Champions never compromise safety for an opportunity to be respected. Preflight checks and good maintenance practices will win
fans over every time. Ben Lanterman photo.
March 2011 49
A guide to preflight inspection of model helicopters
by Anthony N. Avallone
Ready
Liftoff
for
TODAY’S MODEL HELICOPTERS
are sophisticated machines that combine
complicated mechanical and electronic
systems, allowing pilots of all abilities to
enjoy this unique form of flight. These
models are incredibly reliable when you
consider the factors to which they are
exposed, including high-G loads from 3-D
maneuvers, rotor-head speeds exceeding
2,000 rpm, and, in the case of nitropowered
versions, significant vibration.
Because of their complex designs, as
well as the rigors we put them through,
mechanical failures do happen. In the
realm of model helicopters, even a small
defect such as a loose or missing bolt or
nut can lead to a crash. Many defects can
be found and corrected if they are caught
in time through a preflight inspection,
thereby preventing a costly rebuild.
A preflight inspection is normal in fullscale
aviation. No conscientious pilot
would take off in an aircraft that has not
been examined. The risks to well-being
posed by flying model helicopters are not
as high as they are in full-scale aviation,
but they are real. A machine that is out of
control because of a mechanical flaw can
be a danger to the pilot and spectators,
especially during the takeoff phase when
the machine is relatively close.
This article will outline a simple,
systematic approach to inspecting model
helicopters before flying. By detailing reallife
examples with accompanying photos of
problems found while examining my
aircraft, you will learn how many issues that
can lead to crashes can be avoided.
Unfortunately I have learned many of
the lessons I will present from accidents
resulting from inadequate before-flight
inspections.
Preflighting the Helicopter: My
examination begins at the rotor head and
03sig2.QXD_00MSTRPG.QXD 1/24/11 1:25 PM Page 49
50 MODEL AVIATION
Photos by the author except as noted
progresses down the left side of the
frames, back along the boom to the tail,
and finishes with the right side of the
model.
Although the order of inspection does
not matter too much, it is important to
complete the assessment in a systematic
fashion; that is made easier through a
checklist. I have included a sample to get
you started.
At the rotor head I check attachment
bolts to the main shaft, as well as the
various arms and linkages. I pay
particular attention to the blade grips; I
have encountered loose spindles, and they
are rarely obvious. Pulling out on the
blade grips to check for play and pushing
down on one blade grip while pulling up
on the other will unmask a loose spindle
bolt or worn head dampener.
Links can wear out, so check them
regularly for excessive play.
Additionally, ball links can develop splits
following crashes that can be difficult to
see.
Important nuts and bolts are
sometimes in difficult-to-inspect
locations. The bolt securing the main
shaft to the main gear on my Align T-Rex
500 is held in place by a nut that is
captured in a molding. The nut is more
difficult to see than those on other
helicopters because of its placement. I
noticed that it was missing during a
preflight inspection.
Before leaving the rotor head I inspect
each main blade for damage. I recently
lost a starter coupling in a Hirobo X-spec
in flight and did not notice the damage it
caused until a few flights later.
The main blades looked normal
viewed from above, but there was
significant damage on the undersurface
Left: Loaded batteries? Use a cell
balancer to check the charge on
each cell in the pack before every
flight. Keep track of how much
power each flight consumes; a
change might indicate other
problems.
Below: Got a head case? By
pulling out as well as up and
down on the blade grips, you
can check for a loose spindle,
worn bearings, and worn head
dampeners. Allowing blades to
run out of track will quickly
make matters worse.
Hardware nuts? Some attachment nuts are secured
in moldings and can be more difficult to see than
exposed ones. The missing nut securing the drive
gears on this model is an example. Secure metal-tometal
parts with threadlock compound.
Bad wings? Carefully inspect both sides of blade
surfaces. Damage to this blade was visible only
from underneath. When the blades are off, take
the time to ensure that they’re balanced.
03sig2.QXD_00MSTRPG.QXD 1/24/11 1:26 PM Page 50
March 2011 51
near one of the blade roots that could have led to a catastrophic
and potentially dangerous blade loss. To prevent problems, now
I run my hand along the LEs of the blades and look underneath.
After inspecting the head I check the main gear for missing
teeth and belt tightness (or torque-tube gear mesh) in addition
to making sure that the bolts attaching the pipe are tight. Some
helicopter/pipe combinations are notorious for developing
looseness and need to be checked regularly. My YS 91SR
engine/Hatori pipe setup is incredibly reliable and powerful,
but it requires frequent safeguarding to prevent loosened bolts.
The next areas of examination are the servos on the left-side
frame. Make sure that all servos are secured and that screws
that hold the servo horns are in place—not missing or loose.
Working my way back to the tail, I check to make certain
that the boom supports are secure. Many carbon-fiber-frame
machines, especially nitro models, develop loose boom
supports from vibration. If not caught in time, they can become
detached and go through the rotor disk with disastrous results.
I go on to inspect the tail case, to ensure that the bolts are
tight and that the tail components and control rod are free and
secured. The Outrage 550 is a smooth-running electric
machine, but lack of threadlocker leads to bolts loosening from
vibrations that are carried down the boom to the tail
components.
To complete the examination, I make sure that the tail servo
is tight in its mount and that the tail control rod is secure and
running straight through the guides. I check the right-side
frame components in the same fashion as I do the left side.
Issues to check on the frames are fuel leaks, evidenced
under the storage area, and silicone tubing that is past its prime,
such as the pressure nipple on the pipe.
Servos with metal gears can become sloppy over time.
Excessive lash can be noticed only if a pilot regularly inspects
them to understand how a normal amount of play feels.
