Chapter 10 - Canard Construction


Fellow builder, Ray Cronise, visited for the weekend from Alabama. His plan was to delay and distract me. I put him to work. First we dashed down to Kinkos to get a photocopy of the templates. Spent a couple of lazy hours with the band saw and neat little sanding blocks I'd made and soon had five perfect templates. Perfect except that they were about 1/10 th bigger than plans in some areas. The photocopy was about 102%. We scrapped these and redid the templates by cutting up the plans.

Building a hot wire cutter.

Next stop Home Depot for materials. Bought some 1/2 steel tube, a really cheap extension cord, some long wire ties and a couple of grounding clamps. I'd got the hot wire regulator from Wicks. Ray built the cutter. Now Ray's fairly bright, but was embarrased to find the first piece of foam we had to cut was a few inches wider than the cutter. Hmmm. Got another 2 * 4 and we had a bigger cutter in 20 minutes. Builder Dave asked if you get a shock if you touch the steel when you hold the cutter. The answer is no, provided you dont stand in water with bare feet, then you get enough of a tingle to make the cut jiggle!

Cutting (and scrapping) all the foam.

Ray had done this before, so he took the lead. The straight cuts went fine, but the first curvy one (the center spar) was a mess. I had been holding the wire too tight on the template. This time I held it too loose and made a few nasty joggles in the lower surface. We decided to try running the wire through a second time. We agreed that the result was "acceptible", especially since this part hardly sees any air. In the light of day I reconsidered and cut this core again. I think I'd rather have a full set of perfect cores before moving on.

Ray had to leave & catch a flight. Char & I cut the two outboard & inboard sections. I was tired and we started at the trailing edge by mistake. Big error. The leading edge was entirely the wrong shape. Scrapped that one and cut the second one. This went fine, but next morning it didnt seem to fit the template very well. We used the remaining foam (intended for winglet core) to recut the second canard section. Screwed it up royally. I was bitten by a mosquito during the cut (working on a patio in florida has its penalties) and made a couple of bad joggles, so we went through the cut again. Should have just sanded. We ended up 1/10 inch narrow at one end. Unacceptable. Now I have to use the remaining offcut (the second winglet core). Did this the next day when rested. First I reread the plans chap 3 on hot wire cutting and experimented with the voltage setting. We'd had it set at 10 volts the day before and I'd had a feeling the cut was too slow and needed too much pressure causing a lot of wire drag. I found that I could get to about 18 volts before things really start to burn. At around 15 volts (for my wire length, of course) we got a much smoother cut. Almost no resistance, a lot of sizzling, but no smoke. Angle hair followed the wire away from the foam at the end. We recut the center core, and the right side outer / inner with no problems. Perfect cuts every time. I had to order another 64 inch foam block from Wicks to cut the last section. When the replacement foam arrived I decided to cut the elevators first as practice. We cut the remaining piece and the elevators without further problems.

General thoughts on hot wire cutting

See Tips and tricks

Making the sheer web

The plans say "use two 8 foot 2 * 4's. The length of the center core plus the two inner cores is 125inches. I had to add a couple of 2 * 4 pieces on the end. Would have been better to get 10 or 12 foot 2 * 4's in the first place. I jigged the three cores with nails, but could see from looking down the canard that one of the end cores had a slight curve or bow in it. i.e. when in place on the plane the canard would be drooping on one end. I removed the bow by bondoing the nails in pairs and bending the core a little each time, working down the core toward the end. When I was done the canard was perfectly straight.

Attaching the leading edges

I had already made the 10 jigs for this stage while waiting for foam delivery. Everything went fine until I found that I'd missed opening out one of the dowel holes. Had to pull off the section, drill the hole, then put it back. I found that the dowel holes in the sheer web were easy to find, but hard to drill accurately. You can tell how accurate you are by the position of the point on the dowel as it comes through the hole. I had to widen a few of the holes to get the dowel centered. I'd made the contour checking jig in 1/16 ply. Had to remake it in 1/2 particle board so I could put my level on it.

Bottom Spar Cap

This worked out well. I seemed to be getting a lot of glass down into the trough. I'm sure I've used more than half of my roll of 3 inch tape. I'll check this in case I have to order more for the upper cap. After creeping in the recommended 4 inches on each ply I got to the center section where the trough is the same depth and found that I was a little low all the way along. I added a final full span strip of tape and than got me to the right height. The threads are easy to work with once they're wet. Don't try to do too much with them till you've got them completely wetted out. I noticed one strange thing. The masking tape I used [regular white stuff from home depot seemed to react with the epoxy. I tried to remove it while the epoxy was still tacky. It had a skin of hardened epoxy under it and brought up a bit of foam in places. It was quite a chore getting all the bits of masking tape off. Perhaps duct tape would have worked better.

Bottom Skin

The contour template showed me that one of the inner cores was a little out of shape at the trailing edge. The curve was too shallow. I was missing about 1/8 of foam in that area. I decided to try to fix it now rather than wait until after the skin is on. I found a foam offcut from a good core which had the right curve, troweled some dry micro on the canard and pressed the offcut in place with weights. After cure my trailing edge was the correct shape. I've invented a new technique. Hmmm. I think I'll call it a "mold".

I read about the nasty garage gremlins in Wayne Hick's page. I also have gremlins but mine are a little different. Mine are Florida patio gremlins. They have a pool and a hot tub. Occasionally I leave a half empty can of soda or part eaten sandwich out for them. I think they must be happy because my gremlins fix things overnight. I've had many things that were not level at night which were perfect in the morning!

Top spar cap and skin

I sawed off the fishtail and lifted the peel ply. Found I had to cut the foam to get the peel ply up. Quite a lot of foam came with it and I was left with more of a ski jump than a ski ramp. Plans say nothing about filling the void here. Later we fill a similar void in the elevators with dry micro and peel ply. I know we need a glass to glass join here, but I had to do something. I rounded the curve with dry micro leaving plenty of glass trailing edge to bond to. Testing for twist seemed to be a little unscientific. The contour jig is bigger than the canard at this stage to allow for the final skin. It only has to move a tiny bit fore / aft for the level to change by 0.5 degrees or more. In the end I trusted that the jigs had held out any twist, checked this thought with the mark 1 eyeball method, and moved on.

Couldn't find anything about the size of the foam inserts for elevator hinges till Wayne pointed out the scale drawing on M11. Once the inserts were in and dry micro'd flush I started the spar cap. I had exactly 21 yards (half the plans amount for both caps) of glass tape remaining after doing the bottom cap. The Top cap is a little deeper. I probably used one layer too much on the bottom which led to lots of itchy sanding. When I ran out of tape on the top cap I still had a about 1/32 to go for contour. Considered asking the group and/or Nat for advice, then just dived in and made my own decision. I added three ply of UNI spanwise along the cap, then skinned the canard on top of that. Contour worked out pretty well. This layup took me just over 6 hours. Next morning I "popped" off the PVC pipe, removed the jigs and sanded away the bondo. I used a carpenters chalk line on the trailing edge to get it straight.

Canard tips

I made the canard tips to match what I'd seen on other Cozys then, much later, I saw a picture of Klaus Savier's "Unbelievable EZ" on the cover of Sport Aviation. This guy wins practically every race he enters, so he must know something about how to get speed out of a canard. I noticed that his canard tips were quite tall and swept, like mini winglets. Aerodynamically that makes sense to me, so I decided to add some pointy curved canard tips. They may give me another knot or so, but I also like the look of them.

My Cozy has a wing

I set the canard on the fuselage. My "tub" is clearly becoming a flying machine.

A Suggestion for Saab

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