Defensive RC Flying - 2010/08

38 MODEL AVIATION
This arTiclE should help those
aeromodelers who don’t know what they
don’t know by documenting the first 13 of
30 major reasons why our airplanes go in.
In my article “Crashing is Not an
Option” (in the November 2009 MA), I
wrote about equipment failures that cause
our aircraft to collide with the ground. One
can argue that the following items overlap in
cause and effect, but you will learn the main
reasons for accidents and recommendations
to avoid them.
The spreadsheet summary in my previous
article clearly shows that the chief cause of
crashes is setup error. This issue can be
solved through education, so let’s start.
1. Pilot Error: This is usually a result of
inadequate pilot training. A modeler who
understands the “flight envelope” is far less
likely to toast an airplane because of pilot
error than the modeler who doesn’t
understand basic aerodynamics and control
techniques.
To avoid needless crashes, an
aeromodeler needs to understand stall speed
vs. bank angle, load factor vs. bank angle,
how to correct for adverse yaw, torque, Pfactor,
slipstream effect, and a host of other
performance issues related to the “flight
envelope.”
The consequences of not understanding
the basics of the flight envelope are
predictable and are a major cause of
needless crashes.
Recommendation: Obtain flight training
from a competent flight instructor and a
flight-training book called Proficient
Flying, featured in the November article,
which covers all aspects of the modeling
flight envelope.
2. Battery Failure: This is, has been, and
continues to be the leading cause of crashes
outside of pilot error. There is no excuse to
bury an airplane for this reason, but it
happens often. There is no debating that if
you are flying with a single battery and it
quits, your model will crash.
August 2010 39
Don regularly checks engine rpm. A tachometer is an RC
pilot’s tool for knowing the condition of an aircraft; a change
in rpm readings lets him or her know that there’s a problem.
RC FLYING
DEFENSIVE
Recommendation: The simple solution
is to install redundant batteries and
properly load-test the battery before and
after every flight. This is especially
important if you fly Giant Scale aircraft.
3. Switch Failure: Switches that stop
working are the second leading cause of
crashes, following pilot error. If you fly a
single switch and it fails, your airplane
will crash. There is no excuse for this to
cause an accident.
Recommendation: Redundant switches
will prevent this type of crash from
occurring. If you fly Giant Scale, the
weight of a redundant switch is
negligible and immensely responsible.
4. Receiver Failure: Random receiver
failures occur for a variety of reasons,
ranging from crystal breakdown or 72 MHz
receivers going into hold because of metalto-
metal contact, to aeromodelers using 7.0
volts or more unregulated voltage into
receiver/servos rated for 4.8-6.0 volts only.
In the past two years of troubleshooting
customers’ airplanes set up with 2.4 GHz
systems, I have learned that 2.4 GHz
receivers are not immune to ignition and
electrical noise, as they were initially
believed to be. Additionally, a person’s
flying a model on a different bandwidth
An explanation of
the 13 avoidable
RC tragedies
by Don Apostolico
(2.4 GHz vs. 72 MHz) does not decrease the
potential of an electrical failure on a single
receiver.
On large aircraft we carry dual receivers
with the programming set to bring the
throttle to idle and servos to neutral if a
receiver goes into hold. If the problem is
radio frequency (RF)- or vibration-related,
the receiver will usually come out of hold
when the throttle is automatically retarded,
which relieves the vibration and reduces the
metal-to-metal or RF noise.
The result is that control is often
regained. If the receiver doesn’t come back
online, the second operational receiver
allows the model to be landed.
40 MODEL AVIATION
DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING
Some say that radio range is reduced when running dual
receivers. I have diagnosed thousands of customers’ airplanes
throughout many years with range issues. In every case, the reduced
range was caused by inadequate distances between electrical
components, metal-to-metal contact, or, in a few cases, a defective
component.
Recommendation: Install dual 72 MHz or 2.4 GHz receivers.
5. Servo Failure: When running multiple digital servos on a
common control surface and a current meter is not used to check the
servo preload for binding, your servos are probably fighting each
other. Hot-running regulators, erratic-running servos, and quickly
depleted batteries are common symptoms of servos being set up
incorrectly.
When servos fight each other, they can heat up to the extent of
melting the servo or draining the battery within a few flights. A
servo, battery, or regulator is usually blamed for being faulty, rather
than the modeler’s recognizing that the servo or battery failed
because of binding servos, linkage/hinge misalignment, or improper
radio programming.
Current tests need to be made, and appropriate adjustments need
to be made at neutral, endpoints, and midtravel to prevent excessive
current flow, to attain the servos’ normal idle current.
Because of the extreme accuracy of digital servos, proper setup
cannot be consistently and accurately attained by ear; you must use
a meter.
Recommendation: I have observed that normal digital servo
idle current for Futaba, JR, and Hitec units are typically 10-20
mAh. Check your servo specifications to be sure. Use a current
meter to identify problems and properly set up digital servos.
6. Receiver Reboot: Contrary to what many might think, this is not a
new problem. Years ago it was called “battery dropout,” and it is still
caused by the same problem; it’s just more noticeable today because
of higher-powered digital servos.
The technically sloppy setup of 20 years ago was electrically
tolerated because analog servo torque was anemic by today’s
standards. Nowadays, digital servos produce up to 400% more torque
than analog servos of the 1980s and 1990s did.
Many aeromodelers refer to this problem relative to 2.4 GHz
systems, but 72 MHz systems suffer from the same issue. Modelers
try to fix the symptom with fast-reboot receivers, heavy-gauge wire,
giant connectors, and a host of other patches. It’s not wrong to do so,
but why not fix the cause of the problem, which is improper setup?
I have a full-scale analogy for this. Let’s say that a critical piece
of equipment keeps blowing its circuit breaker on a Boeing 747.
Rather than troubleshooting and fixing the problem, the mechanic
installs a bigger circuit breaker.
Wow, I feel safe now. Ha! It might seem ridiculous, but
aeromodelers often do the equivalent.
