Great Planes P-51D Mustang 40 Kit - GPMA0175 - Manual (Page 48)

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 siraight-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 limes, 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 tnm 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
tnm settings. One bump of the transmitter and you have lost
everything. The tnm must be repcaiable, and the only sure way
to do this is to always start with the transmitter control tnms 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 pi tches up.
The tnck 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 vanables,
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.
After you get the inside loops going correctly, do the same
maneuver to the outside, entenng from an inverted position ...
Before you make too many dramatic changes, glance at the
remainder of the chart and note the myriad combination of things
we can do just with the ailerons. Each change you make will
affect all other vanables!
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 tnm without scaling 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 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 Raps 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 charactenstics at low speeds.
The effects noted with the Aileron Coupling tests can also be
caused by an improperly set wing incidence The better lest 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 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 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 im-
prove, too
We wish to acknowledge the Orlando, Florida, club newslet-
ter, 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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