106 MODEL AVIATION
Mike Hurley, 11542 Decatur Ct., Westminster CO 80234; E-mail: [email protected]
RADIO CONTROL SCALE AEROBATICS
Peter Goldsmith is the Team JR manager. He is originally from
Sydney, Australia, but currently lives in Illinois and works for
Horizon Hobby.
Peter with his own-design 46% CAP 232 that he used in the TOC.
He competes on an international level in several forms of RC,
including Soaring, F3A Pattern, and Scale Aerobatics.
ONE OF THE most overlooked—no, forgotten—steps in building a
new model and getting it ready for competition is trimming it for
precision flight. I don’t mean adjusting the aileron and elevator trim. I
mean tuning your airplane to fly to the best of its ability. I’ll admit it;
I’ve never fully trimmed one of my airplanes. I usually end up buying
or building the next big thing! Maybe all I needed to do was spend a
few days out at the field getting it dialed in just right. Trimming is a
forgotten art by many modern competitors.
This is the second of a two-part series by Peter Goldsmith about
trimming and adjusting your competition aircraft for precision flight. In
the first part (in the February 2005 issue) he led us through adjusting
the physical aircraft for fore and aft CG, dynamic balance, and enginethrust
offset. This issue will focus on trimming with your radio,
adjusting differential, and using your radio’s mixing features to reduce
your workload while flying.
If you recall, Peter’s method relies on a sequential series of
adjustments, each building on the corrections made by the last. If you
make any of the adjustments out of order, it may be doing more harm
than good, so you must follow the methodology. And before you start
adjusting your radio mixes, you must have your CG, dynamic balance,
and engine offset adjusted correctly.
Rip these columns by Peter Goldsmith out of the magazine and stuff
them into your flight box. Get out to the field and follow his adjustment
method. You’ll have the best-flying model you’ve ever owned, and all
it will cost you is time. I’ll let Peter take it from here.
Differential: Aileron differential is one of the most important aspects
of model trim. With the multiple point rolls on up- and down-lines in
today’s modern patterns, poor differential can be a real headache.
The good news is that it’s pretty easy to detect and adjust for axial
rolls. You might remember from last time that at this stage of the
game—knowing that CG, thrust, and wing weight are correct—we can
proceed with our differential setup.
Aileron differential is required when the drag of the down-going
aileron does not match the up-going aileron. If your model’s ailerons
are not working in unison, its vertical rolls will look like a mess.
Let me digress. Make absolutely sure that you are not getting
surface blowback. You will never get your differential correct if you
are. It’s easy to check for blowback. Push to a vertical down-line and
roll to the right, stop rolling for a second, and then roll again. The roll
rate should be the same. If it is slowing, your model’s surfaces are not
reaching their intended throws.
Another way to check is if the up-line roll rate is faster than the
down. Do what needs to be done. Either increase the servo power or
improve the geometry by reducing the servo-arm radius and/or by
increasing the distance the control-horn pickup is from the hinge line.
Or, if you have lots of cash, add more servos. Whatever path you take,
you can’t afford to have surface blowback. If you do, flying will never
be consistent.
Okay, where was I? Yes, how do we know when to add
differential?
Make sure you have a way to electronically adjust your aileron
travel individually. Most modern radios have a differential program. I
have used the ATV (Adjustable Travel Volume) function or the
differential function, and both work well.
Checking for differential problems is simple. I have used this
method for years and it works. Use the same technique as before when
checking for the thrust. Fly directly overhead and away from you. This
time pull only to a 45° up-line, making sure you are flying either
directly into the wind or directly downwind.
Using full aileron deflection, roll to the right. If the aircraft “walks
to the right,” you have too much down travel on your ailerons. If the
model “walks to the left” when you roll it to the right, you have too
much up travel in your ailerons. Repeat this process to the left as well
until you are satisfied that your model is tracking true in the roll axis.
As with the thrust angles, don’t expect your model to continue to
roll for 5,000 feet on a string. It just can’t be done. Per previous
recommendations, go for the majority
situation. There are not that many 5,000-foot
up- and down-lines. Fortunately.
With the correct differential on your
model, you will be amazed by how easy it is
to do hesitations on lines. Another benefit is
in point rolls on a horizontal line. The rudder
will have an even feel on both sides, as your
model will not be barreling in the rolls.
Mixing: You will notice that this topic is the
last in the sequence, but it’s where many
people go first! I get phone calls all the time
from excited pilots saying, “Pete, I just testflew
my new Edge; it only has 8% aileron
mix and 4% knife-edge mixing.” Boy, I
think, they sure got to the details of trimming
their models faster than I can. If you stick to
the correct trim sequence, you may be ready
after only 10-20 flights to work on the
mixing to fine-tune your model.
I’ve broken the Program Mix (P-mix)
topic into two sections. The first is the downline
torque offset, or throttle offset mixing.
The second is the traditional rudder to
elevator/aileron mixing. Most pilots have a
fairly good understanding of the latter, but
not many are using throttle offset mixing. I
have seen some, but only in the pitch
compensation. Pay attention to what your
model is doing on a down-line or at reduced
throttle (idle) in the roll or yaw axis.
One of the benefits of judging our events
is that you see many strange trim situations. I
can clearly remember models at the Nats
rolling on down-lines and yawing off-axis,
causing some strange-looking down-line
rolls. It’s almost impossible to have perfect
trim in roll at all speeds. All you can hope for
is to mix in some compensation to help
reduce your workload.
The yaw and the roll axis, in most cases,
have a bigger effect on your model tracking
on down-lines than any other situation.
Imagine what the effects of a 5° error on
every down-line would mean. Over the
height of the box, your airplane can drift in or
out by as much as 150 feet. The same applies
to the roll axis. Have you ever noticed how
hard it is to get the wings level when
approaching a pull corner with little time?
With your model rolling and yawing at
different speeds, you will never be consistent.
It is hard enough to be sure if your wings are
level, let alone chase an out-of-trim situation.
The good news is that it’s fairly easy to
compensate for.
Throttle-to-Aileron Mixing: Let’s do the
roll axis first. You can do this either of two
ways, and both work well. In fact, I suggest
that you try both to get the best input.
The first way is to climb your model to a
high altitude, simulating a typical top-of-thebox
altitude, and fly it directly over your head
and into the wind. Roughly 50-100 feet out
from yourself, push down. Watch carefully to
see if the model is rolling on the down-line.
Most models will roll slightly to the right as
the aileron trim set for full throttle will be too
much at low throttle as the torque effects will
be greatly reduced.
Okay, I know many of you fly with no
aileron trim. That’s great, but I’ll bet you are
carrying trim at reduced throttle. I have never
had a model that hasn’t needed a little left
aileron mix on low throttle.
The second way to check for throttleaileron
mix is to fly along at level flight,
medium height, and reduce the throttle.
Watch carefully and see if your model is
rolling; chances are that it is. Have you ever
wondered why you always have to lean a
little left aileron entering spins or why your
model always falls one way? Perhaps it’s
because your low power trim is not correct.
Throttle-to-Rudder Mixing: The second Pmix
is the throttle to rudder. Again, it’s hard
to get your model to track correctly in the
yaw axis at all speeds. Your only hope is to
apply a small amount of “left” rudder on low
throttle.
To check for this, use the same technique
as the throttle to aileron (in the preceding).
Fly the model above yourself, directly into
the wind, and push down in front of yourself
and watch carefully. You will be amazed,
especially at the start of the down-line. If you
haven’t gotten any throttle offset to rudder,
you are most likely flying around the
problem, and where I find it most challenging
is in figure 9s and vertical and horizontal 8s.
Anytime you are using elevator and are off on
the yaw axis, it’s a bad day.
I can hear all of you saying, “Yes it’s true;
my model could need a little rudder mix on
low throttle.” Give it a try and you will be
amazed.
I know of some fairly experienced
modelers who use the same theory but reverse
where the mix is. They use little to no right
thrust on the engine but have right rudder
mixed on full throttle. That works well too,
I’ve been told, but I haven’t tried it.
Something you may want to experiment
with in both of these scenarios is where the
mix is activated. For a low-throttle left-rudder
mix, I like to have the stick offset start at least
above half and let it progress from there as I
reduce the throttle. It seems to be the best
balance, and I am not getting a sudden mix
input; it progresses more or less with the
model’s speed. This will vary from model to
model, but try to keep the mix activation well
above an idle setting.
