90 MODEL AVIATION
IN RECENT WEEKS you readers have sent me some extremely
cogent and helpful input on topics I’ve mentioned in the last few
columns, such as the revolutionary new British-made RCV fourstroke
engines.
I wrote that no stock commercially available model engine test
mount I knew about would hold the RCV58-CD. Wayne Gladden
(15028 Ashmont Cir., Huntsville AL 35803; Tel.: [256] 881-6048)
sent me one of his F&G Model Engine Break-In Test Stands. The
RCV58-CD does fit into that nicely! Also, the F&G mount’s quickly
adjustable fuel-tank mount makes it easy indeed to set the fuel level
just right.
The F&G test stand is designed to hold RC engines from .25 to
1.20 cubic inches displacement. I especially admire the cleverness of
its positionable throttle lever assembly. That greatly simplifies
alignment of the pushrod with any throttle arm type or location.
Contact Wayne Gladden for pricing and availability of the F&G test
stand.
Several readers have asked me where they can buy RCV engines.
Right now RCV only sells its model engines direct from the British
factory. The company has an extraordinarily informative Web site at
www.rcvengines.com. It contains full technical and pricing data on
RCV products.
From it you can also download and print out the instruction
manuals and dimensioned drawings of the various RCV four-strokes.
Those include the original “inline” designs with 2:1 reduction drive
direct from the rotating sleeve and the newer crankshaft-drive (CD)
engines.
By the time you read this, RCV’s latest model power plant—the
RCV91-CD—will be available. A 1.20-sized CD engine is in the
works.
Admiring the compactness of my RCV58-CD, one of the local RC
fliers inquired about how its unusual rotary cylinder sleeve valve
functions. I explained the advantages of using the rotating sleeve to do
the job that a complex poppet-valve mechanism performs in
conventional four-stroke engine designs.
He then asked, “You mean that all the time the piston is going up
and down in its cylinder, that cylinder keeps spinning around the
moving piston? Doesn’t that create a lot of extra friction and loss of
power?”
To give him an accurate reply, I quickly “worked out the
numbers” and calculated that there is indeed approximately 28%
greater relative motion between the RCV58-CD’s piston and sleeve
surfaces than there is in a conventional stationary-sleeve engine of the
same size, operating at the same speed. (That applies to two- and fourstroke
types.) But as paradoxical as it seems, the RCV’s engine design
actually generates less operating friction between its piston and
cylinder than a conventional engine does!
That’s because (as the French physicist Charles de Coulomb
proved more than 200 years ago) friction between sliding surfaces is
essentially independent of relative velocity and the size of the areas in
contact. But sliding friction is measurably smaller than static friction.
And in a conventional internal-combustion (IC) engine design, twice
for every revolution of the crankshaft, the piston must begin its
motion from a complete standstill relative to its cylinder.
Since an RCV engine’s sleeve is constantly rotating as its piston
travels up and down, all relative motion between the two moving
surfaces takes place in the sliding mode. No “stick-slip” condition
needs to be overcome the way it must as static and sliding friction
alternate twice in each piston stroke of a “traditional” IC engine.
This effect is far from trivial. Rotary-sleeve-valve engines for fullscale
aircraft took full advantage of it. Some of the most powerful
reciprocating aircraft engines ever made; e.g., the WW II Bristol
Joe Wagner
T h e E n g i n e S h o p
212 S. Pine Ave., Ozark AL 36360
F&G combined metal, hardwood, and engineering plastic in
durable, multiadjustable Model Engine Break-In Test Stand.
F&G mount holds engine lugs firmly between metal upper and
lower clamping plates. Note adjustable-height fuel-tank mount.
RCV91-CD four-stroke prototype is 50% larger than earlier .58-
cubic-inch model and has same sleek, compact design.
92 MODEL AVIATION
Centaurus (used in the Hawker Sea Fury that
for years held the speed record for propellerdriven
aircraft) and the Napier Sabre (which
powered the Royal Air Force’s fastest
wartime fighter—the Hawker Tempest). Both
of those engines used rotating cylinder
sleeves instead of poppet valves.
