The Rest of the Crash Story - 2010/10

October 2010 35
by Don Apostolico
THE FOLLOWING documents the last
17 of 30 main causes why models crash.
In my earlier articles, “Crashing is Not an
Option” (November 2009 MA) and
“Defensive RC Flying” (August 2010
MA), I covered some of the reasons.
This last installment will conclude the
identification of issues and make
recommendations so that you can avoid
these problem areas. The listing is in
order of occurrence, but all should be on
your preflight checklist.
14. Control Flutter: Flutter is most often
caused by improper servo choice, wrong
linkage geometry, incorrect hinging, lack
of hinge line sealing, and LEs of control
surfaces being thinner than TEs of the
stabilizer or wing. Flutter on large
airplanes (unlike on 40-size models) is
usually fatal. Proper equipment choices
and setup will prevent this issue.
Choose servos with adequate torque
for the job, avoid poor hinging systems
and alignments, seal hinge gaps, learn the
correct linkage geometry, and use the
proper mechanical advantages and radio
programming for your application. All of
these subjects are covered in detail in the
book Gas Engines and Giant Planes,
which I mentioned in the November
article.
15. Stripped Servo Gears: This is a
setup or modeler issue that is usually
caused by a servo with too small of a
torque rating for its application and/or
incorrect linkage geometry that allows
the servo to move over center, which can
lock and strip the gears.
Bumping/back-loading a control
surface while loading it into or out of the
car, etc. can cause gears to fracture from
a sharp rap. The resulting gear failure
usually causes a crash.
Learn to choose servos with adequate
torque and employ proper linkage
geometry and radio programming to
reduce the possibility of malfunction.
And be careful while carrying your
model.
16. Incorrect Linkage Geometry: This
is a common setup issue, especially on 3-
D airplanes with extreme travel, and it
causes premature servo wear and flutter.
Aeromodelers sometimes complain
about gear slop after 25-50 flights. Setup
is often the cause of this problem. To
obtain extreme travels, modelers
sometimes move the pivot point closer to
the control surface and move the pivot
out on the servo arm, while leaving radio
programming at factory-set, 100% travel
defaults.
Doing that wastes your radio
resolution, wears out the three to four
gear teeth near neutral, and is the
opposite of the correct way travels should
be set to maximize resolution, reduce
flutter, minimize gear wear, and provide
better linkage geometry. To take
The Rest of the Crash Story
More prevention points
to check on your list
Would your model survive a receiver
failure? The author’s did. After the failure
and successful landing, it is still in perfect
condition and has flown for an additional
eight years. Another airplane saved by
proper redundancy!
10sig2_00MSTRPG.QXD 8/20/10 11:05 AM Page 35
36 MODEL AVIATION
Photos by the author
Standard 40 inch-ounce-torque trainer servo gears (L) do not have
gear strength to withstand flight loads from high-performance
aircraft. High-torque servos (R) have heavy-duty gear trains, which
are better able to withstand high loads.
Above: Restrain loose wires, leads, and fuel
tubing to prevent chafing, shorts, leaks, and
other problems. Great-performing models
that are flown often need more protection
from wear.
Left: A heat-outlet area should be three to
four times the inlet area for gas and two to
three times the inlet area for glow, to keep
engine temperatures cool. Simple customfitted
plank boxes are built using the TLAR—
“That Looks About Right!”—method.
Engine cooling won’t ruin the look. Ductwork allows airflow to be
directed over the cylinders, to keep power plants from overheating.
These are identical to those used on full-scale airplanes.
advantage of your radio resolution, do the
following.
Before connecting any linkage, the travel
adjust feature (Adjustable Travel Volume, or
ATV) in your radio endpoint travels should be
set to their maximum—usually 140%-150%.
One can argue that a slightly lower
maximum ATV point, say 5 or so percentage
points below full, will allow for fine-tuning
later.
The higher ATV setting forces the pivotpoint
adjustment to go out on the control
surface and in on the servo arm. Doing so
provides a more stable leverage arm, a higher
tolerance to flutter, better resolution, and
reduced gear train wear around neutral,
because these settings force the servo to use
all of its travel rather than just the few teeth
close to neutral.
Doing the opposite (in on the control
surface and out on the servo) is conducive to
flutter, lower resolution, and gear wear, with
the servos often being blamed for having
sloppy tolerances. If you are using only a few
teeth close to neutral because of improper
setup, don’t blame the servo and don’t be
surprised if you blow through your servo
gears in as few as 25-50 flights.
