Step 8.7, Center section seat ribs

This step prepares the ribs under the pilot an passenger seats.  On one forward end the ribs attach to the center section spar carry-through and on the aft end, the ribs are attached to the F705 bulkhead which, as you know, sits just behind the seats.  The four center ribs are modified in two ways to accommodate the control column linkage. 

First, the lightening hole is enlarged using a fly cutter.  If you've read any of my previous posts on the usage of this most dangerous tool you'll understand the I'm not a big fan.  In retrospect, I now realize that I could have just used a hole saw and been done with it.  Alas, it is my lot in life to observe, ex post facto, the extant solution of least resistance and think, if only.

So the fly cutter is a kind of whirling dervish of tool steel and sharpness that would just as soon kill you as cut  a hole for you.  The first thing I notice as I set up the drill press is that most of the fly cutter's sharpness had somehow leaked away.  Well, I knew at once that it had departed the tool whilst I was in the throes of the conflict now known as the battle of the firewall.  That was quite a match-up, when we pitted the wily and very mean fly cutter vs. the nearly impenetrable stainless steel.  Anyway, to make a long story longer, the cutting tool seriously needed some sharpening.

Now with the fly cutter sharpened, the ductile aluminum ribs are no match for tool steel.

Then the all of the edges are deburred.  Now here are those center section ribs again this time showing the start of the second modification.  The flanges are cut out to permit the control column assembly to drop down into place.  

Here's a quick reminder of the control column assembly.  The seat ribs attach to the face of the gold colored spar carry-through.  It should be readily apparent how very difficult it would be to get the control column in place without the flange cut outs in the ribs.

In order to replace the flanges on the ribs these splice plates are fabricated.  Two come with the kit, the other two are made from sheet stock.  Can you see the difference?  Only their fabricator knows for sure!

The cut out flanges are riveted to the center two holes and the end holes match nut plates on the ribs.  Thus the flanges can be replaced after the control column assembly is installed.

And here is the result.  The seat ribs are match drilled to the spar carry-through (gold) and are ready for match drilling to the center section bottom skin.  In the next installment, we will build up the baggage floor ribs and assemble the center section.