maintenance, and more give you reliable
information about all the “operational
aspects” of model engines. These chapters
not only tell you how to do things; they
explain why.
A topic that Dave’s book doesn’t cover is
propeller selection. I don’t know of any
book that does. Maybe that’s because the
subject is so much more of an art than a
science.
The propeller pulls our models (ducted
fans excepted) through the sky. No matter
how well your engine runs, if it’s spinning
an “improper prop,” your model won’t
perform its best.
And propeller selection depends just as
much on the airplane as it does on the
engine! A slow sport flyer needs a bigger,
flatter-pitch propeller than a speedy
airplane. That seems obvious, yet blade
shape, material, and even stiffness can have
more of an effect than you might think.
It’s not nearly good enough to specify,
say, a 10 x 5 propeller for flying a model.
Propellers of different makes and materials
with the same nominal diameter-pitch
numbers can vary enormously in how well
they fly an airplane.
Awhile back I got hooked on a certain
kind of model engine. I owned
approximately 10 and flew them in FF, CL,
and RC airplanes. I did plenty of carefully
observed test flying to find the optimum
propellers.
I was surprised to discover that each
model needed a different propeller to
perform its best! I used the same fuel and
glow plugs in all the engines too. (Maybe I
could have improved flight performance
even more had I tried altering the plugs and
fuel.)
It is usually a subjective task to
determine the best propeller for a certain
airplane-engine combination. However,
with today’s readily available handheld
radar “speed guns,” a more accurate
method could be used.
If a propeller were 100% efficient it
would pull its vehicle at a speed (in mph)
equal to its pitch (in inches) multiplied by
its rpm (in thousands). A 10 x 5 propeller
spinning at 12,000 rpm would produce an
airplane velocity of 60 mph (5 x 12) at
100% efficiency.
However, we all know that 100%
efficiency is unattainable. To find out what
efficiency a propeller actually delivers on a
given model and engine, divide the
measured speed in flight by the theoretical
speed.
Say the model flies at 42 mph. That
shows that the propeller is working at 70%
efficiency. (That’s pretty good! Some of
the propellers I’ve flight tested came out at
less than 40%—and even the best never
exceeded 75%.)
In general, propellers work more
efficiently at low rpm. Have you ever
TWO-STROKE model engines are
essentially simple devices. With their few
moving parts, it doesn’t seem as though
there could be much complication in
operating them or many things to go wrong.
Yet that’s far from true. In spite of their
simplicity, model-engine operation
involves several subtle interactions that can
greatly affect their power output and
dependability.
One way to educate yourself about these
power plants is personal experience.
Learning that way can take a long time,
though.
A better way is through other people’s
experiences. There’s certainly no lack of
information these days about that—
especially on the Web. Internet forums such
as RCUniverse contain an incredible
amount of data about model engines:
opinions, techniques, ideas, complaints,
suggestions, problems, recommendations,
etc.
Yet much of that model-engine
information is dubious and even
contradictory. Some of it is plain wrong. A
far better source of dependable data on
model airplane engines is Dave Gierke’s
book 2-Stroke Glow Engines for R/C Model
Aircraft.
Published by Air Age, Inc. (which
publishes Model Airplane News)—and
available from AMA’s online store—this
book covers in exquisite detail the design
and operation of two-strokers in their many
versions. It explains everything!
The latter half of the book is particularly
useful to RC fliers. Its well-illustrated
chapters about fuels, starting, break-in,
adjustment, idling technique, cleaning and
April 2007 97
A review of Dave Gierke’s new 2-Stroke Glow Engines for R/C Model Aircraft book
Also included in this column:
• Propellers: more art
than science?
• New Brodak .049
• Engine reassembly tip
The Engine Shop Joe Wagner | [email protected]
Left: Dave Gierke’s well-written, thoroughly
illustrated book tells all about two-stroke
glow power. Above: A sampling of the book’s
complete, easy-to-read information, provided
for beginner and expert power modelers.
Reliable for years, the author’s Cox .15
seized in flight from using only one tankful
of a friend’s favorite glow fuel.
watched one of the new “wind farm” electrical power generators
working and been surprised by how slowly their blades rotate?
There’s a good reason for that, and it applies to model engines
too.
High rpm wastes energy in producing useless turbulence and
noise. Slower spinning results in more of the available energy
being converted into useful work. A few kinds of models, such as
racing airplanes and competition FF aircraft, require high rpm,
but most don’t.
Another way I’ve found to increase my engines’ in-flight
power efficiency is to boost my fuel’s oil content. Many modelers
think minimizing model-engine fuel’s lubricant content will add
power. After all, the part of the fuel that burns is what produces
power, right?
Yes, that’s right. But oil does much more inside a model
engine than make the moving parts slippery. For one thing, it
improves compression.
Another thing it does is absorb excess heat and in a way act
something like the water injection used by World War II fighterairplane
engines for “War Emergency Power.” Reducing the oil
percentage in model-engine fuel can reduce power output to zero!