Ensure that linkage geometry is correct to
avoid flutter, sloppy servo centering, and poor
resolution.
17. Inadequate Servo Torque for Intended
Application: I spoke with an aeromodeler who
was setting up a 30-pound model with trainer
servos equipped with 40 inch-ounce of output.
He was emphatic that this setup would work
because his buddy, who had been flying for
years, said that it would.
It was an accident waiting to happen. The
torque rating on “standard” servos is
inadequate, and the gear train is not robust
enough to consistently withstand flight loads
on a large airplane. If 40 inch-ounce servos
worked safely on this size of model, we would
all be flying the same equipment.
Leave your 40- to 60-size thinking behind
when setting up a big model or you might be
spending your money on lawyers rather than
airplanes. Learn how to determine what servo
torque is adequate to handle the flight loads
for your application.
18. Radio Frequency Crosstalk on 72 MHz
and 2.4 GHz Systems: This can be a setup
issue and/or a faulty component that causes
deficient range checks, or crosstalk.
Equipment separation is paramount when
setting up gas-powered aircraft with a 72
MHz system, and we have learned, through
troubleshooting, that 2.4 GHz systems are also
affected, but to a lesser degree.
Failure to maintain the recommended
distances of radio gear from ignition system is
a typical pilot setup error. Mounting electrical
components too close can spread the radio
frequency infection into other components
and, subsequently, lock out the receiver or
reduce your range.
Ensure that receivers, antennas, and other
electrical components are at least 3 inches
from any other electronic components and at
10sig2_00MSTRPG.QXD 8/20/10 11:09 AM Page 36
October 2010 37
Above: Unsecured parts cause crashes. A
thread-locking product prevents metal nuts,
bolts, and screws from coming loose. A rule
of thumb is that if two parts that thread
together are metal, thread-lock them—even
on electrics.
Above: This elevator is set to 45° of travel. Make sure your test
flights use low and high rates; that usually means approximately
10°-18° of travel for the low side.
Making use of an EZ Balancer or other CG machine prevents needless crashes caused by an
incorrect CG. Nose-heavy models don’t fly well either. Get the CG right on the first try.
Left: High-quality linkages that are set up
properly should be used to prevent
unnecessary crashes caused by linkage
failure. You’ll never be sorry about oversized
accessories working too well.
least 8-12 inches from any part of the ignition
system.
19. Improper Tank Plumbing: Highpowered
engines, gas or glow, operating on
medium-size fuel lines, small clunks, through
small brass tubing often run hot, lean out, or
seize because they can’t be richened.
Mounting the internal clunk too close to the
back of the tank (within 1/2 inch) will cause
fuel-flow issues that can make an engine run
lean, sometimes quit, and, in worse cases,
seize.
Mounting the vent line so that the top of
the tank can close off the vent will cause the
engine to run lean, run hot, or seize. Hardmounting
a tank can bring about fuel foaming
and cause the same symptoms and erratic
operation.
All connections should be secured. Inspect
your tank and replace tubing once each year.
Soft-mount tanks and ensure that vent and
pickup lines are not blocked. Secure all
connections, inside and outside, with zip-ties.
Inspect your model’s tank plumbing
regularly.
20. Inadequate Fuel Filtering: Some
aeromodelers don’t employ filters. If internalcombustion
engines ran consistently without
10sig2_00MSTRPG.QXD 8/20/10 11:12 AM Page 37
filters, they would be designed accordingly
and not use them.
Imagine operating a full-scale aircraft or
your car without filters. Does it make sense to
let contaminants plug the internal orifices of
your carburetor, causing erratic running or
engine failure? Simply performing routine
maintenance to clean or replace a filter that
will keep your carburetor clean makes
sense to me.
We use filters—both on the fuel line and
on the vent line—to keep dust, dirt, grass
seeds, dandelion fuzz, etc. from getting
inside the tank and into the tiny orifices in
the fuel system.
Soft-mount your tank and use, and
periodically clean, fuel and vent line filters.
21. Improper Inlet/Exit Area Cooling
Ratios: Glow engines typically require a
minimum 1:2 and gas engines need a
minimum 1:3 inlet/exit cowl opening ratio. If
a power plant runs hot from improper ratios,
open the bottom or rear of the cowl.
