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YOU LEARN a lot from watching
what happens at the flying field on a Sunday afternoon and even more
from the beginners. You learn what the basic flying skills really are
and, most important, you see the beginners struggling with their
trainers' shortcomings.
In all fairness, even the best of these designs
are often built (or assembled from ARF kits) by inexperienced
enthusiasts. It would be almost impossible for it to be any other way!
So much hard-earned experience goes into building a well-behaved RC
airplane, more goes into installing the mechanical and electronic
systems, and even more goes into adjusting or trimming for best flight
performance. The purpose of this "From the Ground Up" installment is to
make it easier to gather that knowledge and experience.
When I refer to
"best flight performance," I don't mean making your trainer perform like
a P-51; I mean getting your model to perform its intended "mission" as
well as it was designed to. For a trainer that mission is to be well
behaved, predictable, and have solid control, especially during takeoff
and landing.
The mission of sport and Scale airplanes is similar to the
following—with some additions, depending on the type of model. It would
be good for a Scale airplane to be well behaved while performing any
maneuver that is typical of the prototype. For the sport flier it would
be nice if the airplane's predictable behavior helped him or her "look
good" while enjoying the sport.
On the other hand, many airplanes have
what we often call a "personality." That's code for "It ain't quite
right but I'll live with it."
Sometimes experienced fliers do not even
realize they're living with a model's undesirable quirks; either their
skills are good enough to cover for it or maybe they have never had
their hands on a dead-honest airplane. It can be an eye-opening
experience! Students don't have those skills yet, and they have no basis
for comparison at all; and that can be a problem.
That, in a nutshell,
is why we are here: to learn that you don't have to live with it. We can
make it better and your flying will benefit at all skill levels, from
beginner to highly competent. Most important, as a student your learning
curve can be shortened if your airplane is working with you rather than
against you.
Click on photo to view large image with caption
The Kinds of Problems to Be Fixed: Your Model's
"Personality Problems": The list of common trim problems is not that
long. It doesn't have to be because any problem can make flying your
airplane difficult. Multiple problems usually add up to more than the
sum of the individual parts. There is often more than one cause for a
particular problem, and we must figure out where to attack.
1) Poor
aileron control response (especially at low airspeed) and directional
trim that changes at different airspeeds make accurate flying difficult.
These two problems can make it unnecessarily hard to learn to land.
It's
tough enough for a student to learn left from right while on the landing
approach, but if the airplane tends to deviate to one side and then the
control you use for correction becomes sluggish, you have the beginnings
of a panic situation. This is supposed to be fun, and we just don't need
panic situations!
2) A tendency to veer off in one direction (usually
the left) when climbing or when full power is applied adds an
unnecessary workload during takeoff. Combine this with poor aileron
control response, and you have another potentially unsafe combination.
3) If your airplane drastically changes pitch trim with changes in
throttle and airspeed (meaning it's either climbing or diving without
elevator input), it's a problem that can lead to a loss of airspeed and
control at the wrong time. This can combine with both of the preceding
to create even bigger problems.
Depending on the airplane's mission, we
often intentionally set it up to climb with full throttle (but not too
steeply), to maintain level flight at cruise power (maybe a bit more
than half throttle), and to finally descend at a gentle glide slope
(with enough airspeed for good control) at a fast idle.
4) This next
problem is closely related to the preceding problem. If the airplane
does not settle into a predictable glide slope when the throttle is
reduced, this can add to the pilot's workload during final approach and
landing. A proper glide has a predictable sink rate that is just steep
enough to maintain adequate airspeed for good control, but it is not so
steep or so fast that it makes it hard to get the airplane to settle to
the ground in the flare.
The flare is that last portion of the landing,
in which up-elevator is added to almost stop the descent rate and bleed
off the last bit of excess airspeed. This makes the model touch down in
a three-point attitude if it is a tail-dragger or with the main gear
first and the nose wheel an inch off the ground in the case of a
tricycle-geared model.
If the glide is too shallow, the airplane will
mush along with the nose up and with low airspeed, leading to poor
directional control authority. This often leads to the problems in item
1. You will often find experienced pilots landing a particular airplane
"hot," or fast, every time because the model has a controllability
problem at low speed.
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