Mon Jun 7 2010

Popup tipup bellcranks and upper forward structure modifications

It took some searching through my jars of hardware to find just the right washer that allowed me to trace around the tubing stub and give the correct diameter.

A bit of sanding later and these bellcrank arms were smooth. I disassembled the stack and deburred them independently.

The spacing between the plates needs to be 0.312 inches to allow for the rod end bearing, so I stacked some washers between the plates to set these up in preparation for welding. Tom is a good welder, and there are some others in the chapter that weld, so I doubt I'll need to hire someone to weld these up.

Now it's time to start modifying the upper structure. The two fore/aft ribs are going to be swapped compared to the plans to allow more space for guide blocks, so that means some of the cross ribs need their flanges extended while others need them shortened.

My little 12" brake did a nice job of making a new flange from some scrap 0.032 thick aluminum. I clamped it to the existing flange and match drilled.

The new flange has been match drilled 19/32 outboard from the existing flange.

...then just cut off the existing flange and deburr.

...same process for the right side rib.

Here are the two new flanges for the center rib which will effectively make this part 19/32 wider on each side.

Modification of center rib complete!

During the test fit I could see that the notch needed to be deeper to clear the flanges of the fore/aft ribs.

The modified structure is clecoed in place. The parts all fit together well, so no harm done (so far :-).

Here's the fore/aft rib on the right side. You can see that since I've swapped it from the left side, the angle of the flange on the top no longer matches the curvature of the fuselage. This flange is going to have to be replaced as well.

Hrmmm...let's see...that looks like 82 degrees. I'll keep that same angle, but just make it go the other way.

I clecoed on the top forward skin for a test fit.

When it's all said and done, these gaps will be gone and there will be much less opportunity for water to enter the plane and cause havoc with my instruments.