What is the best way to fill pinholes in fiberglass fuselages and / or composite wings?

Bob Matheson, of Cloud-9 Models, suggests the following:
Unless you use more epoxy than legally allowed by law, you are gonna have pinholes. I don't think my method is that different, but maybe the material I use is. So check this out, it goes pretty quick.

Carbon wings usually have wax residue left on them from the bagging process, so I rub it down several times with denatured alcohol. There is still a little wax left, so I wet sand with 400 grit paper. Now get you some Elmers fill-n-finish, its a wood filler- but it sticks real good to fiber glass stuff. The substance is like peanut butter right out of the tub, ( but don't eat it, cause it smells like ammonia). So take a spoonful or two, add water to it till its like sour cream, it will spread lots faster. Now take your favorite credit card, (I recommend your overextended one ), and spread away, scraping as much off as you can.

By the time you get to the other end, you are ready to take a damp, not wet, paper towel and whip off the Elmers residue left on the surface. I go through this process twice and it takes less than twenty-five minutes. OH, guess what, they got so much of that Elmers fill-n-finish at Home Depot, they'll sell you some, cheap. Till nest time fly high and come scream'n down!!

What is the proper technique to repair the cracks around the canopy area in a fiberglass fuselage?

Been there! Done that! So has almost every other thermal pilot who participates in that most sophis-ticated of all tasks, the "Dork" landing. The following technique has been used by me very successfully, on more than one occasion.

Begin by resetting the fuse to it’s original form. This only applies if the fuse is damaged to the extent that when you run your fingers over the damaged areas you can feel a separation ridge. Do as much as you can now to restore the fuse to it’s original form.

In the next step you should sand the inside of fuse to roughen the surface, then clean the area with some alcohol to make sure the area is dust and dirt free.

After the area has dried thoroughly, take some carbon fiber strips (the iron on kind), apply a mist coat of 3M77 spray to one side of the carbon fiber strips and apply them spanwise to the cracked areas. Take a patch of medium weight (4-6 oz.) glass cloth that will cover the inside of the fuse from one side of the canopy to the other and approximately two inches wide and apply a mist coat of 3M77 spray to one side. Fit the fiberglass into the fuse and over the carbon fiber strips so that it lays smoothly against the fuse. Make sure everything is smooth

With an epoxy brush apply a wet coat of West Systems epoxy or 30 minute epoxy to the fiberglass so that the fiberglass appears to disappear showing only the carbon fiber strips and the fuse. Wipe the excess epoxy off your brush with a paper towel and use the brush to remove any excess epoxy on the patch. Put the fuse away and come back in about two days. The fuse should be stiff as a board.

If there are any external cracks that have not been filled by this process, simply take some Bondo Scratch and Dent Repair and fill them in. This may take a couple of sessions before you get it completely smooth but it works. Sand it down, apply some primer, wet sand it until you can start to see the fuse through the primer. Make sure the area is clean then allow to dry. Apply final paint in a few light coats. Let dry for a day or two. The longer the better.

If you wax the area around the repair that you do not want to paint and you restrict - as much as possible - the overspray, removing the overspray can be done easily by polishing the entire fuse with fine polish (Meguiar’s) or, if necessary, apply a coat of white rubbing compound. When all is nice and smooth, apply a coat of wax and the fuse will shine like new.

What’s the best way to wire a Dean’s connector?

I can’t speak for every-one but this is how I was taught and it has worked great for me.

Generally I use the Dean’s 4 pin connector for two wing servo connections (wing with flap and ailerons). As you will note, the Deans connector has one pin which is separated from the other two or three (depending on whether it is a 3 or 4 pin connector). I always connect my positive (+) wire(s) to that pin. I then proceed in the following manner: First pin on other side of the positive pin is where I connect the Ground (-) wire(s). The next pin is used for the flap signal wire and the forth pin is used for the aileron signal wire. If I am only using a three pin connecor (one wing servo) the third pin is for the signal wire.

