Great Planes Ultra Sport 60 Kit - GPMA0420 Pages 28-48 - Manual (Page 16)

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? When you add power again, did the nose
pitch up a bit? 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 short-
cuts. 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 combi-
nation of trim settings. One bump of the transmitter and you
have lost everything. The trim must be repealable, 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 oppo-
site if the nose pilches up. The trick is to use only the ailerons
to get the model up at a 45-degree bank. We almost automati-
cally start feeding in elevator, but that's a no-no. Do the bank
in both directions, just to make sure that you arc 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. Al-
ways 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 remainder of the chart and note the myriad com-
bination 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 discemable 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 rudder errors. Even though we balance the wing stati-
cally 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 interac-
tive. 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.
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