Making a bigger hole in the front
exacerbates the problem; ram air that heats up
in the cowl can’t get out as quickly as it enters.
The engine heat soars and the problem gets
worse—not better.
Inadequate ratios cause erratic running and
can cause vapor lock and seized engines.
Ensure that proper cooling ratios are used.
22. Lack of or Inadequate Baffling on Gas
Engines: Proper baffling can drop cylinder
temperatures by more than 100° and can make
the difference between burning up an engine
or having one that performs terrifically.
Properly baffled gas engines typically run at
180°-220°. (There are a few exceptions.)
Install baffles to direct airflow where it’s
needed. That will keep the power plant
running coolly and consistently.
23. Linkage Failure: Installing 2/56 hardware
October 2010 39
or plastic servo arms on high-performance
models is an accident waiting to happen.
Nylon servo arms get brittle with age and
break, as do the teeth in your comb. Metal
arms with 4-40 bolt-on ball links is the size of
choice for Giant Scale airplanes.
Carbon-fiber pushrods or titanium
turnbuckles are typically used for linkages,
along with machined metal 4-40 servo arms
tapped for 4-40 linkages.
Don’t use welding rod (Are these heattreated,
high-tensile, low-tensile, carbon-steel,
low-carbon-steel rods? Most people don’t
know.) or homemade threaded coat-hanger
wire. Don’t laugh; I’ve had more than one call
about that.
Nyrods that flex are simply unacceptable as
pushrods on Giant Scale, high-performance
aircraft and are conducive to flutter failure. If
you have “gotten away with” using them, you
are on borrowed time.
Does it make sense to build a $3,000-
$6,000 model and save a few dollars on
control linkages by using junk for a primary
control? Of course it doesn’t. Use properly setup,
high-quality linkage hardware to avoid
linkage failure.
24. Loose Hardware and Metal-to-Metal
Noise: Rattling metal parts such as loose
mufflers, engine bolts, landing gear, and tail
wheels or similar components will cause
glitching or a lockout on 72 MHz systems.
Lack of locking devices on threaded items or
not periodically checking for threaded items
that have loosened will cause the same metalto-
metal noise.
Make sure there is no metal-to-metal
rattling; thread-lock your nuts, bolts, and
screws; and periodically check them for
tightness. We use space-age thread lock, which
is used on full-scale aircraft and is approved by
the FAA for use in high-vibration areas.
25. Hooking up or Programming Control
Surfaces Backward: This is a setup/preflight
issue, and it can be avoided merely by testing
control movement and direction before starting
an engine.
Remember that when the stick is moved to
the right, the right aileron should go up as
viewed from the pilot’s seat, and vice versa.
Check controls before every flight.
26. Not Connecting Extension Cords Before
Flight: This is another preflight issue, and it
makes many expert pilots feel like toddlers. A
simple control check before startup will
identify this problem.
27. Vapor Lock: Fuel vaporizes because the
airflow through the cowl is insufficient, either
because of poor or no baffling or inadequate
baffling. In fuel lines that are too close to
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mufflers, the fuel can vaporize, causing
engine failure.
Ensure that air flows through the cowl and
over fuel lines. If you experience vapor lock,
reposition fuel lines away from mufflers or
headers. Wrap aluminum foil around fuel
lines, make sure that you use proper inlet/exit
cowl ratios, and ensure that proper baffling is
in place.
28. Improper Charge Rates for Batteries:
There are all kinds of high-end chargers on
the market for a variety of batteries. Some are
programmable and some are not.
I get regular calls from aeromodelers who
don’t know that they programmed the wrong
settings into their chargers and ruined
batteries, or their batteries caught fire because
of incorrect settings. The battery is blamed
when the cause is applying an incompatible
charge rate.
Review charging instructions and program
correct settings so you don’t create a fire
hazard or severely shorten the life of the pack,
which is the heart of your aircraft.
Another typical mistake is to undercharge
airborne batteries and not load-test batteries
before every flight. The undercharge is
caused by faulty chargers that predict a peak
cutoff too early or charger rates that are set
incorrectly.
Not all batteries are created equal, and the
user sometimes neglects to burn in or testcycle
the pack. This results in a model
running out of battery capacity sooner than
predicted or, worse, can cause a crash
because the pilot lacked a battery redundancy
system.
