The trick to using carbon fiber is to use as little as possible and use the proper type of carbon fiber in the correct locations. I will give you a couple of examples. Well make that four.
"I" Beam Wings: I built a Super Ares two years ago and I used carbon fiber to reinforce the wing in certain areas. The main "I" beam was made from two ¼" balsa sheets with .2 ounce carbon fiber matt laminated between them with slow drying epoxy. The balsa leading and trailing edges had .004 x .250 carbon fiber strips glued to the insides along their full length. In my opinion the C/F makes the wing much stronger for a very little gain in weight.
"D" Tube Wings: One of my latest models is a Scratch Built 57 Nobler (green box) I sandwiched .004 C/F strips between the top of the spars and under the leading edge sheeting. In addition, I used the .5-ounce C/F matt between the balsa fuselage sides and the balsa fuselage doublers. I also used the .2-ounce matt and dope to cover the fuselage and the wing sheeting (I used silkspan on the open areas of the fuselage and wing).
Geodetic Wings: The main wing spar in my G-Force is made up of two sheets of 1/16" balsa that has .2-ounce C/F matt laminated between the two balsa sheets. The leading and trailing edges again, have .004 x .250 strips of C/F glued to the inside. I don't think the .004 C/F strips on the leading and trailing edges was totally necessary but I was glad they were there after hitting a post with the outboard wing at the team trials. It crunched the outer third of the wing but I was able to repair the wing and fly in the trials. One unique thing about the nose of the G-Force is that it has 1/8" balsa doublers with .5-ounce C/F matt laminated between them and the balsa fuselage sides (no plywood). The PA .61 (now it is powered with the .65) is radial mounted to a plywood firewall that was made from two pieces of 1/8" three ply plywood with .5-ounce matt laminated between them. The front end of the G-Force is time proven with seven years of flying (I know I need a new PA Ship).
Profile Fuselages: Use the .5-ounce C/F matt between the plywood fuselage doublers and the ½" balsa fuselage to add a tremendous amount of strength to the front end. The profile fuselage of the Primary Force is made up by laminating two pieces of ¼" balsa together. I found that adding .2-ounce C/F matt between the fuselage sides greatly increased the rigidity of the fuselage and eliminated or remove most of the stabilizer flex common to most profile fuselages.
A lot of people have their own Idea on how to use C/F and that's fine. I am just passing on what I have learned about its use for my applications.
by Tom Dixon
CLOTH HINGES MAKING A COMBACK?
This one's courtesy of Tom Dixon and the Cobb Co. (GA) Skyrebels newsletter: The concept of cloth hinges is "old technology" but is making a resurgence thanks to use and publicity by FAI Team member Bill Werwage and the "Cobra" article in FM by Mike Ditrich. The big advantage of cloth hinges is the automatic sealing of control surface gaps for increased efficiency. Old-style cloth hinges were always done with pinked aircraft tape, but these can be unsightly, and the muslin cloth can wear or rot. "New" cloth hinges are best done with taffeta per the Ditrich article, or, better yet, 1.5 oz. Fibreglass tape from Sig. The Sig tape is available in 1'' and 2'' widths. Cloth hinges should be applied full span to flaps and elevators to get the sealing effect.
To apply, first pre-glue the hinge line areas with Sigment. When dry, apply masking tape to the surface, top & bottom, about ½'' from the hingeline. Install the hinges in alternate "over & under" pattern to trailing edge of stab/wing, overlapping the masking tape. Use adequate Sigment to saturate the cloth, and rub the cloth/glue into the surface with a finger. Let dry.
Now use a sharp X-Acto blade or razor blade to trim the excess hinge material along the edge of the masking tape. Remove masking tape. Next, glue the free end of hinges to elevator/flaps. Tape or pin elevator to stab temporarily to reduce gap to zero. Let dry, remove pins/tape, and flex the surface to remove stiffness. Sand the glued area of the hinges with 220 paper and add a second coat of glue to fill the weave. Sand again when dry. Install your covering material over the hinges. I find it best to cover the whole stab/elevator unit in one piece, then "cut" the hinge line area with a piece of 220 paper folder over. Much neater than trying to cover "up to" the hinge line.
