Also included in this column:
• Thoughts about castor oil
• The Lee Custom .61
is available
• The reason for offset
venturi location
SINCE THIS is my
57th column it seems
appropriate to cover
a “Heinz variety” of
topics in it.
In the previous
column I discussed
O.S.’s new LA
Series engines—the
line of sport-model
power plants with
midnight-blue exteriors. My friend Larry Blews (New Castle,
Pennsylvania), a longtime O.S. user and admirer, asked me “Are
these really an improvement on the older models or are they just
prettier-looking?”
Good question! As it happened, I had an easy way to answer it.
My son John (Dothan, Alabama) has been flying a Sig Seniorita
for years with an O.S. .25. And I have a similarly powered CLer: an
old and frequently flown Flite Streak. We removed the original
power plants from both models and installed new O.S. .25 LAs. After
performing the brief break-in called for in O.S.’s instruction manuals,
we went out to fly.
John and I soon found out that the new O.S. engines are better.
Running on the same propellers and fuel we had used on the earlier
engines, the LAs delivered noticeably better performance.
John’s Seniorita took off from grass faster and climbed more
steeply. Throttle action seemed more linear, and the remote needle
valve (NV) made adjustments safer—although it did need an extra
second or so to take full effect.
My CL Flite Streak also performed better with its new midnightblue
O.S. .25. I like to fly on longer lines than most, and that made it
easy to detect the difference. Besides approximately a 10% shorter
“level lap” time, I noticed that my 70-foot control lines ran straighter
in flight between my handle and the airplane. Then too the O.S. .25.
LA’s “remote NV” worked flawlessly throughout the test flights.
I encountered only one minor problem with my new O.S.; I’ll
need to add a bit of tail weight to its plane. The new engine is slightly
heavier than the old one; that moved the balance point forward
enough to affect maneuverability.
As I’ve mentioned several times, I use castor oil in all my glow
and diesel model fuels. Castor is a superb lubricant that prevents
rust and engine wear. That’s why it was chosen for lubricating the
rotary engines of World War I airplanes such as Nieuports and
Sopwiths. It was also often used in old-time dirt-track and
Indianapolis 500 race-car engines such as Offenhausers.
However, castor has one major drawback: it thickens
gradually—but permanently—after exposure to heat and oxygen.
In World War I airplanes and at auto racetracks this problem was
overcome by draining the crankcase oil soon after the engines
were shut down.
New engines in old airplanes! These O.S. .25 LAs made both
models fly much better than with their older-model O.S. .25s.
Injecting After-Run Oil through the fuel inlet and carburetor body
after flying stops castor-oil buildup and sticky throttle operation.
Available directly from its designer, the Lee Custom .61 is an
updated version of a 1960s contest-winning RC engine.
76 MODEL AVIATION
This Veco .19’s well-radiused intake
extension opening is purposely misaligned.
It gains power and fuel suction from that.
Norvel .25 carburetor intake, left, has been smoothly radiused (with “burr knife,” right)
to remove inlet corner showing on Norvel .15 carburetor at center.
In model engines, where the oil and
fuel are mixed, there’s no “crankcase oil”
reservoir that can be drained. However, the
castor film remaining between the moving
parts will become more viscous with time.
After a week or two it can make an engine
feel “sticky” and hard to turn over.
To prevent that from happening we
inject After-Run Oil (ARO) into our glow
engines after we’re finished flying. (Never
use ARO in model diesels, though!)
In working with model RC engines that
have not been run for a while, I’ve noticed
another area where thickening castor oil
can cause trouble: in the carburetor and
NV assemblies. Oxidized oil-film buildup
can seriously restrict fuel orifices and coat
tapered needles—in effect making them
larger in diameter, thus upsetting their
adjustments.
A sticky castor oil film on a carburetor
barrel makes the throttle servo work
harder. If that becomes excessive, it can
drain a flight battery quickly and perhaps
even cause a crash or a flyaway.
To prevent these difficulties, when you
inject ARO into your engine after flying,
also pull the fuel line off and squirt ARO
through the spraybar. Then work it well
into the carburetor barrel.
