CL Combat - 2012/05

124 Model Aviation May 2012 www.ModelAviation.com
When the first CL enthusiasts came up with the
idea of tying crepe-paper streamers to the back
of a model and chasing it around the sky with a
similarly equipped model, they used hard, metal fuel tanks.
This took place sometime in the early 1950s, long before I
had seen a CL model fly.
The engines these early pioneers used worked hard to suck
the fuel out of the tank (suction system). If the tank was
positioned too high, low, or too far away, the engine would run
inconsistently. They became difficult to start and needle-valve
settings could change after the model was in the air.
The venturi openings for an engine running on suction
are limited. The opening cannot be so large that it prevents
sucking fuel from the tank.
I would have loved to have been there to see the first cut
taken on the first streamer-towing model. At that point, pilots
must have begun their quest to get better engine runs with
more speed, which would help them cut up crepe-paper
streamers.
I don’t know who came up with the idea of a pressure
fuel-delivery system. Pressure fuel systems used the crankcase
pressure created by the piston’s downstroke. Drilling and
tapping the backplate to accept a pressure fitting allowed a
piece of fuel tubing to be connected to a vent in the tank.
The fuel pick-up vent usually went to the rear outboard
corner of the fuel tank and a piece of fuel tubing connected it
to the needle valve. If the tank had only two vents, both fuelline
connections had to be undone in order to fill the tank.
Some manufacturers used two short vents on top of the
tank: one for filling it and the other to accept the tubing from
the pressure tap. After the tank was filled, one of the top two
vents would have to be plugged with a short, knotted piece
of tubing or plugged with a short screw. The fuel pick-up line
could remain attached to the needle valve during the filling
process. Some pilots even added an in-line fuel filter.
Pilots using this system had to be careful not to flood
the engine when they were filling the tank or starting the
engine, because each time the propeller was turned, a little air
pressure went to the tank, forcing fuel to the needle valve.
These pressure fuel systems allowed for large venturi
openings and much better performance from the engine. I
used this type of hard tank throughout the early 1970s with
good results; however, there were many frustrating times
when the vent would crack on its own or because of a rough
landing or crash.
Small pin holes in the fuel tubing caused erratic engine runs.
The hard metal fuel tanks were notorious for collecting dirt
internally and then trying to force-feed it to the engine.
by disassembling the filter and removing the offending crud.
I can remember a day of frustration at Crocker Amazon
Park in San Francisco, when my flying buddy, Doug Bias, had
just finished a beautiful silk-covered VooDoo and was ready to
fly it for the first time. We fired up the SuperTigre G-21 .35
and launched it.
The motor ran somewhat erratically on its maiden flight.
Upon landing we found that the tank had a leak. Doug was so
cl combat
Metal Tank Fuel Delivey
Systems
by Rich Lopez
[email protected]
PLUS:
> Pacifier and
bladder fuel
systems
> Competitions
This is a hard metal tank with all the plumbing that goes to and from the
engine.
The latex rubber-bladder tanks are shown inflated
and at rest. Two-ounce plastic syringes are used to inject
accurate amounts of fuel.
Using rust-colored, squeeze-action fuel
bulbs added to the contamination of the
metal tank, especially if they were old
and starting to deteriorate. Even when
fuel filters were used, enough debris
could collect in the filter screen to stop
the fuel flow. This was easily corrected
This antique Li’l Snip shows
a pacifier tank bulge built
into the structure.
126 Model Aviation May 2012 www.ModelAviation.com
annoyed that he jumped up and down
on the painstakingly built VooDoo.
There was a weight penalty to
be paid with metal tanks, which
prompted a search for lightweight
alternative fuel-delivery systems.
Pacifier and Bladder Systems
The first person I remember
using pacifier fuel tanks was Alex
Sinkevitch at a Western Associated
Modelers contest in Northern
California.
Alex built lightweight Sneeker
models that looked as though they
were dancing in the sky. The models
were modified so that there was a
big bulging compartment behind of
the engine, which would allow the
baby pacifier to expand.
Hollow baby pacifiers could be
purchased at almost any drug store.
A lead-out eyelet was inserted into
a piece of fuel tubing, which was
then inserted into the baby pacifier.
The pacifier was wrapped at the
neck with copper wire or a small
rubber band. The unit weighed
little, lowering the model’s overall
weight.
In those days, some pilots still
used the same rust-colored fuel
bulbs to inflate the baby pacifier
with fuel. This often resulted in
the fuel bulbs coming apart. It was
not an accurate way of knowing
how much fuel you had put in the
pacifier.
Using 2-ounce plastic syringes
solved the pacifier inflation problem
and most Combat pilots still use
them. The pacifiers were limited
by how much fuel they could hold
before they burst and made a mess,
but they provided a steady fuel
flow to the engine no matter what
direction the model was pointing.
Some modelers used pen bladders
in a similar fashion. These could
be purchased at stationary stores.
I owned fountain pens that had
internal bladders. Little levers on
the pen’s barrel served as a pump
to draw ink out of a bottle.
Most Combat pilots currently use
latex tubing to make their bladders.
They are affordable, easy to make,
and can be sized to accommodate
the amount of fuel you want to run.
Latex tubing comes in a variety of
diameter sizes and wall thicknesses.
I like the 1/4-inch ID x 3/8-inch
OD x 1/32-inch wall, opaque black,
super-soft, latex rubber tubing for
FAI bladders. It is McMaster-Carr
item No. 5234K74.
If you fly thin-airfoil 1/2A
models, then you would want a
smaller-diameter tubing such as
5/32- x 3/64-inch McMaster-Carr
item No. 5233K963. McMaster-
Carr has an excellent website
(see “Sources”), and because it is
located in Southern California,
I usually get my orders the next
day via UPS. The company carries
fuel tubing and many little barbed
fittings that can be used as fuel-line
connections.
Bladder end plugs and fuel
delivery ends can be found in the
irrigation section of your local
Home Depot, Lowes, or hardware
store, under the name of Goof
cL combat
Plugs. The 24-gauge wire that I
use to bind the end plugs and fuel
delivery ends can also be found at
the aforementioned places.
Competitions
By the time you read this column,
the Phoenix March Madness contest
will be in the books. If you have any
interest in international competitions,
then you may wish to visit the FAI
calendar section for CL competitions.
This year’s World Championships
will be held in Pazardzhik, Bulgaria,
August 25-September 1. Bill Lee
is the CL team manager and Don
McClave will be his assistant. If
you want to know more about
who is on the team for the various
disciplines, visit Bill’s 2012 CL World
Championships website listed in the
“Sources” section.
The Miniature Aircraft Combat
Association (MACA) is a great source
of information and an organization
that we should all support. Visit its
website listed in “Sources.”
Check out Combat Graffiti for
some great photos of old Combat
models on the Flying Lines website.
Sources :
2012 Control Line World Championships/Team USA
www.2012clwc.org
McMaster Carr
(562) 463-4277
www.mcmaster.com
MACA
www.maca.hobby-site.com:3535
Flying Lines
www.flyinglines.org/kb.graffiti.html
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