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Q1 Plans Chapter 19 Page 19-4

Quickie Straight Edge Test

Step Two: Coarse Filling

You must be extra cautious in this step or you may destroy your structure. When you take a piece of sandpaper and start grinding on your composite structure it’s like using acid to clean a metal wing Spar. It must be done carefully. Start by determining which areas require micro filler as shown using a flexible yard stick and a scale. Prepare the areas to be filled by sanding lightly. Do not try to use a sanding block or spline on these areas.

Don't use a hard sanding block!

Q1 Plans Chapter 19 Page 19-5

Step Three: Feather-Fill

Sand the surfaces lightly by hand or with a soft foam sanding block in preparation for feather fill. A spray or brush coat of feather fill will buildup .02” to .03” thick, fill the glass weave and any medium sized out of contour spots. Feather fill will require several hours curing time before it can be sanded. The cured feather fill is sanded to contour using a spline or soft block and 100-grit sandpaper. Again, extreme caution must be exercised not to damage the glass structure in persuit of a good finish. The contouring must stop immediately when the highest glass peaks begin to be visible as the feather fill is sanded away.

If you find that you have underestimated the fill required or just have a thin coat, don’t hesitate to use a second coat of feather fill. A well prepared surface generally need more than one coat. When you have finished contouring the feather fill, the surface should be basically smooth and fair. The primer to follow is not intended to be contoured heavily, just smoothed with finer sandpaper for a smooth finish while leaving a substantial ultra violet barrier.

Quickie Feather Fill Sanding

After you have filled and contoured, reinspect for sanding damage, it is an easy thing to do. Remember you are only allowed to sand into the first skin ply in local areas no greater than 2 inches in diameter and all of these areas must total less than 10% of the surface area. Wherever there is only one ply, or where the UNI cloth is crossed for strength(e.g. the canard and wing skins), no sanding of the ply is allowed. Be Careful!