90 MODEL AVIATION
A BRIEF MENTION
of model diesel
engines in one of my
recent columns
prompted Ivo Lucchita
(Flagstaff, Arizona) to
e-mail me and ask
why this type of model
engine—his favorite—never became popular in the US. He also
noted that even in Europe, long a stronghold of model diesel usage,
its popularity has declined considerably.
That seems strange to me too. I’ve done a lot of flying with
diesel power. It has several distinct advantages over glow. These
advantages aren’t obvious at first, so I’ll describe them in detail.
Model diesels are adaptable. A diesel can happily spin any size
propeller that will fit onto its shaft.
I demonstrated that once to a skeptic with a 10 x 4 propeller
installed on a .03 diesel. I’ve also had a .09 diesel turning a 3-inchdiameter
impeller in a Kress ducted-fan unit at roughly 27,000 rpm.
Both engines started readily and responded normally to throttling.
They used the same fuel, too.
Speaking of Kress Jets, Bob Kress briefly manufactured a
geared-down version of the Cox Pee Wee .020, to allow it to spin
Model diesel engines’ advantages
The Engine Shop Joe Wagner | [email protected]
Also included in this column:
• Four-stroke techniques
• Engine history book
Below: Bob Kress (ductedfan
guru) modified the
Cox Pee Wee .020 to spin
larger propellers. This one
(courtesy Steve Staples) is
the last made. It ran well
but is three times as heavy
as a stock Pee Wee.
Left: Small diesels have
advantages over 1/2A glow
power—and electrics. The
PAW .049 (front) has a
radial mount. The PAW
.03 runs 40 minutes on an
ounce of fuel.
The .29 diesel in this RC-Assist Cleveland Playboy Sr. is half the
size of the sparker it was designed for, yet it powers it just as
well. Note the exhaust extension.
Model diesels aren’t limited to small displacements. This PAW
.60 hand-starts readily and puts out the power of an old-time
Forster .99. Note the tiny muffler.
02sig3.QXD 12/22/08 12:37 PM Page 90
larger propellers. It worked, although it was heavy and
cumbersome. Model diesels need no such complications.
That amazing adaptability comes from a unique feature of model
diesels: variable compression. This type of model engine has a
movable contrapiston in its head that is adjustable via a screw.
Diesels need no spark or glow plug to ignite their fuel-air
mixture. The heat generated by compression does that job. And
adjusting the compression allows the ignition point to be precisely
optimized for the best running performance. That’s what allows a
tiny .03 diesel to run on a 10-inch propeller and a .09 to spin a 3-
inch ducted-fan impeller.
The model diesel’s adjustable compression makes it especially
useful to model fliers such as Ivo Lucchita, who live at high
altitudes. A diesel starts and runs nicely on the same fuel at 7,500
feet (where Ivo flies) as it does at sea level.
I demonstrated that several years ago on one of my cross-country
car trips. I had a small, easily portable test mount with me, with one
of my favorite glow engines on one side and a favorite diesel on the
other. As I traveled from one environment to another, from time to
time I’d take my dual test mount out and run both engines.
As expected, my glow engine’s performance varied noticeably.
Using the same fuel throughout the trip, I had starting difficulty in
high humidity (Shreveport, Louisiana) and at high altitude (La
Junta, Colorado). The glow’s performance varied too, but the diesel
started easily and ran almost the same everywhere. Adjustable
compression made all the difference.
True, at high altitudes the air is less dense and the diesel’s actual
horsepower output is lessened. However, the decreased air density
also reduces the aerodynamic drag on the spinning propeller blades.
That’s why my diesel could turn the same propeller at the same
rpm as at sea level. Yes, its thrust output went down. But so did that
of the glow engine—but its rpm declined too.
Diesel fuel is different; it’s roughly 40% kerosene, 30% ether,
and 30% castor oil. Its distinct aroma bothers some people, but it
reminds us diesel-power fliers of enjoyable days at the flying field.
The proportion of the ingredients in diesel fuel is noncritical. They
can vary quite a bit.
