Beginner's Guide to Gas Engines-2012/04

G low engines have a solid RC
history and have been around
for a long time. Although glow
engines are extremely popular, the first
ignition engines used in FF models
were gasoline burners. Today you can
find big, four-cylinder, horizontally
opposed, “boxer” engines in the largest
3-D aerobatic airplanes and a new
crop of smaller displacement engines
intended for the .60 to .90 airplane
size.
This article is intended to give a
newcomer to gasoline engines
a solid understanding about the
operation and function of these
user-friendly RC power plants.
Without understanding the basics,
it is easy to become intimidated by
any internal combustion engine.
If you can successfully operate a
lawn mower or a chain saw, then
you’ll find the care and feeding
of RC gas engines is no different.
Let’s take a closer look.
How Gas Engines Run
All two-stroke gasoline engines,
regardless of size or ignition type, require
three things to operate: fuel, air, and heat.
Take any one of these away
and your engine won’t run.
So let’s focus on each one.
Fuel
Start with some fresh
87- to 89-octane gasoline
from the gas station and
buy a new two-gallon
jug to store it in. Your
fuel system—including
For the Giant Scale warbird
crowd, the Zenoah G-62 is the
granddaddy of gas burners.
30 Model Aviation April 2012 www.ModelAviation.com
the fuel tank, fuel line, hardware, and
stopper—needs to be gasoline grade.
Silicone fuel lines and tank stoppers
intended for glow fuel don’t like gasoline
and will eventually degrade when
exposed to gasoline.
The yellow-colored gas fuel line,
available from Sullivan Products, is
what you should use. Sullivan Products
also offers gasoline-conversion kits
that contain all the fittings needed,
along with a short piece of gasolinecompatible
fuel tubing. Du-Bro also
offers gasoline-grade fuel tank stoppers,
fuel fillers, filters, and other gasolinegrade
hardware.
For proper engine lubrication, you’ll
have to mix oil into the gasoline. Any
good oil intended for air-cooled, twostroke
engines will do the trick. You
should be able to find it in a hobby shop
as well as at small engine, motorcycle,
and marine engine shops.
For the first gallon of fuel you run
through your engine, a good mix is
roughly 30:1, and then after that you
can switch to a 40:1 mix or whatever
mix ratio your engine manufacturer
recommends.
Several engine manufacturers warn
against adding any alcohol to your fuel,
adjusted so it can correctly mix air
with the fuel so it can be ignited in the
combustion chamber. Each carburetor
has two needle valves: the high-speed
(or top-end) and low-speed (or idle)
mixtures.
When you pull your new engine out
of its box, these needle valves are usually
set close to their proper settings. When
you first run your engine, let it warm up
slightly, then check its idle performance.
A good idle setting produces a good
transition from idle to full power.
and I agree, but I have not experienced
any ill effects burning gasoline from
the gas station pumps that contains
methanol. Also, there is no need for
higher-octane gas or
expensive aviation gas,
although many Giant
Scale pilots swear by
it. It’s up to you.
Air
Your carburetor
needs to be properly
The DLE 55cc gas engine, sold by Great
Planes, is popular with aerobatics pilots.
The rear-induction engine has an electronic
ignition system.
Right: The Fuji gasoline engine line,
available from Great Planes, is a popular,
reliable brand. Fuji engines come in a
variety of sizes and configurations to suit
nearly any type of RC airplane.
One of the most popular midsize
engines is the Zenoah G-23. The
23cc displacement engine has a
magneto ignition. The flywheel
is located in the back under
the attachment plate.
Photos by the author
www.ModelAviation.com April 2012 Model Aviation 31
For electronic ignition-equipped engines,
a magnetic pickup module and a small
magnet are used to fire the spark plug. The
electronic-ignition module is a separate
unit and it should be carefully installed
following instructions. Foam padding
can cause it to overheat.
This Walbro carburetor has the top cap
removed to show the internal filter screen.
If the engine acts up, clean the screen and
ensure that the gasket is in good shape.
also important to check the gap between
the triggering magnet and the pickup
sensor to produce a strong spark. The
battery pack powering the electronic
ignition system should be fully charged
at the beginning of each flying day.
