Now it’s time to close up the bottom of the fuselage with sheet balsa. This part of the building sequence offers me a fine opportunity to talk about one of the choices of design and construction technique that went into developing this kit. This is something that goes back to the very earliest days of model airplane building, and makes for a fun history lesson. In the beginning such model airplanes as existed at all might just as well have been whittled (OK, carved) out of a solid block of wood. Since the model builders of those days were every bit as smart as we are, it didn’t take long for them to figure out that solid models might look great, but for real flight they were useless unless you were willing to settle for swinging them around on a string. (Important note: real control line flying, which is something very different, was not invented yet.) What did offer promise of flying were models made mostly of air…contained and defined by a collection of intricately shaped long, skinny sticks and some shorter flat pieces that served as fuselage formers and wing ribs. At first the sticks were basswood, spruce or maybe even pine, and the flat stuff might just as often have been cardboard.
Tradition holds that sometime during the 1920’s or thereabout, balsa wood appeared as the miracle material that was going to revolutionize aeromodeling. It did.
Spruce and basswood (along with thin aircraft plywood as it became available) got reserved for things like wing spars and engine mounts (if you were lucky enough to have an engine!). Balsa took over. At first you used it just like the old stuff…longerons and stringers, leading and trailing edges…sticks. It didn’t take long for somebody to figure out that if you used a very thin, fine-toothed table saw you could cut a block of balsa wood into smooth, accurately dimensioned sheets of various convenient thicknesses and sizes AND that it took a whole lot less time and effort (as well as skill, sometimes) to cut out something like a fuselage side from one of those balsa sheets than it did to piece it together from eleventy-odd lengths of stick balsa.
Not surprisingly, considering the independent nature of the sort of people who build model airplanes, a debate ensued as to which was better…built-up (stick) construction with tissue or silk covering or sheet construction which might be covered or not, but didn’t need to be. Built-up structure lends itself to curvey, complex shapes and is by nature light as well. It’s also more demanding to build accurately and perhaps more likely to be fragile. Sheet structures tend, by definition, to be mostly flat and angular. They can be a lot quicker to build. They use up more balsa and often weigh more than built-up equivalents, but they are often tougher in the face of real-world flying. It can be harder to poke a hole through a piece of balsa than through a piece of doped tissue or silk. However, there are some things that you can’t do with fabric covered open structure, like producing a regular convex curved surface such as an engine cowl…without facets (flat spots). For that you need a bent or formed sheet or a carved or molded part. (You can produce an esthetically and mathematically smooth concave surface with fabric, but that’s a tale for another time).
The esthetics-versus-functionality debate that started here is still going on. You might say that it’s with us today as the model building-versus-ARF question. As is usually the case in such matters…in my opinion…there will never be any single right answer. We need them both, and this Stinson SR-9 kit project is an excellent example of how that works out in practice.
That’s all we have room for here, but there’s more. Go to http://www.rcmodel.com/2012/11/building-the-stinson-sr-9-14/ to see all the rest of the details of Stinson blog No. 14