Eric Clutton, “Doctor Diesel,” once told me that if you can smell
ether in your diesel fuel, it has enough. And Andy Woitowicz
(Timmins, Ontario, Canada) has succeeded in starting and running
model diesels with no ether content in the fuel. However, doing so
required preheating the engine.
Obtaining commercial fuel for model diesels used to be more
difficult than for glow engines. Every neighborhood hobby shop
carried glow fuel. But the recent decline in America’s hobby
shops—there isn’t one within 80 miles of my home now, where
there were a dozen 10 years ago—has made glow fuel a mail-order
commodity in much of the country.
However, it’s easy to “home-brew” diesel fuel; the ingredients
are readily available. John Deere-brand Starting Fluid provides the
ether. Kerosene comes in many forms: auto diesel fuel, homeheating
fuel, aviation fuel for jets, and even Wal-Mart’s Odorless
Lamp Oil. As for lubricating oil, castor has long been the standard in
model diesel fuel.
I’ve had a few reports of successful use
of SAE 70 auto oil in diesel fuel, but for
several reasons I prefer castor. Drugstore
castor oil works fine—in glow fuel too—
and with today’s high shipping costs, it’s
no more expensive than mail-ordered castor
oil. Also, model engines using all-castor-oil
lubrication don’t rust.
One advantage of model diesel fuel that
I particularly like is that it doesn’t harm
any kind of model finish. It won’t even
affect decals. Another advantage is that
diesels run roughly 70% longer per ounce
of fuel than similar-size glow engines.
Now for sound. Most of us longtime
piston-power proponents like our models to
be audible. Yet the general public dislikes
model-engine noise, although its decibel
output seldom exceeds that of power lawn
mowers. That’s because of the quality of
the sound.
It’s like the difference between a
clarinet solo by Benny Goodman or Artie
Shaw and the squawking of a rank clarinet
beginner. I once measured the decibel
output of fingernails scraping down a slate
blackboard. That never exceeded 60 dBA
but was almost unbearable to listeners.
Model diesels put out as much power as
glows, with close to the same decibels. But
their sound quality is far less annoying. The
screechy, high-frequency overtones that
glow engines too often produce is absent.
92 MODEL AVIATION
For that reason, model diesels don’t
need the massive mufflers that we have
become used to seeing on our glow
engines. PAW diesels in particular have
exceedingly small mufflers that barely
extend outside the engine’s mounting lugs.
Yes, electric power is far quieter than a
muffled model diesel. At recent
S.M.A.L.L. (Small Model Airplane
Lovers’ League) meets in Little Rock,
Arkansas, it seemed almost spooky to see
the sky crowded with powered RC
models—but with hardly a sound to be
heard. That silence is doubtless one reason
for e-power’s popularity.
Yet piston power has its advantages
too. It’s nice to be able to hear your engine
changing speed in response to throttle
commands, for one thing. And since you
need to start a piston engine by spinning its
propeller, there’s no danger of an
accidental turn-on.
Piston engines cost less than outrunner
electric systems of equivalent power
output. Also, refueling a piston engine for
another flight takes less than a minute.
There’s no need to remove its “fuel tank”
for recharging, either.
My recent mention of starting problems
with a couple of Magnum four-strokers
with unusually high compression brought
in considerable e-mail from readers. This
seems to be a common problem, and
various solutions for it were offered.
One suggestion was to add extra head
gaskets, but doing that alters the valve
timing. And the engines run just fine after
startup, so their high-compression design
can’t be faulted. Several readers came up
with special starting techniques that solved
the problem.
One was to hand-flip the four-stroke’s
propeller backward several times, and then
apply the electric starter. This reduces the
amount of fuel-air mixture in the
combustion chamber for at least one
revolution. And that allows the electric
starter to gain enough rotational
momentum to turn over the engine until it
fires.
Another technique that readers
suggested requires two people. The person
at the transmitter pulls the throttle stick all
the way back and then moves the throttle
trim to cutoff position. The other person at
the airplane hand-flips the propeller
several times, connects the glow plug, and
applies the starter. As soon as the engine
fires, the person at the transmitter instantly
advances the throttle.
