Simple ShyFox racer is great for
beginners to CL Racing
When Dave “McSlow” Hull began Control Line (CL) Racing, he looked for an event to enter at local contests, and noticed that Super Slow Rat (SSR) and
Fox Racing events were held more often than others. His local
hobby shop did not have any kits, so he designed the ShyFox.
The ShyFox was built approximately three weeks before
the 2005 Northern California Racing Championships, so the
design was simple. Dave used 1/16 ribs with capstrips, although
the plans showed 3/32 ribs without capstrips. He also used an
aluminum engine-mounting plate with an integral gear leg.
A stock SSR-class engine, such as the O.S. 25LA Stunt,
was recommended for someone who was inexperienced with
engines. To race in Fox, Dave recommended a Fox . 35 Stunt,
but made readers aware that Fox powerplants used different
design features and materials, and plenty of castor oil.
The fuel tank needed to be built to match the engine to
achieve the correct number of laps. Rules permitted the tank
to be as large as 2 ounces, but most . 25 engines overran on that
much fuel and could be cause for disqualification if the two
required pit stops were not completed.
The fuel shutoff was also an integral part of the system and
considered a safety item for SSR and Fox racing. Dave’s aircraft
was fitted with a small, spring-loaded, drawbar-type shutoff with
a pull-to-actuate trip wire from “Dirty Dale” Long.
The wing had a consistent thickness of 1 inch from root to
wingtip—the required thickness. The best way to make the
wing ribs was to cut an aluminum root and wingtip template,
drill matching holes in the template, drill a set of rectangular
balsa ribs blanks to match, sandwich it together, and
Spar notches were scored and the spars and leading edge were
reinforced with .007 x 1/4-inch carbon-fiber strips laminated to
the inside of each spar.
Dave covered the wing with MonoKote iron-on covering
before installing the balsa and five-ply birch plywood fuselage.
The fuselage and tail were covered with lightweight fiberglass
and epoxy resin. After the rudder was glued to the fuselage and
fillets added, a final shaping and sanding was employed and
KlassKote epoxy was used to seal and fuelproof the wing and
fuselage joint. Dave used Spectra fishing line to create
After making sure the center of gravity was within 1/8 inch of
the location on the plans, the ShyFox was ready for test-flying
and racing. Dave connected .015-inch stranded steel lines and
started with a handle spacing of approximately 2 inches.
The shutoff should be tried while in flight and the sensitivity
set to suit the pilot. The engine should speed up slightly on the
last lap, although the tank should run evenly to the end, which
could be a downside because the pilot might not have much
warning of an impending pit stop.
“From the first flight, it was obvious that the model
performed smoothly and was simple to fly,” Dave noted.
“We were competitive [at the Northern California Racing
Championships] from the start, nabbing a second place among
Dave also competed at the Nats and won first place with the
ShyFox. He mentioned that the straightforward fuel system and
starting procedure made the win possible, and that it flew so
solidly that wind was never a factor.
ShyFox was featured in the March 2010 issue of Model
Aviation as AMA Plans Service number 1039, and is available
for $14, plus shipping and handling. AMA members can access
the MA Digital Library on the magazine’s website to read more
about this airplane and its construction. See page 146 or go to
www.modelaircraft.org/plans.aspx to order.
106 Model Aviation JULY 2017 www.ModelAviation.com