Don’t guess. Make sure you understand
the battery technology and charger you are
using, and charge accordingly. Test batteries
as frequently as necessary to know how much
power is consumed during a flight. A change
in test results should coincide with flight
demands or alert you that a pack is failing.
29. Incorrect CG: Tail-heavy models rarely
fly twice. Nose-heavy airplanes are more
likely to survive a test flight.
Ensure that your aircraft’s CG is properly
set before the test flight. The tank should be
empty when you do so.
You can easily check a large model’s CG
with an EZ Balancer from Southwest
Systems. Despite what some might tell you,
the airplane requires the same balance point
whether it’s powered by a motor or an
internal-combustion engine.
30. Incorrect Control Travels: Models have
crashed because of too little or too much
travel used on the test flights. Many pilots
have buried their Giant Scale airplanes on
maiden flights because of too much travel.
Thousands of dollars worth of aircraft are
needlessly destroyed because of excessive
travel programmed into them. And neither the
model nor the pilot (sometimes both) likes it
enough to handle a landing.
If you don’t know the correct travels, use
8°-10° for low rate and 15°-18° for high rate.
These are safe settings to use on test flights.
As the airplane progresses through trimming
flights, you can adjust the settings for
personal taste and optimum performance.
This travel guide makes the assumption
that an aircraft’s CG, incidence, and thrustline
locations are correct. Check travels with a
deflection meter before the first test flight.
Crashing is a choice. Those who do nothing
to address deficiencies will keep crashing
models and endangering others. I hope no one
gets hurt if the pilot makes the wrong choices.
Correcting problems makes airplanes
safer and more reliable, allowing their pilots
to fly with confidence and safely land them if
a malfunction occurs. It is the aeromodeler’s
responsibility to evaluate the information
presented, make the appropriate decisions
relative to his or her situation/setup, and
safely operate the aircraft.
Mistakes do happen, but crashes should
clearly be the exception rather than the rule. If
you effectively address the issues I have
presented, your models never have to crash.
Fly safely! MA
Don Apostolico
[email protected]
Sources:
Southwest Systems
(805) 527-6337
www.ezbalancer.com
Don’s Hobby Shop
(800) 972-6273
www.donshobbyshop.com
10sig2_00MSTRPG.QXD 8/20/10 11:22 AM Page 39

October 2010 35
by Don Apostolico
THE FOLLOWING documents the last
17 of 30 main causes why models crash.
In my earlier articles, “Crashing is Not an
Option” (November 2009 MA) and
“Defensive RC Flying” (August 2010
MA), I covered some of the reasons.
This last installment will conclude the
identification of issues and make
recommendations so that you can avoid
these problem areas. The listing is in
order of occurrence, but all should be on
your preflight checklist.
14. Control Flutter: Flutter is most often
caused by improper servo choice, wrong
linkage geometry, incorrect hinging, lack
of hinge line sealing, and LEs of control
surfaces being thinner than TEs of the
stabilizer or wing. Flutter on large
airplanes (unlike on 40-size models) is
usually fatal. Proper equipment choices
and setup will prevent this issue.
Choose servos with adequate torque
for the job, avoid poor hinging systems
and alignments, seal hinge gaps, learn the
correct linkage geometry, and use the
proper mechanical advantages and radio
programming for your application. All of
these subjects are covered in detail in the
book Gas Engines and Giant Planes,
which I mentioned in the November
article.
15. Stripped Servo Gears: This is a
setup or modeler issue that is usually
caused by a servo with too small of a
torque rating for its application and/or
incorrect linkage geometry that allows
the servo to move over center, which can
lock and strip the gears.
Bumping/back-loading a control
surface while loading it into or out of the
car, etc. can cause gears to fracture from
a sharp rap. The resulting gear failure
usually causes a crash.
Learn to choose servos with adequate
torque and employ proper linkage
geometry and radio programming to
reduce the possibility of malfunction.
And be careful while carrying your
model.
16. Incorrect Linkage Geometry: This
is a common setup issue, especially on 3-
D airplanes with extreme travel, and it
causes premature servo wear and flutter.
Aeromodelers sometimes complain
about gear slop after 25-50 flights. Setup
is often the cause of this problem. To
obtain extreme travels, modelers
sometimes move the pivot point closer to
the control surface and move the pivot
out on the servo arm, while leaving radio
programming at factory-set, 100% travel
defaults.
