Control Line Aerobatics - 2006/09

156 MODEL AVIATION
Smith of Aero Products. The McCoy .40
shown is a special engine that was
personally redesigned, built, and modified
by the legendary Dick McCoy for the alsolegendary
Ed Southwick.
The SuperTigre .46 is completely stock
and, unlike most other engines of this era,
it has a piston fitted with a compression ring rather than lapped.
The next group contains the Modern engine. I have
subdivided this group into factory-stock, general-purpose engines
and Stunt-specific designs. These engines have a different
porting system for intake and exhaust. They have an additional
fuel-induction port commonly called a boost port.
Shown is the O.S. Max .40 VF. This engine really ushered in
the tuned pipe. Despite the fact that it hasn’t been produced for
more than 20 years, it is still being used by some of the top
competitors and is reliable and powerful.
The other engine shown is the Magnum .36 XLA II, which I
have been using exclusively in
my Diva designs. Many who
have flown the Magnum
engine have commented that
the power is comparable to
that of the O.S. .40 VF with
the same level of consistency.
The Stunt-specific engines
include the Aero .40 Lite RE,
the Aero .65 RE, and the new
Aero Marine .75 RE. These
are a result of collaboration by
Randy Smith and Henry
Nelson. Aero engines are
prolific at any Stunt
competition.
There is another Stuntspecific
engine line by yet
another collaboration,
between Richard Oliver and
Dubby Jett. They made the
RoJett engines, which are
offered in sizes ranging from
WHAT’S NEW? It just so happens that
there is something new in Precision
Aerobatics (Stunt). In fact, it may change
the way we do things forever.
For as long as I can remember, the big
mystery in Stunt has been power. Through
the years there have been many solutions
and methods of getting an acceptable power system to work
consistently. The last significant improvement to the power
systems in general was the tuned pipe. For the majority of top
competitors in the US, a good tuned-pipe system is a “musthave.”
The other big thing has been the availability of engines, which
have either been designed specifically for our purpose or can
easily be adapted for the rigors of Stunt. As these engines have
been put into operation, many people have begun to modify and
tweak them for a variety of reasons.
So how do you begin to put the power puzzle together?
To better understand the
evolution of power systems I
have included photos to show
the progression. As you look at
the pictures, there is a visual of
the past 40 years of Stunt
power-system development.
You might notice that except
for one power plant they look
similar.
For clarity I’ll break these
power plants into three groups,
the first of which I will call the
Classic Glow engines. A photo
shows three: the McCoy .40,
the O.S. Max .35S, and the
SuperTigre .46. All have castiron
pistons and the same
porting system with a single
intake and exhaust.
Notice the anodized blue
head on the O.S. Max .35S. It is
a custom retrofit by Randy
The CL Stunt power package reviewed and explained
[email protected]
Control Line Aerobatics P.T. Granderson
Also included in this column:
• An engine break-in procedure
Upper left (top to bottom): Stunt-specific modern engines PA
.40 RE Lite, PA .65 RE, PA .75 RE. Lower left: General-purpose
engines Magnum .36 XLA II (top), O.S. .40 VF. Upper right: AXI
motor, battery pack. Lower right (top to bottom): McCoy .40,
O.S. .35S, SuperTigre .46.
Top to bottom: Modified McCoy .40, modified O.S. .35S, boxstock
SuperTigre .46. McCoy and O.S. .35S have been fitted
with special heads. See text.
L: Universal AC/DC charger, discharger. R: AXI motor, four-cell
Lithium battery pack, speed controller/sequencer. (At time of
writing Bob Hunt is using the AXI motor and battery pack in
Spain at the CL World Championships.)
09sig5.QXD 7/26/06 9:01 AM Page 156the RoJett .40 to the RoJett .85.
The final power-system group is not
centered around the internal-combustion
engine; it is a motor. This type of power is
new and exciting for Stunt and model
aviation in general. It is also the biggest
mystery.