Doing this takes quick responses, but it
works, because with the carburetor’s barrel
fully closed, the intake stroke draws in
significantly less fuel-air mix. That
reduces the effective compression and lets
the starter spin up the engine.
I enjoyed reading a unique model-engine
book by David Janson. Unlike anything
I’ve seen in this field, his Model Engine
Designer and Manufacturer Profiles is
devoted to interesting details and
backgrounds of mostly unusual power
plants—112 of them—each the subject of
an individual short article.
Among the engines covered in Dave’s
book—which is more about them than
about their designers and manufacturers—
are the Technopower five-cylinder radial,
1940 Syncro B-30 (first of the “cheapie”
all-cast model engines), Herb Wahl
replicas, Moki M6, Krasnorutskij .60 inline
single, G-Mark .30 five-cylinder
radial, Laser .45 four-stroker, Fitzpatrick
.60, Davies-Charlton .29 Twin, and
Hirtenburger (HP) .61.
This book is plastic-comb bound and is
printed on only one side of each page. It is
available for $28 postpaid, direct from the
author. MA
Sources:
PAW diesels:
(931) 455-2256
www.cafes.net/doctordiesel
Other imported diesels:
Carlson Engine Imports
(602) 863-1684
www.carlsonengineimports.net
David R. Janson
2005 Dartmouth Ave.
Boulder CO 80303
Edition: Model Aviation - 2009/02
Page Numbers: 90,91,92
Edition: Model Aviation - 2009/02
Page Numbers: 90,91,92
90 MODEL AVIATION
A BRIEF MENTION
of model diesel
engines in one of my
recent columns
prompted Ivo Lucchita
(Flagstaff, Arizona) to
e-mail me and ask
why this type of model
engine—his favorite—never became popular in the US. He also
noted that even in Europe, long a stronghold of model diesel usage,
its popularity has declined considerably.
That seems strange to me too. I’ve done a lot of flying with
diesel power. It has several distinct advantages over glow. These
advantages aren’t obvious at first, so I’ll describe them in detail.
Model diesels are adaptable. A diesel can happily spin any size
propeller that will fit onto its shaft.
I demonstrated that once to a skeptic with a 10 x 4 propeller
installed on a .03 diesel. I’ve also had a .09 diesel turning a 3-inchdiameter
impeller in a Kress ducted-fan unit at roughly 27,000 rpm.
Both engines started readily and responded normally to throttling.
They used the same fuel, too.
Speaking of Kress Jets, Bob Kress briefly manufactured a
geared-down version of the Cox Pee Wee .020, to allow it to spin
Model diesel engines’ advantages
The Engine Shop Joe Wagner | [email protected]
Also included in this column:
• Four-stroke techniques
• Engine history book
Below: Bob Kress (ductedfan
guru) modified the
Cox Pee Wee .020 to spin
larger propellers. This one
(courtesy Steve Staples) is
the last made. It ran well
but is three times as heavy
as a stock Pee Wee.
Left: Small diesels have
advantages over 1/2A glow
power—and electrics. The
PAW .049 (front) has a
radial mount. The PAW
.03 runs 40 minutes on an
ounce of fuel.
The .29 diesel in this RC-Assist Cleveland Playboy Sr. is half the
size of the sparker it was designed for, yet it powers it just as
well. Note the exhaust extension.
Model diesels aren’t limited to small displacements. This PAW
.60 hand-starts readily and puts out the power of an old-time
Forster .99. Note the tiny muffler.
02sig3.QXD 12/22/08 12:37 PM Page 90
larger propellers. It worked, although it was heavy and
cumbersome. Model diesels need no such complications.
That amazing adaptability comes from a unique feature of model
diesels: variable compression. This type of model engine has a
movable contrapiston in its head that is adjustable via a screw.
Diesels need no spark or glow plug to ignite their fuel-air
mixture. The heat generated by compression does that job. And
adjusting the compression allows the ignition point to be precisely
optimized for the best running performance. That’s what allows a
tiny .03 diesel to run on a 10-inch propeller and a .09 to spin a 3-
inch ducted-fan impeller.
