Mon Jan 2 2017

Working in center tunnel cover

Prior to drilling all the seat attachment hinges to the floor, I decided it would be prudent to see what other opportunities for intereference there were, especially since I have to move the seat backs inboard by 3/16". I spent about a half hour looking for the Z channel required to make the F-741A brackets. Finally found it...on the workbench.


Anyway, after looking at the plans some more, I decided that instead of cutting up that Z channel straightaway, I would make a cardboard template to check the proposed fit.

It looks pretty good at the forward end. The angle at the forward end of the bracket matches the angle of the floor panel pretty well.

...a view of the same cardboard template from the other side.

At the aft end, I had to install the flap actuator mounting channel and some other hardware prior to checking the fit. It doesn't look quite as good as at the forward end.

...a little closer view showing the angle doesn't match too well.

Notice the little notch in the previous photo? That notch is to allow clearance for these two little angle brackets which attach the bottom end of the flap actuator channel to the ribs on either side of the center pushrod tunnel. It's been a long time, but I seem to recall these didn't fit too well when I originally had the fuselage clecoed up.

...sure enough, looking down you can see that the hole for the screw is off by about 1/3 hole. Looks like I'm going to fabricate a replacement for these brackets.

I started by locating a piece of .063 thick 2024-T3 and cutting it roughly to size. I'm thinking about making one bracket instead of two.

Since this material is so thick, I'm going to need a pretty large bend radius. IIRC, the bend radius for 2024-T3 should be 3X the material thickness, minimum. Thus, I need roughly a 3/16 bend radius.

I cut and bent several pieces of scrap -O material in order to generate a radius appropriate for the -T3 bracket I'm fabricating.

Not having a set of radius gauges (how is it that I don't have those?!), I used a 3/8" drill bit to compare the built-up bend radius to. Looks good.

It took a bit of tweaking, but I finally managed to get the bend angle just right. I wanted it to be spot on since it's such a thick piece of material. Any mismatch would mean a lot of stress when screwed down.