Saturday, July 21, 2018

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

The first lifting surface !

Unfortunately, I didn't seem to get many pictures of assembling the leading edge back on to the canard, the bottom spar cap layup, or the bottom skin.  Below are a few pictures with some narrative on the process.

Reassembly of the canard leading edge
Reasssembly of the leading edge was uneventful.  Using Eureka cores made it easy because they come with the alignment holes pre-drilled ready for the dowel rods.

6, 8, 10?
There are lots of discussions in the archives about how many layers of spar tape should fit in the spar trough.  The plans just have you fill the trough.  Some builders have had as many as 9 layers of spar tape on the bottom and 11 on top.  Many have had fewer.  The variables seem to be the spar trough depth if you cut your own cores, buying pre-cut cores, thickness of the spar web layups, ability to squeegee epoxy from the layups, etc.

Canard taped off and ready for the bottom Spar Cap layup
The most helpful discussion I found discussed a mathematical approach based on the thickness of spar tape and the depth of the trough at the center trough and compared that to the callout of 42 yards of spar tape in the materials.  As I recall, the math indicated that the "correct" number of layers was 6 on the bottom and 9 on the top...however this was also reinforced with..."just fill it up, but don't overfill it".

As mentioned before, I purchased pre-cut cores from Eureka CNC and confirmed that the cores match exactly the plans cross section.  I was able to get 7 total layers of spar tape in my bottom spar with the following lengths to each side....

Building up the bottom Spar Cap
Layer     Port Length     C/L     Starboard Length
1                  62.5              .                62.5
2                  61.5              .                61.5
3                  54.5              .                54.5
4                  49.0              .                49.0
5                  38.5              .                38.5
6                  34.5              .                34.5
7                  26.5              .                22.5

18.05 yards total on the bottom spar.

Checking and adjusting the spar
cap profile with the Eureka Jigs
Bottom Skin
Skinning the bottom went according to plans.  Before skinning however I had to sand a bit of the spar cap to eliminate a little overfilling of the spar cap trough in a few spots and ensure the correct profile.

Re-Jig according to the plans and get ready for the top side.

Onward,  cab

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