160 MODEL AVIATION
CONTROL LINE NAVY CARRIER
Dick Perry, 427 Live Oak Ln. NE, Albuquerque NM 87122; E-mail: [email protected]
This rotary version of the exhaust-slide speed control belongs to
Leon Ryktarsyk. This type of speed control can be used in
conjunction with a fuel meter or a modern carburetor.
Mike Greb’s MO-1 sports a Quickie Jett .40 engine and Red-Jett
carburetor. Designed for muffler pressure, it’s an easy approach to
Class I with muffler pressure and 10% fuel.
CORRECTION: Thanks to all of you who correctly identified
Gary Hull’s Douglas TBD Devastator in the January column. I do
indeed know the difference between the SBD and the TBD, but
the late hour, lack of sleep, and impending deadline took their
toll. It’s nice to know that I have so many readers who are paying
attention to the details!
Nats: Ted Kraver has offered to serve as event director for the
official Carrier events at the Nats. Thanks, Ted. There are plenty
of openings for other official and assistant positions. You may
volunteer by contacting me or any of the Navy Carrier Society
officers.
Engine Speed Control: The means by which we throttle our
Carrier models’ engines have seen extensive evolution throughout
the years. I’ve described numerous methods in this column, and I
will provide a summary this month of the history and the
interesting throttle options from the past. I’ll end with the method
that frequent Navy Carrier Nats winner and record holder Pete
Mazur currently uses.
The first Navy Carrier events introduced CL modelers to the
concept of throttle control. Initial efforts at achieving that control
tended to rely on standard bellcranks for elevator and a third line
working against a spring for engine speed control.
The actual mechanism for engine speed control started with
intake restrictors—usually a flapper valve on the intake of a
standard glow engine that put it in a rich setting when closed.
Some engines had dual needle valves that did the same thing,
adding fuel to reduce engine speed through a rich mixture.
Ignition engines had the option of a separate set of ignition
points, which allowed the timing to be changed, reducing the
power. Such systems had essentially two speeds—high and low—
with the low speed preset on the ground.
J. Robert (Bob) Smurthwaite (J. Roberts) soon introduced the
Flight Control balanced three-line bellcrank that we have today.
Brodak manufactures today’s system, and although it looks
slightly different from the J. Roberts units, Bob Smurthwaite
developed both designs.
With infinitely variable throttle position a possibility, Bob also
introduced the Vari-Speed engine speed control: a slide-type
exhaust restrictor which slowed the engine by creating back
pressure in the engine exhaust that limited the fuel that could be
introduced to the cylinder when the intake ports were open. It was
extremely effective on a suction engine since the reduced airflow
through the intake as the engine slowed reduced the fuel flow at
the same time.
As the McCoy, Dooling, and other large glow engines became
prevalent in the Speed circles, they were adapted to Carrier.
Pressure fuel systems allowed more open intakes for more power,
but throttle schemes such as the Vari-Speed were incompatible
with pressure fuel systems because the relatively constant tank
pressure and fixed needle-valve setting produced a constant fuel
flow, which flooded the engine on low speed.
Bill Johnson developed the solution. He used an exhaust slide
coupled with a fuel meter made from brass tubing that restricted
the fuel flow as the exhaust slide closed. The open intake
maintained a relatively constant tank pressure as engine speed
changed.
The low-speed mixture was controlled by varying the closed
position of the slide in relation to the meter, usually via a
bendable connecting link. The midrange mixture was varied by
changing the internal meter geometry, changing the slide
geometry, or changing the length of the arm where the connecting
link attached to the meter. It was a reliable system after the initial
tinkering to produce the optimum settings. Significant changes in
fuel or propeller could require a new set of adjustments.
Refinements came along later and included a meter by Harry
Higley that allowed for internal adjustment of the low-speed
mixture. A rotary variant of the exhaust slide was used by some,
including the one in a photograph on one of Leon Ryktarsyk’s
models.
Intake throttles came to glow engines with radio control. Initial
idle mixture adjustment was via an adjustable air bleed that
changed the intake pressure for the suction fuel system, thus
changing the fuel flow.
