(The Embryo Experience... pg.2)
CONSTRUCTION
DETAILS
Thomas-
On the fuselage I use 7 to 10 lb. 1/16th square balsa
for longerons, and 5 to 7 lb.1/16th square balsa for crosspieces.
I don’t have any special technique of construction
here - I just build the two sides, one on top of the other,
and join ‘em on the plans.
For wings I use 7 to 10 lb.1/16th square balsa for the
leading edge, trailing edge, and spar(s). For ribs I choose
light 1/32nd C-grain (quarter grain) balsa. I cut out
a master template (sometimes from plywood, sometimes balsa)
and make all the ribs. Then I cut the notch for the spar
in the template and use the template to cut out the notches
on all the other ribs.
|
|
Landing gear wire is .025 music wire, formed with needle
nose pliers and sometimes round nose pliers. For wheels
I use 2 cross-grain laminates of 1/32nd balsa. I hardly
ever make wheel-pants, but when I do I make them from
3 sheets of balsa - 2 sides and the inner “fill”.
|
|
Nose
block is usually 3 pieces of 1/8th balsa laminated
cross-grain. CA works well for this application
because it cures fast and I generally need
the weight in front anyway. I have only use
aluminum tubing for the bushing to date but
they wear out faster than brass tubing.
Prop shafts are made from .025 music wire
also, with a reverse “S”
bend and a hook up front - or a Garami
clutch for freewheeling.
|
|
|
For covering I like to use domestic tissue because it’s
so inexpensive, and now I've found some with the same
weight as Japanese tissue (but it is still weaker then
the Japanese tissue). The tissue is pre-shrunk for covering
my lighter wing designs. After sanding the frame I then“prime”
it with thinned white glue.
I cover all my models “dry” using glue-stick
(UHU purple). I let the glue dry for a few hours, and
then I shrink it with pure alcohol on stab, wings, and
fin. On the fuse I use 7 parts alcohol and 3 parts water.
Finally, I seal the tissue with thinned nitrate dope (7
parts thinner 3 parts nitrate dope). 2 coats for the wings,
3 coats for the fuse, and 1 coat for the rest.
|
Joshua-
I select stiff 8 to 9 lb. 1/16” square balsa for
the fuselage longerons, and 5 to 6 lb. 1/16” square
for cross pieces and uprights. Any sheet fill is done
with the lightest 1/16 sheet I can find. The noseblock
and "key" are two pieces of 3/16” or 1/4”
balsa. Once the whole fuselage is built the nose block
is installed, and the whole assembly is sanded while together.
|
|
For the wing I usually make the leading and trailing edges
from 1/16”x1/8” 9 to 10 lb. balsa. These are
laid flat on their wide sides. The ribs are 5 to 6 lb.
1/32” or 1/16” sheet. Usually a single 1/32”
x 1/8” spar is set flat on the top of the wing at
30% of the chord. When sanding the wing I make both the
leading and trailing edges very sharp, to minimize drag.
The stab is normally built similarly to the wing, with
the same size spar and TE, but using a 1/16” sq
LE. Again, all surfaces are sanded smooth. The winglets
and rudders are 1/16” sq.
|
| Covering
is applied as smooth and tight as possible,
usually with plain domestic tissue. The adhesive
is thin white glue. The edges are overlapped
slightly for a smooth finish and all rough
edges are sanded smooth. I always make a small
address label and attach it to the fuselage
with waterproof glue... I put lots of time
into my planes and hate to lose them. |
 |
|
|
|
|
Most of my models receive no finish at all (not even dope)
unless they are intended for wet weather. A pop-up tail
dethermalizer is incorporated on the heavier models, actuated
by a silly putty timer. The landing gear
is made from .020 wire or .015 for lighter models, with
wheels being 1/32” balsa or 1/64” plywood
with 1/16” o.d. aluminum tubing hubs.
P prop blades are usually made from 1/32" sheet sanded
very thin, and formed over a can for helical pitch. I
cover the blades with tissue on both sides and then seal
with dope. The blades attach to 3/32” round bamboo
shafts, which plug into 1/8” o.d. aluminum. tubing
hubs. Spinners are made from solid balsa turned on a Dremel
tool, hollowed out, and attached to the hub. A freewheeling
ramp is made from brass or aluminum tubing. |
|
FLIGHT TRIMMING
Thomas-
I like to trim my embryos as follows:
- Take out rubber, nose block, and prop assembly and
add weights to nose till it glides like an eagle.
Mark the CG with a pencil. Take off the weights and
put the prop assembly, nose block, and rubber back
onto the plane and balance at the CG. Get the CG right!
- Trim for right power climb and right glide
- Wash-out left wing tip and wash-in right wingtip,
so right wingtip will stall first landing it in the
heart of the thermal.
- Give some “up” left elevator.
- Put in some low powered flights with 25 turns, then
100 turns, then 200, and keep going up till 500. Once
its all “good” wind it to max and enjoy!
|
|
Joshua-
My embryos are trimmed this way:
- No warps are used unless absolutely needed (except
for rudders)
- Trim for glide just as Thomas does, without prop,
changing CG to get it right. Strive for a long, smooth,
floating glide with a gentle right turn (right rudder
will do it fine).
- Under power, use the thrustline to achieve a right
turn and a steep climb with no looping tendencies.
In heavier models, this is translated into a steep
spiraling climb resembling a corkscrew.
- At full power, the model should take off from the
ground and climb straight up for 4-5 seconds before
slowly transitioning into the spiral. The entire flight
should be seamless, so smooth that you can’t
even tell when the power is full expended. Work your
way up in power slowly, adjusting at each increment
until the whole flight maximizes the design’s
capabilities.
- A properly trimmed short-winged model can handle
any weather conditions you throw at it. With 20”
or greater wingspans, the models require high power
to cope with high winds, but even they can handle
fairly strong winds.
- If you have a DT on your model, use it on every
flight. These things get lost very easily.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