Doing that wastes your radio
resolution, wears out the three to four
gear teeth near neutral, and is the
opposite of the correct way travels should
be set to maximize resolution, reduce
flutter, minimize gear wear, and provide
better linkage geometry. To take
The Rest of the Crash Story
More prevention points
to check on your list
Would your model survive a receiver
failure? The author’s did. After the failure
and successful landing, it is still in perfect
condition and has flown for an additional
eight years. Another airplane saved by
proper redundancy!
10sig2_00MSTRPG.QXD 8/20/10 11:05 AM Page 35
36 MODEL AVIATION
Photos by the author
Standard 40 inch-ounce-torque trainer servo gears (L) do not have
gear strength to withstand flight loads from high-performance
aircraft. High-torque servos (R) have heavy-duty gear trains, which
are better able to withstand high loads.
Above: Restrain loose wires, leads, and fuel
tubing to prevent chafing, shorts, leaks, and
other problems. Great-performing models
that are flown often need more protection
from wear.
Left: A heat-outlet area should be three to
four times the inlet area for gas and two to
three times the inlet area for glow, to keep
engine temperatures cool. Simple customfitted
plank boxes are built using the TLAR—
“That Looks About Right!”—method.
Engine cooling won’t ruin the look. Ductwork allows airflow to be
directed over the cylinders, to keep power plants from overheating.
These are identical to those used on full-scale airplanes.
advantage of your radio resolution, do the
following.
Before connecting any linkage, the travel
adjust feature (Adjustable Travel Volume, or
ATV) in your radio endpoint travels should be
set to their maximum—usually 140%-150%.
One can argue that a slightly lower
maximum ATV point, say 5 or so percentage
points below full, will allow for fine-tuning
later.
The higher ATV setting forces the pivotpoint
adjustment to go out on the control
surface and in on the servo arm. Doing so
provides a more stable leverage arm, a higher
tolerance to flutter, better resolution, and
reduced gear train wear around neutral,
because these settings force the servo to use
all of its travel rather than just the few teeth
close to neutral.
Doing the opposite (in on the control
surface and out on the servo) is conducive to
flutter, lower resolution, and gear wear, with
the servos often being blamed for having
sloppy tolerances. If you are using only a few
teeth close to neutral because of improper
setup, don’t blame the servo and don’t be
surprised if you blow through your servo
gears in as few as 25-50 flights.
Ensure that linkage geometry is correct to
avoid flutter, sloppy servo centering, and poor
resolution.
17. Inadequate Servo Torque for Intended
Application: I spoke with an aeromodeler who
was setting up a 30-pound model with trainer
servos equipped with 40 inch-ounce of output.
He was emphatic that this setup would work
because his buddy, who had been flying for
years, said that it would.
It was an accident waiting to happen. The
torque rating on “standard” servos is
inadequate, and the gear train is not robust
enough to consistently withstand flight loads
on a large airplane. If 40 inch-ounce servos
worked safely on this size of model, we would
all be flying the same equipment.
Leave your 40- to 60-size thinking behind
when setting up a big model or you might be
spending your money on lawyers rather than
airplanes. Learn how to determine what servo
torque is adequate to handle the flight loads
for your application.
18. Radio Frequency Crosstalk on 72 MHz
and 2.4 GHz Systems: This can be a setup
issue and/or a faulty component that causes
deficient range checks, or crosstalk.
Equipment separation is paramount when
setting up gas-powered aircraft with a 72
MHz system, and we have learned, through
troubleshooting, that 2.4 GHz systems are also
affected, but to a lesser degree.
Failure to maintain the recommended
distances of radio gear from ignition system is
a typical pilot setup error. Mounting electrical
components too close can spread the radio
frequency infection into other components
and, subsequently, lock out the receiver or
reduce your range.
Ensure that receivers, antennas, and other
electrical components are at least 3 inches
from any other electronic components and at
10sig2_00MSTRPG.QXD 8/20/10 11:09 AM Page 36
October 2010 37
Above: Unsecured parts cause crashes. A
thread-locking product prevents metal nuts,
bolts, and screws from coming loose. A rule
of thumb is that if two parts that thread
together are metal, thread-lock them—even
on electrics.
Above: This elevator is set to 45° of travel. Make sure your test
flights use low and high rates; that usually means approximately
10°-18° of travel for the low side.