Gyro tape can age and lose its grip without warning.
Replace the insulating foam tape once a year, and wrap the
gyro with a Velcro strap for safety.
The power switch is a known high-failure point. If it’s not
soft-mounted, expect to replace this component every season.
Many of the problems I have encountered during preflight
inspections are those I have noticed before a helicopter’s first
flight following a repair caused by a crash, which can be a
particularly vulnerable time.
Sometimes during a repair it is unclear which components
are damaged and which are still usable. As a result, it is
necessary to temporarily assemble the components with the
intention of going back and formally completing the fix. But
this process often leads to errors.
Now I know that if I am going to put a part in a helicopter
with the intention of going back and securing it with
threadlocker, I need to write it down! A particularly careful
inspection through a checklist needs to be accomplished before
the initial flight following a crash repair.
Left: Sound problems? The header bolts on this Hatori
muffler mounted to a YS 91 engine tend to loosen and
occasionally come out. Frequent checking will prevent
the O-rings and dampeners from premature wear.
Below: Forgetting things? Following swashplate
setup and adjustment, it is important to
remember to replace the screw holding the servo
wheel onto the output shaft. A bit of silicone on
the screw will prevent it from loosening.
Got evidence? Vibration carried down this
tailboom led to these tail gearbox bolts loosening.
It’s a good assumption that other parts are loose
too; vibration issues must be resolved.
03sig2.QXD_00MSTRPG.QXD 1/24/11 1:27 PM Page 51
Preflighting the Radio: Before each
model flight, the radio should also
undergo an inspection; it takes only a few
moments longer.
Does the transmitter battery have
adequate charge? Has the correct aircraft
been selected for the machine that is
about to fly? Some radios, such as my
Spektrum DX7 and JR X9303, have
“model match,” but the Futaba 10C I use
with a Spektrum module does not have
this feature. That opens up the possibility
of selecting the wrong model.
After turning on the system, the main
and satellite receiver lights for the JR and
Spektrum systems should be lit and
solid—not blinking. If they are, I shut
down the helicopter and restart both the
transmitter and receiver to ensure that the
proper binding has occurred.
Then I question whether or not the
receiver battery or flight pack is fully
charged. The Li-Poly batteries we use are
light and powerful, but they do not
tolerate overdischarge. Even one instance
can significantly shorten their lives or
make them unusable.
The Common Sense RC balancer has
become one of the most-used items in my
flight bag. It allows for quick voltage
checks of each cell in the pack as it cycles
through them, ensuring that each cell has
adequate charge and that no bad cells
exist.
I also like to be sure that the gyro has
booted up correctly. The Spartan gyro on
my Outrage has a solid-blue light in
heading hold that is off in normal mode.
Blinking is a sign that the gyro did not
start correctly and should be shut down
and restarted. Gyros vary in this regard,
so you need to be sure of how the brand
you fly operates.
In nitro-powered helicopters, hot starts
are to be avoided at all costs. They can be
dangerous and usually end up requiring
clutch or clutch-liner replacement.
To avoid a hot start, make sure that the
throttle is working correctly, that it is not
reversed, and that the idle-up switch has
not been inadvertently moved from
normal to an idle-up position.
When you are at the flightline, check
the cyclic and rudder controls prior to
spool-up. Are the controls working
correctly and not reversed?
As you spool up the model, be on the
lookout for abnormal motions. If any
exist, it is best to bring the radio and
model back to the workstand for closer
inspection. A servo that is going bad
will sometimes reveal itself under load.
Finally, is the helicopter a safe
distance from you and well away from
spectators? How about other traffic? In
my club we are able to mix helicopter
and fixed-wing flying by being
courteous and aware of how the two
aircraft types use the runway and
pattern.
Incorporating a proper preflight
inspection—that takes less than 5
minutes—into your helicopter-flying
routine can prevent costly crashes.
Have fun and fly safely. MA
Anthony N. Avallone
[email protected]
Sources:
International Radio Controlled Helicopter
Association
www.ircha.org
52 MODEL AVIATION
Machine:
• Rotor head and vicinity
• Main shaft bolts present and secure
• Control arms and linkages smooth and secure
• Lever and arm movement smooth and slop free
• Blade grips secure with normal in/out as well as vertical spindle play
• Blades are secure, evenly tensioned, and damage free
Left-side main frame and vicinity:
• Drive gears are clean and secure with a full teeth count
• Belt is wear free and at the correct tension
• Muffler is secure and leak free
• Engine is secure and leak free
• Servos, horns, and control rods are tight and free to operate
• All screws are in place
• Fuel tank is full and leak free
Tailboom and tail:
• Boom is tight and damage free
• Boom supports are tight and square
• Tail components and fin orientation are correct
• Control mechanism is secure with slop-free movement
• Tail blades are damage free and evenly tensioned
• Tail blade grip spindle operation is smooth and slop free
• Rudder servo and control system linkages are secure
Right-side main-frame components:
• Servos, horns, and linkages are secure and slop free
• All screws are in place and linkages are secure
• Gyro is secure
• Governor and sensor are secure
• Wires are bound with no evidence of chafing
• Power switch is clean with no evidence of wear
• Battery is secure and fully charged
• Canopy is secure
Radio:
• Has adequate power
• Model memory is set and confirmed
• Switches are in correct position, with throttle at low
• Receiver is bound correctly
• Gyro boot-up confirmation
• Timer is reset
Helicopter Preflight
Checklist
03sig2.QXD_00MSTRPG.QXD 1/25/11 10:41 AM Page 52
Edition: Model Aviation - 2011/03
Page Numbers: 49,50,51,52
Edition: Model Aviation - 2011/03
Page Numbers: 49,50,51,52
Champions never compromise safety for an opportunity to be respected. Preflight checks and good maintenance practices will win
fans over every time. Ben Lanterman photo.
