Interesting Stufff

"What could possibly be so interesting that it's able to distract your
mind from what sounds like serious pain?"

The messages hit the in-tray within minutes of my posting an article
about a mythical 'cancer' engine. Private messages. Probably from
people suffering pain. And if they are afflicted with multiple
myeloma I can damn well guarantee they are in pain. Or drugged to the
point of virtual insensibility. That means this may not be the answer
you were expecting. But follow me through -- I can tell you what
they're doing for me, what I'm doing for myself, and how well either
of them works.

The basic answer is 'kite sticks.' These are scraps of wood about 1/4"
on a side -- about 6.35mm. But in the reality of home-shops and
airplanes, a 'kite stick' is just about any piece of softwood
somewhere between 6 and 7 mm on a side. They can be several feet long
and in virtually all cases, they are SCRAP. We didn't set out to make
them, they are simply the accumulated residue of various operations at
the table saw. But that does not preclude our grabbing a handy hunk
of pine or fir and turning into kite sticks... perhaps even to making
some kites and taking some kids for their first flight.

Some kite sticks presented themselves to me one afternoon. They were
clear-grained cedar, the residue from making a screen door.

I cut two bundles of them, one 8" in length, the other bundle about
6". I marked the center of shorter bundle.

A stick having a cross-section of 0.250" has a surface area of only
0.0625 -- a scant sixteen of a square inch.

I put a dot of glue on the mark showing the center of the shorter
pieces -- three or four will do -- then clamped a long piece
perpendicular to the shorter piece, the end buried in the dot of glue
-- which for this experiment may be any glue that comes easily to
hand... or even home-made casein glue if you have nothing better.
(Casein is easy make and is as strong as most vinyl-type 'white'
glues. You don't want to build an airplane with the stuff but you
COULD.)

The point here is that the cost of such experiments is virtually nil
-- you start with virtually nothing -- some scrap wood, accurately cut
into sticksk, and some glue. By designing an experiment so as to
develop the information in a logical manner, with a couiple of test-
pieces fabricated from real Sitka Spruce, the RECORDS you keep (as
opposed to the pictures, drawings and so forth) can be compared to
historic Forest Products Laboratory experiments that have followed
generally the same procedure.

After the glue has cured you clamp the longer upright in a vise so
that the shorter piece is horizon. Then you break it.

It isn't very strong; it will usually pop apart at the glue-line with
only a modest amount of pressure. It does so because all of the
stresses must be carried by that 0.0625 square inch of GLUEING
SURFACE.

Did they all break at about the same stress? Did the fractures look
about the same?

If you rig a bridle on a ten can, attach the bridle to ONE END of the
top piece and slowly fill the can with BB-shot (or even sand!) you
will have a more accurate method of determining WHEN the joint
failed. (Just don't let the can drop too far.)

In effect, you are determining the amount of strength you can expect
from a gluing surface only a quarter-inch on side. Do it enough times
and you begin to develop a 'feel' for how much stress the little
corner can take. Which isn't a lot but there are many times when you
don't NEED a lot -- and weight is always the enemy of flight.

Things become more interesting if you'll add a GUSSET to the unloaded
side of the 'T'. The gusset, which can be cut from a cereal carton or
paper of similar grade, when mounted on the UNLOADED side of the T-
joint is going to see the stresses in TENSION, in that the stress is
trying to TEAR THE PAPER APART. You can also see the effect of
INCREASING THE GLUE line. For example, if your gussets were 1" by 2"
and mounted asymmetrically, a single-sided gusset would give you a
glue-line of half inch along the top edge and 3/16th of a square inch
0.1875" along the front, for a total glue-line of 0.6875" = about a
ten-fold increase over the original dot of glue. (You may use a
clothes-pin as a clamp.)

Of course, the load would appear only in tension. Do a loop and you
might see enough compression along the forward 'arm' of the T to cause
the thing to fail.

So try it asymmetrically. Then try trimming it, to get of the
corner. Or use TWO gussets, one on either side of the joint and of
thinner stock than the original.

Or slit the sticks and slip a mid-line gusset into the slit (the
object here would be to reduce weight).

