Firewall and Filler Box Questions

[Andy Walker]

Hey all,

I'm working on plans page F17, on the upper firewall and fuel filler box, and have a couple of questions. First, the firewall and the bow strap that fits across the top. I used a 3/4" spacer as the plans call for, and got the thing aligned and centered very well. However, the pre-drilled pilot holes in the bow do not match the flats between the flutes on the firewall:



As you can see, it's not just a matter of things being misaligned and needing to be slightly shifted; the leftmost two holes in the picture are off to the right, and the one on the right is off to the left. So aligning some will further misalign others. I could get out the fluting pliars and make some flat spots for the rivets, but when I've done that in the past the flutes I make look awful and the part tends to warp as the length of the fluted part gets altered. Any other ideas on why this is not lined up well, and how to fix it?

Question two: I pilot drilled my filler box last night, and overall it came out well. But the forward flange of the box end in the plans shows the bend with a curve in it. I did this, and now the holes closest to the ends are a bit close to the edges, and I'm afraid when I dimple them for the countersunk rivets there will not be enough material for a good dimple. The strength should not be an issue as the doubler is underneath, but it might look pretty bad. Here's the pic:



Any thoughts or suggestions?

Thanks!

[kmacht]

The flutes in the upper firewall and the bow strap holes is a know issue with the Sonex. Most of us just straightened out the flutes that interfered with a pair of seaming pliers and then re-fluted a little further over. If you are getting warping when fluting then either put a deeper or shallower flute in depending on which way it is warping. If you over flute, just squeeze it back flat a little bit with the seaming pliers. Adjusting the flutes in or out is how you get the part flat in the first place. It only takes a minor ammount of adjustment to make the whole panel move one way or the other.

Keith
#554

[Andy Walker]

The flutes in the upper firewall and the bow strap holes is a know issue with the Sonex. Most of us just straightened out the flutes that interfered with a pair of seaming pliers and then re-fluted a little further over. If you are getting warping when fluting then either put a deeper or shallower flute in depending on which way it is warping. If you over flute, just squeeze it back flat a little bit with the seaming pliers. Adjusting the flutes in or out is how you get the part flat in the first place. It only takes a minor ammount of adjustment to make the whole panel move one way or the other.

Keith
#554

Thanks Keith, glad I'm not the only one with this issue!

[MichaelFarley56]

Hi Andy,

We've all had these same issues. Keith laid out the steps I used as well. In terms of the filler box, the edge rivet locations I used were close to where your are, but after dimpling and riveting it will be fine. There's not much stress in that area so don't worry!

[Rick524]

I'm just about finished building my upper firewall....in my experience, you need lots of the following: Bits, Boe lube and Band aids. ;)

[Andy Walker]

I'm just about finished building my upper firewall....in my experience, you need lots of the following: Bits, Boe lube and Band aids. ;)

Whew, you got that right!