Gordon Arnaut wrote:
Matt,

You are correct that resizing structural members is not as simple as simply
increasing size by the same percentage amount that the substitute wood
varies in strength.

Yes, you do have to recalculate the structural stresses, but this is not
that difficult. You can do this by applying the bending stress formula. This
will give you the exact dimensions that you will need of the substitute
material, in order to carry the same loads.

There is an old Sport Aviation article that works through this, called
"Selection and Evaluation of Wood," by Noel J. Becar. It is included in the
EAA book, "Wood: Aircraft Building Tecniques."

Yes, not that difficult, but definitely tedious and time consuming. I'd
rather spend a little more time locating quality wood of the species
specified by the designer than recalculating the sizes of all of the
stressed members of the structure - which is a lot of calculation even
on simple airframes.

And then you may have to adjust a lot of other items (brackets, etc.) to
accomodate the different dimensions. All in all, a lot of work and the
increased chance of a miscalculation that could cause problems later.

If someone was planning to make many airplanes using the new wood, then
it would be worthwhile, but for a single airplane, it seems to me that
the work would greatly outweight any benefit of using a different specie.


Matt