Rudder-Aileron Mixing: Earlier I made
reference to pilots applying programmable
mixes in their trim program. This is the last
thing you do. Looking through the sequence,
each trim adjustment has complemented the
next stage. In most cases, for rudder-aileron
mix, a linear P-mix is all that is required.
What I mean by linear P-mix is that you don’t
need a progressive value to the mix; i.e., less
at the start and more at the ends. The mix will
be linear.
What causes adverse roll or proverse roll
coupled to the rudder is the incorrect dihedral.
Most modern designs, with the exception of
biplanes, are really close and only require a
small amount of rudder-aileron mix. Some
like to put their models on knife-edge, but I
like to just do flat turns, simulating rolling
turn inputs.
Rolling turns require more precise mixing
than sustained knife-edge flight. In a contest
your model doesn’t do much flying on its
side, but it sure does a lot of rolling turns. So I
like to do the flat-turn thing. Doing a simple
inside rudder turn to the left, using left rudder,
the model should just yaw, with no roll effect.
If the roll rolls to the left, you need to mix
2%-5% right aileron to left rudder.
My CAP is unique in that it has adverse
roll. When I apply left rudder the model rolls
right, so I need left aileron mixed with left
rudder. Repeat the process with right rudder.
Now I want you to vary the speed at
which your aircraft does flat turns. If you find
that the mix becomes too much as you
increase your model’s speed, you could be
getting surface blowback. I’m sorry to keep
harping on this, but it is important.
With insufficient rudder power, when you
apply a P-mix for roll, or pitch for that matter,
the mix value will become too much as the
rudder throw reduces because of aerodynamic
pressure. I see a few lights going on again.
Could this be why you have your mix perfect
for knife edge, but you chase your aircraft
everywhere doing rolling circles?
Rudder-Elevator Mixing: I think about three
times in my entire life when I had a model
that didn’t need rudder-elevator
compensation. As with the previous rudder
aileron, start by doing a flat turn to the left and
see what happens. If your model pitches down
when rudder is applied, mix a small amount
of up-elevator; if it pitches up, apply a small
amount of down-elevator. In some cases, even
without blowback, the mix value will not be
exactly correct for all throttle settings.
Don’t panic because, as with most modern
radios that are suitable for aerobatics, you can
use what is called a curve mix. It allows you
to have multiple points along your mix curve
to increase or decrease your mix value at
different rudder inputs.
My CAP is a good example of this. At low
rudder throws I need only 1%-2% mix, but as
the throw increases I need as much as 10%. If
I have just a 10% mix, it will be too much at
small rudder inputs. The curve mix is
designed to solve this problem.
Tricks of the Trade: I’m going to share a
few tricks of the trade to help you with your
competition efforts. By now you probably
have an idea of how much work there is in
trimming a model. Considering all things
equal, you will have a hard time beating a
person with the same skills you have but with
a model that is more properly trimmed. It took
me 20 years to figure most of this out.
Be patient, be observant, and be objective.
If your model is not flying right, investigate
why. Chances are that it’s just not trimmed.
Even if your models are not straight, you can
trim them. I can almost guarantee that my
models are at the lower half of building
accuracy. They all carry aileron trim and
elevator trim. I don’t have a nuclear-powered
building bench with warp-speed laser meters,
nor do I have a 12-foot-square by 8-inch-thick
granite table on which to build.
Don’t feel as if you have a disadvantage if
your model is not perfect; you can trim it
pretty well. It makes me laugh to hear people
talk about how straight their models’ wings are
and how perfectly their models are trimmed,
yet even with perfectly trimmed models, they
fly with their inside wings down 5°-10°.
If your model’s not level in all orientations,
vertical and horizontal, at the top and the
bottom of the box, you will have a lot of work
on your hands. Probably the biggest
progression I’ve made in my flying career was
when I learned to fly level. The truth was that I
didn’t know my airplane wasn’t level!
I started watching other pilots and noticed
that everybody flew with their inside wings
down; nobody flew level. From that point I
went home, made three flags—red, white, and
blue—and asked my helper to go out and
stand under the flight path and keep me level.
I think red was for inside wing down, white
was for level, and blue was for outside wing
down.
The next month or so was one of the most
dramatic learning times of my life. My
workload doing maneuvers was reduced
immensely. I found myself just waiting for the
next input—not my normal 54 inputs all the
way up to vertical! I could pay more attention
to corner radius, centering rolls within legs,
and so on. It was a truly amazing
breakthrough. I encourage all of you to
investigate flying level.
Many people ask me the following
questions. “What’s the best thing I can spend
my money and/or time on to improve my
results at events?” “Should I get a more
powerful engine or a better aircraft?” “What
style should I fly?”
The truth is that all of these things are
important, but the best thing you can spend
your money on is gasoline and oil. Practice.
Try to avoid letting your ego be your only
motivation. Be objective, be humble, listen,
watch, and experiment. That’s what all of the
TOC (Tournament of Champions) and
Masters pilots do. Sure, we all have egos, but
at some stage in our lives they let us down; we
are humbled and forced to listen and be
objective.
Stay cool and hopefully we can catch up at
the next Aerobatics event! MA
Edition: Model Aviation - 2005/04
Page Numbers: 106,108,110,114,116
Edition: Model Aviation - 2005/04
Page Numbers: 106,108,110,114,116
106 MODEL AVIATION
Mike Hurley, 11542 Decatur Ct., Westminster CO 80234; E-mail: [email protected]
RADIO CONTROL SCALE AEROBATICS
Peter Goldsmith is the Team JR manager. He is originally from
Sydney, Australia, but currently lives in Illinois and works for
Horizon Hobby.
Peter with his own-design 46% CAP 232 that he used in the TOC.
He competes on an international level in several forms of RC,
including Soaring, F3A Pattern, and Scale Aerobatics.
ONE OF THE most overlooked—no, forgotten—steps in building a
new model and getting it ready for competition is trimming it for
precision flight. I don’t mean adjusting the aileron and elevator trim. I
mean tuning your airplane to fly to the best of its ability. I’ll admit it;
I’ve never fully trimmed one of my airplanes. I usually end up buying
or building the next big thing! Maybe all I needed to do was spend a
few days out at the field getting it dialed in just right. Trimming is a
forgotten art by many modern competitors.
This is the second of a two-part series by Peter Goldsmith about
trimming and adjusting your competition aircraft for precision flight. In
the first part (in the February 2005 issue) he led us through adjusting
the physical aircraft for fore and aft CG, dynamic balance, and enginethrust
offset. This issue will focus on trimming with your radio,
adjusting differential, and using your radio’s mixing features to reduce
your workload while flying.
If you recall, Peter’s method relies on a sequential series of
adjustments, each building on the corrections made by the last. If you
make any of the adjustments out of order, it may be doing more harm
than good, so you must follow the methodology. And before you start
adjusting your radio mixes, you must have your CG, dynamic balance,
and engine offset adjusted correctly.
Rip these columns by Peter Goldsmith out of the magazine and stuff
them into your flight box. Get out to the field and follow his adjustment
method. You’ll have the best-flying model you’ve ever owned, and all
it will cost you is time. I’ll let Peter take it from here.
Differential: Aileron differential is one of the most important aspects
of model trim. With the multiple point rolls on up- and down-lines in
today’s modern patterns, poor differential can be a real headache.
The good news is that it’s pretty easy to detect and adjust for axial
rolls. You might remember from last time that at this stage of the
game—knowing that CG, thrust, and wing weight are correct—we can
proceed with our differential setup.
Aileron differential is required when the drag of the down-going
aileron does not match the up-going aileron. If your model’s ailerons
are not working in unison, its vertical rolls will look like a mess.
Let me digress. Make absolutely sure that you are not getting
surface blowback. You will never get your differential correct if you
are. It’s easy to check for blowback. Push to a vertical down-line and
roll to the right, stop rolling for a second, and then roll again. The roll
rate should be the same. If it is slowing, your model’s surfaces are not
reaching their intended throws.
Another way to check is if the up-line roll rate is faster than the
down. Do what needs to be done. Either increase the servo power or
improve the geometry by reducing the servo-arm radius and/or by
increasing the distance the control-horn pickup is from the hinge line.
Or, if you have lots of cash, add more servos. Whatever path you take,
you can’t afford to have surface blowback. If you do, flying will never
be consistent.
Okay, where was I? Yes, how do we know when to add
differential?
Make sure you have a way to electronically adjust your aileron
travel individually. Most modern radios have a differential program. I
have used the ATV (Adjustable Travel Volume) function or the
differential function, and both work well.
