Merriam-Webster defines a canard as 1) a false or unfounded report or story, or 2) an airplane with horizontal stabilizing and control surfaces in front of supporting surfaces; also : a small airfoil in front of the wing of an aircraft that can increase the aircraft's performance.
Reading through these two definitions makes me wonder if the first definition was written by skeptics before the aviation canard was widely accepted. It also makes me realize that I'm about to describe the building of our canard's canard. At any rate, this post is dedicated to building the small horizontal "wing" that's mounted near the forward end of our aircraft.
The plans call out hot wiring your own foam cores from provided templates, but we opted to skip cutting them ourselves and purchased them from Eureka CNC to save some time.
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| Ah, pretty precision cut foam cores. These are the outboard canard cores. |
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| I know it's blurry, but I need to point out these cores. Starting at top left and moving clockwise: aft center core, leading edge core, leading edge core, one of the two aft inboard cores. Notice the difference in widths of the after center and inboard cores. |
These three cores were aligned and bonded together using micro (resin and glass microballoons). I found this part very stressful since it was the first bond we did on this project and if the cores were misaligned they'd be no good. The canard needs to stay straight and aligned in order to perform correctly.
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| Note the trough in the foam. |
After curing, it was time to install hardware into the canard that would eventually be attach points to the airframe. These nutplates and corresponding lift tabs were purchased from The Cozy Girrrls.
Ced recessed the aluminum nut plates in the canard and cut a jig from some phenolic that was lying around the shop. Pictured later are the MDF pieces used to mark the ends of the phenolic to help line up the jigs later.
The point of the jig is to locate the drilled holes in the aluminum insert. That insert would eventually be buried under several layers of glass and resin, making visibility of the holes difficult.
Once everything was lined up, the nutplate was bonded into the core with micro.
After that bond cured, the plate was scuffed in preparation of glassing and the holes were filled with Vaseline to prevent them filling with resin.
Now it was time to lay up these cores with six plies of unidirectional (UNI) fiberglass cut on a forty-five and one ply of bidirectional (BID) fiberglass, with a little extra after the big stuff was put down. This particular layup is what is known as a shear web layup. The plies are staggered in such a way that the buildup of fiberglass is thicker in the middle and thins out at the ends to support bending loads on the lifting surface.
These plies wrapped down to the joggle, so duct tape was used to mask off the aft end of the cores to help prevent resin running down and making a mess of things. The forward face and spar cap faces (the exposed foam below) was squeegeed with a light coat of micro slurry.
We were ready for the first ply of UNI!
Now, we started the layup mid-morning with the assumption that it would take a few hours of work and we'd be done. Ced had lots of experience with composite work in college. My only experience with composite layups was placing one ply of BID on a vertical tail surface a few years prior - which translates to next to nil. We were both eager, but I wasn't sure what to expect with a multi-layered layup.
With a glint in our eyes we began wetting out the first ply.
We gingerly spread the resin out, squeegeed the excess, and wrapped the first piece of fiberglass around the core with great care.
Due to the length of the canard and the length of the UNI, each ply consisted of two pieces of glass butted against each other.
Realizing we spent quite a bit of time applying one half of one ply out of seven, we tried to quicken our pace.
Finally getting the full first ply down, we celebrated by taking a goofy photo.
And conveniently forgot to take anymore in-progress photos. It took us around six hours to get all UNI down. Each layer was overlapped in a way that created a criss-cross pattern, so great care was taken to make sure we didn't overlay plies in the same direction. After we were done with the UNI, the 39" section of BID was placed in the center, breaching the two aluminum plate inserts (also not photographed).
After the larger BID was placed, 9 plies of 1.5" x 4" BID were stacked over each aluminum insert and the corners were rounded out with micro. A 4" x 8" piece of BID was then placed over this stack and the entire thing was peel plied.
At this point in our project, we only had 1" peel ply tape, which meant we were extremely weary at the end of the layup. But, 1" tape works just as well as a sheet of peel ply, so we used what we had and let the whole thing cure. Once cured, the peel ply was removed.
Now it was time to install the lift tabs. Using the jigs previously made, the holes were relocated and drilled through the fiberglass pad. The tabs were sanded. . .
. .. and floxed into place.
Once those set up, jigs were cut to help align the leading edge cores with the center and inboard cores.
Trying to prevent twist in the canard, the aft portion was bondo'd onto the jigs.
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| Like my homemade weight bags |
At this point, the outboard cores were bonded onto each end of the canard.
Once these bonds were cured, we had a trough to fill with unidirectional glass tape. This layup is what is known as the spar cap, in this case, it's the bottom spar cap.
Laying down the tape was a new experience for both of us. It got trickier as the glass stacked up, but we eventually got an even fill.
The tape was covered in peel ply and allowed to cure.
Now it was time to skin the bottom of the canard. A thin strip of peel ply is tacked into place on the aft end (the fish tail) and the exposed foam is squeegeed with micro. A layer of UNI was placed over the entire bottom surface of the canard. Two smaller sections of BID were placed on each half of the canard with a small portion crisscrossing in the center at the aft end. Another full sheet of UNI was placed over the entire thing and peel ply was laid down.
Once cured, a jig of pvc pipe and and sliced board was added to the bottom side of the canard and the whole thing was flipped over.
The fishtail was sliced down to create a smooth arc on the top side of the canard. That small strip of peel ply that was applied before the bottom skin was laid out was still kept in place for the moment. It would come in useful later.
Just like the bottom spar cap, the trough for the top spar cap was prepped and filled with 3" UNI tape.
Before diving in to finishing off the top skin, six hinge points have to be inserted. Six 1" hi-density PVC foam blocks were cut and placed and inserted into the aft end of the canard. Ced had to dig out the blue foam down to the cured bottom skin. I found that part terrifying, but it turned out in the end. These hinge points will be utilized later when installing the elevators.
Once the foam blocks were cured in place, the bottom leading edge skin was sanded to a point to allow a clean overlap of the top skin.
Like the bottom portion of the canard, the blue foam was coated in micro and three plies of UNI and one ply of BID made up the skin. Before the skin was laid down, that piece of peel ply on the trailing edge was pulled up to allow a glass-to-glass bond. Once everything cured, the canard was broken free of the jigs and we paraded it through the house.
Ok, we really just wanted to weigh the final product - 23 lbs!
Truth be told, this isn't the final canard, but it is the bulk of it. I found it very exciting to have helped build a semi-finished product of airplane goodness. Onward to elevators and wingtips!
