CONTROL LINE COMBAT
Rich von Lopez, 8334 Colegio Dr., Los Angeles CA 90045
Introduction
I have wanted to discuss fuel systems for quite some time, and this is 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.
Fuel-system types
- Suction systems (the older type)
- Pressure systems (more common today)
Suction systems
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 was 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 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 ten 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 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 gone in the near future. The event is quickly being replaced by 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 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 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.
Pressure systems
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:
- Pickup: carried the fuel to the engine.
- Pressure feed: received the pressure from the engine and was used to pressurize the tank while fueling.
- Vent/fill vent: used to let the air out of the tank during the fueling task; it was capped shut when 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.
Bladder tanks
The first bladders used were those from ink pens or baby pacifiers. I never used a 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 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.
Events and upcoming competitions
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 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.
- All the rules for inside the circle will be AMA Fast Combat specifications.
- The idea is to attract many of the World Championships F2D pilots so that the best of the U.S. combat pilots can have a go at them.
So far the idea has been well received by pilots on both sides of the Atlantic. It is hoped that this amount of money will attract a large entry and build some goodwill among the combat pilots of the world.
Transcribed from original scans by AI. Minor OCR errors may remain.
