Q-93: In many of his columns, Dave Robelen says to find light balsa when building micro or indoor type RC aircraft. But what is light balsa? Dave refers to so many pounds of balsa density. This is no help to me. What I need is simply the weight per sheet for the various popular sizes.
A-93: This is another subject that was recently kicked around one of
the popular Internet model forums. What this modeler wanted to do is place his
sheet of balsa on a accurate scale and relate the weight shown on that scale to
the density (light, medium, hard) of the balsa. For example, the grading for
balsa categorized as “Light” is 5.5 to 6.5 pounds/cubic foot. If I wanted to
select a piece of “light” balsa measuring 1/32 x3 x 36 inches, what should that
sheet weigh when placed on a scale?
The forum mentioned several good Web sites that contained helpful information. I
found the Web site established by Tom McCann of Skyhooks & Riggings (in Canada)
to be most helpful. First call up this specific Web site:
http://skyhooks.ca/basheet.htm.
Looking up the chart on this Website, initially select the balsa density for
“Light” which is 6 pounds/cu.ft. Then select your balsa wood sheet size, in this
case 1/32 x 3 x 36 inches. The chart indicates that at the 6 pounds/cu.ft.
density, this size balsa sheet should weigh 0.1875 ounces. If you want this in
grams, multiply 0.1875 by 28.3 and you get 5.3 grams.
My experience has shown that I had to sort through at least a half dozen sheets of balsa before I got close to that 5-gram weight. Obviously that is very lightweight. Just by feel I couldn’t tell the difference between a 5-gram and a 9-gram sheet of balsa, so an accurate scale is an essential part of this grading process. Continuing to use the Skyhooks chart, “Medium” balsa is 8 pounds/cu.ft., “Medium Hard” is 10 to 12 pounds/cu.ft., and “Hard”is 14 to 16 pounds/cu.ft. density.
This same Web site has many interesting facts about balsa relating to the selection process, the strength, type of cuts, etc. You might want to place it on your list of “favorites” for easy reference in the future.