Here is the problem. When a 72 MHz or 2.4 GHz receiver voltage
gets down to nearly 3.5 volts, the receiver shuts down (engages
battery fail-safe). If the airplane does not have enough altitude for the
battery/receiver to recover, it crashes. Don’t blame the receiver for
doing its job.
If your 6.0-volt system, which charges up to 7.0-8.4 volts
(depending on battery type), operates at 3.5 volts, you have a serious
problem. And it’s not a slow- or fast-reboot receiver.
This 40% Carden Extra 330, with 1,250 flights, features true redundancy with no choke
points. It’s equipped with twin receivers, twin batteries/regulators, and twin switches.
Many fliers use high-quality 2.4 GHz
receivers on large models and double them
as they would 72 MHz systems, for
increased redundancy.
Photos by the author
August 2010 41
G DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING
The main reasons why the voltage drops quickly is that the
modeler chooses too small of a battery for the intended application,
servos are fighting each other on the same surface, servos are
overdriving the endpoints, linkage geometry is incorrect, or the
modeler is using high-resistance 26-gauge wire.
These setup errors sap the battery, cause the voltage to go down,
and cause the receiver to shut off. The blame is often placed on
“those digital servos drawing all that current flow.”
I can’t stress enough that improper setup is at the root of most of
these crashes. The blame is often placed on faulty batteries, hotrunning
regulators, receivers that reboot too slowly, etc.
Many have said not to use a digital servo on a throttle because it
will burn out the servo. Numerous models fly successfully with
digital servos used on the throttle; talk to a helicopter pilot.
Burning up a digital servo on throttle is a setup issue—not a servo
issue. A servo that binds at the high and/or low throttle stops, draws
high current, and burns out. Some claim that engine vibration causes
the digital throttle servo to overwork. If your engine/propeller is
creating that much vibration, you have a problem but it’s not the
digital servo.
Recommendation: Fix the problem—not the symptom. Set up
travels correctly so they can’t bind, vertically and horizontally
balance and track the propeller, use a quality spinner, and properly
adjust the needle valves.
Use a current meter to ensure that servos aren’t binding, choose
the correct-size batteries, employ heavy-duty 22-gauge wire for
extensions, and correctly program your radio.
7. Hot-Running Electronics: Heat is the symptom of high current
flow. The cause goes back to improper setup.
Some aeromodelers believe that receivers can’t take high current
from high-performance digital servo setups. Let’s bury this myth
once and for all time. This faulty belief is repeated on the Internet,
and it’s a perfect example of well-meaning aeromodelers passing on
grossly inaccurate information.
Imagine JR or Futaba selling a 10-channel receiver that can
operate only six servos, because if you operate 10 servos you will
burn out the receiver from the high current flow. Rather than
accepting this information and passing it on to the next modeler,
stop and think how silly it is.
If receivers were limited in current capacity relative to our
applications, don’t you think the manufacturer would placard its
receiver to indicate not to use more than six servos on the 10-
channel receiver? Additionally, what’s the point of manufacturing a
10-channel receiver that can operate only six servos?
Most high-performance six- to 14-channel receivers are rated at
10-50 amps, depending on the receiver. I know because I called JR,
Futaba, and Spektrum to get the data.
In contrast, circuit breakers in the home are in the 15- to 30-amp
range. You run vacuum cleaners at 12-15 amps and air conditioners
at 10-30 amps or more. If your model draws anywhere near the
current that your house draws, you have a problem and it’s not the
receiver.
Experience shows that a properly set-up 35%- to 40%-size model
can draw an average of 2-4 amps in flight. Spike loads will be
higher for a split second in a high-G snap, and then current returns
to normal.
Recommendation: See items 5 and 6.
Dual servos on a control surface provides
twice the authority, but careful setup is
required to ensure that the units don’t
fight one another. Such an occurrence can
cancel out the entire model.
For redundancy, choose servos wisely.
Digital units will offer the highest power
with the best accuracy. New high-voltage
types also draw more current and require
higher-capacity batteries.
Testing batteries with the proper load
before and after flight will help identify
problems. When more power than normal
is consumed during a flight, that’s a loud
problem sign.
and, to a lesser degree, on 2.4 GHz if there is ignition noise or
metal-to-metal noise caused by loose nuts, bolts, or screws;
rattling tail wheels; loose muffler bolts; etc.
If the radio is programmed so that the servos move to neutral
and throttle is retarded to idle if these problems are experienced,
the RF noise will decrease, the receiver comes out of hold, and
control is regained. The pilot can use just enough power to land
the model, troubleshoot, and solve the problem, and the airplane
will live to fly another day.
Failure to program the fail-safe and throttle position results in
the throttle staying at full power. The malfunction keeps the
receiver in hold, and the airplane crashes because of zero control.
You might be surprised by how many aeromodelers crash their
aircraft because their fail-safe-hold features are not programmed.
There is no excuse to bury a model because you failed to properly
program a radio safety feature.
Recommendation: Take steps to ensure that there is no metalto-
metal noise. Provide enough separation between any part of
your ignition system and any part of your radio gear; 8-12 inches
is usually adequate. Set and test the fail-safe-hold settings before
the test flight.
13. Improper Needles: This oversight causes flameouts, fowled
plugs on gas engines, or overheated power plants that quit and
needlessly take down airplanes.
If you can’t quantify how many rpm on the rich side of peak
your needles are set, you are guessing that they are adjusted
August 2010 43
blow the bearings out in as little as a single gallon of fuel. If you
ask the seller if he or she has tracked and vertically balanced the
propeller and you get the deer-in-the-headlight look, beware.
Recommendation: Use high-quality, balanced spinners. Learn
how to horizontally and vertically balance and track your
propeller.
11. Electronic Choke Points: I’ve gotten calls from fliers who
have needlessly crashed more than $16,000 worth of Giant Scale
models because the built-in choke points failed. When a chokepoint
failure occurs (engineers call it single-point system failure),
the results are predictable; the model crashes. No debate, opinion,
or discussion is necessary.
Lack of redundancy is a death spike that causes crashes. A few
choke points are single battery, single switch, or single receiver
failure.
