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Monday, November 21, 2016

Ch 10 - Canard - Part 3

Lift tabs and leading edges (10.2 hrs)

The leading edge section of the canard is made out of two 4 foot long pieces. These have been match-drilled to the main foam cores with a 1/4” drill. Using sharpened 1/4” dowels I should be able to reassemble them, and maintain the original alignment of the leading edge to the main cores. Since the holes were randomly drilled through the core/leading edge assembly by Eureka, the dowels make it impossible to mistakenly swap them.  

Wade gave me the 10 dowels, but they needed to be sharpened, and since they are roughly the size of a pencil, I put them in my drill and ran them through a pencil sharpener. 

This was quick and painless

Dowels sharpening the easy way

The next step was to find the holes in the core foam under the fiberglass, and open them up to 1/4”. That sounded pretty easy, but proved quite the opposite since the dark epoxy made it hard to see anything below it, and the closer to centerline, the more the plies of glass, and the harder to see. 

Using a round file to open the dowel holes after drilling the fiberglass first

Anticipating this, I took careful measurements of all hole locations before fiberglassing, but being late at night I still managed to drill one in the wrong place. 


Dry fitting the dowels, note the mistaken hole in the foreground.

Luckily for me I screwed up in an area with only two plies of UNI, so I didn’t lose too much strength. I figured if the shear web can tolerate 10 holes in it (not an original design feature) it would probably still be okay with 11. Just in case, I patched it up with two plies of UNI at the original biases.

Hole filled with micro

2 plies of crossing UNI over the mistake

Meanwhile, I re-erected the jigs that locate the holes for the lift tabs (CLT). These turned out to barely sufficient, and not quite as precise as I had hoped for. Were I to do this again, I would try to make the jig a lot sturdier.

"The jig is up!"

I drilled small holes at first, then stepped through different size drills up to 1/4”.

1/4" drill in action

The big drill bits tended to grab the fiberglass, and I eventually changed tactic, and used a 1/4” end-mill by hand.

This worked very well, and was much more controllable.

I also had a tough time getting some of the Saran wrap out of the threaded holes, however I found that screwing a drywall screw by hand into the packed film makes a perfect wrap remover, a bit like a corkscrew bottle opener.

Turns out Drywall screws are great at removing Saran wrap from threaded holes. "Who knew!"

With the holes drilled, the wrap removed, and the dowels in place temporarily, I dry fitted the lift tabs, and the canard leading edges.

Lift tabs mounted temporarily

Note the raised section of the leading edge foam toward the middle, over the lift tabs.

Obviously the leading edges had to be trimmed in the area of the lift tabs.

Some foam needs to be removed here

Deciding where to remove the foam

This foam is super easy to trim (sometimes too much).

Top side of the leading edge fitting flush now

Bottom side of the leading edge had to conform to the lift tabs

Next, I glued in the dowels, leaving a couple of inches sticking out of the foam cores.

Dowel holes masked in preparation to final installation

Some micro escaped as the dowels were pushed into the tight holes

Micro cleaned up, and dowel stick-out set to approximately 2" (5 cm).

Tape removed, and micro curing.

After mixing some flox, I mounted the lift tabs for the last time, and torqued them down to the 50 in/lb (5.6 N/m) specified in the Roncz plans.

Pure epoxy painted over the CLT area

Flox applied to the tab

Tabs torqued to 50 in/lb

Excess flox cleaned up, tape removed, getting ready for leading edge installation.

Before attaching the leading edges to the canard permanently, I split the foam they came in, and used it to hold them up as I slurried the mating faces.

Splitting the foam that housed the leading edges during shipping.

Reusing the foam to hold the unwieldy leading edges

Next, I added a thick layer of wet micro in preparation for final installation.

Wet micro laid on thick

I also added dry micro to the area around the lift tabs bolts.

Drier micro lumped up over the CLT tabs. This is to take up the dead space in the foam after routing.

Finally, the time came to put it all together.

Leading edge being pushed down, ejecting the extra micro (canard's bottom side).

Micro escaping the top side of the canard

I used the foam that the leading edges came in once again, but upside down this time, as a way to hold some weights over the assembled canard in order to squeeze the excess micro out of the joints.

Weight (perhaps too much of it) added to the leading edge.

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