Checking for differential problems is simple. I have used this
method for years and it works. Use the same technique as before when
checking for the thrust. Fly directly overhead and away from you. This
time pull only to a 45° up-line, making sure you are flying either
directly into the wind or directly downwind.
Using full aileron deflection, roll to the right. If the aircraft “walks
to the right,” you have too much down travel on your ailerons. If the
model “walks to the left” when you roll it to the right, you have too
much up travel in your ailerons. Repeat this process to the left as well
until you are satisfied that your model is tracking true in the roll axis.
As with the thrust angles, don’t expect your model to continue to
roll for 5,000 feet on a string. It just can’t be done. Per previous
recommendations, go for the majority
situation. There are not that many 5,000-foot
up- and down-lines. Fortunately.
With the correct differential on your
model, you will be amazed by how easy it is
to do hesitations on lines. Another benefit is
in point rolls on a horizontal line. The rudder
will have an even feel on both sides, as your
model will not be barreling in the rolls.
Mixing: You will notice that this topic is the
last in the sequence, but it’s where many
people go first! I get phone calls all the time
from excited pilots saying, “Pete, I just testflew
my new Edge; it only has 8% aileron
mix and 4% knife-edge mixing.” Boy, I
think, they sure got to the details of trimming
their models faster than I can. If you stick to
the correct trim sequence, you may be ready
after only 10-20 flights to work on the
mixing to fine-tune your model.
I’ve broken the Program Mix (P-mix)
topic into two sections. The first is the downline
torque offset, or throttle offset mixing.
The second is the traditional rudder to
elevator/aileron mixing. Most pilots have a
fairly good understanding of the latter, but
not many are using throttle offset mixing. I
have seen some, but only in the pitch
compensation. Pay attention to what your
model is doing on a down-line or at reduced
throttle (idle) in the roll or yaw axis.
One of the benefits of judging our events
is that you see many strange trim situations. I
can clearly remember models at the Nats
rolling on down-lines and yawing off-axis,
causing some strange-looking down-line
rolls. It’s almost impossible to have perfect
trim in roll at all speeds. All you can hope for
is to mix in some compensation to help
reduce your workload.
The yaw and the roll axis, in most cases,
have a bigger effect on your model tracking
on down-lines than any other situation.
Imagine what the effects of a 5° error on
every down-line would mean. Over the
height of the box, your airplane can drift in or
out by as much as 150 feet. The same applies
to the roll axis. Have you ever noticed how
hard it is to get the wings level when
approaching a pull corner with little time?
With your model rolling and yawing at
different speeds, you will never be consistent.
It is hard enough to be sure if your wings are
level, let alone chase an out-of-trim situation.
The good news is that it’s fairly easy to
compensate for.
Throttle-to-Aileron Mixing: Let’s do the
roll axis first. You can do this either of two
ways, and both work well. In fact, I suggest
that you try both to get the best input.
The first way is to climb your model to a
high altitude, simulating a typical top-of-thebox
altitude, and fly it directly over your head
and into the wind. Roughly 50-100 feet out
from yourself, push down. Watch carefully to
see if the model is rolling on the down-line.
Most models will roll slightly to the right as
the aileron trim set for full throttle will be too
much at low throttle as the torque effects will
be greatly reduced.
Okay, I know many of you fly with no
aileron trim. That’s great, but I’ll bet you are
carrying trim at reduced throttle. I have never
had a model that hasn’t needed a little left
aileron mix on low throttle.
The second way to check for throttleaileron
mix is to fly along at level flight,
medium height, and reduce the throttle.
Watch carefully and see if your model is
rolling; chances are that it is. Have you ever
wondered why you always have to lean a
little left aileron entering spins or why your
model always falls one way? Perhaps it’s
because your low power trim is not correct.
Throttle-to-Rudder Mixing: The second Pmix
is the throttle to rudder. Again, it’s hard
to get your model to track correctly in the
yaw axis at all speeds. Your only hope is to
apply a small amount of “left” rudder on low
throttle.
To check for this, use the same technique
as the throttle to aileron (in the preceding).
Fly the model above yourself, directly into
the wind, and push down in front of yourself
and watch carefully. You will be amazed,
especially at the start of the down-line. If you
haven’t gotten any throttle offset to rudder,
you are most likely flying around the
problem, and where I find it most challenging
is in figure 9s and vertical and horizontal 8s.
Anytime you are using elevator and are off on
the yaw axis, it’s a bad day.
I can hear all of you saying, “Yes it’s true;
my model could need a little rudder mix on
low throttle.” Give it a try and you will be
amazed.
I know of some fairly experienced
modelers who use the same theory but reverse
where the mix is. They use little to no right
thrust on the engine but have right rudder
mixed on full throttle. That works well too,
I’ve been told, but I haven’t tried it.
Something you may want to experiment
with in both of these scenarios is where the
mix is activated. For a low-throttle left-rudder
mix, I like to have the stick offset start at least
above half and let it progress from there as I
reduce the throttle. It seems to be the best
balance, and I am not getting a sudden mix
input; it progresses more or less with the
model’s speed. This will vary from model to
model, but try to keep the mix activation well
above an idle setting.
Rudder-Aileron Mixing: Earlier I made
reference to pilots applying programmable
mixes in their trim program. This is the last
thing you do. Looking through the sequence,
each trim adjustment has complemented the
next stage. In most cases, for rudder-aileron
mix, a linear P-mix is all that is required.
What I mean by linear P-mix is that you don’t
need a progressive value to the mix; i.e., less
at the start and more at the ends. The mix will
be linear.
What causes adverse roll or proverse roll
coupled to the rudder is the incorrect dihedral.
Most modern designs, with the exception of
biplanes, are really close and only require a
small amount of rudder-aileron mix. Some
like to put their models on knife-edge, but I
like to just do flat turns, simulating rolling
turn inputs.
Rolling turns require more precise mixing
than sustained knife-edge flight. In a contest
your model doesn’t do much flying on its
side, but it sure does a lot of rolling turns. So I
like to do the flat-turn thing. Doing a simple
inside rudder turn to the left, using left rudder,
the model should just yaw, with no roll effect.
If the roll rolls to the left, you need to mix
2%-5% right aileron to left rudder.
My CAP is unique in that it has adverse
roll. When I apply left rudder the model rolls
right, so I need left aileron mixed with left
rudder. Repeat the process with right rudder.
Now I want you to vary the speed at
which your aircraft does flat turns. If you find
that the mix becomes too much as you
increase your model’s speed, you could be
getting surface blowback. I’m sorry to keep
harping on this, but it is important.
With insufficient rudder power, when you
apply a P-mix for roll, or pitch for that matter,
the mix value will become too much as the
rudder throw reduces because of aerodynamic
pressure. I see a few lights going on again.
Could this be why you have your mix perfect
for knife edge, but you chase your aircraft
everywhere doing rolling circles?
Rudder-Elevator Mixing: I think about three
times in my entire life when I had a model
that didn’t need rudder-elevator
compensation. As with the previous rudder
aileron, start by doing a flat turn to the left and
see what happens. If your model pitches down
when rudder is applied, mix a small amount
of up-elevator; if it pitches up, apply a small
amount of down-elevator. In some cases, even
without blowback, the mix value will not be
exactly correct for all throttle settings.
Don’t panic because, as with most modern
radios that are suitable for aerobatics, you can
use what is called a curve mix. It allows you
to have multiple points along your mix curve
to increase or decrease your mix value at
different rudder inputs.
My CAP is a good example of this. At low
rudder throws I need only 1%-2% mix, but as
the throw increases I need as much as 10%. If
I have just a 10% mix, it will be too much at
small rudder inputs. The curve mix is
designed to solve this problem.
Tricks of the Trade: I’m going to share a
few tricks of the trade to help you with your
competition efforts. By now you probably
have an idea of how much work there is in
trimming a model. Considering all things
equal, you will have a hard time beating a
person with the same skills you have but with
a model that is more properly trimmed. It took
me 20 years to figure most of this out.
Be patient, be observant, and be objective.
If your model is not flying right, investigate
why. Chances are that it’s just not trimmed.
Even if your models are not straight, you can
trim them. I can almost guarantee that my
models are at the lower half of building
accuracy. They all carry aileron trim and
elevator trim. I don’t have a nuclear-powered
building bench with warp-speed laser meters,
nor do I have a 12-foot-square by 8-inch-thick
granite table on which to build.
