The Long EZ Build: Troughs and shear web

This is one of those steps you think will take an hour or two - but ends up taking more than 15!

Alright - here's how I did it...

After the top 'lid' was bonded to the spar box, I had to wait 2-3 days for it to fully cure (per plans) before removing it from the jig.

I had some micro spill over onto the jig, so I used a knife blade to un-bond the box from the jig.

I was naive to think the box would just pop off. So I began sticking shims on the back...

That still didn't cut it.. so I stuck shims underneath...

Taaaa-daaa! Finally the box popped off... I guess I should have done a better job of protecting the jig with duct tape.. but oh well, no harm done.

The aftermath on the jig...

Spar box sitting on the table happy as a clam... smiling at me...

The next step was to cut the spar troughs. First thing I did was study the dimensions of these troughs. Of course, they couldn't be simple X" deep, by Z" wide - full span... no... that would be too EZ.

Instead, these troughs not only have varying depths, but the top trough also has a 'twist' - the trough plane leans aft as it extends outboard. Let me explain..

The plans start out by giving us this:

Which is great to know how much trailing edge of the trough needs to be milled out, but what about the leading edge of the trough? So I turned to our full-scale templates on page A11.

I didn't like the idea of simply carving out material until it matched the template. I wanted to fully understand what shape the troughs needed to be. So I figured if I could come up with a jury rigged contour plot, I would know exactly what is going on.

To get the data points I needed to come up with my contour plot, I took a template from A11 (I'm using the BL 55.5 one as an example here) and drew two parallel lines 0.55" inches apart. I knew they had to be 0.55" apart because the small drawing on page 14-2 shows us the trailing edge profile - so the BL55.5 happens to be 0.55".

From this, I was able to measure the leading edge depth at this butt-line. This one happened to be 0.35".

I did this for all templates that were provided and came up with the following contour profile for the top trough: buttline, leading edge and trailing edge:

BL	LE	TE
0	0.5	0.5
15	0.5	0.5
25	0.4	0.4
40	0.37	0.47
55.5	0.35	0.55

So I measured the 3" wide trough and divided it into 3 regions:

This allowed me to use my router to mill out region "A" by removing 0.5" of material. For region "B", I removed 0.4" and then sanded a nice smooth ramp down to "A".

Region "C" is the problem child. Notice how at BL25, it is flat (0.4" both at the trailing and leading edge). However, as it extends outboard, I had to end up at 0.35" at the leading edge and 0.55" at the trailing edge. This meant that as the inboard edge of "C" extends out, the trough has a subtle twist. So I decided to mill out 0.35" using my router, and sand the twist by hand. Let me show you...

I started out by drawing the buttline references on the top lid (BL 0, 15, 25, 40 and 55.5).

I then marked the 0.5", 0.4" and 0.55" on the aft face (at BL 0, 15, 25, 55.5) per the upper right drawing shown on page 14-2 in the plans. I then connected the dots as indicated to do so. This gave me the trailing edge line of the trough.

Showing the trailing edge profile of the top trough on the aft outboard face.

I then labeled the A, B and C regions with different colors so I would know how far to mill out with my router and at what depth. I put too much work into this spar already and didn't want to have an "ooops!" moment.

Here is the flat 0.5" region A (red hash marks):

Here is region B (green hash marks): I milled out 0.4" but then sanded a nice ramp to transition smoothly into region A.

This is where region B meets region C at BL=25.

BL40: showing that the leading edge has to be 0.37" and the trailing edge at 0.47".

The outboard end (BL 55.5): leading edge at 0.35" and trailing edge at 0.55".

Since the shallowest depth of region C is 0.35", I decided to mill out 0.35" using my router and then hand sand from there - so notice region C is marked with 0.35" in this picture to let me know how much to mill off with the router.

With all regions properly labeled, it was time to mill away!

Here I am milling out region A.. removing 0.5" of material.

Region "A" complete!