If using glass cloth and epoxy covering, cut the epoxy with alcohol so the hinge glue won't be softened. Once covered, filled, and sanded, glass cloth hinges are nearly invisible on the surface less visible than pin hinges, in fact. Cloth hinges are especially ideal on control surfaces ¼" or-less in thickness. The hinge line areas for cloth hinges should be "rounded" on both surfaces, rather than the square TE and angled LE used with pin-type hinges.
by John Miller aka JoeBellcrank
For really free hinges, it's most important to get the alignment correct. Whatever method you use to create the hinge slots, please take the time to center them. Make sure they are all in line and true. While most people use epoxies, or some other standard type of glue, the method I'm outlining uses thin Ca. I like the speed and ease I get by using Ca, but before learning this method, I never trusted Ca for hinges. You may doubt the strength, but prove it to yourself. I've never had one fail since I learned this method.
The key is to use an interface, something to help the Ca wick deeply into the slot, and help grab and hold the hinge. The interface of choice is common ordinary Silkspan. Other tissues may work, but since there's always some scrap pieces lying around the shop.......
Cut a strip of silkspan about the same width as the hinge. Cut the strip into lengths that are about 1/4 to 1/2 inches longer than the hinge tab times 2.
Fold these small strips in half.
We'll install the hinges in the movable surface first. There's a reason for this, we'll review why later.
Take one of these folded pieces of silkspan, and slip the hinge tab between the two surfaces of silkspan. push the silkspan and hinge tab into the slot. Do the same for all the hinges, but don't glue just yet. Once all the hinges are basically in place, take a minute to align the barrels.
I promised to explain why we start with the movable surface first. It's so we can align the barrels to help prevent binding later.
You did prepare the hinge barrel relief pockets didn't you? I hope so.
Hold the leading edge of the movable surface against a straight solid surface. A doorframe works well for this purpose. Put pressure against the leading edge. All the barrels should be aligned to the same depth. Those that are too deep should be re-positioned until they all are in line.
Use one of those small tube ca applicators. This allows you to accurately place the Ca exactly where you want it to go. Place the tip against the silkspan that is sticking out of the hinge pocket. You want to be right next to the pocket and the Silkspan. Squeeze in some Ca, not too much, but enough to wick deeply into the pocket. Wait a second, and turn the surface over, and do the other side in the same way.
Wait a few minutes, and you're ready to install the surface onto the fixed surface.
It helps to partially start the silkspan with a spare hinge. Just push them in a fraction of an inch.
Carefully insert the hinge tabs that are mounted in the movable surface. Once all are correctly positioned, and started, put some pressure on the trailing edge of the movable surface and seat all the hinges. Take some care to see that all the hinges are seated to the desired depth, and that the gap is what you want.
Push down slightly on the surface. By down, I mean in the direction of travel, and use your Ca applicator to wick some Ca into the top of the hinge tab. wait a minute, turn the plane over, and push down on the surface again, You'll be bending it opposite from before, and again wick some Ca into the hinge slot. Wait a few minutes. Work the surface a bit to make sure it's free.
Take your exacto knife and cut off the excess Silkspan protruding from the hinges.
Takes longer to type this than it takes to do it.
Good clean, aligned, and, if you did it right, free moving hinges.
Another great thing about this method is you can easily install them after you've finished the plane.
Try it on that old plane first if you have any doubts, Or at least make up a test piece first to try the method before you commit it to your new world beater.
I'm wondering why everything is spinning around?
Keith Varley has outlined how to prepare the hinges with Vasoline so the glue cannot wick into the hinge barrels. Take the time to read.
