HANDS ON
STEP BY STEP
HINTS FOR HOMEBUILDERS
1 STEP 1/ Here’s a completed flared tubing connection, as well as the individual parts you’ll need to make one. The tubing is typically 5052-0 aluminum; you’ll need to know the outside diameter of the tubing to get the correct fittings. You’ll need an AN819 coupling sleeve and an AN818 coupling nut for each connection.
Fabricating Flared Tubing By Joe Norris
RegaRdless of the aiRcRaft you’re working on, sooner or later you’ll need to fabricate a fuel, oil, or hydraulic line. The most common way to connect these lines is with AN fittings. These fittings require the tubing to be terminated with a 37-degree flare. Note that this is different than the flare used on automotive lines, which are typically terminated with a 45-degree flare. This means that you’ll need proper tools to install the fittings on your aviation lines. Don’t use your automotive brake-line flaring tool as this will not give you the proper flare and will end up causing you problems.
Let’s take a look at the process for fabricating these flared connections.
5 STEP 5/ Next you’ll need an aviation flaring tool. This tool will actually form the 37-degree flare on the end of the tubing. There are several styles, but each will do the same job. The flaring tools are typically set up to flare a variety of tubing diameters, so you’ll need to pick the proper die on the tool for the tubing diameter you’re working with. The tool will also include a depth gauge that will allow you to seat your tubing in the tool to the proper depth so that the flare will be correctly formed.
2 STEP 2/ You’ll need several tools. First you’ll need a way to cut the tubing. You can cut it with a hacksaw or cutoff wheel, but the best way is to use a tubing cutter, as shown here. A few turns around the tube with the tubing cutter, tightening the cutter a little at a time and not trying to do too much at once, will result in a clean, straight, true cut and make the rest of the installation go much smoother.
6 STEP 6/ Lubricate the tool with some light oil and turn the handle until the tool bottoms in the die. Don’t force it! You don’t need a lot of pressure to accomplish your goal. Just turn it until it feels like it has bottomed out and stop there.
7 3 STEP 3/ Deburr the end of your tube. Use a hand file or Scotch-Brite wheel for the outside. For the inside you can use a deburring tool as shown here, or you can do it by hand with the tool that comes with your tubing cutter. You want a nice, clean end with no burrs so that your flare will turn out straight and true.
STEP 7/ You’ll end up with a nice, clean, true flare. You’ll want to carefully inspect the flare to make sure you didn’t crack the edge (which will happen if you put too much pressure on the tool when forming the flare). You’ll also want to blow out the tube with some compressed air after you’ve formed the flares on both ends to make sure there’s no debris or contamination in the tube before installing it on your aircraft.
37 ̊ 4 STEP 4/ Don’t forget to put your AN818 coupling nut and AN819 coupling sleeve on your tube before you form the flare. This is especially important if you’ve already flared the other end of the tube, otherwise there’s no way to get the coupling sleeve or nut on the tube after you’ve flared the end.
78 Sport Aviation January 2010
8 STEP 8/ Here’s your finished product! The coupling nut and sleeve will tighten the flare against the appropriate fitting on your aircraft to complete a simple, leak-free connection.
PHOTOGRAPHY BY JIM KOEPNICK
TIe WRAP STAndOFFS
By Joe Norris
Builders have several options for routing and securing cables, lines, and wire bundles. One option is to make standoffs out of tie wraps (sometimes called “zip ties”) and short pieces of hose. Here’s how to do it.
1/ Cut a short piece of hose to use as the standoff. This can be the same hose used for fuel line on a light plane, or it may be vinyl tubing or something similar. (The length of tubing you cut will determine the height of the standoff, assuming that your tie wrap is long enough!) 2/ Pass your tie wrap through your piece of tubing, around the line or bundle being secured, and then back through the tubing again.
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3/ Place the open end of your tie wrap around the tube or structural member you are using to secure the line or bundle. It may be a good idea to cushion the tube with some rubberized tape to prevent the tie wrap from chafing the tube. 4/ Pull the tie wrap tight around the structure, trim off the end, and you’re done!
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HANDS ON
HINTS FOR HOMEBUILDERS
Bending Cap Strips BY JOE NORRIS
WOOD IS A WONDERFUL material for building an aircraft. It has “memory.” That is, it can be deflected to an amazing degree and will still return to its original shape. But this memory can sometimes cause the builder problems during construction. One example is when building wood wing ribs. The top and bottom components of the rib, called cap strips, are curved to give the wing its proper airfoil shape. Of course, the pieces of wood used to build the rib are all straight sticks. Sometimes builders are able to force the straight cap strip pieces into the rib jig and hold them in place while assembling the rib, but it would be better if the cap strips had some curve to them before assembly. Here’s an easy way to pre-form the cap strips. You’ll need a large block of wood that will become your forming jig. A 4-inch by 4-inch post works great for this. Take a length of the 4-by-4 and draw on it an arbitrary curve. You’ll want the curve to be fairly gentle on one end and a bit tighter on the other. The amount of curve is not critical and doesn’t need to be a tight radius. After you’ve drawn your curve, cut the curve with your band saw. View Illustration 1 to see what your block will look like after it’s been cut. The top cap strips for your rib will probably need to be curved a bit more than your bottom cap strips. (The bottom ones may even be straight.) The amount of pre-set curve in your cap strip will depend on how far into the block you put the wood. It might take a couple of trial-and-error attempts before you find the exact curve that works best for your project. The curve doesn’t have to be exact, because all you’re doing is making it easier to fit the cap strips into the rib jig. The jig will hold the cap strips in position for the appropriate airfoil shape when you assemble the rib. You need to soak your cap strips in water to make them flexible and ready to be pre-curved. You can
do this by leaving them in water overnight, or you can heat up water to near boiling and soak the cap strips for a half-hour or so and they’ll be ready. Once you determine how much curve you want to put in the cap strips, you can mark a line on the inside of your block where the end of the cap strip needs to be positioned to get a consistent curve. You can then line up a number of cap strips in the block and clamp the block halves together, trapping the cap strips in the curved jig. Illustration 2 shows the cap strips clamped in the block using a vise. You could also use C-clamps or bar clamps, or you may have another way to clamp the blocks together while the cap strips dry. Just don’t clamp the block together so tightly that you crush the cap strips. You need to put only enough pressure on them to get them to take the curve. Leave the cap strips clamped in the block until they’re completely dry. This will probably be at least overnight, but don’t be in a rush. A full day might be needed to get the cap strips to dry thoroughly. Once the cap strips have dried you can remove them from the block; you’ll find they now have a nice, gentle curve that will fit in your rib jig much more nicely and make assembling your rib a snap!
STEP BY STEP
Illustration 1 shows what your block will look like after it’s been cut.
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Illustration 2 shows the cap strips clamped in the block using a vise.
80 Sport Aviation January 2010
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