What have I gotten myself into!: Center section spar

The foam structure (23.8 hrs)

Having banned Urethane foam from any important structure of my plane, let me introduce you to “le foam du jour”… a combination of ¼” (6.3 mm) PVC, and 1” (2.5 cm) Divinycell.

All the foam needed to build the main spar

Step number one consisted of making the parts I would be needing, by reproducing the plans’ measurements onto the foam, then cutting the blanks out.

Drawing the vertical sections of the spar on the thin foam

Top and bottom pieces of the spar are made of the much thicker 1" (2.5 cm) foam

I used the table saw for the thick foam, and a razor knife for the thin stuff.

A simple razor cuts this foam easily in one step...

...while a table saw helps immensely with this much cutting to do, and all cuts are straight, vertical, and identical in minutes.

Before whipping out the micro, I applied clear tape on the jig anywhere a foam to foam joint would occur. This is standard procedure to avoid gluing the foam to the jig.

Tape as needed, even better tape it all. I missed one spot in the middle that ended up causing me some trouble later.

In order to comply with the jig’s master measurements, I sanded the foam in place on the jig, then finally got to play with the smelly stuff.

Actually this West System epoxy doesn't smell at all, and dries fast (occasionally even too fast)

All rear foam pieces (bottom on the jig) glued together

While the micro cured, I went to work on the blue foam that will become the top and bottom of the spar once it comes out of the jig (remember that the spar is flipped up 90˚ while in the jig).

A little freehand cutting was required

The ends of the top foam pieces required to be carved down to a thickness of 0.7” (1.8 cm), while the bottom ones had to be brought all the way down to 0.4” (1 cm).

From the plans (color added)

This used to be an easy, albeit messy process with Urethane foam, but Divinycell is much tougher, so I opted for the router.

The ends of these top pieces needed to be brought down to 0.7" (1.8 cm)...

... while the bottom ones all the way to 0.4" (1 cm)

I am no good with the router

Unfortunately, since I hardly ever use this treacherous tool, every time I do I always make the same mistakes, and by the time I figure them out the part is done, usually wrong, and in need of some fixing.

This time was like any other, and after going too deep, butchering the foam here and there, I had to go back and fix it with micro. Of course this process took way longer than if I had done it right the first time.

Crap!

What happened there?!

Since the rest of them didn't turn out any better, the micro had to save the day.

A few hours later, I was back in business.

At least this time around I was able to control the dimensions much more accurately than before by sanding gently, repeatedly, and taking lots of measurements, so in the end it wasn't too bad.

Next, I made myself a tool with which to sand the blue foam flush with the jig’s back piece, a process that would have to be repeated for all the blue foam pieces.

Another attempt at making life easier

This worked great... in theory

I suppose it worked okay, but it wasn’t as good as I had hoped for, and still required a little freehand sanding afterward.

Using a regular sand blockwould have probably been faster

One other step that took more time than I had imagined turned out to be trying to keep the bottom blue foam (forward in the jig) perfectly vertical.

You see, while the top piece (rear in the jig) benefits from leaning against the vertical plywood, the bottom piece has no such help in place. Furthermore, this foam has to make a 1.8˚ rearward bend (as seen from above the jig) at ± 9” (22.9 cm) from the centerline, but the tough Divinycell does not change direction well.

I used some of the wood that Aircraft Spruce packs its foam with, and some random steel plates as makeshift vertical members on which to rest the bottom blue foam (forward in the jig) while the micro cured.

Shimming the wood to vertical

Spar top (rear blue foam in the jig) getting microed to the spar back (bottom in the jig)

Spar bottom (forward in the jig) getting microed as well.

Nails added to prevent the foam from sliding on the micro

Every clamp I own got used

Left end (right in the jig) detail of the spar

Making sure the foam remained vertical

Attaching the last bottom piece of the spar (forward in the jig)

Last piece microed and nailed to the rear foam (bottom in the jig)

Left end piece (right in the jig) microed and nailed

While I waited for the micro to dry up, I used Photoshop to add colors to the drawings in chapter 14, and modify them per Long EZ plan change #99, published in Canard Pusher #32, which says "The UND layup #3 & #4 are incorrectly shown to lap onto the CS7 & CS8 bulkheads. The words describing this layup on page 14-2 are correct. Layup #3 & #4 are laid up onto CS2 & CS3 in Sections E-E & F-F and only onto CS1 in Sections G-G & H-H."

After printing the new and improved drawings, I glued them to a piece of cardboard from the same box the foam shipped in. Next, I cut them out, and stapled them to plastic shims.

Cross sections edited drawings glued to a cardboard

Stapling the drawings to plastic shims

Putting each cross section drawing in the exact spot and orientation where it belonged on the spar, helped to make sense of the complex set of layups to come.

Drawings placed in their proper locations

This helped me understand what would be going on at any location

Staggered cross sections

You can get a real sense of how the spar changes going front to back (up to down in the jig)

Once the micro dried up I attached the last piece, the right end cap (left in the jig).

Before the night was over, I decided to get a little more work done, and glassed the inside surface of the forward three panels (top in the jig) of the spar on the worktable.