Shown are the primary components of
the electric system, which include the
motor, battery pack, speed controller, and
charger. How to most effectively apply
this system to CL Stunt is progressing and
evolving daily. There are some advantages
and some drawbacks.
Will this be the future of our sport or
just another option? We will have a much
better idea of the answer by this time next
summer.
Electric power is intriguing, but it is
still very much an experiment. For now
most pilots already have an investment in
glow engines. There is rarely a day when I
go flying when someone isn’t having
engine problems. In fact, engine problems
seem to be the rule rather than the
exception.
To be sure, power can be a dizzying maze
of engines and adjustments. Should you
use a totally stock engine or do you need
one that has been tuned or modified by an
expert? Two-stroke technology is not
difficult to work with if you take your
time and apply some basic elements
during the setup.
Those of us who have been around
engines for a while are careful in
preparing an engine and airplane for
consistent performance. When choosing
engines that are currently available, there
is a good chance that they are
manufactured with relatively uniform fit
and of good-quality materials.
So what does it take to set up a system
that will work consistently? The first thing
to do is break in the engine on a good test
stand. This is generally done with a
propeller that is smaller in diameter than
the one you will use in flight. Following is
the procedure I have used for many years,
and it has proved to be successful on a
variety of engines from different
manufacturers.
Before you begin the break-in process,
it helps to understand why an engine
needs initial break-in. This process allows
an engine’s moving parts to mesh together
at normal operating temperature.
When the moving parts reach their
operating temperature, friction causes
extra heat where the fit of the parts is
tight. The metal parts actually rub
together and wear away the tight spots. To
do this properly, you will need to provide
enough lubrication and at the same time
allow things to move fast enough to
generate a fair amount of heat.
The propeller you select for break-in
should be at least an inch less in diameter
than the one you will use in flight. If you
are using a .40-size engine turning a 10-
to 11-inch propeller in flight, I suggest a 9
x 4 or 8 x 6 propeller for break-in. If you
are using a .60-size engine, try a 10 x 6
for break-in.
Select a good-quality fuel with
reasonable lubrication. Oil content should
be at least 20%. For the past 35 years I
have used fuel that has 20% oil content.
This is a mix of castor and synthetic oils.
This is the same formula for oil used in
virtually all my break-ins and flying. That
formula consists of 20% oil content by
volume, with at least 5% being castor and
the remaining being a good-quality
synthetic that mixes well with castor.
My synthetic oil of choice has been
Klotz. There is a large selection of fuels
available, with different oil content and
formulation. Of the commercially
available brands that are widely
distributed, many have used Sig and
PowerMaster with excellent results. Either
will be good for break-in and flying.
Once you’ve selected the engine, fuel,
and propeller, you are ready for the initial
break-in. The first time you start the
engine, set the needle-valve mixture to a
fast four-stroke. This will be a rich
mixture, which means the engine is not
getting enough air to ignite all the fuel on
its power stroke. Four-stroke operation
allows extra lubrication to reach all the
moving parts without causing excessive
wear.
Do not allow your engine to run more
than four minutes the first time you start
it. Allow it to cool thoroughly after
shutting down. The next runs can be
extended to seven to 10 minutes with
complete cooldown between runs. In
general, modern engines will be ready for
flight after one to two hours of bench
running.
SeptemberNow that the initial break-in is
completed, you can install the engine in
your model and go flying. The next two
to four hours of actual flight time will
complete the break-in process. In flight
your engine will experience different
loads from flying around or maneuvering.
This will cause the parts to find a great fit
and should yield many hours of consistent
runs.
If you have one of the older engines
with a cast-iron piston and liner, use
considerably more castor in your fuel.
When I use these engines I run one tank
of the synthetic/castor mixture through
the engine after three to four hours of
running on the castor-only mixture. This
process seems to clean just enough of the
castor residue to keep everything working
well.
Remember: rely on the fact that
something is working to validate the fact
that it does work. MA
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