Wooden Notes

To All:

The low cost and wide availability of wood in America makes it a good
choice for the budget-minded builder of simple flying machines. The
only problem is that when picking the stacks at the local lumber yard
you need to know a fair amount about wood in order to select the most
suitable pieces. Part of that chore involves visiting the local yards
- - or box stores - - fairly often in order to see the new pallets as
they're put out for sale.

Today I lucked into some outstanding shelving (!) and a pallet of 1x2
furring strips that included some superior wood. I loaded up a cart
with as much as I could afford. Waiting in the line at the register
(Home Depot has a long way to go in that department) another
homebuilder saw me as he entered the store and stopped to chat.

Although I've given demonstrations about grading lumber, including
side-by-side testing in which samples of various woods are compared to
Sitka spruce, my habit of using commonly available wood to fabricate
real airplanes is often treated with humorous condescension, as it was
today.

"Building another airplane?" he said as he started to leave, plus the
patronizing smile.

"Same one," I nodded. Actually, same ones, as in plural, except most
of this wood was destined for an on-going primary glider project.

He looked at the cart-load of lumber, started to say something witty,
finally just walked off with an airy wave. To him it was just a
cart-load of box-store lumber. Had he taken a closer look at the
furring strips he would have seen they were Western Hemlock, ran about
24 annualr-rings per inch and came from a tree that was at least six
feet in diameter(*). The grain had a run-out of less than one inch in
eight feet and most of the sticks were almost perfectly cross-grained.
That's because they were probably sawn from the cauls produced when log
was sawn into a square cant. Back in the old days, the cauls would
have gone into the kiln or boiler as fuel but nowadays they use
laser-guided computers to figure out the maximum yield from every log
and the cauls -- the camber-faced slabs from the sides of the timber --
probably went to an edger instead of the scrap heap and ended up as
saleable pieces, including my bundle of furring strips.

The shelving was another situation entirely, being plantation-grown
stuff running six rings to the inch near the edge and barely eight
toward the middle. The tree was probably about 12" in diameter when it
was harvested and probably about 30 years old. But what made these
particular pieces of shelving candidates for aviation was the fact each
piece on my cart was a center cut.

In producing construction-grade lumber the tree is cut into sections
from 12 to 24 feet in length then each section is squared and run back
& forth through the saw (or in a really big mill, through a continuous
series of saws) and turned into slabs of the desired thickness, as
dictated by the market. By comparison, the wood for masts, spars,
ladder rails, bannisters and aviation-grade lumber is usually
quarter-sawn, an entirely different proposition from plain-sawing.

The point here is that the center-cut of a plain-sawn log has EXACTLY
the same grain orientation as if it were quarter-sawn. That means it
will dry without warping and its characteristics of strength will be
uniform.

So will it be useful in an airplane? Probably. But the wood has the
final say in the matter. It's still pretty wet and the shelving needs
to be re-sawn to isolate the usable outer sections from the center.
Give it a bit of time, turning it occasionally and a fair percentage of
it should prove useable. And if not, I'll use some of it to make
Smilin' Jack and his friends some little toy airplanes; give'm to them
at Christmas; tell them it's for their grandkids.

- - - - - - - - - - - - - - - - -

The furring strips were $1.15 each and I bought twelve. The shelving
was $5.67 each and I bought three pieces. Total was $30.81 at the Home
De-pot on San Marcos Blvd. That eats up my 'airplane wood' budget for
about two months but 'long about March I'll start prowling the stacks
again. Lotta ribs in an SG-38 and every time you take it out you can
count on them kids busting a few. But by the time the thing is mostly
patches the new set of wings will be ready, along with a new crop of
kids.

The Smilin' Jacks don't know what they're missing :-)

-R.S.Hoover

(*) - - Trees are round. With a pocket loupe and your 6" machinist's
scale you can measure the chord across the arc of the annular rings of
a fine-grained scantling with a fair degree of accuracy. With that, you
can calculate the diameter of the tree at that point. Do it enough
times, just looking at the piece will give you a good idea of its
diameter.