The model diesel’s adjustable compression makes it especially
useful to model fliers such as Ivo Lucchita, who live at high
altitudes. A diesel starts and runs nicely on the same fuel at 7,500
feet (where Ivo flies) as it does at sea level.
I demonstrated that several years ago on one of my cross-country
car trips. I had a small, easily portable test mount with me, with one
of my favorite glow engines on one side and a favorite diesel on the
other. As I traveled from one environment to another, from time to
time I’d take my dual test mount out and run both engines.
As expected, my glow engine’s performance varied noticeably.
Using the same fuel throughout the trip, I had starting difficulty in
high humidity (Shreveport, Louisiana) and at high altitude (La
Junta, Colorado). The glow’s performance varied too, but the diesel
started easily and ran almost the same everywhere. Adjustable
compression made all the difference.
True, at high altitudes the air is less dense and the diesel’s actual
horsepower output is lessened. However, the decreased air density
also reduces the aerodynamic drag on the spinning propeller blades.
That’s why my diesel could turn the same propeller at the same
rpm as at sea level. Yes, its thrust output went down. But so did that
of the glow engine—but its rpm declined too.
Diesel fuel is different; it’s roughly 40% kerosene, 30% ether,
and 30% castor oil. Its distinct aroma bothers some people, but it
reminds us diesel-power fliers of enjoyable days at the flying field.
The proportion of the ingredients in diesel fuel is noncritical. They
can vary quite a bit.
Eric Clutton, “Doctor Diesel,” once told me that if you can smell
ether in your diesel fuel, it has enough. And Andy Woitowicz
(Timmins, Ontario, Canada) has succeeded in starting and running
model diesels with no ether content in the fuel. However, doing so
required preheating the engine.
Obtaining commercial fuel for model diesels used to be more
difficult than for glow engines. Every neighborhood hobby shop
carried glow fuel. But the recent decline in America’s hobby
shops—there isn’t one within 80 miles of my home now, where
there were a dozen 10 years ago—has made glow fuel a mail-order
commodity in much of the country.
However, it’s easy to “home-brew” diesel fuel; the ingredients
are readily available. John Deere-brand Starting Fluid provides the
ether. Kerosene comes in many forms: auto diesel fuel, homeheating
fuel, aviation fuel for jets, and even Wal-Mart’s Odorless
Lamp Oil. As for lubricating oil, castor has long been the standard in
model diesel fuel.
I’ve had a few reports of successful use
of SAE 70 auto oil in diesel fuel, but for
several reasons I prefer castor. Drugstore
castor oil works fine—in glow fuel too—
and with today’s high shipping costs, it’s
no more expensive than mail-ordered castor
oil. Also, model engines using all-castor-oil
lubrication don’t rust.
One advantage of model diesel fuel that
I particularly like is that it doesn’t harm
any kind of model finish. It won’t even
affect decals. Another advantage is that
diesels run roughly 70% longer per ounce
of fuel than similar-size glow engines.
Now for sound. Most of us longtime
piston-power proponents like our models to
be audible. Yet the general public dislikes
model-engine noise, although its decibel
output seldom exceeds that of power lawn
mowers. That’s because of the quality of
the sound.
It’s like the difference between a
clarinet solo by Benny Goodman or Artie
Shaw and the squawking of a rank clarinet
beginner. I once measured the decibel
output of fingernails scraping down a slate
blackboard. That never exceeded 60 dBA
but was almost unbearable to listeners.
Model diesels put out as much power as
glows, with close to the same decibels. But
their sound quality is far less annoying. The
screechy, high-frequency overtones that
glow engines too often produce is absent.
92 MODEL AVIATION
For that reason, model diesels don’t
need the massive mufflers that we have
become used to seeing on our glow
engines. PAW diesels in particular have
exceedingly small mufflers that barely
extend outside the engine’s mounting lugs.
Yes, electric power is far quieter than a
muffled model diesel. At recent
S.M.A.L.L. (Small Model Airplane
Lovers’ League) meets in Little Rock,
Arkansas, it seemed almost spooky to see
the sky crowded with powered RC
models—but with hardly a sound to be
heard. That silence is doubtless one reason
for e-power’s popularity.
