September 8, 2013

Repairs:The Art Of Gluing

As I have said many times, I have spent years building static, plastic model kits. When I was a kid I would look at magazines and admire the incredible realism of what the "pros" turned out. I looked forward to the day when I would eventually have an air brush, and really get the true look that could fade from lower camouflage to upper, and was without visible brush strokes. Years later, as an adult with a workshop in my garage, that wish came true, and soon I was into all kinds of techniques for adding rivots, weathering, and obtaining custom decals to get the exact squadron I wanted. It got to the point where I was spending a year to 2 years to complete a model, and as I said, that was when I suddenly realized there had to be a way to get closer to flying without so many hours spent on something that ended up on a shelf. But, those skills have come into play in the RC world! THERE"S NO WAY TO AVOID CRASHING, and the repairs can be relatively easy, and made to look almost indiscernible with some simple techniques.

So for our purposes now, let's stay in the world I was in as a beginner, that of foam planes. One of their advantages is that they are easy and inexpensive to repair, and the results can be quite satisfying as far as their ability to keep flying without major problems in the air. There are two types of glues that you will want to get familiar with...the CA type (cynoacrylates, commonly known as "super glues") and epoxies.

CA glues come in different viscosities, and should be FOAM SAFE. There are no doubt many brands, but the one I have latched onto I got at my local hobby store. The black cap is a thicker glue, as I found the thin was too runny and just got out of control and all over everything! CA glue is very fast usually have just a matter of seconds to position something before it sets. They are very effective for thin cracks, thin parts (especially micro planes), or areas that you want a relatively brittle adhesive, as I descibed in an earlier blog on my first crash. I used epoxy to glue a balsa plate to the wing, and then used CA to glue the plastic landing gear mount to the balsa. The net effect is that when stress occurred, the CA is would be more likely to break away from the balsa, while the balsa remained intact to the wing. So if after a crash, there is a crack in the wing or fuselage that is not wide enough to pry apart for the application of epoxy, then you can drip the CA into the crack, it will spread somewhat, and then with pressure you will be good to go in a minute or two.
Plastic plate on top of balsa
Now an important companion to CA glue is a "setter", or accelerant. This spray will instantly set the CA so there is literally no waiting time, and no need to steady the parts being glued. That can be good news or bad news. If you are completely confident that you can place the two parts together, without hesitation as to the need to align the angle, or adjust the fit, then the strongest approach is to spray one piece with the setter, and then apply CA to the other piece, and touch them together. They will bond instantly. A more common approach would be to use the CA, whether in a crack, or on two pieces, and then when you are confident that all is well, spray,(or have someone as a second set of hands do it) the joint. This will bond any exposed part of your repair, holding it firmly in place, and then you will want to give an additional few minutes for the unexposed portion to adhere. It doesn't take any quantity at all....just a "spritz" and you will see that the liquid is on the joint, and that will be enough.

Now epoxy is a different beast. It comes in two parts, the glue and the hardener, and you can get it in pairs with different curing times. I use the 5 minute, but I confess there have been times when I was applying a large amount of glue to a large area, and I ran out of time as the glue was setting faster than I could apply it. The next step up is 15 minute, and it would be prudent to have some of each. Epoxy has to be mixed, so I keep my boxes that my planes came in, and cut the cardboard into squares as need, using the slick side as the side I mix on. Epoxy is a much more permanent bond, and especially good for larger repairs. If you tore off a wing (as I have), or broke a fuselage (as I have), these are the types that epoxy is great for. I apply it generously, and as I said you will have time to adjust your pieces, and wipe off excess (although as the glue begins to get tacky you have to be careful not to use paper products that will stick to the glue and make a mess of your repair). My hobby store has a great little product that is a little brush on a stick that I can mix the glues with and then scoop the glue and apply it where I want it. It is called Ultrabrush and comes in packs of 10 or so.
The great thing about epoxy is that once it hardens, you can sand it and sculpt it to fill in dings and smooth the repair itself. So knowing that, I apply epoxy generously, and then go back afterward and sand away the excess with the hope of restoring the original shape and intergrity. If the epoxy has not set, you can wipe away the excess with 90% isopropyl alcohol, but be advised, it might take some of the paint! Once hardened, if it's a large amount of glue that has to be removed, I begin with a Dremmel tool and a sanding drum to take away the biggest portion. Then I use finer wet/dry sandpapers in the 200, 400 and 600 grits, working from the coarser to the finer to get the smoothest finish. The epoxy will get into panel lines, and there's nothing you can do about that, but it can be very helpful in filling divots of missing foam, say in a leading edge of a wing. I have also taken foam from the box the plane came in, cut and sculpted pieces of foam that fit a large hole of missing foam in the plane, used CA to glue the piece in, and then used a smaller amount of epoxy to smooth the finished product.

exterior-fuselage completely severed
interior showing same break

When sanding, you just have to watch that you are sanding the glue and not straying off onto the foam, or obviously you will be tearing up the foam. This is particularly true with the Dremmel. The only downside to large quantities of epoxy is that large quantities can add weight, and when you are done you should check the center of gravity from both the wing roots, but also from the propeller to the rudder, and then make any adjustments accordingly. On the P-47 repair you see above (in silver) I had lost both wing tips as the plane caught some protective plastic netting, and sheared the first wing tip, spun the pane around and damaged the other. After my repairs I determined the COG was off, with one wing heavier than the other, so I found some metal dowel, drilled a hole into the wing tip exactly in line with the COG on the wing root, and then when I was satisfied with the balance, I covered the hole, with the dowel inside, with epoxy.

The last phase is the cosmetic cover-up, and that is where having an air brush is handy. I always used Testor's model paints, in enamel, and I just like the way they thinned and worked in my air brush better than acrylics. Enamels are thinner based and acrylics are water based, but to my surprise I have never had any problems with the enamels affecting the foam. I also always finish with a couple of coats of Glosscote, which seals the plane, and gives it a better, more scale appearance of a slightly metallic nature.

If you want to really get into "weathering" your plane, there are washes you can swipe in that give the oily effect (they run into the panel lines, and accentuate them nicely) and you can add rivots using fine point sharpies in either black or silver.

The last option you can explore are custom decals. I have discovered a great source for warbirds at Callie Graphics (www.callie-graphics .com). They are different than the  type I was used to with plastic models....they are more like a tape than a decal, but they can go on wet or dry (I recommend wet, as you will want the second, third and fourth chances to get it right) and it is fun to have something unique that nobody else has. Here's my customized thunderbolt compared to the original.
The original Park Zone "Raging Bull"

the "No Guts No Glory" version

So in conclusion, remember...crashes are inevitable! Nobody is immune, so don't be surprised, or disappointed (even though you will anyway) when they happen. But foam planes are relatively easy to repair, and you can good at getting them close to their original look and flying just as well as before, in no time. When you do, you'll start playing with doing cosmetic things to enhance the look of your model. But if you do, don't get sucked into the trap of feeling like now you can't fly the plane without a knot in your stomach over what will happen if you crash and wreck all your work! Everybody agrees, it's almost a good thing when you have your first crash, because then you can feel free to go ahead and have fun flying without worrying about messing up a pristine plane!

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