A

AndyWW

Well Known Member
I was about to drill the top and bottom skins on the right wing of my SB RV-7 when I noticed that the forward and aft faces of the spar caps are not parallel to each other at the wing root. In particular, the bottom spar cap seems to be rotated as shown by perhaps 1 degree (you will need to look carefully at the left side of the diagram):

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I then checked the left wing, which has already had top skins and leading edge riveted on, and found that the situation is a bit similar. In that case it seems to be the top spar cap that is rotated. I suppose that when the close tolerance bolts go through to attach the wings to the centre section the caps will be forced to line up, but I wonder if the bolts will be very difficult to get in (or perhaps impossible?), or if it will be bad to have pre-loaded wing spars like that. Also I wondered if the angle of incidence of the wings might be affected by forcing the caps to rotate a bit. I can?t really see that anything I have done has caused this, especially on the right wing where I have not drilled anything yet (except the nutplates). I checked with another local RV-7 builder who is slightly ahead of me and he has also noticed something similar. Has anyone else seen this before or have any insight?

Thanks in advance!
 
No-one has seen this before?
I emailed Van's but it would be great to hear some collective wisdom!
 
Andy, I can not comment on the alignment, but will say that the bolt holes are tight and must be in perfect alignment or the bolts will just not go in. I have a set of hardware bolts with a bullet end for mine and a couple are .001" banana shaped, and a bit hard to get in by hand.

You might get a perfectly straight bolt (rotated between centers) slightly smaller than the factory, and push through to check the hole alignment. That is be best method. Ultimately 2 for each side would be much better.

The layered build up of the center spar, leaves the holes ever so slightly misaligned. (maybe .0003 - not much) This means they will be very tight on assembly. This is the reason for a slightly smaller bolt (.0005") for testing. It also must be round, hard to find off the shelf in a non aviation bolt. It must be sanded to shape.

As a comparison - a 10-friend was able to use factory bolts and install and remove his wing, so they are better aligned than my 7. Maybe later 7's are better. My # is 173.
 
Thanks Bill. I can imagine that the spar caps are not easy to twist when the bolts are going in. I hope that perhaps when everything is riveted together and the fuel tanks are attached, things will however straighten up a bit. Presumably the fact that the caps are each attached to the spar web by a single row of rivets down the center, and that the skins are riveted to the spar flange but not the caps, does allow some flex in the system. I'm still a bit surprised that no-one else has seen the same problem, especially since I seem to have it on both spars, and another UK builder with a similar vintage RV-7 kit has spotted it. Van's is still thinking about the issue I guess.
 
Andy, it does seem odd. I suppose a bolt check could verify alignment, but then the surfaces would not be square. Interested to hear what Vans has to say. Cheers.
 
Reply from Van's

Follow-up in case anyone is interested:

After some thought Van's came back saying that they don't foresee any problems with my spars. My LAA inspector in the UK said the same. The consensus seems to be that there is enough flex in the spar web so that when the close-tolerance bolts go in, the spar caps will be forced to rotate slightly until everything is lined up.

I'm feeling very relieved. Perhaps sometimes it's best not to measure things!
 
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