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 adjustments until
you have the thrust line and/or C.G. correct. They are the
basis upon which all other trim settings 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, 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 loss 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 Page 23
22
