27-05 -> 07: Completing Riveting of the Firewall

To complete the firewall, the firewall top and 2 sides of the firewall are riveted together with a couple of 'spanwise' angles at the top. There is a small triangle shaped firewall piece which goes in the centre above the tunnel. 

In order to stop oil and exhaust fumes (or fumes from a fire) from entering the cabin, any place where there is a seam between sheets must be sealed. The plans call for the use of fuel tank sealant, however i have decided to use 3M Firebarrier 2000+ instead. 

The join between the top firewall piece and the 2 sides, has 2 'spanwise' angles - one on top of the other. You initially apply a bead of sealer across the seam, then cleco the top firewall piece to the sides with the lower 'spanwise' doubler in place. There are then 5 rivets on each end which are riveted - but only these 5! (The plans are a little confusing here and based only on the text of the step you could end up riveting the whole angle - which would be wrong!). 

I managed to backrivet the entire firewall using my large backrivet plate and sometimes with the small backrivet plate on top, or the tungsten bucking bar on top. 

The devil is in the detail - they only want the 5 rivets each side at step 4.

The rivets were put in place, then a 1/16" bead of sealant applied.

The first 'spanwise' firewall angle was clecod in place, then 5 rivets backriveted on each side.

Due to the clecos, i used a bucking bar on the large backrivet plate to set the first lot of 5 rivets. 

Next up, i clecod on the tunnel sides, but only at the lower end - i did not put clecos in the location where the firewall centre triangle piece would be located. I then applied a fillet of sealant to the triangle piece and the tunnel side angles, and clecod on the centre triangle piece. I was then able to remove the cleco's along the lower 'spanwise' angle and cleco on the second layer 'spanwise' angle. I left this setup overnight for the sealant to cure. 

The tunnel sides were clecod on, but only at the lower ends (not where the centre triangle firewall piece will go). 

I then applied sealant and clecod on the centre triangle piece ensuring a good squeeze out along the edges.

I ended up swapping the clecos to the back side of the assembly, as this will aid in backriveting later.

I applied a bead of sealant along the inside flange as well.

Cleco's moved to the backside of the tunnel assemblies, and the clecos along the lower 'spanwise' angle are removed.

The second 'spanwise' angle is then cleco'd on and the sealant is left to cure. As you can see, i also applied a bead of sealant along the top of the 'spanwise' angle for extra protection.

The firewall was left to cure in this state overnight

I added the firewall sealant to the sealant coupon board for the build.

The next day

The next day, once the sealant had cured, i was able to strategically remove clecos and backrivet the whole shebang. The process was to plan out how the backrivet plate would fit, then remove the required clecos and add the rivets to the holes (using 3m removable tape to hold them in). I could then flip the assembly and backrivet. I ended up doing the centre triangle first, then working my way across the top 'spanwise' angles from the centre out. I did the long rivets where the thick doublers were last - some people have reported these rivets were too long and tipped over - however i had no issues. Only 1 rivet had an issue - the bucking bar moved! But i managed to get it out and replace it.

Then finally, I completed the lower tunnel side rivets around the angle portions, as well as the nose gear weldments. These were done with the long straight backrivet set - which needed 90psi! for the rivets at the weldments. 

Cleco's were removed and replaced by rivets held in with tape.

I backriveted the whole assembly like this.

Working along the tunnel side angles

Then the centre 'spanwise' angles from the middle out.

The top of the firewall is bend forward slightly - to make sure the plate didn't damage the top part of the firewall and was sitting flush on the rivets, i put it right on the corner of my bench and set the rivets across the edge of the plate. 

I installed the nutplates as i went. Didn't make sense to leave them until the end.

The bar moved under the assembly and was half on this rivet only when i set it.

With so much backriveting at such high pressure, i shattered the roll pin holding my backrivet set together. Fortunately, this has happened before and i had some high quality Chinese import pins in the cupboard.

This works well to get the rivets right up against where the 2 firewall sheets meet - so long as the bar doesn't move! 

The long straight backrivet set was used to get to the lower rivets on the tunnel angles and nose gear weldments.

This is the highest pressure used to rivet yet!

Riveting complete!

This shows how there was sealant squeeze out along all seams between firewall sheets.

The final step was to ream to 0.375" (3/8") for the AN6 bolts. I couldn't work out how this was supposed to work on a drill press, so i just used a machinists square. Such a tiny amount of material was removed anyway - all these parts went together so precisely, it's a real credit to Van's. 

That's it for chapter 27!