An early attempt at varying the fuel
flow throughout the throttle range was
produced by Johnson (Johnson Engines—
not Bill Johnson). The throttle barrel had
a cam slot that changed the position of the
barrel relative to the housing. Rather than
using that movement to change a separate
idle needle position, the Johnson
carburetors changed the position of the
primary (and only) needle valve.
Kavan introduced a carburetor
designed for use with pressurized fuel
systems. It included a fuel meter as well
as an air bleed and a valve that vented the
pressure in the fuel tank as the throttle
was closed. It required more force to
operate than other throttles because of the
valve mechanism and many adjustments
to coordinate the valve opening and meter
settings.
The best use in Carrier was a twoposition
intake “switch” that allowed the
engine to run on pressure, with a large
intake for high speed and switch to
suction at a reduced power setting that
was still sufficient for the higher power
requirements of slow-speed flight—even
the hanging flight of current Carrier
events. The low speed was modulated by
an exhaust restrictor, just like the Vari-
Speed on suction from years before.
Modern RC carburetors have greatly
eased the modern Carrier flier’s enginespeed-
control tasks. Profile Carrier
models, which are required to operate on
suction fuel systems, can use them with
relative ease, although most are designed
to operate on muffler pressure, which is
prohibited in Profile.
The slightly larger intake diameters
allowed by muffler pressure can still
produce sufficient suction for Profile
Carrier because RC carburetors are
designed to operate throughout a large
engine-speed range. That means they
work even with propellers that are too
large for efficient engine operation or with
large variations in tank position relative to
the engine.
By using smaller propellers to allow
our engines to operate at their power peak
and controlling the fuel head with uniflow
tank venting, Carrier modelers can
accommodate significantly larger intake
diameters than standard RC carburetors
provide. Carburetors designed for .60
engines can operate effectively on the .36
engines of Profile Carrier.
Larger carburetors, including those
designed for pump fuel systems, can be
used with pumps or with crankcase
pressure. Crankcase pressure is still
incompatible with intake throttles used
alone because of the wide variation in
pressure as the intake valve closes—
including pressures below atmospheric
pressure at idle.
The best use is in conjunction with an
exhaust restrictor. That is the
configuration Pete Mazur uses on his
models. The throttle is used primarily for
its fuel-metering capabilities. By not
closing the intake throttle to the minimum
necessary for idle with only the carburetor
for speed control, crankcase pressure can
be maintained above atmospheric.
The exhaust slide is a major
contributor to the speed control. By
adjusting the slide’s rate of closure as the
intake throttle closes, mixture can be
controlled throughout the entire engine
speed range.
Start by setting the mixture for fullthrottle
running. Reduce throttle settings
and adjust the mixture using the idle
needle valve while closing the throttle for
appropriate mixture, and set the throttle
stop at the desired idle speed. Open the
throttle to see that the high-speed mixture
is still appropriate, and then start to check
the midrange mixture by slowly closing
the throttle and checking the response
back to open throttle.
Initial adjustments to midrange mixture
can be made by adjusting the length of the
slide pushrod to close the slide sooner for
a lean midrange or to close it later for a
rich midrange mixture. The rate of closure
compared to the intake throttle can also be
changed if that is convenient.
After making the initial change,
readjust the idle setting. The objective at
this stage is to end up with a rich
midrange and acceptable open and closed
mixture settings if an optimum mixture
schedule can’t be maintained throughout
the entire range with the initial slide
configuration. Fine-tune the midrange
mixture throughout the entire range by
enlarging the opening in the slide a little at
a time, starting at the higher engine speed
settings.
If you go too far, set the slide to close
sooner and start again. The result should
be an engine that is running at an optimum
mixture for good high speed, reliable idle,
cool operation, and rapid response from
any throttle setting.
Make sure that all adjustments are
made with the model in the attitude it will
be in during slow flight. An engine that is
set properly for hanging low-speed flight
will probably be too rich to respond
reliably from a prolonged level attitude at
idle settings. An engine adjusted in a level
attitude will probably be too lean when the
nose is raised.
In the next column I’ll write about fuel
tanks for suction and pressure.