Yet piston power has its advantages
too. It’s nice to be able to hear your engine
changing speed in response to throttle
commands, for one thing. And since you
need to start a piston engine by spinning its
propeller, there’s no danger of an
accidental turn-on.
Piston engines cost less than outrunner
electric systems of equivalent power
output. Also, refueling a piston engine for
another flight takes less than a minute.
There’s no need to remove its “fuel tank”
for recharging, either.
My recent mention of starting problems
with a couple of Magnum four-strokers
with unusually high compression brought
in considerable e-mail from readers. This
seems to be a common problem, and
various solutions for it were offered.
One suggestion was to add extra head
gaskets, but doing that alters the valve
timing. And the engines run just fine after
startup, so their high-compression design
can’t be faulted. Several readers came up
with special starting techniques that solved
the problem.
One was to hand-flip the four-stroke’s
propeller backward several times, and then
apply the electric starter. This reduces the
amount of fuel-air mixture in the
combustion chamber for at least one
revolution. And that allows the electric
starter to gain enough rotational
momentum to turn over the engine until it
fires.
Another technique that readers
suggested requires two people. The person
at the transmitter pulls the throttle stick all
the way back and then moves the throttle
trim to cutoff position. The other person at
the airplane hand-flips the propeller
several times, connects the glow plug, and
applies the starter. As soon as the engine
fires, the person at the transmitter instantly
advances the throttle.
Doing this takes quick responses, but it
works, because with the carburetor’s barrel
fully closed, the intake stroke draws in
significantly less fuel-air mix. That
reduces the effective compression and lets
the starter spin up the engine.
I enjoyed reading a unique model-engine
book by David Janson. Unlike anything
I’ve seen in this field, his Model Engine
Designer and Manufacturer Profiles is
devoted to interesting details and
backgrounds of mostly unusual power
plants—112 of them—each the subject of
an individual short article.
Among the engines covered in Dave’s
book—which is more about them than
about their designers and manufacturers—
are the Technopower five-cylinder radial,
1940 Syncro B-30 (first of the “cheapie”
all-cast model engines), Herb Wahl
replicas, Moki M6, Krasnorutskij .60 inline
single, G-Mark .30 five-cylinder
radial, Laser .45 four-stroker, Fitzpatrick
.60, Davies-Charlton .29 Twin, and
Hirtenburger (HP) .61.
This book is plastic-comb bound and is
printed on only one side of each page. It is
available for $28 postpaid, direct from the
author. MA
Sources:
PAW diesels:
(931) 455-2256
www.cafes.net/doctordiesel
Other imported diesels:
Carlson Engine Imports
(602) 863-1684
www.carlsonengineimports.net
David R. Janson
2005 Dartmouth Ave.
Boulder CO 80303
Edition: Model Aviation - 2009/02
Page Numbers: 90,91,92
90 MODEL AVIATION
A BRIEF MENTION
of model diesel
engines in one of my
recent columns
prompted Ivo Lucchita
(Flagstaff, Arizona) to
e-mail me and ask
why this type of model
engine—his favorite—never became popular in the US. He also
noted that even in Europe, long a stronghold of model diesel usage,
its popularity has declined considerably.
That seems strange to me too. I’ve done a lot of flying with
diesel power. It has several distinct advantages over glow. These
advantages aren’t obvious at first, so I’ll describe them in detail.
Model diesels are adaptable. A diesel can happily spin any size
propeller that will fit onto its shaft.
I demonstrated that once to a skeptic with a 10 x 4 propeller
installed on a .03 diesel. I’ve also had a .09 diesel turning a 3-inchdiameter
impeller in a Kress ducted-fan unit at roughly 27,000 rpm.
Both engines started readily and responded normally to throttling.
They used the same fuel, too.
Speaking of Kress Jets, Bob Kress briefly manufactured a
geared-down version of the Cox Pee Wee .020, to allow it to spin
Model diesel engines’ advantages
The Engine Shop Joe Wagner | [email protected]
Also included in this column:
• Four-stroke techniques
• Engine history book
Below: Bob Kress (ductedfan
guru) modified the
Cox Pee Wee .020 to spin
larger propellers. This one
(courtesy Steve Staples) is
the last made. It ran well
but is three times as heavy
as a stock Pee Wee.