I then adjusted the router to a depth of 0.4" and milled region "B" away! Notice the step between region A and region B - this later gets sanded smooth.

I then readjusted my router to a depth of 0.35" and milled region C away.

All 3 regions milled away with the router. It was now time to sand manually - I was not looking forward to this part!

By the way, this router business is messy! That's just my left arm... my whole body was equally covered!

My garage floor - thank god for a good shop vac!

Any who, back to work..

So here is region A...

Region B...

And region C...

I sanded region B to a smooth ramp, matching the trailing edge profile on the aft face. Region A now has a perfect transition into region B... both regions with no twist (i.e. flat pitch).

Remember that the trailing edge outboard end of region C is supposed to go down to 0.55".. I only milled out 0.35" since the leading edge only goes down to 0.35".

To help me get a head start (and keep my elbow/shoulder from falling off), I called in the big guns! I only used the belt sander on the outboard trailing edge...

Down enough to where it got close to the trailing edge line. I then hand sanded the rest...

Notice the twist here. The leading edge was already at 0.35". Only the trailing edge had to be sanded down to the 0.55" line.

The twist is more noticeable when looking at it from this angle...

As I got closer inboard (and closer to region B), I lessened the twist so that by the time I was butting up with region B, I was back to being flat.

Here I am noting how much 'twist' is at BL40... not much...

Compared to a more severe twist at BL 55.5.

Both left and right sides complete..

Once I was happy with my top trough, I moved on to shaping the 'top shelf' part of the top spar. Again, using a similar method to the one described above, I obtained measurements from the templates and figured out how much material I had to remove. I calculated that 0.15" of material needed to be removed from the trailing edge of the shelf at BL55.5 (no material removed at the leading edge of the shelf on BL 55.5) - so I drew a line showing the ramp...

According to the templates, by the time the shelf reaches BL 40, the shelf is pretty much back to being flat. So I drew a dot at BL40...

And drew a line connecting the 0.15" dot at BL55.5 to the 0.05" dot on BL40... (very hard to see the line in this picture. It's not the line on the aft face of the spar box; it's the red line drawn on the aft face of the shelf).

I then sanded the shelf portion down to the line... keeping the leading edge of the shelf untouched... and ramped from 0.15" at BL55.5 to 0.05" at BL40...

Here I am showing the end result at BL 55.5.. the leading edge of the shelf with no material removed.. and the trailing edge with 0.15" removed.

Notice how the trailing edge of the shelf ramps up as it extends inboard...

By the time the shelf gets to BL40 - it's more or less back to being flat.

With the top of the spar box milled out to my liking, it was time to make the actual templates and verify my contours. So I cut all the templates from A11... and traced them onto the cheap home depot foam... notice the pins holding the template in place while I traced it out..

Using my band saw, I trimmed the template away..

All 4 top and 4 bottom templates complete...

Moment of truth...

Not bad!! Looking gooood! The contour plot worked really well!

On both left and right sides..

Ok... so that takes care of the top trough... what about the bottom?

The bottom trough is a bit easier and less thinking involved - since there is no twist. The top right drawing on page 14-2 gives us the profile. It starts at 0.39" at centerline...

And remains at 0.39" up to BL 13...

It then ramps from 0.39" at BL 13... to 0.16" at BL 55.5.

Drawing an accurate ramp with such small numbers is pretty difficult... so I came up with the following equation to let me know what the depth should be between BL13 and BL55.5:

Z = 0.46 - (BL x 0.00537)

where Z is equal to the depth of material to remove for the bottom trough between BL13 and 55.5.

Here's how it works.. to know how deep the trough should be at BL 26, I multiply 26 by 0.00537 and subtract that result from 0.46.

Z = 0.46 - (26 x 0.00537) = 0.32"

So at BL 26, I need to remove 0.32" of material...

Using the same equation... at BL 36, the trough should be 0.267" below the surface..

At BL 46, it should be at 0.2135" below the surface..

