Initial application of the blue painter’s tape to the wing (above left), just aft of the leading edge. Blue tape is preferred because its low tack makes it safer to use on delicate structures. A long sanding block (above right) is used to begin
Shaping down
One of the more onerous tasks of building a wing is shaping the leading and trailing edges. It’s all too easy to get overenthusias- tic with the sanding block, and booger up the rib profiles. It’s especially important to be careful when you’re building with sliced or formed ribs, as there isn’t much wood to be lost. So, let’s look at a way to help you per- fectly fair the leading edge and trailing edge into the ribs.
The first thing you will need is a long sanding block. It really doesn’t matter what it’s made of, but it wants to be stiff and flat. I like a block that’s a third of a sheet of sand- paper cut lengthwise, though I will some- times make them longer. Use spray adhe- sive to glue a piece of 180-grit sandpaper on one side, and 220-grit on the other. The next thing you need is a smooth, flat work sur- face. You will also need some low-tack blue painter’s tape.
Next you need to sand the bottom of the wing flat. I have a flat 9 × 22-inch board on which I have glued two sheets of 180-grit sandpaper. This makes a great sanding
removing material. The author works on a flat board with 180-grit sandpaper attached via spray adhesive. The rough surface helps to hold the material in place while its being worked.
table for the bottoms of wings and other flat surfaces, and also serves as a good work sur- face for the rest of our procedure, as the sandpaper helps keep the wing panels from shifting about.
Once the wing bottoms are sanded, vacu- um off the balsa dust from the table and po- sition one wing panel at the edge of the work surface. Run the blue painter’s tape across the top, with one edge running right up against the back of the LE or TE material and leaving it long at the ends so you can se- cure the whole shebang down to your table. Gently tack the tape down to the ribs. The idea is that the tape will protect the ribs while you are sanding the bulk of the mate- rial away with the 180 sandpaper, and will give you a visual indicator when you have almost sanded through to them. When the tape starts to show abrasion, switch to the 220 to slow things down a bit. A few final swipes will take you through the tape and to the ribs themselves.
You will almost certainly find that some of your ribs are a little higher than others, and that you have to go a little further to get the
material faired in all along the wing. That’s okay, just keep a close eye on everything and proceed with caution. Work the whole edge, and resist the urge to “spot sand” at areas that are low—you’re aiming for a straight, true leading and trailing edge after all. When you see the tape sand away on the last holdout rib, stop, you’re done. If things are really out of alignment, you may need to reconsider your wing building method! It’s possible that your building board, work sur- face or sanding block—or all three—are not flat. Check ’em all with a straightedge be- fore beginning your next model.
A promise I’ve gotten a lot of feedback on my column about doing markings with a computer— most of them wondering when I’ll get to dis- cussing the Windows way to do it! I promise to get to it ASAP, and will continue to try and do so in a way that can be understood by those who are not “native” speakers of Computerese. That group includes me, by the way, so know ye that my objective is clear.
The third rib from the left end is the holdout (above)! A couple more light swipes with the sanding block and this leading edge is ready for final profiling. The trailing edge (at right) is worked in exactly the same fashion. Note that the tape has been extended beyond the ends of the wing, to help hold the wing in place while sanding.
FLYING MODELS 59
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