Third Line Theme for Control Line Throttle
August 1957 American
I'm 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.
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.
Although 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.
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. 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.
System consists of three lines (which you provide),
the handle and the "Plane-Unit" (photo A).
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 ... "
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, full-speed position.
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.
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.
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.
Glen Magree of Cleveland took first in Senior Carrier using Flight Control
to operate a Roto-valve on the Fox 59 in his scale model "Bearcat."
Besides 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
Bob 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 engine.
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