Old-Timers-2010/08

126 MODEL AVIATION
The Foxacoy event
Old-Timers Bob Angel | [email protected]
A seated Dave Lewis launches his Lanzo Bomber during the
Southwest Regionals. Professional photographer Doug Klassen is
at a safe distance using a telephoto lens.
Luther Peters of Fountain Hills
AZ enjoys displaying his 1/2A Scale
Messerschmitt M 17. SAM has
many small-engine events. Steve
Roselle photo.
Below: John Pratt test-launches his FF rubber-powered airplane
in Northern California. Ned Nevels photo.
Also included in this column:
• Fox .35 Stunt engines
• McCoy .35 Stunt engines
• Messerschmitt M 17 for
1/2A Scale
• Another coil saver
• A scratch-building tool
FOXACOY IS ONE of the Society of Antique Modelers’ (SAM’s)
many special RC events. Along with 1/2A Texaco, it’s a good starting
place for a newcomer to Old-Timer building and flying.
The event is slightly more popular in the Eastern US, where it
began a few years ago. It made its SAM Championships debut in 1993
at Claremore, Oklahoma. Only stock Fox .35 or McCoy .35 front-rotor
redhead CL Aerobatics (Stunt) engines are allowed, hence the name
“Foxacoy.” Later-model McCoys with the lightning bolt on the case
are ineligible.
The originators of Foxacoy felt that those two plain-bearing, non-
Schnuerle, modestly powerful, readily available, and relatively
inexpensive engines were roughly equal in performance. Any pre-1943
model design is eligible, but it must have at least 788 square inches of
wing area and a 10-ounce-per-square-foot wing loading. Airplanes can
be scaled to achieve the minimum area or larger.
The Foxacoy competition flight regime consists of an ROG (riseoff-
ground) launch and an engine run time of 35 seconds. A max flight
is 7 minutes, and the sum of the best two of four allowed flights
comprises the score.
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Fox .35s dominated CL Stunt for years
and have been in continuous production since
1948. They had a reputation for running
steadily and could be needled to allow them to
“break” from a so-called four-cycle mode to a
stronger two-cycle mode when pulled up into
a maneuver from level flight. Designer Duke
Fox was an innovator who didn’t make
copycat engines.
Probably the main secret to that steady
running was a simple but unique needle-valve
design. Instead of the conventional round,
symmetrical, pointed needle, Fox employed a
uniform-diameter, rod-shaped needle with a
tapered flat ground on the end. This was in the
days before fuel filters became widely
available.
That needle tip presented a large orifice at
the metering point in the spray bar, allowing
larger chunks of debris to pass through
without restricting fuel flow. Conventional
needles presented the same cross-sectional
metering area, but distributed in a torus shape
that would catch and hold the slightest speck
of dirt, leaning out the engine.
After fuel filters came into widespread use,
we noticed that the unique Fox needle shape
had a slight drawback. That same needle-tip
shape that allowed debris to pass through the
fuel system was not as effective at holding a
fuel charge in the line for easy hand-starting.
After choking, the fuel charge would gravitate
back toward the tank, which sat lower when
the airplane was on the ground.
Hand-starting was the norm because few
starters were in use at the time. Conventional
pointed needles held the fuel charge in the line
better, because a stronger surface tension was
presented by the torus-shaped outlet.
After fuel filters came into general use,
many CL fliers ended up buying a McCoy
Stunt needle-valve assembly and using it on
the Fox engine along with a fuel filter. At that
time, small parts for popular power plants
were readily available in hobby shops.
The McCoy Stunt engines became popular
among CL sport and Stunt fliers because they
were cheap, reliable, and easy to start and run.
Probably their only drawback was a relatively
soft piston/cylinder combination, which didn’t
tolerate too many lean runs. But if you wore it
out, you could buy a new one and get change
back from $10.
Their needle-valve assembly was good,
with a reliable clicker spring that held a
setting well, but the McCoys also had a small
needle-valve oddity. The engines came from
the factory with the needle assembly installed
backward for practical use.
The knurled needle adjustment was on the
exhaust side. Needling a side-mounted
McCoy in a profile model was awkward
because the needle was under the engine and
near the exhaust. Additionally, that put the
fuel line over the top of the engine instead of
below, where it could initially draw fuel more
easily during hand-choking.