Put small amount of Vasoline in metal jar lid and lay it on your monocoat iron till it liquefies then with the hinge folded in half dip the hinge side in the very thin layer of melted vasoline and flip it inside out and do the same thing with the other side then let it sit for a minute till the applied vasoline solidifies and start with the slow cure epoxy trick. If you glue the hinges in the control surface first rather than the wing or tail surface you can push the folded hinges against a flat surface and at least the hinge pins are lined up in a straight line then that epoxy dries like several hours later you can epoxy (slow cure again) the hinges into the wing or stab . Of course watch to see if any epoxy squeezes out if the slot and wipe it off with a q tip (just like Dan says) and the next day after it is all cured you have a perfect hinge job. . The vasoline seems to prevent the epoxy from entering the dreaded pin part. Hi Keith Varley
by Randy Ryan
1. Cleanliness; clean the areas to be joined and a good portion around them. After you have them bright and clean, clean them. Not being funny, solder will not work in the presents of oxidation of the parent metal OR the plating that might be on it. CLEAN IT BRIGHT!
2. Fluxes; there are many, but the most easily obtained and applied is common Plumbers Paste. Contrary to common belief, this paste works well on all solderable metals, including steel. It is also the easiest to clean up with a little lacquer or dope thinner. It not only keeps the metal clean when being heated, it aids in heat transfer. I use it in all of my soldering except electronics. A thin coat on the tank parts will improve the flow ability of the solder tremendously. Apply AFTER CLEANING!!
3. Fits; solder is not a great gap filler though it will do some, make sure your parts fit well with a minimum of gaps.
4. The tools; I use a gun for most of my soldering including tanks. The common Weller gun has a tip that is held into the heating elements via 2 hollow jam nuts. I have found almost exclusively that people trying to use these have trouble with heating the tip. This is because the thermal cycling of use both loosens the nuts and oxidizes the tip were its supposed to make contact. Before starting to solder, loosen and snug these nuts a couple times, you'll be amazed at the difference in heating speed and transfer. This holds true for the smaller irons with removable tips too, loosen and snug to get a good joint that will transfer heat well.
The tips (soldering end) are also a point were much difficulty arises. The most common shape with gun tips is a chisel point, some irons use this as well as a pyramid shaped tip. During the use of the gun or iron, the tip erodes and will become pitted. Its odd that its normally the flats that erode while the edges tend to remain intact. Always inspect the tip before you start, if you see ANY pitting or evidence of concavity, file the tip until the surface shows only copper, apply a film of paste, heat and "tin" the tip. The solder should readily cover the surfaces, if not one of two things has occurred. Either the surface wasn't clean enough, or you waited too long to apply the solder and it overheated. A good practice it to test the heat while heating by brushing the solder over the tip, when the temp is right, the solder will melt.
A damp rag or sponge are handy for wiping away burn flux and debris from the tip occasionally.
5. Soldering; now that the parts and tools are ready there is a third problem allot of folks experience, getting the solder on the parts. The first thing to do is make sure your tool is hot enough. In the case of the gun, test it as above to make sure its heated enough, DO NOT place it against the work while it heats, this will both slow down the process and cause "cold" joints. With the heat right, touch the tip to the work and the solder to the WORK, not the tool, at the tip, touching the tip is OK, but you won't know if the work is hot enough to be soldered unless you put the solder on it. When I solder I normally lead the tip with the solder along a seam with it just barely touching the tip, you want the work to melt the solder or the joint will be bad. When soldering tubes, apply the tip to both the tank and tube simultaneously and then the solder to the join. If you cleaned and fluxed it properly and the tool is in good condition and heated properly, the solder will flow around the tube readily and "sweat" the tube into the tank. When soldering things like washers to LG axles, apply heat to the end of the wire and the solder to the wire between the tip and washer. As soon as the melt occurs, lead the molten solder down to the joint and it will flow right in.
Another thought, when soldering washers to wire, make a cardboard dam that fits snuggly to the wire. Put this on followed by the washer then solder. This will do a couple things for you, first it hold a clearance between the washer and the part the wire is being retained in, usually a wheel. Second it will slow the heat flow down the wire, third, it will help keep flux out of the wheel or bushing of the part you are retaining.