Control Line Combat - 2004/04

158 MODEL AVIATION
I HAVE WANTED to discuss fuel systems
for quite sometime, and this is going to be
my attempt at giving you some insight
based on my 40 years of experience
tinkering with model aircraft.
There are really only two basic types of
fuel systems in use by model-aircraft pilots.
There are many variations of these systems,
as you will see when I describe each of
them. Plenty of modelers will want to
disagree and put their spin on what I will try
to describe for you. However, my intent is
to provide concrete information that will get
your model in the air with a reliable and
consistent engine run.
The oldest of the two is the “suction”
system, which the earliest modelers used to
provide fuel to the engines. This requires
some sort of container—also known as a
“tank”—to hold the fuel. This container
must have a number of hard pipes and soft
or flexible tubing that will allow the fuel to
flow from the container to the engine
venturi. Placement of the hard pipes within
the container is critical since a Control Line
model will be circulating with gravity and
centrifugal force acting on the fuel within
the tank.
A suction system relies on the vacuum
created by the movement of the piston going
up and down in the cylinder of the engine
and traveling through the rotating crankshaft
opening, or bore, and eventually up the
venturi to where the spraybar opening is
located. This vacuum sucks the fuel out of
the opening in the spraybar.
Many things can go wrong with this type
of system, starting with a venturi having an
opening that is too large, causing a loss of
suction directly to the opening of the
spraybar. Also, the location of the tank can
have a significant impact on the engine’s
ability to draw a steady flow of fuel to the
engine.
The most common type of tank for a
suction system is made from metal,
although these days numerous plastic tanks
are in use in Control Line and Radio Control
applications. Most models vibrate to some
extent, and some vibrate a lot. Vibration can
wreak havoc on a metal tank’s solder joints.
A metal tank buried in a model that springs
a leak can be frustrating.
Doug Bias was an outstanding builder
from the San Francisco, California, area in
the 1960s and 1970s. He constructed a
Voodoo in yellow silk with orange trim that
he took way too much time on, applying
eight to 10 coats of dope. I was there to
launch the model for its first flight. The run
was a bit erratic, and we discovered that the
CONTROL LINE COMBAT
Rich von Lopez, 8334 Colegio Dr., Los Angeles CA 90045
This typical use of a bladder pressure system is shown in an uninflated state.
The Lubbock boys and a couple of Flukers (L-R): 1982 World Champion Tom Fluker Jr.,
Andy Mears, Tom Fluker Sr., Bobby Mears, and Riley Wooten.
Mike Whillance and Graham Ives of the UK liked the idea of a money contest in the USA.
April 2004 159
tank had a leak. Doug jumped up and down
on the new Voodoo.
If the tank is too far away from the
engine, the fuel will be unable to travel the
distance needed with the amount of suction
produced by the engine. Plenty of modelers
have mastered the hard-tank suction system
and can get consistent runs time and time
again. Suction tanks are still used in AMA
Slow Combat models, but they are
disappearing rapidly.
The AMA Slow Combat models may be
completely gone in the near future. The event
is quickly being replaced by the speed-limit
events that have become popular throughout
the country. These events allow any type of
model and any type of fuel system as long as
they do not exceed the speed limit, which is
typically 75 or 80 mph.
Another type of suction system uses a
balloon with a piece of tubing with an eyelet
or a short piece of copper or brass tubing.
The hard tubing is used so that the flexible
tubing will not be crushed or closed off when
the end of the balloon is wrapped with
copper wire or secured with a rubber band.
Fill the balloon just to the capacity of its
uninflated size. It is then held in some sort of
box on the model, and then the engine can
suck the fuel from it.
I have seen the Lubbock, Texas, boys use
this system successfully. There was quite a
controversy about it in 1984 at the Reno,
Nevada, AMA National Championships.
Some of the competitors claimed that this
was a pressure fuel system and that the
Mears and Wooten team members were
cheating.
A protest was filed, and Riley Wooten’s
demonstration on the judges’ table proved
that the fuel would not come out of the
balloon when full. There may have been
other flaws with this type of tank since it
never caught on.
The other, more common fuel-delivery
system is the one that uses some sort of
pressure. The object is to pressurize the tank
by using crankcase pressure or muffler
pressure. This is how you pressurize a hard
tank. Bladder tanks use the elasticity of the
material they are made from to force the fuel
to the engine.
My first Voodoo used a hard tank that
was pressurized by a piece of tubing running
from a fitting in the backplate of the engine
to a vent in the tank. There were three vents
on the tank, one of which was the “pickup”;
it carried the fuel to the engine. There were
two vents on the top of the tank; one received
the pressure from the engine and was used to
fuel the tank, and the other was used to let
the air out of the tank during the fueling task.
It was capped shut when the fueling was
finished.
Once you were familiar with the
operation of this system, it would provide
you with reliable runs. The tanks cost
slightly less than what the model cost. A
Voodoo kit in the 1960s would set you
back $3. Riley Wooten designed the
Voodoo and received royalties from Carl
Goldberg that allowed him to build his
palatial estate in Lubbock, Texas.
The downside to hard tanks had to do
with crash resistance—or nonresistance, to
be exact. Inverted landings would more often
than not result in broken filler vents. Harder
crashes would end with crumpled tanks with
leaks at the seams. I have not used a hard
tank since the mid-1970s, when my last
Nemesis model bit the dust.
The first bladders used were those from
ink pens or baby pacifiers. I never used a pen
bladder; I guess I was never curious enough
to take apart some of the fountain pens I
received as gifts for special occasions.
However, I did visit plenty of drugstores to
buy baby pacifiers. They could be made to
work with some consistency, but I seemed to
get changes in the runs throughout the flight.
Using surgical tubing as bladders solved
many of the fuel-flow problems. Surgical
tubing is available in a variety of diameters
and wall thicknesses. A modeler needs to
experiment with the length to see how much
fuel the tubing will hold per inch.
Typical Fast Combat models will carry
roughly 4 ounces of fuel; this amount will
allow a thirsty Nelson Combat engine to run
approximately two minutes. This same
amount of fuel will be enough to get a .36-
size engine set up for 80 mph Combat
through a five-minute match without a pit
stop.
So why would you want to use a pressure
fuel system? Because it will give you
consistent runs and deliver more power. The
power comes from the fact that you can use a
much larger venturi that will allow more air
into the engine.
This is the time of year to start thinking
about any travel plans you might want to
make for the summer. The premier event for
Control Line will be the World
Championships held July 4-10 in Muncie,
Indiana.
This competition has not been held in the
United States since 1984. It will give you an
opportunity to see the best pilots in their
disciplines from around the world. The AMA
National Championships will be held the
week immediately following the World
Championships. Two consecutive weeks of
Control Line Combat competition has not
taken place during my long modeling career.
I am working on rounding up a total of
$3,000 for a truly special competition that
will be held the Monday and Tuesday—July
11-12—following the World Championships;
we are putting together an Open F2D contest
with AMA Fast Combat rules.
Everything in the pits will be to F2D
specifications, and all the rules for inside the
circle will be to AMA Fast Combat
specifications. The idea is to attract many of
the World Championships F2D pilots so that
the rest of the US Combat pilots can have a
go at them.
So far the idea has been well received by
pilots on both sides of the Atlantic Ocean. It
is hoped that this amount of money will
attract a large entry and build some good will
among the Combat pilots of the world. MA