Author: Bob Angel
Edition: Model Aviation - 2010/08
Page Numbers: 126,128,130
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The Foxacoy event

Foxacoy is one of the Society of Antique Modelers' (SAM) 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.

Eligibility and rules

  • Any pre-1943 model design is eligible.
  • Minimum wing area: 788 square inches (models may be scaled to achieve this or larger).
  • Minimum wing loading: 10 ounces per square foot.
  • Launch: ROG (rise-off-ground).
  • Engine run time: 35 seconds.
  • Maximum flight: 7 minutes.
  • Scoring: sum of the best two of four allowed flights.

Engines: Fox .35 and McCoy .35

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, the unique Fox needle shape had a slight drawback: the 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.

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, which made needling a side-mounted McCoy in a profile model awkward because the needle was under the engine and near the exhaust. That also 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. 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. Years later, the probable reason became clear: 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 thousands of premanufactured boxes and make new ones.

Safety suggestion: if you're using an old McCoy Stunt engine, reverse the 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.

1/2A RC Scale and 1/2A Soaring

The Messerschmitt M 17 is a favorite subject in 1/2A RC Scale—the angle of the design makes it visually appealing. There is no scale judging in this event, so results are determined purely by performance (numbers), not politics or favoritism.

The flying rules for 1/2A RC Scale 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 to reduce drag.

For Scale enthusiasts who want something more appealing but possibly less competitive in the Soaring portion, there is the Concours event held at every SAM Champs. The Concours award requires a qualifying flight, but the only requirement is for the model to become airborne—there's no timing involved and no landing requirement (though models usually land in some manner).

Other favorite scale designs suitable for 1/2A Soaring include the Avro, Wren, J-2 Cub, Klemm, Taylorcraft, and a handful of others. The requirement is any pre-1943 vintage design of a man-carrying airplane; motor gliders are excluded. If anyone discovers a good subject, please share it.

Electronic coil-saver units

By the time you read this, another coil saver will be on the market. In June 2009 it was suggested that someone develop a modern circuit to shut down power to a spark coil to prevent burnout when the engine stops with the points closed. Larry Davidson responded with a unit providing that function.

Now Marvin Stern of AeroTech Electronics is offering two products:

  • Mark II: 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. Best suited for FF or CL fliers who normally use an auxiliary manual switch to arm the system. It can also be used by RC fliers with a servo and micro switch or a separate electronic switch for in-air engine shutdown.
  • Mark III: uses the Mark II circuitry with the added function of an electronic RC shutoff that plugs into the receiver’s throttle channel (or any other channel you choose). It eliminates the need for RC pilots to have an additional servo/micro switch or a separate electronic switch for engine shutdown. The Mark III has an LED that glows when the radio switches the unit on and includes a provision for wiring in an external battery for use as a starting booster or to test-run an engine without the radio.

Building aid: Bob Holman Plans

Bob Holman Plans had good response to its little laser-cut triangular alignment aids for the scratch builder, and has produced 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. A set of 10 sells 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.

Sources

Transcribed from original scans by AI. Minor OCR errors may remain.