Center section spar - part 4

Prepping for Step 4 (6.5 hrs)

Since fiberglassing the inside of the spar was going to be a big job, I decided to get as much prepared ahead of time as possible, and while it was still fairly easy to do, I also marked all Butt Lines (BL) on the center-section spar, for future reference.

Marking Butt lines every 5" (12.7 cm)

BL 35

BL 55

Next came the 6 aluminum plates (LWA1) that would be bonded to the inside of the spar. The easiest way to cut these 2” (5 cm) wide tabs is to buy a 2” wide strip of aluminum then cut as needed, so that’s what I did.

Marking the aluminum tabs for cutting

Six tabs are required inside the spar

One requirement for these tabs is to have one corner rounded to a radius of 0.100” (2.5 mm). Since I butchered my first attempt at sanding such radius on the first tab, and sanded part of my my gloves, I decided to leverage technology in order to make the job easier, and to preserve my digits.

Cutting the LWA1 radius with a CNC mill

The result speaks for itself…

That is exactly a 0.100" radius

Over and over and over...

With the radius situation under control, I scuffed all the tabs, and Alodined them.

A bit Neandertal after the previous CNC operation

This Alodine is a bit weak

Alodine is pretty expensive, and degrades quickly over time. My one year old Alodine required 15 minutes for a thin covering, while 1 to 2 minutes was normal when new.

Anyway, next item on the list was to make the interior bulkheads CS6 and CS7.

Finding a scrap piece of foam that fit

Here's a brand new bulkhead

Finally, I cut all the fiberglass I would be needing.

Scraps of cardboard taped together to make a fiberglass cutting template

BID getting marked at 45˚

BID for layup #2 getting cut

Cutting the BID for layups #3 and #4

Testing the BID of layup #4

Testing the BID of layup #3

Cutting the UNI for layups #3 and #4

Testing the UNI of layup #3

Testing the UNI of layup #4

All fiberglass and bulkheads sealed in ziplock bags awaiting "the day".

CS7 inner bulkhead and fiberglass in a ziplock bag

CS6 inner bulkhead and fiberglass in a ziplock bag

Fiberglass for the outer bulkhead CS5 in a ziplock bag

Fiberglass for the outer bulkhead CS8 in a box (I ran out of ziplock bags)

The plans require the use of a 5 lbs (2.3 kg) weight over each tab during cure. However, because of the slant in the spar, the weights tend to slide off the tabs. 

One excellent tip I received from BizMan was to fashion some kind of device ahead of time, in order to keep the weights from moving.

Introducing the EZ-Puppy…

Leveling the legs

This system actually worked great

Being a four legged animal adept at carrying weight, it should have perhaps been named the EZ-Mule.

One last small tip I picked up from Valerie Harris from EZ-Jets, was to cut the handle off the paintbrushes in order to reach inside the spar more easily.

That's how you know Valerie has done this many times

I would grow to appreciate her advice over the next couple of  days.