One day I was having such fun flying my CL Chickadee that I
used up all the fuel I had brought with me. To save me the trouble
of driving home for more, a friend offered to let me use some of
his. Without thinking about it, I accepted.
I filled up the Chickadee’s tank with my buddy’s glow fuel
and started its Cox Medallion .15 engine. It roared to life
immediately. But the flight turned out to be quite short; the
engine seized after just a few laps. The fuel’s low oil content did
it; Cox engines require lots of castor in their fuel.
On the topic of CL flying, Brodak Manufacturing (one of the
supreme sources for CL flying supplies of all kinds) has come out
with another CL engine. It’s an .049 and an addition to, rather
than a replacement for, the Chinese-made 1/2A Brodak engines I
described in an earlier column.
The new Brodak .049 Mark II is a Schnuerle-ported design
and has a chrome-plated aluminum piston running in an
aluminum cylinder. That should make it a lightweight engine, but
it’s slightly heavier than the old Cox “Killer Bee” .049.
However, the Brodak .049 Mk II is ruggedly built with a hefty
crankshaft and case casting. It uses a standard glow plug and its
cylinder is retained with three easily accessible socket-head
screws. (That feature can come in handy. The engine is supplied
with extra cylinder-head gaskets to make compression adjustment
easy.) The .049 runs well on fuels with 10%-20% nitromethane,
but it needs 23%-26% oil content.
No muffler or RC throttle is available for the new Brodak
.049. It’s meant for use in 1/2A CL Stunt (Precision Aerobatics)
and Combat models. I think it would also make an excellent
power plant for some of yesteryear’s sport FF models such as the
Midwest Sniffer (now available again from BMJR Model
Products).
I have a “handy hint” to share. When you’re reassembling an
engine with gaskets, after thoroughly cleaning the sealing surfaces,
dip the gasket (a new one if possible) in castor oil and let it soak
for a few minutes before installing. Put a little castor on the screws
too.
Then when you reassemble the engine, the castor oil will help
in tightening the screws firmly. In a few days the oil film’s
thickening from time and oxidation will ensure an airtight seal on
the gasketed surfaces and protection against screws loosening from
vibration.
(It’s good practice to retighten the screws after a couple days.
Gaskets can and do compress.) MA
Above: Propeller
brands and types
can make a huge
difference in model
p e r f o r m a n c e .
Specifying diameter
and pitch isn’t
enough.
Left: Brodak’s
newest CL engine.
This potent .049
has no muffler or
throttle. It will be
hard to beat in
events such as 1/2A
Combat.
Edition: Model Aviation - 2007/04
Page Numbers: 97,98
Edition: Model Aviation - 2007/04
Page Numbers: 97,98
maintenance, and more give you reliable
information about all the “operational
aspects” of model engines. These chapters
not only tell you how to do things; they
explain why.
A topic that Dave’s book doesn’t cover is
propeller selection. I don’t know of any
book that does. Maybe that’s because the
subject is so much more of an art than a
science.
The propeller pulls our models (ducted
fans excepted) through the sky. No matter
how well your engine runs, if it’s spinning
an “improper prop,” your model won’t
perform its best.
And propeller selection depends just as
much on the airplane as it does on the
engine! A slow sport flyer needs a bigger,
flatter-pitch propeller than a speedy
airplane. That seems obvious, yet blade
shape, material, and even stiffness can have
more of an effect than you might think.
It’s not nearly good enough to specify,
say, a 10 x 5 propeller for flying a model.
Propellers of different makes and materials
with the same nominal diameter-pitch
numbers can vary enormously in how well
they fly an airplane.
Awhile back I got hooked on a certain
kind of model engine. I owned
approximately 10 and flew them in FF, CL,
and RC airplanes. I did plenty of carefully
observed test flying to find the optimum
propellers.
I was surprised to discover that each
model needed a different propeller to
perform its best! I used the same fuel and
glow plugs in all the engines too. (Maybe I
could have improved flight performance
even more had I tried altering the plugs and
fuel.)
It is usually a subjective task to
determine the best propeller for a certain
airplane-engine combination. However,
with today’s readily available handheld
radar “speed guns,” a more accurate
method could be used.
If a propeller were 100% efficient it
would pull its vehicle at a speed (in mph)
equal to its pitch (in inches) multiplied by
its rpm (in thousands). A 10 x 5 propeller
spinning at 12,000 rpm would produce an
airplane velocity of 60 mph (5 x 12) at
100% efficiency.
However, we all know that 100%
efficiency is unattainable. To find out what
efficiency a propeller actually delivers on a
given model and engine, divide the
measured speed in flight by the theoretical
speed.
Say the model flies at 42 mph. That
shows that the propeller is working at 70%
efficiency. (That’s pretty good! Some of
the propellers I’ve flight tested came out at
less than 40%—and even the best never
exceeded 75%.)
In general, propellers work more
efficiently at low rpm. Have you ever
TWO-STROKE model engines are
essentially simple devices. With their few
moving parts, it doesn’t seem as though
there could be much complication in
operating them or many things to go wrong.
