C/L Half-A Proto Speed Event
October 1967 American Modeler
line speed models and contests have been around nearly since the existence
of engine-powered model airplanes. As with all sports, the state of
the art in materials and design advances significantly over time, as
does the contest flyers' skills. Entering into the realm can be daunting,
especially if you do not have access to a mentor. From what I've read
on the North
American Speed Society's website, the 1/2A Profile Proto class was
created specifically to provide an opportunity to try your hand (pun
intended) at speed modeling without the need for expensive equipment
or pre-existing building and flying experience. Per the AMA's "Rules
Governing Model Aviation Competition in the United States, Control Line
Speed," 1/2A Proto models must use engines with displacements from
0.0000* to 0.0504 in3,
weigh no more than 9 oz., and fly on a pair of 42-foot long, 0.010-inch
diameter lines. The
Model Aeronautics Association of Canada stipulates identical parameters.
* See "The
Zero Displacement Engine"
C/L Half-A Proto Speed Event
These five C/L 1/2A Proto Speed models
typify those entered in this AMA event. Note configurations developed
by modelers within the rules framework.
Half-A Proto is a control-line speed event for two types of models.
For Juniors (those under 16) profile type models are acceptable; older
contestants must have models with conventional fuselages and completely
The object of Proto class events is to feature
speed flying with model size and designs tailored to specific requirements,
as compared with non-proto speed events which have no restrictions other
than engine size. And Half-A Proto is intended to hold the cost factor
down - the many cheap and efficient small engines available offer top
performance so that it is less necessary to be an engine expert to win.
Another major difference between Proto and other speed events
is in timing - in Proto the timing of official speed starts from the
instant the model is released, whereas in all-out speed events timing
does not start until the model is in the - air and contestant signals
that he wants timing to commence. Also, the length of timed flight is
longer: One-half mile for Half-A - 10 laps, as compared with 5 laps
for non-Proto speed.
For Juniors, Profile Proto is intended
to permit the simplest type models to be flown so that newcomers may
easily try competition flying, with models which are typical of those
flown for fun. Simple all-balsa types which are not much more than hand-launched
gliders with an engine, landing gear and control system, are capable
of very good performance. They are easy and cheap to build and to repair.
And the use of stock engines and fuel offers adequate performance so
that it is the flying rather than the power element which is emphasized.
Many low cost and simple to build kits are available, both profile
or full-fuselage. They may be found in practically all hobby shops although
most aren't identified as Half-A Proto type models. A scalelike appearance
is called for - true scale is not necessary - and the model must be
large enough to meet the wing and fuselage size requirements. Almost
all Half-A control-line kit designs which resemble full scale airplanes
may be used. Ready-to-fly plastic models, while not permitted in sanctioned
competition of the type which requires the model to be built by the
flyer, may be used as trainer airplanes for this event.
Profiles like these are cheap, simple,
good flyers; need AMA numbers to enter sanctioned competition.
Small control-line models tend to bank and roll toward the pilot in
the center of the circle due to the torque effect of an engine when
rotating the propeller in the typical direction. This, plus the effect
of control line drag, when the model is flown in the conventional counter-clockwise
circle, tends to turn the model into the pilot This tends to slacken
the control lines which causes loss of control - the lines need to be
taut for control to be maintained, unless torsion-type Monoline is used.
Some tricks are used to counter this tendency. Offset engines, or vertical
tails set at an angle, to keep the model turned outward, or weights
in the outboard wingtip, or offset attachment of control lines to the
model, are typical gimmicks used to force a model outward, But they
tend to decrease speed by wasting power or increasing drag.
Engine size - up to .050 cubic inches.
Min. wingspan - 18" (12" for biplanes).
Min. wing area - 45 square inches.
Design features required: a. clear canopy or cabin;
b. fixed landing gear, with min. of 2 permanently attached main
wheels of equal diameter, laterally separated from each other by
at least two wheel diameters.
engine completely cowled, except plug and head fins may be exposed.
Control line length - 42 feet (from center
of handle grip to center line of model).
size - one line: .012", two lines: .006" ea.
Timed flight - 1/2 mile (10 laps) from instant
of model release.
Safety pull test - 32
times wt. of model.
Appearance - must be
colorfully painted, or trimmed, if a clear finish is used; AMA license
numbers on upper right wing.
- model must takeoff from the ground or runway under own power.
A Half-A Proto technique which overcomes this problem takes advantage
of the ability of reed valve engines to run in either direction. This
permits a left hand prop to be used on an engine, running in the opposite
from usual direction, so that engine torque acts to pull the model outboard
of the circle, maintaining line tension and control even when wind tries
to blow the model off course. Availability of left hand props is the
key factor affecting use of this technique. Unless a commercial prop
is obtainable, hand-carving is required.
It might seem that
a simpler solution would be to fly the model in a clockwise direction.
For left-handed people this is a natural solution to the problem. But
most right-handed people find. that clockwise flying is not natural
so they must contend with the tricks involved. The rules, however, permit
flying in either direction.
The lighter the plane, the higher
the prop pitch may be - five to six inches of pitch seems to be maximum
for models weighing between 41/2 to 6 oz. If weight is above 6 oz.,
a 4" pitch "paddle" blade prop is recommended by event experts.
A lightweight plane will take off fast but not fly well in windy
weather. A good compromise for all around flying performance has been
found to be at least 5 oz., since windy conditions are more common than
calm, especially true in some parts of the country.
otherwise for Proto models, the official AMA regulations pertaining
to control-line speed models are applicable. These include the standard
control-line 32-g pull-test, which requires that an official will test
the control system before each flight with a load equal to 32 times
the weight of the model. Also required are steel or metal control lines
of equivalent strength, in good condition and free of kinks and rust.
No swivels are to be used as part of the control system for CL speed
Here are three 1/2A C/L Proto models showing
different styles of engine mounting: left to right - upright, sidewinder
(on a profile design), and inverted.
Typical Operating Features -
1/2A C/L Proto Model
Posted February 23, 2013
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