Installation of the Leading Edges...
Re-assembling the leading edges back on to the cores went per plans with no issues. The Eureka cores make it easy because they already have the alignment holes ready for the dowel rods to be inserted. The only thing I'll say you need to watch is to be sure you don't get the micro too thick between the leading edges and the face of the spar web because doing so can result in you still getting the leading edge slightly tilted up or down despite the alignment dowels.
Jigging the canard for the bottom spar...
As mentioned earlier, I bought the Eureka canard jig templates...highly recommended. After attaching the templates, the leading edges, and the outer core sections, the only thing left was to make sure the canard was straight and not twisted.
To check twist, I used a ~4" wide flat aluminum plate as a base for my digital level and placed it across the spar trough at multiple places across the full length of the canard. I only noted .5 degree differences across the full length. Small variations in the foam or the slightest misalignment where the cores connect can cause slight angle differences. It's hard to be perfect.
To check straightness, I used a length of fishing line pulled tight between two clamps. I aligned it with various parts of the canard, like the bottom edge of the fishtail, the tangent point of the leading edge, etc. to determine if it was straight.
6, 9, 11 plys?
There always seems to be questions about how many plys of spar tape you should use when building the spar. The Cozy archives have reports from 6 to 11 and more in either the top or bottom canard spars. The best answer to this I found was a mathematical discussion that used the thickness of a properly cut center canard core, the thickness of a ply of spar tape, the theoretical thickness of spar web, and the plans callout for 42 yards of spar tape to arrive at a theoretical "correct" number of plys. The math indicated 6 on the bottom and 9 on the top spar were correct...or in terms of yards of tape, 18yds on the bottom and 24 yds on the top. Don't take my word for this, do your own research. In any case, recommendations are always to fill up the trough without overfilling...but if you find you can only get 5 plys of spar tape in the bottom spar, it might be time to check your process and see why.
Spar...again...
With the canard in place and aligned, it was time for the bottom spar layup. This was my 2nd canard build up and I don't mind saying I was more than a little nervous about doing this spar work again. So much so that it took me many months to finally do it. Rebuilding the canard isn't a cheap decision, but it was the right thing to do for such a critical part. I don't want to have to do it again.
There was an additional complication this time. I purchased new spar tape from Aircraft Spruce and it was made just after they had months of downtime with the Rube Goldberg machine that makes the stuff. See this link if you want to see it in action. The tape wasn't as wide, 2.7" vs 3.0", which wasn't a big deal, but it also didn't have as many bundles of glass in it...25 vs 30 compared to some older tape I compared it with. To check, I cut 21" of both old and new tape, pulled the key thread and cross threads, and weighed each. Both samples weighed in within 1g of each other giving me confidence that although there were fewer bundles of glass, there was basically the same amount in each sample.
This was my setup...everything taped up with my roll of spar tape mounted at the end to make it easy to roll out.
Working away
The key thread and cross threads from each layer...my evidence of how many layers of spar tape I used, 8.
I also noted the length of each layer so I knew how much I used.
Ply Length each side of center
1 62.5
2 60.5
3 54.5
4 46.5 (tapered to 50.5)
5 38.5 (tapered to 42.5)
6 38.5
7 30.5 (tapered to 34.5)
8 22.5 (tapered to 26.5)
Total of 19.6 yards.
Bottom Skin
After cure I checked the contour and had to do some minor sanding...nothing serious. With that I started prepping for the bottom skin. The skin layup was uneventful. This time, rather than wetting up the glass directly on the canard, I wet all the glass out on the table, on plastic sheet, first, then transferred the plys one at a time to the canard. I think that worked out better and perhaps may have been quicker.
Tip: One thing I think I would do different is that I would try to place a layer of box tape under the peel play at the trailing edge. After flipping the canard, you'll have to pull the peel ply off...and it took hours to get it off. It only came off in small pieces and was hard to tell if I had gotten it all or not. Using some tape beneath it I think would have acted like a release layer and made the job of removing it take only minutes vs hours.
Ok...time to flip it over.
Re-assembling the leading edges back on to the cores went per plans with no issues. The Eureka cores make it easy because they already have the alignment holes ready for the dowel rods to be inserted. The only thing I'll say you need to watch is to be sure you don't get the micro too thick between the leading edges and the face of the spar web because doing so can result in you still getting the leading edge slightly tilted up or down despite the alignment dowels.Jigging the canard for the bottom spar...
As mentioned earlier, I bought the Eureka canard jig templates...highly recommended. After attaching the templates, the leading edges, and the outer core sections, the only thing left was to make sure the canard was straight and not twisted.
To check twist, I used a ~4" wide flat aluminum plate as a base for my digital level and placed it across the spar trough at multiple places across the full length of the canard. I only noted .5 degree differences across the full length. Small variations in the foam or the slightest misalignment where the cores connect can cause slight angle differences. It's hard to be perfect.
To check straightness, I used a length of fishing line pulled tight between two clamps. I aligned it with various parts of the canard, like the bottom edge of the fishtail, the tangent point of the leading edge, etc. to determine if it was straight.
6, 9, 11 plys?
There always seems to be questions about how many plys of spar tape you should use when building the spar. The Cozy archives have reports from 6 to 11 and more in either the top or bottom canard spars. The best answer to this I found was a mathematical discussion that used the thickness of a properly cut center canard core, the thickness of a ply of spar tape, the theoretical thickness of spar web, and the plans callout for 42 yards of spar tape to arrive at a theoretical "correct" number of plys. The math indicated 6 on the bottom and 9 on the top spar were correct...or in terms of yards of tape, 18yds on the bottom and 24 yds on the top. Don't take my word for this, do your own research. In any case, recommendations are always to fill up the trough without overfilling...but if you find you can only get 5 plys of spar tape in the bottom spar, it might be time to check your process and see why.
Spar...again...
With the canard in place and aligned, it was time for the bottom spar layup. This was my 2nd canard build up and I don't mind saying I was more than a little nervous about doing this spar work again. So much so that it took me many months to finally do it. Rebuilding the canard isn't a cheap decision, but it was the right thing to do for such a critical part. I don't want to have to do it again.
 |
| Old Sample |
 |
| New Sample |
Working away
Peel plied and
ready to cure
The key thread and cross threads from each layer...my evidence of how many layers of spar tape I used, 8.I also noted the length of each layer so I knew how much I used.
Ply Length each side of center
1 62.5
2 60.5
3 54.5
4 46.5 (tapered to 50.5)
5 38.5 (tapered to 42.5)
6 38.5
7 30.5 (tapered to 34.5)
8 22.5 (tapered to 26.5)
Total of 19.6 yards.
 |
| Peel Ply added to the trailing edge...ready to apply the skin. |
After cure I checked the contour and had to do some minor sanding...nothing serious. With that I started prepping for the bottom skin. The skin layup was uneventful. This time, rather than wetting up the glass directly on the canard, I wet all the glass out on the table, on plastic sheet, first, then transferred the plys one at a time to the canard. I think that worked out better and perhaps may have been quicker.
 |
| 1st ply of UND on, working on applying the BID layer. |
Ok...time to flip it over.
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