If you’d like to fly your RC airplane with
a custom-built engine—a modern version
of a famous power plant that won many
contests (including a few Nats RC events)
40 years ago—Clarence Lee (the engine’s
original designer) is again personally
assembling his Lee Custom .61s. They are
available from C.F. Lee Manufacturing
Co., 10112 Woodward Ave., Sunland CA
91040; Tel.: (818) 352-3766.
The Lee Custom .61 is a ringed-piston
engine with a carburetor based on the wellproven
Perry Carburetor, but with a remote
NV. (This Randy Linsalato-designed NV
assembly is a bit bulkier than most, yet it’s
exceptionally precise in use. It’s ruggedly
built and includes a clever adjustable
friction lock that also provides an airtight
seal around the needle.)
This newly upgraded combination of
well-proven design features and
meticulous assembly is powerful,
responsive, and reliable. It’s an ideal
power plant for old-time RC Pattern
aircraft such as the Kwik-Fly and Taurus
that are being newly built and flown these
days.
At model events I attend, someone will
often do a double take when looking at my
engine installation and say “Hey, your
venturi has slipped out of alignment!”
Then I have to explain that my off-center
air inlet was made that way on purpose.
That offbeat feature has its roots in
experiments Hi Johnson and I made in the
1950s. As most FFers have known for
decades, propeller slipstream doesn’t flow
straight back. The whirling propeller puts a
spin on the air that passes through it.
It occurred to me and Hi that we might
gain a bit of extra performance by angling
a front rotary engine’s venturi opening into
that spiraling slipstream. We tested our
theory on the model-engine dynamometer I
had built for the development of Veco
engines. Sure enough, it did make a
difference.
Later, after Hi left Veco and began
manufacturing his own Johnsonbilt line of
model engines, he used offset air inlets on
some of the custom-assembled engines he
made for CL Combat fliers. As for me, I
like long inlet passages and routinely add
intake extensions to my Fox .35s, Veco
.19s, and even a few RC engines.
Whenever I do that I angle the opening
15°-25°, depending on what pitch propeller
I expect to use. (I use a larger angle for
lower-pitch propellers.)
Something else I do to my engine air
inlets is eliminate sharp corners at the
entry. Smoothly contouring this edge can
make more difference than you’d expect,
in power output and reliable fuel suction.
Why? Getting down to basics, the
performance of any internal combustion
(IC) engine depends primarily on how
much air mass enters its combustion
chamber(s).
That’s why an IC engine puts out less
power at high altitudes than at sea level.
Its incoming air is less dense and provides
less oxygen for combustion. That’s also
why a supercharged engine develops more
power. The pressurized air delivered to the
engine by the blower is denser, contains
more oxygen, and can therefore burn more
fuel in each power stroke.
Back to the reason for my contoured-lip
model-engine intakes, sharp corners at an
air intake’s open end can cause an adverse
condition known as “inlet stall.” Air
flowing into the engine over those corners
behaves much like it would passing over a
square-cornered wing airfoil: it becomes
turbulent. And turbulent air not only
doesn’t flow smoothly, but its density is
reduced.
My custom-made intake extensions are
usually thick-walled. There’s ample
material for shaping their entries into
smoothly curved contours, but it’s possible
to round over the sharp-edged inner corners
of most of today’s model-engine intakes. I
do that by hand on my engines.
An X-Acto knife will work for this job,
but I prefer a tool called a “burr knife.” It
has a rigid, three-cornered, hardened-steel
cutting edge and can be bought via mail
order from sources such as Harbor Freight
Tools (www.harborfreight.com). This tool
is inexpensive and much easier to control
than a model knife. It’s far less likely to
slip out of the intake opening and gash
your holding hand.
In any case, reshaping the inlet entry is
a gradual, cut-only-a-little-at-a-time
process. You can reduce the effort
somewhat by starting with a hand
countersink. That will bevel the inside
corner but still leaves an edge. The burr
knife can then be used to shave that edge
away and form a smoothly curved entry for
the all-important incoming airflow.
How much power gain can this inlet
rework achieve? That’s hard to say since
there are so many variables.
However, I’d estimate a minimum of
4%; that’s 600 extra top-end rpm if your
stock engine turns up 15,000. At the other
extreme, my lengthened, offset, carefully
contoured Fox .35 extensions gave me
close to 15% more power than the stock
venturi did.
