94 MODEL AVIATION
Pattern until he came to the US in 2000, and he was the Australian
National champ from 1995 until 2000. During that time he was also
a member of the Australian National team for the World
Championships, making the finals in three of the five World
Championships, and he was named Oceanic Champion three times.
In SA, Pete has multiple top-level performances at the Masters
and won it in 2001. He has placed second in the AMA Nats three
times and won the Freestyle National Championship in 2002. He
competed in the TOC from 1992 until its end in 2002.
Peter is currently the JR Team Manager and continues to
compete at the top level. One of the most telling aspects of Peter’s
RC career is that he has always flown and competed with his own
designs—built from scratch and trimmed based on his 25+ years of
experience.
At this point I’ll let him take over.
Competing in the 2004 Don Lowe Masters, I was inspired by the
raw talent in pilots half my age; I was honored to place seventh! I
began thinking about all of the help I had received throughout the
years and felt driven to give back to the new pilots of the Aerobatics
community, as had been done with me many years ago.
Earlier in 2004 in a discussion with Mike Hurley at the Nats, I
shared with him how passionate I am to share my life’s aerobatic
knowledge, and he invited me to write something about trimming
and mixing.
A properly trimmed model can reduce your workload in an
Aerobatics sequence by an enormous amount. I judged at the Nats
last year and thoroughly enjoyed the experience. I was impressed
with the skills, especially in the lower classes, that pilots displayed,
but I noticed most of them trying to fly around a poor trim setup. It
drove me crazy to watch!
I remember bouncing out of my judging chair and saying to
Mike, “Boy, I need to help these people!” So here are some thoughts
from my 25 years of experience and involvement with people who
shared their thoughts
on trimming with
me.
I have observed
that there is no such
thing as a perfectly
trimmed model. Our
goal is to reduce our
workload in flight
when executing
sequences. Even if
we could get our
models perfectly
trimmed, we would
need perfect flying
conditions to benefit
from the perfect
setup!
Servo and Control
Setup: 3-D trim and
precision trim
typically work against
each other. When
pilots set up their new
40% something, they
Mike Hurley, 11542 Decatur Ct., Westminster CO 80234; E-mail: [email protected]
RADIO CONTROL SCALE AEROBATICS
WHAT IF, from the beginning, you learned to fly RC with the radio
upside-down? Then two years later someone said you needed to turn
it over and fly right-side up? It would probably be tough because
you learned all of the habits the wrong way.
Flying an airplane that is not fully trimmed is almost as bad. You
get into the habit of correcting for poor flying characteristics and end
up chasing the model around the sky during the whole flight. Then
when you move to a new airplane, you have to start over and learn
how to compensate for its different set of problems.
In a conversation with top-rated Tournament of Champions
(TOC) pilot Peter Goldsmith at the 2004 Nats, he noted that it didn’t
look as though many of the models were trimmed well. Some of the
pilots, even in the top classes, were chasing their airplanes around
the sky rather than flying the maneuvers.
Peter was excited to do something about that problem, and I
asked if he would write something for this column. He graciously
agreed. I think this is one of the most important topics that you could
get from this column. Peter’s approach is systematic and
comprehensive. In this first of two installments, he covers subjects
related to trimming the physical airframe.
In the next Scale Aerobatics (SA) column he’ll review how to set
up your radio to compensate for poor flight characteristics using a
variety of mixing techniques. Tear these pages out of this magazine
and put them in a notebook or your flight box. If you follow these
steps in the proper sequence, you’re guaranteed to have a betterflying
airplane than your competitors who didn’t!
Peter Goldsmith was born and raised in Sydney, Australia, and
he began flying RC at 11 years old. He still remembers his first radio
transmitter, called a Bionic Baby—a two-channel, dry-cell system
that his mother bought for him in Singapore. Young Pete had two
weeks before his mother arrived home with the new radio, so he put
that time to good use and designed and built his first RC aircraft.
Growing up, he would design and build his own models out of
necessity. So he was a designer from the beginning.
Peter’s first love in RC has been sailplanes and Soaring. He
loved doing aerobatics with those models, and through an evolution
of events he decided to try F3A (FAI RC Aerobatics). His first
contest was in 1978. He competed on an Australian National level in
Peter Goldsmith with his own-design 46% CAP 232 that he uses in
competitions such as the Masters, the Nats, and the TOC.
Peter always has a smile on his face and
is happy to help other pilots. As JR
Team Manager, he takes pride in his team
being helpful and knowledgeable.
Peter Goldsmith’s first passion in RC was sailplanes and
Soaring, and he continues to compete in that arena today.
go straight for the big rates: 35°, 40°, and in some cases 50° of
throw. Has anybody thought about how this can affect the servo
resolution and, more important, the servo power?
Most SA events allow a separate aircraft for Freestyle. Why not
have your Free aircraft set up specifically for that event and then
have a precision setup for Known and Unknown sequences? A
model just for Freestyle is something I aim to have in the future.
That’s not always a realistic option, so if you’re using the same
model for precision and Free, bias it toward a precision control
setup.
For precision flying I would expect your model to be running
between 12° and 15° of elevator throw. If you feel you need more
than this, check your exponential because it may be too high. As a
starting point, 35% expo is what I call a linear feel. What I like to
have with my expo is approximately 50% of the reaction of full stick
when at half stick. Roughly 35%-40% expo gives you this with
modest control deflections.
If I have my stick at full travel, my aircraft will roll roughly 360°
per second, which is about right for precision. When I only move my
stick halfway, I should be looking for 180° per second.
