Leading edge shells are complete

They're done.  Done!

This wasn't meant to be a composite aircraft, so the amount of fiberglass and foam work should have been relatively low.  And so it feels wonderful to have the leading edge shells - the last expected composite work - on the wings and completed.

Starting back at the beginning of the leading edge shells, I am fortunate enough to have built a DIY CNC router which was put to use cutting the pile of 1 inch thick foam from Home Depot.  It took several hours, and was done way back in July of 2016:

All of the foam parts were gently sanded and then the backside of them were given a layer of 6 oz, tight-weave fiberglass using epoxy resin.  This cured and was trimmed flush with the edge of the foam:

For alignment, a long string pulled from tip to root provides a reference straight-edge:

After a dry fit and trimming with a sharp utility knife, the shells were ready to be bonded to the aluminum.  A gentle scuff with 220 grit sandpaper and cleaning with alcohol was the preparations.  To bond them in, very thick epoxy was spread onto the surfaces that would touch the aluminum, particularly in the corner as shown below:

It took a surprising amount of effort for all the fitting and bonding in place.  Some strips of masking tape helped to hold the leading edge down to the aluminum tube.

Some of the foam sections had complications, such as the leading edge bolts for the the compression struts shown below.  I generally hogged out some foam from the backside with a utility knife and cleaned up the hole edges and bottom.

I actually didn't take great photos of the fairing process, but it took several rounds of using household lightweight spackle to fill in the cracks and fair in the ribs.  Sanding with a small block smoothed everything out nicely.  I'd say it was maybe six rounds of spackle and sanding mostly during random weekday evenings.

Now it was time for the fiberglassing of the outer layer.  The design calls for just a layer of epoxy to cover the foam, but I much prefer this fiberglass sandwich for stiffness and ding-resistance.  Let's get to it!  Here are the preparations:

To join the outer layer to the backside fiberglass was a sharp, 90 degree corner that needed some help.  I sanded in a thin slit at the corner with a small carbide file, which also scuffed the back of the backside fiberglass for better adhesion.  This slit would get filled with thickened epoxy to provide a structural bond between the two fiberglass face sheets.

Here is a shot of the slit filled with epoxy and showing the outer fiberglass about to wrap around:

Each fiberglass piece was about 36 inches wide, which covered two rib bays nicely.  Shown here is the first piece of fiberglass going down.  The foam was first well-coated with un-thickened epoxy (and it has been HOT in northern Virginia, so it was extra runny) and the fiberglass carefully laid on top.  A brush (or a hand) helped smooth the cloth on the surface to start absorbing the epoxy.  Over time, the white glass turned transparent, as shown here:

I'll spare you details of the repetitive nature of this.  I also used peel-ply on the open edges to prevent sharp pointy splinters, and came back with a sanding block after it cured to smooth everything over.  Really only the ends were tricky, with the root being perhaps the toughest (not really that bad, especially compared to the custom seat).

Over the course of three consecutive weekends, I cleared all the fiberglassing on both wings.  Wahoo, all done!  And notably, the stiffness of the leading edge shells is impressive with just a single layer of 6 ounce tight-weave on either side.  This does sufficient justice to the purpose of providing rigidity for the airfoil at the leading edge.

Next up is a round of thorough garage cleaning to rid myself of all the dust, then do a close inspection of everything in preparation for covering.  Covering?  Covering!

Another backyard test assembly!

We did an assembly of Goat on occasion of having some friends in from out of town, which was especially fun when watching their 9 year-old, who is interested in aviation, enjoy wiggling the stick.  As a group, we pushed Goat up the small backyard hill and rolled it down to give the feeling of movement.  Big smiles all the way around.

 

It was a useful exercise to reassemble actually.  This meant putting the new strut eyebolts to the test, and making sure I have all the parts and pieces.  No issues with the struts.  I was missing a single nano-clip for the elevator.

One thing that popped out from the assembly was an issue where the ailerons would not fold-up flat on the wing upper surface like the plans call out.  The flaps seem to fold just fine, and you can see the difference in fold-up angles below.

 

The problem stems from the location of the linkage on the ailerons and how they interfere with the rib to trailing edge intersection, shown below. 

There is no great way to address this interference that I can figure, without rebuilding the ailerons.  Since these un-bolt, I'm going to power forward and think about building new ones in the future.  Maybe.  If it's a problem.

Making a small modification on Goat

The angle bracket from last update is trimmed and updated, on both left and right.  What's the process for doing this modification?  Let's step through...

Before trimming, the bracket protruded forward of the airfoil profile.  This is the leading edge tube the marked aluminum bracket is what will be cut off.  Originally, the shape was for the kingpost attachment, but I switched to a strut-braced wing for (hopefully) lower drag.  Time to cut this bracket.

This one is easy enough to cut by hand, chucked in rubber soft-jaws of the bench-top vice.

Tada, cut and filed with fillets.

Here's where the bracket goes.  Really fun that modifications like this can simply be un-bolted and re-bolted once the change is done!

And here's the same bracket bolted back in place.  Time for the foam leading edge shells.

A bent eyebolt from load testing.

I found another bent bolt from the load test:

This is the right wing's leading edge outer strut attachment eyebolt.  The eyebolt is loaded on a weird angle, rather than a traditional tension direction, which definitely explains why its head is bent over.  Yes, the symmetric left wing has the same bent bolt.  It has been almost two years since the load test and I'm just now finding this.

Excellent that the bolt bent, instead of a brittle failure.  This means it is possible to inspect for over-loading conditions.  My plan is to replace this eyebolt with the next size up, because seeing it bent over that much is frankly terrifying.

I'm something of a fair weather builder when it comes to Goat.  The garage isn't the most pleasant work location in the sweltering summer humidity in Washington, DC, and it can get quite cold here for extended periods of time too.  That leaves a window of opportunity during the spring and fall.  It just so happens to be tolerably nice outside right now ... and I'm trying to mentally find a hobby outside of work projects right now too.

The leading edge shells are going on smoothly.  This shot was the next five with a few left to go.  The missing hole closest to the camera needs that bent eyebolt replaced.

At the wing root, since I switched from the cable-braced wing design to the strut-braced design, the upper angle bracket that mounts the root airfoil can be trimmed back a bit.  The sharpie line is where I ended up cutting that bracket, with associated radiused corners to round it out.  The edge will eventually get taped before covering anyway.

 

That's really all there is to update.  Only took two years...  One bolt at a time though!