Don’t feel as if you have a disadvantage if
your model is not perfect; you can trim it
pretty well. It makes me laugh to hear people
talk about how straight their models’ wings are
and how perfectly their models are trimmed,
yet even with perfectly trimmed models, they
fly with their inside wings down 5°-10°.
If your model’s not level in all orientations,
vertical and horizontal, at the top and the
bottom of the box, you will have a lot of work
on your hands. Probably the biggest
progression I’ve made in my flying career was
when I learned to fly level. The truth was that I
didn’t know my airplane wasn’t level!
I started watching other pilots and noticed
that everybody flew with their inside wings
down; nobody flew level. From that point I
went home, made three flags—red, white, and
blue—and asked my helper to go out and
stand under the flight path and keep me level.
I think red was for inside wing down, white
was for level, and blue was for outside wing
down.
The next month or so was one of the most
dramatic learning times of my life. My
workload doing maneuvers was reduced
immensely. I found myself just waiting for the
next input—not my normal 54 inputs all the
way up to vertical! I could pay more attention
to corner radius, centering rolls within legs,
and so on. It was a truly amazing
breakthrough. I encourage all of you to
investigate flying level.
Many people ask me the following
questions. “What’s the best thing I can spend
my money and/or time on to improve my
results at events?” “Should I get a more
powerful engine or a better aircraft?” “What
style should I fly?”
The truth is that all of these things are
important, but the best thing you can spend
your money on is gasoline and oil. Practice.
Try to avoid letting your ego be your only
motivation. Be objective, be humble, listen,
watch, and experiment. That’s what all of the
TOC (Tournament of Champions) and
Masters pilots do. Sure, we all have egos, but
at some stage in our lives they let us down; we
are humbled and forced to listen and be
objective.
Stay cool and hopefully we can catch up at
the next Aerobatics event! MA
Edition: Model Aviation - 2005/04
Page Numbers: 106,108,110,114,116
106 MODEL AVIATION
Mike Hurley, 11542 Decatur Ct., Westminster CO 80234; E-mail: [email protected]
RADIO CONTROL SCALE AEROBATICS
Peter Goldsmith is the Team JR manager. He is originally from
Sydney, Australia, but currently lives in Illinois and works for
Horizon Hobby.
Peter with his own-design 46% CAP 232 that he used in the TOC.
He competes on an international level in several forms of RC,
including Soaring, F3A Pattern, and Scale Aerobatics.
ONE OF THE most overlooked—no, forgotten—steps in building a
new model and getting it ready for competition is trimming it for
precision flight. I don’t mean adjusting the aileron and elevator trim. I
mean tuning your airplane to fly to the best of its ability. I’ll admit it;
I’ve never fully trimmed one of my airplanes. I usually end up buying
or building the next big thing! Maybe all I needed to do was spend a
few days out at the field getting it dialed in just right. Trimming is a
forgotten art by many modern competitors.
This is the second of a two-part series by Peter Goldsmith about
trimming and adjusting your competition aircraft for precision flight. In
the first part (in the February 2005 issue) he led us through adjusting
the physical aircraft for fore and aft CG, dynamic balance, and enginethrust
offset. This issue will focus on trimming with your radio,
adjusting differential, and using your radio’s mixing features to reduce
your workload while flying.
If you recall, Peter’s method relies on a sequential series of
adjustments, each building on the corrections made by the last. If you
make any of the adjustments out of order, it may be doing more harm
than good, so you must follow the methodology. And before you start
adjusting your radio mixes, you must have your CG, dynamic balance,
and engine offset adjusted correctly.
Rip these columns by Peter Goldsmith out of the magazine and stuff
them into your flight box. Get out to the field and follow his adjustment
method. You’ll have the best-flying model you’ve ever owned, and all
it will cost you is time. I’ll let Peter take it from here.
Differential: Aileron differential is one of the most important aspects
of model trim. With the multiple point rolls on up- and down-lines in
today’s modern patterns, poor differential can be a real headache.
The good news is that it’s pretty easy to detect and adjust for axial
rolls. You might remember from last time that at this stage of the
game—knowing that CG, thrust, and wing weight are correct—we can
proceed with our differential setup.
Aileron differential is required when the drag of the down-going
aileron does not match the up-going aileron. If your model’s ailerons
are not working in unison, its vertical rolls will look like a mess.
Let me digress. Make absolutely sure that you are not getting
surface blowback. You will never get your differential correct if you
are. It’s easy to check for blowback. Push to a vertical down-line and
roll to the right, stop rolling for a second, and then roll again. The roll
rate should be the same. If it is slowing, your model’s surfaces are not
reaching their intended throws.
Another way to check is if the up-line roll rate is faster than the
down. Do what needs to be done. Either increase the servo power or
improve the geometry by reducing the servo-arm radius and/or by
increasing the distance the control-horn pickup is from the hinge line.
Or, if you have lots of cash, add more servos. Whatever path you take,
you can’t afford to have surface blowback. If you do, flying will never
be consistent.
Okay, where was I? Yes, how do we know when to add
differential?
Make sure you have a way to electronically adjust your aileron
travel individually. Most modern radios have a differential program. I
have used the ATV (Adjustable Travel Volume) function or the
differential function, and both work well.
Checking for differential problems is simple. I have used this
method for years and it works. Use the same technique as before when
checking for the thrust. Fly directly overhead and away from you. This
time pull only to a 45° up-line, making sure you are flying either
directly into the wind or directly downwind.
Using full aileron deflection, roll to the right. If the aircraft “walks
to the right,” you have too much down travel on your ailerons. If the
model “walks to the left” when you roll it to the right, you have too
much up travel in your ailerons. Repeat this process to the left as well
until you are satisfied that your model is tracking true in the roll axis.
As with the thrust angles, don’t expect your model to continue to
roll for 5,000 feet on a string. It just can’t be done. Per previous
recommendations, go for the majority
situation. There are not that many 5,000-foot
up- and down-lines. Fortunately.
With the correct differential on your
model, you will be amazed by how easy it is
to do hesitations on lines. Another benefit is
in point rolls on a horizontal line. The rudder
will have an even feel on both sides, as your
model will not be barreling in the rolls.
Mixing: You will notice that this topic is the
last in the sequence, but it’s where many
people go first! I get phone calls all the time
from excited pilots saying, “Pete, I just testflew
my new Edge; it only has 8% aileron
mix and 4% knife-edge mixing.” Boy, I
think, they sure got to the details of trimming
their models faster than I can. If you stick to
the correct trim sequence, you may be ready
after only 10-20 flights to work on the
mixing to fine-tune your model.
I’ve broken the Program Mix (P-mix)
topic into two sections. The first is the downline
torque offset, or throttle offset mixing.
The second is the traditional rudder to
elevator/aileron mixing. Most pilots have a
fairly good understanding of the latter, but
not many are using throttle offset mixing. I
have seen some, but only in the pitch
compensation. Pay attention to what your
model is doing on a down-line or at reduced
throttle (idle) in the roll or yaw axis.
One of the benefits of judging our events
is that you see many strange trim situations. I
can clearly remember models at the Nats
rolling on down-lines and yawing off-axis,
causing some strange-looking down-line
rolls. It’s almost impossible to have perfect
trim in roll at all speeds. All you can hope for
is to mix in some compensation to help
reduce your workload.
The yaw and the roll axis, in most cases,
have a bigger effect on your model tracking
on down-lines than any other situation.
Imagine what the effects of a 5° error on
every down-line would mean. Over the
height of the box, your airplane can drift in or
out by as much as 150 feet. The same applies
to the roll axis. Have you ever noticed how
hard it is to get the wings level when
approaching a pull corner with little time?
With your model rolling and yawing at
different speeds, you will never be consistent.
It is hard enough to be sure if your wings are
level, let alone chase an out-of-trim situation.
The good news is that it’s fairly easy to
compensate for.
Throttle-to-Aileron Mixing: Let’s do the
roll axis first. You can do this either of two
ways, and both work well. In fact, I suggest
that you try both to get the best input.
The first way is to climb your model to a
high altitude, simulating a typical top-of-thebox
altitude, and fly it directly over your head
and into the wind. Roughly 50-100 feet out
from yourself, push down. Watch carefully to
see if the model is rolling on the down-line.
Most models will roll slightly to the right as
the aileron trim set for full throttle will be too
much at low throttle as the torque effects will
be greatly reduced.
Okay, I know many of you fly with no
aileron trim. That’s great, but I’ll bet you are
carrying trim at reduced throttle. I have never
had a model that hasn’t needed a little left
aileron mix on low throttle.
