Tail Spring Mount (Tail Dragger)

Hopefully there is a tail dragger builder that can comment on part number U-00018 (tail spring mount) and its attachment to the aft most bulkhead F-01412. On page 10-18, the mount is shown as having three pre-drilled holes that align with holes in the bulkhead. My mount has no pre-drilled holes and when I match drilled the indicated "keeper rivet" holes, the flat flange of the mount ended up having a slight cant (1 degree or so) instead of being perpendicular in relation to the vertical axis of the bulkhead. I am concerned that this will cause the aft fuselage to twist slightly and vertical stab to not be vertical when the other flange of the mount is bolted in place.

Did anyone else have a mount that did not have the three pre-drilled holes? Should I be concerned that the mount alignment error will be amplified when everything comes together?

Calling Vans tomorrow but am curious if anyone else had this issue.

Rob

Mine did not come with the three holes. I think we are to leave them udrilled, until the vertical stab installation. The thing is, the other two holes in the rudder hinge mount don't line up with the "keeper" holes.

My call to Vans didn't help much, as there is not much RV14 taildragger knowledge there yet.

The three preexisting holes in the aft web of the weldment are a mistake in the drawing which will be corrected in the next revision release.
The delivered part should only have a single center hole which is for production only, an not used during installation.

It is not fully clear to me from your description, what direction the misalignment is.
You mean the aft web is not exactly vertical? But rotated very slightly (approx.1 deg.)?

Rob,

There are many places on the airframe where you need to consider what the proper fit of the part needs to be. Sometimes that proper fit will trump what is shown in the plans, or necessitate new holes, shims, new flanges, or other surgery.

I'd suggest that you probably want the tailspring aligned with the centerline and should do whatever it takes to put it there. Shim it. Cut and re-weld it. Or whatever is needed.

Same for the vertical stab rear spar. Put it where it needs to be. I've seen far too many RVs with slightly twisted fuselages where the builder made the decision to fit the VS to the twisted bulkhead instead of putting it on plumb. it can be quite obvious later when sighting against the wings, etc.

The only good news is that the RVs fly great even with gobs of noticeable boo-boos.

This was very much the case on the older legacy kits, but very rarely would apply to the newest prepunched kits.
Making weldments fit properly is probably the only place it is likely to be needed in the newest kits.
In this particular case on the RV-14, the plans actually specify that shims may be needed in a specific location and prepunched shims in a variety of sizes are supplied

RVbuilder2002, the aft flange of the mount is riveted flush against the bulkhead, but when looking aft at the bulkhead, the flange is rotatated abou 1 degree or so clockwise (top edge not level if bulkhead is vertical). So in theory when the front flange is bolted into position, the vertical axis of the aft flange (and therfore the bulkhead) is not plumb with the vertical centerline. Does that make sense? In hindsight, I should have clamped the mount to the bulkhead prior to drilling. With no clecos directly holding the parts or pre-matched holes, I assume the setup moved while match drilling the rivet holes.

I am going to re-assemble the aft fuselage and cleco all the parts together except for the forward bolts through the mount. When its all together, I will try to insert the bolts. If they don't fit, I will drill out the "keeper rivets," insert the bolts, and drill new keeper rivert holes in through the bulkhead and flange.

I talked to Vans today and they said that idea would work. Extra holes in the mount/bulkhead should not be a problem.

Yes, that makes sense
1 degree rotation on the back won't be any issue.
The main thing is that you end up with proper edge distance on the bolts, and that small of a variation won't be a factor.

I could see the deflection and guessed a degree or 2. Over a 5' or so distance to the vertical stab tip, this would be a couple inches of error.

I reassembled the aft fuselage area with every cleco installed and when I tried to insert the bolts through the front flange they would not fit. I drilled out the keeper rivets, bolted the forward flange to the other bulkhead and match drilled two new holes just below the old ones in the aft bulkhead/mount flange. I could see the old holes were slightly out of alignment. I riveted the new holes and the mount is now straight in relation to the aft bulkhead. Problem solved, I hope. Just two extra holes in flange and bulkhead.

My original error was I was lazy in clecoing the aft fuselage area before match drilling the original holes. I skipped several rivet holes. There are many tight fitting components in that area. I would recommend you cleco every hole in the lower aft/side skin and bulkheads in the last couple feet of fuselage before match drilling the mount. Lesson learned!