Mating spars

[dbdevkc]

I had posted a question about this a few years ago, but then life got in the way and I stopped working on the project and making any progress. I am back at it now.

I am ready to mate the spars and plan to up drill the wing mounting holes to 3/8 (actually following Bryan Cotton's lead, up drill and ream to .3725). Before I do so, do the following steps sound right?

1) I assume that I need to align the spars using the wing mount holes (currently reamed to 3/16") and the 3 alignment holes (currently #40)
2) Clamp together
3) Drill the alignment holes to 1/4 using something to assure straight drilling - maybe an egg cup drill stand/bushing holder.
4) Bolt together using those (now 1/4") alignment holes (not sure if I really need this step since the spars are clamped together already?).
4) Figure out a way to get the full spar assembly up on the drill press table and level.
5) Up drill the spars through the wing mount blocks in steps to 23/64" (.3594), then use a .3725 reamer.

[sonex892.]

I updrilled the alignment holes to 1/4" and used bolts to clamp the spars together while drilling.

I found it easier to remove the drill press from its stand and place it on the floor.

With the spars clamped, I just updrilled attach blocks in 2 steps. 1/4" then straight to 3/8".
Steve
Sonex 892

[dbdevkc]

I have now read every thread I could find on this process - there are a lot.

I noticed a few things now that I aligned the holes and clamped the spars together, and I would like a sanity check:

- It seems that the bottom edge of the lower spar cap of the right wing spar is slightly lower than the left. Photos attached.
- The end of both spars are right up against the indexed bolt head holding the opposite spar root attach assembly. I assume this is ok.
- the space between the ends of the lower spar caps is 5/16". Not sure what is normal/expected.

Thanks.

[dbdevkc]

I think this photo may have been misinterpreted as a photo of just one of the spars with the root rib attach angle, and the root wing attach block. It is not. It is a very close photo of the two spars mated, with the END attach angle/block, where it is up against the other spar. It is not on that circled bolt, just up against the indexed edge of the side bolt head. I mean, that is why the plans say to index the bolt head.

[Area 51%]

We had a miserable time trying to get the spars to lie flat against each other when the time came to drill the holes through the mounting angles. We had up-drilled (reamed) the spars together on the drill press without issue, but when the wings were inserted in the spar tunnel, that bolt was hanging up ever-so-slightly on the opposing spar, holding them apart. Ended up removing 1/32in or so from the bottom of the spars at that area for clearance.

FYI

[dbdevkc]

So, you up drilled/reamed the spar mounting blocks/angles with the spars bolted/clamped together, but then when you attempted to assemble the wings to the fuselage the spar then hit that bolt head? Or did you up drill/ream each of the spars separately? I am trying to visualize how that would happen (so I don't run into it). Seems that if you try to add more dihedral, that is the direction that the spar end would go - toward that bolt head. Unless there is some constraint in the spar channel - I haven't gotten that far yet so I don't know.

As long as I have you, does this "gap" at the lower spar caps look correct? It is in the center of where the spars overlap each other. My spar plans sheet only has a very small drawing of the spars mated and it seems to show that, but doesn't indicate any type of measurement.

[Bryan Cotton]

Kevin,
I blindly assumed the pilot holes in the spar were good and I was not disappointed. I don't remember what the spar looked like. I have pictures somewhere but can't get to them for a bit.

[Rynoth]

Just some food for thought (and to muddy the waters a bit I suppose), but the way the plans call for wing rigging (i.e. not pre-updrilling the spars) has you rig the rear spars to the fuselage prior to updrilling the main spar holes. Since the main spars aren't exactly clamped together in their final installation (it's more of a pin versus a torqued bolt) there exists the possibility that rigging your wings per the specs/plans means that your spars may not be perfectly face-to-face (which is probably OK and accounts for tiny amounts of twist/variance in your home-built wing.) You might be enforcing this face-to-face alignment by using a pre-updrill/clamp method, perhaps introducing a pre-load on the bolts and/or making bolt insertion difficult. Whether this actually matters in practice I'm not sure. I followed the plans.

[Area 51%]

A: The gap looks normal to me. At least if it's not, there are two of us.

B: Yes, I drilled/reamed the spars as one on the drill press

C: When rigging the wings, I put a .025 shim between the spar and lower longeron. My reasoning was to avoid any future fretting between the two due to any sag after the drilling process. I'm thinking that action, rather than lifting the whole wing assembly, probably induced a slight dihedral increase(due to play in the alignment holes?) and caused the contact.
I understand Ryan's thinking about the spars not necessarily being in the same place during rigging as they were on the drill press, but this was something different as the rear tunnel assembly would not fit into place because the spars were being held apart by that contact between themselves and that bolt head.

D: I would do it exactly the same way again.

[dbdevkc]

Oh boy, that does muddy the waters a bit. So you are saying that if I up drill/ream mount blocks all the way to 3/8" (or .3725" as I had planned), with the spars mated and clamped/bolted together... I run the risk of the holes not being in perfect alignment when I assemble the wings to the fuselage and rig the rear spars to the fuselage - the flush spar faces not being as perfectly clamped face to face as they were when they are being mated off the plane.

I certainly have read of the all the builders that have had trouble doing all the up drilling from 1/4" all the way to 3/8" when mounting the wings. And have not read of mis-alignment issues upon wing-to-fuselage rigging when doing the up drilling when mating the spars. This is the first I have heard it explained that way.

I thought that I read that with the B model, the instructions are to to the full up drilling is done while mating the spars. Maybe I am wrong about that?

If that is indeed the case, or a possibility, I wonder if then up drilling to 5/16" or 11/32" when mating the spars would be a way to handle that. It would mean that up drilling while rigging the wings to the fuse would be easier than going from 1/4" and yet still give the little bit of drilling for final hole alignment. But that would mean obtaining/fabricating a different sized drill bushing.