The Long EZ Build: Avionics hatch

The original plans doesn't have a dedicated avionics hatch. Instead, the canopy is left long - the idea being you can access the avionics bay whenever you open your canopy. I was never a big fan of that design, since it exposes the avionics every time you open the canopy. Some builders make an avionics "shield" to go over it, but I decided to trim my canopy short and have a dedicated avionics hatch.

I also wanted a design that didn't have any camlocs or screw heads exposed - if you've been following my blog, you should know I lean towards the side of OCD :p so I came up with a piano hinge design.. read on, and you'll see!

Never mind the purple blanket - I placed it there to protect the canopy bubble while I worked on the avionics hatch. To make the hatch itself, I taped cling wrap to the existing surface..

I then laid 3 plies of carbon fiber over the cling wrap. The middle ply was at 45, the top and bottom were perpendicular. Why carbon? I had some leftover from my canopy frame and figured why not - it will make for a nice, strong, stiff hatch!

After cure, I taped the hatch's trim line...

And popped it off... with the cling wrap underneath, it came right off.

I brought it to the bench and trimmed all around..

Placed it back in position...

And built a jig over it so that it will maintain its shape while I work on the inside surface.. I used 2x1's and bondo.

I really wanted the side edges to be held down, so I cut a few mixing sticks to length, and used hot glue gun to bond them in place. They worked perfectly!

Once everything cured, I popped the assembly off...

The jig allowed me to place the assembly upside-down on my bench and held its shape perfectly...

I then sanded the entire inside surface...

I now needed to bond a foam doubler to the hatch to make it structure sound. I had a few scraps of 3/8" thick H45 foam leftover from the strakes (chapter 21), so I cut two triangles to fill the center..

With everything prepped, I painted plain epoxy to the surface, then a thin layer of micro, and placed the foam pieces on...

I used a few bricks to help weigh the foam down... notice I placed a sheet of cling wrap between the foam and bricks to help prevent them from sticking...

I also used clamps to help the foam edges bend to the shape of the hatch...

Before I could trim the foam on the inside panel of the hatch, I needed to know the final dimension of the avionics bay opening.. so I measured and marked the opening, keeping in mind I needed lips on the sides to attach piano hinges.

Still to this day, my adrenalin flows when I take a saw to the plane!

Recall from earlier posts that there is a good 2" of foam under this hatch, so I used a hand-held hacksaw blade to trim through the foam portion...

Taaaaa-daaaaaa!

I then used a large drill bit to make round corners... and trimmed up to the red lines...

Final cutout with rounded corners!

It was now time to contour the inside foam of the avionics compartment... a sanding drum on a drill worked great for this!

Now that I had the opening cut to final dimension, I placed the hatch back on...

And used a marker to trace out the outline onto the hatch foam... reaching in from F28 bulkhead...

Lifting the hatch out, you can see the outline...

I took it back to the bench and trimmed the excess foam off...

No worries, all that micro and excess foam gets sanded off too!

I put the hatch layups on hold and focused on laying up the inside of the avionics compartment...

Here's an inside shot of the avionics compartment...

Notice I sanded the foam completely off about 0.75" around the entire opening for a nice glass-to-glass bond... even more on the sides to all the piano hinge installation later on...

With the foam and surfaces prepped, I laid 2 plies of BID all around. This layup wasn't as bad as I thought it was going to be. I took it slow and one strip at a time.. using a paint brush to wet it out in place..

After cure, I trimmed off the excess...

And sanded all the edges nice and flush...

With the inside of the avionics compartment complete, it was time to focus on the avionics hatch!

I placed the hatch back on, and marked space for the piano hinges...

I needed to remove foam on the sides for the piano hinges...

Foam removed... and sanded the surfaces to remove all traces of micro...

It was now time to bevel all the foam edges... here is the before pic...

And after pic...

This will allow a nice transition for the glass...

With everything prepped, I painted plain epoxy on all mating surfaces... and micro slurry on the foam surface...

I laid 3 plies glass. I decided to go with glass instead of carbon fiber here since glass is softer around the edges and will transition the foam bevels better. I peel plied the surfaces for a nice finish...

After everything cured, I took it back to the fuselage to test its fit, and removed the 2x1 jig...

Happy with its fit, I trimmed the edges all around... I purposely left the borders long and will trim to final size later...

With the hatch complete, it was time to install the piano hinges.. I started by cutting the inside hinge to length... I left them 0.5" longer than the opening for better retention..

I then clamped the hinge in place to allow me to play with its position...

My plan was to have the pins of the piano hinge accessible through the canopy rain lip...

Here I am playing with the orientation so that the pin would align perfectly where I wanted...

Here's a better pic of the mark I was shooting for.. I wanted to make sure both sides were symmetrical...

Happy with the alignment, I drilled through the rain lip wall...

And passed the pin through...

Here's a good shot showing the pin going through the rain lip wall and through the piano hinge...

Before floxing the hinges in place, I applied tape to the hinges hoops to keep flox from getting inside..

I prepped all the mating surfaces for a good bond...

I also prepped the pin outlet to make it easier to install a conduit later on..

I painted plain epoxy onto the hinge and sides of the avionics compartment, applied wet flox to the hinge...

And installed them in place. Notice the pins are in place and going through the hinge and canopy rain lip - this was to make sure the hinges were perfectly aligned..

After everything cured, I tested removing and reinstalling the pins from the rain lip - they were perfectly aligned and had no problem removing and reinserting the pins. Happy with the fit, I removed the clamps..

I then marked where I needed to drill for the rivets.. and clamped the hinge to keep it from popping off while drilling..

Drilling a #30 hole...

Using a 120-deg countersink for the rivet heads...

And installed BSC-44 pop rivets...

Perfectly flush with the top surface so the avionics hatch can lay perfectly flat!

With the inside hinges permanently installed, it was time to focus on the hatch hinges. I cut them to length and installed them with the pin. Because the hinge is slightly bent to follow the top contour, the hinge stays in place without falling down...

Which is perfect - since this allows me to place the hatch on top of them while the flox cures..

But before I mixed up any flox, I prepped the surfaces...

I also needed a way to know exactly where to place the hatch without moving it around too much since I didn't want the flox to spread around... so I put duct tape all around...