If Freestyle/3-D flying is your bag, you’re stuck with the
downside of long servo arms and will have to pay attention to the
servo power delivered in this environment. With my 46% CAP 232,
I use 1-inch servo arms on all surfaces except rudder; it is 11⁄4
inches. I have 28° on aileron, 32° on elevator, and 35° of throw on
rudder. This is a good compromise for precision and Freestyle
flying, but it’s biased toward Free.
With 1-inch servo arms, and 11⁄2 inches of distance from the
control-horn attachment point to the center of the hinge line, I’m
getting a 1:1.5 ratio. More important, I am maximizing servo power
and control geometry. With 1-inch servo arms, my resolution is
better, control slop is reduced, and servo wear is greatly reduced.
Another bonus is that I don’t need as many servos per surface.
Give it a try next time you set up your aircraft. You may be
surprised. In some cases you may see no difference in control
responsiveness by going to 1-inch servo arms, but with the better
geometry you may be reducing any control-surface blowback.
One of the biggest challenges I see pilots dealing with is surface
blowback, which is when the servos are overpowered by the amount
of pressure on a given control surface during full deflection, causing
the surface to lose holding power and start to push back toward the
neutral position. It can also happen when in neutral, trying to hold
the airplane stable or stop it when exiting a maneuver.
With blowback, your snaps will be all over the place—entries
and exits. Flying consistently is almost impossible. Every time your
speed changes, your control response will change. Hmm. I suspect a
few lights just went on. Yep! It could be that the fact you’re
consistently missing your snap exits is not because of your skills but
because of control blowback.
When setting up your servos, make sure you run the numbers, do
the math, and figure out exactly how much power you are delivering
to the surface. All servos are rated at inch-ounce; that is, at an inch
from the center of the servo. An 8611 is 266 inch-ounce on 6 volts.
With a 2-inch servo arm, the applied force is reduced to only 133
inch-ounce, and it’s roughly 200 inch-ounce with a 11⁄2-inch servo
arm.
Years ago, I was able to measure the forces on my CAP. The
ailerons required well more than 30 pounds of force to deflect at 100
mph! Today there are much bigger ailerons than mine. Please pay
attention to the following; it is vital to consistent flying. If you have
to use 11⁄2-inch servo arms or 2-inch servo arms, you will need more
servos.
Sequencing: My concept of sequencing the trimming process is
simple. I can’t emphasize enough that it is crucial to trim your model
in the correct sequence to make sure each adjustment has no effect
on the previous adjustment.
There is an order in which I recommend trimming an airplane,
and model balance—CG—is first. You can’t move ahead until you
have a CG that you’re happy with. If you change the CG later, you
will need to start over and check your entire trim setup. Differential,
knife-edge flight, and down-line tracking will be affected by the CG.
Next is dynamic balancing, or “wingtip weight.” Then comes
thrust angles, then aileron differential, and finally P mixing, knifeedge
tracking, roll coupling, down-line track, and so on. Oh, and if
you change your propeller, your whole trim setup will change. Duh.
Been there? I know I have.
Make sure you’re trimming with the same propeller you plan to
compete with. When I went from a two- to a three-blade propeller
on my 46% Hangar 9 Ultimate, I needed 2° more upthrust and 1°
more right thrust, and everything else changed as well—knife-edge
tracking, differential, etc. I had to start over again. The lesson is to
determine what propeller you’ll want to use before you start this
trim process.
Balance: How do I know the correct CG for my model? If in doubt,
read your model’s instructions; that’s usually a good place to start.
For precision flying, forward is better—but too far forward can be a
problem. I can’t put into writing what is the best feel for each pilot,
other than it is a feel thing. However, I can give you some
symptoms of too far back, too far forward, and some simple tests I
use to check.
One of my favorite ways to determine the correct CG is spin
entries. If, when entering a spin, your model mushes and kind of
slides into the spin with no real stall visible, your CG may be too far
forward. Another sign of forward CG is excessive down-elevator
needed for inverted flight. This is not always the reason, but it is a
sign.
Rear CG is probably easier for most pilots to see. Some obvious
clues are that the model is sensitive in pitch, unpredictable around
the stall, or climbs when on an inverted 45° line. Again, CG is
mainly about feel.
The important thing is to determine your CG before you work on
any other aspect of trimming your aircraft. I recommend at least 10-
15 flights before making the commitment to where the CG needs to
be if you’re trimming a new model.
Dynamic Balance: Okay, you’re happy with the CG. The next trim
step is dynamic balance. This is really only relevant with wingtip
weight. Most other axes on a model aircraft are not affected too
much by the dynamic effects of high-G loads, but the wings are. Just
because they weigh the same and don’t carry any aileron trim
doesn’t mean you can’t have a wing-weight problem.
I have seen myriad ways to test for wing-weight trim: loops,
pulling to vertical, and so on. Think about the sequencing argument.
If you do loops, or pull to a vertical up-line, the engine thrust can
have an effect. But you haven’t trimmed the thrust angles yet, so
how do you check this? What could you do to check your model’s
wingtip weight in flight that will not be affected by thrust?
Some of you may have figured this out, but I put the model into
a vertical dive with the throttle back (minimum of three to four
seconds) and pull a hard corner at the bottom. No matter where the
wings are in roll, when you pull to level, the
wings must be level. Check this concept with
your stick airplane. It really doesn’t matter
where your model’s wings are. As you pull to
horizontal flight, the wings must be level.