Recommendation: Evaluate your aircraft for choke points and
avoid them.
12. Poor Programming: Failure to properly program a radio will
result in a crash if random RF is introduced. Conversely, proper
programming usually saves a model if random RF problems occur.
Let’s examine a classic programming error. Today’s high-end
radios have a fail-safe-hold feature that is designed to allow the
flier to program preselected control positions, in case an RF
problem occurs.
That could be RF interference experienced on 72 MHz radios
This laser temperature gun is used to
check cylinder head temperatures, to
measure baffle and cooling efficiency.
Normal is 180°-220° for most gas engines.
Use a meter instead of your ear.
A high-quality device such as the
Fromeco TNC Tachometer
(accurate to 1 rpm) makes it
easier to set needles and check
performance.
Is your propeller flat? No propeller comes tracked.
Proper tracking to square the hub greatly
eliminates vibration. Combining that with propeller
balancing will reduce wear throughout the airframe.
DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING
1. Pilot error
2. Battery failure
3. Switch failure
4. Receiver failure
5. Burned-up digital servos
6. Receiver reboot
7. Hot-running regulators, servos, and
extensions
8. Failure to load-test batteries before
flight
9. Incorrect use or lack of 6.0-volt regulator
10. Inadequate propeller balancing
DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING
11. Lack of electronic choke points
12. Improper radio programming
13. Improper needle settings
14. Control flutter
15. Stripped servo gears
16. Incorrect linkage geometry
17. Inadequate servo torque
18. RF crosstalk on 72 MHz and 2.4 GHz
systems
19. Improper tank plumbing
20. Inadequate fuel filtering
21. Improper inlet- or exit-area cooling ratios
22. Lack of or inadequate baffling
23. Linkage failure
24. Nuts, bolts, and screws vibrating
loose
25. Backward control surfaces
26. Not connecting extension cords
before flight
27. Engine vapor lock
28. Improper charge rates used on
batteries
29. Incorrect CG
30. Incorrect control travels
The Order of Failure
correctly. You might guess right from time to time, but the most
common complaint with gas engines is that they vibrate, have an
erratic midrange, and run roughly.
The most common reason for the latter or hard starting is
misadjusted needle valves. Because you turn the needles doesn’t
mean they are correctly adjusted. The engine might run, but not
as it should.
Using the old pinch test, the high and low end on a two- or
four-stroke glow engine are typically adjusted 200 rpm on the
rich side of peak. A gas engine is typically adjusted 100 rpm on
the rich side of peak, with the exception of the BME 110/116; it’s
set 200 rpm on the rich side of peak.
Assuming that baffling and inlet or exit area ratios are correct,
these will be close to the final flight settings. You will make final
microadjustments with flight tests. If these settings are far from
your final flight settings, there are other issues you need to
address.
The spark plug is a good barometer of your needle setting. The
electrode should be tan in color. If it’s black, the setting is too
rich; if it’s white, the setting is too lean.
Another needle-adjustment issue is related to those who say
that two- and four-stroke engines run poorly inverted. Think
about this.
If two- and four-stroke power plants didn’t run well inverted,
would virtually every competition RC Aerobatics model in the
world have them configured that way? They run fine inverted.
What do competitors know that sport fliers don’t? The
modeler must learn how to properly set up engine fuel systems
and correctly adjust needles with a tachometer, as I have
described.
Recommendation: Don’t guess. Use a quality tachometer and
precisely set needles with the pinch test as a starting point for your
test flight, and ensure that your fuel system is set up properly.
Throughout the many years I have owned Don’s Hobby Shop, I
have spoken to tens of thousands of people, solved problems,
and helped customers set up and equip their aircraft. In the
process, I have learned that there are no new reasons why models
crash; those causes were identified many years ago.
Since we know the why, crash avoidance is not difficult.
However, the aeromodeler must learn what the issues are to
avoid the problems and apply the fixes.
The remaining causes of crashes will be featured in a future
article. Until then, your challenge is to apply the information I have
presented to your circumstances so you can fly safely and with
confidence. MA
Don Apostolico
[email protected]
44 MODEL AVIATION

38 MODEL AVIATION
This arTiclE should help those
aeromodelers who don’t know what they
don’t know by documenting the first 13 of
30 major reasons why our airplanes go in.
In my article “Crashing is Not an
Option” (in the November 2009 MA), I
wrote about equipment failures that cause
our aircraft to collide with the ground. One
can argue that the following items overlap in
cause and effect, but you will learn the main
reasons for accidents and recommendations
to avoid them.
The spreadsheet summary in my previous
article clearly shows that the chief cause of
crashes is setup error. This issue can be
solved through education, so let’s start.
1. Pilot Error: This is usually a result of
inadequate pilot training. A modeler who
understands the “flight envelope” is far less
likely to toast an airplane because of pilot
error than the modeler who doesn’t
understand basic aerodynamics and control
techniques.
To avoid needless crashes, an
aeromodeler needs to understand stall speed
vs. bank angle, load factor vs. bank angle,
how to correct for adverse yaw, torque, Pfactor,
slipstream effect, and a host of other
performance issues related to the “flight
envelope.”
The consequences of not understanding
the basics of the flight envelope are
predictable and are a major cause of
needless crashes.
Recommendation: Obtain flight training
from a competent flight instructor and a
flight-training book called Proficient
Flying, featured in the November article,
which covers all aspects of the modeling
flight envelope.
2. Battery Failure: This is, has been, and
continues to be the leading cause of crashes
outside of pilot error. There is no excuse to
bury an airplane for this reason, but it
happens often. There is no debating that if
you are flying with a single battery and it
quits, your model will crash.
August 2010 39
Don regularly checks engine rpm. A tachometer is an RC
pilot’s tool for knowing the condition of an aircraft; a change
in rpm readings lets him or her know that there’s a problem.
RC FLYING
DEFENSIVE
Recommendation: The simple solution
is to install redundant batteries and
properly load-test the battery before and
after every flight. This is especially
important if you fly Giant Scale aircraft.
