Working with aluminum

Model Airplane News, Apr 2004 by van Mourik, Dick

Many of us have a weak spot for the classic biplanes of the '30s. Not only do they represent the last of the biplane generation of fighters, but to many, they also epitomize the utmost in aircraft design. Many aircraft of the so-called Golden Age are known for their striking color schemes, often covered in natural metal with brightly colored roundels and striping. But when it comes to making models, many people are-regrettably-put off by such subjects because of the difficulty involved in re-creating a realistic natural-metal look.

Some commercially available paints and coverings are said to produce a realistic-looking chrome finish, but when it comes down to it, you can't beat the real thing. Only one thing can be substituted for metal: metal.

During construction of my Hawker Fury, I decided to put this theory to the test using a variety of materials. First, I tried lithoplate. For those who are unfamiliar with this product, it is a very thin (about 0.256- and 0.128-inch-thick) aluminum plate used in the offset printing process. The most common way to form aluminum (and many other metals) is to heat it and then let it cool so it can be bent or hammered to shape. Unfortunately, as one can imagine, materials as thin as lithoplate are not very conducive to being hammered, so I was soon forced to abandon that option.

Molded-aluminum buffet trays have proven to be very useful for modeling purposes. They are cheap, light and made of very soft material. This is the material 1 selected to form most of the Fury's cowl. You could also use several other varieties of aluminum in various thicknessness; many are available at modeling trade shows and scale fly-ins.

ANNEALING

Heating aluminum to a certain temperature causes it to release its inner tension so that it can be molded to shape; this process is called annealing. There are two commonly accepted methods of annealing, and you begin both by rubbing ordinary hand soap (wetted) on the aluminum sheet. The soap acts as a temperature indicator (much like chalk does for steel). The sheet can then be gently heated with a blowtorch until the soap blackens. (Note: the soap must turn dark brown or black.)

At this point, the two methods differ. In one, you allow the aluminum to cool at room temperature; in the other, you submerge the heated sheet in cold water. Despite several attempts, I have not been able to determine which method is better; I suspect that it merely depends on the kind of aluminum being cooled.

CUTTING

Before you cut the aluminum, it's a good idea to make templates out of card stock. Remember to cut the templates (and the metal) slightly larger than needed; this allows you excess room to clamp the aluminum into position and to account for any errors that may occur during assembly. The actual size of the individual panels is not as important as are the positions; try to replicate those as accurately as you can. For the most part, I was able to do that on the Fury's cowl with the exception of the panel on the underside. Though it was supposed to be a one-piece panel, I had to split mine lengthwise. Fortunately, most of the separation line is concealed by the hole I had to cut in the cowl for the engine and by a non-scale but very convincing-looking hatch.

Aluminum can be cut with either a pair of scissors or a sharp hobby knife. When using a knife, make several passes and simply snap the pieces apart. Do not worry about the rough edges this will create; they can later be smoothed with steel wool.

SHAPING

First and foremost, make a plug on which to form the cowl. Old newspapers and magazines work well here, but if you make your own fiberglass cowl, as I did on the Fury, you can use the negative mold to form the aluminum. This is probably the simplest method; it is, after all, easier to form in a negative shape than over a positive one.

Several tools can be used to help shape the aluminum, but I prefer to use a wooden spoon as a shaping tool. Its convex shape lends itself nicely to such a project, and the smooth surface will not scratch the aluminum. Plastic jar lids and screwdriver handles are also suitable. Metal tools are another possibility, but they are also capable of scratching the soft aluminum.

When rubbing the aluminum to shape in (or over) the plug, always start from the center and work toward the outside; gently rub out any wrinkles as you go.

When forming double curved pieces such as cowls out of aluminum, it pays to think in reverse. For example: when forming a piece of aluminum sheet over a ball and trying to bend it into shape, you'll notice that it tends to wrinkle wherever there is a surplus of material. The most important thing to learn about this stretching isn't that there's excessive material where it wrinkles but that there's a lack of material where it doesn't. We cannot prevent the aluminum from wrinkling, but we can stretch the aluminum and rub out the wrinkles.

ODDS AND ENDS

Forming aluminum causes it to re-harden, and that makes it neccesary to anneal it every couple of minutes. In the beginning, the aluminum will harden fairly quickly, so don't stretch the panels to their limits. It's far better to work a little bit at a time and continually repeat the annealing process; it will not affect the aluminum's characteristics. You'll be surprised by the extent to which aluminum can be stretched, as evidenced by the air intake on my Fury's cowl; it was formed from a piece of V64-inch aluminum sheet. Patience is key here!