If you attempt to pull a hard vertical from
horizontal, you must be absolutely sure that
your wings are level. I don’t know about you,
but I am not that good! If you go from
vertical to horizontal, not only will the engine
thrust have no effect, but your wings can be
anywhere as you’re on a vertical down-line.
When you pull the corner, the aircraft may be
pointing in a different direction than you
planned, but that is okay as long as the wings
are level.
When some of you try this experiment,
you will notice that one wing will
consistently drop. You may have to add some
weight to the opposite wingtip. I was never
really sure if my tip weight was correct until I
went to this method.
Make sure you only use elevator through
the corner. Perhaps just for the trimming
process you can increase the aileron stick
tension to ensure that you don’t accidentally
input a bit of aileron with the elevator and
that the elevators track correctly when you
pull the stick back.
Don’t be quick to make a decision! Have
patience and have a friend observe the
proceedings. Do many pullouts and make
absolutely sure before you move on to the
next step of trimming.
Thrust Angles: It’s time to put aesthetics
aside and get that thrust correct. I see many
spinners lining up perfectly to the cowl these
days. One of the biggest deterrents to
adjusting for the correct thrust angles is that
once the model is built and you make an
adjustment, the spinner won’t line up
anymore. Again, when building your model,
pay attention to the instructions. Chances are
that somebody has figured it out or is pretty
close.
I like to test-fly the model before I paint
the cowl. Once I am happy with thrust, I can
make the appropriate cosmetic changes to
complete the model before painting. For all
the money you spend traveling and time you
spend practicing, do put good model trim
ahead of aesthetics!
Setting up the correct thrust angles is
fairly simple. Well, it’s simple to identify but
harder to adjust. Now that you know your
model’s wingtip weight is correct, you should
be able to pull to some accurate vertical uplines
with confidence.
The most important issue with this is
making sure your aircraft’s wings are level.
Don’t guess; be absolutely sure of this before
pulling to a vertical. I have seen people add
unnecessary right thrust because the wings
were not level when pulling corners, leaving
an inside wing down (normal human
behavior), and the model would lean to the
left. I like to fly directly overhead, into the
wind, where I can clearly see the wings, and
then pull to a vertical up-line.
All right, up you go. The first 100 feet is
good. The next 100 feet is good. Now your
aircraft is moving through 500 feet and still
tracking well. Your model is higher than
1,000 feet now and still straight. If you work
at it, the best you can hope for is 1,000 or so
feet—plenty for most figures.
Speed will have a huge effect on thrust
angle on a vertical up-line. Entry speed,
compared to speed under load after climbing
to 100 feet, will be as much as 30-40 mph
slower. My goal is to trim as best as I can for
the first 1,000 feet. If I go for 2,000 feet, I
typically end up with too much right thrust at
the start of the climb and not enough at the
finish. Play the numbers, look at the figures
we fly, and set up your model accordingly.
I have a great little tip for making the
adjustments. Let’s say that after many
pullups, you really need more right thrust. As
your model passes through 500 feet, you can
clearly see it drifting to the left. The cool tip is
to apply right rudder trim, and continue to
apply it until the airplane tracks straight.
Bring the model in to land, and check the
rudder deflection. Use a protractor to see how
many degrees of rudder were required for a
straight vertical. Whatever it is, divide it by
two, and that will be what you need to add to
the right thrust. If you have 2° of right rudder,
you will need to add 1° more of right thrust. It
works both ways. If you need left rudder (too
much right thrust), you can use the same
equation.
Next month Peter will continue his trimming
sequence with steps for getting your airplane
set up for competition with radio mixing.
There’s more to it than you may think, so
don’t miss it. MA
Edition: Model Aviation - 2005/02
Page Numbers: 94,96,98
Edition: Model Aviation - 2005/02
Page Numbers: 94,96,98
94 MODEL AVIATION
Pattern until he came to the US in 2000, and he was the Australian
National champ from 1995 until 2000. During that time he was also
a member of the Australian National team for the World
Championships, making the finals in three of the five World
Championships, and he was named Oceanic Champion three times.
In SA, Pete has multiple top-level performances at the Masters
and won it in 2001. He has placed second in the AMA Nats three
times and won the Freestyle National Championship in 2002. He
competed in the TOC from 1992 until its end in 2002.
Peter is currently the JR Team Manager and continues to
compete at the top level. One of the most telling aspects of Peter’s
RC career is that he has always flown and competed with his own
designs—built from scratch and trimmed based on his 25+ years of
experience.
At this point I’ll let him take over.
Competing in the 2004 Don Lowe Masters, I was inspired by the
raw talent in pilots half my age; I was honored to place seventh! I
began thinking about all of the help I had received throughout the
years and felt driven to give back to the new pilots of the Aerobatics
community, as had been done with me many years ago.
Earlier in 2004 in a discussion with Mike Hurley at the Nats, I
shared with him how passionate I am to share my life’s aerobatic
knowledge, and he invited me to write something about trimming
and mixing.
A properly trimmed model can reduce your workload in an
Aerobatics sequence by an enormous amount. I judged at the Nats
last year and thoroughly enjoyed the experience. I was impressed
with the skills, especially in the lower classes, that pilots displayed,
but I noticed most of them trying to fly around a poor trim setup. It
drove me crazy to watch!
I remember bouncing out of my judging chair and saying to
Mike, “Boy, I need to help these people!” So here are some thoughts
from my 25 years of experience and involvement with people who
shared their thoughts
on trimming with
me.