Color Coding for Your Spark Plug
A good thing to do regularly is check
the condition of your spark plug. If
needed, adjust its gap, which should be
Slowly advance the throttle to run the
engine at full power. Don’t try to set the
high end by sound; check the maximum
rpm with a digital tachometer. Slowly
lean out the high-speed needle a bit at a
time and then check the rpm with the
tachometer.
When you get to a point where
further leaning does not result in
an increase in rpm, you are at the
maximum power setting. Now richen it
slightly and check with the tachometer
for a 200- to 300-rpm drop.
Check the low speed again. Adjusting
one needle valve has a slight affect on
the other, so it can take a little effort to
zero in on good overall performance.
Once set, most gasoline engines won’t
need their needle valves adjusted for a
long time.
As a safety note, always shut down
the engine before making adjustments
to the needle valves. Make adjustments
an eighth-turn at a time and check the
engine rpm with a digital tachometer.
AMA regulations also require the
installation of an ignition grounding/
kill switch (for magneto engines) or an
on/off switch for an electronic ignition
system. A kill switch allows you to
quickly shut down your engine and
it also prevents accidental starts. You
should also consider adding an onboard,
radio-operated kill switch.
Heat
The heat or fire part of the equation
is produced by the engine’s ignition
system. Whether you have a magneto or
an electronic ignition system, it needs to
operate properly to fire the spark plug.
Magnetos consist of a flywheel, a coil,
and a condenser to produce the spark
energy. The flywheel gap needs to be set
properly. Typically 0.015 to 0.020 inch
is right, but refer to your engine manual
to be sure.
With electronic ignition systems, it is
Popular aircraft in the 50 cc
size range, such as this Great
Planes 25% Pitts M-12S, include
biplanes, aerobatic aircraft,
warbirds, and sport models.
32 Model Aviation April 2012 www.ModelAviation.com
The new O.S. GT55 is a greatrunning
55cc power plant. It
comes with a compact size
spark plug and looks more like a
giant glow engine than a typical
gasoline burner.
open the throttle fully. Turn the ignition
switch to the on position and keep the
choke closed.
Use an electric starter or a chicken
stick and flip the propeller several
times until you hear the engine rumble,
telling you that it has enough prime
and is ready to start. Open the choke
and reduce the throttle to a few clicks
above idle. Spin the propeller again and
the engine should start. Let it warm up
before testing the engine’s performance.
What’s Wrong?
So you can’t get the engine to fire up.
What do you do next? If you are hand
propping your engine, check the position
of your propeller relative to the magneto
magnets or the electronic ignition’s
triggering magnet.
Often a small adjustment in blade
set before you install it in your engine.
Depending on the brand you use, it
should be set from 0.025 to 0.035 inch.
For optimum engine performance,
I usually replace my spark plugs every
two years or so, depending on how often
I run the engine. Check the spark plug
after every gallon of fuel. A black, wet,
oil-soaked plug means you’re running
your engine too rich; a white or silvery
color means you are running your engine
too lean.
A properly adjusted engine and
carburetor will produce a light- to
medium-brown color on the bottom of
the spark plug.
Startup Procedure
For constant starts, you should always
use the same starting procedure. First,
always have a flying buddy secure the
tail of your model and make certain the
propeller is properly tightened down.
Switch the ignition kill switch off,
close the choke, and flip the propeller
a few times. The fuel should begin to
fill the fuel line going to the carburetor.
When the gas reaches the fuel fitting,
Oil/Gas Mix
What is a fuel mix
exactly? It’s the amount
of two-stroke engine
lubrication oil (in
ounces) you add to your
gallon of gasoline. Here
are the most common RC
gasoline engine ratios.
RATIO OZ./GALLON
100:1 1.28
90:1 1.42
75:1 1.7
64:1 2
50:1 2.5
40:1 3.2
32:1 4
24:1 5.3
16:1 8
Below: This is the basic setup for a Zenoah G-26EI.
This shows the needle locations on a typical gas engine.
position can make a big difference. I like
to start my engines using my left hand
and set the propeller so that the blade is
at 11 o’clock and I swing it downward
to the 7 o’clock position. The magneto
produces spark at approximately 9
o’clock. If you aren’t sure about hand
propping, there’s nothing wrong with
using an electric starter.
