Scioly.org

rigor_boi wrote:"Industrial Strength" seems pretty good to me in terms of bond strength.

Note that industrial strength could apply to a specific combination of materials. Super glue works great for balsa and similar woods, but not acrylic or metal sheets. And one Amazon listing of the glue you've mentions "flexible hold," which might not be what you want.

Some advice on cost-effectiveness: you do not need to use industrial strength CA glue if you cannot afford it. Standard Loctite CA works well too, especially the gel. The key is to let it cure overnight before moving or testing the bridge.

I do not like gel super glue for structures. It does not penetrate very deep, so it is prone to pulling off the outer growth ring or two if is on that side. For a tower, you will be gluing to both sides of the main support.
CA works fine on airplanes and gliders, but why not use thin and a kicker?? No long wait and quite strong.
My preference is still Duco with a 50-50 primer and followed by near full strength. It does not add that much weight. It does add time, but has the advantage of re-positioning members that are not exactly where you intended them to be. Also, you can undo a member joint fairly quickly with acetone. It takes a lot longer with CA and if you do not sand the old joint, new CA sometimes does not stick well. Personal experiences.

I agree with the comment on gel cyanoacrylates... They don't penetrate deeply enough, so even though the joint hold, the wood behind the joint shears. The thin viscosity glues are very difficult to control, and even though it penetrates well, there may not be enough left at the joint for a really solid bond. I'm in favor of the medium viscosity cyanacrylates, but these too have their flaws. Any type of "super glue" will dry and become brittle. This is fine if you are building the week before competition, but I would not expect it to be as strong a month or 2 later. As for the industrial strength glues, these are unnecessary. A bridge is like a chain... only as strong as the weakest link. It is very rare that a bridge fails due to the strength of the glue. More likely the failure is a result of the quality of the joint, and even more likely it is due to a member being undersized or less dense than needed, or having an internal flaw within the wood.