Do you shim the spar-fuselage attach points?

[Battson]

My IA raised a question during the inspection of the plane, about the attachment fittings where the wing spars bolt onto the fuselage. There is room for the wing to move forward or back, because the fittings are larger than the spars. Should one of those connections have shims to prevent movement? and if so: Which one (FWD or AFT fitting)? and should the wing be shimmed fully forward, fully aft, or centred?

[Mark Goldberg]

The aft fitting was left intentionally a bit bigger so scratch built wings would fit on our fuselages. You could put washers in the gaps if you wanted. I will ask Bob Barrows your question when I talk with him next. This is really a Bob Barrows/engineering type question. Mark

[Mark Goldberg]

Bob said nothing is really needed because of the way the load is on these wings - only one direction. You could put a washer in the aft fitting if the gap was big if you want. But not required. The only reason to put a washer in there is so you can tighten slightly the bolt/nut. But you do not want to over tighten that nut so the upper longeron attach fittings bend. Mark

[Glenn Patterson]

If the front attachment is snug then it should be no issues as the wing cannot move for & aft. A lot of shaft designs are set up so that one point on a shaft is locked and the second point floats. The attach points are on the same axis so one tight and one loose should be no issue as long as the bolt fit through the fitting holes are snug. Snug the rear bolt up like a spark plug hand tight and then tighten gently with a wrench and that is safe. We set the wing attach fittings up with the front tight and some clearance in the rear. As long as the hinge is tight then there are no issues. If it bothers you or you need to satisfy the inspector you could check the clearances with feeler gauge & purchase some SS shim stock.
Glenn
BH727

[Untainted123]

I hung my wings today, and noticed a gap in the rear spar attach point enough for 2 washers probably. The front spar attach I could fit maybe a washer or a little less. Based on this thread, I didn’t shim either one, and put the nuts on. After rereading this thread again, I realized maybe Bob is saying only the back doesn’t need shims, if the front is snug? But, the front is only “just” snug after tightening (I don’t feel like I compressed the ears on the fuselage, but they did “snug” up enough I could not get a washer in now, but maybe a thin shim?) Anyway, more confused and less confident about whether I made the right decision than earlier today.

[svyolo]

I called Bob a while back on this. He said shims were "a good idea", but he didn't say they were necessary. I used mostly washers, and a couple of home made "shims".

[Untainted123]

In that case I think I would like to take up any potential for shifting, and put shims in. However it’s a bear to try and remove the bolts again to get washers in, so I am thinking and upside down U shape shim, slid in from the tops. Thoughts?

In addition, wouldn’t any shifting there cause your wing root fairings and windshield leading edge to not align anymore? Or perhaps there’s enough play in those if you don’t shim? Am I overthinking it?

[Battson]

My experience has been the wing will slide all the way back and stay there.
I did put some washers in to shim it, but it's not a tight fit. I figure it shouldn't be allowed to bounce around on a rough landing.
Inspected it in the weekend, after around a dozen years and 1,200 hours of flight. Everything is looking good as new.