• If your engine starts, but then
quickly dies, this indicates a fuel-draw
issue. Check your fuel lines for any
pinch points, blockage, or something
preventing the flow of fuel.
• If the carburetor won’t draw any
fuel, check to make sure the needle
valves are open. Also, check to make
sure the carburetor is snugly fastened
and positioned so the small pressure
passage from the engine to the
carburetor isn’t blocked.
• Check the internal screen filter and
make sure it is clean. It’s located under
the top carburetor cap (held in place
with a center screw.) If it’s dirty, remove
it and flush it with some fresh gas.
• Check that the engine cylinder is
tightly fastened to the engine case and
that the gasket is undamaged. A small
air leak will prevent the engine from
starting.
• Do you have a good spark? If not,
check the kill switch. With electronic
ignitions, make sure the battery is fully
charged and the timing sensor wire is
still connected.
Pumper Carburetors
Most gas engines use a Walbro or
some other type of pumper carburetor.
These have built-in diaphragms that are
driven by pulse pressure caused by the
up-and-down motion of the piston. This
draws the fuel into the carburetor and
also makes fuel tank placement in the
airplane less critical than that in a glowpowered
airplane.
The Walbro carburetor has two
needle valves on the left side of the
carburetor body. A third larger screw
is the idle adjustment screw and it has
a tapered end that adjusts the throttle
stop position. In most cases, you can
remove this screw and use your servo’s
travel adjustment to set your idle
position.
Gasoline engines are simple to operate,
and after you understand the basics,
you will find that they are easy to
run and user-friendly. They produce
good torque and when set up with the
correct propeller, will provide years of
trouble-free service. They come in a
variety of displacement and types. Give
gas power a try; you’ll quickly become
a believer.
—Aaron Baldwick
[email protected]
Sources:
Sullivan
(410) 732-3500
www.sullivanproducts.com
Du-Bro
(800) 848-9411.
www.dubro.com
O.S. Engines
(800) 637-7660
www.osengines.com
Zenoah Engines
(800) 338-4639
www.zenoah.com
DLE Engines
(800) 637-7660
www.dle-engines.com
Fuji Engines
(800) 637-7660
www.fuji-imvac.com

G low engines have a solid RC
history and have been around
for a long time. Although glow
engines are extremely popular, the first
ignition engines used in FF models
were gasoline burners. Today you can
find big, four-cylinder, horizontally
opposed, “boxer” engines in the largest
3-D aerobatic airplanes and a new
crop of smaller displacement engines
intended for the .60 to .90 airplane
size.
This article is intended to give a
newcomer to gasoline engines
a solid understanding about the
operation and function of these
user-friendly RC power plants.
Without understanding the basics,
it is easy to become intimidated by
any internal combustion engine.
If you can successfully operate a
lawn mower or a chain saw, then
you’ll find the care and feeding
of RC gas engines is no different.
Let’s take a closer look.
How Gas Engines Run
All two-stroke gasoline engines,
regardless of size or ignition type, require
three things to operate: fuel, air, and heat.
Take any one of these away
and your engine won’t run.
So let’s focus on each one.
Fuel
Start with some fresh
87- to 89-octane gasoline
from the gas station and
buy a new two-gallon
jug to store it in. Your
fuel system—including
For the Giant Scale warbird
crowd, the Zenoah G-62 is the
granddaddy of gas burners.
30 Model Aviation April 2012 www.ModelAviation.com
the fuel tank, fuel line, hardware, and
stopper—needs to be gasoline grade.
Silicone fuel lines and tank stoppers
intended for glow fuel don’t like gasoline
and will eventually degrade when
exposed to gasoline.
The yellow-colored gas fuel line,
available from Sullivan Products, is
what you should use. Sullivan Products
also offers gasoline-conversion kits
that contain all the fittings needed,
along with a short piece of gasolinecompatible
fuel tubing. Du-Bro also
offers gasoline-grade fuel tank stoppers,
fuel fillers, filters, and other gasolinegrade
hardware.
For proper engine lubrication, you’ll
have to mix oil into the gasoline. Any
good oil intended for air-cooled, twostroke
engines will do the trick. You
should be able to find it in a hobby shop
as well as at small engine, motorcycle,
and marine engine shops.
