82 MODEL AVIATION
I’LL START THIS month’s column with a clarification. In
discussing the Rotary Sleeve Valve (RCV) four-stroke model
engines recently in this magazine, I mentioned some full-scale
aircraft engines that also used rotary sleeves instead of poppet
valves for their intake and exhaust functions.
These engines’ sleeve valves did rotate—but not all the way
around, the way the RCV engines’ cylinder sleeves do. (To me,
the word “rotary” doesn’t necessarily imply complete rotation,
such as in the case of the old “rotary dial” telephones.)
In an earlier column I wrote about nylon fuel tubing that used to
be available from auto-parts stores—but isn’t now. Bill Baker
(Norman OK) then sent me a length of “plain nyrod” inner
(“pushrod”) tubing. This is exactly the right size to substitute for
brass in fuel tanks! It’s available inexpensively in bulk from
Hobby Lobby (5614 Franklin Pike Cir., Brentwood TN 37027;
Tel.: [615] 377-6948; Web site: www.hobbylobby.com).
The only problem with using nylon tubing for plumbing
model fuel tanks is making bends in it. Bill forms his around the
tip of a 30-watt soldering iron. However, I’ve discovered a better
way.
Drill a 1⁄8-inch hole in a fair-sized block of hardwood, and
push the nylon tubing end partway down that. Then heating the
tubing just above the block with a narrow-nozzle MonoKote Heat
Gun will soften it enough for kinkless bending.
This method works better than bending the tubing around a
hot soldering iron because the entire perimeter of the tubing at
the bend location is evenly heated by the hot air—not just its
inner surface.
On the subject of nylon, the molded nylon propellers so
frequently used in model flying sometimes have too small a hub
hole, which needs enlarged to fit its shaft. Unless you do the
enlarging job with a handheld chuck, don’t try opening the hole
with a drill bit.
The cutting edges of a “twist drill bit” tend to pull it deeper
into the hole. In soft materials (such as plastics), this can result in
sudden and violent “digging in.” Trying to enlarge nylonpropeller
hub holes with a power drill may cause grabbing of the
bit into the hole, instantly converting the propeller into a whirling
flesh cutter.
A better way is with a “propeller reamer” such as the one that
Tower Hobbies sells. However, if only a small amount of hole
enlargement is needed in a nylon propeller, the reamer may not
work. It’s characteristic of nylon to resist reaming—or any other
kind of minor material removal with a cutting tool. The tool
edges merely push the plastic aside instead of cutting. After that,
the displaced material will move right back where it was.
Therefore, if you have a nylon propeller (plain or reinforced)
with a too-tight propeller shaft hole, the best way to enlarge the
hole may be to wrap a strip of roughly 120-grit abrasive paper
around a suitable-size dowel or metal tube and use that to open
up the shaft hole.
Or lacking a handheld chuck, you could make one. It’s easy
and inexpensive. You’ll need a wooden file handle, a “spare
parts” chuck for a Black & Decker drill motor, and a steel bolt
that threads into the chuck’s base. Hacksaw the head off the bolt,
epoxy the cutoff end into the file handle, screw on the chuck, and
you’re finished.
Another topic I recently mentioned in this column was my
successfully hand-starting and running a glow engine—with a
Joe Wagner
T h e E n g i n e S h o p
212 S. Pine Ave., Ozark AL 36360
Tower Hobbies’ “4-Step” propeller reamer avoids digging-in
difficulties when enlarging hub holes in propellers.
Here’s all you need to make a custom handheld drill chuck. (The
one in back is several years old and is used frequently.)
Homemade modification to Enya’s muffler solved an irritating
problem. Note “key” in the middle of the muffler intake.
07sig3.QXD 4/23/04 1:04 pm Page 82
small actual gain in performance—on fuel containing 20% water.
Bob Angel (Santa Maria CA), who is the newsletter editor for
the Central Coast Chapter of the Society of Antique Modelers,
wrote to tell of similar experiments that he’d conducted a few
years ago with a Cox reed-valve .049.
Instead of adding the water to his glow fuel all at once, as I
did, Bob made his water additions gradually. He noticed no
difference in the engine’s performance until he reached 15%
water content.
I suggested that the difference between my recent results with
a Johnson .29 and his with a Cox .049 was because of the 1⁄2A
engines’ larger cooling area in proportion to their combustionchamber
volumes. Thus those naturally run cooler than larger
engines—and the addition of noncombustible water to the fuel for
a 1⁄2A would cause a performance loss at a lower percentage
level.
