Let’s Build a Real Old-Time Balsa Model Airplane Part 1

We’ll start with a closer look at that picture of a ragged old cardboard box and the stuff I found inside it. Comet model airplane kits, as produced by Comet Model Hobbycraft, Inc. of Chicago, have been around since well before America entered World War II in 1941. Both their pre-War products and the model airplane kits they sold for a decade or so afterward pretty well define the popular notion of those balsawood model planes you cut out and glue together. Along with that recognition, unfortunately, came the contention that they always crash, they never fly! Generations of the people who insist on building them anyway have devoted time and effort beyond measure working to prove that this does not have to be true. I know. I have been one of them for nearly my entire life. What you are reading now is my most recent contribution to that legacy of optimism, along with what I hope you will find to be an interesting history lesson.

I built my first Comet kit (with a lot of help from my father) in 1949. It was a Firefly, a basic rubber-powered model with just a stout balsa stick for a fuselage. It cost twenty-five cents and came in a box very similar to the one we are talking about now, and it is entirely possible that this same Comet L-7 PIPER CUB box of balsa and paper was resting on a nearby store shelf at that very moment. Somebody bought it, but never built it. The subject…the “real” airplane the model represents…is a Piper J5-A Cub Cruiser, seventy-five horsepower three-seat civilian light airplane that first appeared on the market in 1940. It was customary in those days for nearly all the model airplane manufacturers to introduce miniature versions of each and every new airplane, civilian and military alike, as soon as possible after the general public became aware of them. Comet was at the head of the line with this practice, but I have not been able to determine whether they actually produced and sold L-7 PIPER CUB kits during the War. The earliest reference to it I can uncover describes it as being in the 1945 product line, but this box design did not appear until 1950. It was a common practice to repackage old stocks of kits like this using redesigned box art. It would appear that this is an older kit which got that treatment, because the kit itself holds a key to its own chronology.

During World War II a lot of things ended up being rationed…gasoline, rubber for tires, silk and plenty of food items vital to the War Effort among them. Basic model airplane kits like this one were not rationed, but the balsa they were designed to use was. Younger model airplane builders…those who had not gone off to war…got used to finding a slip of paper bearing this declaration in such kits as were available.

IMPORTANT NOTICE
BALSA IS A CRITICAL WAR MATERIAL AND NOW MAY BE USED ONLY IN DIRECT WAR PRODUCTION
We are called upon as patriotic Americans to cheerfully make this further contribution to our Victory.
Parts of this kit are, therefore, supplied with substitute materials such as pine, basswood, cardboard, etc…

Another of those substitute materials was poplar wood, of which this saw-cut “spray” of strip wood is an excellent example. It turned out that there were a lot of those wartime kits still around When the time came to repackage them with postwar box art, it became clear that nobody found it necessary to sort through them and replace stuff like this with real balsawood. Perhaps half of the Comet kits I built prior to 1955 were like this one. At the age of nine or so I had never heard of poplar. I accepted that this was some strange variety of balsa and it was my responsibility to figure out how to make it work. Poplar is heavier than balsa, as well as being tougher and more difficult to sand or to cut accurately with a razor blade. It is also more oily than balsa to the extent that cellulose model airplane doesn’t stick to it very well. I am seriously committed to preserving those old time model building skills, but my interest in historical accuracy is not even close to being enough to persuade me to use that poplar in this airplane!

When kits like this were common on hobby shop shelves, you could count on there being a generous selection of sheet balsa as well as precisely saw-cut balsa strip to match just about any material dimension you were likely to find in any of those kits. Then, as now, the standard length of a sheet of model airplane balsa wood was thirty-six inches. A strip, or stick, of 1/16” x ¼” might cost something like five cents. Like a lot of other kids in those days it took me a while to realize that I could replace all that miserable poplar with good, honest hobby shop balsa for far less than the cost of another kit that might contain useable wood. You can still do that today…if you can find a store that stocks balsa along with modern RC planes…but the smart way is to cut your own strips from sheet balsa with a balsa stripper like this one. Here I am cutting a supply of 1/16” x ¼” and 1/16” x 1/8” strips from a leftover piece of 1/16” sheet. You’ll see them put to use as we start the actual building.

Back in that first photo there are two folded-up sheets of paper. The one with pattern markings printed on it is the original plan sheet. The orange-looking material under it is the tissue covering that came in the box. We’ll take a closer look at that later. Before we have any sort of airplane structure to cover, however, we need to get that paper spread out flat on a suitable building surface. Because that piece of paper is about seventy years old, doing that required some special extra effort. No matter how carefully I worked to open up those brittle folds, most of them threatened to fall apart. It happens that I could search the various aeromodelling archives and probably find a repro copy of that Comet Kit L-7 plan, but I wanted the challenge of working with what came in the box as if it were the only option. The solution the problem turned out to be using some ordinary white wrapping paper as a backing sheet big enough to support the entire plan. Very carefully I spread out the eight or ten separate fragments of the old plan and arranged them into as close a match to their original alignment as I could. Having any of those fragile pieces stick to the new backing prematurely would have ruined it, so I used extra-hold hair spray to tack them down. Left to dry overnight that held everything in place well enough that I was able to attach a clear plastic cover sheet and then run the assembly through a commercial copier and make some durable black-and-white working plan sheets.