Most modelers reversed that needle
assembly because it was simple to do. Those
engines were produced for many years in
three sizes, .19, .29 and .35, so people often
wondered why the company didn’t make that
little change during assembly. I’m sure that
more than one person made the suggestion to
McCoy.
Years later, as an engine collector, the
probable reason dawned on me. The power
plants came packaged in a neatly molded
plastic box; if the needle were reversed, the
engines wouldn’t fit in the box properly. It
simply wouldn’t have been cost-effective to
scrap maybe thousands of premanufactured
boxes and make new ones.
I have a safety suggestion for anyone
using one of the old McCoy Stunt engines:
reverse that needle-valve assembly if it hasn’t
already been done. Adjusting the needle when
it’s situated between a spinning propeller and
a hot exhaust can be hazardous.
The Messerschmitt M 17, shown, is a
favorite subject in 1/2A RC Scale. The angle
of the photo clearly shows why. There’s no
scale judging in this event, so there’s no room
for politics or favoritism; it’s pure numbers.
The flying rules are the same as for 1/2A
Texaco. Since it’s a typical climb-and-glide
competition, most modelers opt for a design
with a high aspect ratio and a minimum
number of struts and wires, which produce
drag.
For those Scale enthusiasts who would like
to build something more appealing yet
possibly less competitive in the Soaring
portion, there’s the Concours event that is
held at every SAM Champs.
The Concours award requires a qualifying
flight, but the only requirement is for a model
to become airborne. There’s no timing
involved. There’s no landing requirement, but
that normally takes care of itself in some
manner or another.
Other favorite scale designs suitable for
1/2A Soaring include the Avro, Wren, J-2 Cub,
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130 MODEL AVIATION
Klemm, Taylorcraft, and a handful of others.
Scale fliers are always on the lookout for
something new and different, but with a fairly
high-aspect-ratio wing.
The requirement is for any pre-1943
vintage design of a man-carrying airplane.
Motor gliders are excluded. If anyone
discovers a good subject, please let us all
know.
By the time you read this, another coil saver
will be on the market. I mentioned in my
June 2009 column that it would be nice if
someone would come up with a more modern
circuit to shut down power to a spark coil, to
prevent burnout when the engine stops with
the points closed. In recent columns I
mentioned the response by Larry Davidson,
who is providing such a unit.
Now Marvin Stern of AeroTech
Electronics is responding with two
products. One is designated the Mark II
and is a basic electronic ignition circuit
with an auto-cutoff feature that activates
when the points are closed for a second or
two. It reactivates quickly when the points
are reopened.
As with Larry’s unit, the Mark II is best
suited for FF or CL fliers who normally use
an auxiliary manual switch to arm the system.
It can also be employed by RC fliers in
conjunction with a servo and micro switch or
a separate electronic switch as required for inair
engine shutdown.
Marvin’s Mark III unit utilizes the Mark II
circuitry with the added function of an
electronic RC shutoff that plugs into the
receiver’s throttle channel or any other of
your choosing. It eliminates the need for RC
pilots to have an additional servo/micro
switch or a separate electronic switch for
engine shutdown.
To aid in the initial setup, the Mark III has
an LED that glows when the radio switches
the unit on. It also has a provision for wiring
in an external battery for use as a starting
booster or to test-run an engine without the
radio.
Bob Holman Plans had such good response
to its little laser-cut triangular alignment aids
for the scratch builder that Bob has come up
with a simple design for gluing wing ribs in
vertical alignment.
It is a 1/8 plywood, laser-cut gadget with a
snap-on base that can be pinned to a building
board if necessary. He sells a set of 10 for $5
plus $2.50 shipping.
These aids have precisely cut slots for 1/16,
3/32, or 1/8 ribs, so you must specify which
size set you need. MA
Sources:
AeroTech Electronics
(732) 928-0884
[email protected]
Larry Davidson
(540) 721-4563
[email protected]
Bob Holman Plans
(909) 885-3959
www.bhplans.com
SAM Champs 2010:
Dave Harding, contest manager
(610) 872-1457
www.samchamps.org
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