put them on my chad web site:

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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

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to get anearest 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

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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.