I have observed
that there is no such
thing as a perfectly
trimmed model. Our
goal is to reduce our
workload in flight
when executing
sequences. Even if
we could get our
models perfectly
trimmed, we would
need perfect flying
conditions to benefit
from the perfect
setup!
Servo and Control
Setup: 3-D trim and
precision trim
typically work against
each other. When
pilots set up their new
40% something, they
Mike Hurley, 11542 Decatur Ct., Westminster CO 80234; E-mail: [email protected]
RADIO CONTROL SCALE AEROBATICS
WHAT IF, from the beginning, you learned to fly RC with the radio
upside-down? Then two years later someone said you needed to turn
it over and fly right-side up? It would probably be tough because
you learned all of the habits the wrong way.
Flying an airplane that is not fully trimmed is almost as bad. You
get into the habit of correcting for poor flying characteristics and end
up chasing the model around the sky during the whole flight. Then
when you move to a new airplane, you have to start over and learn
how to compensate for its different set of problems.
In a conversation with top-rated Tournament of Champions
(TOC) pilot Peter Goldsmith at the 2004 Nats, he noted that it didn’t
look as though many of the models were trimmed well. Some of the
pilots, even in the top classes, were chasing their airplanes around
the sky rather than flying the maneuvers.
Peter was excited to do something about that problem, and I
asked if he would write something for this column. He graciously
agreed. I think this is one of the most important topics that you could
get from this column. Peter’s approach is systematic and
comprehensive. In this first of two installments, he covers subjects
related to trimming the physical airframe.
In the next Scale Aerobatics (SA) column he’ll review how to set
up your radio to compensate for poor flight characteristics using a
variety of mixing techniques. Tear these pages out of this magazine
and put them in a notebook or your flight box. If you follow these
steps in the proper sequence, you’re guaranteed to have a betterflying
airplane than your competitors who didn’t!
Peter Goldsmith was born and raised in Sydney, Australia, and
he began flying RC at 11 years old. He still remembers his first radio
transmitter, called a Bionic Baby—a two-channel, dry-cell system
that his mother bought for him in Singapore. Young Pete had two
weeks before his mother arrived home with the new radio, so he put
that time to good use and designed and built his first RC aircraft.
Growing up, he would design and build his own models out of
necessity. So he was a designer from the beginning.
Peter’s first love in RC has been sailplanes and Soaring. He
loved doing aerobatics with those models, and through an evolution
of events he decided to try F3A (FAI RC Aerobatics). His first
contest was in 1978. He competed on an Australian National level in
Peter Goldsmith with his own-design 46% CAP 232 that he uses in
competitions such as the Masters, the Nats, and the TOC.
Peter always has a smile on his face and
is happy to help other pilots. As JR
Team Manager, he takes pride in his team
being helpful and knowledgeable.
Peter Goldsmith’s first passion in RC was sailplanes and
Soaring, and he continues to compete in that arena today.
go straight for the big rates: 35°, 40°, and in some cases 50° of
throw. Has anybody thought about how this can affect the servo
resolution and, more important, the servo power?
Most SA events allow a separate aircraft for Freestyle. Why not
have your Free aircraft set up specifically for that event and then
have a precision setup for Known and Unknown sequences? A
model just for Freestyle is something I aim to have in the future.
That’s not always a realistic option, so if you’re using the same
model for precision and Free, bias it toward a precision control
setup.
For precision flying I would expect your model to be running
between 12° and 15° of elevator throw. If you feel you need more
than this, check your exponential because it may be too high. As a
starting point, 35% expo is what I call a linear feel. What I like to
have with my expo is approximately 50% of the reaction of full stick
when at half stick. Roughly 35%-40% expo gives you this with
modest control deflections.
If I have my stick at full travel, my aircraft will roll roughly 360°
per second, which is about right for precision. When I only move my
stick halfway, I should be looking for 180° per second.
If Freestyle/3-D flying is your bag, you’re stuck with the
downside of long servo arms and will have to pay attention to the
servo power delivered in this environment. With my 46% CAP 232,
I use 1-inch servo arms on all surfaces except rudder; it is 11⁄4
inches. I have 28° on aileron, 32° on elevator, and 35° of throw on
rudder. This is a good compromise for precision and Freestyle
flying, but it’s biased toward Free.
With 1-inch servo arms, and 11⁄2 inches of distance from the
control-horn attachment point to the center of the hinge line, I’m
getting a 1:1.5 ratio. More important, I am maximizing servo power
and control geometry. With 1-inch servo arms, my resolution is
better, control slop is reduced, and servo wear is greatly reduced.
Another bonus is that I don’t need as many servos per surface.
Give it a try next time you set up your aircraft. You may be
surprised. In some cases you may see no difference in control
responsiveness by going to 1-inch servo arms, but with the better
geometry you may be reducing any control-surface blowback.
One of the biggest challenges I see pilots dealing with is surface
blowback, which is when the servos are overpowered by the amount
of pressure on a given control surface during full deflection, causing
the surface to lose holding power and start to push back toward the
neutral position. It can also happen when in neutral, trying to hold
the airplane stable or stop it when exiting a maneuver.
With blowback, your snaps will be all over the place—entries
and exits. Flying consistently is almost impossible. Every time your
speed changes, your control response will change. Hmm. I suspect a
few lights just went on. Yep! It could be that the fact you’re
consistently missing your snap exits is not because of your skills but
because of control blowback.
When setting up your servos, make sure you run the numbers, do
the math, and figure out exactly how much power you are delivering
to the surface. All servos are rated at inch-ounce; that is, at an inch
from the center of the servo. An 8611 is 266 inch-ounce on 6 volts.
