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Balsa Density Charts In addition to the type of cut, balsa density is also important. The lighter a model is, the better it will fly – so we need a way to determine wood density. The Balsa Density Charts were created to measure the density of standard size balsa sheets. One chart is used for 3” x 36” sheets, and the other for 4” x 36” sheets. First measure the weight of the sheet (you’ll need a good scale), then find the chart line for the sheet’s thickness. This will give you the wood density in pounds-per-cubic foot. Balsa Density Calculator This useful little program will calculate densities of non-standard balsa sizes. Great for blocks, strip wood or odd pieces of sheet. It will also calculate the “stiffness coefficient” of wood, which deserves some explanation… Both density and grain (type of cut) determine the strength of any piece of balsa. We can't take any piece of “C” grain wood and say it’s stronger than any piece of “B” grain. Nor can we say that heavier wood is always stronger. A good gauge of strength is “stiffness,” which can be measured by experiment. Simply put, a piece of wood is mounted vertically and a load is applied to the top. The load is increased until the wood buckles. The “buckling load,” combined with the dimensions of the wood, will yield a stiffness coefficient. It’s beyond the scope of this article to describe how to set up a buckling test, but we hope to convey an understanding of how density and wood grain work together to create strength. Airfoil Plotter Here’s a simple program to draw logarithmic curves. This is the type of curve often used for airfoils. You can select the thickness you desire, and the program draws an airfoil to accommodate it (bottom of airfoil will always be flat). Use this tool to design wing ribs, make templates for sliced ribs, or build jigs for laminated ribs. There must be other uses also! Unit Converter This a marvelous program that you’ll find all kinds of uses for – above and beyond modeling! The Unit Converter will convert anything to anything! You name it! I have yet to find any type of unit that cannot be converted by this tool, and it’s especially useful to me in the kitchen. Now how many cups are in a quart again?
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