Dennis Hansen (Spruce Head ME) has
proved that an old modeling problem with
molded-nylon model parts is still with us
today: brittleness. As Dennis was marking the
engine-bolt locations on a radial engine
mount, one of its beams snapped right off at
the base.
At first he wondered if low temperature
had caused the fracture. He told me that his
shop was “kind of chilly” at the time he was
working on the mount. But I don’t believe
that climate had anything to do with Dennis’s
engine-mount failure; I think it’s the same
problem that modelers too often experienced
with nylon propellers decades ago.
At that time, we model fliers were advised
to boil a nylon propeller for a half hour or so
before putting one on an engine. The theory
was that the boiling treatment “relieved
stresses” in the molded plastic. And it
worked!
However, the true cause of brittleness in
molded-nylon parts—plain and fiber
reinforced—is a chemical/physical
characteristic of that particular plastic. As do
concrete and plaster of paris, nylon contains
H2O as part of its structure. But unlike
concrete and plaster, whose water content
combines permanently with the other
constituents, the H2O content in nylon can
vary. And as it varies, so does the nylon’s
strength and flexibility.
Nylon is molded at temperatures of
roughly 500°—much hotter than water’s
vaporization temperature. That’s why “asmolded”
nylon parts can be low in H2O
content and reduced in strength as a result.
Nylon doesn’t need much H2O to regain
its strength—only 4% to 5% by weight. And
in thin sections, nylon can reabsorb the water
it needs from atmospheric humidity, but that
takes time. And in thick sections—such as
model propeller hubs and molded radial
engine mounts—it can take a lot of time.
That’s the real reason why boiling nylon
helps. At high temperatures, H2O can migrate
back into the plastic more readily than it can
at room temperature. And surrounded by
water in a pot on the stove, nylon parts have
unlimited access to H2O molecules for
replenishing their moisture content and
regaining their optimum physical properties.
It’s good practice to boil all molded-nylon
model parts thicker than approximately 3⁄32
inch before using them—not only propellers
and engine mounts, but bellcranks and
retractable landing-gear mechanisms too. A
half hour ought to be the minimum; for thick
parts I’d feel safer with at least a couple hours
in boiling water before use.
Another topic from previous columns that
has drawn comment from readers is the type
of aluminum container Larry Renger gave me
to use as a model diesel fuel bottle. Larry has
used them for fueling his diesel-powered
models, and he gave me one last year so I
could join in the fun.
I thought it was a water bottle. Not so! It’s
a container for campers’ stove and lantern
fuel, such as Coleman’s. A good mail-order
source for these aluminum bottles is
Campmor at (800) 226-7667 or
www.campmor.com.
A brand name that Campmor carries is
MSR. Those kind are inexpensive and
come in 11-, 22-, and 33-fluid-ounce sizes.
All have stoppers sealed with O-rings,
which will prevent any ether evaporation
Dennis Hansen proved that molded nylon can still become brittle—
even fiber-reinforced type from which this mount was made.
Customized diesel-fuel bottles and tools employed. (Drilling
stopper holes by hand keeps bit from tearing plastic.)
94 MODEL AVIATION
from diesel fuel in the container.
I’ve modified two of these aluminum fuel
bottles for use with my “never-open” diesel
filling and fueling technique. My
customization method is to hand-drill and tap
a pair of #10-32 holes in the stopper. In those
I install fueling tubes that I modify from stock
3⁄4-inch-long brass screws. I epoxy those into
place in the stopper to make sure of an
evaporation-proof seal.
In use at the field, after filling the bottle I
connect the two fueling-tube ends with a
length of plastic tubing. (Vinyl, Tygon, or
neoprene work fine, but neither rubber nor
silicone tubing can stand exposure to the
kerosene content of model diesel fuel.)
To refuel a model, I pull free one end of
the plastic tubing on the bottle and attach that
to the model’s fuel-tank fitting. Then I tilt the
bottle and let gravity do the transfer. (Air will
vent freely into the open tube in the bottle as
the fuel passes into the model’s tank.)
