Super AVA and/or AVA Empennage Repair

[Riserflier]

My Super AVA is in need of two repairs and I’m interested in hearing about others’ experiences and advice before taking action.

1. Fracture in fin hold down post: the fore hold down post (or whatever it is called) has a slight fracture in its side. Sooner or later, it will fail. I am reluctant to drop thin CA in it as it may clog the female threads or not be strong enough over time.
2. Loose stab hold down stud: if I hold the stab mount steady I can move the male threaded post ever so slightly. It seems to have adequate pull out resistance… for now. But, over time, I am sure it will become looser and eventually give way if not allow the stab’s performance to become dangerously sloppy.

Anyone have comparable experience and good repair advice?

[Andy W]

That stud is a disaster waiting to happen. Here's a quote from my AVA build thread..
Getting it ready to fly, as I attached the horizontal, the stud just pulled right out of the mount plate!!!

Don't have pics handy, but the stud was simply glued into the thicker part of that pivot plate - and only 3-4mm of it is all that holds the stab on!! I had been careful to not over-tighten that part.

We ended up making a field repair that is a good, solid solution. Dremelled out a slot underneath that thicker part to drop in a 3mm nut, and cut a 3mm bolt long enough so that it threads into that nut. There's no way it's going to be able to pull out (it's also loctited AND epoxied in place, with carbon shavings mixed in with the epoxy!) Finally, I have a little more sticking up than stock as well.

Here's how mine looks now (the fin behind it is from a DLG sitting next to it on the shelf)..
827306

I'm not following your other problem - can you post a pic?
..a

[Riserflier]

Andy W, I like the stab repair.

Makes me wonder if the replacement stud (bolt) is long enough that I could use a washer/nut on top of the stab and get rid of that stupid female threaded post nut (would probably need to fill the oversized hole in the stab). If you loose that little thing, you're screwed as Barry Kennedy is challenged to make replacements available.

I suppose if I replaced the stud with non-metric (imperial?) threads, I could easily find replacement post nuts or other appropriate fasteners.

Re the fin post fracture. Any photo I could take would not be detailed enough to show the very fine fracture. So, I'll describe again although my terminology may not be correct.

The problem has to do with the two CF posts onto which the fin is connected. These posts have female threads. On my Super AVA (maybe others as well) the threaded holes are not exactly centered in the posts. That means the wall thickness is thin on one side. Apparently, it is thin enough that the hold-down screw and/or other stress from the fin has created a very small fracture in the side of the post. I want to avoid a larger fracture that would make the post pretty useless as a hold-down point for the fin. Replacing the post does not seem practical as the assembly it is part of is epoxied to the boom.

I got a suggestion to wrap and epoxy CF or Kevlar tow around the post and then enlarge the hole in the fin to fit. That doesn't sound too difficult.

Comments? Ideas? Suggestions?

[kablair]

I like the idea of wrapping carbon tow around the support. But instead of enlarging the hole, if it's only a bit loose, I would put some CA in the hole and 'ream' it out with the screw. I'd save enlarging the hole as a fall-back position.


-Keith

[Andy W]

I don't have a problem with the provided stab retainer - if I take the stab off, it goes right back on the stud so it can't get lost. :)

Now watch I'll lose it!

I see what you are saying about the fin mounts. As they are a REALLY tight fit into the fin (at least, mine are), there's virtually no chance of it splitting open while assembled. If you don't want to wrap it and enlarge the hole (that would be my preference) then you could just run some medium or thick CA into the crack, clamping the gap closed, then check on it every now and then. A little CA isn't going to prevent the screw from going in (although a LOT will!)

..a