Edition: Model Aviation - 2007/02
Page Numbers: 75,76,78
Edition: Model Aviation - 2007/02
Page Numbers: 75,76,78
Also included in this column:
• Thoughts about castor oil
• The Lee Custom .61
is available
• The reason for offset
venturi location
SINCE THIS is my
57th column it seems
appropriate to cover
a “Heinz variety” of
topics in it.
In the previous
column I discussed
O.S.’s new LA
Series engines—the
line of sport-model
power plants with
midnight-blue exteriors. My friend Larry Blews (New Castle,
Pennsylvania), a longtime O.S. user and admirer, asked me “Are
these really an improvement on the older models or are they just
prettier-looking?”
Good question! As it happened, I had an easy way to answer it.
My son John (Dothan, Alabama) has been flying a Sig Seniorita
for years with an O.S. .25. And I have a similarly powered CLer: an
old and frequently flown Flite Streak. We removed the original
power plants from both models and installed new O.S. .25 LAs. After
performing the brief break-in called for in O.S.’s instruction manuals,
we went out to fly.
John and I soon found out that the new O.S. engines are better.
Running on the same propellers and fuel we had used on the earlier
engines, the LAs delivered noticeably better performance.
John’s Seniorita took off from grass faster and climbed more
steeply. Throttle action seemed more linear, and the remote needle
valve (NV) made adjustments safer—although it did need an extra
second or so to take full effect.
My CL Flite Streak also performed better with its new midnightblue
O.S. .25. I like to fly on longer lines than most, and that made it
easy to detect the difference. Besides approximately a 10% shorter
“level lap” time, I noticed that my 70-foot control lines ran straighter
in flight between my handle and the airplane. Then too the O.S. .25.
LA’s “remote NV” worked flawlessly throughout the test flights.
I encountered only one minor problem with my new O.S.; I’ll
need to add a bit of tail weight to its plane. The new engine is slightly
heavier than the old one; that moved the balance point forward
enough to affect maneuverability.
As I’ve mentioned several times, I use castor oil in all my glow
and diesel model fuels. Castor is a superb lubricant that prevents
rust and engine wear. That’s why it was chosen for lubricating the
rotary engines of World War I airplanes such as Nieuports and
Sopwiths. It was also often used in old-time dirt-track and
Indianapolis 500 race-car engines such as Offenhausers.
However, castor has one major drawback: it thickens
gradually—but permanently—after exposure to heat and oxygen.
In World War I airplanes and at auto racetracks this problem was
overcome by draining the crankcase oil soon after the engines
were shut down.
New engines in old airplanes! These O.S. .25 LAs made both
models fly much better than with their older-model O.S. .25s.
Injecting After-Run Oil through the fuel inlet and carburetor body
after flying stops castor-oil buildup and sticky throttle operation.
Available directly from its designer, the Lee Custom .61 is an
updated version of a 1960s contest-winning RC engine.
76 MODEL AVIATION
This Veco .19’s well-radiused intake
extension opening is purposely misaligned.
It gains power and fuel suction from that.
Norvel .25 carburetor intake, left, has been smoothly radiused (with “burr knife,” right)
to remove inlet corner showing on Norvel .15 carburetor at center.
In model engines, where the oil and
fuel are mixed, there’s no “crankcase oil”
reservoir that can be drained. However, the
castor film remaining between the moving
parts will become more viscous with time.
After a week or two it can make an engine
feel “sticky” and hard to turn over.
To prevent that from happening we
inject After-Run Oil (ARO) into our glow
engines after we’re finished flying. (Never
use ARO in model diesels, though!)
In working with model RC engines that
have not been run for a while, I’ve noticed
another area where thickening castor oil
can cause trouble: in the carburetor and
NV assemblies. Oxidized oil-film buildup
can seriously restrict fuel orifices and coat
tapered needles—in effect making them
larger in diameter, thus upsetting their
adjustments.
A sticky castor oil film on a carburetor
barrel makes the throttle servo work
harder. If that becomes excessive, it can
drain a flight battery quickly and perhaps
even cause a crash or a flyaway.
To prevent these difficulties, when you
inject ARO into your engine after flying,
also pull the fuel line off and squirt ARO
through the spraybar. Then work it well
into the carburetor barrel.
