Great Planes Ultra Sport 40 Kit - GPMA0410 - Manual (Page 46)

that you arc 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 thrustline 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, 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 the C.G., we roll the model up to
a 45-degree 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-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 into play here, so be
patient and eliminate the variables, one-by-one. The
maneuveris 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.
After you get the inside loops going correctly, do
the same maneuver to the outside, entering from an
inverted position... Before you make too many dramatic
changes, glance at the remainderofthe chart and note the
myriad combination of things we can do just with the
ailerons. Each change you make will affect all other
variables!
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. Actually, we prefer the Hammerhead
as a better test for a heavy wing. 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 ruddererrors. 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. 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.
The effects noted with the Aileron Coupling
tests can also be caused by an improperly set wing
incidence. The better test for this is knife-edge flight..
If the model tends to pull upward, i.e., it swings toward
a nose up direction, then reduce the wing incidence. If the
model tries to go off heading toward the bottom side of
the plane, then increase incidence.
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.
Retrimming 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 leam 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 Manufac-
turing Company, courtesy of Scale R/C Modeler maga-
zine. Pat Potega, Editor, August, 1983 issue.
46