Aft fuselage beef up

The aft section of the fuselage gets a beef-up session. This is required in order to provide enough structural reinforcement for the center-section spar and main landing gear attachment points.

First, the aft portion of the lower longeron gets upgraded from a triangular cross-section into a square. This is done by wet floxing another triangular stiffener into place. After cutting this doubler to size, I cut the end so that it would give a nice transition into the rest of the lower triangular longeron.

Here is a close up of the transition cut.

Here is a shot of the doubler clamped into place while allowing the wet flox to cure. Notice how I used small pieces for peel ply under the clamp to prevent the clamp from adhering itself onto the longeron.

Here is a top view. The doubler did not require nails nor notches to bend since it is relatively short in length.

 

 Same thing on the other fuselage side.

 After the doubler has cured, I trimmed it to size and sanded the edges flush. I then traced out a piece of foam and micro'd it into place.

Same for the other side...

I then placed a heavy box (the duraflame box) over the foam and allowed to cure. Meanwhile, I started to cut out the cloth - the 6 plies of BID that go over the entire area enclosed by the LWY, LWX and lower longeron (times 2 - for both the left and right fuse)... and the 15 plies (times 4!) for the landing gear attachment pads.

Holy crap this is going to be a lot of lasagna work!

I started out by filling in the voids between the foam and wood parts using dry micro. I then slurryed the area and prepped for the 6-ply layup...

And for the other side...

And layer number one...

 And onto the other side...

And after 6 layups...

Just when I was happy to finish the 6 layups... Oh that's right, there's ANOTHER fuselage.... And 6 more layups...

I then laid the 60 plies (15 per pad) out... that's when I knew I couldn't do this alone... I called for back-up!!

And Elle' to the rescue!! Hazmat suit on... check! She did all the prepreg work while I started setting up for installing the prepregged pads.

 I started off by marking where the pads needed to go (measured from the aft edge of the fuselage).

After the first 15 layup pad was complete, I peeled it off from my workbench and simply placed it in the middle of the markings I had made earlier. I did not trim the edges since I wanted a gentle "ramp" onto the pads. I should also note that I brushed on some epoxy onto the mating area before placing the prepregged layup into position.

Notice how I positioned scrap foam on the edges so that the overhang would not bend...


I then peel plied it...

 And then the aft pad...

And then the OTHER fuselage... fwd pad....

And finally the fourth pad...

Notice how I left all edges as they were. Again, I prefer to use the "trim after cure" method instead of knifing trimming. It is my opinion that knife trimming thick layups disrupts the layup. I prefer to let it cure and post trim later, which is not hard to do using the vibrating multi tool and router.

 Here I am trimming the edges with the multi tool... it took a little more work than usual to go through the 15 layers... but the tool still did the job fine. Again, I left a 1/8" overhang to be trimmed flush with the router later.

Here is what it looked like BEFORE using the router...

Here is the router cutting the fiberglass flush with the wood edge. Notice how the roller rides along the edge giving a perfectly flush edge.

I stopped halfway to take a picture of the "before" and "after". Notice the difference between the trimmed edge vs the to-be-trimmed edge.

 Here is the result after using the router... perfectly smooth, flush edges all around!

 The router went through the 15 layups like butter!

Oh, that's right... repeat for the OTHER fuselage side...

Multi-tool trimmed...

 Post router trim...

 Looking good... looking reeeeeeeal gooooooood!

Next up was to trim the top portion of the aft pad down flush to the same height as the 6-ply layup. Drawing A-5 specifies that the top portion of the aft pad should stop at WL 12.35 (this is an inch below the top edge of LWY). And the router to the rescue... yet again! I positioned scrap foam above LWY to give the router a surface to slide along.

I used a marker to label the 12.35 waterline, and began removing material using a square bit (with no roller). I adjusted the bit height such that it was perfectly level with the top surface of the 6-ply layup.

I stopped in the middle to take this picture and show how the router does a fine job of milling out the unwanted material.

Here is the end result! A perfectly straight line at WL 12.35.

  Oh, that's right... there's ANOTHER fuselage side... repeat...

And there you have it... two fuselage sides with beefed up aft sections ready for a center section spar and landing gear attachment points!