The second way to check for throttleaileron
mix is to fly along at level flight,
medium height, and reduce the throttle.
Watch carefully and see if your model is
rolling; chances are that it is. Have you ever
wondered why you always have to lean a
little left aileron entering spins or why your
model always falls one way? Perhaps it’s
because your low power trim is not correct.
Throttle-to-Rudder Mixing: The second Pmix
is the throttle to rudder. Again, it’s hard
to get your model to track correctly in the
yaw axis at all speeds. Your only hope is to
apply a small amount of “left” rudder on low
throttle.
To check for this, use the same technique
as the throttle to aileron (in the preceding).
Fly the model above yourself, directly into
the wind, and push down in front of yourself
and watch carefully. You will be amazed,
especially at the start of the down-line. If you
haven’t gotten any throttle offset to rudder,
you are most likely flying around the
problem, and where I find it most challenging
is in figure 9s and vertical and horizontal 8s.
Anytime you are using elevator and are off on
the yaw axis, it’s a bad day.
I can hear all of you saying, “Yes it’s true;
my model could need a little rudder mix on
low throttle.” Give it a try and you will be
amazed.
I know of some fairly experienced
modelers who use the same theory but reverse
where the mix is. They use little to no right
thrust on the engine but have right rudder
mixed on full throttle. That works well too,
I’ve been told, but I haven’t tried it.
Something you may want to experiment
with in both of these scenarios is where the
mix is activated. For a low-throttle left-rudder
mix, I like to have the stick offset start at least
above half and let it progress from there as I
reduce the throttle. It seems to be the best
balance, and I am not getting a sudden mix
input; it progresses more or less with the
model’s speed. This will vary from model to
model, but try to keep the mix activation well
above an idle setting.
Rudder-Aileron Mixing: Earlier I made
reference to pilots applying programmable
mixes in their trim program. This is the last
thing you do. Looking through the sequence,
each trim adjustment has complemented the
next stage. In most cases, for rudder-aileron
mix, a linear P-mix is all that is required.
What I mean by linear P-mix is that you don’t
need a progressive value to the mix; i.e., less
at the start and more at the ends. The mix will
be linear.
What causes adverse roll or proverse roll
coupled to the rudder is the incorrect dihedral.
Most modern designs, with the exception of
biplanes, are really close and only require a
small amount of rudder-aileron mix. Some
like to put their models on knife-edge, but I
like to just do flat turns, simulating rolling
turn inputs.
Rolling turns require more precise mixing
than sustained knife-edge flight. In a contest
your model doesn’t do much flying on its
side, but it sure does a lot of rolling turns. So I
like to do the flat-turn thing. Doing a simple
inside rudder turn to the left, using left rudder,
the model should just yaw, with no roll effect.
If the roll rolls to the left, you need to mix
2%-5% right aileron to left rudder.
My CAP is unique in that it has adverse
roll. When I apply left rudder the model rolls
right, so I need left aileron mixed with left
rudder. Repeat the process with right rudder.
Now I want you to vary the speed at
which your aircraft does flat turns. If you find
that the mix becomes too much as you
increase your model’s speed, you could be
getting surface blowback. I’m sorry to keep
harping on this, but it is important.
With insufficient rudder power, when you
apply a P-mix for roll, or pitch for that matter,
the mix value will become too much as the
rudder throw reduces because of aerodynamic
pressure. I see a few lights going on again.
Could this be why you have your mix perfect
for knife edge, but you chase your aircraft
everywhere doing rolling circles?
Rudder-Elevator Mixing: I think about three
times in my entire life when I had a model
that didn’t need rudder-elevator
compensation. As with the previous rudder
aileron, start by doing a flat turn to the left and
see what happens. If your model pitches down
when rudder is applied, mix a small amount
of up-elevator; if it pitches up, apply a small
amount of down-elevator. In some cases, even
without blowback, the mix value will not be
exactly correct for all throttle settings.
Don’t panic because, as with most modern
radios that are suitable for aerobatics, you can
use what is called a curve mix. It allows you
to have multiple points along your mix curve
to increase or decrease your mix value at
different rudder inputs.
My CAP is a good example of this. At low
rudder throws I need only 1%-2% mix, but as
the throw increases I need as much as 10%. If
I have just a 10% mix, it will be too much at
small rudder inputs. The curve mix is
designed to solve this problem.
Tricks of the Trade: I’m going to share a
few tricks of the trade to help you with your
competition efforts. By now you probably
have an idea of how much work there is in
trimming a model. Considering all things
equal, you will have a hard time beating a
person with the same skills you have but with
a model that is more properly trimmed. It took
me 20 years to figure most of this out.
Be patient, be observant, and be objective.
If your model is not flying right, investigate
why. Chances are that it’s just not trimmed.
Even if your models are not straight, you can
trim them. I can almost guarantee that my
models are at the lower half of building
accuracy. They all carry aileron trim and
elevator trim. I don’t have a nuclear-powered
building bench with warp-speed laser meters,
nor do I have a 12-foot-square by 8-inch-thick
granite table on which to build.
Don’t feel as if you have a disadvantage if
your model is not perfect; you can trim it
pretty well. It makes me laugh to hear people
talk about how straight their models’ wings are
and how perfectly their models are trimmed,
yet even with perfectly trimmed models, they
fly with their inside wings down 5°-10°.
If your model’s not level in all orientations,
vertical and horizontal, at the top and the
bottom of the box, you will have a lot of work
on your hands. Probably the biggest
progression I’ve made in my flying career was
when I learned to fly level. The truth was that I
didn’t know my airplane wasn’t level!
I started watching other pilots and noticed
that everybody flew with their inside wings
down; nobody flew level. From that point I
went home, made three flags—red, white, and
blue—and asked my helper to go out and
stand under the flight path and keep me level.
I think red was for inside wing down, white
was for level, and blue was for outside wing
down.
The next month or so was one of the most
dramatic learning times of my life. My
workload doing maneuvers was reduced
immensely. I found myself just waiting for the
next input—not my normal 54 inputs all the
way up to vertical! I could pay more attention
to corner radius, centering rolls within legs,
and so on. It was a truly amazing
breakthrough. I encourage all of you to
investigate flying level.
Many people ask me the following
questions. “What’s the best thing I can spend
my money and/or time on to improve my
results at events?” “Should I get a more
powerful engine or a better aircraft?” “What
style should I fly?”
The truth is that all of these things are
important, but the best thing you can spend
your money on is gasoline and oil. Practice.
Try to avoid letting your ego be your only
motivation. Be objective, be humble, listen,
watch, and experiment. That’s what all of the
TOC (Tournament of Champions) and
Masters pilots do. Sure, we all have egos, but
at some stage in our lives they let us down; we
are humbled and forced to listen and be
objective.
Stay cool and hopefully we can catch up at
the next Aerobatics event! MA
Edition: Model Aviation - 2005/04
Page Numbers: 106,108,110,114,116
106 MODEL AVIATION
Mike Hurley, 11542 Decatur Ct., Westminster CO 80234; E-mail: [email protected]
RADIO CONTROL SCALE AEROBATICS
Peter Goldsmith is the Team JR manager. He is originally from
Sydney, Australia, but currently lives in Illinois and works for
Horizon Hobby.
Peter with his own-design 46% CAP 232 that he used in the TOC.
He competes on an international level in several forms of RC,
including Soaring, F3A Pattern, and Scale Aerobatics.
ONE OF THE most overlooked—no, forgotten—steps in building a
new model and getting it ready for competition is trimming it for
precision flight. I don’t mean adjusting the aileron and elevator trim. I
mean tuning your airplane to fly to the best of its ability. I’ll admit it;
I’ve never fully trimmed one of my airplanes. I usually end up buying
or building the next big thing! Maybe all I needed to do was spend a
few days out at the field getting it dialed in just right. Trimming is a
forgotten art by many modern competitors.
This is the second of a two-part series by Peter Goldsmith about
trimming and adjusting your competition aircraft for precision flight. In
the first part (in the February 2005 issue) he led us through adjusting
the physical aircraft for fore and aft CG, dynamic balance, and enginethrust
offset. This issue will focus on trimming with your radio,
adjusting differential, and using your radio’s mixing features to reduce
your workload while flying.
If you recall, Peter’s method relies on a sequential series of
adjustments, each building on the corrections made by the last. If you
make any of the adjustments out of order, it may be doing more harm
than good, so you must follow the methodology. And before you start
adjusting your radio mixes, you must have your CG, dynamic balance,
and engine offset adjusted correctly.