This interchange led to further “technical correspondence” on
model-engine fuel between Bob and me. He had often wondered
why methanol is the preferred “maximum power fuel” for model
airplanes, race cars, etc. when gasoline is known to have a far
higher energy content.
The reason for this paradoxical situation lies in the fact that
what limits the power output of an internal-combustion engine (of
any type, large or small) is the amount of air available in the
combustion chamber for burning the fuel. (That’s why
supercharging boosts power output; it packs more air into the
cylinder.)
Combustion is a complicated process, with many possible
variables—as anyone can learn from the section on combustion in
Van Nostrand’s Scientific Encyclopedia. The fundamental facts
(for complete combustion) are:
• Methyl alcohol produces 10,000 British Thermal Units (BTU)
per pound and needs approximately seven times its weight of air
to do that.
• Ethyl alcohol produces 12,000 BTU per pound and needs
roughly 14 times its weight of air to do that.
• Gasoline (which isn’t a single chemical compound—not even a
standardized blend of hydrocarbons) produces roughly 20,000
BTU per pound and needs more than 30 times its weight of air for
that.
Therefore, if a given internal-combustion engine’s air-intake
ability is a constant, only approximately one-quarter as much
gasoline can be burnt in it per revolution as methanol.
Since gasoline’s energy content (and potential power output)
is 20,000 BTU and methanol’s is 10,000 BTU, it follows that an
engine burning four times as much methanol as gasoline will
produce roughly double the power. (As for ethyl alcohol, the
numbers given in the preceding show that there’s no power
advantage in using it instead of methanol or gasoline.)
Also on the subject of model-engine fuel, Dale Steiner
(Detroit MI) asked whether the aluminum fuel containers
(described in an earlier “The Engine Shop” column, with
reference to model diesel fuel) would also work for glow.
Yes! They’re suitable for any kind of model fuel, and the
modifications I suggested allow convenient, gravity-flow fueling
of all kinds of model airplanes. No pump or syringe is needed,
and the aluminum containers won’t rust or split a seam. Designed
for safe use by backpacking campers, they can stand up to
considerable rough handling.
I’m now retired from doing model-engine rework, but from time
to time an old friend will come over with a “small problem” that
needs fixing. Last year one of them brought in an Enya .15 R/C
with an annoying habit: its strap-on muffler kept sliding off in
flight, no matter how much its retaining screws had been
tightened. I fixed that problem in a jiffy—and almost entirely
with hand tools.
I found a length of rectangular aluminum bar in my “scrap
box,” hacksawed off a short piece, and then filed that to fit snugly
into the inlet passage of the Enya’s muffler. This acted as a “key”
to stop the muffler from slipping away from its proper position on
the engine’s exhaust stack. Then to prevent this added key from
being shifted by vibration, I drilled a small hole through the
muffler and key to admit a piece of solid copper electrical wire.
Slightly countersinking both external ends of this hole allowed
me to use the copper wire as a rivet. That was far easier to do—
and neater-looking when finished—than using a machine screw
and nut. (And rivets never vibrate loose!)
Making minor modifications such as this used to be a common
activity of most “power fliers.” Some of the changes made to
their engines were more or less to personalize a modeler’s power
plant. Other revisions were intended to improve performance in
some way. Whether they accomplished that or not, the results
were almost always educational—one way or another.
Many older model engines that are in good condition are still
available for cheap. These can provide excellent subjects for
experimentation. You don’t necessarily need a machine shop;
considerable work can be done with hand tools.
To handle more ambitious projects, Hobby Lobby sells a
tabletop-sized Taig Micro metal-cutting lathe, which can handle
parts as large as 41⁄2 inches in diameter. It even has an optional
milling attachment for work such as slotting and other straightline
cutting of metal, wood, and plastic.
For several years in the late 1950s, I did all my own modelengine
modifications with a similar mini machine tool. That took
ingenuity and time; small metal lathes lack the power for making
deep cuts in one pass. But the work provided me with a pleasant
challenge and a rewarding pastime. MA
July 2004 83
This McCoy “9” from the 1950s lacks much value as a collectors’
item and makes a fine “guinea pig” to experiment with.
Made on a minilathe, the custom carburetor on A-M .10 diesel
functions far better than its original factory throttle.
