Center section spar - part 11

Top spar-cap (16.0 hrs)

The top spar-cap went down pretty much the same way the bottom one did, except it took 25% longer. Work started at 9 am and finished at 9 pm. Twelve nonstop hours of fiberglassing nirvana (I wonder how many braincells the epoxy fumes claimed this time).

Having said that, I won’t spend a lot of time explaining the process again. I will mostly post pictures, and perhaps comment where I think it might help clear things up.

Since the damming material from the bottom spar-cap layup was still usable, and already cut to length, I pressed it into service once again. 

This time around though I used grey duct tape, as opposed to clear tape, directly on the shear-web and beneath the damming material. I reasoned this would later make it clearer to see where the tape hadn't come off completely.

Taping up the shear-web's rear face

I also ditched the glue gun in favor of the 5 minute epoxy. This seemed to allow for smaller gaps between the dam and the spar (good thing) for flox to find its way out the bottom, and for me to have to clean up once hardened.

Cutting the spar-cap tape

Various lengths of staggered tape marked onto the spar

Flox escaping through the small gap at the bottom of the rear dam would require time consuming cleanup once hardened. I hoped I had minimized the potential for this seepage to occur.

Closing the rounded gap with the rear dam with a flox fillet

One good tip I received from Wade was to cut the UNI's red thread toward the middle of the spar-cap strips, and pull it out from either side. This worked well to minimize the distortion of the fibers induced by pulling such a long thread out of the weave from one side alone.

Look closely and you'll see the red thread about to be cut near the middle of the UNI tape

UNI tape starting to soak up the pure epoxy

A couple of layers deep already

The straightness of the fibers is of paramount importance to ensure the strength of the spar

As the spar tape pieces get shorter and shorter, progress becomes faster.

Drone view of the spar... just kidding.

Marco's secret weapon at work

One thing I didn't spend much time explaining last time, was how I used my "secret weapon". As you probably imagined, I initially use it as a rake, to grossly separate and realign tangled strands. The grooves it creates also help the epoxy penetrate and soak the UNI layer more quickly.

Initial rough combing

Unfortunately, this pick has just 12 teeth spread over 3" (7.6 cm), and there is only so much combing you can do with a 4 tooth per inch pick (12 teeth ÷ 3"). 

But what if you had double the tooth per inch ratio? You could then straighten the UNI to a much finer degree, right? 

By angling the pick to 30º an effective doubling of the tooth per inch count can be achieved (12 teeth ÷ [3" * sin30º] = 8), and a higher amount of straight fibers is the result. To prevent knotting at the combing edge, this only works after a thorough initial straightening has been achieved. 

I suppose one could get carried away with this, going to shallower and shallower angles, however 30º seemed to work well enough for me, even though it tripled the workload.

Fine combing with pick at 30º (front side)

Combing the back side at 30º

This was definitely more work, but I was very happy with the results.

Last little piece of the puzzle going in

Because I followed the advice of LPC #26, my sheer-web is 2 UNI plies instead of 3 BID plies. That, and probably a slightly heavy hand while sanding the spar-cap trough, made it so that the trough did not get filled all the way up with the standard layup schedule. This was not unexpected, so I added two full length plies, then peel-plied over the whole thing.

Trough completely filled

Though unfortunate, the extra weight is almost negligible. Fortunately, it also contributes the overall strengths.

Peel-ply being added to the top spar-cap

My lovely assistant removing the peel-ply the next morning

Looking weird with the damming material removed

You can start to see where the gray duct tapes is trapped below the flox that seeped through past the dam.

Isometric view

 Though I tried my best with the 5 minute epoxy, there is little one can do to prevent the flox from getting past the damming material. Using the gray tape makes it very obvious  to see where the problem lies.

In need of much cleanup

We shall see if cleaning up the top spar-cap proves any easier than the two day ordeal I had to endure to remove the dreadful transparent tape from the bottom spar-cap.