I selected this wiring system because it made sense to me. The flap servo is closest and the aileron is beyond that. With this system, I never have to worry about cross wiring.

Whats the best way to solder the wires to the connector?

Ron Scharck
First, strip just enough insulation off the wire to allow the bare wires to lay on the pin. Then, take the two positive leads and twist them so that the exposed wires becomes one. Do the same for the ground leads (I also twist each signal wire to make sure of a tight cable wind). I then dip the exposed wires into a flux paste and proceed to tin the exposed tips with solder. Use the thin silver solder for electical connections that you can buy at Radio Shack. I likewise lightly tin each of the 4 pins (no need to use flux on the pins).

Now cut four pieces of small diameter heat shrink tubing approximately 1/2 " long. Slip a piece of the tubing over each lead and move it far enough back from the solder joint to insure it doesn't shrink during the solder process. With the Deans connector held securely in a "third hand" devise, I tin the end of the solder pencil and place the pencil on the pin and place the wires on top of the pin. There should be an instant solder joint that takes place. You know you have a good solder joint when the solder shines after the solder pencil is withdrawn and the joint cools.

Always test your solder joint visually and with a good pull. If you do not have a complete solder joint between the pin and the wires, touch the solder pencil to the joint, remove the wire and try again. Always remember that each solder joint can, if not done properly, cost you a plane and possible a airborn pack. After you have completed all four connections, slide the heat shrink tubing over the joints and shrink with your heat gun. As an extra precaution, I will slip another, larger (just large enough to fit over the Deans connector) piece of heat shrink material over the four connections and halfway onto the Deans connector and than shrink it down. This helps prevent stress on the wires at the end of the solder joint.

Soldering is an art. But, with a little practice, you can become an artist.

What is the best way to install servos in the wing of my plane?

There are a number of ways to mount servos in your wings. Here are a few of the better ways:

Joe Thomas
Servos can be taped in place in the wings if they fit tightly to begin with. I cut my servo holes to the shape and depth of the servo for a snug fit. The only areas that are loose are around the output shaft and the wire inlet. The holes are marked, then routed out with a Dremel tool. If your existing holes are too large for the servos you want to use, fill the holes with some foam.

I recently removed four wing servos that were mounted with RTV silicone. They were not difficult to remove, and the foam was not damaged. Use a small amount of RTV. If the servos fit snugly, they won't come loose.

Karlton Spindle
If you glue your servos in they are hard if not impossible to service. Sung up the fit with balsa and tape in place. Or better yet, use SERVO CANS by Critter Bits.

Fred Guilfoyle
I line the bottom of my servo "well" with a piece of 1/64 or (epoxied in place), then I mix a small batch of 5 min epoxy with some cabosil in it to thicken it to peanut butter consistency, I put 4 little dabs on the corners of the servo and push it into the well. If you need to remove the servo, I've found that they will "pop" out if you pry on them a little. Use a dental tool to get 'under' the servo. The epoxy does not seem to bond with a death grip on the servo. I've been able to chip off all the old epoxy from case after removal. By the way, I've found that you can go to a sign shop and buy colored vinyl to use for servo covers. They are thicker than Monokote and are somewhat flexible.

Herb Stober
Have you given consideration to mounting the servo on the hatch covering the servo well?

Mike Hines
One method that I have been pleased with is to cut a cover of 1/64 ply slightly larger than the well in the wing.

After cutting a slot or notch for the servo arm test fit to wing and make a ledge around well so that the cover is flush with the wing surface. Then I attach the servo to the cover with a dab of PFM. Make sure to get the glue only on the body of the servo and not the cover or you won't be able to remove it later for service.

After the glue has set place the servos in the wing and do your initial setup, when satisfied that you are close to what you want simply tape the covers to the bottom of the wing with a piece of 3" clear tape, the packing variety seems to work fine. Of course this is but one of a number of options, but it works for me.

I am in the finishing stages of completing a Climmax hand launch glider, and was wondering what is the optimum method and location of the launch grip?