To fill the diesel-fuel bottle itself, I use the
same technique I just described. I’ve modified
a one-gallon, metal fuel-can cap with two
diametrically opposite soldered-in brass tubes.
And I gravity-pour fuel from the gallon-size
“commercial can” into the smaller fuel bottle
the same way I fill a model’s tank from the
bottle.
Handling model diesel fuel this way stops
ether evaporation almost perfectly. It has
eliminated the strong aroma in my model
shop that used to inform everyone who came
into it that I’m a habitual flier of dieselpowered
model airplanes. MA
This month we list those who have donated $10 or more in support of the
Academy’s programs, the National Model Aviation Museum and the
Aeromodeling Center, and those organizations that have provided grants for
which AMA has applied and received. These people have made more than a
donation—they have made an investment in the future of aeromodeling.
When you see these folks, thank them! They are now among the
thousands who have given back to model aviation part of what model
aviation has given to them. Many things will be possible due to the their
thoughtful giving and generosity.
We list our supporters monthly. These donations represent amounts
processed in the month of January 2004. If your name is not listed, please
write to the Membership Department and include a canceled check. We
want to recognize all contributors!
Thank you.
$100 up to $500
Steven R Adams - NC
Arvada Associated Modelers - CO
William H Asplund - CT
James L Barnaby - PA
David A Bossert - CA
Robert A Bruce - CA
Michael J Contreras - CA
James A Cook - IL
Billy G Dilworth III - FL
James E Dunkin - MO
Greg D Edster - MO
Jon M Edy - CO
J Ronald Esak - FL
Jack B Feir - PA
Todd M Fellage - CT
John C Frothingham - ME
Bernard Fullett - IL
Andrew N Garello - MA
Donald G Garofalow - NJ
Michael Lee Gottfried - OH
Gerald M Gregorek - OH
Thomas D Griffiths - CO
Clifford C Gustafson - CT
Tom Hartvigsen - TN
William L Holder - GA
M Hotra - NJ
Charles A Lawhon - IN
David B Malcolm - FL
Rolland Mast - MI
Stephen D Remington - CA
Ashton T Reynolds - AK
Paul P Schnepp - CA
Clarence Stephens - OH
Frank Tiano - FL
Edward Vargo - MI
Alan H Wells - GA
David J Werner - NH
$10 up to $100
Your Contributions do Make a Difference!
Dionel E Aviles - TX
Robert E Leiper - CT
David A Seuferling - MO
Western Illinois Soaring Soc - IL
Edition: Model Aviation - 2004/05
Page Numbers: 90,92,94
Edition: Model Aviation - 2004/05
Page Numbers: 90,92,94
90 MODEL AVIATION
IN RECENT WEEKS you readers have sent me some extremely
cogent and helpful input on topics I’ve mentioned in the last few
columns, such as the revolutionary new British-made RCV fourstroke
engines.
I wrote that no stock commercially available model engine test
mount I knew about would hold the RCV58-CD. Wayne Gladden
(15028 Ashmont Cir., Huntsville AL 35803; Tel.: [256] 881-6048)
sent me one of his F&G Model Engine Break-In Test Stands. The
RCV58-CD does fit into that nicely! Also, the F&G mount’s quickly
adjustable fuel-tank mount makes it easy indeed to set the fuel level
just right.
The F&G test stand is designed to hold RC engines from .25 to
1.20 cubic inches displacement. I especially admire the cleverness of
its positionable throttle lever assembly. That greatly simplifies
alignment of the pushrod with any throttle arm type or location.
Contact Wayne Gladden for pricing and availability of the F&G test
stand.
Several readers have asked me where they can buy RCV engines.
Right now RCV only sells its model engines direct from the British
factory. The company has an extraordinarily informative Web site at
www.rcvengines.com. It contains full technical and pricing data on
RCV products.
From it you can also download and print out the instruction
manuals and dimensioned drawings of the various RCV four-strokes.
