrating.......

Carl Raichle

 

[BruceW]

Carl. I had to redo the horns on the elevator of my finished -7 when I was replacing the HS for the spar crack SB.
Had to redo the horn hole once. I measured the trailing edges, not the counter balance arms.
Was still off a little, 1/16 or 3/32" as I recall. Was concerned about how it would fly.
Next flight showed no difference in roll or yaw. Still flying this way.

 

[nzrv8]

Common issue it seems. If I aligned my counterbalance arms flush with the HS, my trailing edges were misaligned by about 1/4". I decided to split the difference, so my trailing edges and counterbalance arms are misaligned by about 1/8" each. From what I have read, it isn't an issue in flight.

 

[Stoo]

Minor misalignment can be handled by enlarging one hole ensuring that it is round and concentric with the hole in the other horn. A shouldered steel washer is then turned in the lathe to tightly fit the enlarged hole.
Stewart Willoughby, 6

 

[Desert Rat]

If the trailing edges are reasonably even I'd just live with it. You could drive yourself crazy chasing 0.1". Especially on something you're building in your garage with no jigs.

As far as why it happens, no matter how carefully you set it up, there is still room for stuff to wiggle around a bit until the rivets are set or to drill the center hole a slight bit crooked, even if you're using a drill block.

 

[JonJay]

Search the forum for dozens of conversation on this common topic.

 

[carlrai]

Thanks for all the replies. I've had the hole welded over (AGAIN!) primed, painted and will give it another try with a steel guide block in a day or so. Will probably go with whatever I end up with. Getting pretty frustrated.

 

[StephenC]

Carl I discovered the same problem when I carried out the service bulletins on the tailplane. I discovered the original builder had recently replaced the elevator skin before selling and had manipulated the elevator counterbalance horn to make it all align. When I replaced the end of the elevator and made sure all was straight it became obvious that the actuator horns were miss aligned by about 1/16”. I welded up one hole and found I needed to make a bush to put between the horns and clamp them tightly. The hole in the bush helped to keep the drill bit aligned while I drilled the second hole. What I did find after it was all finished was that there was more deflection of the elevator as the offset horns were shortening the distance between stops.

 

[Av8torTom]

Thanks for all the replies. I've had the hole welded over (AGAIN!) primed, painted and will give it another try with a steel guide block in a day or so. Will probably go with whatever I end up with. Getting pretty frustrated.
View attachment 56162

Don't feel bad - I drilled mine PERFECTLY, then proceeded to enlarge the hole to the next upsized bolt (brain fart). I had to have the holes welded closed and redrill. When I clamped my elevators to the horizontal stabilizer my trailing edges lined-up perfectly, drilled one horn, then clamped a metal block with a hole drilled in it between the horns and drilled thru the other horn (this time the right size hole). After all that, one elevator is about 1/8" off from the other and the airplane flies hands off, straight as an arrow.

 

[carlrai]

So this was ultimately my solution after 2 unsuccessful tries at drilling the elevator horns.
Drill the selected horn to the dimension called on the plans. Deburr the hole
The bushing is the same size as the drilled hole and accepts a #40 bit.
Place the bushing and block (fabricated to the necessary width) between the horns with the bushing through the previously drilled hole.
Clamp the counter balance arms in place on the horizontal stabilizer.
Clamp the block/bushing assembly between the horns as called in the instructions and drill a #40 pilot hole in the other horn.
Open the just drilled hole in the horn to #12 as called out on the instructions. Take your time and drill a couple sizes up to #12 following up with a deburring.

This ended up with perfect alignment for me. That aluminum block was machined to .720 thickness and was probable overkill. Hard maple milled to the required thickness would work and a lot simpler. The key was the drill bushing. All very similar to drilling the hinge bearing.

Hope this helps someone.