3. Switch Failure: Switches that stop
working are the second leading cause of
crashes, following pilot error. If you fly a
single switch and it fails, your airplane
will crash. There is no excuse for this to
cause an accident.
Recommendation: Redundant switches
will prevent this type of crash from
occurring. If you fly Giant Scale, the
weight of a redundant switch is
negligible and immensely responsible.
4. Receiver Failure: Random receiver
failures occur for a variety of reasons,
ranging from crystal breakdown or 72 MHz
receivers going into hold because of metalto-
metal contact, to aeromodelers using 7.0
volts or more unregulated voltage into
receiver/servos rated for 4.8-6.0 volts only.
In the past two years of troubleshooting
customers’ airplanes set up with 2.4 GHz
systems, I have learned that 2.4 GHz
receivers are not immune to ignition and
electrical noise, as they were initially
believed to be. Additionally, a person’s
flying a model on a different bandwidth
An explanation of
the 13 avoidable
RC tragedies
by Don Apostolico
(2.4 GHz vs. 72 MHz) does not decrease the
potential of an electrical failure on a single
receiver.
On large aircraft we carry dual receivers
with the programming set to bring the
throttle to idle and servos to neutral if a
receiver goes into hold. If the problem is
radio frequency (RF)- or vibration-related,
the receiver will usually come out of hold
when the throttle is automatically retarded,
which relieves the vibration and reduces the
metal-to-metal or RF noise.
The result is that control is often
regained. If the receiver doesn’t come back
online, the second operational receiver
allows the model to be landed.
40 MODEL AVIATION
DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING
Some say that radio range is reduced when running dual
receivers. I have diagnosed thousands of customers’ airplanes
throughout many years with range issues. In every case, the reduced
range was caused by inadequate distances between electrical
components, metal-to-metal contact, or, in a few cases, a defective
component.
Recommendation: Install dual 72 MHz or 2.4 GHz receivers.
5. Servo Failure: When running multiple digital servos on a
common control surface and a current meter is not used to check the
servo preload for binding, your servos are probably fighting each
other. Hot-running regulators, erratic-running servos, and quickly
depleted batteries are common symptoms of servos being set up
incorrectly.
When servos fight each other, they can heat up to the extent of
melting the servo or draining the battery within a few flights. A
servo, battery, or regulator is usually blamed for being faulty, rather
than the modeler’s recognizing that the servo or battery failed
because of binding servos, linkage/hinge misalignment, or improper
radio programming.
Current tests need to be made, and appropriate adjustments need
to be made at neutral, endpoints, and midtravel to prevent excessive
current flow, to attain the servos’ normal idle current.
Because of the extreme accuracy of digital servos, proper setup
cannot be consistently and accurately attained by ear; you must use
a meter.
Recommendation: I have observed that normal digital servo
idle current for Futaba, JR, and Hitec units are typically 10-20
mAh. Check your servo specifications to be sure. Use a current
meter to identify problems and properly set up digital servos.
6. Receiver Reboot: Contrary to what many might think, this is not a
new problem. Years ago it was called “battery dropout,” and it is still
caused by the same problem; it’s just more noticeable today because
of higher-powered digital servos.
The technically sloppy setup of 20 years ago was electrically
tolerated because analog servo torque was anemic by today’s
standards. Nowadays, digital servos produce up to 400% more torque
than analog servos of the 1980s and 1990s did.
Many aeromodelers refer to this problem relative to 2.4 GHz
systems, but 72 MHz systems suffer from the same issue. Modelers
try to fix the symptom with fast-reboot receivers, heavy-gauge wire,
giant connectors, and a host of other patches. It’s not wrong to do so,
but why not fix the cause of the problem, which is improper setup?
I have a full-scale analogy for this. Let’s say that a critical piece
of equipment keeps blowing its circuit breaker on a Boeing 747.
Rather than troubleshooting and fixing the problem, the mechanic
installs a bigger circuit breaker.
Wow, I feel safe now. Ha! It might seem ridiculous, but
aeromodelers often do the equivalent.
Here is the problem. When a 72 MHz or 2.4 GHz receiver voltage
gets down to nearly 3.5 volts, the receiver shuts down (engages
battery fail-safe). If the airplane does not have enough altitude for the
battery/receiver to recover, it crashes. Don’t blame the receiver for
doing its job.
If your 6.0-volt system, which charges up to 7.0-8.4 volts
(depending on battery type), operates at 3.5 volts, you have a serious
problem. And it’s not a slow- or fast-reboot receiver.
This 40% Carden Extra 330, with 1,250 flights, features true redundancy with no choke
points. It’s equipped with twin receivers, twin batteries/regulators, and twin switches.
Many fliers use high-quality 2.4 GHz
receivers on large models and double them
as they would 72 MHz systems, for
increased redundancy.
Photos by the author
August 2010 41
G DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING
The main reasons why the voltage drops quickly is that the
modeler chooses too small of a battery for the intended application,
servos are fighting each other on the same surface, servos are
overdriving the endpoints, linkage geometry is incorrect, or the
modeler is using high-resistance 26-gauge wire.
These setup errors sap the battery, cause the voltage to go down,
and cause the receiver to shut off. The blame is often placed on
“those digital servos drawing all that current flow.”
I can’t stress enough that improper setup is at the root of most of
these crashes. The blame is often placed on faulty batteries, hotrunning
regulators, receivers that reboot too slowly, etc.
Many have said not to use a digital servo on a throttle because it
will burn out the servo. Numerous models fly successfully with
digital servos used on the throttle; talk to a helicopter pilot.
Burning up a digital servo on throttle is a setup issue—not a servo
issue. A servo that binds at the high and/or low throttle stops, draws
high current, and burns out. Some claim that engine vibration causes
the digital throttle servo to overwork. If your engine/propeller is
creating that much vibration, you have a problem but it’s not the
digital servo.
Recommendation: Fix the problem—not the symptom. Set up
travels correctly so they can’t bind, vertically and horizontally
balance and track the propeller, use a quality spinner, and properly
adjust the needle valves.
Use a current meter to ensure that servos aren’t binding, choose
the correct-size batteries, employ heavy-duty 22-gauge wire for
extensions, and correctly program your radio.