Those include the original “inline” designs with 2:1 reduction drive
direct from the rotating sleeve and the newer crankshaft-drive (CD)
engines.
By the time you read this, RCV’s latest model power plant—the
RCV91-CD—will be available. A 1.20-sized CD engine is in the
works.
Admiring the compactness of my RCV58-CD, one of the local RC
fliers inquired about how its unusual rotary cylinder sleeve valve
functions. I explained the advantages of using the rotating sleeve to do
the job that a complex poppet-valve mechanism performs in
conventional four-stroke engine designs.
He then asked, “You mean that all the time the piston is going up
and down in its cylinder, that cylinder keeps spinning around the
moving piston? Doesn’t that create a lot of extra friction and loss of
power?”
To give him an accurate reply, I quickly “worked out the
numbers” and calculated that there is indeed approximately 28%
greater relative motion between the RCV58-CD’s piston and sleeve
surfaces than there is in a conventional stationary-sleeve engine of the
same size, operating at the same speed. (That applies to two- and fourstroke
types.) But as paradoxical as it seems, the RCV’s engine design
actually generates less operating friction between its piston and
cylinder than a conventional engine does!
That’s because (as the French physicist Charles de Coulomb
proved more than 200 years ago) friction between sliding surfaces is
essentially independent of relative velocity and the size of the areas in
contact. But sliding friction is measurably smaller than static friction.
And in a conventional internal-combustion (IC) engine design, twice
for every revolution of the crankshaft, the piston must begin its
motion from a complete standstill relative to its cylinder.
Since an RCV engine’s sleeve is constantly rotating as its piston
travels up and down, all relative motion between the two moving
surfaces takes place in the sliding mode. No “stick-slip” condition
needs to be overcome the way it must as static and sliding friction
alternate twice in each piston stroke of a “traditional” IC engine.
This effect is far from trivial. Rotary-sleeve-valve engines for fullscale
aircraft took full advantage of it. Some of the most powerful
reciprocating aircraft engines ever made; e.g., the WW II Bristol
Joe Wagner
T h e E n g i n e S h o p
212 S. Pine Ave., Ozark AL 36360
F&G combined metal, hardwood, and engineering plastic in
durable, multiadjustable Model Engine Break-In Test Stand.
F&G mount holds engine lugs firmly between metal upper and
lower clamping plates. Note adjustable-height fuel-tank mount.
RCV91-CD four-stroke prototype is 50% larger than earlier .58-
cubic-inch model and has same sleek, compact design.
92 MODEL AVIATION
Centaurus (used in the Hawker Sea Fury that
for years held the speed record for propellerdriven
aircraft) and the Napier Sabre (which
powered the Royal Air Force’s fastest
wartime fighter—the Hawker Tempest). Both
of those engines used rotating cylinder
sleeves instead of poppet valves.
Dennis Hansen (Spruce Head ME) has
proved that an old modeling problem with
molded-nylon model parts is still with us
today: brittleness. As Dennis was marking the
engine-bolt locations on a radial engine
mount, one of its beams snapped right off at
the base.
At first he wondered if low temperature
had caused the fracture. He told me that his
shop was “kind of chilly” at the time he was
working on the mount. But I don’t believe
that climate had anything to do with Dennis’s
engine-mount failure; I think it’s the same
problem that modelers too often experienced
with nylon propellers decades ago.
At that time, we model fliers were advised
to boil a nylon propeller for a half hour or so
before putting one on an engine. The theory
was that the boiling treatment “relieved
stresses” in the molded plastic. And it
worked!
However, the true cause of brittleness in
molded-nylon parts—plain and fiber
reinforced—is a chemical/physical
characteristic of that particular plastic. As do
concrete and plaster of paris, nylon contains
H2O as part of its structure. But unlike
concrete and plaster, whose water content
combines permanently with the other
constituents, the H2O content in nylon can
vary. And as it varies, so does the nylon’s
strength and flexibility.