Rip these columns by Peter Goldsmith out of the magazine and stuff
them into your flight box. Get out to the field and follow his adjustment
method. You’ll have the best-flying model you’ve ever owned, and all
it will cost you is time. I’ll let Peter take it from here.
Differential: Aileron differential is one of the most important aspects
of model trim. With the multiple point rolls on up- and down-lines in
today’s modern patterns, poor differential can be a real headache.
The good news is that it’s pretty easy to detect and adjust for axial
rolls. You might remember from last time that at this stage of the
game—knowing that CG, thrust, and wing weight are correct—we can
proceed with our differential setup.
Aileron differential is required when the drag of the down-going
aileron does not match the up-going aileron. If your model’s ailerons
are not working in unison, its vertical rolls will look like a mess.
Let me digress. Make absolutely sure that you are not getting
surface blowback. You will never get your differential correct if you
are. It’s easy to check for blowback. Push to a vertical down-line and
roll to the right, stop rolling for a second, and then roll again. The roll
rate should be the same. If it is slowing, your model’s surfaces are not
reaching their intended throws.
Another way to check is if the up-line roll rate is faster than the
down. Do what needs to be done. Either increase the servo power or
improve the geometry by reducing the servo-arm radius and/or by
increasing the distance the control-horn pickup is from the hinge line.
Or, if you have lots of cash, add more servos. Whatever path you take,
you can’t afford to have surface blowback. If you do, flying will never
be consistent.
Okay, where was I? Yes, how do we know when to add
differential?
Make sure you have a way to electronically adjust your aileron
travel individually. Most modern radios have a differential program. I
have used the ATV (Adjustable Travel Volume) function or the
differential function, and both work well.
Checking for differential problems is simple. I have used this
method for years and it works. Use the same technique as before when
checking for the thrust. Fly directly overhead and away from you. This
time pull only to a 45° up-line, making sure you are flying either
directly into the wind or directly downwind.
Using full aileron deflection, roll to the right. If the aircraft “walks
to the right,” you have too much down travel on your ailerons. If the
model “walks to the left” when you roll it to the right, you have too
much up travel in your ailerons. Repeat this process to the left as well
until you are satisfied that your model is tracking true in the roll axis.
As with the thrust angles, don’t expect your model to continue to
roll for 5,000 feet on a string. It just can’t be done. Per previous
recommendations, go for the majority
situation. There are not that many 5,000-foot
up- and down-lines. Fortunately.
With the correct differential on your
model, you will be amazed by how easy it is
to do hesitations on lines. Another benefit is
in point rolls on a horizontal line. The rudder
will have an even feel on both sides, as your
model will not be barreling in the rolls.
Mixing: You will notice that this topic is the
last in the sequence, but it’s where many
people go first! I get phone calls all the time
from excited pilots saying, “Pete, I just testflew
my new Edge; it only has 8% aileron
mix and 4% knife-edge mixing.” Boy, I
think, they sure got to the details of trimming
their models faster than I can. If you stick to
the correct trim sequence, you may be ready
after only 10-20 flights to work on the
mixing to fine-tune your model.
I’ve broken the Program Mix (P-mix)
topic into two sections. The first is the downline
torque offset, or throttle offset mixing.
The second is the traditional rudder to
elevator/aileron mixing. Most pilots have a
fairly good understanding of the latter, but
not many are using throttle offset mixing. I
have seen some, but only in the pitch
compensation. Pay attention to what your
model is doing on a down-line or at reduced
throttle (idle) in the roll or yaw axis.
One of the benefits of judging our events
is that you see many strange trim situations. I
can clearly remember models at the Nats
rolling on down-lines and yawing off-axis,
causing some strange-looking down-line
rolls. It’s almost impossible to have perfect
trim in roll at all speeds. All you can hope for
is to mix in some compensation to help
reduce your workload.
The yaw and the roll axis, in most cases,
have a bigger effect on your model tracking
on down-lines than any other situation.
Imagine what the effects of a 5° error on
every down-line would mean. Over the
height of the box, your airplane can drift in or
out by as much as 150 feet. The same applies
to the roll axis. Have you ever noticed how
hard it is to get the wings level when
approaching a pull corner with little time?
With your model rolling and yawing at
different speeds, you will never be consistent.
It is hard enough to be sure if your wings are
level, let alone chase an out-of-trim situation.
The good news is that it’s fairly easy to
compensate for.
Throttle-to-Aileron Mixing: Let’s do the
roll axis first. You can do this either of two
ways, and both work well. In fact, I suggest
that you try both to get the best input.
The first way is to climb your model to a
high altitude, simulating a typical top-of-thebox
altitude, and fly it directly over your head
and into the wind. Roughly 50-100 feet out
from yourself, push down. Watch carefully to
see if the model is rolling on the down-line.
Most models will roll slightly to the right as
the aileron trim set for full throttle will be too
much at low throttle as the torque effects will
be greatly reduced.
Okay, I know many of you fly with no
aileron trim. That’s great, but I’ll bet you are
carrying trim at reduced throttle. I have never
had a model that hasn’t needed a little left
aileron mix on low throttle.
The second way to check for throttleaileron
mix is to fly along at level flight,
medium height, and reduce the throttle.
Watch carefully and see if your model is
rolling; chances are that it is. Have you ever
wondered why you always have to lean a
little left aileron entering spins or why your
model always falls one way? Perhaps it’s
because your low power trim is not correct.
Throttle-to-Rudder Mixing: The second Pmix
is the throttle to rudder. Again, it’s hard
to get your model to track correctly in the
yaw axis at all speeds. Your only hope is to
apply a small amount of “left” rudder on low
throttle.
To check for this, use the same technique
as the throttle to aileron (in the preceding).
Fly the model above yourself, directly into
the wind, and push down in front of yourself
and watch carefully. You will be amazed,
especially at the start of the down-line. If you
haven’t gotten any throttle offset to rudder,
you are most likely flying around the
problem, and where I find it most challenging
is in figure 9s and vertical and horizontal 8s.
Anytime you are using elevator and are off on
the yaw axis, it’s a bad day.
I can hear all of you saying, “Yes it’s true;
my model could need a little rudder mix on
low throttle.” Give it a try and you will be
amazed.
I know of some fairly experienced
modelers who use the same theory but reverse
where the mix is. They use little to no right
thrust on the engine but have right rudder
mixed on full throttle. That works well too,
I’ve been told, but I haven’t tried it.
Something you may want to experiment
with in both of these scenarios is where the
mix is activated. For a low-throttle left-rudder
mix, I like to have the stick offset start at least
above half and let it progress from there as I
reduce the throttle. It seems to be the best
balance, and I am not getting a sudden mix
input; it progresses more or less with the
model’s speed. This will vary from model to
model, but try to keep the mix activation well
above an idle setting.
Rudder-Aileron Mixing: Earlier I made
reference to pilots applying programmable
mixes in their trim program. This is the last
thing you do. Looking through the sequence,
each trim adjustment has complemented the
next stage. In most cases, for rudder-aileron
mix, a linear P-mix is all that is required.
What I mean by linear P-mix is that you don’t
need a progressive value to the mix; i.e., less
at the start and more at the ends. The mix will
be linear.
What causes adverse roll or proverse roll
coupled to the rudder is the incorrect dihedral.
Most modern designs, with the exception of
biplanes, are really close and only require a
small amount of rudder-aileron mix. Some
like to put their models on knife-edge, but I
like to just do flat turns, simulating rolling
turn inputs.
Rolling turns require more precise mixing
than sustained knife-edge flight. In a contest
your model doesn’t do much flying on its
side, but it sure does a lot of rolling turns. So I
like to do the flat-turn thing. Doing a simple
inside rudder turn to the left, using left rudder,
the model should just yaw, with no roll effect.
If the roll rolls to the left, you need to mix
2%-5% right aileron to left rudder.
My CAP is unique in that it has adverse
roll. When I apply left rudder the model rolls
right, so I need left aileron mixed with left
rudder. Repeat the process with right rudder.
Now I want you to vary the speed at
which your aircraft does flat turns. If you find
that the mix becomes too much as you
increase your model’s speed, you could be
getting surface blowback. I’m sorry to keep
harping on this, but it is important.
With insufficient rudder power, when you
apply a P-mix for roll, or pitch for that matter,
the mix value will become too much as the
rudder throw reduces because of aerodynamic
pressure. I see a few lights going on again.
Could this be why you have your mix perfect
for knife edge, but you chase your aircraft
everywhere doing rolling circles?