Paul Naton
The location of the rear bulk-head will guide you as to where the launch grip should be located. Charlie (Richardson) and I tested every peg position and the 'stock location' has been proven to be the best. It looks far back, but it gives you good rotation on launch especially when the CG is set close to neutral.

As to type (method) of launch grip, I prefer a carbon fiber hollow peg centered in the fuse and butted up behind the bulk head. Any 1/4" peg will work. I get much better control and power from the round peg and you don't weaken the fuse with a (finger) hole.

Another form of launch method is what I call 'Wings', which are finger rests on either side of the fuse that are generally made out of 1/8" plywood. The reason I call them wings is because they are usually shaped so as to reduce parasitic drag. While the theory is good, "wings" can cause quick blisters if not shaped right. For me, the peg seems to give good surface area and really no drag penalty.

What is "memory" in nicads and what causes it?

Extracted from a Ni-Cd seminar by Red Scholefield
Memory is a step in the discharge curve of a cell. Contrary to popular belief, the memory effect is not a loss of cell capacity. Actually there are two ways to create a step in the voltage profile. One is a precisely repetitive partial discharge followed by a slow full charge. The discharge must be to exactly thesame point every discharge in order for this effect to appear.

The second and more frequently encountered effect is voltage depression which is also called memory. This is caused by continuous overcharge at the overnight rate. If a battery is left on slow charge for long periods, the crystals of active material in the plates grow larger. As the crystals grow, the surface area of active material in contact with the electrolyte decreases and this phenomenon manifests itself as a very slight increase in internal resistance, plus a decrease in the open circuit voltage.

The voltage step will occur at different times, depending upon how long the overcharge occurs and the temperature of the battery in overcharge. As the overcharge continues, the area of voltage depression will occur earlier in the discharge curve. The area of depression can be removed by one or more discharge/charge cycles, thereby returning the cell's voltage profile to normal. Today's cell designs have improved to the point where this condition is seldom exhibited.

How many ounces of epoxy is enough to sheet a 60 inch wing panel?

Rob Glover
It somewhat depends on the sheeting material. Here is what I do and the results.

Balsa — I use slightly thickened laminating resin, wipe it on and then wipe off all of it that I can. No puddles, No sheen. If the resin will soak through a sheet of 1/32'' soft balsa then it needs to be thicker.

Obeche — I use more thickened (peanut butter consistency) laminating resin, spread it on then wipe nearly all of it back off. No puddles, maybe just a little sheen. Cut some notches in the edge of a spreader like a tile glue spreader has. Better yet, stick with balsa. It's gonna be lighter, and works better.

The weight gain should be well under an ounce. Thicken the resin with equal parts cabosil and micro balloons to the desired working consistency. If it's cool where your bags are curing your wife obviously needs a new electric blanket. The old one may be wrapped around the curing parts, turned on high, and left overnight. Works great, I even use one in the summer.

How do you remove monokote smears ?

Thomas Akers
If you use Monokote, sooner or later you will find one color "bleeding" onto the other. Actually, this is the Monokote adhesive melting at the seam line that is causing this problem. Not to worry. After you have finished monokoting your plane, simply reach over and get some acetone and, with a protective rubber glove on hand, moisten a folded paper towel with the acetone and gently wipe along the seam lines. Like magic, it’s gone.

Another method I have read about is Monokote Trim solvent. According to the article it works great. Monokote Trim Solvent is available at most hobby shops that carry Monokote. It contains cyclohexanone, naphtha, and acetone. I use acetone because it works, it’s readily available (any place that sells paint) and it is relatively inexpensive. Actually I use acetone for quite a few things around my shop. Always use products like this in a well ventilated area (outdoors is best) with protective gloves, eyewear,etc. If used properly acetone is safe to use.

Is there a problem pouring unuesd epoxy resin and hardner back into their respective containers?

This is a definite shop no-no! Never pour resin back into its container.Contaminates will undoubtedly find their way into the cups that you are using and then you will allow them to find their way to your resin.

