Spar fwd face and end caps

The last few steps of any chapter is pretty exciting since I can start to see the light at the end of the tunnel.. and that's what these next few steps show.

According to the plans, I was supposed to have floxed the LWA2 and LWA3 aluminum pucks in place before letting layup #6 (the outside layup) cure; however, I ended up feeling rushed and decided to peel ply the mating surfaces and do it post-cure.


Before continuing, I trimmed the end overhangs of the outside layup...



On both sides...


I then flipped the spar over..


...and removed the 2x4 stand.


I then trimmed the overhang skirts of the outside layup...


Looking good... but now I had to fine trim it...


...and what better tool to do this than my beloved router! Look at that flush trim!








I also used the router to flush trim the ends...


With all the overhangs of the outside layup trimmed, it was time to prep the aft surfaces to receive the aluminum LWA2 and LWA3 pucks. I started out by removing the peel ply and sanding the surfaces smooth.


Here's prepping the inboard surfaces...


...and outboard surfaces...


Ok, now the spar is ready to receive the pucks! Notice how I also prepped the spar's top and bottom surfaces (for the outboard hard points) and the top surface (for the inboard hard points) since they will be receiving UNI strips that go over the pucks.


I pre-cut the 3" UNI strips that will go over the LWA2 and LWA3 pucks (16.75", 14.75", 12.75" for the outboard strips and 7", 9", 11" for the inboard strips). I also cut the 5" wide ply BID at 45 that goes over these UNI strips (this single ply of BID only goes on the aft face of the spar - it does not wrap around to the top or bottom).


I prepped the aluminum pucks by sanding them dull and cleaning them up. Mixed up some flox and spread a good amount onto the back faces...


I then painted plain epoxy onto the mating surface of the spar... right on top of the existing pucks...


And positioned the pucks in place...



I then added a flox fillet all around each puck...




With the pucks in place, it was time to prepreg the UNI strips. I started out with the smallest length first so that it would end up on the top surface after installing it onto the aluminum puck.


I centered it the best I could...


And peeled the plastic off gently...


The inboard puck UNI strips only wrap around the top of the spar (not the bottom).


I gently passed my finger over the fillet edges to assure there were no air bubbles and that it had a nice transition from metal to glass...




With all the UNI strips installed, I then applied the single ply of BID over the UNI strips (on the aft face only). Notice how the sides wetted out first - that's because I dabbed plain epoxy onto the sides prior to placing the BID ply... so that the BID would transition smoothly.


Same thing for the inboard pucks...


I then used a paint brush to wet the BID ply out completely...


And same for the outboard pucks...


I assure you those are not air bubbles under that ply of BID... I think the reflection of the light makes it appear that way in this picture..


Once I made sure there were no air bubbles and everything had a nice transition, I added peel ply...


I waited for everything to cure and moved on to milling out the center section spar baggage access hole. The plans say to cut out a 5" by 14" hole; however, I figured why cut the hole out now? I decided to mill out the foam, but keep the underlying fiberglass to make the fwd face layup go a bit smoother.

I measured out the 5" by 14" hole (I should have measured 5.5" by 14.5" to account for a 0.25" glass-to-glass lip - which I ended up correcting for later).


Using my router, I milled out the foam...


A bit sloppy in the middle, but that's because I didn't care too much about the middle part of this hole... I was only concerned about the perimeter that will be glass-to-glass...


Using 80 grit, I sanded away a nice beveled edge all around the perimeter....


It was here that I realized that the actual hole opening is 5" by 14"... so in order to have a glass-to-glass lip, I needed to shave off another 0.25" all around. So I drew out my new outline...


I removed the 0.25" foam lip and re-beveled the edge. Now when I glass the forward face of the spar, I will end up with a 0.25" glass-to-glass lip all around, and the physical opening will be 5" tall by 14" wide. Also note how I sanded the perimeter down to the glass to have a true glass-to-glass bond. Again, the center is not important since that will later get cut off.


I then cut my two plies of UNI at 45 for the forward face of the spar. Each ply required 3 sections... so I ended up cutting 6 sections. Note that the original plans calls for 3 plies of BID at 45... but following CP#25 (page 4), it gives the ok to substitute these 3 plies of BID for 2 plies of UNI at +45 and -45 bias.



As I cut the pieces, I laid them on top of the spar to make sure I had enough...




I then prepped the spar's forward face and beveled leading edges to receive layup #8 (the forward face layup). Notice how I also sanded the leading edge of the bevel round so that the UNI cloth will transition nicely between the forward face foam and the existing cured glass that currently makes up the beveled edge.


Ok, the spar is now ready to receive layup #8!


I started out by slurrying the foam surfaces, and painting plain epoxy onto the beveled edges...


I should also note that I used dry micro to level out any imperfections at the ends...


First section of ply number 1...


Elle is helping me wet out the second piece of the first ply... notice how I intentionally wetted out the forward face and kept the 'wings' (the cloth that will bond to the beveled edges) up so that it allowed me to trim them down to a 1" overhang. After trimming them lengthwise, I used a paint brush to fold them into position onto the beveled edges.


The baggage access hole was a lot easier than I had expected. It was actually fun since it reminded me of way back when I did the passenger seat back bulkhead! I made sure the 0.25" glass-to-glass lip was sound... the rest, I didn't even bother to waste epoxy on since it will later be trimmed off.


The second ply was put at the opposing 45 degree bias...


After trimming the 'wings' and wetting everything out, I peel plied the external butted edges of the UNI sections...




After letting it cure, it was time to trim things up..


I used my multi tool to trim the ends...


The router to flush things up...


And a little hand sanding to really clean things up...



Next was cutting out the baggage access hole. I started out by drawing the 5" by 14" circuit...


Notice how 5" by 14" leaves a nice 0.25" glass-to-glass lip all around...


I drilled a hole to give my router bit a starting point...


And trimmed away...


The router is a beast! So rather than trying to get exactly up towards the red line, I trimmed close enough to it...


I then hand sanded the rest to fine tune up to the red line...



With the baggage access hole complete, it was time to put some end caps onto this spar! I started out by using my dremel to make a small flox corner all around...


Used a metal file to make sure I will get a nice flox-to-glass bond all around..


That's a nice flox corner! I then sanded the entire foam face to make sure it was flat and even...


I slurried the foam surfaces on both ends and mixed up some flox... I used the baker's icing trick to apply the flox into the flox corner...


The ends were now ready to receive the one ply of BID at 45...






I then painted plain epoxy to wet the BID ply out... and squeegeed as much as I could.


After letting it cure, I used a knife to trim all around the edges...


I then used my router to flush trim all around...


One final sand touch up and the end caps were complete!


Daaaamn! That is one good looking end cap! (again, those are not air bubbles!!)


Here is a closer look...


And there you have it!! The center section spar is complete and ready to be installed onto the fuselage!



3 comments:

Olivia, Alex and Caroline said...

Beautiful - nice hard points!

Anonymous said...

Clearly you're enjoying the results of your perfectionism. Enjoyable to follow. Would you mind posting the large view of your pics in a bit higher res?

Ary Glantz said...

Thanks for the comments!

As for high-res pictures, I have to shrink them down in order to not pay a ridiculous amount of money to host them on the server. If you make a donation, I could send you a CD with all my build pictures in high-res.

www.aryjglantz.com/p/donate.html