Left: Small diesels have
advantages over 1/2A glow
power—and electrics. The
PAW .049 (front) has a
radial mount. The PAW
.03 runs 40 minutes on an
ounce of fuel.
The .29 diesel in this RC-Assist Cleveland Playboy Sr. is half the
size of the sparker it was designed for, yet it powers it just as
well. Note the exhaust extension.
Model diesels aren’t limited to small displacements. This PAW
.60 hand-starts readily and puts out the power of an old-time
Forster .99. Note the tiny muffler.
02sig3.QXD 12/22/08 12:37 PM Page 90
larger propellers. It worked, although it was heavy and
cumbersome. Model diesels need no such complications.
That amazing adaptability comes from a unique feature of model
diesels: variable compression. This type of model engine has a
movable contrapiston in its head that is adjustable via a screw.
Diesels need no spark or glow plug to ignite their fuel-air
mixture. The heat generated by compression does that job. And
adjusting the compression allows the ignition point to be precisely
optimized for the best running performance. That’s what allows a
tiny .03 diesel to run on a 10-inch propeller and a .09 to spin a 3-
inch ducted-fan impeller.
The model diesel’s adjustable compression makes it especially
useful to model fliers such as Ivo Lucchita, who live at high
altitudes. A diesel starts and runs nicely on the same fuel at 7,500
feet (where Ivo flies) as it does at sea level.
I demonstrated that several years ago on one of my cross-country
car trips. I had a small, easily portable test mount with me, with one
of my favorite glow engines on one side and a favorite diesel on the
other. As I traveled from one environment to another, from time to
time I’d take my dual test mount out and run both engines.
As expected, my glow engine’s performance varied noticeably.
Using the same fuel throughout the trip, I had starting difficulty in
high humidity (Shreveport, Louisiana) and at high altitude (La
Junta, Colorado). The glow’s performance varied too, but the diesel
started easily and ran almost the same everywhere. Adjustable
compression made all the difference.
True, at high altitudes the air is less dense and the diesel’s actual
horsepower output is lessened. However, the decreased air density
also reduces the aerodynamic drag on the spinning propeller blades.
That’s why my diesel could turn the same propeller at the same
rpm as at sea level. Yes, its thrust output went down. But so did that
of the glow engine—but its rpm declined too.
Diesel fuel is different; it’s roughly 40% kerosene, 30% ether,
and 30% castor oil. Its distinct aroma bothers some people, but it
reminds us diesel-power fliers of enjoyable days at the flying field.
The proportion of the ingredients in diesel fuel is noncritical. They
can vary quite a bit.
Eric Clutton, “Doctor Diesel,” once told me that if you can smell
ether in your diesel fuel, it has enough. And Andy Woitowicz
(Timmins, Ontario, Canada) has succeeded in starting and running
model diesels with no ether content in the fuel. However, doing so
required preheating the engine.
Obtaining commercial fuel for model diesels used to be more
difficult than for glow engines. Every neighborhood hobby shop
carried glow fuel. But the recent decline in America’s hobby
shops—there isn’t one within 80 miles of my home now, where
there were a dozen 10 years ago—has made glow fuel a mail-order
commodity in much of the country.
However, it’s easy to “home-brew” diesel fuel; the ingredients
are readily available. John Deere-brand Starting Fluid provides the
ether. Kerosene comes in many forms: auto diesel fuel, homeheating
fuel, aviation fuel for jets, and even Wal-Mart’s Odorless
Lamp Oil. As for lubricating oil, castor has long been the standard in
model diesel fuel.
I’ve had a few reports of successful use
of SAE 70 auto oil in diesel fuel, but for
several reasons I prefer castor. Drugstore
castor oil works fine—in glow fuel too—
and with today’s high shipping costs, it’s
no more expensive than mail-ordered castor
oil. Also, model engines using all-castor-oil
lubrication don’t rust.