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

In late May I made a batch of 'T's and 'L's using redwood and cedar,
most salvaged from an old house. A few tests told me the old original-
growth redwood (about 28 TPI !) was superior in every way to some
'certified' spruce I happened to be working with at the time and,
initially, I was only interested in developing the properies of the
salvaged wood, thinking of using it as spar caps. Other than a few
splinters, the redwood did extremely well and I made a test rib and
other parts, subjecting them to destructive testing and recording the
results. Then I became ill and nothing was done for about a month so
that now, I am just regaining my interest in what was meant to be a
quick and fairly primative test. But ribs have gussets and when I was
able to fumble around in the shop I found the experiment waiting for
me, with batches of well-cured parts and a notebook that showed signs
of delirium which lead to my hospitalization.

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

There are other projects going on. It isn't hi-tek. In fact, you
could probably do a scratch-built of your own design using nothing
more than photos of previously successful airframes. Under those
conditions I don't think such exercises could serve as a regular means
of pain prevention... but for the short-term, and under the right
conditions such experiments have provided me with hours of
distraction.

Much of what I know about softwoods for use in airframes, kayaks and
the like, are the product of such tests. In some cases my experiments
DID NOT agree with the generally accepted numbers provided by the
FPL. In most others, the tests serve to confirm the safe, convenient
SUBSTITUTION of materials, not only because Spruce has become so
expensive but more so because some alternatives have proven SUPERIOR
to spruce, in that the finished structure not only weighed less, on
destructive testing it proved to be stronger.

At that point you really run into the exciting stuff, because it means
your home-made scratch-built has the potential to be constructed at
LESS WEIGHT but EQUAL STRENGH. It's a lot of trouble, of course. But
at the grass-roots level the home-builder is usually forced to accept
a GAIN in weight rather than an increase. Sick or not, when such
numbers begin developing across your spread-sheet, it sez your home-
built is liable to be SUPERIOR structure, it's simply too important to
ignore.

-R.S.Hoover

Bob
absolutely true!
I'm using Alaskan yellow cedar that is imported into western australia
for decking planks of all things. it is inch thick by 6 inches wide
and 10, 11 or 12ft long. lots of knots but I am sawing the wood up
myself and using sound pieces between the knots. picture in the mind
straight grained timber that works easily, has growth rings about
1/32" apart, is nominally 5% stronger than spruce, nominally 10%
heavier.
truely it is stunningly good wood. I scout around about 10 bunnings
stores to buy the best I can. I have some totally knot free specimins
about 12ft in length but these are rare.
I stumbled on to this wood quite by accident and became convinced of
it's suitability using simple tests like bob advocates.
I sent some samples of the wood to an aeronautical engineer friend and
he was stunned by the quality. ...and I buy it in bunnings (Home Depot
for you yanks)

for guys who want to follow bob's recipes for testing the wood
strengths there are a stunning variety of suitable woods available.

plywoods?? marine grade queensland hoop pine plywood is lovely stuff
to work with.

spruce isnt a religion, it's just a wood.
Stealth Pilot


On Sat, 12 Jul 2008 00:04:24 -0700 (PDT), "
wrote:

"What could possibly be so interesting that it's able to distract your
mind from what sounds like serious pain?"

The messages hit the in-tray within minutes of my posting an article
about a mythical 'cancer' engine. Private messages. Probably from
people suffering pain. And if they are afflicted with multiple
myeloma I can damn well guarantee they are in pain. Or drugged to the
point of virtual insensibility. That means this may not be the answer
you were expecting. But follow me through -- I can tell you what
they're doing for me, what I'm doing for myself, and how well either
of them works.

The basic answer is 'kite sticks.' These are scraps of wood about 1/4"
on a side -- about 6.35mm. But in the reality of home-shops and
airplanes, a 'kite stick' is just about any piece of softwood
somewhere between 6 and 7 mm on a side. They can be several feet long
and in virtually all cases, they are SCRAP. We didn't set out to make
them, they are simply the accumulated residue of various operations at
the table saw. But that does not preclude our grabbing a handy hunk
of pine or fir and turning into kite sticks... perhaps even to making
some kites and taking some kids for their first flight.

Some kite sticks presented themselves to me one afternoon. They were
clear-grained cedar, the residue from making a screen door.

I cut two bundles of them, one 8" in length, the other bundle about
6". I marked the center of shorter bundle.

A stick having a cross-section of 0.250" has a surface area of only
0.0625 -- a scant sixteen of a square inch.

I put a dot of glue on the mark showing the center of the shorter
pieces -- three or four will do -- then clamped a long piece
perpendicular to the shorter piece, the end buried in the dot of glue
-- which for this experiment may be any glue that comes easily to
hand... or even home-made casein glue if you have nothing better.
(Casein is easy make and is as strong as most vinyl-type 'white'
glues. You don't want to build an airplane with the stuff but you
COULD.)

