Greetings,

I had posted a thread before about the fact that I had to lengthen the main spar on my LT-40 wing. I proceded to CA the extra quarter inch that I needed to make it the right length. I then posted here and was recommended to either leave it alone, put a dowel into a drilled hole, or do a scarf joint.

Of the three choices, I have narrowed it down to leave it alone or a scarf joint. I could easily cut the extended piece off and create a scarf joint. From what I can gather you would simply cut the piece six times the width. In my case, the spar is 1/2". So I would cut an angled piece of wood with the hypotenuse being 3"? Is this simply to create more surface area for the CA to bond to? BTW, the main spar is spruce. I would have to do this with both the spruce and the balsa spars.

I am trying to build this kit as "perfectly" as possible. Not only for the challenge of learning new building techniques etc, but so I can have a nice flying solid plane when I am done.

Also, to make my situation more clear hear is a picture. You can see that the last rib notch on the left is slightly off the line-up, I originally cut the spars according to the plan, but since the last W5 rib notch was beyond where I made the cut, I CA'ed those 1/4" pieces in. Based on what you see and the location of the gluing (This is at the wing tip, not the wing root and there will also be another spar at the top which will help support any stresses), should I transform this to a scarf joint?

Yes, you have the definition of a scarf joint correct. However, if it is Spruce, don't use CA, use a good woodglue like Elmers or Titbond. Spruce is slightly acidic and CA's do not work well with acidic materials. If you must use CA, then coat the mating surfaces very lightly with plain old household baking soda first. This neutralizes the acidity and CA's love basic chemistry. The baking soda is a basic and will accelerate CA's cure.

A 1/4 inch piece glued to the end of the spar(s) like in your picture is NOT going to make any difference as long as the piece feels solidly attached. CA or not.

There will be so little stress placed on those glue joints (by the time the other spar is added, the wingtips built, and the wing covered), that it will not be an issue. If you're still concerned, add a thin strip of balsa to each side of those joints as stiffeners.

I'd highly recommed continuing with your construction and chalking this one up to "lessons learned".
Dennis-