If you’d like to fly your RC airplane with
a custom-built engine—a modern version
of a famous power plant that won many
contests (including a few Nats RC events)
40 years ago—Clarence Lee (the engine’s
original designer) is again personally
assembling his Lee Custom .61s. They are
available from C.F. Lee Manufacturing
Co., 10112 Woodward Ave., Sunland CA
91040; Tel.: (818) 352-3766.
The Lee Custom .61 is a ringed-piston
engine with a carburetor based on the wellproven
Perry Carburetor, but with a remote
NV. (This Randy Linsalato-designed NV
assembly is a bit bulkier than most, yet it’s
exceptionally precise in use. It’s ruggedly
built and includes a clever adjustable
friction lock that also provides an airtight
seal around the needle.)
This newly upgraded combination of
well-proven design features and
meticulous assembly is powerful,
responsive, and reliable. It’s an ideal
power plant for old-time RC Pattern
aircraft such as the Kwik-Fly and Taurus
that are being newly built and flown these
days.
At model events I attend, someone will
often do a double take when looking at my
engine installation and say “Hey, your
venturi has slipped out of alignment!”
Then I have to explain that my off-center
air inlet was made that way on purpose.
That offbeat feature has its roots in
experiments Hi Johnson and I made in the
1950s. As most FFers have known for
decades, propeller slipstream doesn’t flow
straight back. The whirling propeller puts a
spin on the air that passes through it.
It occurred to me and Hi that we might
gain a bit of extra performance by angling
a front rotary engine’s venturi opening into
that spiraling slipstream. We tested our
theory on the model-engine dynamometer I
had built for the development of Veco
engines. Sure enough, it did make a
difference.
Later, after Hi left Veco and began
manufacturing his own Johnsonbilt line of
model engines, he used offset air inlets on
some of the custom-assembled engines he
made for CL Combat fliers. As for me, I
like long inlet passages and routinely add
intake extensions to my Fox .35s, Veco
.19s, and even a few RC engines.
Whenever I do that I angle the opening
15°-25°, depending on what pitch propeller
I expect to use. (I use a larger angle for
lower-pitch propellers.)
Something else I do to my engine air
inlets is eliminate sharp corners at the
entry. Smoothly contouring this edge can
make more difference than you’d expect,
in power output and reliable fuel suction.
Why? Getting down to basics, the
performance of any internal combustion
(IC) engine depends primarily on how
much air mass enters its combustion
chamber(s).
That’s why an IC engine puts out less
power at high altitudes than at sea level.
Its incoming air is less dense and provides
less oxygen for combustion. That’s also
why a supercharged engine develops more
power. The pressurized air delivered to the
engine by the blower is denser, contains
more oxygen, and can therefore burn more
fuel in each power stroke.
Back to the reason for my contoured-lip
model-engine intakes, sharp corners at an
air intake’s open end can cause an adverse
condition known as “inlet stall.” Air
flowing into the engine over those corners
behaves much like it would passing over a
square-cornered wing airfoil: it becomes
turbulent. And turbulent air not only
doesn’t flow smoothly, but its density is
reduced.
My custom-made intake extensions are
usually thick-walled. There’s ample
material for shaping their entries into
smoothly curved contours, but it’s possible
to round over the sharp-edged inner corners
of most of today’s model-engine intakes. I
do that by hand on my engines.
An X-Acto knife will work for this job,
but I prefer a tool called a “burr knife.” It
has a rigid, three-cornered, hardened-steel
cutting edge and can be bought via mail
order from sources such as Harbor Freight
Tools (www.harborfreight.com). This tool
is inexpensive and much easier to control
than a model knife. It’s far less likely to
slip out of the intake opening and gash
your holding hand.
In any case, reshaping the inlet entry is
a gradual, cut-only-a-little-at-a-time
process. You can reduce the effort
somewhat by starting with a hand
countersink. That will bevel the inside
corner but still leaves an edge. The burr
knife can then be used to shave that edge
away and form a smoothly curved entry for
the all-important incoming airflow.
How much power gain can this inlet
rework achieve? That’s hard to say since
there are so many variables.
However, I’d estimate a minimum of
4%; that’s 600 extra top-end rpm if your
stock engine turns up 15,000. At the other
extreme, my lengthened, offset, carefully
contoured Fox .35 extensions gave me
close to 15% more power than the stock
venturi did.
