The two projects I currently am working on are examples of how much modeling has changed. For the first project, I am in the middle of repairing and repainting my Jet-Teng Models EDF XXX Jet, a prepainted composite ARF model. I simply had to drop in the equipment and it was ready to fly. As I started this project, I realized that the jets that I am actively flying are all prepainted composite ARFs.
I have always enjoyed building my own airplanes, which is my motivation for my other project. I have begun constructing an original-design jet. Nothing beats the feeling of flying a model that you made. The skills to create, repair, and maintain models are only part of the complete experience for me, and are skills that many modelers who begin the sport with ARF aircraft have not learned.
In my early aeromodeling days, my local model club meetings included time for show and tell. Many models were incomplete and under construction for learning and sharing new building techniques. I remember presentations such as how to cover a model with MonoKote.
It appears that this tradition has gone away (at least in my area), but don’t despair. It has been replaced by build threads on the Internet. These skills are still practiced by many modelers and still shared. Check out these threads for learning experiences. We learn from each other, and we never seem to quit developing our building skills, so the fun continues.
Now back to the XXX Jet’s nose section repairs. I began working on it at Jets Over Kentucky last year as a community project. The nose section comes off for shipping with four bolts, separating at a split line between the inlets (typical of ARF jets). All items were removed for best access to the areas that needed to be repaired, including the nose gear retract. The broken fiberglass was forward of the front former to which the nose gear retract mounts.
At Jets Over Kentucky, we used CA glue to position all of the broken pieces of the fiberglass back into place. When doing this, take your time and get them as close to perfect as possible. Uneven or out-of-alignment areas require more filler in the later stages to restore the correct shape. I was fortunate to have the help of master builders during this stage. The repairs were so well done that I actually flew the XXX Jet for the rest of the season. It was straight and structurally sound for flying.
To finish the repairs, all of the cracks must be reinforced so they won’t crack again and show through the paint. This can be done with some fiberglass cloth and laminating or finishing epoxy, which is thinner and flows better than regular epoxy. Why did I choose epoxy? The XXX Jet is an epoxy-molded fuselage. If it was a polyester-molded fuselage, such as the old Byron models’ fuselages, a polyester finishing resin could be used. Don’t mix resin types.
The plan is to reinforce the damaged seams with fiberglass cloth, preferably only placed on the inside. Fiberglass reinforcements on the outside are more difficult to finish because they build height to the outer surface. Getting the shape back is also difficult.
How is the fiberglass cloth positioned? Access to the forward nose section of the XXX Jet is blocked, so I will have to reach through the nose gear former. My hands are not that small, so I must use sticks to extend my reach. I plan to cut some fiberglass cloth into convenient sizes to place behind the damaged areas. The cloth weight can range from 3-6 ounces per yard. (The fiberglass cloth available at auto supply stores is typically 6 ounces per yard, which is fine for these repairs.)
After I have decided which pieces to place where, I will need carriers to support the fiberglass cloth. Carrier material, in this case, will be aluminum foil. Its advantage in this application is that it can be bent into a curve, allowing it to pass through the tight openings of the nose gear former.
Wear nitrile gloves when working with laminating epoxies to protect your skin from the chemicals. I cut my aluminum foil, then mix the epoxy and wet out the fiberglass cloth when it is positioned on the carrier. Using an acid brush with a stick taped to it for the long reach required in the forward section, I brush on some epoxy in the repair area.
Using sticks, I position the repair patch in place, pushing it down to get good contact, and remove the aluminum foil if I can. With my stick, I press down the fiberglass cloth to get uniform contact. Don’t worry if you can’t remove the aluminum foil carrier. It can stay there forever. Allow the epoxy to cure for at least 24 hours.
With the structure sound, I can begin the cosmetic repairs. I like this part; finishing is fun. Coarsely sand the outer skin to aid in filler adhesion. I plan to use an automotive lightweight, easy-to-sand, two-part filler. Lightweight filler sands and shapes easier than regular filler. Put a layer of filler over the depressions and let it cure.
Always use a sanding block from this point on to get a flat, smooth surface with no waves. Holding sandpaper in bare hands will create waves. I have two sanding blocks for most of my work: an 11-inch aluminum T-bar from Great Planes, and a hardwood 1 x 2 x 11-inch sanding block. My heavy work is done with the aluminum T-bar using 60-grit sandpaper, and finishing work is done with the hardwood block with 120-grit sandpaper on one side and 220-grit sandpaper on the other side.
Start with the 60-grit sandpaper to smooth the filler. The goal is to get a flat surface. It will take a couple of coats of filler to get all of the relief areas filled and back to shape, so take your time.
The next step is to sand the rough scratches caused by the course sandpaper, first with the 120-grit sanding block, then with the 220-grit paper. Use contact cement to attach the sandpaper to the sanding blocks.
To remove worn sandpaper, warm the old glue with your MonoKote heat gun, peel the sandpaper off of your sanding block, then use contact cement to adhere your new piece.
In my next column, I’ll discuss priming and painting. Until then, let’s burn some kerosene. See you at the field.