Rudder-Elevator Mixing: I think about three
times in my entire life when I had a model
that didn’t need rudder-elevator
compensation. As with the previous rudder
aileron, start by doing a flat turn to the left and
see what happens. If your model pitches down
when rudder is applied, mix a small amount
of up-elevator; if it pitches up, apply a small
amount of down-elevator. In some cases, even
without blowback, the mix value will not be
exactly correct for all throttle settings.
Don’t panic because, as with most modern
radios that are suitable for aerobatics, you can
use what is called a curve mix. It allows you
to have multiple points along your mix curve
to increase or decrease your mix value at
different rudder inputs.
My CAP is a good example of this. At low
rudder throws I need only 1%-2% mix, but as
the throw increases I need as much as 10%. If
I have just a 10% mix, it will be too much at
small rudder inputs. The curve mix is
designed to solve this problem.
Tricks of the Trade: I’m going to share a
few tricks of the trade to help you with your
competition efforts. By now you probably
have an idea of how much work there is in
trimming a model. Considering all things
equal, you will have a hard time beating a
person with the same skills you have but with
a model that is more properly trimmed. It took
me 20 years to figure most of this out.
Be patient, be observant, and be objective.
If your model is not flying right, investigate
why. Chances are that it’s just not trimmed.
Even if your models are not straight, you can
trim them. I can almost guarantee that my
models are at the lower half of building
accuracy. They all carry aileron trim and
elevator trim. I don’t have a nuclear-powered
building bench with warp-speed laser meters,
nor do I have a 12-foot-square by 8-inch-thick
granite table on which to build.
Don’t feel as if you have a disadvantage if
your model is not perfect; you can trim it
pretty well. It makes me laugh to hear people
talk about how straight their models’ wings are
and how perfectly their models are trimmed,
yet even with perfectly trimmed models, they
fly with their inside wings down 5°-10°.
If your model’s not level in all orientations,
vertical and horizontal, at the top and the
bottom of the box, you will have a lot of work
on your hands. Probably the biggest
progression I’ve made in my flying career was
when I learned to fly level. The truth was that I
didn’t know my airplane wasn’t level!
I started watching other pilots and noticed
that everybody flew with their inside wings
down; nobody flew level. From that point I
went home, made three flags—red, white, and
blue—and asked my helper to go out and
stand under the flight path and keep me level.
I think red was for inside wing down, white
was for level, and blue was for outside wing
down.
The next month or so was one of the most
dramatic learning times of my life. My
workload doing maneuvers was reduced
immensely. I found myself just waiting for the
next input—not my normal 54 inputs all the
way up to vertical! I could pay more attention
to corner radius, centering rolls within legs,
and so on. It was a truly amazing
breakthrough. I encourage all of you to
investigate flying level.
Many people ask me the following
questions. “What’s the best thing I can spend
my money and/or time on to improve my
results at events?” “Should I get a more
powerful engine or a better aircraft?” “What
style should I fly?”
The truth is that all of these things are
important, but the best thing you can spend
your money on is gasoline and oil. Practice.
Try to avoid letting your ego be your only
motivation. Be objective, be humble, listen,
watch, and experiment. That’s what all of the
TOC (Tournament of Champions) and
Masters pilots do. Sure, we all have egos, but
at some stage in our lives they let us down; we
are humbled and forced to listen and be
objective.
Stay cool and hopefully we can catch up at
the next Aerobatics event! MA
Edition: Model Aviation - 2005/04
Page Numbers: 106,108,110,114,116
106 MODEL AVIATION
Mike Hurley, 11542 Decatur Ct., Westminster CO 80234; E-mail: [email protected]
RADIO CONTROL SCALE AEROBATICS
Peter Goldsmith is the Team JR manager. He is originally from
Sydney, Australia, but currently lives in Illinois and works for
Horizon Hobby.
Peter with his own-design 46% CAP 232 that he used in the TOC.
He competes on an international level in several forms of RC,
including Soaring, F3A Pattern, and Scale Aerobatics.
ONE OF THE most overlooked—no, forgotten—steps in building a
new model and getting it ready for competition is trimming it for
precision flight. I don’t mean adjusting the aileron and elevator trim. I
mean tuning your airplane to fly to the best of its ability. I’ll admit it;
I’ve never fully trimmed one of my airplanes. I usually end up buying
or building the next big thing! Maybe all I needed to do was spend a
few days out at the field getting it dialed in just right. Trimming is a
forgotten art by many modern competitors.
This is the second of a two-part series by Peter Goldsmith about
trimming and adjusting your competition aircraft for precision flight. In
the first part (in the February 2005 issue) he led us through adjusting
the physical aircraft for fore and aft CG, dynamic balance, and enginethrust
offset. This issue will focus on trimming with your radio,
adjusting differential, and using your radio’s mixing features to reduce
your workload while flying.
If you recall, Peter’s method relies on a sequential series of
adjustments, each building on the corrections made by the last. If you
make any of the adjustments out of order, it may be doing more harm
than good, so you must follow the methodology. And before you start
adjusting your radio mixes, you must have your CG, dynamic balance,
and engine offset adjusted correctly.
Rip these columns by Peter Goldsmith out of the magazine and stuff
them into your flight box. Get out to the field and follow his adjustment
method. You’ll have the best-flying model you’ve ever owned, and all
it will cost you is time. I’ll let Peter take it from here.
Differential: Aileron differential is one of the most important aspects
of model trim. With the multiple point rolls on up- and down-lines in
today’s modern patterns, poor differential can be a real headache.
The good news is that it’s pretty easy to detect and adjust for axial
rolls. You might remember from last time that at this stage of the
game—knowing that CG, thrust, and wing weight are correct—we can
proceed with our differential setup.
Aileron differential is required when the drag of the down-going
aileron does not match the up-going aileron. If your model’s ailerons
are not working in unison, its vertical rolls will look like a mess.
Let me digress. Make absolutely sure that you are not getting
surface blowback. You will never get your differential correct if you
are. It’s easy to check for blowback. Push to a vertical down-line and
roll to the right, stop rolling for a second, and then roll again. The roll
rate should be the same. If it is slowing, your model’s surfaces are not
reaching their intended throws.
Another way to check is if the up-line roll rate is faster than the
down. Do what needs to be done. Either increase the servo power or
improve the geometry by reducing the servo-arm radius and/or by
increasing the distance the control-horn pickup is from the hinge line.
Or, if you have lots of cash, add more servos. Whatever path you take,
you can’t afford to have surface blowback. If you do, flying will never
be consistent.
Okay, where was I? Yes, how do we know when to add
differential?
Make sure you have a way to electronically adjust your aileron
travel individually. Most modern radios have a differential program. I
have used the ATV (Adjustable Travel Volume) function or the
differential function, and both work well.
Checking for differential problems is simple. I have used this
method for years and it works. Use the same technique as before when
checking for the thrust. Fly directly overhead and away from you. This
time pull only to a 45° up-line, making sure you are flying either
directly into the wind or directly downwind.
Using full aileron deflection, roll to the right. If the aircraft “walks
to the right,” you have too much down travel on your ailerons. If the
model “walks to the left” when you roll it to the right, you have too
much up travel in your ailerons. Repeat this process to the left as well
until you are satisfied that your model is tracking true in the roll axis.
As with the thrust angles, don’t expect your model to continue to
roll for 5,000 feet on a string. It just can’t be done. Per previous
recommendations, go for the majority
situation. There are not that many 5,000-foot
up- and down-lines. Fortunately.
With the correct differential on your
model, you will be amazed by how easy it is
to do hesitations on lines. Another benefit is
in point rolls on a horizontal line. The rudder
will have an even feel on both sides, as your
model will not be barreling in the rolls.
Mixing: You will notice that this topic is the
last in the sequence, but it’s where many
people go first! I get phone calls all the time
from excited pilots saying, “Pete, I just testflew
my new Edge; it only has 8% aileron
mix and 4% knife-edge mixing.” Boy, I
think, they sure got to the details of trimming
their models faster than I can. If you stick to
the correct trim sequence, you may be ready
after only 10-20 flights to work on the
mixing to fine-tune your model.
I’ve broken the Program Mix (P-mix)
topic into two sections. The first is the downline
torque offset, or throttle offset mixing.
The second is the traditional rudder to
elevator/aileron mixing. Most pilots have a
fairly good understanding of the latter, but
not many are using throttle offset mixing. I
have seen some, but only in the pitch
compensation. Pay attention to what your
model is doing on a down-line or at reduced
throttle (idle) in the roll or yaw axis.