And the end should be at 0.16"...

To make life a little easier, I divided the bottom trough into a few regions so that I could mill out a large portion of material away with my router...

So I milled out the following steps....

And then sanded them smooth...

Niiiiiiiice!

I then wrapped a squeegee card with sand paper and sanded the aft face of the shelf straight...

Ok.. now we are in business!

Bottom trough complete!

One last check.. verifying my depths... 0.16" at the tip (BL 55.5)...

0.39" from centerline to BL 13...

This is a good picture showing how the trough tapers off from BL13 towards BL 55.5...

Ok, one last check with the templates...

Looking real goooood!

Now to cut the 0.5" x 1" angle on both top and bottom edges. I first drew the angles onto the box...

Full span...

I adjusted my jig saw to the proper angle and trimmed away...

Better shot of the angle...

I then sanded the cut smooth...

Oooooo!! Nice angle!

Not quite ready for the shear web just yet... first I had to bond LWA4 and LWA5 pucks... I started out by drawing the locations of the pucks...

And used my router to remove the foam..

Since the router has a round bit, it didn't make for a good fit...

So I squared the edges off with a knife blade...

That's much better!

I repeated for all four LWA4...

The inboard pucks were a bit more tricky since the router doesn't have a flat surface to rest on (it's right next to where the spar sweeps so it ramps)... I had to use my dremel to remove the foam...

Here's a close up...

I didn't want to eat into the fiberglass, so I only removed enough foam to get me close. The rest had to be sanded off. After trying to sand it by hand, I came up with this idea - I took the largest drill bit that I have and wrapped/taped sand paper to it...

This made sanding the foam off down to the fiberglass a breeze!

I made sure to remove all the micro that was between the foam and fiberglass... I used a metal file to get all the way around the edges...

Ok, now to bond the aluminum pucks... first I applied plain epoxy onto the surface...

I then covered the backside of the pucks with wet flox...

And installed the pucks in place..

LWA4...

LWA5...

LWA4...

I then placed saran wrap over the pucks and placed a quarter on top of it.. this was so that the weight I added on top of the quarter would weigh the puck down and not rest on the foam (although the foam and pucks are pretty much close to 100% flush).

With the pucks cured.. it was time to round the edges and do layup #5 - the shear web... here is a shot before rounding the edges..

And after rounding the edges...

The aft face needed a bit of cleaning up... a lot of dry flox and micro on here...

Using the palm sander (100 grit), it cleaned up fairly quick...

The full span of the shear web requires 3 plies of BID at 45 per original plans. It states that it is ok to overlap 1" if required but not to stack more than one overlap in any one location (which makes sense - you don't want to end up with a location that has 5 or 6 plies and later have a bumpy spar cap).

I should note here that I chose not to adopt the optional LPC #26 (found on CP #25) which states: "To save work and weight substitute UND for BID as shown on page 4 [on CP#25]." The shear web is layup #5.

The main reason I chose to stick to the original plans was because I know a few Long-EZ's that were built per original plans that happen to fly in the Reno Air Races and pull upwards of 3 to 4 G's and have been doing so for over 20+ years. If they can withstand those G's after all these years, that's all the proof I need that the original design works.

So to get 3 plies full span of BID, I had to cut six strips of BID at 45 degrees (19" wide)... two strips overlapping 1" accounts for a single full-span ply.

Slurried the foam...

Removed all slurry from the puck surfaces and covered them with wet flox... notice how I covered the shelf portion of the spar with tape to protect it from any run off during the layup...

Applied the BID at 45...

And wetted everything out. I just let the skirts overhang for now. I then proceed to layup all 3 plies.. making sure the overlap seems between plies occurred in different locations every time as to not break the "do not overlap plies more than once at any one location" rule...

I was surprised at how much epoxy this layup took - about a quart or more of resin!

While the epoxy was still tacky, I trimmed the skirts all the way around. I used a squeegee card and a knife blade where the trough meets the top shelf...