Rocket tables: balsa density and tube ratios

The balsa thread led me to dig out 2 tables that I've made years back and put them on my chad web site:
This is an extension to something I found in an old MIT journal, that I use when buying balsa in the hobby store. By eye I select wood for lighter color, which translates to lighter weight; and desired grain, often C-grain. I can compare weight between sheets to pick the lighter ones. But I've never been able to tell what the density actually is without weighing it. It's not convenient to carry an Ohaus triple beam balance from store to store. So I use something like to get a nearest gram estimate of what the sheet weighs. Then I look up the dimensions of the sheet on this table, go down the weight column until I find the weight of the sheet, and read the pounds per cubic foot off the left.
Both the scale and a hard copy of this table fit in my wallet.
I've only posted the tables for 3" and 4" sheets. I made them for strips as small as 1/16" and sheets as big as 12", but you can easilly adjut for common sizes. If you have a sheet that is 1/8" x 2", treat it as a 1/16" x 4" sheet. A 1" x 1" block is the same as a 1/4" x 4" sheet. A 12x24x1/8" piece of plywood is the same as 4x36x1/4", although the weight may be off the scale. So divide the real weight by 2 (or 4 or whatever), then multiply the density by the same factor.
If you carry a calculator then
    density = grams / (width * thickness * 9.45)
for 36" sheets
I generated the first of these tube tables back when building my first real scale model for NARAM-25. The model had 2 different diameters, so I needed to find 2 tubes with a matching ratio. To use this table, calculate the ratio for the real rocket (in my case 38:44 or .8636, or 1.157 if you flip the fraction - either will work), then search the table for something close. In my case, .853 is BT70:BT80, which is what I built.
The original version of this table, with maybe a dozen different tubes, was published in The Leading Edge around 1983-4. I was surprised to see it return in Peter Alway's "The Art of Scale Rocketry" a decade later. Alas, this great book is out of print, but this greatly expanded table is still handy.
Bob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)! <<<
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