March 2011 49
A guide to preflight inspection of model helicopters
by Anthony N. Avallone
Ready
Liftoff
for
TODAY’S MODEL HELICOPTERS
are sophisticated machines that combine
complicated mechanical and electronic
systems, allowing pilots of all abilities to
enjoy this unique form of flight. These
models are incredibly reliable when you
consider the factors to which they are
exposed, including high-G loads from 3-D
maneuvers, rotor-head speeds exceeding
2,000 rpm, and, in the case of nitropowered
versions, significant vibration.
Because of their complex designs, as
well as the rigors we put them through,
mechanical failures do happen. In the
realm of model helicopters, even a small
defect such as a loose or missing bolt or
nut can lead to a crash. Many defects can
be found and corrected if they are caught
in time through a preflight inspection,
thereby preventing a costly rebuild.
A preflight inspection is normal in fullscale
aviation. No conscientious pilot
would take off in an aircraft that has not
been examined. The risks to well-being
posed by flying model helicopters are not
as high as they are in full-scale aviation,
but they are real. A machine that is out of
control because of a mechanical flaw can
be a danger to the pilot and spectators,
especially during the takeoff phase when
the machine is relatively close.
This article will outline a simple,
systematic approach to inspecting model
helicopters before flying. By detailing reallife
examples with accompanying photos of
problems found while examining my
aircraft, you will learn how many issues that
can lead to crashes can be avoided.
Unfortunately I have learned many of
the lessons I will present from accidents
resulting from inadequate before-flight
inspections.
Preflighting the Helicopter: My
examination begins at the rotor head and
03sig2.QXD_00MSTRPG.QXD 1/24/11 1:25 PM Page 49
50 MODEL AVIATION
Photos by the author except as noted
progresses down the left side of the
frames, back along the boom to the tail,
and finishes with the right side of the
model.
Although the order of inspection does
not matter too much, it is important to
complete the assessment in a systematic
fashion; that is made easier through a
checklist. I have included a sample to get
you started.
At the rotor head I check attachment
bolts to the main shaft, as well as the
various arms and linkages. I pay
particular attention to the blade grips; I
have encountered loose spindles, and they
are rarely obvious. Pulling out on the
blade grips to check for play and pushing
down on one blade grip while pulling up
on the other will unmask a loose spindle
bolt or worn head dampener.
Links can wear out, so check them
regularly for excessive play.
Additionally, ball links can develop splits
following crashes that can be difficult to
see.
Important nuts and bolts are
sometimes in difficult-to-inspect
locations. The bolt securing the main
shaft to the main gear on my Align T-Rex
500 is held in place by a nut that is
captured in a molding. The nut is more
difficult to see than those on other
helicopters because of its placement. I
noticed that it was missing during a
preflight inspection.
Before leaving the rotor head I inspect
each main blade for damage. I recently
lost a starter coupling in a Hirobo X-spec
in flight and did not notice the damage it
caused until a few flights later.
The main blades looked normal
viewed from above, but there was
significant damage on the undersurface
Left: Loaded batteries? Use a cell
balancer to check the charge on
each cell in the pack before every
flight. Keep track of how much
power each flight consumes; a
change might indicate other
problems.
Below: Got a head case? By
pulling out as well as up and
down on the blade grips, you
can check for a loose spindle,
worn bearings, and worn head
dampeners. Allowing blades to
run out of track will quickly
make matters worse.
Hardware nuts? Some attachment nuts are secured
in moldings and can be more difficult to see than
exposed ones. The missing nut securing the drive
gears on this model is an example. Secure metal-tometal
parts with threadlock compound.
Bad wings? Carefully inspect both sides of blade
surfaces. Damage to this blade was visible only
from underneath. When the blades are off, take
the time to ensure that they’re balanced.
03sig2.QXD_00MSTRPG.QXD 1/24/11 1:26 PM Page 50
March 2011 51
near one of the blade roots that could have led to a catastrophic
and potentially dangerous blade loss. To prevent problems, now
I run my hand along the LEs of the blades and look underneath.
After inspecting the head I check the main gear for missing
teeth and belt tightness (or torque-tube gear mesh) in addition
to making sure that the bolts attaching the pipe are tight. Some
helicopter/pipe combinations are notorious for developing
looseness and need to be checked regularly. My YS 91SR
engine/Hatori pipe setup is incredibly reliable and powerful,
but it requires frequent safeguarding to prevent loosened bolts.
The next areas of examination are the servos on the left-side
frame. Make sure that all servos are secured and that screws
that hold the servo horns are in place—not missing or loose.
Working my way back to the tail, I check to make certain
that the boom supports are secure. Many carbon-fiber-frame
machines, especially nitro models, develop loose boom
supports from vibration. If not caught in time, they can become
detached and go through the rotor disk with disastrous results.
I go on to inspect the tail case, to ensure that the bolts are
tight and that the tail components and control rod are free and
secured. The Outrage 550 is a smooth-running electric
machine, but lack of threadlocker leads to bolts loosening from
vibrations that are carried down the boom to the tail
components.
To complete the examination, I make sure that the tail servo
is tight in its mount and that the tail control rod is secure and
running straight through the guides. I check the right-side
frame components in the same fashion as I do the left side.
Issues to check on the frames are fuel leaks, evidenced
under the storage area, and silicone tubing that is past its prime,
such as the pressure nipple on the pipe.
Servos with metal gears can become sloppy over time.