7. Hot-Running Electronics: Heat is the symptom of high current
flow. The cause goes back to improper setup.
Some aeromodelers believe that receivers can’t take high current
from high-performance digital servo setups. Let’s bury this myth
once and for all time. This faulty belief is repeated on the Internet,
and it’s a perfect example of well-meaning aeromodelers passing on
grossly inaccurate information.
Imagine JR or Futaba selling a 10-channel receiver that can
operate only six servos, because if you operate 10 servos you will
burn out the receiver from the high current flow. Rather than
accepting this information and passing it on to the next modeler,
stop and think how silly it is.
If receivers were limited in current capacity relative to our
applications, don’t you think the manufacturer would placard its
receiver to indicate not to use more than six servos on the 10-
channel receiver? Additionally, what’s the point of manufacturing a
10-channel receiver that can operate only six servos?
Most high-performance six- to 14-channel receivers are rated at
10-50 amps, depending on the receiver. I know because I called JR,
Futaba, and Spektrum to get the data.
In contrast, circuit breakers in the home are in the 15- to 30-amp
range. You run vacuum cleaners at 12-15 amps and air conditioners
at 10-30 amps or more. If your model draws anywhere near the
current that your house draws, you have a problem and it’s not the
receiver.
Experience shows that a properly set-up 35%- to 40%-size model
can draw an average of 2-4 amps in flight. Spike loads will be
higher for a split second in a high-G snap, and then current returns
to normal.
Recommendation: See items 5 and 6.
Dual servos on a control surface provides
twice the authority, but careful setup is
required to ensure that the units don’t
fight one another. Such an occurrence can
cancel out the entire model.
For redundancy, choose servos wisely.
Digital units will offer the highest power
with the best accuracy. New high-voltage
types also draw more current and require
higher-capacity batteries.
Testing batteries with the proper load
before and after flight will help identify
problems. When more power than normal
is consumed during a flight, that’s a loud
problem sign.
and, to a lesser degree, on 2.4 GHz if there is ignition noise or
metal-to-metal noise caused by loose nuts, bolts, or screws;
rattling tail wheels; loose muffler bolts; etc.
If the radio is programmed so that the servos move to neutral
and throttle is retarded to idle if these problems are experienced,
the RF noise will decrease, the receiver comes out of hold, and
control is regained. The pilot can use just enough power to land
the model, troubleshoot, and solve the problem, and the airplane
will live to fly another day.
Failure to program the fail-safe and throttle position results in
the throttle staying at full power. The malfunction keeps the
receiver in hold, and the airplane crashes because of zero control.
You might be surprised by how many aeromodelers crash their
aircraft because their fail-safe-hold features are not programmed.
There is no excuse to bury a model because you failed to properly
program a radio safety feature.
Recommendation: Take steps to ensure that there is no metalto-
metal noise. Provide enough separation between any part of
your ignition system and any part of your radio gear; 8-12 inches
is usually adequate. Set and test the fail-safe-hold settings before
the test flight.
13. Improper Needles: This oversight causes flameouts, fowled
plugs on gas engines, or overheated power plants that quit and
needlessly take down airplanes.
If you can’t quantify how many rpm on the rich side of peak
your needles are set, you are guessing that they are adjusted
August 2010 43
blow the bearings out in as little as a single gallon of fuel. If you
ask the seller if he or she has tracked and vertically balanced the
propeller and you get the deer-in-the-headlight look, beware.
Recommendation: Use high-quality, balanced spinners. Learn
how to horizontally and vertically balance and track your
propeller.
11. Electronic Choke Points: I’ve gotten calls from fliers who
have needlessly crashed more than $16,000 worth of Giant Scale
models because the built-in choke points failed. When a chokepoint
failure occurs (engineers call it single-point system failure),
the results are predictable; the model crashes. No debate, opinion,
or discussion is necessary.
Lack of redundancy is a death spike that causes crashes. A few
choke points are single battery, single switch, or single receiver
failure.
Recommendation: Evaluate your aircraft for choke points and
avoid them.
12. Poor Programming: Failure to properly program a radio will
result in a crash if random RF is introduced. Conversely, proper
programming usually saves a model if random RF problems occur.
Let’s examine a classic programming error. Today’s high-end
radios have a fail-safe-hold feature that is designed to allow the
flier to program preselected control positions, in case an RF
problem occurs.
That could be RF interference experienced on 72 MHz radios
This laser temperature gun is used to
check cylinder head temperatures, to
measure baffle and cooling efficiency.
Normal is 180°-220° for most gas engines.
Use a meter instead of your ear.
A high-quality device such as the
Fromeco TNC Tachometer
(accurate to 1 rpm) makes it
easier to set needles and check
performance.
Is your propeller flat? No propeller comes tracked.
Proper tracking to square the hub greatly
eliminates vibration. Combining that with propeller
balancing will reduce wear throughout the airframe.
DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING
1. Pilot error
2. Battery failure
3. Switch failure
4. Receiver failure
5. Burned-up digital servos
6. Receiver reboot
7. Hot-running regulators, servos, and
extensions
8. Failure to load-test batteries before
flight
9. Incorrect use or lack of 6.0-volt regulator
10. Inadequate propeller balancing
DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING
11. Lack of electronic choke points
12. Improper radio programming
13. Improper needle settings
14. Control flutter
15. Stripped servo gears
16. Incorrect linkage geometry
17. Inadequate servo torque
18. RF crosstalk on 72 MHz and 2.4 GHz
systems
19. Improper tank plumbing
20. Inadequate fuel filtering
21. Improper inlet- or exit-area cooling ratios
22. Lack of or inadequate baffling
23. Linkage failure
24. Nuts, bolts, and screws vibrating
loose
25. Backward control surfaces
26. Not connecting extension cords
before flight
27. Engine vapor lock
28. Improper charge rates used on
batteries
29. Incorrect CG
30. Incorrect control travels
The Order of Failure
correctly. You might guess right from time to time, but the most
common complaint with gas engines is that they vibrate, have an
erratic midrange, and run roughly.