07sig3.QXD 4/23/04 1:04 pm Page 83
Edition: Model Aviation - 2004/07
Page Numbers: 82,83
Edition: Model Aviation - 2004/07
Page Numbers: 82,83
82 MODEL AVIATION
I’LL START THIS month’s column with a clarification. In
discussing the Rotary Sleeve Valve (RCV) four-stroke model
engines recently in this magazine, I mentioned some full-scale
aircraft engines that also used rotary sleeves instead of poppet
valves for their intake and exhaust functions.
These engines’ sleeve valves did rotate—but not all the way
around, the way the RCV engines’ cylinder sleeves do. (To me,
the word “rotary” doesn’t necessarily imply complete rotation,
such as in the case of the old “rotary dial” telephones.)
In an earlier column I wrote about nylon fuel tubing that used to
be available from auto-parts stores—but isn’t now. Bill Baker
(Norman OK) then sent me a length of “plain nyrod” inner
(“pushrod”) tubing. This is exactly the right size to substitute for
brass in fuel tanks! It’s available inexpensively in bulk from
Hobby Lobby (5614 Franklin Pike Cir., Brentwood TN 37027;
Tel.: [615] 377-6948; Web site: www.hobbylobby.com).
The only problem with using nylon tubing for plumbing
model fuel tanks is making bends in it. Bill forms his around the
tip of a 30-watt soldering iron. However, I’ve discovered a better
way.
Drill a 1⁄8-inch hole in a fair-sized block of hardwood, and
push the nylon tubing end partway down that. Then heating the
tubing just above the block with a narrow-nozzle MonoKote Heat
Gun will soften it enough for kinkless bending.
This method works better than bending the tubing around a
hot soldering iron because the entire perimeter of the tubing at
the bend location is evenly heated by the hot air—not just its
inner surface.
On the subject of nylon, the molded nylon propellers so
frequently used in model flying sometimes have too small a hub
hole, which needs enlarged to fit its shaft. Unless you do the
enlarging job with a handheld chuck, don’t try opening the hole
with a drill bit.
The cutting edges of a “twist drill bit” tend to pull it deeper
into the hole. In soft materials (such as plastics), this can result in
sudden and violent “digging in.” Trying to enlarge nylonpropeller
hub holes with a power drill may cause grabbing of the
bit into the hole, instantly converting the propeller into a whirling
flesh cutter.
A better way is with a “propeller reamer” such as the one that
Tower Hobbies sells. However, if only a small amount of hole
enlargement is needed in a nylon propeller, the reamer may not
work. It’s characteristic of nylon to resist reaming—or any other
kind of minor material removal with a cutting tool. The tool
edges merely push the plastic aside instead of cutting. After that,
the displaced material will move right back where it was.
Therefore, if you have a nylon propeller (plain or reinforced)
with a too-tight propeller shaft hole, the best way to enlarge the
hole may be to wrap a strip of roughly 120-grit abrasive paper
around a suitable-size dowel or metal tube and use that to open
up the shaft hole.
Or lacking a handheld chuck, you could make one. It’s easy
and inexpensive. You’ll need a wooden file handle, a “spare
parts” chuck for a Black & Decker drill motor, and a steel bolt
that threads into the chuck’s base. Hacksaw the head off the bolt,
epoxy the cutoff end into the file handle, screw on the chuck, and
you’re finished.
Another topic I recently mentioned in this column was my
successfully hand-starting and running a glow engine—with a
Joe Wagner
T h e E n g i n e S h o p
212 S. Pine Ave., Ozark AL 36360
Tower Hobbies’ “4-Step” propeller reamer avoids digging-in
difficulties when enlarging hub holes in propellers.
Here’s all you need to make a custom handheld drill chuck. (The
one in back is several years old and is used frequently.)
Homemade modification to Enya’s muffler solved an irritating
problem. Note “key” in the middle of the muffler intake.
07sig3.QXD 4/23/04 1:04 pm Page 82
small actual gain in performance—on fuel containing 20% water.
Bob Angel (Santa Maria CA), who is the newsletter editor for
the Central Coast Chapter of the Society of Antique Modelers,
wrote to tell of similar experiments that he’d conducted a few
years ago with a Cox reed-valve .049.
Instead of adding the water to his glow fuel all at once, as I
did, Bob made his water additions gradually. He noticed no
difference in the engine’s performance until he reached 15%
water content.
I suggested that the difference between my recent results with
a Johnson .29 and his with a Cox .049 was because of the 1⁄2A
engines’ larger cooling area in proportion to their combustionchamber
volumes. Thus those naturally run cooler than larger
engines—and the addition of noncombustible water to the fuel for
a 1⁄2A would cause a performance loss at a lower percentage
level.