With a 2-inch servo arm, the applied force is reduced to only 133
inch-ounce, and it’s roughly 200 inch-ounce with a 11⁄2-inch servo
arm.
Years ago, I was able to measure the forces on my CAP. The
ailerons required well more than 30 pounds of force to deflect at 100
mph! Today there are much bigger ailerons than mine. Please pay
attention to the following; it is vital to consistent flying. If you have
to use 11⁄2-inch servo arms or 2-inch servo arms, you will need more
servos.
Sequencing: My concept of sequencing the trimming process is
simple. I can’t emphasize enough that it is crucial to trim your model
in the correct sequence to make sure each adjustment has no effect
on the previous adjustment.
There is an order in which I recommend trimming an airplane,
and model balance—CG—is first. You can’t move ahead until you
have a CG that you’re happy with. If you change the CG later, you
will need to start over and check your entire trim setup. Differential,
knife-edge flight, and down-line tracking will be affected by the CG.
Next is dynamic balancing, or “wingtip weight.” Then comes
thrust angles, then aileron differential, and finally P mixing, knifeedge
tracking, roll coupling, down-line track, and so on. Oh, and if
you change your propeller, your whole trim setup will change. Duh.
Been there? I know I have.
Make sure you’re trimming with the same propeller you plan to
compete with. When I went from a two- to a three-blade propeller
on my 46% Hangar 9 Ultimate, I needed 2° more upthrust and 1°
more right thrust, and everything else changed as well—knife-edge
tracking, differential, etc. I had to start over again. The lesson is to
determine what propeller you’ll want to use before you start this
trim process.
Balance: How do I know the correct CG for my model? If in doubt,
read your model’s instructions; that’s usually a good place to start.
For precision flying, forward is better—but too far forward can be a
problem. I can’t put into writing what is the best feel for each pilot,
other than it is a feel thing. However, I can give you some
symptoms of too far back, too far forward, and some simple tests I
use to check.
One of my favorite ways to determine the correct CG is spin
entries. If, when entering a spin, your model mushes and kind of
slides into the spin with no real stall visible, your CG may be too far
forward. Another sign of forward CG is excessive down-elevator
needed for inverted flight. This is not always the reason, but it is a
sign.
Rear CG is probably easier for most pilots to see. Some obvious
clues are that the model is sensitive in pitch, unpredictable around
the stall, or climbs when on an inverted 45° line. Again, CG is
mainly about feel.
The important thing is to determine your CG before you work on
any other aspect of trimming your aircraft. I recommend at least 10-
15 flights before making the commitment to where the CG needs to
be if you’re trimming a new model.
Dynamic Balance: Okay, you’re happy with the CG. The next trim
step is dynamic balance. This is really only relevant with wingtip
weight. Most other axes on a model aircraft are not affected too
much by the dynamic effects of high-G loads, but the wings are. Just
because they weigh the same and don’t carry any aileron trim
doesn’t mean you can’t have a wing-weight problem.
I have seen myriad ways to test for wing-weight trim: loops,
pulling to vertical, and so on. Think about the sequencing argument.
If you do loops, or pull to a vertical up-line, the engine thrust can
have an effect. But you haven’t trimmed the thrust angles yet, so
how do you check this? What could you do to check your model’s
wingtip weight in flight that will not be affected by thrust?
Some of you may have figured this out, but I put the model into
a vertical dive with the throttle back (minimum of three to four
seconds) and pull a hard corner at the bottom. No matter where the
wings are in roll, when you pull to level, the
wings must be level. Check this concept with
your stick airplane. It really doesn’t matter
where your model’s wings are. As you pull to
horizontal flight, the wings must be level.
If you attempt to pull a hard vertical from
horizontal, you must be absolutely sure that
your wings are level. I don’t know about you,
but I am not that good! If you go from
vertical to horizontal, not only will the engine
thrust have no effect, but your wings can be
anywhere as you’re on a vertical down-line.
When you pull the corner, the aircraft may be
pointing in a different direction than you
planned, but that is okay as long as the wings
are level.
When some of you try this experiment,
you will notice that one wing will
consistently drop. You may have to add some
weight to the opposite wingtip. I was never
really sure if my tip weight was correct until I
went to this method.
Make sure you only use elevator through
the corner. Perhaps just for the trimming
process you can increase the aileron stick
tension to ensure that you don’t accidentally
input a bit of aileron with the elevator and
that the elevators track correctly when you
pull the stick back.
Don’t be quick to make a decision! Have
patience and have a friend observe the
proceedings. Do many pullouts and make
absolutely sure before you move on to the
next step of trimming.
Thrust Angles: It’s time to put aesthetics
aside and get that thrust correct. I see many
spinners lining up perfectly to the cowl these
days. One of the biggest deterrents to
adjusting for the correct thrust angles is that
once the model is built and you make an
adjustment, the spinner won’t line up
anymore. Again, when building your model,
pay attention to the instructions. Chances are
that somebody has figured it out or is pretty
close.
I like to test-fly the model before I paint
the cowl. Once I am happy with thrust, I can
make the appropriate cosmetic changes to
complete the model before painting. For all
the money you spend traveling and time you
spend practicing, do put good model trim
ahead of aesthetics!
Setting up the correct thrust angles is
fairly simple. Well, it’s simple to identify but
harder to adjust. Now that you know your
model’s wingtip weight is correct, you should
be able to pull to some accurate vertical uplines
with confidence.