Keep your hook dry. MA
Edition: Model Aviation - 2005/04
Page Numbers: 160,161
Edition: Model Aviation - 2005/04
Page Numbers: 160,161
160 MODEL AVIATION
CONTROL LINE NAVY CARRIER
Dick Perry, 427 Live Oak Ln. NE, Albuquerque NM 87122; E-mail: [email protected]
This rotary version of the exhaust-slide speed control belongs to
Leon Ryktarsyk. This type of speed control can be used in
conjunction with a fuel meter or a modern carburetor.
Mike Greb’s MO-1 sports a Quickie Jett .40 engine and Red-Jett
carburetor. Designed for muffler pressure, it’s an easy approach to
Class I with muffler pressure and 10% fuel.
CORRECTION: Thanks to all of you who correctly identified
Gary Hull’s Douglas TBD Devastator in the January column. I do
indeed know the difference between the SBD and the TBD, but
the late hour, lack of sleep, and impending deadline took their
toll. It’s nice to know that I have so many readers who are paying
attention to the details!
Nats: Ted Kraver has offered to serve as event director for the
official Carrier events at the Nats. Thanks, Ted. There are plenty
of openings for other official and assistant positions. You may
volunteer by contacting me or any of the Navy Carrier Society
officers.
Engine Speed Control: The means by which we throttle our
Carrier models’ engines have seen extensive evolution throughout
the years. I’ve described numerous methods in this column, and I
will provide a summary this month of the history and the
interesting throttle options from the past. I’ll end with the method
that frequent Navy Carrier Nats winner and record holder Pete
Mazur currently uses.
The first Navy Carrier events introduced CL modelers to the
concept of throttle control. Initial efforts at achieving that control
tended to rely on standard bellcranks for elevator and a third line
working against a spring for engine speed control.
The actual mechanism for engine speed control started with
intake restrictors—usually a flapper valve on the intake of a
standard glow engine that put it in a rich setting when closed.
Some engines had dual needle valves that did the same thing,
adding fuel to reduce engine speed through a rich mixture.
Ignition engines had the option of a separate set of ignition
points, which allowed the timing to be changed, reducing the
power. Such systems had essentially two speeds—high and low—
with the low speed preset on the ground.
J. Robert (Bob) Smurthwaite (J. Roberts) soon introduced the
Flight Control balanced three-line bellcrank that we have today.
Brodak manufactures today’s system, and although it looks
slightly different from the J. Roberts units, Bob Smurthwaite
developed both designs.
With infinitely variable throttle position a possibility, Bob also
introduced the Vari-Speed engine speed control: a slide-type
exhaust restrictor which slowed the engine by creating back
pressure in the engine exhaust that limited the fuel that could be
introduced to the cylinder when the intake ports were open. It was
extremely effective on a suction engine since the reduced airflow
through the intake as the engine slowed reduced the fuel flow at
the same time.
As the McCoy, Dooling, and other large glow engines became
prevalent in the Speed circles, they were adapted to Carrier.
Pressure fuel systems allowed more open intakes for more power,
but throttle schemes such as the Vari-Speed were incompatible
with pressure fuel systems because the relatively constant tank
pressure and fixed needle-valve setting produced a constant fuel
flow, which flooded the engine on low speed.
Bill Johnson developed the solution. He used an exhaust slide
coupled with a fuel meter made from brass tubing that restricted
the fuel flow as the exhaust slide closed. The open intake
maintained a relatively constant tank pressure as engine speed
changed.
The low-speed mixture was controlled by varying the closed
position of the slide in relation to the meter, usually via a
bendable connecting link. The midrange mixture was varied by
changing the internal meter geometry, changing the slide
geometry, or changing the length of the arm where the connecting
link attached to the meter. It was a reliable system after the initial
tinkering to produce the optimum settings. Significant changes in
fuel or propeller could require a new set of adjustments.
Refinements came along later and included a meter by Harry
Higley that allowed for internal adjustment of the low-speed
mixture. A rotary variant of the exhaust slide was used by some,
including the one in a photograph on one of Leon Ryktarsyk’s
models.
Intake throttles came to glow engines with radio control. Initial
idle mixture adjustment was via an adjustable air bleed that
changed the intake pressure for the suction fuel system, thus
changing the fuel flow.
