Control Line Scale - 2010/10

Also included in this column:
• New, sophisticated electronic
system
• The standard three-line
system revisited
• RC in CL: Has its time come?
Line-tension problems
[[email protected]]
Control Line Scale Bill Boss
Well built, component matched, and balanced for proper performance, the three-line
system will give a CL pilot great performance. Sketch by the author.
This sophisticated seven-channel electronic control system—
CL.7.Tx—is a unique design by John Rist, who is an electronics
engineer. The unit provides flexibility in channel use, allowing for
greater realism in a model’s operational features. Rist photo.
John Rist (R) discusses with fellow modeler Ty Marcucci the
problem of line drag and loss of line tension that led to the demise
of John’s Eindecker. Joe Garret photo.
IN THE APRIL 2010 column I wrote about
a multichannel electronic system that Joe
Eiben and Will Hubin developed. It was
actuated through the use of a microswitch and
the throw of the throttle arm of a standard
three-line bellcrank.
The column read that if an aeromodeler
wanted to operate the system independent of
the bellcrank throttle position, the leads that
would have been connected to the
microswitch could be connected directly to
two insulated lines from the control handle
and the system could be triggered by a
momentary button switch at the handle. It
also suggested that one insulated line could
be used.
John Rist sent in an e-mail message
claiming that he had used one insulated line
with his electronic system design and lost an
aircraft because of it. He wrote that when you
go into low throttle, the line tension
decreases. The larger insulated line has more
drag and tends to pull the model in a
direction (up or down) depending on where
the line is placed.
John had used the single insulated line
for up line and, as chance would have it, he
was flying on a windy day. When he cut
power to the Eindecker he was flying and it
came into the wind, enough drag was
created on the up line to drive the model up
and over the top. That resulted in a crash and
its destruction.
If you use any electronic system, do not
use a single insulated line on the up or down
flying line. If a single insulated line is to be
used with the three-line bellcrank, avoid
trouble and use the throttle line.
Any additional drag on the throttle line
would probably not interfere with the overall
control of the model, as might happen with
the up and down lines. John’s experience
also indicates that using one insulated line
with a two-line system might be a bad idea.
John submitted two of this month’s
photos. One shows him and a fellow
modeler, Ty Marcucci, discussing the
problem of the one insulated line that caused
excess drag and the demise of John’s
Eindecker.
The other picture is of John’s great oneof-
a-kind electronic handle that he
designated “Model CL.7.Tx.” He is an
electronics engineer, and he devised the
handle for his use. It is currently being used
to control an Extra 300S powered with a
SuperTigre .90 engine.
The handle has seven operational
channels, four of which are used for control
of the Extra 300S. The bottom slide is
Channel 1 and is used for throttle control.
The black knob on the left-hand side of the
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control box is designated as trim control for
the throttle channel; it can be set to control
the engine idle and have sufficient range to
shut down the engine after making a taxi run.
The left-hand knob (Channel 2) on the
face of the unit controls the ailerons. It is
used for preflight demonstration and realism
of the full-scale Extra’s operational feature
for extra points.
The right-hand knob (Channel 3) controls
the rudder. During takeoff procedure, John
can do ground steering for realism. When the
airplane is ready for flight, the control is set
to a center detent position that puts the
rudder in the proper position for flight and
proper line tension.
The switch in the extreme upper left
(Channel 4) is used on the Extra to control a
servo that switches smoke control on and off.
John notes that turning on the smoke is a
crowd pleaser and adds a great deal of
realism to the flight.
All four switches provide servo operation
in the same manner. Switch up, the servo
goes to one end. Switch down, the servo goes
to the other extreme. There are also internal
adjustments that can be made for the
direction and travel of the switch-operated
servos.
John claimed that one day he might try to
build a military-type model that would allow
for the operation of flaps, bomb drop, retracts,
etc. That way he could take advantage of his
electronic control system’s full potential.
On the subject of line tension and the
problems outlined in the preceding, and since
it has been several years since I have covered
this topic, I thought it would be appropriate
to revisit the operation of a standard threeline
system. It might also benefit new sport
fliers or those who are interested in Navy
Carrier or Scale.
The accompanying sketch shows the basic
three-line system, bellcrank, and handle, in
both high- and low-speed positions with
regard to the operation of an engine throttle.
The finger trigger at the top of the handle is
moved back and forth, and it moves the
sliding portion of the bellcrank.
A key to successful operation of the
three-line system is that it is in balance. To
achieve the balanced system, the three flying
lines must be of equal length and have equal
tension at all times.
During operation, a major consideration in
having a balanced system is that the handle
and bellcrank must be a set. That is, the travel
of the bellcrank and control handle lever
should be the same.
Mixing handles and bellcranks by
different manufacturers, such as old LR
products and J. Roberts units, leads to excess
or insufficient travel of the third line,
providing an unbalanced system and major
problems during flight. The only supplier I
know of from which you can be certain to get
matched bellcranks and handles is Brodak
Manufacturing.
Notice in the upper sketch that the center,
or throttle control, leadout is 21/8 inches
longer than the elevator control leadouts. The
measurement must be made when the
elevator leadouts are pulled tight and the
bellcrank is in the system’s high-speed
position.
The additional length of the longer third,
or center, leadout is to accommodate the
length of the shorter throttle lead of the
control handle and the cam action of the
control handle. Again, the secret to having a
good, smooth-operating system is balance.
RC for CL? Through the years CL has
evolved from simple two-line setups to the
three-line system, to modified radio systems
and current simple and sophisticated
electronic systems. There have also been
attempts to use radio control in connection
with CL, but they were halted because of
possible interference problems with other
models, creating a possible safety hazard.
Because of that risk of interference,
“Control Line General” rules, paragraph 2, in
the AMA rule book was established. It
permits only electrical impulses sent up the
control lines to be used in CL models.
However, now there are radio systems
using 2.4 GHz frequencies that, I understand,
all but eliminate the possibility of interference
with other radio systems. Although I am not
too knowledgeable about radio systems, I am
sure that some of you are and can look into
the feasibility of using 2.4 GHz with CL.
Are we ready for a change? Are we ready
for the next step in controlling CL aircraft?
Any such change would require rules
modifications. Let me hear what you
think. MA
Sources:
John Rist’s Model CL.7.Tx electronic
handle:
[email protected]
Brodak Manufacturing
(724) 966-2726
www.brodak.com
2.4 GHz information:
http://2.4gigahertz.com
Weatronic 2.4 GHz system:
www.weatronic-usa.com
Spektrum RC
(800) 338-4639
www.spektrumrc.com
Bill Boss
77-06 269th St.
New Hyde Park NY 11040
National Association of Scale Aeromodelers
www.nasascale.org