Every thing from the wax on the cups to floating balsa particles are hazerdous to the life expectancy of your resin. Heaven forbid what would happen if you absent mindedly mixed up the cups!

What is the best way to mount the flight pack in a HLG?

I have tried a number of mounting systems with varying degrees of success. The one that I am now using, and I believe to to the best, actually came from Fred Mallett.

Take a piece of basswood (a 1/8" by the width of the servos you are using by how ever long you need to mount your servos, receiver and, if you like, your battery pack) and drill a hole in the center of the wood strip large enough to sink a 2-56 blind nut (use two nuts, one front - one rear, if mounting the battery pack on the same rail).

The servos are glued to the strip with "Household Goop". Then you apply a strip of Velcro (the hook side) to the strip in the same manner. Then apply the "felt side" of the Velcro to the bottom of the receiver. Goop takes a while to cure but once it does, your set (if you need to, you can cut the glue joint with a hobby knife). I apply pressure to the glue joints while they are curing. When all is dry, press the receiver into place and you have what you see below.

Use the pack to balance the plane, locate the hole(s) for the blind nut(s) and drill through the bottom of the fuse. Secure with 2-56 bolts. If you need to switch airborne packs all you need is a screwdriver. Is this neat or what?

What’s the best way to install a wing rod in a fiberglass fuse?

Carl Otto
Take some 1/8' plywood, drill a hole the appropriate size (best with a drill press so it is vertical and not oversized) for the wing rod. With the rod through the ply AND the wing, trace the outline of the root onto the ply. Take the plywood off, trim down the excess, put it back on and trim/sand it as close as you can to the shape of the wing root. Now take the plywood off and tape it on the fuse in the best position, like making the top of the rib flush with the top of the fuse. Repeat this entire procedure for the other side. Make sure the these plywood forms are now symmetrically attached; eyeballing it, feeling it and simple measurements will suffice. You now have a template to drill the holes in the fuse (through the holes in the plywood rib). I do the alignment pins as a separate last step.

I personally like this method better because you can run your finger along the top and know whether or not it is flush with the fuse and whether or not both sides feel the same. I think the biggest advantage is that it gives you a guide for the drill bit. I have done three planes like this and they all came out perfectly. I have used the paper template method with less than ideal results but read on for the cure!

If things somehow get screwed up, don't despair. If the wings don't fit properly, drill out the holes until you can get the wings fitting properly. This will leave you with some oversized holes in the fuse. Spray the wing rod with mold release, or something similar, and let it dry. Mix up some epoxy, I usually use the good stuff that cures overnight. Cover the wing roots with Scotch tape and poke a hole through that for the wing rod. Put the wing rod in the fuse, put some epoxy around it in the oversized hole and wipe any excess off the outside of the fuse. Put the wings on, adjust them to proper fit with the fuse, tape in place and let it all cure overnight. Next day take the wings off, mix up some more epoxy and fill in any space left around the wing rod. You can also make a little fillet around the wing rod inside the fuse if you want. After this sets overnight again, tap the wing rod out. It should release easily. Clean up any excess with an exacto blade or sand paper and you end up with a perfect fit.

After the wing fit is perfect, then I do the alignment pins. I use a separate pin in each wing. I drill the hole in the fuse first and then corresponding but slightly oversized hole in the wing rib. I try to put the pin 1/2' into the wing with at least 1/2' going into the fuse. I fill the hole in the fuse with epoxy, cover with scotch tape, and then poke the pin into the wing. With the wing rod in place I slide wing on. I use a hemostat to be sure at least 1/2' sticks into the fuse. I do this on both sides, and then use an incidence meter to make sure the wing incidences match, then fix the wings in place. I check the incidence of the wings a couple more times, then let the epoxy set up. An advantage to the oversize hole in the wing root for the incidence pin is that if you do mess up the incidence, you can heat the epoxy and make some adjustment to the pin.

This all sounds rather complex when written out, but really is pretty simple and doesn't take that much time and the wings come out perfect.

What is a good primer on Aerodynamics?

