Edge Distance Concern when Mounting Horizontal Stabilizer

I am concerned about the edge distance when I mounted the Horizontal Stabilizer. The pictures shows what im concerned about, its hard to get a real good picture because of where its at so Ill try to explain it best i Can. This is the intersection of HS-714, Longeron, and the Top Angle of F-710. The instructions say to ensure you have the proper edge distance from the longeron but doesn't say anything about F-710. The edge distance on the longeron is perfect. What are your thoughts?



-david

I would talk to Vans

about the edge distance to the left of the undriven rivet in the photo. the hole without a rivet inserted to the right of the undriven rivet looks a little close, but probably OK. Call them. They'll probably say to forge ahead, but you'll feel better hearing it from them.

I contacted Vans in the beginning of my horiz stab work with some questions on edge distance. This was their reply :

"The e.d. "rules" are not absolutes, they are guides. "

I had the same thing

I had the exact same issue when I drilled mine a few years ago. Vans too wasn't concerned about it. However, Gus suggested that I put a backing plate up there in that area. Here is part of what I wrote Vans back then:

1-I made a drill guide out of a thick aluminum block and aligned one end with the outboard edge of the #30 hole in the HS attach angle. This ensured that I wouldn't decrease my edge distance anymore. Gus suggested that I file the hole bigger but I really wanted a clean hole with no slop. It seemed to work well. I drilled to the final size.

2-I then made a doubler out of some .187 aluminum (the same stock that the 711 attach points for the rear HS spar is made from). The doubler extends from the longerons out about 2 inches to the first rivet in the crossing angle. This did improve the edge distance to the end of the crossing angle but not by much. It looks like I have about 1/16" edge distance now.

To which Gus replied:

It'll be fine with that fix. The edge distance on the doubler is small,
but there's not much load sideways, and it's thick material so that's
OK.

So then, I asked:

Is there a chance for a fatigue crack in this area due to the twist of the tail during turbulence?

To which he replied:

No way to know, but it's very unlikely given the the thickness of the
material and the absence of any movement. ie it's no more likely
than if it was built exactly per plans.

So, sounds like it's not a big deal. I could forward my correspondence with Vans along with pictures to you if you want. Let me know.

Those are bolt holes; that 'undriven rivet' has threads. The edge distance is just fine. You may have to trim a washer to fit next to the longeron and I'd support it with some epoxy in the gap between the F-710B and the longeron. You can fill the gap just before you stick the washer in place, then run the bolt through and tighten the nut. If you ever have to remove the bolt, it will likely break free even if a little epoxy oozes but the washer will probably stay in place.

Talked to Ken this morning. As long as the bulkhead angle is nestled in the longeron there is nothing else you can do. Drive on.

-davis

Re-opening this one because it looks like I'm about to have the same problem as Davis did. I'm doing all the measuring in preparation for drilling that long AN3 bolt hole through the HS-714 angle, F-798 shim, Aft Deck, Longeron, and F-710B angle. HS is aligned and clamped down. Did a quick peek below deck and got that sinking feeling:



We're looking up at the intersection between the F-710B angle and the longeron. It looks like I made that angle about 1/8" too short. So, instead of centering the bolt hole inside the 5/8" of horizontal on the leg of the longeron (BLUE), I need to center it inside of the remaining 1/2" in order to maximize edge distance for both pieces of metal.

Even if my drilling technique was perfect and I managed to put it through right in the middle of that 1/2", I will have only 5/32" of metal between the hole and the outboard edge of F-710B, and 5/32" of metal between the hole and the inboard edge of the longeron. Not sufficient.

Reading this old thread, it looks like Van's consistent opinion has been that the loads in this area are vertical and I might be able to live with this. The alternative would be drilling that F-710B angle out and re-making it 1/8" longer, which will be... not very pleasant now that the aft deck is attached. I'm probably gonna just let 'er rip. If I bust edge distance on the longeron, I'm in a world of pain. If I bust edge distance too far on the F-710B I'm looking at probably a day re-working that piece, so I'll err a little bit towards the longeron center. If there's anything else I haven't thought of, I'd love to know now

Also: glad I looked. The shop head on that rivet though the longeron is awful. I'll have to remember to drill that one out and re-do it too.

Yes you are probably going to bust edge distance on the lower angle. I agree also that getting the correct spacing on the longeron is more important. As far as the edge distance on the lower angle, an email to Van's is warranted for your records as they are probably going to tell you to not worry about it or put a doubler there. I have seen this a few times on the forums now.

For those that see this before working on the aft fuselage make sure that when you construct the F-710B angle get a good fit with the longerons. It took me a little extra time but it fits right up to the vertical face of the longerons after rounding the edges of F-710B.