Kevin wrote:You can guess all you want.
Naturally!
I'm hoping to get the core put together this evening. I need some glue to hold the foam to the planks, what I was going to use was setup solid as a rock. I'm thinking I can use pins to hold the core pieces together and down to the outer part while the epoxy sets up. I was going to use micro fibers for strength and flexibility and silica to thicken my epoxy.
I used "Gorilla" glue to glue the saddles to the planks, a little dab every foot or so, then some small weights to hold the saddles down while it sets.
To glue the cores to the spline, I imagine you'll want to use a mixture that will be fillet-worthy, since those radii are probably going to be filled in the process of gluing together the spline. So yeah, a microfiber/silica blend is good. (For simple core to "other stuff" bonding, a mayonnaise paste with Microlight is fine- it will vastly exceed the strength of the foam. The idea there is to reduce the foam's absorption of higher density material, like straight epoxy. This should be used as the first step before laminating the skins to the foam, for instance.)
Anyone else confused by Joe's comment on my blog and why he sliced his rudder cores horizontally. If it was hollow, I'd understand the need for the supports, but the foam should provide the support of the skin and the spline is at max width prevent crushing and it has quite a bit of hoop strength with the uni/cloth/uni/cloth lamination schedule.
It's pretty rare (!) to see an I-beam where the web is a bunch of segments turned sideways to the beam. But maybe Joe has discovered a new engineering methodology?
There
is a setup used in woodworking primarily, called a torsion box. Basically make an egg crate type grid of thin stuff, and then bond thin skins top and bottom- sort of a primitive form of cored construction. It's a nifty way to make fairly large panels, pretty light and pretty strong. In the case of a rudder where the skins already meet at the front and the back, those lateral webs just become redundant. And in a small rudder with carbon skins, torsion along the blade is not the mode of failure- by the time the rudder is strong enough to not bend, it can't help but be over-built in torsion. Unless you use nothing but 0 degree uni...
I made the planks from 3/4" MDF and they are excellent but heavy. I may need to add a support block to my stand so that they don't break the core after I add the skin layup.
Yes, I did the same thing when I did mine. The tip of my core was very small, and I was very worried about breaking it off- I ran a couple 4" screws through the end plate into the core to help. But the whole thing sways and shimmies a bit while you apply the cloth- it's nerve wracking. I would wet out the cloth on a table before applying it to the core, if I did it again. The Solo method of brush-wetting the cloth in place is pretty crude, I think.
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