The most common reason for the latter or hard starting is
misadjusted needle valves. Because you turn the needles doesn’t
mean they are correctly adjusted. The engine might run, but not
as it should.
Using the old pinch test, the high and low end on a two- or
four-stroke glow engine are typically adjusted 200 rpm on the
rich side of peak. A gas engine is typically adjusted 100 rpm on
the rich side of peak, with the exception of the BME 110/116; it’s
set 200 rpm on the rich side of peak.
Assuming that baffling and inlet or exit area ratios are correct,
these will be close to the final flight settings. You will make final
microadjustments with flight tests. If these settings are far from
your final flight settings, there are other issues you need to
address.
The spark plug is a good barometer of your needle setting. The
electrode should be tan in color. If it’s black, the setting is too
rich; if it’s white, the setting is too lean.
Another needle-adjustment issue is related to those who say
that two- and four-stroke engines run poorly inverted. Think
about this.
If two- and four-stroke power plants didn’t run well inverted,
would virtually every competition RC Aerobatics model in the
world have them configured that way? They run fine inverted.
What do competitors know that sport fliers don’t? The
modeler must learn how to properly set up engine fuel systems
and correctly adjust needles with a tachometer, as I have
described.
Recommendation: Don’t guess. Use a quality tachometer and
precisely set needles with the pinch test as a starting point for your
test flight, and ensure that your fuel system is set up properly.
Throughout the many years I have owned Don’s Hobby Shop, I
have spoken to tens of thousands of people, solved problems,
and helped customers set up and equip their aircraft. In the
process, I have learned that there are no new reasons why models
crash; those causes were identified many years ago.
Since we know the why, crash avoidance is not difficult.
However, the aeromodeler must learn what the issues are to
avoid the problems and apply the fixes.
The remaining causes of crashes will be featured in a future
article. Until then, your challenge is to apply the information I have
presented to your circumstances so you can fly safely and with
confidence. MA
Don Apostolico
[email protected]
44 MODEL AVIATION

38 MODEL AVIATION
This arTiclE should help those
aeromodelers who don’t know what they
don’t know by documenting the first 13 of
30 major reasons why our airplanes go in.
In my article “Crashing is Not an
Option” (in the November 2009 MA), I
wrote about equipment failures that cause
our aircraft to collide with the ground. One
can argue that the following items overlap in
cause and effect, but you will learn the main
reasons for accidents and recommendations
to avoid them.
The spreadsheet summary in my previous
article clearly shows that the chief cause of
crashes is setup error. This issue can be
solved through education, so let’s start.
1. Pilot Error: This is usually a result of
inadequate pilot training. A modeler who
understands the “flight envelope” is far less
likely to toast an airplane because of pilot
error than the modeler who doesn’t
understand basic aerodynamics and control
techniques.
To avoid needless crashes, an
aeromodeler needs to understand stall speed
vs. bank angle, load factor vs. bank angle,
how to correct for adverse yaw, torque, Pfactor,
slipstream effect, and a host of other
performance issues related to the “flight
envelope.”
The consequences of not understanding
the basics of the flight envelope are
predictable and are a major cause of
needless crashes.
Recommendation: Obtain flight training
from a competent flight instructor and a
flight-training book called Proficient
Flying, featured in the November article,
which covers all aspects of the modeling
flight envelope.
2. Battery Failure: This is, has been, and
continues to be the leading cause of crashes
outside of pilot error. There is no excuse to
bury an airplane for this reason, but it
happens often. There is no debating that if
you are flying with a single battery and it
quits, your model will crash.
August 2010 39
Don regularly checks engine rpm. A tachometer is an RC
pilot’s tool for knowing the condition of an aircraft; a change
in rpm readings lets him or her know that there’s a problem.
RC FLYING
DEFENSIVE
Recommendation: The simple solution
is to install redundant batteries and
properly load-test the battery before and
after every flight. This is especially
important if you fly Giant Scale aircraft.
3. Switch Failure: Switches that stop
working are the second leading cause of
crashes, following pilot error. If you fly a
single switch and it fails, your airplane
will crash. There is no excuse for this to
cause an accident.
Recommendation: Redundant switches
will prevent this type of crash from
occurring. If you fly Giant Scale, the
weight of a redundant switch is
negligible and immensely responsible.
4. Receiver Failure: Random receiver
failures occur for a variety of reasons,
ranging from crystal breakdown or 72 MHz
receivers going into hold because of metalto-
metal contact, to aeromodelers using 7.0
volts or more unregulated voltage into
receiver/servos rated for 4.8-6.0 volts only.
In the past two years of troubleshooting
customers’ airplanes set up with 2.4 GHz
systems, I have learned that 2.4 GHz
receivers are not immune to ignition and
electrical noise, as they were initially
believed to be. Additionally, a person’s
flying a model on a different bandwidth
An explanation of
the 13 avoidable
RC tragedies
by Don Apostolico
(2.4 GHz vs. 72 MHz) does not decrease the
potential of an electrical failure on a single
receiver.
On large aircraft we carry dual receivers
with the programming set to bring the
throttle to idle and servos to neutral if a
receiver goes into hold. If the problem is
radio frequency (RF)- or vibration-related,
the receiver will usually come out of hold
when the throttle is automatically retarded,
which relieves the vibration and reduces the
metal-to-metal or RF noise.
The result is that control is often
regained. If the receiver doesn’t come back
online, the second operational receiver
allows the model to be landed.
40 MODEL AVIATION
DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING
Some say that radio range is reduced when running dual
receivers. I have diagnosed thousands of customers’ airplanes
throughout many years with range issues. In every case, the reduced
range was caused by inadequate distances between electrical
components, metal-to-metal contact, or, in a few cases, a defective
component.
Recommendation: Install dual 72 MHz or 2.4 GHz receivers.
5. Servo Failure: When running multiple digital servos on a
common control surface and a current meter is not used to check the
servo preload for binding, your servos are probably fighting each
other. Hot-running regulators, erratic-running servos, and quickly
depleted batteries are common symptoms of servos being set up
incorrectly.