Excessive lash can be noticed only if a pilot regularly inspects
them to understand how a normal amount of play feels.
Gyro tape can age and lose its grip without warning.
Replace the insulating foam tape once a year, and wrap the
gyro with a Velcro strap for safety.
The power switch is a known high-failure point. If it’s not
soft-mounted, expect to replace this component every season.
Many of the problems I have encountered during preflight
inspections are those I have noticed before a helicopter’s first
flight following a repair caused by a crash, which can be a
particularly vulnerable time.
Sometimes during a repair it is unclear which components
are damaged and which are still usable. As a result, it is
necessary to temporarily assemble the components with the
intention of going back and formally completing the fix. But
this process often leads to errors.
Now I know that if I am going to put a part in a helicopter
with the intention of going back and securing it with
threadlocker, I need to write it down! A particularly careful
inspection through a checklist needs to be accomplished before
the initial flight following a crash repair.
Left: Sound problems? The header bolts on this Hatori
muffler mounted to a YS 91 engine tend to loosen and
occasionally come out. Frequent checking will prevent
the O-rings and dampeners from premature wear.
Below: Forgetting things? Following swashplate
setup and adjustment, it is important to
remember to replace the screw holding the servo
wheel onto the output shaft. A bit of silicone on
the screw will prevent it from loosening.
Got evidence? Vibration carried down this
tailboom led to these tail gearbox bolts loosening.
It’s a good assumption that other parts are loose
too; vibration issues must be resolved.
03sig2.QXD_00MSTRPG.QXD 1/24/11 1:27 PM Page 51
Preflighting the Radio: Before each
model flight, the radio should also
undergo an inspection; it takes only a few
moments longer.
Does the transmitter battery have
adequate charge? Has the correct aircraft
been selected for the machine that is
about to fly? Some radios, such as my
Spektrum DX7 and JR X9303, have
“model match,” but the Futaba 10C I use
with a Spektrum module does not have
this feature. That opens up the possibility
of selecting the wrong model.
After turning on the system, the main
and satellite receiver lights for the JR and
Spektrum systems should be lit and
solid—not blinking. If they are, I shut
down the helicopter and restart both the
transmitter and receiver to ensure that the
proper binding has occurred.
Then I question whether or not the
receiver battery or flight pack is fully
charged. The Li-Poly batteries we use are
light and powerful, but they do not
tolerate overdischarge. Even one instance
can significantly shorten their lives or
make them unusable.
The Common Sense RC balancer has
become one of the most-used items in my
flight bag. It allows for quick voltage
checks of each cell in the pack as it cycles
through them, ensuring that each cell has
adequate charge and that no bad cells
exist.
I also like to be sure that the gyro has
booted up correctly. The Spartan gyro on
my Outrage has a solid-blue light in
heading hold that is off in normal mode.
Blinking is a sign that the gyro did not
start correctly and should be shut down
and restarted. Gyros vary in this regard,
so you need to be sure of how the brand
you fly operates.
In nitro-powered helicopters, hot starts
are to be avoided at all costs. They can be
dangerous and usually end up requiring
clutch or clutch-liner replacement.
To avoid a hot start, make sure that the
throttle is working correctly, that it is not
reversed, and that the idle-up switch has
not been inadvertently moved from
normal to an idle-up position.
When you are at the flightline, check
the cyclic and rudder controls prior to
spool-up. Are the controls working
correctly and not reversed?
As you spool up the model, be on the
lookout for abnormal motions. If any
exist, it is best to bring the radio and
model back to the workstand for closer
inspection. A servo that is going bad
will sometimes reveal itself under load.
Finally, is the helicopter a safe
distance from you and well away from
spectators? How about other traffic? In
my club we are able to mix helicopter
and fixed-wing flying by being
courteous and aware of how the two
aircraft types use the runway and
pattern.
Incorporating a proper preflight
inspection—that takes less than 5
minutes—into your helicopter-flying
routine can prevent costly crashes.
Have fun and fly safely. MA
Anthony N. Avallone
[email protected]
Sources:
International Radio Controlled Helicopter
Association
www.ircha.org
52 MODEL AVIATION
Machine:
• Rotor head and vicinity
• Main shaft bolts present and secure
• Control arms and linkages smooth and secure
• Lever and arm movement smooth and slop free
• Blade grips secure with normal in/out as well as vertical spindle play
• Blades are secure, evenly tensioned, and damage free
Left-side main frame and vicinity:
• Drive gears are clean and secure with a full teeth count
• Belt is wear free and at the correct tension
• Muffler is secure and leak free
• Engine is secure and leak free
• Servos, horns, and control rods are tight and free to operate
• All screws are in place
• Fuel tank is full and leak free
Tailboom and tail:
• Boom is tight and damage free
• Boom supports are tight and square
• Tail components and fin orientation are correct
• Control mechanism is secure with slop-free movement
• Tail blades are damage free and evenly tensioned
• Tail blade grip spindle operation is smooth and slop free
• Rudder servo and control system linkages are secure
Right-side main-frame components:
• Servos, horns, and linkages are secure and slop free
• All screws are in place and linkages are secure
• Gyro is secure
• Governor and sensor are secure
• Wires are bound with no evidence of chafing
• Power switch is clean with no evidence of wear
• Battery is secure and fully charged
• Canopy is secure
Radio:
• Has adequate power
• Model memory is set and confirmed
• Switches are in correct position, with throttle at low
• Receiver is bound correctly
• Gyro boot-up confirmation
• Timer is reset
Helicopter Preflight
Checklist
03sig2.QXD_00MSTRPG.QXD 1/25/11 10:41 AM Page 52
Edition: Model Aviation - 2011/03
Page Numbers: 49,50,51,52
Champions never compromise safety for an opportunity to be respected. Preflight checks and good maintenance practices will win
fans over every time. Ben Lanterman photo.
