Great Planes Giant Aeromaster Kit - GPMA0502 - Manual (Page 49)

A model is not a static object Unlike a car, which can only hunt
left or right on the road (technically a car does yaw in corners and
pitches when the brakes are applied) a plane moves through that
fluid we call air in all directions simultaneously The plane may
look like it's going forward but it could also be yawing slightly,
slipping a little and simultaneously climbing or diving a bit. The
controls interact Yaw can be a rudder problem, a lateral balance
problem or an aileron rigging problem We must make many
flights, with minor changes between each, to isolate and finally
correct the problem.
The chart accompanying this article is intended to serve as a
handy field reference when trimming your model Laminate it in
plastic and keep it in your flight box You just might have need to
consult it at the next contest' The chart is somewhat self-
explanatory, but we will briefly run through the salient points
First, we are assuming that the model has been C G balanced
according to the manufacturer s directions There s nothing sacred
about that spot — frankly it only reflects the balance point where
a prototype model handled the way the guy who designed it
thought it should If your model s wing has a degree more or less
of incidence then the whole balance formula is incorrect for you.
But, it's a good ballpark place to start.
The second assumption is that the model has been balanced
laterally Wrap a strong string or monofilament around the prop
shaft behind the spinner then tie the other end to the tail wheel or
to a screw driven into the bottom of the aft fuse Make the string
into a bridle harness and suspend the entire model inverted (yes,
with the wing on
1
) If the right wing always drops, sink some
screws or lead into the left wing tip, etc You may be surprised to
find out how much lead is needed.
At this point the model is statically trimmed It's only a starting
point, so don't be surprised if you wind up changing it all One
other critical feature is that the ailerons must have their hinge gap
sealed If shoving some Scotch tape or MonoKote into the hinge
gap to prevent the air from slipping from the top of the wing to the
bottom and vice-versa, bothers you, then don't do it.
To achieve the maximum lateral trim on the model, the hinge gap
on the ailerons should be sealed The easiest way to do this is to
disconnect the aileron linkages and fold the ailerons as far over
the top of the wing as possible (assuming they are top or center
hinged) Apply a strip of clear tape along the joint line. When the
aileron is returned to neutral the tape will be invisible and the gap
will be effectively sealed Depending on how big the ailerons are,
and how large a gaping gap you normally leave when you install
hinges you could experience a 20 percent increase in aileron
control response just by this simple measure
Your first flights should be to ascertain control centering and
control feel Does the elevator always come back to neutral after a
180-degree turn or Split-S? Do the ailerons tend to hunt a little
after a rolling maneuver? Put the plane through its paces Control
centering is either a mechanical thing (binding servos, stiff
linkages, etc), an electronic thing (bad servo resolution or dead-
band in the radio system), or C.G. (aft Center of Gravity will make
the plane wander a bit) The last possibility will be obvious, but
don't continue the testing until you have isolated the problem and
corrected it.
Let's get down to the task of trimming the model. Use the
tachometer every time you start the engine to insure consistent
results These trim flights must be done in calm weather Any wind
will only make the model weather-vane Each "maneuver" on the
list assumes that you will enter it dead straight-and-level The
wings must be perfectly flat, or else the maneuver will not be
correct and you II get a wrong interpretation. That's where your
observer comes in Instruct him to be especially watchful of the
wings as you enter the maneuvers
Do all maneuvers at full throttle The only deviation from this is if
the plane will be routinely flown through maneuvers at a different
power setting
Let's commence with the "engine thrust angle" on the chart. Note
that the observations you make can also be caused by the C.G , so
be prepared to change both to see which gives the desired result
Set up a straight-and-level pass The model should be almost
hands-off Without touching any other control on the transmitter,
suddenly chop the throttle Did the nose drop
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When you add
power again, did the nose pitch up a bit 7 If so you need some
downthrust, or nose weight. When the thrust is correct, the model
should continue along the same flight path for at least a dozen
plane lengths before gravity starts to naturally bring it down
Do each maneuver several times, to make sure that you are
getting a proper diagnosis Often, a gust, an accidental nudge on
the controls, or just a poor maneuver entry can mislead you The
thrust adjustments are a real pain to make On most models, it
means taking the engine out, adding shims, then reassembling
the whole thing. Don't take shortcuts Don t try to proceed with the
other trim adjustments until you have the thrust line and/or C G
correct They are the basis upon which all other trim setting
are made.
Also, while you have landed, take the time to crank the clevises
until the transmitter trims are at neutral Don't leave the airplane so
that the transmitter has some odd ball combination of trim settings
One bump of the transmitter and you have lost everything The trim
must be repeatable, the only sure way to do this is to always start
with the transmitter control trims at the middle.
The next maneuver is somewhat more tricky than it looks To
verify the C G , we roll the model up to a 45 degree bank, then
take our hands o f f the c o n t r o l s The model should go a
reasonable distance with the fuse at an even keel If the nose
pitches down remove some nose weight and the opposite if the
nose pitches up The trick is to use only the ailerons to get the
model up at a 45-degree bank We almost automatically start
feeding in elevator, but that's a no no Do the bank in both
directions, just to make sure that you are getting an accurate
reading of the longitudinal balance.
We now want to test the correct alignment of both sides of the
elevator (even if they aren't split, like a Pattern ship's they can
still be warped or twisted). Yaw and lateral balance will also come
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