(Sparky
Rediscovered... pg2)
I reviewed the folding propellor assembly, and
more critically, the built up spinner assembly.
The spinner feature appeared to be the most challenging
portion of the design , and in the end I abandoned
the idea in favor of a spinner-shaped nose block
with a non-spinnered free wheeling prop.
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I built up the nose block and turned it to
shape using my drill press as a lathe, and
installed a large Peck thrust button at both
the front and rear of the assembly. This was
pretty much in accordance with what was shown
on the plans for the stock front end. I also
duplicated the pins that are used to keep
the nose block in place with rubber bands,
the only mod here was to use T-pins on the
fuselage sides instead of a beaded pin.
The propellor is carved from a one inch thick
hard balsa blank, 9 ½ inches in long,
with the blades 1 ½ inches wide at
the widest point. I added lengths of .015
music wire to the finished prop L.E. to help
prevent damage here as another modification. |
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The free wheel is simply .024 aluminum which is
used to face the front and rear of the balsa hub,
with one end of the front tang bent up and filed
off at a shallow angle to allow the prop shaft to
easily freewheel. Typical Earl Stahl stuff that
works well.
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Wheels
were fabricated from slices of end grain
balsa, turned to shape on my drill press.
Wing and tail construction are quick and
straightforward. I encountered no difficulty
in assembling these components. |
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Everything was covered with white Japanese tissue.
The hardest part to deal with is the area of the
wing pylon from the rear cabin uprights to the spine
on the dorsal area. Following the plan indication
to orient the tissue grain on the diagonal here
seemed to work - I had no wrinkling on these areas
at all.
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I found the flat pattern for the windshield to be
very accurate when test fitting. I neatly Scotch
taped the trailing edges of the clear windshield
to the tissue covering to secure the basic part,
and then used tissue strips to define the borders
and cover the taped area. This all was sealed with
clear dope, and held the clear plastic in place
just fine.
After two coats of 50% thinned dope on everything,
the color trim was the only part left to perform.
I airbrushed Aero Gloss Stearman Red as the trim
color, following the scheme shown on the plan sheet.
Instead of masking with tape, I made masking paper
templates of the scalloped trim on the fuselage
side, and positioned these in place. Once located,
I brushed clear dope under the edges to adhere the
masking paper to the tissue, and seal the edge from
paint bleed through. The windshield area was carefully
masked with tape, to give a nice border to the color.
I then employed my Paasche airbrush to apply thinned
red dope to the forward fuselage, wheels, landing
gear wire, and the prop and noseblock assembly.
With the airbrush, the color goes on in a very even
and translucent manner - the end result is a very
transparent finish that looks as if it is part of
the tissue itself.
For the wing and tail L.E. color, I simply located
a strip of masking paper along the L.E., slightly
aft to the dimensions of the edging color I wanted
to add. I did not mask or seal this edge of the
paper down to the tissue covering - I simply held
the airbrush at a slight angle that would always
push the paint away from the edge of the mask. The
result was a stenciled edge - very crisp, with no
risk of damaging the tissue due to peeling away
tape. This works well for a fairly low contoured
surface.
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Prior to first flight, I attempted to balance Sparky.
The finished model with an eight strand motor was
fairly tailheavy, so I added the usual bits of lead
to get the CG where I thought it should be. During
my initial hand launch test flights, the model appeared
to be overly nose heavy. Perplexed, I started removing
lead until I had a perfect flat glide and painless
wheel landing - then looked at the balance point
again. It had moved considerably aft, and then it
dawned on me why this apparent anomaly was there.
The lifting horizontal tail surface was making the
flight performance work out in spite of the balance
point being so far aft. I assume this to be a strategy
to eliminate extra nose ballast weight in the design...
very clever.
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The first power flight was totally perfect
with no nasty habits at all. The coarse pitch
prop just ticked slowly through the air, pulling
Sparky along into a shallow right turning
climb to about 75 feet, and then cruised along
until the free wheel started, at which point
it settled gently back to earth for a nice
wheel landing. |
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The second flight with more winds produced a longer
and higher result, a perfect cruise with the early
morning sun lighting up the translucent covering
against the blue sky-the stuff dreams are made of!
To date, I’ve only made five flights, and
have not begun to explore additional power. Eight
strands of 1/8 does not appear to challenge this
model too much-it could probably go with quite a
bit more power safely.
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Anyway, this Sparky came out of the blue to me -
I truly enjoyed building it, and am having even
greater joy in flying it. When I brought it out,
I thought it was a somewhat obscure design, not
knowing anything about it. But everyone at the field
came over to see it, and let me know about all the
Sparky models they had each built in the past! So
I had lots of help that morning, and I’m sure
they all enjoyed seeing one of their favorite models
in the air again.
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