March 2011 49
A guide to preflight inspection of model helicopters
by Anthony N. Avallone
Ready
Liftoff
for
TODAY’S MODEL HELICOPTERS
are sophisticated machines that combine
complicated mechanical and electronic
systems, allowing pilots of all abilities to
enjoy this unique form of flight. These
models are incredibly reliable when you
consider the factors to which they are
exposed, including high-G loads from 3-D
maneuvers, rotor-head speeds exceeding
2,000 rpm, and, in the case of nitropowered
versions, significant vibration.
Because of their complex designs, as
well as the rigors we put them through,
mechanical failures do happen. In the
realm of model helicopters, even a small
defect such as a loose or missing bolt or
nut can lead to a crash. Many defects can
be found and corrected if they are caught
in time through a preflight inspection,
thereby preventing a costly rebuild.
A preflight inspection is normal in fullscale
aviation. No conscientious pilot
would take off in an aircraft that has not
been examined. The risks to well-being
posed by flying model helicopters are not
as high as they are in full-scale aviation,
but they are real. A machine that is out of
control because of a mechanical flaw can
be a danger to the pilot and spectators,
especially during the takeoff phase when
the machine is relatively close.
This article will outline a simple,
systematic approach to inspecting model
helicopters before flying. By detailing reallife
examples with accompanying photos of
problems found while examining my
aircraft, you will learn how many issues that
can lead to crashes can be avoided.
Unfortunately I have learned many of
the lessons I will present from accidents
resulting from inadequate before-flight
inspections.
Preflighting the Helicopter: My
examination begins at the rotor head and
03sig2.QXD_00MSTRPG.QXD 1/24/11 1:25 PM Page 49
50 MODEL AVIATION
Photos by the author except as noted
progresses down the left side of the
frames, back along the boom to the tail,
and finishes with the right side of the
model.
Although the order of inspection does
not matter too much, it is important to
complete the assessment in a systematic
fashion; that is made easier through a
checklist. I have included a sample to get
you started.
At the rotor head I check attachment
bolts to the main shaft, as well as the
various arms and linkages. I pay
particular attention to the blade grips; I
have encountered loose spindles, and they
are rarely obvious. Pulling out on the
blade grips to check for play and pushing
down on one blade grip while pulling up
on the other will unmask a loose spindle
bolt or worn head dampener.
Links can wear out, so check them
regularly for excessive play.
Additionally, ball links can develop splits
following crashes that can be difficult to
see.
Important nuts and bolts are
sometimes in difficult-to-inspect
locations. The bolt securing the main
shaft to the main gear on my Align T-Rex
500 is held in place by a nut that is
captured in a molding. The nut is more
difficult to see than those on other
helicopters because of its placement. I
noticed that it was missing during a
preflight inspection.
Before leaving the rotor head I inspect
each main blade for damage. I recently
lost a starter coupling in a Hirobo X-spec
in flight and did not notice the damage it
caused until a few flights later.
The main blades looked normal
viewed from above, but there was
significant damage on the undersurface
Left: Loaded batteries? Use a cell
balancer to check the charge on
each cell in the pack before every
flight. Keep track of how much
power each flight consumes; a
change might indicate other
problems.
Below: Got a head case? By
pulling out as well as up and
down on the blade grips, you
can check for a loose spindle,
worn bearings, and worn head
dampeners. Allowing blades to
run out of track will quickly
make matters worse.
Hardware nuts? Some attachment nuts are secured
in moldings and can be more difficult to see than
exposed ones. The missing nut securing the drive
gears on this model is an example. Secure metal-tometal
parts with threadlock compound.
Bad wings? Carefully inspect both sides of blade
surfaces. Damage to this blade was visible only
from underneath. When the blades are off, take
the time to ensure that they’re balanced.
03sig2.QXD_00MSTRPG.QXD 1/24/11 1:26 PM Page 50
March 2011 51
near one of the blade roots that could have led to a catastrophic
and potentially dangerous blade loss. To prevent problems, now
I run my hand along the LEs of the blades and look underneath.
After inspecting the head I check the main gear for missing
teeth and belt tightness (or torque-tube gear mesh) in addition
to making sure that the bolts attaching the pipe are tight. Some
helicopter/pipe combinations are notorious for developing
looseness and need to be checked regularly. My YS 91SR
engine/Hatori pipe setup is incredibly reliable and powerful,
but it requires frequent safeguarding to prevent loosened bolts.
The next areas of examination are the servos on the left-side
frame. Make sure that all servos are secured and that screws
that hold the servo horns are in place—not missing or loose.
Working my way back to the tail, I check to make certain
that the boom supports are secure. Many carbon-fiber-frame
machines, especially nitro models, develop loose boom
supports from vibration. If not caught in time, they can become
detached and go through the rotor disk with disastrous results.
I go on to inspect the tail case, to ensure that the bolts are
tight and that the tail components and control rod are free and
secured. The Outrage 550 is a smooth-running electric
machine, but lack of threadlocker leads to bolts loosening from
vibrations that are carried down the boom to the tail
components.
To complete the examination, I make sure that the tail servo
is tight in its mount and that the tail control rod is secure and
running straight through the guides. I check the right-side
frame components in the same fashion as I do the left side.
Issues to check on the frames are fuel leaks, evidenced
under the storage area, and silicone tubing that is past its prime,
such as the pressure nipple on the pipe.
Servos with metal gears can become sloppy over time.