The point here is that the cost of such experiments is virtually nil
-- you start with virtually nothing -- some scrap wood, accurately cut
into sticksk, and some glue. By designing an experiment so as to
develop the information in a logical manner, with a couiple of test-
pieces fabricated from real Sitka Spruce, the RECORDS you keep (as
opposed to the pictures, drawings and so forth) can be compared to
historic Forest Products Laboratory experiments that have followed
generally the same procedure.

After the glue has cured you clamp the longer upright in a vise so
that the shorter piece is horizon. Then you break it.

It isn't very strong; it will usually pop apart at the glue-line with
only a modest amount of pressure. It does so because all of the
stresses must be carried by that 0.0625 square inch of GLUEING
SURFACE.

Did they all break at about the same stress? Did the fractures look
about the same?

If you rig a bridle on a ten can, attach the bridle to ONE END of the
top piece and slowly fill the can with BB-shot (or even sand!) you
will have a more accurate method of determining WHEN the joint
failed. (Just don't let the can drop too far.)

In effect, you are determining the amount of strength you can expect
from a gluing surface only a quarter-inch on side. Do it enough times
and you begin to develop a 'feel' for how much stress the little
corner can take. Which isn't a lot but there are many times when you
don't NEED a lot -- and weight is always the enemy of flight.

Things become more interesting if you'll add a GUSSET to the unloaded
side of the 'T'. The gusset, which can be cut from a cereal carton or
paper of similar grade, when mounted on the UNLOADED side of the T-
joint is going to see the stresses in TENSION, in that the stress is
trying to TEAR THE PAPER APART. You can also see the effect of
INCREASING THE GLUE line. For example, if your gussets were 1" by 2"
and mounted asymmetrically, a single-sided gusset would give you a
glue-line of half inch along the top edge and 3/16th of a square inch
0.1875" along the front, for a total glue-line of 0.6875" = about a
ten-fold increase over the original dot of glue. (You may use a
clothes-pin as a clamp.)

Of course, the load would appear only in tension. Do a loop and you
might see enough compression along the forward 'arm' of the T to cause
the thing to fail.

So try it asymmetrically. Then try trimming it, to get of the
corner. Or use TWO gussets, one on either side of the joint and of
thinner stock than the original.

Or slit the sticks and slip a mid-line gusset into the slit (the
object here would be to reduce weight).

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

In late May I made a batch of 'T's and 'L's using redwood and cedar,
most salvaged from an old house. A few tests told me the old original-
growth redwood (about 28 TPI !) was superior in every way to some
'certified' spruce I happened to be working with at the time and,
initially, I was only interested in developing the properies of the
salvaged wood, thinking of using it as spar caps. Other than a few
splinters, the redwood did extremely well and I made a test rib and
other parts, subjecting them to destructive testing and recording the
results. Then I became ill and nothing was done for about a month so
that now, I am just regaining my interest in what was meant to be a
quick and fairly primative test. But ribs have gussets and when I was
able to fumble around in the shop I found the experiment waiting for
me, with batches of well-cured parts and a notebook that showed signs
of delirium which lead to my hospitalization.

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

There are other projects going on. It isn't hi-tek. In fact, you
could probably do a scratch-built of your own design using nothing
more than photos of previously successful airframes. Under those
conditions I don't think such exercises could serve as a regular means
of pain prevention... but for the short-term, and under the right
conditions such experiments have provided me with hours of
distraction.

Much of what I know about softwoods for use in airframes, kayaks and
the like, are the product of such tests. In some cases my experiments
DID NOT agree with the generally accepted numbers provided by the
FPL. In most others, the tests serve to confirm the safe, convenient
SUBSTITUTION of materials, not only because Spruce has become so
expensive but more so because some alternatives have proven SUPERIOR
to spruce, in that the finished structure not only weighed less, on
destructive testing it proved to be stronger.

At that point you really run into the exciting stuff, because it means
your home-made scratch-built has the potential to be constructed at
LESS WEIGHT but EQUAL STRENGH. It's a lot of trouble, of course. But
at the grass-roots level the home-builder is usually forced to accept
a GAIN in weight rather than an increase. Sick or not, when such
numbers begin developing across your spread-sheet, it sez your home-
built is liable to be SUPERIOR structure, it's simply too important to
ignore.

-R.S.Hoover