Center Section Spar: Part I

While working on the nose of the Cozy last summer, we also built the center section box spar. The plans describe this structure as "the heart of your wing," so a lot of care was taken while putting it together.

To start out, a jig must be built. Ced had his NC machine cut out all the pieces of the jig, because, well, why not?

With all the pieces free of the MDF sheet, they were assembled with bondo.

This was the first labor-intensive step to a very, very long process, so bear with me.

PVC foam is laid down on the bottom of the template to form the aft face of the spar box.

The "sides" were created from urethane foam. . .

and temporary jigging was set in place to hold the free standing side in place. . .

while the urethane foam was bonded to the PVC foam.

Once the micro cured, the bulkhead positions were laid out.

With locations marked, one ply of BID was laid up in the interior of the box.

Micro slurry applied.

BID portion in place.

Once the interior BID layup cured, the bulkheads were installed.

Aluminum hardpoints were manufactured and installed with several plies of BID tape.

Here's an image to get a feel for the small working space of these layups. They were a little tedious.

Once all of those layups cured, the box could be removed from the jig and shown off.

This image lets you get a feel for the length of the spar. Oi.

The BID surpassing the edges of the foam was trimmed and the top surface was prepped for closeout. Also, holes were punched through the bulkheads to allow airflow.

Panels of PVC foam were glassed on one side ahead of time for the closeout.

Micro was piped along the forward face of the box. . .

and the panels were laid down in sections.

Once the forward face panels cured, the whole thing was flipped over to prepare the sides for hardpoints and spar caps.

Around this point Ced's parents had come to visit. This was great news for us because we took full advantage of the extra help. I also think it was good to share some of the steps it takes to build an airplane. It is a laborious task which is difficult to fully describe with just words and photos. (This might be turning into a plug for recruiting more help. *ahem*)

Ced and his dad, Mr. T, spent some time sanding down the urethane sides to create troughs for spar caps.

Once one trough was sanded down, the whole thing was flipped over and the sanding process started on the other side.

With the troughs carved it was time to install a few more aluminum hardpoints.

While Ced rounded the edges of the PVC foam, Mr. T worked on rounding edges of each of the aluminum bits.

With everything fit checked, the aluminum tabs were floxed into placed.

Now it was time for the aft face shear web layup.

The entire length of the spar was covered in a micro slurry to fill the foam pores.

Ced and I demonstrated applying the first section of the first ply of UNI. . .

and Ced and Mr. T finished laying down the rest of the UNI (four layers across the whole spar). It was nice having the help because this large layup went a bit quicker than expected.

Inspection!

A final layer of peel ply and the first shear web of the spar was complete.

Whoo!