On Dec 23, 5:38*am, "Morgans" wrote:

Yep, basswood would be a real good guess, and birch would be my second
guess.
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Dear Jim and the Group,

Some of you have been asking if this thread has anything to do with
the Chugger Project, and if so, shouldn't it be included there. The
answer is a qualified 'Yes,' in that the structure will appear in both
the Chugger as well as the Primary Glider, assuming I live long
enough.

Right now, the thread has to do with fast-curing epoxy and it's
availability through Harbor Freight. That brought some mail wanting
to know just HOW this applied to the Chugger/Primary experiments, so
I've concluded this message with an explanation that will hopefully
answer many of your questions.

So let's get back to the show :-)
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I don''t think you'll see any spruce tongue depressors. Not in North
America. Poplar and birch but no softwoods at all. This is based on
about two dozen samples, purloined from examining rooms at medical
facilities in northern San Diego county between June and December,
2008. Since some of the examining rooms were in the same facility
it's fair to assume they had the same source of supply so the two-
dozen figure should be adjusted downward to about six ordering
sources. (Even then, I've a hunch some of those will be dupes.)

The 'ice cream' size sticks were hardwoods; probably poplar, but
that's based on only two samples: New surplus 'Hobby Sticks' in one
case, 'mixer/stirer' sticks in the other, the latter purchased from a
local composites retailed, the former ordered via mail from American
Science & Surplus.

Why the interest in the specie & source? Because of the material's
strength in the first case, and the chance of the wood being treated
with an antibacterial compound on the other. Mixing or 'hobby' sticks
(ie,'ice cream sticks) won't have any antibacterial treatment. Tongue
depressors MAY be treated if they're shipped 'bare' -- about fifty in
a sealed plastic pouch. But some are shipped individually sealed in a
paper sleeve bearing advertising for various drug dealers and the
paper or the tongue depressor emits a mild chemical odor indicating
some form of antibacterial treatment. Tests with epoxy shows the
chemical does NOT interfere with making bond that passes the FPL's
standard shear-strength test, albeit one that has been scaled down to
match the material.

Size-wise an average of five gave the following dimensions: Tongue
depressors, length = 5-29/32" (5.94") 150.889mm, width
29/32" (0.90625) 23mm, thickness 1/16" (0.068) x 1.727mm
Ice stick dimensions: Length 4-7/16" (4.423) 112.344mm, width
3/8" (0.478) 12.14mm, thickness 1/16" (0.084) 2.13mm

I've mentioned the sizes here because one of the Chugger's experiments
is the use of redwood plaster lath instead of spruce as a building
material. The reason for this is because all six varieties of redwood
are a close match for Sitka Spruce when it comes to weight & strength,
plus the spec for plaster lath is that it must have a run-out of not
less than 1:16 (ie, the distance between studs in a wall), and it must
be clear -- no knots! Plaster lath comes in lengths up to 8 feet.
It's nominal width is 1-1/4" wide x 1/4" thick but it is ROUGH SAWN
and deliberately left brash, so as to offer a maximum amount of
'tooth' for the plaster. And it's relatively inexpensive. The
problem is that brashness. The surface is so rough that it's
impossible to get a good glue bond unless you use a filled adhesive OR
take the trouble to run the lath through a surface plane. Alas, the
typical plane wants a sixteen of an inch. Take that off both sides
and you're left with a rather whippy stick barely an eighth of an inch
thick. Which is fine if you're making wing-tip bows, or the Chuggers
rudder.

I've used redwood lath for the spars in a simple tail group, in which
the C-type hinges were made from steel strapping. This stuff is
pretty whippy being only .023" thick. But it's steel and it's free,
if you do a bit of dumpster diving, plus it's easy to work with. One
problem with it: It's so thin it will cut through the typical hinge-
pin ( a nail or Cotter key ) in about 100,000 movements at max load.
The solution (for me) was to add more hinges, which meant doing the
ends first then aligning the others with a length of thread, fixing
them in place with neatly shaped pieces of ice-cream sticks and FAST-
SETTING EPOXY. Once I'd boxed the fitting, I drilled through it for
8-32 hardware. The hinges sit atop a foundation of tongue depressors,
which solves the problem of the rough-sawn surface of the redwood.

Alignment of the rudder and elevator is even easier: Simply attach
the mating half of each particular C-type hinge to its partner, attach
the rudder spar to the vert. stabilizer spar using only the END
hinges, then align those in between, fixing the hinges into place
using the method described above.

This method meets the Chugger's design philosophy of minimum cost.
Tests indicate the hinges are more than strong enough. (See the blog
article 'Tail flapper failure.') The parts are locally available for
most of us.

The purpose of the hinge is rather subtle and from a design point of
view, you want the encountered loads to appear across the hinges. To
get them there, you use ribs or diagonals that are stiff enough so as
not to buckle. Redwood stringers and door-skin shear-webs on ribs
that are fabricated in place work perfectly well. But so does bamboo
shish-kabob skewers and fiber gussets, and they weigh but a fraction
of the traditional spar-cap/shear-web design.

-R.S.Hoover