One of the benefits of judging our events
is that you see many strange trim situations. I
can clearly remember models at the Nats
rolling on down-lines and yawing off-axis,
causing some strange-looking down-line
rolls. It’s almost impossible to have perfect
trim in roll at all speeds. All you can hope for
is to mix in some compensation to help
reduce your workload.
The yaw and the roll axis, in most cases,
have a bigger effect on your model tracking
on down-lines than any other situation.
Imagine what the effects of a 5° error on
every down-line would mean. Over the
height of the box, your airplane can drift in or
out by as much as 150 feet. The same applies
to the roll axis. Have you ever noticed how
hard it is to get the wings level when
approaching a pull corner with little time?
With your model rolling and yawing at
different speeds, you will never be consistent.
It is hard enough to be sure if your wings are
level, let alone chase an out-of-trim situation.
The good news is that it’s fairly easy to
compensate for.
Throttle-to-Aileron Mixing: Let’s do the
roll axis first. You can do this either of two
ways, and both work well. In fact, I suggest
that you try both to get the best input.
The first way is to climb your model to a
high altitude, simulating a typical top-of-thebox
altitude, and fly it directly over your head
and into the wind. Roughly 50-100 feet out
from yourself, push down. Watch carefully to
see if the model is rolling on the down-line.
Most models will roll slightly to the right as
the aileron trim set for full throttle will be too
much at low throttle as the torque effects will
be greatly reduced.
Okay, I know many of you fly with no
aileron trim. That’s great, but I’ll bet you are
carrying trim at reduced throttle. I have never
had a model that hasn’t needed a little left
aileron mix on low throttle.
The second way to check for throttleaileron
mix is to fly along at level flight,
medium height, and reduce the throttle.
Watch carefully and see if your model is
rolling; chances are that it is. Have you ever
wondered why you always have to lean a
little left aileron entering spins or why your
model always falls one way? Perhaps it’s
because your low power trim is not correct.
Throttle-to-Rudder Mixing: The second Pmix
is the throttle to rudder. Again, it’s hard
to get your model to track correctly in the
yaw axis at all speeds. Your only hope is to
apply a small amount of “left” rudder on low
throttle.
To check for this, use the same technique
as the throttle to aileron (in the preceding).
Fly the model above yourself, directly into
the wind, and push down in front of yourself
and watch carefully. You will be amazed,
especially at the start of the down-line. If you
haven’t gotten any throttle offset to rudder,
you are most likely flying around the
problem, and where I find it most challenging
is in figure 9s and vertical and horizontal 8s.
Anytime you are using elevator and are off on
the yaw axis, it’s a bad day.
I can hear all of you saying, “Yes it’s true;
my model could need a little rudder mix on
low throttle.” Give it a try and you will be
amazed.
I know of some fairly experienced
modelers who use the same theory but reverse
where the mix is. They use little to no right
thrust on the engine but have right rudder
mixed on full throttle. That works well too,
I’ve been told, but I haven’t tried it.
Something you may want to experiment
with in both of these scenarios is where the
mix is activated. For a low-throttle left-rudder
mix, I like to have the stick offset start at least
above half and let it progress from there as I
reduce the throttle. It seems to be the best
balance, and I am not getting a sudden mix
input; it progresses more or less with the
model’s speed. This will vary from model to
model, but try to keep the mix activation well
above an idle setting.
Rudder-Aileron Mixing: Earlier I made
reference to pilots applying programmable
mixes in their trim program. This is the last
thing you do. Looking through the sequence,
each trim adjustment has complemented the
next stage. In most cases, for rudder-aileron
mix, a linear P-mix is all that is required.
What I mean by linear P-mix is that you don’t
need a progressive value to the mix; i.e., less
at the start and more at the ends. The mix will
be linear.
What causes adverse roll or proverse roll
coupled to the rudder is the incorrect dihedral.
Most modern designs, with the exception of
biplanes, are really close and only require a
small amount of rudder-aileron mix. Some
like to put their models on knife-edge, but I
like to just do flat turns, simulating rolling
turn inputs.
Rolling turns require more precise mixing
than sustained knife-edge flight. In a contest
your model doesn’t do much flying on its
side, but it sure does a lot of rolling turns. So I
like to do the flat-turn thing. Doing a simple
inside rudder turn to the left, using left rudder,
the model should just yaw, with no roll effect.
If the roll rolls to the left, you need to mix
2%-5% right aileron to left rudder.
My CAP is unique in that it has adverse
roll. When I apply left rudder the model rolls
right, so I need left aileron mixed with left
rudder. Repeat the process with right rudder.
Now I want you to vary the speed at
which your aircraft does flat turns. If you find
that the mix becomes too much as you
increase your model’s speed, you could be
getting surface blowback. I’m sorry to keep
harping on this, but it is important.
With insufficient rudder power, when you
apply a P-mix for roll, or pitch for that matter,
the mix value will become too much as the
rudder throw reduces because of aerodynamic
pressure. I see a few lights going on again.
Could this be why you have your mix perfect
for knife edge, but you chase your aircraft
everywhere doing rolling circles?
Rudder-Elevator Mixing: I think about three
times in my entire life when I had a model
that didn’t need rudder-elevator
compensation. As with the previous rudder
aileron, start by doing a flat turn to the left and
see what happens. If your model pitches down
when rudder is applied, mix a small amount
of up-elevator; if it pitches up, apply a small
amount of down-elevator. In some cases, even
without blowback, the mix value will not be
exactly correct for all throttle settings.
Don’t panic because, as with most modern
radios that are suitable for aerobatics, you can
use what is called a curve mix. It allows you
to have multiple points along your mix curve
to increase or decrease your mix value at
different rudder inputs.
My CAP is a good example of this. At low
rudder throws I need only 1%-2% mix, but as
the throw increases I need as much as 10%. If
I have just a 10% mix, it will be too much at
small rudder inputs. The curve mix is
designed to solve this problem.
Tricks of the Trade: I’m going to share a
few tricks of the trade to help you with your
competition efforts. By now you probably
have an idea of how much work there is in
trimming a model. Considering all things
equal, you will have a hard time beating a
person with the same skills you have but with
a model that is more properly trimmed. It took
me 20 years to figure most of this out.
Be patient, be observant, and be objective.
If your model is not flying right, investigate
why. Chances are that it’s just not trimmed.
Even if your models are not straight, you can
trim them. I can almost guarantee that my
models are at the lower half of building
accuracy. They all carry aileron trim and
elevator trim. I don’t have a nuclear-powered
building bench with warp-speed laser meters,
nor do I have a 12-foot-square by 8-inch-thick
granite table on which to build.
Don’t feel as if you have a disadvantage if
your model is not perfect; you can trim it
pretty well. It makes me laugh to hear people
talk about how straight their models’ wings are
and how perfectly their models are trimmed,
yet even with perfectly trimmed models, they
fly with their inside wings down 5°-10°.
If your model’s not level in all orientations,
vertical and horizontal, at the top and the
bottom of the box, you will have a lot of work
on your hands. Probably the biggest
progression I’ve made in my flying career was
when I learned to fly level. The truth was that I
didn’t know my airplane wasn’t level!
I started watching other pilots and noticed
that everybody flew with their inside wings
down; nobody flew level. From that point I
went home, made three flags—red, white, and
blue—and asked my helper to go out and
stand under the flight path and keep me level.
I think red was for inside wing down, white
was for level, and blue was for outside wing
down.
The next month or so was one of the most
dramatic learning times of my life. My
workload doing maneuvers was reduced
immensely. I found myself just waiting for the
next input—not my normal 54 inputs all the
way up to vertical! I could pay more attention
to corner radius, centering rolls within legs,
and so on. It was a truly amazing
breakthrough. I encourage all of you to
investigate flying level.
Many people ask me the following
questions. “What’s the best thing I can spend
my money and/or time on to improve my
results at events?” “Should I get a more
powerful engine or a better aircraft?” “What
style should I fly?”
The truth is that all of these things are
important, but the best thing you can spend
your money on is gasoline and oil. Practice.
Try to avoid letting your ego be your only
motivation. Be objective, be humble, listen,
watch, and experiment. That’s what all of the
TOC (Tournament of Champions) and
Masters pilots do. Sure, we all have egos, but
at some stage in our lives they let us down; we
are humbled and forced to listen and be
objective.
Stay cool and hopefully we can catch up at
the next Aerobatics event! MA