Wings Fus.
I'm hoping this project will be enlighten to you as it probably will be for me, as it unfolds. I'm not going to try to reinvent the wheel, the way these works of art have been built for years instead, I'm going to build mine, to my methods and style of building, where I feel changes can be made, and maybe, in my eyes anyway, some better ways of doing things. This page is more of a compliment to the French site and their building style but, a little more detailed with regards to the way I'm going to do it and some points they haven't touched upon.
After looking and studying some of the European models, I'm going to copy the Bondarsoko/Lerner wing pattern and construction detail from a model on loan from Dick Lambert, his fastest plane.
Probably the most important part is the wood selection, a tough chore, this stuff, at least the good wood, is worth it's weight in gold, light and C-grain is the choice stuff. I'm sure some of the balsa cutters like Lone Star can help but, I prefer to cut my own. I have a fixture that I can mount a block to and can rotate it to pull out the choice C-grain, there's alot of waste doing this but, I feel it makes a more rigid structure. I plan on using 5/16" as my wing cord thickness and cut some .110" for the inboard planel which I'll explain as this project happens. I cut four blocks that ranged from 4.2 to 4.5 lb density, I managed to get 13 sheets of 5/16" and 10 pieces of the .110" and the leftover is 1" thick, this is the part that the mounting fixture hangs on to while cutting. I use a CNC vertical mill with a fine tooth, 10" HSS blade and can get some exceptional cuts that don't require sanding which I, along with a bunch of indoor modelers feel that sanding damages, the cellular stucture and makes it weaker. The seperate sheets ranged from 5.24 to 3.87 lb in density, there is inconsistentcy in blocks so, one can't expect to get the weights that the blocks originally were and I got about 50% c-grain, 25% b-grain and the other 25% a-grain, I can't stand to loose that much wood to get all the choice c-grain. I also remount the block frequently because the block can start to bow because of internal stresses being released while cutting and I'm looking for straight wood.
I started by cutting the pieces to build up the leadout grooves, this is the inboard panel from the c/l in only and where that .110" balsa comes into play, they're the 4.4 lb outside skins and, I'll be using 4 lb, 3/32" for the core. I'm going to laminate the assembly with .75 lb glass, it'll stiffen the leadout grooves and when done weighs in at 8.8 gm or a density of 5.75 lb, I can live with that.
To the right is the sanding board I use to straighten and square up the edge joints. When sanding I tend to hold the sheet in the center, this cuts down on the rocking effect that tends to cause the ends to taper. I also stroke in the center of the sheet and run off the end of the sanding board to cut alittle more in the center. You want these edges to be perfect because, if not, and you try to force the joints together, you'll induce stress and the wing will probably start warping while sanding. I will use Elmer brand Carpenders Indoor Wood Glue to bond the wood together, starting with the butt joining of the leadout groove section and the front part of the outboard wing, 4.8 lb. Once glued, I use Scotch tape to hold them together and then insert between wax paper and two pieces of plate glass to cure for a couple of hours then start adding the inboard side pieces, stick between the glass for a few more hours and finish up the wing, one section at a time until completed. All the the remaining sections are single pieces with the grain running span wise. I want all the grain to run in the same direction vs the jigsaw puzzle method to minimize the different forces, or tension and hopefully reduce the chance of warpage.
The finished lamination is cut to size, at this point it weighs in at 66.5 gm before adding the hardwood. I'm going to add six round toothpicks on the outboard wing section 1.75" long spaced 1.5" from each other, running front to back on the horizontal centerline, behind the hardwood leading edge, this will help the balsa from being crushed from the blow of catching the model.
On the right is a picture of the leadout guide, it is made from a brass slug 5/8" diameter .073" thick, cut out a pie wedge, fold a piece of .010 brass shim stock and solder the wedge between, it'll give you a nice radius arcing back to prevent the lines from kinking, leave 5/32" for your line loops inside, I've also milled out the hardwood tip piece for the guide to be inserted into.
I'm going to use 3/16" x 9/32" basswood for the outboard wing leading edge and tips, 1/8" x 1/8" for the inboard side, ( none on the TE, carbon will be used here ) it's alittle easier to use these in a smaller thickness to facilitate sanding and, while the glue is drying, I'll insert the wing between my two pieces of glass.
Now it's time to start carving the airfoil. I mark the highpoint and then divide that into three, carve the first segment on one side then flip and carve the other, when the first segments are done, I mark another line in the middle of the carved segment and carve from the second segment to that one and so on, the same for the TE. I've found this way easy because you can hold the wing on the flat segments while carving. To taper the wing, carve from the TE to the first segment forward of the highpoint and then remark the forward lines and recarve the last segment of the LE.
For carving I use a small plane, 80 grit paper on a 6" t-bar type sanding block, 100 on a small 2 1/2" x 3 1/2" block, finish with a 320 block and then a 320 foam backed pad. Carve the TE to about .045" thick and taper the tips to .145".
