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 | CRACKS
Plastic engine cowls always look great on you airplane....until you start the
engine. Minor bumping, engine vibration eventually leads to cracks. You can stop the
crack from growing by drilling a hole at the end point of the crack. This "crack
stopper" is actually a device to relieve the high stress area at the end of the crack
and is a common practice in working with sheet metal. Reinforcement as outlined below will
help this in not occurring.
FIBERGLASS CLOTH
Fiberglass cloth and the blue ABS cement (the same stuff that you use to
glue your lawn sprinkler pipe together),makes good reinforcement for cowlings or wing
tips. Lay cloth inside the ABS part then paint on the blue goo. Let the glue set up and
you're ready to go.
Another is to rough up the inside of the cowl with heavy sandpaper (50-80 grit) or by
scratching with the sharp point of a #11 Xacto blade. Mix up a batch of resin (epoxy or
polyester) and lay fiberglass cloth inside the cowl. The bigger the cowl, the heavier the
cloth should be.
Still another method is use a product from SIG manufacturing called CELASTIC. It
comes in large sheets and is about 1/16" thick and is fairly rigid. Cut a section of
this material suitable for the area you want to reinforce and moisten it with acetone
until it become limp and mushy. This does not take long, nor does it take much acetone.
Now lay this material inside the cowl and form it to the contours of the cowl with your
fingers. The acetone will literally melt the cowl plastic and the Celastic together and
make a rigid, tough structure. After the Celastic dries out it can be sanded, cut,
drilled, etc and it will retain its strength.
PLASTIC MATERIALS
Two liter Coke bottles have a black plastic reinforcement on the bottom of the
bottle. This reinforcement piece makes an excellent radial engine cowling for your next
project.
REINFORCEMENT OF CENTER SECTIONS
Fabric and yardage stores sell a material product known as "pellon". This
can be used for general reinforcement and is especially good for wing center sections. Be
careful when you do apply it, as it does have "grain" and should be applied in
the direction that affords maximum strength.
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| RUBBER BANDS
Alliance brand rubber bands are the preferred brand for wing hold downs and other
model applications. They do not deteriorate as rapidly as American brand (and others). Try
them!
SECURING YOUR WINGS SECURING
YOUR WINGS
I suggest it takes two # 64 rubber bands for each
pound of total aircraft weight. Therefore, a six pound airplane would require at least six
rubber bands on each side of the airplane to properly secure the wing. If you see your
wing separate
separate from the fuselage while pulling out of a dive.. is another indicator that you do
not have enough rubber bands.
As a general rule I always use a minimum of 8 rubber bands for any given aircraft.
When you get the wing mounted and all the rubber bands you need over the wing,
put one more rubber band on the rear dowell going across the fuselage (not back over the
wing). When you are done flying for the day, slide your hold down rubber bands off the
front dowell. This rear rubber band will keep the others from flying all over the place.
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