Final measurements - 22/07/2012

The tank is mounted on the left wing spar. I had to touch up the dimples in the rear spar and put some primer on them. Then closed the open rivets on the top line in the flange of the spar where no skin is attached underneath the tank skin. (rib to spar flange).

I clecoed on the top skins and remeasured for twist as I wanted to be absolutly sure that all was still level before starting to rivet.

The measurement between skin rear spar position and the plumb bob read 2 inch 20/32nds on the outboard position

The measurement between skin rear spar position and the plumb bob read 2 inch 20/32nds on the middle position

The measurement between skin rear spar position and the plumb bob read 2 inch 19/32nds on the inboard position.

I was again puzzled by this 1/32" difference. Although it's well within acceptable limits, I kept wondering how this can be.

In the end, the explanation is very simple. The aft side of the wing walk doubler plate is squeezed between the rear spar and the top skin. That means that the layer there is thicker then it is in the middle and outboard position. It accounts for more or less 1/32".

In other words, there is NO twist at all on my left wing ! Jihaaaa !

Before rivetting, make sure that all holes get a cleco for maximum skin thightness. What you don't want is 'wobble' sounds when you push between the ribs.

I also took a picture of the 3 inboard z-bracket attach points. I still had to set these nutplates.

They are a real pain in the ass. You can reach in with the bucking bar but the nutplate ears are very close to the doublers on the spar and it is easy to mar or damage them when bucking. I taped them of with duct tape and was very carefull on the bucking.

Used the backrivet set on the other side for the rivets near the border because you can't reach them with the mushroom head. Not sure if this is such a good idea as now I have some small smiley markings on my spar web by using that.