Building the (Old) FLYLINE Great Lakes 2T-1A Kit (19)

Before we get to start covering this model, there’s one more detail I want to work on. If you are interested in models of those “Golden Age” airplanes, sooner or later you are going to have to deal with LOUVERS. In real life, these rows of cooling air openings that look somewhat like fishes’ gills are made from sheet metal using a punch press and forming die. We can do that for models as well, but to get it right we need to do some serious metal machine work. Very few of us have the requisite tooling in our model shops for that, and to be honest, very few of the models we build justify the expense of custom tool and die work. If I were building a model for Top Gun or equivalent competition, I’d be ready to do that, but that’s not what this little Great Lakes is for.

We could also do some careful mold making and use a vacuum forming box to make louver sets from styrene or some other suitable plastic sheet. That’s an approach I’d like to discuss as part of some some future project, but this time around I’m going to show you how I made four rows of cowling louvers as as ‘one-time” project, the old way, by carving and sanding balsa wood.

In blog post 17 I described building the cowl for this airplane, and closed by indicating that the next step would be covering and finishing. As it turns out I decided to finish the louver details first; however, I wanted to get a finish base onto the balsa structure first. Very soon I’ll get into the covering and finishing of the Great Lakes using a product many of you may not have heard about, but I used my old tried-and-true wet silkspan and dope over bare balsa system on the cowl. You might want to look at my article in the May, 2011 issue of Model Aviation magazine for some background reading on that technique.

Here's the cowl front/face with silkspan applied wet and given a heavy coat of clear nitrate dope. Covering right across openings like these is the easiest way to do the job.

Cutting the dry silkspan from the various openings and trimming it with a sanding block made for the job provides a sharp, clean edge. Here I rolled a piece of 100 grit paper around a short length of leftover steel tube.

This is the lower portion of the cowl with a layer of silkspan attached wet, doped, and sanded lightly when dry. You may not be able to see the difference, but all the wood grain has been filled and a bit of stiffness added to the structure, which is now ready for finishing.

This is the top cowl section. The plans show the location of the opening for the exhaust stacks on the full scale airplane. I have transferred that info to the cowl, marked it in pencil, and delineated the cut lines with masking tape.

The good old single edge razor blade is my favorite tool for cuts through balsa like this one. The tape serves as a guide to help keep the cut straight.

This is the exhaust opening cut out. Later I'll build a set of dummy exhaust stacks to mount here.

The top cowl also has a silkspan finish base. I'm going to add the lover detail over that, before getting into the priming and sanding stuff. The actual louvers on this model are cut from a piece of soft 1/4" sheet balsa. Because the side of the cowl incorporates a slight curvature, I want to shape the blank from which the individual louvers will be cut to match it. I have taped a piece of 100 grit paper to the area where the louvers will go and used it to sand exactly the right shape into the base of the blank.

Using measurements from the plan I drew the location of the row of louvers onto the cowl and marked off the interval (3/16") at which I will cut individual louvers as slices from the blank.

These rough strips will become the finished louvers we want by virtue of the old time model builder

I started the carving process by squaring off the upper and lower ends of the row of louvers with a sanding block.

The next step was to bevel the ends at an angle to match my pictures of the full scale cowl.

I sanded the entire row down to the correct depth, or distance off the face of the cowl. There is also a slight curvature to the top of the row of louvers that matches the countour of the cowl.

I used a No. 11 blade to rough carve each louver close to final shape. There is no substitute for care and patience on a job like this…you must take the time to get it right.

All the louvers of this row are rough carved to the right outline and cross section. The next step is to sand each of them in turn as smooth as I can…individually.

With the louvers sanded to their final contour, I used a narrow strip of wet silkspan, attached with full tautening clear nitrate dope, to seal the grain and fill those stubborn little crevices around the base of each piece.

There are times when we can take advantage of the fact that nitrate dope, left to its own devices, shrinks a lot. This is one of them. I am working a thorough wet coat of dope down into the silkspan-covered row of louvers.

Let a heavy coat of dope - even a little one - dry overnight before you sand it out. When that's done it looks like this. Remember that this is tougher than it might look...these louvers are only one inch across.

That's about as far as I'm going to get without giving the sandpaper some help. There are all kinds of sanding sealer, or primer/surfacer, around. With nitrate dope I prefer to make my own by mixing varying proportions of talc (baby powder) into the clear dope. The more you add, the thicker it gets. Too thin and you don't add much of a sanding base. Too thick and the dried material may crack or crumble. Experiment to see what works for you. This stuff was about the consistency of really heavy whipping cream when I put it on.

Now sand it some more. I made a custom sanding tool from a piece of hard 1/8" sheet balsa, sanded into a streamline cross section with some 100 grit production paper glued to it. In places like this you have to work very deliberately, not just scrub away with the abrasive.

This is ready for the next step. Remember that there are four separate rows of louvers on this cowl, and I'm working on each of them in turn.

Now it's time for the fun part. The louvers on this particular airplane were built into the cowl as separate panels of sheet metal, so I want my louvers to look as though they were pressed as separate parts and then attached. A classic way of making a panel on a model airplane is to mask off the area in question to exactly the shape of the panel with several layers of masking tape...more layers permits more buildup of primer/sealer and a thicker part.

I brushed a really heavy coat of talc-dope sealer into the area that will become the louver panel and let it dry dry enough not to be runny.

I gave it another coat, wet and sloppy enough that I could hold the cowl flat and allow gravity and surface tension to form a meniscus (tension film) in the wet primer.

There will always be some little bumps and rough spots...sand it some more.

When the shaping job was done the way I wanted it to be I pulled away the double thickness of masking tape.

Here's the "raw" panel as it comes out from under the masking tape. I'll need to get rid of the mold flashing, or rough edges.

More sanding, this time VERY CAREFULLY around the edges, and the filler looks almost like a raised panel edge. The final prime and paint coats will finish the job.

One Comment