Hi Phil,
The pultruded carbon rod I purchased from Jim Marske was .092" x .220", and you're correct - it's the overall cross-sectional area of the bundled rods that is important. You should be able to modify my spreadsheet to your own design and the smaller cross-sectional rods Jim is selling now. The spreadsheet is based on the method and formulae given in his Composite Design Manual.
I came across another supplier of continuous pultruded carbon strip (rather than rod) that is being used by AC Light Aircraft in the Netherlands. I haven't got a sample of it yet, but it is another possibility for my next project.
I bundled my rods together using very narrow (2mm) strips of masking tape to hold them together at intervals for easier handling and placement during the wing spar lay-up. You can see how I did this here:
I made a decision early on that I wanted a 3 part wing (which has its pros and cons in daily use... but was definitely more work to fabricate than was worth it!) and so I made two separate leading edge molds for one wing (the inner and outer sections each got a separate mold). For the other wing I decided to just make one long mold and laid up the inner and outer sections of that leading edge in separate operations - this was *a lot* less work... and gave me the option of making a 2-part wing at a later date if I ever feel mad enough to go down that road again!... but that will necessitate either joining my two-part LE molds into one or making an altogether new mold for that LE - naa, I'm not going there!!
I didn't have enough space in my workshop to leave the leading edges in their molds so I could assemble the ribs and spars in one go, so I ended up bonding the forward and aft ribs to the spar followed by the aft spar and finally the leading edge skins. You should be able to follow my process here:
The original plans call for each drag spar to be made in two parts and assembled either side of aft rib #2. I fabricated my drag spars in one piece, and laminated a single .092" x .220" pultruded rod into each of the drag spar caps to help carry the loads. I also molded a recess into the flat edge of the drag spar cap flanges, which I later filled with a twisted 'rope' of carbon and kevlar tows as per the original plans. Again, you should be able to see this in photos 110 - 122.
Throughout the build I used a thixsotropic (stiff / non-runny / will not drip off the mixing spatula) mix of epoxy and cotton flock for bonding ribs to spars and leading edges to ribs, etc. Beware! This is where 90% of unnecessary weight is added to my glider!! Make sure you wipe off as much of the excess squeeze-out cotton flock mix as you can. It is amazing how quickly the weight adds up here! I've lost my original weight measurements for my naked spars, ribs and leading edges, but I do remember that the total weight was significantly more than the combined weight of the individual components! I started out applying the epoxy/flock mix with a spatula but quickly moved over to using a big fat 'horse' syringe, which delivered a more uniform and controlled bead of glue than the spatula method. My pharmacist eventually asked me why I was always buying so many big syringes, and I smiled sheepishly and told him I had a monster drugs habit!
All the rigs were fabricated with a 5-10mm wide flange around their edges. This is fine for bonding to the spar, but I was concerned that it wouldn't be wide enough to bond the wing skin cloth to, so I fabricated a large flat sheet of 2 layers of 195gsm carbon and cut that into 25mm (1") wide strips, which I bonded onto the long curved edges of each rib. The ends of these strips, where they meet the leading edge D-skin and aft spar gap cover are simple butt joints. Any irregularities were sanded out and fared with a skim of car body filler (more weight!) I don't seem to have any photos of the process, but you can see the faring process and end result here:
I covered my wings using products from Stewart Systems Ltd. (Super Flite 103 UL dacron/polyester cloth and their Eco-Poly 2-part paint system), which I am super happy with! I built my glider on a budget (the whole reason for building it was because a mate bought a Swift Light and I wasn't about to let him conquer the skies with that sort of cheque book aviation! The problem was, I couldn't afford to splash that much cash (€30,000+) on a toy, so I built my CD for around just €3 - 4K (including rocket parachute.) My penury also limited my options when it came to covering the wings. I had hoped to use Oratex UL pre-painted cloth, but I just couldn't afford it at the time. I have seen the finish you can get with Oratex on the Archaeopteryx gliders I rub shoulders with in France and it is *excellent* stuff. Oratex also heat-shrinks preferentially along its length rather than across its width, so you will not get (or you'll get less) scolloping between the wing ribs. I really, really wish I could have aforded to use Oratex on my CD, but that's life! As I said, I'm super happy with the system I used, even if it is a bit heavier.
I think that about covers it! I'll investigate the Les Homan video this weekend for my homework!
All the best,
Phil.