The most important issue with this is
making sure your aircraft’s wings are level.
Don’t guess; be absolutely sure of this before
pulling to a vertical. I have seen people add
unnecessary right thrust because the wings
were not level when pulling corners, leaving
an inside wing down (normal human
behavior), and the model would lean to the
left. I like to fly directly overhead, into the
wind, where I can clearly see the wings, and
then pull to a vertical up-line.
All right, up you go. The first 100 feet is
good. The next 100 feet is good. Now your
aircraft is moving through 500 feet and still
tracking well. Your model is higher than
1,000 feet now and still straight. If you work
at it, the best you can hope for is 1,000 or so
feet—plenty for most figures.
Speed will have a huge effect on thrust
angle on a vertical up-line. Entry speed,
compared to speed under load after climbing
to 100 feet, will be as much as 30-40 mph
slower. My goal is to trim as best as I can for
the first 1,000 feet. If I go for 2,000 feet, I
typically end up with too much right thrust at
the start of the climb and not enough at the
finish. Play the numbers, look at the figures
we fly, and set up your model accordingly.
I have a great little tip for making the
adjustments. Let’s say that after many
pullups, you really need more right thrust. As
your model passes through 500 feet, you can
clearly see it drifting to the left. The cool tip is
to apply right rudder trim, and continue to
apply it until the airplane tracks straight.
Bring the model in to land, and check the
rudder deflection. Use a protractor to see how
many degrees of rudder were required for a
straight vertical. Whatever it is, divide it by
two, and that will be what you need to add to
the right thrust. If you have 2° of right rudder,
you will need to add 1° more of right thrust. It
works both ways. If you need left rudder (too
much right thrust), you can use the same
equation.
Next month Peter will continue his trimming
sequence with steps for getting your airplane
set up for competition with radio mixing.
There’s more to it than you may think, so
don’t miss it. MA
Edition: Model Aviation - 2005/02
Page Numbers: 94,96,98
94 MODEL AVIATION
Pattern until he came to the US in 2000, and he was the Australian
National champ from 1995 until 2000. During that time he was also
a member of the Australian National team for the World
Championships, making the finals in three of the five World
Championships, and he was named Oceanic Champion three times.
In SA, Pete has multiple top-level performances at the Masters
and won it in 2001. He has placed second in the AMA Nats three
times and won the Freestyle National Championship in 2002. He
competed in the TOC from 1992 until its end in 2002.
Peter is currently the JR Team Manager and continues to
compete at the top level. One of the most telling aspects of Peter’s
RC career is that he has always flown and competed with his own
designs—built from scratch and trimmed based on his 25+ years of
experience.
At this point I’ll let him take over.
Competing in the 2004 Don Lowe Masters, I was inspired by the
raw talent in pilots half my age; I was honored to place seventh! I
began thinking about all of the help I had received throughout the
years and felt driven to give back to the new pilots of the Aerobatics
community, as had been done with me many years ago.
Earlier in 2004 in a discussion with Mike Hurley at the Nats, I
shared with him how passionate I am to share my life’s aerobatic
knowledge, and he invited me to write something about trimming
and mixing.
A properly trimmed model can reduce your workload in an
Aerobatics sequence by an enormous amount. I judged at the Nats
last year and thoroughly enjoyed the experience. I was impressed
with the skills, especially in the lower classes, that pilots displayed,
but I noticed most of them trying to fly around a poor trim setup. It
drove me crazy to watch!
I remember bouncing out of my judging chair and saying to
Mike, “Boy, I need to help these people!” So here are some thoughts
from my 25 years of experience and involvement with people who
shared their thoughts
on trimming with
me.
I have observed
that there is no such
thing as a perfectly
trimmed model. Our
goal is to reduce our
workload in flight
when executing
sequences. Even if
we could get our
models perfectly
trimmed, we would
need perfect flying
conditions to benefit
from the perfect
setup!
Servo and Control
Setup: 3-D trim and
precision trim
typically work against
each other. When
pilots set up their new
40% something, they
Mike Hurley, 11542 Decatur Ct., Westminster CO 80234; E-mail: [email protected]
RADIO CONTROL SCALE AEROBATICS
WHAT IF, from the beginning, you learned to fly RC with the radio
upside-down? Then two years later someone said you needed to turn
it over and fly right-side up? It would probably be tough because
you learned all of the habits the wrong way.
Flying an airplane that is not fully trimmed is almost as bad. You
get into the habit of correcting for poor flying characteristics and end
up chasing the model around the sky during the whole flight. Then
when you move to a new airplane, you have to start over and learn
how to compensate for its different set of problems.
In a conversation with top-rated Tournament of Champions
(TOC) pilot Peter Goldsmith at the 2004 Nats, he noted that it didn’t
look as though many of the models were trimmed well. Some of the
pilots, even in the top classes, were chasing their airplanes around
the sky rather than flying the maneuvers.
Peter was excited to do something about that problem, and I
asked if he would write something for this column. He graciously
agreed. I think this is one of the most important topics that you could
get from this column. Peter’s approach is systematic and
comprehensive. In this first of two installments, he covers subjects
related to trimming the physical airframe.
In the next Scale Aerobatics (SA) column he’ll review how to set
up your radio to compensate for poor flight characteristics using a
variety of mixing techniques. Tear these pages out of this magazine
and put them in a notebook or your flight box. If you follow these
steps in the proper sequence, you’re guaranteed to have a betterflying
airplane than your competitors who didn’t!