Here’s one of those copies looking ragged, but complete and accurate enough to spread out on my “small model work table” and start some actual building.

Now is the time to talk about what the term printwood kit means. In those days mechanical reproduction of parts was the only option. Electronic image transfer/copying was
not much more than something out beyond the distant horizon of creative imagination. If you wanted to make accurate reproduction of things like model airplane parts you traced out patterns by hand from printed original drawings. At that time the best source of model airplane information was via model airplane magazines. It didn’t take long to figure out that if you could prepare the necessary printing plates to publish those plans, there was no reason not to go one step further and print parts outlines directly on the wood that went into each kit. That was printwood, which is what we are working with here.

Around 1950, when this Cub was produced, kits featuring die-cut parts began showing up on the shelves, and that process quickly became the default for making kits with cut-out parts. It depended on intricate, hand-built arrangements of sharpened steel rule stock that replicated the parts patterns and cut them into appropriate sized sheets of balsa. It didn’t take long for advertising terms like pre-cut, prefabricated, quick assembly and so on to become common, and just about as quickly most everyone who wanted to build model airplanes began to agree that cutting out parts by hand from that printwood was too hard and took too long. It soon became clear that well made cutting dies could produce parts that were more accurate than the ones most guys could cut out with an old razor blade. But…even when cutting balsa wood, steel dies wear out and get progressively less sharp, and this is exactly what happened to the quality of the parts that came from them. Before long a new term, die-crunched balsa, came into common use. A skilled, patient model builder could match the accuracy of a new (sharp) die when cutting parts by hand, but again, most could not. Human nature being what it is, though, die-cutting quickly became the model airplane kit industry standard and by the end of the ‘50’s new printwood kits had just about disappeared. In recent years the quality offered by laser cutting technology has made everything else obsolete. Even that patient, experienced model builder would have difficulty cutting balsa parts of better quality…but this fact does not necessarily apply to the quality of the experience of traditional model airplane building. There are times when doing it all by hand makes it better. This is one of them.

It all comes down to this. I am using a modern hobby knife handle with the default No. 11 blade to begin cutting out Part E-6 from this piece of 1/16” thick balsa printwood. There are several subtle techniques it’s necessary to master in order to get this part right.
Using a really sharp, new blade you might manage a one-stroke, along-the-grain cut in light balsa like this, but in this game there are no extra points for using the smallest possible number of knife strokes. Trying to do that just about guarantees forcing the blade, which is one of the most common causes of sloppy work. Make all straight line cuts with your blade supported by a straightedge. Curved cuts like this one are easiest to follow with a pointed blade. It’s difficult to find metal cutting templates that will fit all these different curves. If you’re not sure you can trace the printed lines exactly, cut outside the part. The margin of extra balsa this provides will be easy sand to shape later. If the balsa you have is too thick and/or too hard, again don’t force the blade. Any balsa more substantial than medium-hard 1/8” sheet may be challenging to cut accurately with a hand-held blade. This is the time to think about using a hand-held coping saw or even better, a powered scroll saw. It is also a bad idea to try to conserve blades. Most of the disposable razor/craft blades around today are made of steel that will not hold an edge well. You should be able to cut most 1/8” balsa diagonally or even straight across the grain with firm, even finger pressure on the blade and get a muffled pop as the edge completes a clean cut. When the cut edges of the balsa appear mushy rather than clean your blade is no longer sharp enough to make the kind of cuts you want. If you can afford to, toss that blade and use a new one. Our goal here should be to build wonderful model airplanes, not to see how long we can keep cutting with a worn-out tool.

After all that, a newly-cut part should come out of the balsa printwood matrix like this. In this case the picture is indeed worth more than any more words.

Let’s start putting this airplane together! Right here in this first step we can see four of the established “conventions” of stick-and-tissue model building in use. First, you can see how the plan sheet is spread out flat and fastened down (there are thumbtacks outside the frame).

Glue sticks to plans made of paper. When this kit was new model builders used waxed paper as a plans protector. The clear plastic wrapping film we have today works much better. Once that’s in place we assemble and glue the basic structural parts right over the pattern. On small models like this straight pins are the preferred means of temporarily holding parts in place until the glue dries. Wherever possible (when the parts are small enough) holding them by crossing pins over them rather than sticking them through the wood is best. Even little holes compromise structural strength. Here you can see that the cut-out balsa leading edge is in place along with a center section end and a stabilizer trailing edge made from some of that 1/16” x 1/8” balsa I stripped earlier.

Here’s the rest of the horizontal stabilizer outline in place. Just as I am doing here, use as many pins as necessary to keep everything in line. There is a lot of the tail assembly left to build. We’ll work on that next time.