As I'm just about to move out of what Raymer would call "Conceptual Phase" design and into "Preliminary Phase" design on my sailplane project, I thought I'd start looking ahead to loads and structures.
My thinking on this airplane has been KISS all the way - nothing fancy. With that in mind, I've been envisioning the wing structure as full-depth, Rutan-style foam and glass. However, I've never seen actual plans for any of his designs, only schematic drawings. I've got the old "Building the Rutan Composites" videotape and Rutan's "Homebuilt Composite Aircraft Construction" books (as well as Strojnik's books), so I think I've got the gist of how such structures go together, but I'd like to bounce my overall wing structure concept off of you guys who have lots of composite experience and see what you think. At this point everything is just schematic - if the concept is good, I'll design the sizes and thicknesses of the various parts you see here after I've got the applied loads figured out.
Figure 1 is the exploded view of the whole structure. A basic foam core wing section with a C-section glass spar. Not shown are the overall outer fiberglass skins. The main spar takes bending loads, while the skin takes torsion. The drag and forward-lift-vector loads are taken by the forward section skins and spar acting as a D-cell. The aft 'spar' essentially closes out the wing box and provides a place to mount control surfaces, etc.
To build this, I picture the process going like this:
The portions of the core forward of the spar and aft of the spar are hotwired separately, including indentations for the thicknesses of the main and aft spars. The shear web and aft spar (shown in orange) are laid up directly on their respective cores, as shown in Figure 2. Both are laminates of UNI E-glass with the plies at a 90 deg bias to each other and 45 degrees to the spar-axis of the wing. All of the exposed surfaces of the shear web and aft spar get peel-ply at the end of the layup.
After cure, the peel ply is removed and the 'rear' core is bonded to the shear web of the front section with microslurry. Once cured, the main spar caps (S-glass UNI tapes, shown in green) are laid up on top of the shear web, filling up the 'slot' in the core and (hopefully) coming up level with the surface of the surrounding foam, as shown in Figure 3.
The outer skins are UNI laminates. I haven't determined the bias schedule yet. I understand that commonly varies between 45 and 60 degrees to the spar-axis? The actual angles are determined by the particular loads on a given wing design, yes?
QUESTION: Would it be better to:
1) Lay up, say, the upper surface cap with peel-ply, let it cure, then do the underside cap, also with peel-ply and let that cure as well, then remove the peel-ply and apply the skins.
-or-
2) Lay up the upper surface cap, then proceed to apply the outer skin plies immediately before the spar cures. Once the upper surface cap and skin cures, repeat with the lower surface cap and skin in the same manner.
I don't know which would be the better procedure. My gut says probably #2, but that's an awfully long layup, and very thick once the skins are on. Would this method be in danger of exotherm?
So, what (if anything) have I overlooked? I'm working with no actual experience in these materials, so is there a better way to do this? What would it be?
Next after this is how to do a wing-attach at the root, but one step at a time... :gig:
My thinking on this airplane has been KISS all the way - nothing fancy. With that in mind, I've been envisioning the wing structure as full-depth, Rutan-style foam and glass. However, I've never seen actual plans for any of his designs, only schematic drawings. I've got the old "Building the Rutan Composites" videotape and Rutan's "Homebuilt Composite Aircraft Construction" books (as well as Strojnik's books), so I think I've got the gist of how such structures go together, but I'd like to bounce my overall wing structure concept off of you guys who have lots of composite experience and see what you think. At this point everything is just schematic - if the concept is good, I'll design the sizes and thicknesses of the various parts you see here after I've got the applied loads figured out.
Figure 1 is the exploded view of the whole structure. A basic foam core wing section with a C-section glass spar. Not shown are the overall outer fiberglass skins. The main spar takes bending loads, while the skin takes torsion. The drag and forward-lift-vector loads are taken by the forward section skins and spar acting as a D-cell. The aft 'spar' essentially closes out the wing box and provides a place to mount control surfaces, etc.
To build this, I picture the process going like this:
The portions of the core forward of the spar and aft of the spar are hotwired separately, including indentations for the thicknesses of the main and aft spars. The shear web and aft spar (shown in orange) are laid up directly on their respective cores, as shown in Figure 2. Both are laminates of UNI E-glass with the plies at a 90 deg bias to each other and 45 degrees to the spar-axis of the wing. All of the exposed surfaces of the shear web and aft spar get peel-ply at the end of the layup.
After cure, the peel ply is removed and the 'rear' core is bonded to the shear web of the front section with microslurry. Once cured, the main spar caps (S-glass UNI tapes, shown in green) are laid up on top of the shear web, filling up the 'slot' in the core and (hopefully) coming up level with the surface of the surrounding foam, as shown in Figure 3.
The outer skins are UNI laminates. I haven't determined the bias schedule yet. I understand that commonly varies between 45 and 60 degrees to the spar-axis? The actual angles are determined by the particular loads on a given wing design, yes?
QUESTION: Would it be better to:
1) Lay up, say, the upper surface cap with peel-ply, let it cure, then do the underside cap, also with peel-ply and let that cure as well, then remove the peel-ply and apply the skins.
-or-
2) Lay up the upper surface cap, then proceed to apply the outer skin plies immediately before the spar cures. Once the upper surface cap and skin cures, repeat with the lower surface cap and skin in the same manner.
I don't know which would be the better procedure. My gut says probably #2, but that's an awfully long layup, and very thick once the skins are on. Would this method be in danger of exotherm?
So, what (if anything) have I overlooked? I'm working with no actual experience in these materials, so is there a better way to do this? What would it be?
Next after this is how to do a wing-attach at the root, but one step at a time... :gig:
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