Nylon is molded at temperatures of
roughly 500°—much hotter than water’s
vaporization temperature. That’s why “asmolded”
nylon parts can be low in H2O
content and reduced in strength as a result.
Nylon doesn’t need much H2O to regain
its strength—only 4% to 5% by weight. And
in thin sections, nylon can reabsorb the water
it needs from atmospheric humidity, but that
takes time. And in thick sections—such as
model propeller hubs and molded radial
engine mounts—it can take a lot of time.
That’s the real reason why boiling nylon
helps. At high temperatures, H2O can migrate
back into the plastic more readily than it can
at room temperature. And surrounded by
water in a pot on the stove, nylon parts have
unlimited access to H2O molecules for
replenishing their moisture content and
regaining their optimum physical properties.
It’s good practice to boil all molded-nylon
model parts thicker than approximately 3⁄32
inch before using them—not only propellers
and engine mounts, but bellcranks and
retractable landing-gear mechanisms too. A
half hour ought to be the minimum; for thick
parts I’d feel safer with at least a couple hours
in boiling water before use.
Another topic from previous columns that
has drawn comment from readers is the type
of aluminum container Larry Renger gave me
to use as a model diesel fuel bottle. Larry has
used them for fueling his diesel-powered
models, and he gave me one last year so I
could join in the fun.
I thought it was a water bottle. Not so! It’s
a container for campers’ stove and lantern
fuel, such as Coleman’s. A good mail-order
source for these aluminum bottles is
Campmor at (800) 226-7667 or
www.campmor.com.
A brand name that Campmor carries is
MSR. Those kind are inexpensive and
come in 11-, 22-, and 33-fluid-ounce sizes.
All have stoppers sealed with O-rings,
which will prevent any ether evaporation
Dennis Hansen proved that molded nylon can still become brittle—
even fiber-reinforced type from which this mount was made.
Customized diesel-fuel bottles and tools employed. (Drilling
stopper holes by hand keeps bit from tearing plastic.)
94 MODEL AVIATION
from diesel fuel in the container.
I’ve modified two of these aluminum fuel
bottles for use with my “never-open” diesel
filling and fueling technique. My
customization method is to hand-drill and tap
a pair of #10-32 holes in the stopper. In those
I install fueling tubes that I modify from stock
3⁄4-inch-long brass screws. I epoxy those into
place in the stopper to make sure of an
evaporation-proof seal.
In use at the field, after filling the bottle I
connect the two fueling-tube ends with a
length of plastic tubing. (Vinyl, Tygon, or
neoprene work fine, but neither rubber nor
silicone tubing can stand exposure to the
kerosene content of model diesel fuel.)
To refuel a model, I pull free one end of
the plastic tubing on the bottle and attach that
to the model’s fuel-tank fitting. Then I tilt the
bottle and let gravity do the transfer. (Air will
vent freely into the open tube in the bottle as
the fuel passes into the model’s tank.)
To fill the diesel-fuel bottle itself, I use the
same technique I just described. I’ve modified
a one-gallon, metal fuel-can cap with two
diametrically opposite soldered-in brass tubes.
And I gravity-pour fuel from the gallon-size
“commercial can” into the smaller fuel bottle
the same way I fill a model’s tank from the
bottle.
Handling model diesel fuel this way stops
ether evaporation almost perfectly. It has
eliminated the strong aroma in my model
shop that used to inform everyone who came
into it that I’m a habitual flier of dieselpowered
model airplanes. MA
This month we list those who have donated $10 or more in support of the
Academy’s programs, the National Model Aviation Museum and the
Aeromodeling Center, and those organizations that have provided grants for
which AMA has applied and received. These people have made more than a
donation—they have made an investment in the future of aeromodeling.
When you see these folks, thank them! They are now among the
thousands who have given back to model aviation part of what model
aviation has given to them. Many things will be possible due to the their
thoughtful giving and generosity.
We list our supporters monthly. These donations represent amounts
processed in the month of January 2004. If your name is not listed, please
write to the Membership Department and include a canceled check. We
want to recognize all contributors!
