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Building Tips and technical articles. => Building techniques => Topic started by: Jim Morris on August 03, 2013, 06:16:02 PM
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Well I got some new wood today to make stiffer flaps for the Vector,heavy BTW but stiff. How can I keep it from warping while the dope drys? Its been a while and I used to get away with it somehow but could someone please tell me some good advise on what you all do.Thanks.
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Thanks for the reply. I think I figured this out. I bought some C grain balsa from Sig and it is very stiff and light,love this stuff.I sanded the flaps to taper and started doping, no warps and all is good. While Im on the subject and I have been out of this for a while, what size sanding rods do I use for a 3/8 thick elevator to make the taper? Im not too good at the fraction math.
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That's easy. If you want a 1/8" thickness at the trailing edge, you use a 3/8" rod at the LE and for the first side and a 1/4" rod at the TE. Flip it over after sanding and again use the 3/8" rod at the LE and switch to a 1/8" rod at the TE. If you want a 1/16" TE thickness, the first TE rod would be 7/32". Then a 1/16" rod would be used for the final taper sanding.
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Thanks, thats what I thought but wanted to be sure. Good news is,I have the rods.
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Jim, all good advice above!
All I might suggest you consider is that you dope or epoxy woven fibreglas (.5 or /.6 oz/sq yd) on the sanded flaps after basically shaping them. Comments I've seen make sense. CF, by itself, does not have stiffness "directions." Woven fibreglass does. Fibreglas also has its own strength, where CF (a mat of random fibers) does not.
Both fibreglas and CF rely on the 'binder' as much as on their inherent strength. For fibreglas, dope is adequate to hold its greater strength to the structure, but dope does have a tendency to warp. Properly done, using medium cure epoxy (30 minute or thereabouts) you can jig the flaps true, and they will cure - and stay - true.
Jigging them true may involve binding them onto the rods, separated by plastic wrap or even waxed paper, but should be certain.
And, as with iron-on coverings, the surface should be as smooth and dust-free as possible. Any flaws will show at the finished surface.
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Long ago, I got tired of flaps warping when made of one piece of balsa, regardless of grain. I make flaps built-up from 1/16 sheet. A hard piece of 1/4" sq. (or 3/8") used for leading edge. Ribs made out of almost anything, tapered. No tedious sanding. Uses ordinary balsa sheet.
Floyd
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I have been laminating balsa flaps cutting the grain so that the laminates are angled at around 30 degrees. Glued with epoxy, scraping as much off as possible. The blanks are weighted down on a flat surface to dry. The result is rigid and straight.