An early attempt at varying the fuel
flow throughout the throttle range was
produced by Johnson (Johnson Engines—
not Bill Johnson). The throttle barrel had
a cam slot that changed the position of the
barrel relative to the housing. Rather than
using that movement to change a separate
idle needle position, the Johnson
carburetors changed the position of the
primary (and only) needle valve.
Kavan introduced a carburetor
designed for use with pressurized fuel
systems. It included a fuel meter as well
as an air bleed and a valve that vented the
pressure in the fuel tank as the throttle
was closed. It required more force to
operate than other throttles because of the
valve mechanism and many adjustments
to coordinate the valve opening and meter
settings.
The best use in Carrier was a twoposition
intake “switch” that allowed the
engine to run on pressure, with a large
intake for high speed and switch to
suction at a reduced power setting that
was still sufficient for the higher power
requirements of slow-speed flight—even
the hanging flight of current Carrier
events. The low speed was modulated by
an exhaust restrictor, just like the Vari-
Speed on suction from years before.
Modern RC carburetors have greatly
eased the modern Carrier flier’s enginespeed-
control tasks. Profile Carrier
models, which are required to operate on
suction fuel systems, can use them with
relative ease, although most are designed
to operate on muffler pressure, which is
prohibited in Profile.
The slightly larger intake diameters
allowed by muffler pressure can still
produce sufficient suction for Profile
Carrier because RC carburetors are
designed to operate throughout a large
engine-speed range. That means they
work even with propellers that are too
large for efficient engine operation or with
large variations in tank position relative to
the engine.
By using smaller propellers to allow
our engines to operate at their power peak
and controlling the fuel head with uniflow
tank venting, Carrier modelers can
accommodate significantly larger intake
diameters than standard RC carburetors
provide. Carburetors designed for .60
engines can operate effectively on the .36
engines of Profile Carrier.
Larger carburetors, including those
designed for pump fuel systems, can be
used with pumps or with crankcase
pressure. Crankcase pressure is still
incompatible with intake throttles used
alone because of the wide variation in
pressure as the intake valve closes—
including pressures below atmospheric
pressure at idle.
The best use is in conjunction with an
exhaust restrictor. That is the
configuration Pete Mazur uses on his
models. The throttle is used primarily for
its fuel-metering capabilities. By not
closing the intake throttle to the minimum
necessary for idle with only the carburetor
for speed control, crankcase pressure can
be maintained above atmospheric.
The exhaust slide is a major
contributor to the speed control. By
adjusting the slide’s rate of closure as the
intake throttle closes, mixture can be
controlled throughout the entire engine
speed range.
Start by setting the mixture for fullthrottle
running. Reduce throttle settings
and adjust the mixture using the idle
needle valve while closing the throttle for
appropriate mixture, and set the throttle
stop at the desired idle speed. Open the
throttle to see that the high-speed mixture
is still appropriate, and then start to check
the midrange mixture by slowly closing
the throttle and checking the response
back to open throttle.
Initial adjustments to midrange mixture
can be made by adjusting the length of the
slide pushrod to close the slide sooner for
a lean midrange or to close it later for a
rich midrange mixture. The rate of closure
compared to the intake throttle can also be
changed if that is convenient.
After making the initial change,
readjust the idle setting. The objective at
this stage is to end up with a rich
midrange and acceptable open and closed
mixture settings if an optimum mixture
schedule can’t be maintained throughout
the entire range with the initial slide
configuration. Fine-tune the midrange
mixture throughout the entire range by
enlarging the opening in the slide a little at
a time, starting at the higher engine speed
settings.
If you go too far, set the slide to close
sooner and start again. The result should
be an engine that is running at an optimum
mixture for good high speed, reliable idle,
cool operation, and rapid response from
any throttle setting.
Make sure that all adjustments are
made with the model in the attitude it will
be in during slow flight. An engine that is
set properly for hanging low-speed flight
will probably be too rich to respond
reliably from a prolonged level attitude at
idle settings. An engine adjusted in a level
attitude will probably be too lean when the
nose is raised.
In the next column I’ll write about fuel
tanks for suction and pressure.
Keep your hook dry. MA