When servos fight each other, they can heat up to the extent of
melting the servo or draining the battery within a few flights. A
servo, battery, or regulator is usually blamed for being faulty, rather
than the modeler’s recognizing that the servo or battery failed
because of binding servos, linkage/hinge misalignment, or improper
radio programming.
Current tests need to be made, and appropriate adjustments need
to be made at neutral, endpoints, and midtravel to prevent excessive
current flow, to attain the servos’ normal idle current.
Because of the extreme accuracy of digital servos, proper setup
cannot be consistently and accurately attained by ear; you must use
a meter.
Recommendation: I have observed that normal digital servo
idle current for Futaba, JR, and Hitec units are typically 10-20
mAh. Check your servo specifications to be sure. Use a current
meter to identify problems and properly set up digital servos.
6. Receiver Reboot: Contrary to what many might think, this is not a
new problem. Years ago it was called “battery dropout,” and it is still
caused by the same problem; it’s just more noticeable today because
of higher-powered digital servos.
The technically sloppy setup of 20 years ago was electrically
tolerated because analog servo torque was anemic by today’s
standards. Nowadays, digital servos produce up to 400% more torque
than analog servos of the 1980s and 1990s did.
Many aeromodelers refer to this problem relative to 2.4 GHz
systems, but 72 MHz systems suffer from the same issue. Modelers
try to fix the symptom with fast-reboot receivers, heavy-gauge wire,
giant connectors, and a host of other patches. It’s not wrong to do so,
but why not fix the cause of the problem, which is improper setup?
I have a full-scale analogy for this. Let’s say that a critical piece
of equipment keeps blowing its circuit breaker on a Boeing 747.
Rather than troubleshooting and fixing the problem, the mechanic
installs a bigger circuit breaker.
Wow, I feel safe now. Ha! It might seem ridiculous, but
aeromodelers often do the equivalent.
Here is the problem. When a 72 MHz or 2.4 GHz receiver voltage
gets down to nearly 3.5 volts, the receiver shuts down (engages
battery fail-safe). If the airplane does not have enough altitude for the
battery/receiver to recover, it crashes. Don’t blame the receiver for
doing its job.
If your 6.0-volt system, which charges up to 7.0-8.4 volts
(depending on battery type), operates at 3.5 volts, you have a serious
problem. And it’s not a slow- or fast-reboot receiver.
This 40% Carden Extra 330, with 1,250 flights, features true redundancy with no choke
points. It’s equipped with twin receivers, twin batteries/regulators, and twin switches.
Many fliers use high-quality 2.4 GHz
receivers on large models and double them
as they would 72 MHz systems, for
increased redundancy.
Photos by the author
August 2010 41
G DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING
The main reasons why the voltage drops quickly is that the
modeler chooses too small of a battery for the intended application,
servos are fighting each other on the same surface, servos are
overdriving the endpoints, linkage geometry is incorrect, or the
modeler is using high-resistance 26-gauge wire.
These setup errors sap the battery, cause the voltage to go down,
and cause the receiver to shut off. The blame is often placed on
“those digital servos drawing all that current flow.”
I can’t stress enough that improper setup is at the root of most of
these crashes. The blame is often placed on faulty batteries, hotrunning
regulators, receivers that reboot too slowly, etc.
Many have said not to use a digital servo on a throttle because it
will burn out the servo. Numerous models fly successfully with
digital servos used on the throttle; talk to a helicopter pilot.
Burning up a digital servo on throttle is a setup issue—not a servo
issue. A servo that binds at the high and/or low throttle stops, draws
high current, and burns out. Some claim that engine vibration causes
the digital throttle servo to overwork. If your engine/propeller is
creating that much vibration, you have a problem but it’s not the
digital servo.
Recommendation: Fix the problem—not the symptom. Set up
travels correctly so they can’t bind, vertically and horizontally
balance and track the propeller, use a quality spinner, and properly
adjust the needle valves.
Use a current meter to ensure that servos aren’t binding, choose
the correct-size batteries, employ heavy-duty 22-gauge wire for
extensions, and correctly program your radio.
7. Hot-Running Electronics: Heat is the symptom of high current
flow. The cause goes back to improper setup.
Some aeromodelers believe that receivers can’t take high current
from high-performance digital servo setups. Let’s bury this myth
once and for all time. This faulty belief is repeated on the Internet,
and it’s a perfect example of well-meaning aeromodelers passing on
grossly inaccurate information.
Imagine JR or Futaba selling a 10-channel receiver that can
operate only six servos, because if you operate 10 servos you will
burn out the receiver from the high current flow. Rather than
accepting this information and passing it on to the next modeler,
stop and think how silly it is.
If receivers were limited in current capacity relative to our
applications, don’t you think the manufacturer would placard its
receiver to indicate not to use more than six servos on the 10-
channel receiver? Additionally, what’s the point of manufacturing a
10-channel receiver that can operate only six servos?
Most high-performance six- to 14-channel receivers are rated at
10-50 amps, depending on the receiver. I know because I called JR,
Futaba, and Spektrum to get the data.
In contrast, circuit breakers in the home are in the 15- to 30-amp
range. You run vacuum cleaners at 12-15 amps and air conditioners
at 10-30 amps or more. If your model draws anywhere near the
current that your house draws, you have a problem and it’s not the
receiver.
Experience shows that a properly set-up 35%- to 40%-size model
can draw an average of 2-4 amps in flight. Spike loads will be
higher for a split second in a high-G snap, and then current returns
to normal.
Recommendation: See items 5 and 6.
Dual servos on a control surface provides
twice the authority, but careful setup is
required to ensure that the units don’t
fight one another. Such an occurrence can
cancel out the entire model.
For redundancy, choose servos wisely.
Digital units will offer the highest power
with the best accuracy. New high-voltage
types also draw more current and require
higher-capacity batteries.
Testing batteries with the proper load
before and after flight will help identify
problems. When more power than normal
is consumed during a flight, that’s a loud
problem sign.
and, to a lesser degree, on 2.4 GHz if there is ignition noise or
metal-to-metal noise caused by loose nuts, bolts, or screws;
rattling tail wheels; loose muffler bolts; etc.
