Spar outside layup

Now that the top and bottom spar caps were complete, it was time to move on to step 8 of Chapter 14. This involves installing the 4 spruce wood blocks (they will later let me bolt the engine mount extrusions to the spar) and then do layup #6 - which is the outside layup (top, bottom and aft faces of the spar box).

The original plans has us use 3 plies of BID for this layup; however, following CP#25, LPC #26 says we can substitute these 3 BID plies with 4 plies of UNI (alternating at +/- 45 degrees).

Before I could begin, I needed to sand the spar cap "steps"...

Not only did caps need sanding, but so did the aft face...

Also, the forward lip of the cap that meets the foam needed some cleaning up...

Ok, so let's get started because we have a lot of work ahead. These weren't your typical 0.009" steps... I was going to need some help to smooth these big dogs...

So I called in for some real help from the beast... the belt sander! (with 80 grit)

I didn't want to damage the spar caps, so when I removed a small amount, I switched to the palm sander... (60 and 80 grit)

And as I got closer to a perfectly smooth cap, I switched to manual mode... (with 120 grit)

Oooooo that is looking gooooood! Notice how I also sanded the foam shelf flush with the cap.



Since layup #6 wraps around the top, aft, and bottom faces of the spar box, I used my router to give the edges a nice 1/8" radius...



This was much smoother and straighter than if I would have done it with a hard sanding block as the plans indicate.

With the surfaces prepped, it was time to install the spruce wood blocks. These are simple 1"x1"x3" spruce wood pegs that get micro'd in place. Builder Hints in CP#42 gives us a cross-sectional sketch of what this looks like. (Although this sketch is not accurate in that the spruce blocks are installed at BL 7.5; the sketch shows a LWA5 aluminum puck installed. In other words, they used a wrong cross section to show where the spruce block goes. That said, it does do a good job at showing us how they need to be embedded in the foam.)

So I started out by measuring 7.5" from centerline...



Made the appropriate marks to mill out the foam...

I needed to know how deep to set my router to. So I measured it with the depth gauge of my digital calipers...

I then set my router to something slightly less than 0.89"... since I did not want to eat into the fiberglass below...

Also notice how I didn't mill out the forward most lip (i.e., I did not remove any part of CS4) as the sketch in CP#42 indicates. I then used my dremel to remove the remaining foam - without damaging the fiberglass underneath.

The dremel left rounded corners... so I used a blade to square them off...

Oooooo... that is nice looking pocket! I used a little bit of sand paper to make sure I was going to bond directly with the fiberglass below.

I then repeated this procedure for the remaining 3 pockets...



I then trimmed my spruce pegs to fit inside the pockets. Each one was 'custom' trimmed to fit lengthwise - so I labeled them to know which one had to be installed in what pocket. I then outlined the side edges so that I could trim them down with the band saw..

Took me 2 seconds to trim the tip with the band saw... I then sanded them smooth... leaving them slightly taller than they needed to be so that I could sand them flush with the foam post-cure.

Notice how I also rounded the bottom edges all around. This was so that the bottom surface would mate with the fiberglass below.. I didn't want the edges to prevent me from installing them all the way down..

I positioned the spar box fwd face up so that I could micro all pegs at the same time. Notice how I protected the spar caps with tape to prevent contact with micro runoff...

Mixed up some micro and poured it into the pockets. I did one side at a time, so I rotated the spar box top side up first...

Micro'd the peg...

And positioned it in place...

I cleaned up the excess.. rotated the box bottom side up and repeated the procedure to install the remaining two pegs on the other side...

When all 4 pegs were installed, I rotated the box fwd side up, placed saran wrap over the pegs...

and clamped them tight..

After cure, I sanded them level with the foam surface...

Since layup #6 overhangs the sides, I had to build a stand to prop the spar box a few inches off the table. I screwed the 2x4 to the fwd face of the spar box - making sure to only screw into the area that will later be cut off for the baggage hole compartment.

Ok.. almost there... just have to cut some UNI.. a lot of UNI. To get 1 ply at 45 degrees, I needed about 3 sections per ply to cover the whole length of the spar box. Since there are 4 plies, this required 12 pieces of UNI.. about 27" wide each (perpendicular to the 45 degree edge).

I should note that for this layup, I adopted the optional LPC #26 (found on CP #25) which states: "To save work and weight substitute UND for BID as shown on page 4 [on CP#25]." The outside layup is layup #6 in the table below. If you are wondering why I adopted it here, but not for layup #5 - I leaned toward the conservative side (for layup #5, 3 plies of BID is stronger than 2 plies of UNI; for layup #6, 4 plies of UNI is stronger than 3 plies of BID) - yes, this adds a bit of weight but for a good cause in my opinion.

Once I cut all of the UNI, I made sure all glass surfaces were sanded dull...

Including the aft face of the spar box...

Well.. here we go.. covered all glass surfaces with plain epoxy (a liberal amount).. then slurried all foam surfaces and then finally covered all foam voids with dry micro. The slurry part was a bit difficult - but using a brush, it went on pretty smoothly.

Here is my Elle helping me with the layup.. it's also a good shot of my time-lapse camera - how else do you think I come up with those videos?!

And of course, my buddy Adam. He's been getting more involved with the project.. I think I asked him if the epoxy fumes were too strong right before I took this picture.

Here is a good close up showing how the UNI sections were butted... not overlapped...

The process went something like this: placing the cloth into position... trimming the side skirts to a 1" overhang.. wetting the aft face out (since it's flat and simple)... then using a brush, one person would apply the epoxy to the sides (the top and bottom faces of the spar box) and another person would use a squeegee card to distribute the epoxy evenly and make sure everything wetted out properly.

Here is a good shot of applying epoxy to the forward beveled edges of the spar box...

I should also note that I marked the centerline of all the cloth pieces prior to starting the layup with dashed lines. This made placing the cloth into position pretty easy..

The plans say to go ahead and install LWA2 and LWA3.. but I decided to peel ply these areas and do them later. I also peel plied the areas where the UNI sections butted up against each other so that the outside layup would have a nice smooth transition.

Another shot showing how I peel plied where the LWA3 puck will be installed later.

 A shot showing how much overhang I left on the ends... about an inch or so...

 Here is a good shot showing the skirt overhang...



Here is the part where Elle tells me, "Stop touching it or you will ruin it!! It's fine! Let it cure in peace!"

Next up will be trimming the overhangs, installing LWA2/LWA3 and moving on to step 9!