Excessive lash can be noticed only if a pilot regularly inspects
them to understand how a normal amount of play feels.
Gyro tape can age and lose its grip without warning.
Replace the insulating foam tape once a year, and wrap the
gyro with a Velcro strap for safety.
The power switch is a known high-failure point. If it’s not
soft-mounted, expect to replace this component every season.
Many of the problems I have encountered during preflight
inspections are those I have noticed before a helicopter’s first
flight following a repair caused by a crash, which can be a
particularly vulnerable time.
Sometimes during a repair it is unclear which components
are damaged and which are still usable. As a result, it is
necessary to temporarily assemble the components with the
intention of going back and formally completing the fix. But
this process often leads to errors.
Now I know that if I am going to put a part in a helicopter
with the intention of going back and securing it with
threadlocker, I need to write it down! A particularly careful
inspection through a checklist needs to be accomplished before
the initial flight following a crash repair.
Left: Sound problems? The header bolts on this Hatori
muffler mounted to a YS 91 engine tend to loosen and
occasionally come out. Frequent checking will prevent
the O-rings and dampeners from premature wear.
Below: Forgetting things? Following swashplate
setup and adjustment, it is important to
remember to replace the screw holding the servo
wheel onto the output shaft. A bit of silicone on
the screw will prevent it from loosening.
Got evidence? Vibration carried down this
tailboom led to these tail gearbox bolts loosening.
It’s a good assumption that other parts are loose
too; vibration issues must be resolved.
03sig2.QXD_00MSTRPG.QXD 1/24/11 1:27 PM Page 51
Preflighting the Radio: Before each
model flight, the radio should also
undergo an inspection; it takes only a few
moments longer.
Does the transmitter battery have
adequate charge? Has the correct aircraft
been selected for the machine that is
about to fly? Some radios, such as my
Spektrum DX7 and JR X9303, have
“model match,” but the Futaba 10C I use
with a Spektrum module does not have
this feature. That opens up the possibility
of selecting the wrong model.
After turning on the system, the main
and satellite receiver lights for the JR and
Spektrum systems should be lit and
solid—not blinking. If they are, I shut
down the helicopter and restart both the
transmitter and receiver to ensure that the
proper binding has occurred.
Then I question whether or not the
receiver battery or flight pack is fully
charged. The Li-Poly batteries we use are
light and powerful, but they do not
tolerate overdischarge. Even one instance
can significantly shorten their lives or
make them unusable.
The Common Sense RC balancer has
become one of the most-used items in my
flight bag. It allows for quick voltage
checks of each cell in the pack as it cycles
through them, ensuring that each cell has
adequate charge and that no bad cells
exist.
I also like to be sure that the gyro has
booted up correctly. The Spartan gyro on
my Outrage has a solid-blue light in
heading hold that is off in normal mode.
Blinking is a sign that the gyro did not
start correctly and should be shut down
and restarted. Gyros vary in this regard,
so you need to be sure of how the brand
you fly operates.
In nitro-powered helicopters, hot starts
are to be avoided at all costs. They can be
dangerous and usually end up requiring
clutch or clutch-liner replacement.
To avoid a hot start, make sure that the
throttle is working correctly, that it is not
reversed, and that the idle-up switch has
not been inadvertently moved from
normal to an idle-up position.
When you are at the flightline, check
the cyclic and rudder controls prior to
spool-up. Are the controls working
correctly and not reversed?
As you spool up the model, be on the
lookout for abnormal motions. If any
exist, it is best to bring the radio and
model back to the workstand for closer
inspection. A servo that is going bad
will sometimes reveal itself under load.
Finally, is the helicopter a safe
distance from you and well away from
spectators? How about other traffic? In
my club we are able to mix helicopter
and fixed-wing flying by being
courteous and aware of how the two
aircraft types use the runway and
pattern.
Incorporating a proper preflight
inspection—that takes less than 5
minutes—into your helicopter-flying
routine can prevent costly crashes.
Have fun and fly safely. MA
Anthony N. Avallone
[email protected]
Sources:
International Radio Controlled Helicopter
Association
www.ircha.org
52 MODEL AVIATION
Machine:
• Rotor head and vicinity
• Main shaft bolts present and secure
• Control arms and linkages smooth and secure
• Lever and arm movement smooth and slop free
• Blade grips secure with normal in/out as well as vertical spindle play
• Blades are secure, evenly tensioned, and damage free
Left-side main frame and vicinity:
• Drive gears are clean and secure with a full teeth count
• Belt is wear free and at the correct tension
• Muffler is secure and leak free
• Engine is secure and leak free
• Servos, horns, and control rods are tight and free to operate
• All screws are in place
• Fuel tank is full and leak free
Tailboom and tail:
• Boom is tight and damage free
• Boom supports are tight and square
• Tail components and fin orientation are correct
• Control mechanism is secure with slop-free movement
• Tail blades are damage free and evenly tensioned
• Tail blade grip spindle operation is smooth and slop free
• Rudder servo and control system linkages are secure
Right-side main-frame components:
• Servos, horns, and linkages are secure and slop free
• All screws are in place and linkages are secure
• Gyro is secure
• Governor and sensor are secure
• Wires are bound with no evidence of chafing
• Power switch is clean with no evidence of wear
• Battery is secure and fully charged
• Canopy is secure
Radio:
• Has adequate power
• Model memory is set and confirmed
• Switches are in correct position, with throttle at low
• Receiver is bound correctly
• Gyro boot-up confirmation
• Timer is reset
Helicopter Preflight
Checklist
03sig2.QXD_00MSTRPG.QXD 1/25/11 10:41 AM Page 52
Edition: Model Aviation - 2011/03
Page Numbers: 49,50,51,52
Champions never compromise safety for an opportunity to be respected. Preflight checks and good maintenance practices will win
fans over every time. Ben Lanterman photo.
