Wing Attachment

[Paul Johnson]

I am attaching my wings after painting and cannot remember how the attachment hardware was configured, as I said in earlier posts I did not build the aircraft.
On the drawings it has two washers for each bolt on the main and rear spar, do you put both washers under the nut or one under the bolt and one under the nut, or does it not matter?

Regards

[peter anson]

Hi Paul, It's not critical as the bolt is loaded in shear and the washers are just there to make sure that the slots in the nut match up with the split pin hole in the bolt, however when two washers are fitted it is usual to have one under the head of the bolt and one under the nut. If there was only room to fit one washer I would be inclined to have it under the nut.

Peter

[NWade]

Typically, washers serve four purposes:

1. As a cushion, to ensure that as you twist the nut to tighten it down that it doesn't gouge into the main structural material. Remember that best practice is to twist the nut while holding the bolt head still - so the risk of gouging & material-damage is typically on the nut side of things.
2. To adjust the position of the bolt in the material it is securing. Best practice is for the grip (the unthreaded portion of the bolt shank) to be slightly longer than the thickness of the material its passing through - so that none of the shear loads are being applied to the threaded part of the fastener. Sometimes - due to limits on bolt sizing - the grip is a fair bit longer than the thickness of the material being fastened. In that case you might put a washer under the head of the bolt so that there's only a modest amount of grip showing through the far side.
3. To enable the bolt & nut combo to be fully tightened down without the nut bottoming out at the base of the threads. If the grip is longer than the thickness of the material being fastened (per the point above), then you need a washer to take up the "extra" space and ensure that the nut is actually compressing the fastened materials when you torque it down.
4. In the case of castellated nuts & drilled bolts, an extra washer might sometimes be used to ensure that the nut is at the proper level of snugness at the same time as being at a good angle for passing a cotter pin through the drilled bolt.

Take care,

--Noel

[Paul Johnson]

Thank you for the replies, wings are now on and should have the aircraft in the air next week.

[pfhoeycfi]

Question regarding the Sonex root rib attach angle at the rear spar...

This angled component is very narrow and the AN3 bolt head (or nut if turned around) is just touching the inside radius of the angle so that the bolt head (or nut) will not sit flat and therefore will not tighten correctly.

...just curious as to what builders do in this situation, ie trim a washer, file the angle etc....

thank you,

peter
SNB0021

[GordonTurner]

If I’m thinking of the same spot, I remember the plans called out making a little aluminum shin out of something like 1/8th inch stock.

[pfhoeycfi]

If I’m thinking of the same spot, I remember the plans called out making a little aluminum shin out of something like 1/8th inch stock.

Yes that's exactly what I did...I made a 1/2 x 1/8 shim and filed a radius onto one edge.

Thank you,

Peter