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Building technique: Utilizing a Wing-Jig, Scale P-51 "Speed Wing"
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03-01-2015, 12:47 AM
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Iron Dog
Join Date: Feb 2009
Location: Sacramento, CA
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General Wing Assembly
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16. Using a small razor saw, trim down much of the excess overhanging spar material extending beyond the root and tip sections of the wing. It is recommended to leave just a slight amount of material overhanging the root and tip ribs. In other words, do not attempt to cut the spars completely flush, or you may slice into the ribs and/or leave a gap in the spar material when the center sections are later glued together. (This material will be sanded flush when the panel is eventually removed from the jig.)
17. If excess glue was not appropriately wiped from the joints, or spars were not carefully seated during the gluing process, some minor sanding of the spar-to-rib joints may be necessary, prior to sheeting the wing. Be very careful during this process. Because the glue and spruce material is much harder than the thin balsa ribs, it is far too easy to accidentally sand the ribs and alter the shape of the airfoil.
(I have accidentally done this, many times over the years, and will illustrate the consequences, here.)
To better avoid this situation, sand very lightly and carefully with a finer grade of sand paper. If using a sanding block, be sure to move it from front-to-back, rather than side-to-side, and try to utilize the harder plywood ribs (W4, W5, and W7) as a guide, as much as possible. In some cases, it may be better to lightly sand with a folded piece of sandpaper, instead.
If the worse happens, and you accidentally alter a rib’s shape
(especially critical with rib W2, which needs to match the wing saddle of the fuse),
remember you have a back-up copy of the pattern of each rib from the original laser-cut sheets. A small section with the original airfoil shape can be traced and/or cut out using the original rib pattern from one of these cut-sheets, and this small “repair piece” can then be glued to an inside edge of the altered rib – thus restoring the airfoil’s proper shape.
An example of airfoil's shape being altered due to "less than careful" sanding at the spar.
Use saved cut-sheet to trace/cut section from scrap balsa. Remaining tab from spar cut-out is a handy reference.
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