March 2011 49
A guide to preflight inspection of model helicopters
by Anthony N. Avallone
Ready
Liftoff
for
TODAY’S MODEL HELICOPTERS
are sophisticated machines that combine
complicated mechanical and electronic
systems, allowing pilots of all abilities to
enjoy this unique form of flight. These
models are incredibly reliable when you
consider the factors to which they are
exposed, including high-G loads from 3-D
maneuvers, rotor-head speeds exceeding
2,000 rpm, and, in the case of nitropowered
versions, significant vibration.
Because of their complex designs, as
well as the rigors we put them through,
mechanical failures do happen. In the
realm of model helicopters, even a small
defect such as a loose or missing bolt or
nut can lead to a crash. Many defects can
be found and corrected if they are caught
in time through a preflight inspection,
thereby preventing a costly rebuild.
A preflight inspection is normal in fullscale
aviation. No conscientious pilot
would take off in an aircraft that has not
been examined. The risks to well-being
posed by flying model helicopters are not
as high as they are in full-scale aviation,
but they are real. A machine that is out of
control because of a mechanical flaw can
be a danger to the pilot and spectators,
especially during the takeoff phase when
the machine is relatively close.
This article will outline a simple,
systematic approach to inspecting model
helicopters before flying. By detailing reallife
examples with accompanying photos of
problems found while examining my
aircraft, you will learn how many issues that
can lead to crashes can be avoided.
Unfortunately I have learned many of
the lessons I will present from accidents
resulting from inadequate before-flight
inspections.
Preflighting the Helicopter: My
examination begins at the rotor head and
03sig2.QXD_00MSTRPG.QXD 1/24/11 1:25 PM Page 49
50 MODEL AVIATION
Photos by the author except as noted
progresses down the left side of the
frames, back along the boom to the tail,
and finishes with the right side of the
model.
Although the order of inspection does
not matter too much, it is important to
complete the assessment in a systematic
fashion; that is made easier through a
checklist. I have included a sample to get
you started.
At the rotor head I check attachment
bolts to the main shaft, as well as the
various arms and linkages. I pay
particular attention to the blade grips; I
have encountered loose spindles, and they
are rarely obvious. Pulling out on the
blade grips to check for play and pushing
down on one blade grip while pulling up
on the other will unmask a loose spindle
bolt or worn head dampener.
Links can wear out, so check them
regularly for excessive play.
Additionally, ball links can develop splits
following crashes that can be difficult to
see.
Important nuts and bolts are
sometimes in difficult-to-inspect
locations. The bolt securing the main
shaft to the main gear on my Align T-Rex
500 is held in place by a nut that is
captured in a molding. The nut is more
difficult to see than those on other
helicopters because of its placement. I
noticed that it was missing during a
preflight inspection.
Before leaving the rotor head I inspect
each main blade for damage. I recently
lost a starter coupling in a Hirobo X-spec
in flight and did not notice the damage it
caused until a few flights later.
The main blades looked normal
viewed from above, but there was
significant damage on the undersurface
Left: Loaded batteries? Use a cell
balancer to check the charge on
each cell in the pack before every
flight. Keep track of how much
power each flight consumes; a
change might indicate other
problems.
Below: Got a head case? By
pulling out as well as up and
down on the blade grips, you
can check for a loose spindle,
worn bearings, and worn head
dampeners. Allowing blades to
run out of track will quickly
make matters worse.
Hardware nuts? Some attachment nuts are secured
in moldings and can be more difficult to see than
exposed ones. The missing nut securing the drive
gears on this model is an example. Secure metal-tometal
parts with threadlock compound.
Bad wings? Carefully inspect both sides of blade
surfaces. Damage to this blade was visible only
from underneath. When the blades are off, take
the time to ensure that they’re balanced.
03sig2.QXD_00MSTRPG.QXD 1/24/11 1:26 PM Page 50
March 2011 51
near one of the blade roots that could have led to a catastrophic
and potentially dangerous blade loss. To prevent problems, now
I run my hand along the LEs of the blades and look underneath.
After inspecting the head I check the main gear for missing
teeth and belt tightness (or torque-tube gear mesh) in addition
to making sure that the bolts attaching the pipe are tight. Some
helicopter/pipe combinations are notorious for developing
looseness and need to be checked regularly. My YS 91SR
engine/Hatori pipe setup is incredibly reliable and powerful,
but it requires frequent safeguarding to prevent loosened bolts.
The next areas of examination are the servos on the left-side
frame. Make sure that all servos are secured and that screws
that hold the servo horns are in place—not missing or loose.
Working my way back to the tail, I check to make certain
that the boom supports are secure. Many carbon-fiber-frame
machines, especially nitro models, develop loose boom
supports from vibration. If not caught in time, they can become
detached and go through the rotor disk with disastrous results.
I go on to inspect the tail case, to ensure that the bolts are
tight and that the tail components and control rod are free and
secured. The Outrage 550 is a smooth-running electric
machine, but lack of threadlocker leads to bolts loosening from
vibrations that are carried down the boom to the tail
components.
To complete the examination, I make sure that the tail servo
is tight in its mount and that the tail control rod is secure and
running straight through the guides. I check the right-side
frame components in the same fashion as I do the left side.
Issues to check on the frames are fuel leaks, evidenced
under the storage area, and silicone tubing that is past its prime,
such as the pressure nipple on the pipe.
Servos with metal gears can become sloppy over time.