Thank you.
$100 up to $500
Steven R Adams - NC
Arvada Associated Modelers - CO
William H Asplund - CT
James L Barnaby - PA
David A Bossert - CA
Robert A Bruce - CA
Michael J Contreras - CA
James A Cook - IL
Billy G Dilworth III - FL
James E Dunkin - MO
Greg D Edster - MO
Jon M Edy - CO
J Ronald Esak - FL
Jack B Feir - PA
Todd M Fellage - CT
John C Frothingham - ME
Bernard Fullett - IL
Andrew N Garello - MA
Donald G Garofalow - NJ
Michael Lee Gottfried - OH
Gerald M Gregorek - OH
Thomas D Griffiths - CO
Clifford C Gustafson - CT
Tom Hartvigsen - TN
William L Holder - GA
M Hotra - NJ
Charles A Lawhon - IN
David B Malcolm - FL
Rolland Mast - MI
Stephen D Remington - CA
Ashton T Reynolds - AK
Paul P Schnepp - CA
Clarence Stephens - OH
Frank Tiano - FL
Edward Vargo - MI
Alan H Wells - GA
David J Werner - NH
$10 up to $100
Your Contributions do Make a Difference!
Dionel E Aviles - TX
Robert E Leiper - CT
David A Seuferling - MO
Western Illinois Soaring Soc - IL
Edition: Model Aviation - 2004/05
Page Numbers: 90,92,94
90 MODEL AVIATION
IN RECENT WEEKS you readers have sent me some extremely
cogent and helpful input on topics I’ve mentioned in the last few
columns, such as the revolutionary new British-made RCV fourstroke
engines.
I wrote that no stock commercially available model engine test
mount I knew about would hold the RCV58-CD. Wayne Gladden
(15028 Ashmont Cir., Huntsville AL 35803; Tel.: [256] 881-6048)
sent me one of his F&G Model Engine Break-In Test Stands. The
RCV58-CD does fit into that nicely! Also, the F&G mount’s quickly
adjustable fuel-tank mount makes it easy indeed to set the fuel level
just right.
The F&G test stand is designed to hold RC engines from .25 to
1.20 cubic inches displacement. I especially admire the cleverness of
its positionable throttle lever assembly. That greatly simplifies
alignment of the pushrod with any throttle arm type or location.
Contact Wayne Gladden for pricing and availability of the F&G test
stand.
Several readers have asked me where they can buy RCV engines.
Right now RCV only sells its model engines direct from the British
factory. The company has an extraordinarily informative Web site at
www.rcvengines.com. It contains full technical and pricing data on
RCV products.
From it you can also download and print out the instruction
manuals and dimensioned drawings of the various RCV four-strokes.
Those include the original “inline” designs with 2:1 reduction drive
direct from the rotating sleeve and the newer crankshaft-drive (CD)
engines.
By the time you read this, RCV’s latest model power plant—the
RCV91-CD—will be available. A 1.20-sized CD engine is in the
works.
Admiring the compactness of my RCV58-CD, one of the local RC
fliers inquired about how its unusual rotary cylinder sleeve valve
functions. I explained the advantages of using the rotating sleeve to do
the job that a complex poppet-valve mechanism performs in
conventional four-stroke engine designs.
He then asked, “You mean that all the time the piston is going up
and down in its cylinder, that cylinder keeps spinning around the
moving piston? Doesn’t that create a lot of extra friction and loss of
power?”
To give him an accurate reply, I quickly “worked out the
numbers” and calculated that there is indeed approximately 28%
greater relative motion between the RCV58-CD’s piston and sleeve
surfaces than there is in a conventional stationary-sleeve engine of the
same size, operating at the same speed. (That applies to two- and fourstroke
types.) But as paradoxical as it seems, the RCV’s engine design
actually generates less operating friction between its piston and
cylinder than a conventional engine does!
That’s because (as the French physicist Charles de Coulomb
proved more than 200 years ago) friction between sliding surfaces is
essentially independent of relative velocity and the size of the areas in
contact. But sliding friction is measurably smaller than static friction.
