Sat Sep 26 2020

Forward fuselage and canopy structure

In order to verify the fit of the skin from the firewall to the canopy frame bow, I need to have the width of the bow set correctly and that weldment slid forward so that its forward face is in contact with the aft face of this plywood bulkhead.

It's already obvious that with the splice plate well clamped in position, the canopy bow is slightly narrower than the fuselage. How much, though? I attempted to take (as precise as possible) a measurement of the fuselage at the aft surface of this plywood bulkhead. Placed the tape measure on the 1" mark.

Okay, so the width of the fuselage here is just on the far side of the 41 11/16" mark (making the fuselage ~40 11/16 wide).

It's hard to see here, but I used this aluminum extrusion to span from corner to corner of the canopy bow and made a very slight mark with a sharpie of the width of that canopy bow. It appears to be almost exactly 1/8" narrower than the fuselage., I readjusted the clamps on the splice plate with a 1/8" gap between the two halves.

Canopy frame weldment back in position. Looks pretty good, but of course, the clamps are preventing it from sliding all the way forward. They're getting hung up on the particle board doubler of the plywood bulkhead.

I also noticed that the bow is about 1/16" lower than it was before, convincing me that the ony way to ensure repeatable fit tests is to rivet the splice plate in position. In the interest of making that splice plate as rigid of a connection as possible, I want to use some rivets through the bottom flange of the splice plate and the bottom flange of the bow. However, I don't want these rivets (not in the plans) to interfere with the canopy reinforcement I'll be adding later. So, I pulled out the center section of the canopy reinforcement kit and marked the rivet locations.

Match drilling the web of the canopy bow using the (already drilled) holes of the splice plate.

With the splice plate clecoed in position, you can see that it sags down about 1/16" from where it was previously.

...but it's close enough to use the poster board to check how the skin will fit from the firewall to the canopy bow, and especially how it fits over the aft-pointing curved triangle arms. Good appears that the skin follows these curved triangle arms very well, confirming that my puzzlement and frustration from yesterday was due to somewhat incorrectly marked loft lines.

At the firewall, I marked where the rivets need to go through the skin to the firewall flanges.

Because of the curvature of the top edge of the firewall, the flanges cause some curvature in the firewall. I decided to flute the flanges to eliminate the curvature. Of course, there are hinges that get riveted to the inside surface of these firewall flanges for cowling attachment, and these flutes will prevent those from sitting flat, but I checked the thickness of the fiberglass cowling, and shims will be needed anyway between the hinge half and the firewall flanges. However, some of these flutes are of sufficent depth that I'll need a thick shim, and a thin shim between the cowling and it's hinge half.

Fluting complete. Firewall is nice and flat now.

Because I'm going to be making my own skin, I'll need to drill from the inside of the canopy bow outward through the skin. However, the two flanges of the canopy bow are so close together that my angle drill won't fit...even with the stubby drill bit. So, I'm likely going to need to first drill through the outer (upper) canopy bow flange down through the lower canopy bow flange. Then, I can use these holes to drill from the inside out...through the lower canopy bow flange, through the upper (prepunched) canopy bow flange, and through the skin. Similar to at the center of the canopy bow, if I'm going to be making extra holes through the lower canopy bow flange, I need to ensure they don't interfere with the locations where the canopy braces I marked those rivet locations.

Back to the splice plate...I laid out and drilled for some AN426AD3 rivets through the lower flange of the bow and the splice plate flange. These rivet locations are positioned to conform to rivet spacing rules and will not interfere with the center canopy reinforcement.

Countersunk for the AN426AD3 rivets.

Match drilled #30 through the splice plate and the web of the canopy bow.

...and countersunk on the forward face.

Last item for today was to prime the canopy frame bow in the area of the splice plate, and the splice plate itself. I also applied primer to the areas of the popup tipup arms where filing the rivets had removed the original coat of primer.