Yet that’s far from true. In spite of their
simplicity, model-engine operation
involves several subtle interactions that can
greatly affect their power output and
dependability.
One way to educate yourself about these
power plants is personal experience.
Learning that way can take a long time,
though.
A better way is through other people’s
experiences. There’s certainly no lack of
information these days about that—
especially on the Web. Internet forums such
as RCUniverse contain an incredible
amount of data about model engines:
opinions, techniques, ideas, complaints,
suggestions, problems, recommendations,
etc.
Yet much of that model-engine
information is dubious and even
contradictory. Some of it is plain wrong. A
far better source of dependable data on
model airplane engines is Dave Gierke’s
book 2-Stroke Glow Engines for R/C Model
Aircraft.
Published by Air Age, Inc. (which
publishes Model Airplane News)—and
available from AMA’s online store—this
book covers in exquisite detail the design
and operation of two-strokers in their many
versions. It explains everything!
The latter half of the book is particularly
useful to RC fliers. Its well-illustrated
chapters about fuels, starting, break-in,
adjustment, idling technique, cleaning and
April 2007 97
A review of Dave Gierke’s new 2-Stroke Glow Engines for R/C Model Aircraft book
Also included in this column:
• Propellers: more art
than science?
• New Brodak .049
• Engine reassembly tip
The Engine Shop Joe Wagner | [email protected]
Left: Dave Gierke’s well-written, thoroughly
illustrated book tells all about two-stroke
glow power. Above: A sampling of the book’s
complete, easy-to-read information, provided
for beginner and expert power modelers.
Reliable for years, the author’s Cox .15
seized in flight from using only one tankful
of a friend’s favorite glow fuel.
watched one of the new “wind farm” electrical power generators
working and been surprised by how slowly their blades rotate?
There’s a good reason for that, and it applies to model engines
too.
High rpm wastes energy in producing useless turbulence and
noise. Slower spinning results in more of the available energy
being converted into useful work. A few kinds of models, such as
racing airplanes and competition FF aircraft, require high rpm,
but most don’t.
Another way I’ve found to increase my engines’ in-flight
power efficiency is to boost my fuel’s oil content. Many modelers
think minimizing model-engine fuel’s lubricant content will add
power. After all, the part of the fuel that burns is what produces
power, right?
Yes, that’s right. But oil does much more inside a model
engine than make the moving parts slippery. For one thing, it
improves compression.
Another thing it does is absorb excess heat and in a way act
something like the water injection used by World War II fighterairplane
engines for “War Emergency Power.” Reducing the oil
percentage in model-engine fuel can reduce power output to zero!
One day I was having such fun flying my CL Chickadee that I
used up all the fuel I had brought with me. To save me the trouble
of driving home for more, a friend offered to let me use some of
his. Without thinking about it, I accepted.
I filled up the Chickadee’s tank with my buddy’s glow fuel
and started its Cox Medallion .15 engine. It roared to life
immediately. But the flight turned out to be quite short; the
engine seized after just a few laps. The fuel’s low oil content did
it; Cox engines require lots of castor in their fuel.
On the topic of CL flying, Brodak Manufacturing (one of the
supreme sources for CL flying supplies of all kinds) has come out
with another CL engine. It’s an .049 and an addition to, rather
than a replacement for, the Chinese-made 1/2A Brodak engines I
described in an earlier column.
The new Brodak .049 Mark II is a Schnuerle-ported design
and has a chrome-plated aluminum piston running in an
aluminum cylinder. That should make it a lightweight engine, but
it’s slightly heavier than the old Cox “Killer Bee” .049.
However, the Brodak .049 Mk II is ruggedly built with a hefty
crankshaft and case casting. It uses a standard glow plug and its
cylinder is retained with three easily accessible socket-head
screws. (That feature can come in handy. The engine is supplied
with extra cylinder-head gaskets to make compression adjustment
easy.) The .049 runs well on fuels with 10%-20% nitromethane,
but it needs 23%-26% oil content.
No muffler or RC throttle is available for the new Brodak
.049. It’s meant for use in 1/2A CL Stunt (Precision Aerobatics)
and Combat models. I think it would also make an excellent
power plant for some of yesteryear’s sport FF models such as the
Midwest Sniffer (now available again from BMJR Model
Products).
I have a “handy hint” to share. When you’re reassembling an
engine with gaskets, after thoroughly cleaning the sealing surfaces,
dip the gasket (a new one if possible) in castor oil and let it soak
for a few minutes before installing. Put a little castor on the screws
too.
Then when you reassemble the engine, the castor oil will help
in tightening the screws firmly. In a few days the oil film’s
thickening from time and oxidation will ensure an airtight seal on
the gasketed surfaces and protection against screws loosening from
vibration.
(It’s good practice to retighten the screws after a couple days.
Gaskets can and do compress.) MA
Above: Propeller
brands and types
can make a huge
difference in model
p e r f o r m a n c e .
Specifying diameter
and pitch isn’t
enough.
Left: Brodak’s
newest CL engine.
This potent .049
has no muffler or
throttle. It will be
hard to beat in
events such as 1/2A
Combat.