And in a conventional internal-combustion (IC) engine design, twice
for every revolution of the crankshaft, the piston must begin its
motion from a complete standstill relative to its cylinder.
Since an RCV engine’s sleeve is constantly rotating as its piston
travels up and down, all relative motion between the two moving
surfaces takes place in the sliding mode. No “stick-slip” condition
needs to be overcome the way it must as static and sliding friction
alternate twice in each piston stroke of a “traditional” IC engine.
This effect is far from trivial. Rotary-sleeve-valve engines for fullscale
aircraft took full advantage of it. Some of the most powerful
reciprocating aircraft engines ever made; e.g., the WW II Bristol
Joe Wagner
T h e E n g i n e S h o p
212 S. Pine Ave., Ozark AL 36360
F&G combined metal, hardwood, and engineering plastic in
durable, multiadjustable Model Engine Break-In Test Stand.
F&G mount holds engine lugs firmly between metal upper and
lower clamping plates. Note adjustable-height fuel-tank mount.
RCV91-CD four-stroke prototype is 50% larger than earlier .58-
cubic-inch model and has same sleek, compact design.
92 MODEL AVIATION
Centaurus (used in the Hawker Sea Fury that
for years held the speed record for propellerdriven
aircraft) and the Napier Sabre (which
powered the Royal Air Force’s fastest
wartime fighter—the Hawker Tempest). Both
of those engines used rotating cylinder
sleeves instead of poppet valves.
Dennis Hansen (Spruce Head ME) has
proved that an old modeling problem with
molded-nylon model parts is still with us
today: brittleness. As Dennis was marking the
engine-bolt locations on a radial engine
mount, one of its beams snapped right off at
the base.
At first he wondered if low temperature
had caused the fracture. He told me that his
shop was “kind of chilly” at the time he was
working on the mount. But I don’t believe
that climate had anything to do with Dennis’s
engine-mount failure; I think it’s the same
problem that modelers too often experienced
with nylon propellers decades ago.
At that time, we model fliers were advised
to boil a nylon propeller for a half hour or so
before putting one on an engine. The theory
was that the boiling treatment “relieved
stresses” in the molded plastic. And it
worked!
However, the true cause of brittleness in
molded-nylon parts—plain and fiber
reinforced—is a chemical/physical
characteristic of that particular plastic. As do
concrete and plaster of paris, nylon contains
H2O as part of its structure. But unlike
concrete and plaster, whose water content
combines permanently with the other
constituents, the H2O content in nylon can
vary. And as it varies, so does the nylon’s
strength and flexibility.
Nylon is molded at temperatures of
roughly 500°—much hotter than water’s
vaporization temperature. That’s why “asmolded”
nylon parts can be low in H2O
content and reduced in strength as a result.
Nylon doesn’t need much H2O to regain
its strength—only 4% to 5% by weight. And
in thin sections, nylon can reabsorb the water
it needs from atmospheric humidity, but that
takes time. And in thick sections—such as
model propeller hubs and molded radial
engine mounts—it can take a lot of time.
That’s the real reason why boiling nylon
helps. At high temperatures, H2O can migrate
back into the plastic more readily than it can
at room temperature. And surrounded by
water in a pot on the stove, nylon parts have
unlimited access to H2O molecules for
replenishing their moisture content and
regaining their optimum physical properties.
It’s good practice to boil all molded-nylon
model parts thicker than approximately 3⁄32
inch before using them—not only propellers
and engine mounts, but bellcranks and
retractable landing-gear mechanisms too. A
half hour ought to be the minimum; for thick
parts I’d feel safer with at least a couple hours
in boiling water before use.
Another topic from previous columns that
has drawn comment from readers is the type
of aluminum container Larry Renger gave me
to use as a model diesel fuel bottle. Larry has
used them for fueling his diesel-powered
models, and he gave me one last year so I
could join in the fun.