For the first gallon of fuel you run
through your engine, a good mix is
roughly 30:1, and then after that you
can switch to a 40:1 mix or whatever
mix ratio your engine manufacturer
recommends.
Several engine manufacturers warn
against adding any alcohol to your fuel,
adjusted so it can correctly mix air
with the fuel so it can be ignited in the
combustion chamber. Each carburetor
has two needle valves: the high-speed
(or top-end) and low-speed (or idle)
mixtures.
When you pull your new engine out
of its box, these needle valves are usually
set close to their proper settings. When
you first run your engine, let it warm up
slightly, then check its idle performance.
A good idle setting produces a good
transition from idle to full power.
and I agree, but I have not experienced
any ill effects burning gasoline from
the gas station pumps that contains
methanol. Also, there is no need for
higher-octane gas or
expensive aviation gas,
although many Giant
Scale pilots swear by
it. It’s up to you.
Air
Your carburetor
needs to be properly
The DLE 55cc gas engine, sold by Great
Planes, is popular with aerobatics pilots.
The rear-induction engine has an electronic
ignition system.
Right: The Fuji gasoline engine line,
available from Great Planes, is a popular,
reliable brand. Fuji engines come in a
variety of sizes and configurations to suit
nearly any type of RC airplane.
One of the most popular midsize
engines is the Zenoah G-23. The
23cc displacement engine has a
magneto ignition. The flywheel
is located in the back under
the attachment plate.
Photos by the author
www.ModelAviation.com April 2012 Model Aviation 31
For electronic ignition-equipped engines,
a magnetic pickup module and a small
magnet are used to fire the spark plug. The
electronic-ignition module is a separate
unit and it should be carefully installed
following instructions. Foam padding
can cause it to overheat.
This Walbro carburetor has the top cap
removed to show the internal filter screen.
If the engine acts up, clean the screen and
ensure that the gasket is in good shape.
also important to check the gap between
the triggering magnet and the pickup
sensor to produce a strong spark. The
battery pack powering the electronic
ignition system should be fully charged
at the beginning of each flying day.
Color Coding for Your Spark Plug
A good thing to do regularly is check
the condition of your spark plug. If
needed, adjust its gap, which should be
Slowly advance the throttle to run the
engine at full power. Don’t try to set the
high end by sound; check the maximum
rpm with a digital tachometer. Slowly
lean out the high-speed needle a bit at a
time and then check the rpm with the
tachometer.
When you get to a point where
further leaning does not result in
an increase in rpm, you are at the
maximum power setting. Now richen it
slightly and check with the tachometer
for a 200- to 300-rpm drop.
Check the low speed again. Adjusting
one needle valve has a slight affect on
the other, so it can take a little effort to
zero in on good overall performance.
Once set, most gasoline engines won’t
need their needle valves adjusted for a
long time.
As a safety note, always shut down
the engine before making adjustments
to the needle valves. Make adjustments
an eighth-turn at a time and check the
engine rpm with a digital tachometer.
AMA regulations also require the
installation of an ignition grounding/
kill switch (for magneto engines) or an
on/off switch for an electronic ignition
system. A kill switch allows you to
quickly shut down your engine and
it also prevents accidental starts. You
should also consider adding an onboard,
radio-operated kill switch.
Heat
The heat or fire part of the equation
is produced by the engine’s ignition
system. Whether you have a magneto or
an electronic ignition system, it needs to
operate properly to fire the spark plug.
Magnetos consist of a flywheel, a coil,
and a condenser to produce the spark
energy. The flywheel gap needs to be set
properly. Typically 0.015 to 0.020 inch
is right, but refer to your engine manual
to be sure.
With electronic ignition systems, it is
Popular aircraft in the 50 cc
size range, such as this Great
Planes 25% Pitts M-12S, include
biplanes, aerobatic aircraft,
warbirds, and sport models.
32 Model Aviation April 2012 www.ModelAviation.com
The new O.S. GT55 is a greatrunning
55cc power plant. It
comes with a compact size
spark plug and looks more like a
giant glow engine than a typical
gasoline burner.
open the throttle fully. Turn the ignition
switch to the on position and keep the
choke closed.
