<May 18, 2008>
F-796Bs Round Two
Alright, after the small issues I had with the fit of the F-796s, I decided to do things a little differently than what the directions say to do. First order of business was to start over with the F-796s. Fortunately I have enough angle to make them many times over. I took my sweet time today, but I am really happy with the way it all came out.
The new (round two) F-796B Shims. Except this time, I didn't drill them.
I found that when I tried to install the F-796B and C Spacers they would interfere with the inside bend of the flanges on the F-902 Bulkheads. A little work on the sander and deburring wheel fixed that. However, if I were making these spacers again, I would leave them undrilled until I test fit them. To make things easy on myself, I used a little bit of double sided tape to hole the two spacers together.
After sanding and polishing, they fit perfectly. I also used a bit of double sided tape to hold them into position.
I them clamped and drilled them using the skin and bulkhead as a guide.
Next, removed the clamp and inserted some 3-3.5 rivets into the holes to help keep the spacers aligned. To keep the rivets in place I taped over their heads with masking tape. The double-sided tape helped hold the spacers into position while I inserted the rivets.
This is what it then looked like from the inside. Can you see where I am going here? I also put some double-sided tape on the exposed face of the spacers to help me with the next step.
I then clamped the F-796B Shim (is it really a shim?) into place over the spacers. You might notice that I have a little bit of a space between the F-796B and the Lower longeron. I guess I was a little overzealous with the sander on this side, but there are so many bolts holding this part in place I am not sure if I am going to do anything about this.
I added another clamp to reduce the risk of it moving while I drilled.
Using the skin and a guide, I then drilled the F-796Bs through the skin/spacers/longerons. To do this I removed my keeper rivets one at a time and put in a cleco after the hole was drilled.
I then enlarged the top (bottom in pic) hole to accept a AN3 bolt by using my 3/16" reamer. The edge distance here isn't ideal (in the shim) but this way I was able to ensure the edge distance in the auxiliary longeron was perfect, and I think that is the more critical component here, but that's just my opinion.
Now, on the outside, I drew a line down the center of the rivet holes and bolted the F-796A Tank Attach Bracket into place. I was able to use a #40 cleco from the inside-out in the hole that was barely covered by the bracket. This helped keep everything aligned for drilling. Another option would have been to use a long keeper rivet from the inside out.
This was kind of scary, but it came out perfect. I used my 6" #30 drill bit to first drill a pilot hole centered in the bolt hole of the bracket. I took it slow and I was able to keep it perfectly centered by hand. Risky, but it worked. Once the pilot hole was drilled I enlarged it to 3/16" with the reamer.
Here's the end result. All the holes line up perfectly. By the way, these are just some scrap AN3 bolts I use in situations like this. The real bolts will be longer.
Looks good from the outside too.
With the F-796Bs and F-796As drilled and bolted into place I clecoed the forward bottom skin in place in preparation for drilling the lower longerons. It seems that the directions never tell you to do this, so I am just following the lead of several other builders.
Here's what it looks like from the inside.
All drilled. I just realized, I don't have any clecoes along the bottom flange of the firewall. Shame on me.
A goody of mine was delivered about a week ago. This is my sealed bearing tailwheel from JustPlaneWorks. It is maintenance free, lighter than stock, and it comes with these slick little hubcaps. Necessary? Hardly! Cool? Yes!
Here I am. I figured that I better throw in a picture once in a while to prove that I am actually building this thing.