Chris Bruner
Buy Martin Simons's "Model Aircraft Aerodynamics." Read it, think about it, then read it again. Then read it again after flying for six months with what you learned the first two times.

I am a professional aerodynamicist, and I've read this book at least six times over the years. No, you don't need an engineering degree to understand it. It's excellent!

How do you make a good building board?

There are building boards and there are BUILDING BOARDS! "How much room do you have?" Seriously, the answer is "as long and wide, as true and straight as possible. The ideal board for me is 4’x8’. This is the size I use now. Regardless of the size, the emphasis is on "true and straight."

Let’s start with the basics. The absolute minimum building board I would make would be 24"x 48". My first building board consisted of a piece of 5/8" plywood, 24"x 48" in size. I bought a good grade of plywood and made sure that it was straight and true. The reason for the good grade of thicker ply is that it will hold its shape.

The next step is to buy a 24"x 48" ceiling tile (Celotex is the same material as ceiling tile) preferably without any holes on the painted side. Now tape the ceiling tile onto the plywood securely with masking tape so that it is one with the ply. The Celotex will allow you to pin down things which you will need to do when you are building. When one side gets used up, turn it over and you have a new surface.

Now find a piece of scrap plate glass at least 1/4" thick. Have it cut to 18"x48" (if you find a piece that is slightly smaller than this use it . Tape the edges, or better yet bevel the edges, to keep from cutting yourself. Lay the glass on top of the Celotex. Why glass? It makes a perfect cutting surface, particularly for covering material and fiberglass cloth in conjunction with a rotary wheel cutter. Glue, CA and epoxy may be scrapped off with a razor blade I leave mine on my work bench at all times, except when I need to pin something.

How much does all this cost? At the outside, the plywood is approximately $10, the Celotex tile $3 and the plate glass? How much time do you want to spend finding a piece of scrap plate glass. I told a friend of mine who goes to garage sales all the time to keep an eye out for the glass. Two weeks and $5 later I owned a piece of 3/8" beveled glass 17"x50" with a chip in one corner...darn it!

Other sources of building board include: Doors (stick with a solid core door if possible. Try and find one that is damaged slightly. It won’t hurt your building but it will help your wallet.); Folding tables; thick glass (1/2" or better).

Whatever you use for a base, be it plywood, a door, a folding table, etc., make sure that it is straight and level. Your planes will fly better!

What is the proper way to dispose of NiCad batteries?

Cadmium is highly toxic. It should NOT go to the landfill. Both Hobby Shack and Discount Hobby Warehouse have nicad battery recycling centers. Radio Shack stores also accept used NiCads for recycling. Many towns and cities also have a NiCad program, but drop off sites are usually few and far between.

What is the real difference between the "Standard" and "2M" Hi-Start ? I am flying a DAW 1-26.

Bob Sliff
The thicker stuff (Standard) will recoil quicker and with more force, so it will accellerate a larger/heavier ship to flying speed quicker. In fact, a small rubber hi start may not even be able to impart enough acceleration to get a larger/heavier plane to its needed flying speed. On the other hand, if you have a really weakly designed model (of which your 1-26 is not) the standard hi start can over stress the wing and possibley break it.

After the initial acceleration and the general relaxing of the rubber, it is the breeze that gets you to the full length of the line. With no breeze, you only get as highas the rubber recoil can toss you.

The recoil of the tubing can only get you so high on its own. You need a breeze to get you the rest of the way, much as a kite works. Usually, if you are able to reach the top where the plane has the line and tubing pulled full length straight up, you are really at that point where you are restretching the rubber. You can then use this restretch to add some extra accelleration to the model, and thus produce a mild zoom launch.

What is the best way to repair the cut in my hi-start’s rubber tubing?

Russ Young
I use little precut dowels that I get at the big hardware stores. These little dowels are about 1.5" long and 1/4" dia. and have little ridges running the length all the way around. I think these are normally used for building furnature. I coat the inside of the tubing with CA, then pushed the dowel halfway in...hurry...you don't get a second chance! Then coat the other side and push it so the tubing meets in the middle.

