Making Smoke Signals
This smoke trailing Decathlon is powered by a
Saito .90 4-cycle and the smoke system that was used is described here so
you can start making smoke signals with your 4-stroke powered
In setting up your model for producing smoke there are a
couple of basic requirements you must have in place to make the system
feasible. First, the model must be of sufficient size so that there is
room for the extra fuel tank for the smoke fluid and that it can carry the
extra weight (don't forget to rebalance the plane after installation!).
Secondly, you will need an extra channel on your radio system to activate
the smoker valve. This can simply be controlled by a non-proportional
channel with a 2-position switch.
Once you have determined that your model is capable of adding a
smoke system, gather the items required as shown in the diagram.
The only special tools required are a drill (#36) and 6-32 tap (part
number DUB362) to install the pressure nipple that comes with the Du-Bro
Super Smoker Valve.
How the System Works
When your engine is operating, the
pressure in your muffler chamber will rise and fall, depending on the
point in the combustion cycle. We can use the positive pressure created to
pressurize the smoke fluid tank. To filter out the negative pressure in
the cycle, we use a one-way or check valve between the muffler and
The pressurized tank forces the smoke fluid through the tubing to the
muffler. The Super Smoker Valve, activated by the servo of an extra
channel, can cut-off or allow the fluid to flow. To produce proper smoke,
the smoke fluid must be pre-heated and this is accomplished with the help
of the soft brass tube coil wrapped around the muffler header. This
pre-heating vapourizes the smoke fluid to produce beautiful, bellowing
smoke. Four stroke engines are ideal for this as their mufflers tend to
run much hotter than with two strokes.
A Fourmost tee fitting is used in the pressure line between the check
valve and the tank to provide a way of relieving the pressure in the tank
after your flight, and allowing the air to escape when you are filling.
The Fourmost fitting is used as a plug after filling. The Du-Bro Kwik
Fueling Valve is an ideal way to fill your smoke fluid tank and is placed
in the line between the muffler coil and the Smoker Valve. Ideally it
would be better to put the Kwik Fueling Valve between the Smoker Valve and
the tank so you would not have to turn the radio on to open the valve for
refueling, however, the Smoker Valve would be typically located further
back in the fuselage with the Kwik Fueling Valve nearer the engine,
usually mounted in the cowling area. This would require a considerable
amount of plumbing to accomplish. Choose the format that best suits your
For storing, carrying, and loading your smoke fluid, we recommend the
Du-Bro EZ Fill Fuel Pump(DUB520) which is suitable for gas or glow fuel as
well as smoke fluid. Note that all components of the system must be rated
for gasoline use rather than glow, to be compatible with the smoke
Using the tap and drill, install one of the
pressure fittings included with the Smoker Valve to the body of your
muffler and the second to the header for smoke fluid injection. Install
this fitting as close to the head as practical. Wrap the soft brass tubing
around the header, making a closely spaced coil. Use the JB Weld to secure
the coil in place. We actually wrapped the coil on both sides of the
installed nipple to help keep it secure. You may need to use some brass
tubing to create the bend between the coil and the nipple as the neoprene
may kink, depending on your setup.
Install the rest of the components as shown in the diagram. Ensure that
the check valve is in the proper direction giving pressure to the tank.
Again, don't forget to rebalance your aircraft once complete. If you can
mount your smoke tank at the center of gravity, so much the better.
Remember, not all kinds of smoking are bad for your health. This kind
of smoking can create all kinds of excitement!