Making use of an EZ Balancer or other CG machine prevents needless crashes caused by an
incorrect CG. Nose-heavy models don’t fly well either. Get the CG right on the first try.
Left: High-quality linkages that are set up
properly should be used to prevent
unnecessary crashes caused by linkage
failure. You’ll never be sorry about oversized
accessories working too well.
least 8-12 inches from any part of the ignition
system.
19. Improper Tank Plumbing: Highpowered
engines, gas or glow, operating on
medium-size fuel lines, small clunks, through
small brass tubing often run hot, lean out, or
seize because they can’t be richened.
Mounting the internal clunk too close to the
back of the tank (within 1/2 inch) will cause
fuel-flow issues that can make an engine run
lean, sometimes quit, and, in worse cases,
seize.
Mounting the vent line so that the top of
the tank can close off the vent will cause the
engine to run lean, run hot, or seize. Hardmounting
a tank can bring about fuel foaming
and cause the same symptoms and erratic
operation.
All connections should be secured. Inspect
your tank and replace tubing once each year.
Soft-mount tanks and ensure that vent and
pickup lines are not blocked. Secure all
connections, inside and outside, with zip-ties.
Inspect your model’s tank plumbing
regularly.
20. Inadequate Fuel Filtering: Some
aeromodelers don’t employ filters. If internalcombustion
engines ran consistently without
10sig2_00MSTRPG.QXD 8/20/10 11:12 AM Page 37
filters, they would be designed accordingly
and not use them.
Imagine operating a full-scale aircraft or
your car without filters. Does it make sense to
let contaminants plug the internal orifices of
your carburetor, causing erratic running or
engine failure? Simply performing routine
maintenance to clean or replace a filter that
will keep your carburetor clean makes
sense to me.
We use filters—both on the fuel line and
on the vent line—to keep dust, dirt, grass
seeds, dandelion fuzz, etc. from getting
inside the tank and into the tiny orifices in
the fuel system.
Soft-mount your tank and use, and
periodically clean, fuel and vent line filters.
21. Improper Inlet/Exit Area Cooling
Ratios: Glow engines typically require a
minimum 1:2 and gas engines need a
minimum 1:3 inlet/exit cowl opening ratio. If
a power plant runs hot from improper ratios,
open the bottom or rear of the cowl.
Making a bigger hole in the front
exacerbates the problem; ram air that heats up
in the cowl can’t get out as quickly as it enters.
The engine heat soars and the problem gets
worse—not better.
Inadequate ratios cause erratic running and
can cause vapor lock and seized engines.
Ensure that proper cooling ratios are used.
22. Lack of or Inadequate Baffling on Gas
Engines: Proper baffling can drop cylinder
temperatures by more than 100° and can make
the difference between burning up an engine
or having one that performs terrifically.
Properly baffled gas engines typically run at
180°-220°. (There are a few exceptions.)
Install baffles to direct airflow where it’s
needed. That will keep the power plant
running coolly and consistently.
23. Linkage Failure: Installing 2/56 hardware
October 2010 39
or plastic servo arms on high-performance
models is an accident waiting to happen.
Nylon servo arms get brittle with age and
break, as do the teeth in your comb. Metal
arms with 4-40 bolt-on ball links is the size of
choice for Giant Scale airplanes.
Carbon-fiber pushrods or titanium
turnbuckles are typically used for linkages,
along with machined metal 4-40 servo arms
tapped for 4-40 linkages.
Don’t use welding rod (Are these heattreated,
high-tensile, low-tensile, carbon-steel,
low-carbon-steel rods? Most people don’t
know.) or homemade threaded coat-hanger
wire. Don’t laugh; I’ve had more than one call
about that.
Nyrods that flex are simply unacceptable as
pushrods on Giant Scale, high-performance
aircraft and are conducive to flutter failure. If
you have “gotten away with” using them, you
are on borrowed time.
Does it make sense to build a $3,000-
$6,000 model and save a few dollars on
control linkages by using junk for a primary
control? Of course it doesn’t. Use properly setup,
high-quality linkage hardware to avoid
linkage failure.
24. Loose Hardware and Metal-to-Metal
Noise: Rattling metal parts such as loose
mufflers, engine bolts, landing gear, and tail
wheels or similar components will cause
glitching or a lockout on 72 MHz systems.
Lack of locking devices on threaded items or
not periodically checking for threaded items
that have loosened will cause the same metalto-
metal noise.
