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Building Tips and technical articles. => Building techniques => Topic started by: Jim Thomerson on July 27, 2009, 10:47:09 AM
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There are a number of older designs which use a single central spar, either a horribly warped piece of oak, or a less warped (maybe) 1/2 sq balsa. Examples are the Zilches, the Mackey profile, many of Larry Scarenzi's (sp?) designs, etc. I have dealt with this in two ways. For the hardwood spar, I make a laminated spar with basswood top and bottom and balsa in between. One could put a strip or two of carbon in if desired. Make a laminated spar straight and it will stay straight. For the 1/2 square spars I have laminated two pieces of triangle stock. I also move the spar down in the wing a little so the leadouts clear and adjustable leadouts can be used.
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Good practise John. I tend to go with flat 1/8" X 3/8" spars, mounted about 1/8" or perhaps a little more, to allow for covering sag. I feel that by using these two spars, seperated as much as I can, offer better strength, with less weight, and allow for the use of adjustable leadouts.
In either case, the reultant structure will be better than the original.