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!

Quick Bobbin Rack

This past weekend I was putting things away in the office and came across a box of these little metal bits. Not really having a need for their designed purpose, I decided to put them to another use. I grabbed some foamcore, hanging wire, and a sewing machine needle and got to work.

The needle really helped punch through the foam core and provided a clean channel to feed through the hanging wire. Each metal piece was mounted to the foam core by two tiny twists of wire.

It took a little bit of time punching and twisting, but all thirty bits were eventually attached to the foamcore.

Once complete, the foamcore was mounted on the wall. It's a homemade bobbin rack!

No more fumbling through my overstuffed sewing basket for me. Now my thread is in plain sight and organized. Hoorah!

Nosewheel well

With the nose gear prepped and the nose floor and wall in place, it was time to flip the tub over.

Why would we flip it over? So we could cut into the floor and install the nose wheel well. It would be pretty silly to have a retractable nose gear and nowhere for the gear to retract. To get started, the gear was bolted into place once more...

and the contour of where the gear retracted was traced onto the exterior.

From there, a symmetrical door with margin was drawn.

Marking up the exterior is one thing, but cutting a hole in the fuselage is another. Despite the terrifying idea of slicing away at the floor of the fuselage, the hole was cut without incident.

This prefab strut cover (purchased from Feather Lite (sorry, no website for those folk)) was dry fit into place.

With the holes cut in the fuselage, it was time to cut a couple more holes in this prefab wheel well, also purchased from Feather Lite. It's dead useful to put little windows in the wheel well. This way you can actually see if your gear is up or not. Visual confirmation!

 The plexi is a little smudged here, but you get the idea.

Instead of bothering with flipping the fuselage back over to bond the wheel well in, Ced just opted to do a quick bond and use duct tape to hold the thing in place while it cured.

The bridge between the wheel well and strut cover needed a little extra trimming for clearance.

The strut cover was a little too shallow, so it needed to be modified.

The sides of the cover were slit and popsicle sticks were used to hold the sides apart while a few plies of glass were added.

 

Ah, that's better.

The strut cover was then bonded in place and the fuselage tub flipped back over.

A micro fillet and tapes were added around the wheel well cover and the little window was tested out.

With everything fitting properly, it was time to prep the nose gear doors. Taking the bit that was cut from the fuselage floor, the urethane foam (yellow stuff) was removed from the pvc foam (green stuff). 

The urethane bit was discarded...

and the pvc foam split in half.

From here, the plan is to mount the doors so they swing outward when the gear extends. We're not at the point to mount them, yet, so they're in storage.

Rudder Pedal Install

Back in February during the nose build, the rudder pedals were installed. That is, of course, a deceivingly simple statement. Let's walk through what went into putting those pedals in.

Remember the nose gear box post? Those NG-30s are the mounting surface for the pedals. The photo below is a reference for what part is being worked on. Those two blue circles in the lower right portion of the NG-30s are the markers for where the pedals will go.

Drilling ensues. . .

and hardware is inserted.

As you can see, half of the pedals are missing due to the need to modify the walls a bit and install additional hardware.

Rudder pedal pivot blocks are carved from high density foam and bonded into place on the outer nose gear walls.

Using the pedal tube as a guide, the nutplate location is identified.

What's a nutplate, you ask? It's a bit of hardware that one makes in order to have a mounting surface for metal-type interfaces. In short, you can't just shove a bolt in foam and fabric and expect things to work well.

This little labor-intensive piece is fitted and bonded into place.

One last fit check. . .

and the nutplate holes are packed with vaseline and the whole thing is covered in 4 plies of BID.

The holes are drilled out again and the pedals are finally installed. Yay!

I may need pedal extensions for my side, but they rotate fluidly. Excellent.