I thought it was a water bottle. Not so! It’s
a container for campers’ stove and lantern
fuel, such as Coleman’s. A good mail-order
source for these aluminum bottles is
Campmor at (800) 226-7667 or
www.campmor.com.
A brand name that Campmor carries is
MSR. Those kind are inexpensive and
come in 11-, 22-, and 33-fluid-ounce sizes.
All have stoppers sealed with O-rings,
which will prevent any ether evaporation
Dennis Hansen proved that molded nylon can still become brittle—
even fiber-reinforced type from which this mount was made.
Customized diesel-fuel bottles and tools employed. (Drilling
stopper holes by hand keeps bit from tearing plastic.)
94 MODEL AVIATION
from diesel fuel in the container.
I’ve modified two of these aluminum fuel
bottles for use with my “never-open” diesel
filling and fueling technique. My
customization method is to hand-drill and tap
a pair of #10-32 holes in the stopper. In those
I install fueling tubes that I modify from stock
3⁄4-inch-long brass screws. I epoxy those into
place in the stopper to make sure of an
evaporation-proof seal.
In use at the field, after filling the bottle I
connect the two fueling-tube ends with a
length of plastic tubing. (Vinyl, Tygon, or
neoprene work fine, but neither rubber nor
silicone tubing can stand exposure to the
kerosene content of model diesel fuel.)
To refuel a model, I pull free one end of
the plastic tubing on the bottle and attach that
to the model’s fuel-tank fitting. Then I tilt the
bottle and let gravity do the transfer. (Air will
vent freely into the open tube in the bottle as
the fuel passes into the model’s tank.)
To fill the diesel-fuel bottle itself, I use the
same technique I just described. I’ve modified
a one-gallon, metal fuel-can cap with two
diametrically opposite soldered-in brass tubes.
And I gravity-pour fuel from the gallon-size
“commercial can” into the smaller fuel bottle
the same way I fill a model’s tank from the
bottle.
Handling model diesel fuel this way stops
ether evaporation almost perfectly. It has
eliminated the strong aroma in my model
shop that used to inform everyone who came
into it that I’m a habitual flier of dieselpowered
model airplanes. MA
This month we list those who have donated $10 or more in support of the
Academy’s programs, the National Model Aviation Museum and the
Aeromodeling Center, and those organizations that have provided grants for
which AMA has applied and received. These people have made more than a
donation—they have made an investment in the future of aeromodeling.
When you see these folks, thank them! They are now among the
thousands who have given back to model aviation part of what model
aviation has given to them. Many things will be possible due to the their
thoughtful giving and generosity.
We list our supporters monthly. These donations represent amounts
processed in the month of January 2004. If your name is not listed, please
write to the Membership Department and include a canceled check. We
want to recognize all contributors!
Thank you.
$100 up to $500
Steven R Adams - NC
Arvada Associated Modelers - CO
William H Asplund - CT
James L Barnaby - PA
David A Bossert - CA
Robert A Bruce - CA
Michael J Contreras - CA
James A Cook - IL
Billy G Dilworth III - FL
James E Dunkin - MO
Greg D Edster - MO
Jon M Edy - CO
J Ronald Esak - FL
Jack B Feir - PA
Todd M Fellage - CT
John C Frothingham - ME
Bernard Fullett - IL
Andrew N Garello - MA
Donald G Garofalow - NJ
Michael Lee Gottfried - OH
Gerald M Gregorek - OH
Thomas D Griffiths - CO
Clifford C Gustafson - CT
Tom Hartvigsen - TN
William L Holder - GA
M Hotra - NJ
Charles A Lawhon - IN
David B Malcolm - FL
Rolland Mast - MI
Stephen D Remington - CA
Ashton T Reynolds - AK
Paul P Schnepp - CA
Clarence Stephens - OH
Frank Tiano - FL
Edward Vargo - MI
Alan H Wells - GA
David J Werner - NH
$10 up to $100
Your Contributions do Make a Difference!
Dionel E Aviles - TX
Robert E Leiper - CT
David A Seuferling - MO
Western Illinois Soaring Soc - IL
