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( 3 / 30 )I tried breaking the extra "T". Those joints are TOUGH! Supporting the top of the "T" about 1/2" on each side of the gusset, I tried pulling on the stem of the "T". I was expecting a bending or shear failure in the top of the "T", but I couldn't grip the stem hard enough to apply the force needed to break it. I was able to pull with maybe 100-150 lbs of force. In the process, I crushed the end of the stem with the grips.
I cut off the crushed part and tried pushing on the stem in a vise with the top supported similarly to above. The top broke just outside the glue joint. Bending failure in the tension fibers. Just for kicks I pushed sideways on the T until it broke. Same result.
With the next test piece, I intend to devise a better way to apply tension to the stem - perhaps by gusseting another crosspiece to the bottom to form an "I". I also want to try the compression test again by supporting the top closer to the gusset to induce shear failure in the top or compression failure in the stem. If I can get a test that consistently fails the stem in compression or tension (not bending), then I can be reasonably sure that I am testing the joint to its fullest capacity.
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( 3 / 30 )The waxed paper is started to show wear. The epoxy drips are starting to stick, so I am going to have to replace release layer soon. If I were starting over, I might give that plexiglass surfaced jig a shot. As it is, I am just going to replace the waxed paper with transparency film. That should hold up better..
I also made a few extra test pieces. I took 4 strips of plywood and lapped them together to make two strips. One set had sanded gluing surfaces, the other did not. The area of bonded surface is the same for each strip. I am hoping to break these to get a feel for how critical sanding the gusset faces is.
I made an extra gusseted "T" just to play with some test procedures and to get a feel for how strong these things are.
1 hr
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( 3 / 30 )I've noticed a small problem with this rib. The top capstrip was not milled perfectly square. Therefore, not all of the joints clamped up tight. In particular, the large gusset near the aileron cutaway did not lay flat, leaving a 1/32" gap. I know that T-88 can bridge up to 1/16" gaps, but I think I've just made my first test rib.
1 hr
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( 2.9 / 21 )The system is working fairly well.
The images below show a couple of details. The first picture is just a joint showing the epoxy coated gusset and sticks. You can see the mitered ends as well as the typical fillet of epoxy formed from the squeeze-out.
The second picture shows the bond release tape that I applied to the lower capstrip doubler where the aileron is cut away. Once the ribs are assembled on the spars, the lower capstrip and part of the gusset in this area will be cut away with a router. Once exposed, this tape will be removed, and a clean surface will remain for bonding the aileron runners.
1 hr
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( 3 / 30 )Made Rib #3
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