not sure how long the 3rd-line for throttle control has been around,
but this article from the August 1957 edition of American Modeler seems
to suggest that it was introduced formally around time of the 1957 model
hobby industry trade show in Chicago - maybe a few years before. There
in an exhibitors' booth was a special bellcrank featuring a three-wire
control line system offered by the J. Roberts Model Manufacturing Company,
of Baker, OR.
Third Line Theme
scene is the big annual trade show for the model-hobby industry in Chicago.
Three large halls are jammed with exhibit booths of new plane, train,
and boat kits, engines (glow) and motors (d.c.), accessory and supply
Sauntering about are fat-cat distributors and
their coveys of salesmen, rival manufacturers, solemn-looking designers
checking the other guy's brainstorm -and almost lost in the vast crowd,
a few build-it-yourself control line modelers.
outnumbered a hundred to one, it's easy to spot the yo-yo fans. All
you have to do is plant yourself in front of the small display by a
small concern from a small town in Oregon. This booth features "Flight
Control;" a three-wire control line system offered by the J. Roberts
Model Mfg. Co., of Baker, Ore.
Here come some CL'ers;
quickly come their comments. "Hey, look at that landing gear retract!"
"Now that's what I call a real sharp motor control . . ."
etc., etc. You get the idea.
What is this third line deal that's
the theme of J. Robert "Bob" Smurthwaite's pitch? Bob describes it as
"a mechanical triple-control connection in which three wires can be
selectively manipulated while an equalizing pull or tension is exerted
on all three."
Translated from the Patent Office lingo it means
you move the Roberts Flight Control handle (photo E) like any standard
Ukie handle for "Up" and "Down"; at the same time you can trigger a
third line back and forth. Different, claims JRS, is the fact that
the centrifugal pull of the airplane in flight is divided among the
3 control lines which share equally the pull load.
of three lines (which you provide), the handle and the "Plane-Unit"
Lines hook up and detach in conventional manner
for storing on any standard reel. Most modelers are surprised to find
no springs in the set-up. Reason; a doubled leverage mechanism within
the handle compensates for every action of the plane-unit regardless
of the maneuver or control operation.
as Smurthwaite points out, it requires very little line tension to maintain
full control. As a result solo flight operations are possible. In fact,
the first motor-speed control flight with the experimental unit was
a I-man deal from hooking up the lines, starting the engine, walking
to the center of the circle, then taking off the model. A spring held
the motor speed restrictor at low when the lines were slack.
This original test plane was a scale model of the Danish KZ-3 lightplane.
The 5-pound, 54" wingspan model used a Madewell .49 on ignition. An
exhaust rotary restrictor had been installed in a stack extension. After
8 years of flying Bob's first all-aluminum plane-unit is still in good
condition. Its bulkiness has been cut down in the latest version. Final
tests are near completion on a small one for use on planes with motors
up to .15 cu. in. displacement. Regardless of the size of the plane-unit
or model, the one size handle works with all.
Ron Moulton, noted
English designer, reported to Bob that "the great revelation was that
the control can be set and left alone. We had been under the impression
that it would be essential to maintain finger tension on the 3rd line
to retain engine setting, but in fact, this is only required when ...
(one) blips the motor ... "
in sketch D is the new style full-length "slide-restrictor" Smurthwaite
now recommends. This type which fits almost every size and shape exhaust
stack works more smoothly and wears longer with its lengthened, edge
surfaces. You make this by drilling starting holes in the saw blade
"slide" material and filing out the open "port." It is best to grind
and fit the blank slide to the necessary incisions and tracks that you
make in the exhaust stack before drilling and porting the slide. Your
motor, naturally, starts each time with restrictor slide back in open,
The Oregon manufacturer sees the Navy Carrier,
the new Air Force Rocketry event (AM, pg 42, 2/57) and rat racing as
logical places for his units. Beyond that he thinks motor speed control
and wheel brake possibilities will stimulate greater activity in all
phases of control line flying be it sport or competition.
recent years," declares JRS, "precision aerobatic events have been won
by flyers who enter large models with stunt flaps in the wing. A smaller
precision-stunt model utilizing Flight Control will wrap up more points
than ever before possible with the following advantages: The necessity
of stunt-flaps to perform those square comers can be eliminated by the
combination of a fullpower ,surge and up/down elevator control at:
the same moment to snap the plane around sharply. Smaller models can
be slowed to a smooth cruising speed between each maneuver to allow
the judges more time to record maneuvers.
smaller model, I refer to a model without stunt-flaps with a span between
38 and 46 inches and a wing area from 320 to 450 square inches."
Production-line control units were first used at the Dallas National
Meet last July. Donald Storner (photo B), 15, of Belleville, Ill., won
first in Junior Navy Carrier using Flight Control to operate a Bramco
throttle on a Fox 35 motor. His friend from Belleville, 16-year-old
John Corrough, won second in Senior Carrier event with the same combination-both
flew J. Roberts "Sabre" models equipped with their own version carrier-hooks.
John's model is shown on ground in photo B.
of Cleveland took first in Senior Carrier using Flight Control to operate
a Roto-valve on the Fox 59 in his scale model "Bearcat."
the. items mentioned JRS says his system can be utilized to operate
landing flaps, carrier-arresting hooks, bomb-bay doors and racks and
related mechanism to drop any desired number of bombs at any time from
any position including dive-bombing, also multi-engine control, landing
lights, pilot ejection seat, even change of propeller pitch.
is an old-time modeler having been a fan of this magazine since its
Bill Barnes days. He recalls building from our early plans Gordon Light's
1935 Wakefield winner and Al Judge's '36 championship plane as wen as
many of Alan Booton's scale jobs. As owner of one of the first Ohlsson
.23 power plants, he scaled down Ben Shereshaw's Cavalier to take that
Bob's forthcoming kit models includes a scale-line
prop-driven Crusader (photo F) for Navy Carrier and other racing events.
Span is 28", length is 30"; it takes .29 to .35 motor. Original has
carrier-hook; complete horizontal tail surface moves like the full scale
job. All-balsa molded construction to be featured; kit ready by mid-summer.
Later he promises the scale Corsair for Fox 59 with motor-speed (photo
C). Model has retractable landing gear, including tail-wheel, controllable
rudder offset, droppable carrier-hook-all operating through one handle.