What have I gotten myself into!: Ch 19 - Wings and ailerons

Wing attachment points (45.0 hrs)

"How many bolts does it take to mount a Long EZ wing to the fuselage?"

"Three."

Yep, you read it right, only three bolts are needed to keep each wing attached to the center-section spar, and the wing bolts attachment points (aka metal plates) are all installed in the first foam block (FC1).

Eureka CNC plans broken down by major foam blocks

Two of these bolts are accessed through two small dedicated depressions cut into the top and bottom of the wing, and one from the wing root pocket.

Using JT to illustrate the location of the wing's top bolt...

... and the wing's bottom and inner bolts

The plans will have you do the work of creating these pockets with the foam blocks already in the jig, but it is much easier to do it before glueing FC1 to the rest of the wing.

Let’s work on the root pocket first, then we’ll do the other two.

This process involves slicing off a part of FC1, hollowing it out, then glueing it back to FC1, then installing the first one of many metal plates.

Marking the cut line on the wing root foam block

Using two nails on the black line as guides for the ruler

Clamped one ruler on the wing foam top, and another one on the wing foam bottom.

Using the rulers as guides for the saw

This will become the wing root pocket

Using the rulers as guides again

Cutting off the critical 0.6" (15 mm) dimension

Front face to be reattached later, 0.6" non-critical perimeter marked in black.

Creating the wing root cavity

The inner piece of foam will be reused to stabilize the now delicate foam perimeter

Front face reattached to the perimeter foam, curing around the inner core

Wing root section with micro, in preparation for getting reattached to FC1 foam block.

Wing root section curing after being reattached to FC1

Talking about metal plates, I had already made most of them years ago when I was working on the center-section spar, but a few of them weren’t mentioned in the spar chapter, so I had to make some new ones.

Two LWA4 ¼" (6.35 mm) 2024 Al plates, and two WI8 0.016" (0.4 mm) 2024Al sheet

Etched then Alodined the metal parts

My Alodine is a bit weak, so I used aviation style etching primer on the plates

We will use these a little bit later. First we have to create the depressions for the outer two wing bolts, one on top of the wing, the other on the bottom, then glass them.

I often colorize the plans' photos in the blog to make them a little easier to understand

Unfortunately the depth of the two depressions are not only different, but also decreasing the further back one goes due to the slant of the wing profile.

Measuring the deepest part of the slot (gray= metal, blue = foam)

Bottom slot is 0.030" (0.76 mm) shallower

The floor of the depression however is perpendicular to the front face of the foam block, so with a little ingenuity (thanks Ary) it is possible to cut the foam as in the plans.

Drawing dimensions on foam is difficult. I learned this trick from Walter Grantz (R.I.P. my dear friend).

It's just regular painter's tape, nothing fancy, but the pen marks are much more readable.

Bottom slot dimensions marked

Establishing a reference plane (plexiglass) perpendicular to the front face of the foam

Using the reference plane as an aid to cut the slot to the charted depth

This was Ary's idea, and worked quite well.

The obligatory photograph for a future DAR (Designated Airworthiness Representative)

Slow progress precision foam removal

Here's a perfect variable depth slot perpendicular to the foam face

Shimming the square to establish the reference plane on the opposite side

Bottom slot cut using the same technique

Wow, that was a little bit weird, but worked quite well. Time to glass the pockets.

I think I use as much duct tape as I do fiberglass building this plane

Two plies of BID cut at 45º bias

Foam slurried, and micro fillet applied to the edges.

BID prepregged

BID applied and peel-plied

Always use a bigger piece of glass than needed, then trim later.

What a difference a day makes!

Slot trimmed and lightly sanded to remove all peel-ply strands

Most of you probably already know what’s going on here, but for those new to fiberglassing let’s look at this process again in detail on the bottom side of the wing.

FC1 flipped over to repeat the process on the bottom slot

One can never have too much duct tape

Painting on the micro-slurry

Wetting the BID cloth with pure epoxy in between plastic sheets

The result is what we call pre-preg

Pre-preg means previously impregnated, referring to a ready-to-use epoxy soaked fiberglass sheet.

Pre-preg is easier and less messy to work with. Just peel the backing plastic, and stick where needed.

Then one works it down to the foam with an epoxy soaked brush

Peel-ply added over the fiberglass (not required in this instance)

The glass should have lapped slightly over the metal plates, but I chose to install them later.

Peel-ply removal time

Cleanup is alway a bit tedious

Bottom slot ready for business

I like the way those pockets came out. Now we just need to recess them, and the foam, so that we can fit the metal plates through which the wing bolts will connect to the main spar.

The two metal plates I should have mounted before glassing the slots

Setting the Dremel tool to a depth equal to the thickness of the LWA4

Ready to remove material

Foam and glass removed to accommodate the LWA4 plate

Test fitting the bottom LWA4

LWA4s need to be flush with the foam as they will be glassed over by the shear-web

The plate didn’t line up exactly the way I would have liked, so I used toothpicks to hold it in place for the next step.

Creating a flox corner by removing foam, and sanding the micro-slurry off the back of the glass.

Using toothpicks to make up for my previous lack of control with the Dremel tool

The toothpick trick worked amazingly well in lining up LWA4 precisely

Flox in the corner (hence the flox-corner name)

LWA4 and WI8 floxed to the slot

In case you were wondering, I did not remove the toothpicks. There was really no need to do so, as the toothpick are stronger than the foam they displace anyway.

You might notice I used flox instead of micro here. I did this for two reasons. First, I wanted to create a flox corner between the fiberglass of the slot, and the fiberglass of the shear-web that will go over it (and the metal plates). Second, since I didn't lap the fiberglass slightly up the metal plate in the pocket (as seen in section B-B on page 19-12), a little extra strength there made me feel better. Probably not necessary, but definitely didn’t hurt anything.

The toothpick trick worked well by the way, and the plates lined up with the foam surface correctly.