Great Planes Extra 300S 1.60 ARF - GPMA1365 - Manual (Page 27)

combination of trim settings. One bump of the transmitter
and you have lost everything. The trim must be repeatable,
and 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 C.G., we roll the model up to a 45° bank, then take our
hands off the controls. 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° 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 into play here, so be patient and eliminate the
variables, one-by-one. The maneuver is a simple loop, but it
must be entered with the wings perfectly level. Position the
maneuver so that your assistant can observe it end-on.
Always loop into the wind. Do several loops, and see if the
same symptom persists. Note if the model loses heading on
the front or back side of the loop. If you lose it on the way up,
it’s probably an aileron problem, while a lose of heading on
the way back down is most likely a rudder situation.
Note that the Yaw test is the same looping sequences. Here,
however, we are altering rudder and ailerons, instead of the
elevator halves. We must repeat that many airplanes just will
not achieve adequate lateral trim without sealing the hinge
gaps shut. The larger you make the loops (to a point), the
more discernable the errors will be.
The Lateral Balance test has us pulling those loops very
tightly. Pull straight up into a vertical and watch which wing
drops. A true vertical is hard to do, so make sure that your
assistant is observing from another vantage point. Note that
the engine torque will affect the vertical fall off, as will rudder
errors. Even though we balance the wing statically before
leaving for the field, we are now trimming it dynamically.
The Aileron Coupling (or rigging), is also tested by doing
Hammerheads Stalls. This time, however, we want to
observe the side view of the model. Does the plane want to
tuck under a bit? If so, then try trimming the ailerons down
a small bit, so that they will act as flaps. If the model tends
to want to go over into a loop, then rig both ailerons up a few
turns on the clevises. Note that drooping the ailerons will
tend to cancel any washout you have in the wing. On some
models, the lack of washout can lead to some nasty
characteristics at low speeds.
Again, we reiterate that all of these controls are interactive.
When you change the wing incidence, it will influence the
way the elevator trim is at a given C.G. Re-trimming the wing
will also change the rigging on the ailerons, in effect, and
they may have to be readjusted accordingly.
The whole process isn’t hard. As a matter of fact it’s rather
fun — but very time consuming. It’s amazing what you will
learn about why a plane flies the way it does, and you’ll be
a better pilot for it. One thing we almost guarantee, is that
your planes will be more reliable and predictable when they
are properly trimmed out. They will fly more efficiently, and
be less prone to doing radical and surprising things. Your
contest scores should improve, too.
We wish to acknowledge the Orlando, Florida, club
newsletter, from which the basics of the chart presented
here were gleaned.
Reprinted in part by Great Planes Model Manufacturing
Company, courtesy of Scale R/C Modeler magazine, Pat
Potega, Editor, August 1983 issue.
See the Flight Trimming Chart on the back cover
ENGINE MOUNT TEMPLATE
Photocopy or cut out this template and use it
to mount your engine.
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