Use an electric starter or a chicken
stick and flip the propeller several
times until you hear the engine rumble,
telling you that it has enough prime
and is ready to start. Open the choke
and reduce the throttle to a few clicks
above idle. Spin the propeller again and
the engine should start. Let it warm up
before testing the engine’s performance.
What’s Wrong?
So you can’t get the engine to fire up.
What do you do next? If you are hand
propping your engine, check the position
of your propeller relative to the magneto
magnets or the electronic ignition’s
triggering magnet.
Often a small adjustment in blade
set before you install it in your engine.
Depending on the brand you use, it
should be set from 0.025 to 0.035 inch.
For optimum engine performance,
I usually replace my spark plugs every
two years or so, depending on how often
I run the engine. Check the spark plug
after every gallon of fuel. A black, wet,
oil-soaked plug means you’re running
your engine too rich; a white or silvery
color means you are running your engine
too lean.
A properly adjusted engine and
carburetor will produce a light- to
medium-brown color on the bottom of
the spark plug.
Startup Procedure
For constant starts, you should always
use the same starting procedure. First,
always have a flying buddy secure the
tail of your model and make certain the
propeller is properly tightened down.
Switch the ignition kill switch off,
close the choke, and flip the propeller
a few times. The fuel should begin to
fill the fuel line going to the carburetor.
When the gas reaches the fuel fitting,
Oil/Gas Mix
What is a fuel mix
exactly? It’s the amount
of two-stroke engine
lubrication oil (in
ounces) you add to your
gallon of gasoline. Here
are the most common RC
gasoline engine ratios.
RATIO OZ./GALLON
100:1 1.28
90:1 1.42
75:1 1.7
64:1 2
50:1 2.5
40:1 3.2
32:1 4
24:1 5.3
16:1 8
Below: This is the basic setup for a Zenoah G-26EI.
This shows the needle locations on a typical gas engine.
position can make a big difference. I like
to start my engines using my left hand
and set the propeller so that the blade is
at 11 o’clock and I swing it downward
to the 7 o’clock position. The magneto
produces spark at approximately 9
o’clock. If you aren’t sure about hand
propping, there’s nothing wrong with
using an electric starter.
• If your engine starts, but then
quickly dies, this indicates a fuel-draw
issue. Check your fuel lines for any
pinch points, blockage, or something
preventing the flow of fuel.
• If the carburetor won’t draw any
fuel, check to make sure the needle
valves are open. Also, check to make
sure the carburetor is snugly fastened
and positioned so the small pressure
passage from the engine to the
carburetor isn’t blocked.
• Check the internal screen filter and
make sure it is clean. It’s located under
the top carburetor cap (held in place
with a center screw.) If it’s dirty, remove
it and flush it with some fresh gas.
• Check that the engine cylinder is
tightly fastened to the engine case and
that the gasket is undamaged. A small
air leak will prevent the engine from
starting.
• Do you have a good spark? If not,
check the kill switch. With electronic
ignitions, make sure the battery is fully
charged and the timing sensor wire is
still connected.
Pumper Carburetors
Most gas engines use a Walbro or
some other type of pumper carburetor.
These have built-in diaphragms that are
driven by pulse pressure caused by the
up-and-down motion of the piston. This
draws the fuel into the carburetor and
also makes fuel tank placement in the
airplane less critical than that in a glowpowered
airplane.
The Walbro carburetor has two
needle valves on the left side of the
carburetor body. A third larger screw
is the idle adjustment screw and it has
a tapered end that adjusts the throttle
stop position. In most cases, you can
remove this screw and use your servo’s
travel adjustment to set your idle
position.
Gasoline engines are simple to operate,
and after you understand the basics,
you will find that they are easy to
run and user-friendly. They produce
good torque and when set up with the
correct propeller, will provide years of
trouble-free service. They come in a
variety of displacement and types. Give
gas power a try; you’ll quickly become
a believer.
—Aaron Baldwick
[email protected]
Sources:
Sullivan
(410) 732-3500
www.sullivanproducts.com
Du-Bro
(800) 848-9411.
www.dubro.com
O.S. Engines
(800) 637-7660
www.osengines.com
Zenoah Engines
(800) 338-4639
www.zenoah.com
DLE Engines
(800) 637-7660
www.dle-engines.com
Fuji Engines
(800) 637-7660
www.fuji-imvac.com