Need a FREE wheel to store your hi start? I was looking to buy a reel in the same store. There on the wall in the electrical section, were rows and rows of hi-start reels. Most of them had electrical wire on them, but there were at least three that were empty. The reels had molded plastic sides and a large, thick cardboard tube for the center section. The sides have the holes in all the right places for winding, etc. The clerk gives them away to anyone that asks.

Repairing Fiberglass

Don Clark
Editors Note: Don Clark knows what he is writing about as In a previous life the author designed and built yachts and world-class racing sailboats using advanced composit techniques and materials.

There seems to be as many different approaches to repairing composite airplanes as there are pilots. Most of these different techniques probably work out pretty well but, as in any other construction, composite structures and repairs should be engineered for maximum strength and light weight. Also, there always is an easy way and a hard way to accomplish a task. Maybe some of the ideas presented here will be easier than the ones you’re used to.

Listed below are some of the tools and materials you’ll need.

The Tools

• Popsicle sticks or other mixing sticks
• Plastic mixing pots, one to three oz. size
• Sandpaper, wet-or-dry 120, 180 and 220 grit
• Dremel tool with sanding drum and carbide routing tool (the straight one with a round end)
• A good pair of scissors
• Glue brushes with 1/3 of the bristle length cut off
• Razor saw
• File, about ¾" wide and six inches long with a half round side
• Blue masking tape

The Materials

• One quart kit of West, System 3 or similar laminating epoxy
• Fast and slow hardeners for the epoxy and the mixing pumps if available
• Five minute epoxy
• Epoxy board, 1/16" thick (G-10)
• Microballoons
• Cab-O-Sil (colloidal silica) filler
• ¾ oz. plain weave fiberglass cloth
• 2 oz. plain weave fiberglass cloth
• Carbon fiber tape-the thin kind that comes in four ¼" wide strips loosely fastened together
• CA glue

How this stuff works

The matrix of epoxy and fiber materials such as fiberglass, carbon fiber or Kevlar is commonly called a composite structure. This structure depends on the strength of the fiber materials for the overall strength of the structure. The epoxy part of the composite merely holds the fiber strands in alignment. The fiber strands are incredibly strong in tension and it is fairly easy to construct the tension side of a structure. Compression, however, is another problem entirely. It is very difficult to engineer the compression side to be both strong and light as it takes thickness to resist buckling and most skin panels get heavy really fast as the thickness increases. For this reason, almost all of the failures on our composite airplanes are failures in compression.

Epoxy cures with a tacky surface unless surfacing agents or waxes are blended into the epoxy. The waxy material floats to the surface to seal the epoxy from the air to attain a tack-free cure. Most available epoxies are formulated with such an additive. You must remove this waxy coating by scrubbing with acetone and paper towels and then abrading the surface with 120 grit sandpaper in order to get a secondary bond.

The molded side of the epoxy is another story. There, the surface of the mold is prepared with waxes and a special water soluble mold release agent that transfers onto the finished part. To prepare this surface for a secondary bond, scrub with soap and water and follow up by abrading with 180 grit sandpaper.

What you are after is to form both a chemical and mechanical bond. Any wax or mold release agent will get in the way of the chemical bond and the abraded surface helps attain the best mechanical bond.

Don’t use CA or anything other than a good laminating epoxy for bonding and laminating anything to an epoxy surface. It won’t work for long. The only exception that comes to mind is using silicone to bond servos into a fuse. Even here, remember to prep the surface by washing with acetone and abrading with sandpaper.

Let’s do a repair to a glass fuse that is broken in half somewhere between the wing and the tail. First try to maneuver the two pieces into their original alignment. If necessary, trim off the edges until the parts can be held exactly in their original alignment. When it looks good, dribble some CA into the broken areas and squirt with some accelerator. I know what I said earlier about CA, but here we’re using CA only to temporarily align the parts. When the parts are stable add some more CA and accelerator until all the frayed and broken edges are securely fused together. Now, if you hide the break with your hand the fuse should look like new. It’s just really weak.