Make sure there is no metal-to-metal
rattling; thread-lock your nuts, bolts, and
screws; and periodically check them for
tightness. We use space-age thread lock, which
is used on full-scale aircraft and is approved by
the FAA for use in high-vibration areas.
25. Hooking up or Programming Control
Surfaces Backward: This is a setup/preflight
issue, and it can be avoided merely by testing
control movement and direction before starting
an engine.
Remember that when the stick is moved to
the right, the right aileron should go up as
viewed from the pilot’s seat, and vice versa.
Check controls before every flight.
26. Not Connecting Extension Cords Before
Flight: This is another preflight issue, and it
makes many expert pilots feel like toddlers. A
simple control check before startup will
identify this problem.
27. Vapor Lock: Fuel vaporizes because the
airflow through the cowl is insufficient, either
because of poor or no baffling or inadequate
baffling. In fuel lines that are too close to
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mufflers, the fuel can vaporize, causing
engine failure.
Ensure that air flows through the cowl and
over fuel lines. If you experience vapor lock,
reposition fuel lines away from mufflers or
headers. Wrap aluminum foil around fuel
lines, make sure that you use proper inlet/exit
cowl ratios, and ensure that proper baffling is
in place.
28. Improper Charge Rates for Batteries:
There are all kinds of high-end chargers on
the market for a variety of batteries. Some are
programmable and some are not.
I get regular calls from aeromodelers who
don’t know that they programmed the wrong
settings into their chargers and ruined
batteries, or their batteries caught fire because
of incorrect settings. The battery is blamed
when the cause is applying an incompatible
charge rate.
Review charging instructions and program
correct settings so you don’t create a fire
hazard or severely shorten the life of the pack,
which is the heart of your aircraft.
Another typical mistake is to undercharge
airborne batteries and not load-test batteries
before every flight. The undercharge is
caused by faulty chargers that predict a peak
cutoff too early or charger rates that are set
incorrectly.
Not all batteries are created equal, and the
user sometimes neglects to burn in or testcycle
the pack. This results in a model
running out of battery capacity sooner than
predicted or, worse, can cause a crash
because the pilot lacked a battery redundancy
system.
Don’t guess. Make sure you understand
the battery technology and charger you are
using, and charge accordingly. Test batteries
as frequently as necessary to know how much
power is consumed during a flight. A change
in test results should coincide with flight
demands or alert you that a pack is failing.
29. Incorrect CG: Tail-heavy models rarely
fly twice. Nose-heavy airplanes are more
likely to survive a test flight.
Ensure that your aircraft’s CG is properly
set before the test flight. The tank should be
empty when you do so.
You can easily check a large model’s CG
with an EZ Balancer from Southwest
Systems. Despite what some might tell you,
the airplane requires the same balance point
whether it’s powered by a motor or an
internal-combustion engine.
30. Incorrect Control Travels: Models have
crashed because of too little or too much
travel used on the test flights. Many pilots
have buried their Giant Scale airplanes on
maiden flights because of too much travel.
Thousands of dollars worth of aircraft are
needlessly destroyed because of excessive
travel programmed into them. And neither the
model nor the pilot (sometimes both) likes it
enough to handle a landing.
If you don’t know the correct travels, use
8°-10° for low rate and 15°-18° for high rate.
These are safe settings to use on test flights.
As the airplane progresses through trimming
flights, you can adjust the settings for
personal taste and optimum performance.
This travel guide makes the assumption
that an aircraft’s CG, incidence, and thrustline
locations are correct. Check travels with a
deflection meter before the first test flight.
Crashing is a choice. Those who do nothing
to address deficiencies will keep crashing
models and endangering others. I hope no one
gets hurt if the pilot makes the wrong choices.
Correcting problems makes airplanes
safer and more reliable, allowing their pilots
to fly with confidence and safely land them if
a malfunction occurs. It is the aeromodeler’s
responsibility to evaluate the information
presented, make the appropriate decisions
relative to his or her situation/setup, and
safely operate the aircraft.
Mistakes do happen, but crashes should
clearly be the exception rather than the rule. If
you effectively address the issues I have
presented, your models never have to crash.
Fly safely! MA
Don Apostolico
[email protected]
Sources:
Southwest Systems
(805) 527-6337
www.ezbalancer.com
Don’s Hobby Shop
(800) 972-6273
www.donshobbyshop.com
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