Originally Posted by Viper1GJ
I started this thread to expand discussion from my previous "1.4 oz vs .75 oz Fiberglass Cloth For Balsa Finishing" thread that morphed into other building discussions. Great ideas there but many of follow up questions were off topic.
I like scratch building but have been severely limited by time the last several years. Retirement is approaching and I want to start again. So I want to pick the brains of you builders that use composite materials that I want to use.
Specifically for this thread the techniques for cutting and prepping foam cores for large 100" plus aircraft.
What type of foam do you prefer and where do you get it and what it costs?
What type of foam cutter do you use for large cores? Many online ideas show glider wings with short chords. What works well with chords of 24" and larger and thick airfoils? Hand bow, suspended bow, double wire, swing arm,etc. Photos would be great.
How you cut channels for wing spar tubes, wood spar channels, wire channels, etc?
How you make lightening holes, servo well, gear well, etc in the foam cores.
Bob (Sensei), if you are there, how do you make your panel templates for cutting the lightening holes? Do you jig saw, router, etc the templates. Do you have a photo of one of your template sets in use? I see in your gallery a foam core with lines on it for the lightening holes. I assume you would have to reapply the template to top and bottom to make the foam cuts. Do you have a photo of your foam cutter for the lightening holes? Bow, hand held wire, etc.
Surface prep of foam before glue, sanding, sealing, etc.?
Materials other than balsa for skinning the foam.
What type glues
Looking forward to collecting all your ideas.
Gary, I stumbled on your thread and you ask some good questions. My answers may have been covered by others, I don't know, I didn't read most of it.
I use a bow to cut foam. It is a simple fiberglass reflector post from Home Depot, about 3/8" in diameter and about 45" long, and flexes just right for applying tension on the cutting wire. The posts are about 6 feet long, The extra material is used as the ends of the bow, glued at about 110 degree angle and reinforced with some scrap 1/16 ply
I suspend my bow from a shelf to counterbalance its weight. I use the gravity technique with pull strings for moving the bow through the foam
My power supply is the Burt Rutan Special from Aircraft Spruce. Simple and inexpensive to make....Works fine. Search under Foam Cutting Supplies.
My templates used to be rather elaborate polished phenolic. What a pita to make those......Well there had to be a simpler way. Now I use simple plywood templates. The edges are lined with teflon adhesive backed tape. Nothing is slipperier than teflon so this works better than anything else I've tried regards to templates. Of couse a CNC cutter uses no templates and is likely more accurate but I'm not about to spend a few 000's for a foam CNC cutter.
Regarding glues, for the past 25 years I've used laminating epoxy. Since I vacuum bag all my panels, very little is required. I use epoxy with about 90 min pot life which gives me plenty of working time. Gorilla glue is also used by many, except, you have got to work fast or it kicks off right before your eyes.
On skinning, I've used regular cardboard stock from Staples years ago. It builds rather heavy tho. Many moons ago I used 1/64 birch ply veneer from Aircraft Spruce, but used it only once. Sure wings were bullet proof but they were also far too heavy.
Nothing but 1/16" contest grade balsa since. It also allows taper sanding the balsa for further reduction in weight. But if you like to paint stuiff as I do, finishing balsa can be a pita. Time honored nitrate and Esaki tissue over balsa simplifies things and keeps things light, but it's an awful lot of work, work that I do willingly on all my competition models where lightness and weight specs count the most
Lately I've been experimenting with casting fiberglass onto plate glass first to form and cure the stock sheets, vacuum bagging that to the smooth finish of the plate glass. Then epoxying that onto foam directly. G10 sheets are similar, except I control where to place the strength and control its weight. The glass smooth finish is hard to beat and it is done with almost no effort. I haven't worked an optimal glass weight versus strength yet, but it's coming. It isn't lighter than balsa but does offer considerable ding resistance and much less work in the long run.....