Excessive lash can be noticed only if a pilot regularly inspects
them to understand how a normal amount of play feels.
Gyro tape can age and lose its grip without warning.
Replace the insulating foam tape once a year, and wrap the
gyro with a Velcro strap for safety.
The power switch is a known high-failure point. If it’s not
soft-mounted, expect to replace this component every season.
Many of the problems I have encountered during preflight
inspections are those I have noticed before a helicopter’s first
flight following a repair caused by a crash, which can be a
particularly vulnerable time.
Sometimes during a repair it is unclear which components
are damaged and which are still usable. As a result, it is
necessary to temporarily assemble the components with the
intention of going back and formally completing the fix. But
this process often leads to errors.
Now I know that if I am going to put a part in a helicopter
with the intention of going back and securing it with
threadlocker, I need to write it down! A particularly careful
inspection through a checklist needs to be accomplished before
the initial flight following a crash repair.
Left: Sound problems? The header bolts on this Hatori
muffler mounted to a YS 91 engine tend to loosen and
occasionally come out. Frequent checking will prevent
the O-rings and dampeners from premature wear.
Below: Forgetting things? Following swashplate
setup and adjustment, it is important to
remember to replace the screw holding the servo
wheel onto the output shaft. A bit of silicone on
the screw will prevent it from loosening.
Got evidence? Vibration carried down this
tailboom led to these tail gearbox bolts loosening.
It’s a good assumption that other parts are loose
too; vibration issues must be resolved.
03sig2.QXD_00MSTRPG.QXD 1/24/11 1:27 PM Page 51
Preflighting the Radio: Before each
model flight, the radio should also
undergo an inspection; it takes only a few
moments longer.
Does the transmitter battery have
adequate charge? Has the correct aircraft
been selected for the machine that is
about to fly? Some radios, such as my
Spektrum DX7 and JR X9303, have
“model match,” but the Futaba 10C I use
with a Spektrum module does not have
this feature. That opens up the possibility
of selecting the wrong model.
After turning on the system, the main
and satellite receiver lights for the JR and
Spektrum systems should be lit and
solid—not blinking. If they are, I shut
down the helicopter and restart both the
transmitter and receiver to ensure that the
proper binding has occurred.
Then I question whether or not the
receiver battery or flight pack is fully
charged. The Li-Poly batteries we use are
light and powerful, but they do not
tolerate overdischarge. Even one instance
can significantly shorten their lives or
make them unusable.
The Common Sense RC balancer has
become one of the most-used items in my
flight bag. It allows for quick voltage
checks of each cell in the pack as it cycles
through them, ensuring that each cell has
adequate charge and that no bad cells
exist.
I also like to be sure that the gyro has
booted up correctly. The Spartan gyro on
my Outrage has a solid-blue light in
heading hold that is off in normal mode.
Blinking is a sign that the gyro did not
start correctly and should be shut down
and restarted. Gyros vary in this regard,
so you need to be sure of how the brand
you fly operates.
In nitro-powered helicopters, hot starts
are to be avoided at all costs. They can be
dangerous and usually end up requiring
clutch or clutch-liner replacement.
To avoid a hot start, make sure that the
throttle is working correctly, that it is not
reversed, and that the idle-up switch has
not been inadvertently moved from
normal to an idle-up position.
When you are at the flightline, check
the cyclic and rudder controls prior to
spool-up. Are the controls working
correctly and not reversed?
As you spool up the model, be on the
lookout for abnormal motions. If any
exist, it is best to bring the radio and
model back to the workstand for closer
inspection. A servo that is going bad
will sometimes reveal itself under load.
Finally, is the helicopter a safe
distance from you and well away from
spectators? How about other traffic? In
my club we are able to mix helicopter
and fixed-wing flying by being
courteous and aware of how the two
aircraft types use the runway and
pattern.
Incorporating a proper preflight
inspection—that takes less than 5
minutes—into your helicopter-flying
routine can prevent costly crashes.
Have fun and fly safely. MA
Anthony N. Avallone
[email protected]
Sources:
International Radio Controlled Helicopter
Association
www.ircha.org
52 MODEL AVIATION
Machine:
• Rotor head and vicinity
• Main shaft bolts present and secure
• Control arms and linkages smooth and secure
• Lever and arm movement smooth and slop free
• Blade grips secure with normal in/out as well as vertical spindle play
• Blades are secure, evenly tensioned, and damage free
Left-side main frame and vicinity:
• Drive gears are clean and secure with a full teeth count
• Belt is wear free and at the correct tension
• Muffler is secure and leak free
• Engine is secure and leak free
• Servos, horns, and control rods are tight and free to operate
• All screws are in place
• Fuel tank is full and leak free
Tailboom and tail:
• Boom is tight and damage free
• Boom supports are tight and square
• Tail components and fin orientation are correct
• Control mechanism is secure with slop-free movement
• Tail blades are damage free and evenly tensioned
• Tail blade grip spindle operation is smooth and slop free
• Rudder servo and control system linkages are secure
Right-side main-frame components:
• Servos, horns, and linkages are secure and slop free
• All screws are in place and linkages are secure
• Gyro is secure
• Governor and sensor are secure
• Wires are bound with no evidence of chafing
• Power switch is clean with no evidence of wear
• Battery is secure and fully charged
• Canopy is secure
Radio:
• Has adequate power
• Model memory is set and confirmed
• Switches are in correct position, with throttle at low
• Receiver is bound correctly
• Gyro boot-up confirmation
• Timer is reset
Helicopter Preflight
Checklist
03sig2.QXD_00MSTRPG.QXD 1/25/11 10:41 AM Page 52