Edition: Model Aviation - 2007/02
Page Numbers: 75,76,78
Also included in this column:
• Thoughts about castor oil
• The Lee Custom .61
is available
• The reason for offset
venturi location
SINCE THIS is my
57th column it seems
appropriate to cover
a “Heinz variety” of
topics in it.
In the previous
column I discussed
O.S.’s new LA
Series engines—the
line of sport-model
power plants with
midnight-blue exteriors. My friend Larry Blews (New Castle,
Pennsylvania), a longtime O.S. user and admirer, asked me “Are
these really an improvement on the older models or are they just
prettier-looking?”
Good question! As it happened, I had an easy way to answer it.
My son John (Dothan, Alabama) has been flying a Sig Seniorita
for years with an O.S. .25. And I have a similarly powered CLer: an
old and frequently flown Flite Streak. We removed the original
power plants from both models and installed new O.S. .25 LAs. After
performing the brief break-in called for in O.S.’s instruction manuals,
we went out to fly.
John and I soon found out that the new O.S. engines are better.
Running on the same propellers and fuel we had used on the earlier
engines, the LAs delivered noticeably better performance.
John’s Seniorita took off from grass faster and climbed more
steeply. Throttle action seemed more linear, and the remote needle
valve (NV) made adjustments safer—although it did need an extra
second or so to take full effect.
My CL Flite Streak also performed better with its new midnightblue
O.S. .25. I like to fly on longer lines than most, and that made it
easy to detect the difference. Besides approximately a 10% shorter
“level lap” time, I noticed that my 70-foot control lines ran straighter
in flight between my handle and the airplane. Then too the O.S. .25.
LA’s “remote NV” worked flawlessly throughout the test flights.
I encountered only one minor problem with my new O.S.; I’ll
need to add a bit of tail weight to its plane. The new engine is slightly
heavier than the old one; that moved the balance point forward
enough to affect maneuverability.
As I’ve mentioned several times, I use castor oil in all my glow
and diesel model fuels. Castor is a superb lubricant that prevents
rust and engine wear. That’s why it was chosen for lubricating the
rotary engines of World War I airplanes such as Nieuports and
Sopwiths. It was also often used in old-time dirt-track and
Indianapolis 500 race-car engines such as Offenhausers.
However, castor has one major drawback: it thickens
gradually—but permanently—after exposure to heat and oxygen.
In World War I airplanes and at auto racetracks this problem was
overcome by draining the crankcase oil soon after the engines
were shut down.
New engines in old airplanes! These O.S. .25 LAs made both
models fly much better than with their older-model O.S. .25s.
Injecting After-Run Oil through the fuel inlet and carburetor body
after flying stops castor-oil buildup and sticky throttle operation.
Available directly from its designer, the Lee Custom .61 is an
updated version of a 1960s contest-winning RC engine.
76 MODEL AVIATION
This Veco .19’s well-radiused intake
extension opening is purposely misaligned.
It gains power and fuel suction from that.
Norvel .25 carburetor intake, left, has been smoothly radiused (with “burr knife,” right)
to remove inlet corner showing on Norvel .15 carburetor at center.
In model engines, where the oil and
fuel are mixed, there’s no “crankcase oil”
reservoir that can be drained. However, the
castor film remaining between the moving
parts will become more viscous with time.
After a week or two it can make an engine
feel “sticky” and hard to turn over.
To prevent that from happening we
inject After-Run Oil (ARO) into our glow
engines after we’re finished flying. (Never
use ARO in model diesels, though!)
In working with model RC engines that
have not been run for a while, I’ve noticed
another area where thickening castor oil
can cause trouble: in the carburetor and
NV assemblies. Oxidized oil-film buildup
can seriously restrict fuel orifices and coat
tapered needles—in effect making them
larger in diameter, thus upsetting their
adjustments.
A sticky castor oil film on a carburetor
barrel makes the throttle servo work
harder. If that becomes excessive, it can
drain a flight battery quickly and perhaps
even cause a crash or a flyaway.
To prevent these difficulties, when you
inject ARO into your engine after flying,
also pull the fuel line off and squirt ARO
through the spraybar. Then work it well
into the carburetor barrel.