One advantage of model diesel fuel that
I particularly like is that it doesn’t harm
any kind of model finish. It won’t even
affect decals. Another advantage is that
diesels run roughly 70% longer per ounce
of fuel than similar-size glow engines.
Now for sound. Most of us longtime
piston-power proponents like our models to
be audible. Yet the general public dislikes
model-engine noise, although its decibel
output seldom exceeds that of power lawn
mowers. That’s because of the quality of
the sound.
It’s like the difference between a
clarinet solo by Benny Goodman or Artie
Shaw and the squawking of a rank clarinet
beginner. I once measured the decibel
output of fingernails scraping down a slate
blackboard. That never exceeded 60 dBA
but was almost unbearable to listeners.
Model diesels put out as much power as
glows, with close to the same decibels. But
their sound quality is far less annoying. The
screechy, high-frequency overtones that
glow engines too often produce is absent.
92 MODEL AVIATION
For that reason, model diesels don’t
need the massive mufflers that we have
become used to seeing on our glow
engines. PAW diesels in particular have
exceedingly small mufflers that barely
extend outside the engine’s mounting lugs.
Yes, electric power is far quieter than a
muffled model diesel. At recent
S.M.A.L.L. (Small Model Airplane
Lovers’ League) meets in Little Rock,
Arkansas, it seemed almost spooky to see
the sky crowded with powered RC
models—but with hardly a sound to be
heard. That silence is doubtless one reason
for e-power’s popularity.
Yet piston power has its advantages
too. It’s nice to be able to hear your engine
changing speed in response to throttle
commands, for one thing. And since you
need to start a piston engine by spinning its
propeller, there’s no danger of an
accidental turn-on.
Piston engines cost less than outrunner
electric systems of equivalent power
output. Also, refueling a piston engine for
another flight takes less than a minute.
There’s no need to remove its “fuel tank”
for recharging, either.
My recent mention of starting problems
with a couple of Magnum four-strokers
with unusually high compression brought
in considerable e-mail from readers. This
seems to be a common problem, and
various solutions for it were offered.
One suggestion was to add extra head
gaskets, but doing that alters the valve
timing. And the engines run just fine after
startup, so their high-compression design
can’t be faulted. Several readers came up
with special starting techniques that solved
the problem.
One was to hand-flip the four-stroke’s
propeller backward several times, and then
apply the electric starter. This reduces the
amount of fuel-air mixture in the
combustion chamber for at least one
revolution. And that allows the electric
starter to gain enough rotational
momentum to turn over the engine until it
fires.
Another technique that readers
suggested requires two people. The person
at the transmitter pulls the throttle stick all
the way back and then moves the throttle
trim to cutoff position. The other person at
the airplane hand-flips the propeller
several times, connects the glow plug, and
applies the starter. As soon as the engine
fires, the person at the transmitter instantly
advances the throttle.
Doing this takes quick responses, but it
works, because with the carburetor’s barrel
fully closed, the intake stroke draws in
significantly less fuel-air mix. That
reduces the effective compression and lets
the starter spin up the engine.
I enjoyed reading a unique model-engine
book by David Janson. Unlike anything
I’ve seen in this field, his Model Engine
Designer and Manufacturer Profiles is
devoted to interesting details and
backgrounds of mostly unusual power
plants—112 of them—each the subject of
an individual short article.
Among the engines covered in Dave’s
book—which is more about them than
about their designers and manufacturers—
are the Technopower five-cylinder radial,
1940 Syncro B-30 (first of the “cheapie”
all-cast model engines), Herb Wahl
replicas, Moki M6, Krasnorutskij .60 inline
single, G-Mark .30 five-cylinder
radial, Laser .45 four-stroker, Fitzpatrick
.60, Davies-Charlton .29 Twin, and
Hirtenburger (HP) .61.
This book is plastic-comb bound and is
printed on only one side of each page. It is
available for $28 postpaid, direct from the
author. MA
Sources:
PAW diesels:
(931) 455-2256
www.cafes.net/doctordiesel
Other imported diesels:
Carlson Engine Imports
(602) 863-1684
www.carlsonengineimports.net
David R. Janson
2005 Dartmouth Ave.
Boulder CO 80303
