Ch 10.4-.5: Canard Bottom Spar Cap & Skin

The 1st Lifting Surface...for the 2nd Time !...continued

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.

Old Sample

New Sample

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

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.

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.

1st ply of UND on, working on applying
the BID layer.

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.

Ch 10.1-.3: Canard Assembly & Shear Web

The 1st Lifting Surface...for the 2nd Time !

I was not satisfied with my first canard build.  I overfilled the spar cap with plans to sand it down to meet the contour, however I had to sand much more on the top spar than I planned and I started to question if I had sanded too much, broken too many fibers mid-span, etc.  I think it's probably just fine, but rather than always have that question in my mind, I decided to rebuild this most critical part of the airplane...but now with improved skills.

The next few posts are the original canard build posts but edited where needed to reflect the 2nd canard build.  Many of the pics and description are still the same...I just did it better.

To Hot Wire or Not to Hot Wire...
I decided not to hot wire my own cores for the canard...and likely won't for the wings either.  Since Eureka CNC does such a great job at a reasonable price, I figured why mess with trying to get the cores correct and the templates shaped perfectly for such important pieces.  I would have ordered the entire canard/wing package deal but I didn't have anywhere to store the wing cores until I was able to start building them.

Assembled canard cores minus the leading edge,
outboard cores, and tips aligned in the 2x4 jig. 

Gettin Jiggy...
The cores were perfectly cut and assembled easily.  I built the 2x4 canard jig per the plans.  The FAQs on the Cozy page discuss using 12" 2x4s for this, and you certainly can, but 10" works just fine.  You'll have approx 1' hanging off of each end but it's not enough to create any problems.

If you're wondering about the thin ply underneath the jig...I glued the 2x4s to this thin ply rather than the table top so that I could move it if needed.

Fishing line used for alignment of cores

To ensure the 3 cores all aligned, I tied fishing line to clamps at each end of the canard and pulled it tight like a guitar string.  Then by aligning it close, but not touching the cores, I could easily tell if there were any alignment issues I needed to deal with.  On the 1st canard, I failed to make sure the cores were aligned straight up and down in the jig.  if they aren't, later you'll end up with angled lift tabs that you'll have to correct.  Make sure they are straight now...lengthwise, vertical with no twist between cores.  Take your time here...it will pay off.

Fishing line running just above, but not touching
the top of the cores helped with alighnment

Attachment Tabs...
I followed the plans to dig out the foam and install the lift tab nut plates with no issues.  I purchased the canard lift tabs and nut plates from the Cozy Girrls.  They are very nice, already abraded and ready to install hardware.  If I haven't said it, I highly recommend the hardware available from the CG Products.

Be sure to clearly mark the nut plate jig as to the direction it goes and whether it's left/right or port/starboard or whatever.  You'll re-use these to drill the bolt holes through the glass once the shear web hard points cure.

Well marked Jig

After installing the nut plates, glassing of the shear web went per plans with few issues.  I recommend using good masking tape to tape off the portions of the cores below the spar trough.  I used a mediocre duct tape which didn't stick very well and allowed epoxy to leak below the tapeline causing me some clean up work later to ensure the airfoil contour was not disturbed.  Gorilla duct tape and the like is too sticky I think...might pull foam out when you remove it.

Port lift tab installed
(w/peel ply around it)

Starboard lift tab installed
(w/peel ply around it)

Next, the leading edge was reinstalled per plans, and the canard was set in the template K jig blocks and aligned nice and straight.  PS...I also purchased the canard jigs from Eureka CNC and highly recommend those as well.  You just don't get better than 10 identical CNC machined jigs.  I had spent time building a very flat bench where I used two 30" solid core doors as the bench top.  The top was flat to within .1% of my digital level.  I felt that as long as the top was flat, there should be no reason to have to shim anything unless the canard was twisted when the cores were assembled. If so, this is the time to shim if needed to set it straight.  Time for the bottom spar cap.

Onward.