If you’d like to fly your RC airplane with
a custom-built engine—a modern version
of a famous power plant that won many
contests (including a few Nats RC events)
40 years ago—Clarence Lee (the engine’s
original designer) is again personally
assembling his Lee Custom .61s. They are
available from C.F. Lee Manufacturing
Co., 10112 Woodward Ave., Sunland CA
91040; Tel.: (818) 352-3766.
The Lee Custom .61 is a ringed-piston
engine with a carburetor based on the wellproven
Perry Carburetor, but with a remote
NV. (This Randy Linsalato-designed NV
assembly is a bit bulkier than most, yet it’s
exceptionally precise in use. It’s ruggedly
built and includes a clever adjustable
friction lock that also provides an airtight
seal around the needle.)
This newly upgraded combination of
well-proven design features and
meticulous assembly is powerful,
responsive, and reliable. It’s an ideal
power plant for old-time RC Pattern
aircraft such as the Kwik-Fly and Taurus
that are being newly built and flown these
days.
At model events I attend, someone will
often do a double take when looking at my
engine installation and say “Hey, your
venturi has slipped out of alignment!”
Then I have to explain that my off-center
air inlet was made that way on purpose.
That offbeat feature has its roots in
experiments Hi Johnson and I made in the
1950s. As most FFers have known for
decades, propeller slipstream doesn’t flow
straight back. The whirling propeller puts a
spin on the air that passes through it.
It occurred to me and Hi that we might
gain a bit of extra performance by angling
a front rotary engine’s venturi opening into
that spiraling slipstream. We tested our
theory on the model-engine dynamometer I
had built for the development of Veco
engines. Sure enough, it did make a
difference.
Later, after Hi left Veco and began
manufacturing his own Johnsonbilt line of
model engines, he used offset air inlets on
some of the custom-assembled engines he
made for CL Combat fliers. As for me, I
like long inlet passages and routinely add
intake extensions to my Fox .35s, Veco
.19s, and even a few RC engines.
Whenever I do that I angle the opening
15°-25°, depending on what pitch propeller
I expect to use. (I use a larger angle for
lower-pitch propellers.)
Something else I do to my engine air
inlets is eliminate sharp corners at the
entry. Smoothly contouring this edge can
make more difference than you’d expect,
in power output and reliable fuel suction.
Why? Getting down to basics, the
performance of any internal combustion
(IC) engine depends primarily on how
much air mass enters its combustion
chamber(s).
That’s why an IC engine puts out less
power at high altitudes than at sea level.
Its incoming air is less dense and provides
less oxygen for combustion. That’s also
why a supercharged engine develops more
power. The pressurized air delivered to the
engine by the blower is denser, contains
more oxygen, and can therefore burn more
fuel in each power stroke.
Back to the reason for my contoured-lip
model-engine intakes, sharp corners at an
air intake’s open end can cause an adverse
condition known as “inlet stall.” Air
flowing into the engine over those corners
behaves much like it would passing over a
square-cornered wing airfoil: it becomes
turbulent. And turbulent air not only
doesn’t flow smoothly, but its density is
reduced.
My custom-made intake extensions are
usually thick-walled. There’s ample
material for shaping their entries into
smoothly curved contours, but it’s possible
to round over the sharp-edged inner corners
of most of today’s model-engine intakes. I
do that by hand on my engines.
An X-Acto knife will work for this job,
but I prefer a tool called a “burr knife.” It
has a rigid, three-cornered, hardened-steel
cutting edge and can be bought via mail
order from sources such as Harbor Freight
Tools (www.harborfreight.com). This tool
is inexpensive and much easier to control
than a model knife. It’s far less likely to
slip out of the intake opening and gash
your holding hand.
In any case, reshaping the inlet entry is
a gradual, cut-only-a-little-at-a-time
process. You can reduce the effort
somewhat by starting with a hand
countersink. That will bevel the inside
corner but still leaves an edge. The burr
knife can then be used to shave that edge
away and form a smoothly curved entry for
the all-important incoming airflow.
How much power gain can this inlet
rework achieve? That’s hard to say since
there are so many variables.
However, I’d estimate a minimum of
4%; that’s 600 extra top-end rpm if your
stock engine turns up 15,000. At the other
extreme, my lengthened, offset, carefully
contoured Fox .35 extensions gave me
close to 15% more power than the stock
venturi did.