If the radio is programmed so that the servos move to neutral
and throttle is retarded to idle if these problems are experienced,
the RF noise will decrease, the receiver comes out of hold, and
control is regained. The pilot can use just enough power to land
the model, troubleshoot, and solve the problem, and the airplane
will live to fly another day.
Failure to program the fail-safe and throttle position results in
the throttle staying at full power. The malfunction keeps the
receiver in hold, and the airplane crashes because of zero control.
You might be surprised by how many aeromodelers crash their
aircraft because their fail-safe-hold features are not programmed.
There is no excuse to bury a model because you failed to properly
program a radio safety feature.
Recommendation: Take steps to ensure that there is no metalto-
metal noise. Provide enough separation between any part of
your ignition system and any part of your radio gear; 8-12 inches
is usually adequate. Set and test the fail-safe-hold settings before
the test flight.
13. Improper Needles: This oversight causes flameouts, fowled
plugs on gas engines, or overheated power plants that quit and
needlessly take down airplanes.
If you can’t quantify how many rpm on the rich side of peak
your needles are set, you are guessing that they are adjusted
August 2010 43
blow the bearings out in as little as a single gallon of fuel. If you
ask the seller if he or she has tracked and vertically balanced the
propeller and you get the deer-in-the-headlight look, beware.
Recommendation: Use high-quality, balanced spinners. Learn
how to horizontally and vertically balance and track your
propeller.
11. Electronic Choke Points: I’ve gotten calls from fliers who
have needlessly crashed more than $16,000 worth of Giant Scale
models because the built-in choke points failed. When a chokepoint
failure occurs (engineers call it single-point system failure),
the results are predictable; the model crashes. No debate, opinion,
or discussion is necessary.
Lack of redundancy is a death spike that causes crashes. A few
choke points are single battery, single switch, or single receiver
failure.
Recommendation: Evaluate your aircraft for choke points and
avoid them.
12. Poor Programming: Failure to properly program a radio will
result in a crash if random RF is introduced. Conversely, proper
programming usually saves a model if random RF problems occur.
Let’s examine a classic programming error. Today’s high-end
radios have a fail-safe-hold feature that is designed to allow the
flier to program preselected control positions, in case an RF
problem occurs.
That could be RF interference experienced on 72 MHz radios
This laser temperature gun is used to
check cylinder head temperatures, to
measure baffle and cooling efficiency.
Normal is 180°-220° for most gas engines.
Use a meter instead of your ear.
A high-quality device such as the
Fromeco TNC Tachometer
(accurate to 1 rpm) makes it
easier to set needles and check
performance.
Is your propeller flat? No propeller comes tracked.
Proper tracking to square the hub greatly
eliminates vibration. Combining that with propeller
balancing will reduce wear throughout the airframe.
DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING
1. Pilot error
2. Battery failure
3. Switch failure
4. Receiver failure
5. Burned-up digital servos
6. Receiver reboot
7. Hot-running regulators, servos, and
extensions
8. Failure to load-test batteries before
flight
9. Incorrect use or lack of 6.0-volt regulator
10. Inadequate propeller balancing
DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING DEFENSIVE RC FLYING
11. Lack of electronic choke points
12. Improper radio programming
13. Improper needle settings
14. Control flutter
15. Stripped servo gears
16. Incorrect linkage geometry
17. Inadequate servo torque
18. RF crosstalk on 72 MHz and 2.4 GHz
systems
19. Improper tank plumbing
20. Inadequate fuel filtering
21. Improper inlet- or exit-area cooling ratios
22. Lack of or inadequate baffling
23. Linkage failure
24. Nuts, bolts, and screws vibrating
loose
25. Backward control surfaces
26. Not connecting extension cords
before flight
27. Engine vapor lock
28. Improper charge rates used on
batteries
29. Incorrect CG
30. Incorrect control travels
The Order of Failure
correctly. You might guess right from time to time, but the most
common complaint with gas engines is that they vibrate, have an
erratic midrange, and run roughly.
The most common reason for the latter or hard starting is
misadjusted needle valves. Because you turn the needles doesn’t
mean they are correctly adjusted. The engine might run, but not
as it should.
Using the old pinch test, the high and low end on a two- or
four-stroke glow engine are typically adjusted 200 rpm on the
rich side of peak. A gas engine is typically adjusted 100 rpm on
the rich side of peak, with the exception of the BME 110/116; it’s
set 200 rpm on the rich side of peak.
Assuming that baffling and inlet or exit area ratios are correct,
these will be close to the final flight settings. You will make final
microadjustments with flight tests. If these settings are far from
your final flight settings, there are other issues you need to
address.
The spark plug is a good barometer of your needle setting. The
electrode should be tan in color. If it’s black, the setting is too
rich; if it’s white, the setting is too lean.
Another needle-adjustment issue is related to those who say
that two- and four-stroke engines run poorly inverted. Think
about this.
If two- and four-stroke power plants didn’t run well inverted,
would virtually every competition RC Aerobatics model in the
world have them configured that way? They run fine inverted.
What do competitors know that sport fliers don’t? The
modeler must learn how to properly set up engine fuel systems
and correctly adjust needles with a tachometer, as I have
described.
Recommendation: Don’t guess. Use a quality tachometer and
precisely set needles with the pinch test as a starting point for your
test flight, and ensure that your fuel system is set up properly.
Throughout the many years I have owned Don’s Hobby Shop, I
have spoken to tens of thousands of people, solved problems,
and helped customers set up and equip their aircraft. In the
process, I have learned that there are no new reasons why models
crash; those causes were identified many years ago.
Since we know the why, crash avoidance is not difficult.
However, the aeromodeler must learn what the issues are to
avoid the problems and apply the fixes.
The remaining causes of crashes will be featured in a future
article. Until then, your challenge is to apply the information I have
presented to your circumstances so you can fly safely and with
confidence. MA
Don Apostolico
[email protected]
44 MODEL AVIATION