CONTROL LINE AEROBATICS - 2003/04
Curt Contrata, 6783 Nightwind Cir., Orlando FL 32818; E-mail: [email protected]
A good airplane
A good airplane is much more fun to fly than a lousy one. This is true whether you are a Sunday flier or trying to win the Nationals. I define "good" not just as an excellent-flying airplane, but one that is not plagued with problems or compromises. I describe a model that always performs well and never gives you a hard time. A good airplane is a pleasure to fly and quickly becomes a natural extension of you.
So how does one create such a model? More than anything, it is a commitment of two things: attention to detail and a realization that each model you make will be better than the previous model. Your attention to detail must be consistent throughout the construction process. You cannot decide to start building a straight airplane at the time you are installing the wing into the fuselage. A straight airplane begins when you are cutting out the parts.
Just because you are assembling the wing on a board or in a fixture does not mean you cannot build a warp into it. Attention to detail means that every spar slot in every rib aligns perfectly. Take your time with the ribs, making sure that when they're stacked they all match at the leading edge, the spars, and the trailing edge. (If you are building on rods, the holes for them must be cut accurately.) During this process I mark the tops of the inboard ribs with one color marker and the tops of the outboard ribs with a different color. This way I can quickly put them back in the same order when construction starts. A straight wing starts with a set of ribs that are true. Never assume a set of kit ribs to be perfect; stack the ribs, check them for accuracy, and mark the tops in contrasting colors.
Avoid building stresses
You want to avoid building stresses into the model. This can occur when parts don't quite fit together and you force them to. It can also happen when two pieces are warped and you force them straight during construction. A common occurrence of this is at the trailing edge. Wings often call for 1/16" balsa on the top and bottom of the trailing edge. If one straight piece of 3-inch stock is simply split in half, it will typically generate two slightly curved pieces.
If those curved trailing-edge pieces are used to construct a wing by being forced straight during assembly, the wing will usually develop a warp at some point—often sooner than later. Try cutting long parts out by cutting them a little at a time from each side, to sort of sneak up on a straight part. The problem is that each time you make a long cut on a sheet, the sheet will curl. It curls less with each cut. Alternating sides as you cut will result in straighter parts.
It is okay to waste a little wood here; use the scrap for cap strips or stabilizer ribs, but don't use curved pieces for trailing-edge parts. Paying attention to detail is harder than you think. You can never stop or be relaxed; that is the difficult part. Every part of the construction process is important, and every part will directly contribute to the model's ultimate success. The more you think this way, the easier it becomes to care about each step, and the desire to make the next model even better becomes a natural thought process.
Have you ever had a stabilizer go crooked in the fuselage when you glued on the top and bottom blocks? Straight parts and perfect fits are always important. Twisted parts will twist your airplane every time. How much is your time worth? I suspect it is worth more than the bit of balsa you will throw away. Perfect fits with unstressed parts should be your goal.
Models built this way are not just straighter—they are stronger and lighter. They are lighter because perfect fits require less glue.
On ARFs and craftsmanship
If ARFs (Almost Ready-to-Flys) are indeed the future of this hobby, realize that each model you build is among the last to be built. Fewer and fewer people are doing what we do, so enjoy every step as if you were among the last remaining craftsmen. Take pride in everything you do, including making your own tools. The most important tools you can make only take a minute. I generally make one or two more every time I build a model; they are my sanding blocks.
Sanding blocks and small tools
You should have a large collection of sanding blocks of various sizes, shapes, and materials. Your small blocks should be lightweight and true. A block of 3/8" balsa might make a nice small block to sand with for a while, but it will not maintain a flat shape over time. Glue a piece of 1/16" plywood to the bottom of it, then sand it flush to the edges. Use cyanoacrylate (CyA) glue or waterproof glue, and you can wet-sand with it too.
I made my rectangular blocks in sizes that can get nice cuts from one sheet of sandpaper. The smaller you make the blocks, the more cuts you will get per sheet of sandpaper. It is best to use fresh sandpaper, and smaller pieces are easier for me to throw away.
Another great block I have was made from one of the core pieces of a foam wing. At 3 inches long and wrapped with 1/64" plywood, it is perfect to sand a hollow into something, such as a scoop on a cowl. It is better than a dowel because it won't gouge. Shaped like a small leading edge back to the high point, it is a "multiradius sanding block." I also use it when I am blending a canopy. That fillet is typically difficult to use a block on.
I have several different blocks for fillets. My first used a carbon arrow shaft. I made a slot on one side using a cutting wheel. I inserted 1/16" plywood into the slot to make a handle, then I built up the handle flush to the shaft with balsa and CyA. My style has since changed, and my fillets have gotten smaller with each model. I am finding myself making a new fillet block for each model. The last few have been made from maple.
I do need to stress the purpose of using a block in the first place. You are trying to accurately shape something—to knock down the high spots and reveal the low ones. On a fillet, you are trying to maintain the same radius on every one for the entire model. If you make your own radius on a maple block, make sure it is the same radius on both ends of the block. All mine have been approximately 2 inches long.
Make a maple sanding block for notching your flaps for hinges. I have one that is just wider than the hinges I use, with a piece of 220-grit sandpaper glued to one side and trimmed clean along the edges. After I have the flap slotted for the hinge, I use this block to cut the notch to inset the hinge. As with all the blocks, I use the same one throughout the finishing process with finer and finer grits.
Foam blocks are a newer addition to my block collection. 3M makes them, and they are black foam pads that are great for wet-sanding. Roughly 1/4" thick, they are thin enough for you to maintain the feeling of the surface, but scratch less since your fingertips are not pressing on two or three small spots.
You should also have at least a couple aluminum bar sanders. They come in many sizes and shapes, but you should definitely have a 6- and a 36-inch T-bar sander.
- The refill self-adhesive paper for them is great when stuck to your bench for sanding parts' edges.
Accurate sanding and finishing
Accurate sanding is an important part of accurate building. Every part I cut is sanded before assembly. Sometimes I find it easier to sand a part to shape than to cut it out.
Pay attention to sound and feel. When shaping, it is common for high spots to be the hard ones, such as glue or hardwood. Hard spots sound different when they are being sanded, so listen closely. A hard-surfaced, lightweight block, used with light pressure, will allow you to feel the shape develop better than a heavy rubber one, and you will be able to better hear what you are sanding.
You will appreciate the better fit of the parts during assembly. The assembled accurate parts will more easily become a straight wing and fuselage, and the perfect fits create stronger, lighter joints. Aligning a true wing into a true fuselage will be easier because each will be straight. Not having to decide "which centerline" to use, it will almost align itself.
When you get to the finish, the care in construction and the use of sanding blocks throughout will have produced a model that will be much easier to finish. And typically when people take the time to be real craftsmen in their construction, they are less likely to bang a wingtip into the edge of the bench. This means there should be fewer dings to fill as well.
Once in the air, a well-built model is its own reward.
Transcribed from original scans by AI. Minor OCR errors may remain.