Since the break is at a place where the inside of the fuse cannot be reached easily to prep by washing with acetone and sanding, you’ll have to do the repair on the outside. Sure, some of you like to place glass cloth and epoxy inside the fuse and hold it against the fuse skin by inflating a balloon inside the fuse. Cool idea, but unless the fuse is prepped the patch will crack off the next time this part of the plane is stressed.

Wrap some blue masking tape around the fuse about one inch forward of and aft of the edge of the break. At this point you’ll probably have two bands of tape around the fuse about three inches apart with the break in the middle. Now sand off all the high bumps with the Dremel drum sander. Be careful not to sand all the way through the CA’d part, causing the fuse to fall apart. Sand up to the tape edges just taking off the surface paint and into the resin but not into any fiber material.

It is tempting to now fill the low spots level with spackle or microballoon mix. Don’t. We want as much of the epoxy and cloth patch to bond directly to the original fuse as possible. Cut four pieces of carbon fiber tape 1" long by ¼" wide. Cut four pieces of ¾ oz cloth long enough to go almost around the fuse but not all the way around and wide enough to easily overlap the tape. Handling the cloth will be more fun if you cut along the weave and never on the bias.

Mix up about 1 oz of epoxy with the fast cure hardener. This is simple with West epoxy, just one stroke of each pump. Stir thoroughly. Use your customized glue brush to paint a light coat of epoxy between the tape bands staying 1/8" away from the tape. If the fuse is round, place the four carbon strips lengthwise and centered over the breaks on the sides and the bottom and top of the fuse. If the fuse is squarish, place the strips at the corners. Lightly wet out the carbon with the glue brush. Always be careful to have only a tiny bit of epoxy on the brush in order to keep the epoxy to a minimum. Place one piece of cloth over the area centering the patch on the bottom of the fuse and working to the top. Press the patch in place with the brush dry of epoxy. Don’t worry about the edges near the tape.

When the first piece looks good, do a patch from the top working toward the bottom. This piece may require some extra epoxy to wet it out. Be sparing with the epoxy and do not wet out the cloth all the way to the edge of the tape. The fabric should look completely transparent with the surface showing plainly and looking dry. If there are wet spots, wipe your brush dry and daub at them trying to transport epoxy from the wet spot to a wad of paper towels. Check now to see that the fabric is tightly bonded down. Set the fuse aside for a day. The leftover pieces of cloth are in case you screw up.

Note: We didn’t use 3M 77 to hold the fabric in place. Don’t do this. It reduces the bond area that for the epoxy.

The next day use an Xacto knife to trim the loose cloth. Cut close to the bonded edge but don’t worry about the dry, frayed cloth ends. Use 120 grit sandpaper to feather the edges of the patch and remove the loose strands. In addition, wipe the surface of the patch down with acetone and sand it so fairing putty will stick. Now is a good time to block sand the patch and remove any high spots. If the patch is pretty smooth with no deep pits you can just use spackle and block sand smooth and you’re ready to paint. Fill deeper pits with a mixture of epoxy and microballoons. I usually use five minute epoxy here. To easily mix stuff like microballoons into epoxy, mix in a cup. It is nearly impossible on a flat mixing plate. Mix this putty up thick. It is too heavy if mixed thin.

To bond things like servo trays, control cable housings and the like to the inside of a fuse, use a thick mixture of colloidal silica and epoxy. Even though a microballoon mix will be much lighter, it lacks the necessary adhesive strength. Remember, you must prep the surface of the fuse for the secondary bond. Epoxy seems to stick well to the plastic control cable housings (if they are sanded) to allow a mechanical bond.

For safety, people who experience an allergic reaction should have someone else do their epoxy work. Sensitivity increases with exposure and can cause serious reactions. Wear disposable vinyl gloves and a paper particle mask to minimize exposure. Set the mixing pot outside when you finish with it to keep from breathing the noxious fumes created when the epoxy cooks off.