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Old Feb 09, 2013, 10:01 AM
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Originally Posted by TOSSPilot View Post
It is the Mirage. The wing strength is probably decent in stock form and I know this would be an over kill but I do plan on flying it in open class competition and would like the extra launch/winch ability without worry.

I do plan on wrapping the joiner boxes with kevlar thread. Not sure if I am creating a major stress point at the wing joiner box going from carbon spar back to bass wood in the tip panels?

The cost is about $25 vs. $8 for the tape but not really a big concern if it is easier than laminating carbon tape and sanding down the wood for the correct fit.

I have not seen too many post about just replacing the entire spar cap with a pure carbon cap.

Thank you again for the thoughts


Originally Posted by John Walter View Post
The Miarage is a great plane. The key to its design is the balance among all is components.

A solid CF spar will weigh too much. Without changing the rest of the spar, you would simlpy tear off the tips before the main spar saw any substantial load. Also, since there is no balsa sheeting, the wing would flutter long before the main spar loads became an issue.

.007 CF on the top spar, or .014 top and .007 bottom would give more than plenty of strength.
The bend load decreases rapidly as you move from the root to the tip, so that should not be a problem. I have attached a good article that I got somewhere, but don't remember where. Apologies to the author for not giving proper credit....

I tend to agree with JW on this. 14 top and 7 bottom should be quite sufficient as long as you don't try to give it a full-pedal launch with a killer zoom at the end.

One other thing....and very important.... be sure the pieces of your spar fit together well.... no gaps or sloppy workmanship allowed. The webs need to fit precisely between the upper & lower caps, and the ribs.
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