Peter Goldsmith was born and raised in Sydney, Australia, and
he began flying RC at 11 years old. He still remembers his first radio
transmitter, called a Bionic Baby—a two-channel, dry-cell system
that his mother bought for him in Singapore. Young Pete had two
weeks before his mother arrived home with the new radio, so he put
that time to good use and designed and built his first RC aircraft.
Growing up, he would design and build his own models out of
necessity. So he was a designer from the beginning.
Peter’s first love in RC has been sailplanes and Soaring. He
loved doing aerobatics with those models, and through an evolution
of events he decided to try F3A (FAI RC Aerobatics). His first
contest was in 1978. He competed on an Australian National level in
Peter Goldsmith with his own-design 46% CAP 232 that he uses in
competitions such as the Masters, the Nats, and the TOC.
Peter always has a smile on his face and
is happy to help other pilots. As JR
Team Manager, he takes pride in his team
being helpful and knowledgeable.
Peter Goldsmith’s first passion in RC was sailplanes and
Soaring, and he continues to compete in that arena today.
go straight for the big rates: 35°, 40°, and in some cases 50° of
throw. Has anybody thought about how this can affect the servo
resolution and, more important, the servo power?
Most SA events allow a separate aircraft for Freestyle. Why not
have your Free aircraft set up specifically for that event and then
have a precision setup for Known and Unknown sequences? A
model just for Freestyle is something I aim to have in the future.
That’s not always a realistic option, so if you’re using the same
model for precision and Free, bias it toward a precision control
setup.
For precision flying I would expect your model to be running
between 12° and 15° of elevator throw. If you feel you need more
than this, check your exponential because it may be too high. As a
starting point, 35% expo is what I call a linear feel. What I like to
have with my expo is approximately 50% of the reaction of full stick
when at half stick. Roughly 35%-40% expo gives you this with
modest control deflections.
If I have my stick at full travel, my aircraft will roll roughly 360°
per second, which is about right for precision. When I only move my
stick halfway, I should be looking for 180° per second.
If Freestyle/3-D flying is your bag, you’re stuck with the
downside of long servo arms and will have to pay attention to the
servo power delivered in this environment. With my 46% CAP 232,
I use 1-inch servo arms on all surfaces except rudder; it is 11⁄4
inches. I have 28° on aileron, 32° on elevator, and 35° of throw on
rudder. This is a good compromise for precision and Freestyle
flying, but it’s biased toward Free.
With 1-inch servo arms, and 11⁄2 inches of distance from the
control-horn attachment point to the center of the hinge line, I’m
getting a 1:1.5 ratio. More important, I am maximizing servo power
and control geometry. With 1-inch servo arms, my resolution is
better, control slop is reduced, and servo wear is greatly reduced.
Another bonus is that I don’t need as many servos per surface.
Give it a try next time you set up your aircraft. You may be
surprised. In some cases you may see no difference in control
responsiveness by going to 1-inch servo arms, but with the better
geometry you may be reducing any control-surface blowback.
One of the biggest challenges I see pilots dealing with is surface
blowback, which is when the servos are overpowered by the amount
of pressure on a given control surface during full deflection, causing
the surface to lose holding power and start to push back toward the
neutral position. It can also happen when in neutral, trying to hold
the airplane stable or stop it when exiting a maneuver.
With blowback, your snaps will be all over the place—entries
and exits. Flying consistently is almost impossible. Every time your
speed changes, your control response will change. Hmm. I suspect a
few lights just went on. Yep! It could be that the fact you’re
consistently missing your snap exits is not because of your skills but
because of control blowback.
When setting up your servos, make sure you run the numbers, do
the math, and figure out exactly how much power you are delivering
to the surface. All servos are rated at inch-ounce; that is, at an inch
from the center of the servo. An 8611 is 266 inch-ounce on 6 volts.
With a 2-inch servo arm, the applied force is reduced to only 133
inch-ounce, and it’s roughly 200 inch-ounce with a 11⁄2-inch servo
arm.
Years ago, I was able to measure the forces on my CAP. The
ailerons required well more than 30 pounds of force to deflect at 100
mph! Today there are much bigger ailerons than mine. Please pay
attention to the following; it is vital to consistent flying. If you have
to use 11⁄2-inch servo arms or 2-inch servo arms, you will need more
servos.
Sequencing: My concept of sequencing the trimming process is
simple. I can’t emphasize enough that it is crucial to trim your model
in the correct sequence to make sure each adjustment has no effect
on the previous adjustment.
There is an order in which I recommend trimming an airplane,
and model balance—CG—is first. You can’t move ahead until you
have a CG that you’re happy with. If you change the CG later, you
will need to start over and check your entire trim setup. Differential,
knife-edge flight, and down-line tracking will be affected by the CG.
Next is dynamic balancing, or “wingtip weight.” Then comes
thrust angles, then aileron differential, and finally P mixing, knifeedge
tracking, roll coupling, down-line track, and so on. Oh, and if
you change your propeller, your whole trim setup will change. Duh.
Been there? I know I have.
Make sure you’re trimming with the same propeller you plan to
compete with. When I went from a two- to a three-blade propeller
on my 46% Hangar 9 Ultimate, I needed 2° more upthrust and 1°
more right thrust, and everything else changed as well—knife-edge
tracking, differential, etc. I had to start over again. The lesson is to
determine what propeller you’ll want to use before you start this
trim process.
Balance: How do I know the correct CG for my model? If in doubt,
read your model’s instructions; that’s usually a good place to start.
