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Balance. We all need it in everything we do and our
model planes are no exception. Having
your model balance at the correct CG can make the difference between having
an aircraft that flies properly or has the possibility of an extremely short
life. Thus, came into being the CG
MACHINE from Great Planes to help make this task easier to do.  I’ve used any number of methods in
the past to set the CG of my planes but I’ve never been fully satisfied that
I’ve done it correctly. I’ve used
fingers, pencils with the triangle caps, strings and several other odd ball
methods. The least satisfactory has
been fingers and I’ve always wondered why assembly instructions lots of times
call for you to put your fingers at point x on either side of the wing and
balance the model that way. I’ve found
long ago that is the most primitive method of all. Thus we come to the CG Machine.
First,
make sure that the model has everything in it (radio, engine, fuel tank,
servos, spinner, cowl, etc), basically a finished model minus fuel in the
tank. At the top of the machine are
two pads that the plane will rest on. You move the two bases apart to
match the width of the fuselage so that a pad will be under the wing on
either side of the fuselage as close to the fuselage as you can get.  Then you place the plane on to the pads and adjust the position of the plane on the pads, till the wire pointers at the end of the Balancer Scale just touch the leading edge and are at 90° to the leading edge. Once you have gotten the model into this position, you are ready to balance. I usually have some pieces of lead and other heavy objects already at hand before I start. Now it is just a question of |
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seeing if the plane is nose or tail heavy and adding weights until the plane balances level or slightly nose
down. Once you have the plane in
balance, you then will know where and how much weight you need to add to
bring the plane into proper balance. Install the balancing weights and then retest on the CG machine. If all is well you’ll see something like
this:  All in all it is a fairly simple and easy tool to use, resulting in a
plane that has Balance! The CG Machine
does have 2 things to watch out for but are easily corrected. First has to do with the pads. They snap on and swivel on a pivot ball
that is at the end of a long rod. The pad has to move freely on
these balls and I mean freely. They
can not ‘stick’ in any position. I
found that one of my pads was extremely free from the start and the other had
some ‘stickiness’. The problem here is
that the plastic that makes up the pads is only so precise. The answer is NOT to lubricate the ball but
rather to use some fine Emory cloth to polish the ball till the pad does move
freely. Do not use a power tool to do
this. It will take some time but the
result is very satisfying.  The other thing to watch for is the Balancer scale. The actual ruler is accurate, however, you
assemble the ruler into the end caps of the scale with the wire
pointers. In doing so you glue the
ruler into place and make sure it is 90° to the wire pointers. Again because plastic is only so precise,
you have to see how accurate the distance from the back of the wire pointers
to some number on the rulers are. In
my case, measuring from the back of the pointer to the 2” mark, I found that
the 2” mark was really 2 1/16” from the back of the wire pointer. The other was 2 1/32” from the back of the
wire pointer. This is not a
problem. You just have to take it into
account. So to get 2” on my left ruler
I set it for 1 15/16” and similarly
adjust my other side. This is an inexpensive, simple to
use tool that will help you to correctly balance your model aircraft and I
highly recommend it being part of your shop. |
Great Planes CG Machine
by Rick Hanners |
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