Finished matchdrilling the firewall - 2 hours

So now that I have the word from Van’s that the edge distance at the top of the fire wall is not an issue. I was ready to start match drilling the firewall to the fuselage. I started drilling all the holes along the bottom of the fuse (top from my perspective). Then I started drilling the sides starting at the longerons as per the plans.

The edge distance at the top most hole ends up super close to the edge of the relief in the flange. Eeesh!


 The edge distance on the corner weldments are really good. The blue line represents minimum edge distance (to center of the hole) so lots of room to work with here.

Still messing with the firewall fitment - 6 hours

After quite a number of small build sessions in the evenings, lots of fitting and checking, trimming the longeron(s) and repeat the process. But I seem to have everything figured out. Its taken quite a lot of time to get things to fit right. Tip: the best method I found was to start fitting the longerons to the firewall using the AD4 rivets first.....Then cleco the side skins to the longeron. It doesn't work well if you cleco first and then try to slip the rivets in. Its a very tight fit for everything.

The last little item before drilling the firewall that I notice is that I have one hole each side that has a questionable edge distance issue.

Edge distance issue at the top most hole of F-770 side skin
 





































I've put up a post out on the Van's forums to see what the consensus is as not many people note this item on their build-logs, and I couldn't find any other pictures of this area on other builds. Looks like I might be the first one?

Called Van's the next morning and the advice on my particular edge distance issue was to build-on. Technical support was extremely helpful offering additional advice on recommended cowling attachment. I won't dive into the details for the blog but we had talked about sky-bolt fasteners and a good practice is to tighten up spacing of them along the bottom. Once again, Van's is 10/10 for service and support! 

Here's some misc. pics of me messing with the fit over the last couple days so you can see the fit.

More fitting the firewall and fitting floor stiffners - 4 hours

I started off by removing the firewall and moving the centerline on the F-601M-1 angle/stiffener aft by about 1/32". This allows the forward face of the firewall to sit exactly 5/8" aft of the side and bottom skin edge.



I refit the firewall to the fuselage and then carefully drilled the outermost holes and clecoed them.

I now checked the required 5/8" distance along the sides and towards the op of the firewall and it looks like I am going to do some work to get things sitting correct. The sides of the firewall are bowed a slight bit and is not sitting well/in-line with the side skins. I  will have to remove the firewall and "massage the side flanges" to get a better fit. I also see that I have to trim just a small amount of longeron to get the proper 5/8" distances.

I'm putting that on the side for now, and I opted to check how the floor stiffeners fit. I first marked edge distances on all sides of the angles so I can easily identify trouble spots.


I then used the edge distances to help forward/aft placement of the angles


I was able to see how the angles interfere at the firewall. I could then easily mark and trim the floor stiffener to fit around the firewall angles.


An excellent fit!

Fitting the firewall - 2 hours

Again, another short day in the garage today. I drew a line halfway on the F-601M-1 firewall angle. Then I managed to get the firewall supported via the wife’s ironing board and I got the firewall temporally clamped into place. First I lined up the second line of holes in the F-772 bottom skin with the centerline I had just drawn. 
 
I then started to measure the firewall and the measurement was a bit larger than 5/8” (just proud by about 1/32”). This seems to be in line with all other build logs out there. Looks like I will need to make some slight adjustments. 
 

Trimmed the Longerons for the Firewall - 2 hours

A short day in the garage today. Very much a plane day, but just not productive. I drove out to the airport this morning and took the Cessna out for a spin. Was great to get out but my radio work is rusty.  Ugh.

After picking up some lunch I started working in the garage and measured out the 3/4” that I need to trim the longerons back. Doing a little research on what people did doesn’t reveal a whole lot on info. Not many people seem to talk about it. I ended up drawing reference lines 3/4” back from the edge of the side skin.



Then I used a square to transfer these lines onto the longeron.

One thing to note is that I purposely left my longerons extra long from what the plans said, fully intent on cutting them down. As you can see, I really left a lot of material.

 After clamping a block of wood as protection, I used my dremel and a cut off wheel to cut the longerons. In the process....I lost my dremel. Yup...It got too hot and died. So now I have to run to the store and buy another one. Darn!
After getting the new dremel, I finished cutting the angles, then went to work with the files and cleaned up the ends to the line.

I test fit the firewall, and it appears that I could even go another 1/64th of 1/32” more with a file...I’ll take a better look at it tomorrow when I can get a proper temporary support under the firewall.

Finished assembly of Firewall #2 - 3.5 hours

A longer day in the garage today compared to recent build days. Good to get back into the groove again. I started off with a bit of a snafu in the riveting. I managed to rivet the entire lower right engine mount to the firewall with a rivet size of AD-6.5. When I started the left side, I noticed the AD-6.5 rivets are a tad too short and the AD-7’s are a better fit with the gauge. I checked the rivets and while acceptable they are on the line for set thickness. I opted to drill the all out and re-set with the longer AD-7 rivets. Not ideal....but I feel it was the right choice. I’ll touch up some of the powder coating around the re-set rivets. Here is the final installation;

The rest of the 3 engine mounts were riveted with the AD-7 rivets and the result was excellent.

I’m finally back to where I left off after messing up my first firewall.....Dear lord, only took 6 months and $1500. Sheesh. Reminder to self....Don’t screw up.

More assembly of firewall #2 - 2 hours

I’ve come to the dreaded F-601J angles. I sure didn’t like riveting these on the first firewall. I really don’t like how close the inboard rivets sit in the inside radius of the angle. Not an easy rivet job. A combination of gun/backing bar and my shaved down backrivet set did the trick. Unfortunately I’m short on AD-9 rivets, so I’ll put in an order to Aircraft Spruce for more of those.







On a side note. The spring pin in my back rivet set broke. I’ll have to find a new spring pin to fix it and it appears to be an odd size - 7/64", not going to be easy.

Started assembly of firewall #2 - 2 hours

Very excited and nervous to get the firewall riveted...Again. Much quicker process now that I’ve been through it once before and know how best to set up the back rivet plate

I managed to get a few angles back riveted onto the firewall. All of the rivets are upsized by half or a full rivet size compared to what the plans called for. (Plans rivet spec’s are a tad short in this area)

Primed Firewall #2 pieces - 2 hours

A short day in the garage today, managed to get all of the pieces prep’d. Washed with maroon scotchbrite, cleanbrite acid wash, MEK and prime. Same old story.