For precision flying, forward is better—but too far forward can be a
problem. I can’t put into writing what is the best feel for each pilot,
other than it is a feel thing. However, I can give you some
symptoms of too far back, too far forward, and some simple tests I
use to check.
One of my favorite ways to determine the correct CG is spin
entries. If, when entering a spin, your model mushes and kind of
slides into the spin with no real stall visible, your CG may be too far
forward. Another sign of forward CG is excessive down-elevator
needed for inverted flight. This is not always the reason, but it is a
sign.
Rear CG is probably easier for most pilots to see. Some obvious
clues are that the model is sensitive in pitch, unpredictable around
the stall, or climbs when on an inverted 45° line. Again, CG is
mainly about feel.
The important thing is to determine your CG before you work on
any other aspect of trimming your aircraft. I recommend at least 10-
15 flights before making the commitment to where the CG needs to
be if you’re trimming a new model.
Dynamic Balance: Okay, you’re happy with the CG. The next trim
step is dynamic balance. This is really only relevant with wingtip
weight. Most other axes on a model aircraft are not affected too
much by the dynamic effects of high-G loads, but the wings are. Just
because they weigh the same and don’t carry any aileron trim
doesn’t mean you can’t have a wing-weight problem.
I have seen myriad ways to test for wing-weight trim: loops,
pulling to vertical, and so on. Think about the sequencing argument.
If you do loops, or pull to a vertical up-line, the engine thrust can
have an effect. But you haven’t trimmed the thrust angles yet, so
how do you check this? What could you do to check your model’s
wingtip weight in flight that will not be affected by thrust?
Some of you may have figured this out, but I put the model into
a vertical dive with the throttle back (minimum of three to four
seconds) and pull a hard corner at the bottom. No matter where the
wings are in roll, when you pull to level, the
wings must be level. Check this concept with
your stick airplane. It really doesn’t matter
where your model’s wings are. As you pull to
horizontal flight, the wings must be level.
If you attempt to pull a hard vertical from
horizontal, you must be absolutely sure that
your wings are level. I don’t know about you,
but I am not that good! If you go from
vertical to horizontal, not only will the engine
thrust have no effect, but your wings can be
anywhere as you’re on a vertical down-line.
When you pull the corner, the aircraft may be
pointing in a different direction than you
planned, but that is okay as long as the wings
are level.
When some of you try this experiment,
you will notice that one wing will
consistently drop. You may have to add some
weight to the opposite wingtip. I was never
really sure if my tip weight was correct until I
went to this method.
Make sure you only use elevator through
the corner. Perhaps just for the trimming
process you can increase the aileron stick
tension to ensure that you don’t accidentally
input a bit of aileron with the elevator and
that the elevators track correctly when you
pull the stick back.
Don’t be quick to make a decision! Have
patience and have a friend observe the
proceedings. Do many pullouts and make
absolutely sure before you move on to the
next step of trimming.
Thrust Angles: It’s time to put aesthetics
aside and get that thrust correct. I see many
spinners lining up perfectly to the cowl these
days. One of the biggest deterrents to
adjusting for the correct thrust angles is that
once the model is built and you make an
adjustment, the spinner won’t line up
anymore. Again, when building your model,
pay attention to the instructions. Chances are
that somebody has figured it out or is pretty
close.
I like to test-fly the model before I paint
the cowl. Once I am happy with thrust, I can
make the appropriate cosmetic changes to
complete the model before painting. For all
the money you spend traveling and time you
spend practicing, do put good model trim
ahead of aesthetics!
Setting up the correct thrust angles is
fairly simple. Well, it’s simple to identify but
harder to adjust. Now that you know your
model’s wingtip weight is correct, you should
be able to pull to some accurate vertical uplines
with confidence.
The most important issue with this is
making sure your aircraft’s wings are level.
Don’t guess; be absolutely sure of this before
pulling to a vertical. I have seen people add
unnecessary right thrust because the wings
were not level when pulling corners, leaving
an inside wing down (normal human
behavior), and the model would lean to the
left. I like to fly directly overhead, into the
wind, where I can clearly see the wings, and
then pull to a vertical up-line.
All right, up you go. The first 100 feet is
good. The next 100 feet is good. Now your
aircraft is moving through 500 feet and still
tracking well. Your model is higher than
1,000 feet now and still straight. If you work
at it, the best you can hope for is 1,000 or so
feet—plenty for most figures.
Speed will have a huge effect on thrust
angle on a vertical up-line. Entry speed,
compared to speed under load after climbing
to 100 feet, will be as much as 30-40 mph
slower. My goal is to trim as best as I can for
the first 1,000 feet. If I go for 2,000 feet, I
typically end up with too much right thrust at
the start of the climb and not enough at the
finish. Play the numbers, look at the figures
we fly, and set up your model accordingly.
I have a great little tip for making the
adjustments. Let’s say that after many
pullups, you really need more right thrust. As
your model passes through 500 feet, you can
clearly see it drifting to the left. The cool tip is
to apply right rudder trim, and continue to
apply it until the airplane tracks straight.
Bring the model in to land, and check the
rudder deflection. Use a protractor to see how
many degrees of rudder were required for a
straight vertical. Whatever it is, divide it by
two, and that will be what you need to add to
the right thrust. If you have 2° of right rudder,
you will need to add 1° more of right thrust. It
works both ways. If you need left rudder (too
much right thrust), you can use the same
equation.
Next month Peter will continue his trimming
sequence with steps for getting your airplane
set up for competition with radio mixing.
There’s more to it than you may think, so
don’t miss it. MA