Heavy Compression Rib

Earlier I ground down the end of the Heavy Compression Rib to fit over the interplane strut fitting.  The factory just made the rib short by the thickness of the of the steel and used a piece of 3/32 plywood to fill the gap beyond the fitting.  I may do that on the last 2 wings.  The factory kept changing what they did after all.

Case in point, the wing assembly drawing shows 2 screws holding that compression rib in position.  One screw directly into the spar and the other through a hole in the strut fitting.

The old spars only have one screw and the other end was nailed in place, no second screw.  Go figure.

It turns out the forward end of the rib on the lower wing is the only place the screw in the hole and the second screw actually go in straight.  All the other positions require one of the screws to go in at about a 45 degree angle.  It may be that they drilled the hole in the fittings in different locations on each wing.  We need to go back and check all the fittings.  I've located the holes based on the fittings I had at the time.  Even then some of the screws need to go at an angle.

To get the screw to align with the hole I marked the holes on the end of the ribs, then used a #40 drill back to the corner where the screw head will set.  Then I re-drilled the hole with a #10 drill.

The screw sets nicely in the corner.

You can see the one hole in the corner and the other located where it's properly square to the wood.

I went back to the #40 drill, from inside the rib, through the hole in the fitting.

I stuck a drill bit in the hole so you can see it worked out well.

The Upper wing forward and aft screws both go at an angle through the fitting, and straight into the wood above the fittings.

The lower aft end goes straight though the hole but at an angle to clear the edge of the fitting.

When the wires are tight it's hard to imagine these moving even without the screws.