This interchange led to further “technical correspondence” on
model-engine fuel between Bob and me. He had often wondered
why methanol is the preferred “maximum power fuel” for model
airplanes, race cars, etc. when gasoline is known to have a far
higher energy content.
The reason for this paradoxical situation lies in the fact that
what limits the power output of an internal-combustion engine (of
any type, large or small) is the amount of air available in the
combustion chamber for burning the fuel. (That’s why
supercharging boosts power output; it packs more air into the
cylinder.)
Combustion is a complicated process, with many possible
variables—as anyone can learn from the section on combustion in
Van Nostrand’s Scientific Encyclopedia. The fundamental facts
(for complete combustion) are:
• Methyl alcohol produces 10,000 British Thermal Units (BTU)
per pound and needs approximately seven times its weight of air
to do that.
• Ethyl alcohol produces 12,000 BTU per pound and needs
roughly 14 times its weight of air to do that.
• Gasoline (which isn’t a single chemical compound—not even a
standardized blend of hydrocarbons) produces roughly 20,000
BTU per pound and needs more than 30 times its weight of air for
that.
Therefore, if a given internal-combustion engine’s air-intake
ability is a constant, only approximately one-quarter as much
gasoline can be burnt in it per revolution as methanol.
Since gasoline’s energy content (and potential power output)
is 20,000 BTU and methanol’s is 10,000 BTU, it follows that an
engine burning four times as much methanol as gasoline will
produce roughly double the power. (As for ethyl alcohol, the
numbers given in the preceding show that there’s no power
advantage in using it instead of methanol or gasoline.)
Also on the subject of model-engine fuel, Dale Steiner
(Detroit MI) asked whether the aluminum fuel containers
(described in an earlier “The Engine Shop” column, with
reference to model diesel fuel) would also work for glow.
Yes! They’re suitable for any kind of model fuel, and the
modifications I suggested allow convenient, gravity-flow fueling
of all kinds of model airplanes. No pump or syringe is needed,
and the aluminum containers won’t rust or split a seam. Designed
for safe use by backpacking campers, they can stand up to
considerable rough handling.
I’m now retired from doing model-engine rework, but from time
to time an old friend will come over with a “small problem” that
needs fixing. Last year one of them brought in an Enya .15 R/C
with an annoying habit: its strap-on muffler kept sliding off in
flight, no matter how much its retaining screws had been
tightened. I fixed that problem in a jiffy—and almost entirely
with hand tools.
I found a length of rectangular aluminum bar in my “scrap
box,” hacksawed off a short piece, and then filed that to fit snugly
into the inlet passage of the Enya’s muffler. This acted as a “key”
to stop the muffler from slipping away from its proper position on
the engine’s exhaust stack. Then to prevent this added key from
being shifted by vibration, I drilled a small hole through the
muffler and key to admit a piece of solid copper electrical wire.
Slightly countersinking both external ends of this hole allowed
me to use the copper wire as a rivet. That was far easier to do—
and neater-looking when finished—than using a machine screw
and nut. (And rivets never vibrate loose!)
Making minor modifications such as this used to be a common
activity of most “power fliers.” Some of the changes made to
their engines were more or less to personalize a modeler’s power
plant. Other revisions were intended to improve performance in
some way. Whether they accomplished that or not, the results
were almost always educational—one way or another.
Many older model engines that are in good condition are still
available for cheap. These can provide excellent subjects for
experimentation. You don’t necessarily need a machine shop;
considerable work can be done with hand tools.
To handle more ambitious projects, Hobby Lobby sells a
tabletop-sized Taig Micro metal-cutting lathe, which can handle
parts as large as 41⁄2 inches in diameter. It even has an optional
milling attachment for work such as slotting and other straightline
cutting of metal, wood, and plastic.
For several years in the late 1950s, I did all my own modelengine
modifications with a similar mini machine tool. That took
ingenuity and time; small metal lathes lack the power for making
deep cuts in one pass. But the work provided me with a pleasant
challenge and a rewarding pastime. MA
July 2004 83
This McCoy “9” from the 1950s lacks much value as a collectors’
item and makes a fine “guinea pig” to experiment with.
Made on a minilathe, the custom carburetor on A-M .10 diesel
functions far better than its original factory throttle.
07sig3.QXD 4/23/04 1:04 pm Page 83