What have I gotten myself into!: Center section spar

Closing up this case (22.2 hrs)

Completed center-section spar

Needless to say, a bit more work still separated me from the picture above, so let’s look at the missing link.

One of the items I needed to reproduce was the baggage hole in the spar. Actually, although the spar can be used as storage, it would be improper to call it that. The hole is there primarily to allow the builder access to the inner wing bolts with a wrench.

Anyhow…regardless of its reason for being, a hole is a hole is a hole, and the dimensions are featured in the manual on page 14-5.

Dimensions for the hole in the spar circled in red

Now, instead of removing the core foam and inner fiberglass, I decided to leave the glass in place temporarily to avoid leaking epoxy all over the inside of the spar while glassing, and opted for a later removal of the hardened UNI/BID sandwich.

Drawing the hole

Routing the strait edges first with an edge attachment

Caution when routing... the "floor" of this hole is very flimsy being just 1 ply thick.

It is at this point that I realized I needed to remove more foam to create the lip for the glass to glass bond, so back to drawing and routing I went, followed by shaping the transition by hand.

Measuring the lip

Transferring the lip dimensions on the foam

Ready to route once more

Trimming the foam corners after the additional routing of the lip

The modified layup schedule of LPC#26 called for two layers of UND (aka UNI) cut at ±45º, so I started by cutting all the necessary material, and prepping the spar.

UNI cut at 45º

Two plies of UNI rolled up and ready to go

The layup is pretty straight forward, and lacked any excitement, which is always a good thing.

Foam prep with micro-slurry

First UNI ply being laid on the forward face of the spar

These UNI strips ended up a bit oversize

First piece wetted with epoxy

Butting the second piece of UNI to the first one

Midway through the second ply layup

Last piece of UNI going on. Note the excess off the end.

Layup #8 completed

This is where the hole will go

Masking paper removed

Peel-ply over all transitions

Resting overnight

The next day, with the new layup cured, I finally got to cut the access hole, and let the inside of the spar taste the fresh shop air once again.

I've been waiting to do this cut for a long time

Rough hole

Finished hole

This spar is nearly finished

Getting to this point of the center-section spar construction was very satisfying, but there was still a little more work left to do at its far ends to close this baby up once and for all.

Removing foam for a flox corner joint

Foam and micro removed

Wetting with pure epoxy

I used a little cab-o-sil mixed with the flox to help it stay put

UNI at 45º

Same thing at the other end of the spar

While that went down very quickly, it still had to rest for overnight. So, I left the shop heater on, and drove to Lowes to purchase a hole saw that would allow me to cut the 2.25” (5.7 cm) bolt access holes.

Hole saws are a weird thing, I usually buy only the one size I need at the time, then misplace it, and end up buying a different brand one the next time. Sure enough, I always end up with an incompatible mixed brand set of hole saws that are always just too big or too small for tomorrows job.

This time I decided to splurge a little, and get something that will cover most sizes, and come in a box that will be hopefully more difficult to misplace.

Hole saw kit from Lowes

Plenty of choices for present and future needs

One very important thing to note at this point is where not to cut the holes into the spar. The holes go right up against the spar-caps, while not cutting into them.

Burt is pretty straight forward on this point… “Cutting a hole into the spar caps is cause for reject.”… which translate into… “If you cut into the spar-caps, you cannot fix it, and will have to throw away your spar and start over!”

I’d say that’s important.

I worried a lot about this hole's location

You know you are getting comfortable with fiberglass when you live it, breath it, and… eat it?!

Your typical composite builder's breakfast

Blue Oreo cookies anyone?

Corny, I know! Sorry, I just couldn't resist.

Ok, moving on…

After the usual edge cleanup I replaced the blue foam with flox instead of micro, this after BizMan (aka Beasley) told me that these areas get abused quite a bit by wrenches while working on the wing bolts.

36 grit sand paper strip folded over, used to clean micro and foam from inside the holes.

That "tool" cleans the edges so nicely that only fiberglass is left behind

Pure epoxy wetting

Flox with a little cab-o-sil

While I was at it, I also cut 2.25” (5.7 cm) holes in the far ends to allow wirings to exit the spar.

The location and size of the end holes are not critical

I made all holes the same size

Another flox corner

Left spar tip completed

Right spar tip completed

A look inside the spar from the "baggage hole". Note the wiring hole previously cut through the bulkhead.

CS spar done!

I sat the finished spar in its approximate Fuselage Station location just to see how much shop room it would have consumed had I installed it at this stage (as the plans indicate). I found out it would pretty much take out one stall of a two car garage, making getting around in the shop much more difficult.