It's not really very difficult to set up our model airplanes with a good effective smoke system if we follow some basic guidelines. Follow along with me and I'll attempt to describe some of the things I've learned either through first hand knowledge or from what others have written.

Every activity or task is easier when it is broken down into elements. So it is with
smoke systems. These elements are 1, A heat source; 2, Smoke fluid; 3, Fluid delivery
systems; and 4, Control systems. The following is a closer look at each of these
elements:

1) The Heat Source
The heat producer that we have readily available to us is the internal combustion
engine that powers our model. With some exceptions, we use three different types of
engines: gasoline fueled two-stroke, glow fueled four-stroke and glow fueled two stroke engines. I've listed these in the order of being most effective smoke producers to less effective.

The reason that the gasoline two-stroke engine is the best for producing smoke is
that the exhaust is the hottest of the three types listed while the exhaust from a
glow fueled two-stroke is relatively cool by comparison. This is important because it
is the exhaust gas that creates the heat that in turn produces smoke.

To overcome the relatively cool temperature of the two-stroke glow engine, a smoke
fluid pre-heater is very desirable. This can be as simple as a coil of brass or aluminum
tubing wrapped around the muffler. A more effective pre-heater is a coil inside the
muffler. The idea is to warm the smoke fluid before spraying it into the path of the
exhaust inside the muffler. One approach I've seen but don't recommend is a coil
around the cylinder head. This could cause the engine to overheat. While a pre-heater
is not essential for a gas engine, it can be helpful. I don't use one on my Chipmunk
but I will on my Waco. Very good after-market smoke mufflers are available. Two
vendors I can think of are B & B Specialties and Slim Line.

2) Smoke Fluid
Good commercial smoke fluids are available and carried by our local hobby shops. I've
used the Super Dri brand with good results. For you more adventurous types, there
are several formulas for home brews. These include:

• #2 diesel oil
• Kerosene
• 50 - 50 diesel & kerosene
• Diesel & automatic transmission fluid
• Diesel & concrete form release oil

• Engine pressure driven diaphragm pump
• Electric pump
• Oscillating pump
• Pressurized fluid tanks

There are pros & cons for each.
The Diaphragm Pump
This pump is driven by engine crankcase pressure. These are generally used with gas engines and are not suitable for four-stroke or small glow two-stroke engines. The engine is fitted with a crankcase pressure tap and a pressure line hooks to the pump. The pump draws the fluid from the tank and delivers it to the muffler. It doesn't pressurize the tank - a big advantage!

The Electric Pump
These are as the name implies a small pump driven by an electric motor. These pumps can be used with all types of engines. I've just purchased the "Simple Smoke Pump" for my Waco from Tejera Microsystems and it looks like a wellengineered unit with a good reputation. The disadvantage of electric pumps is that they require a separate battery pack. Also, you must insure by means of a good radio range test that the electric motor isn't sending out spurious signals that can cause glitching. But you routinely range check anyway don't you. As with the diaphragm pump, electric pumps draw the smoke fluid from the tank.

The Oscillating Pump
This style pump has an oscillating piston that is driven by engine vibration. These are particularly useful with four-stroke engines. One disadvantage is that they don't deliver the volume of the other two types of pumps. Like the others though, they draw the fluid from the tank. Connelly Mfg. (formerly Perry Mfg.) offers a pump of this type.

Pressurized Fluid Tanks
This system relies on engine pressure to pressurize the
fluid tank to deliver the smoke fluid to the muffler. This is usually achieved with a
pressure tap on the engine crankcase or muffler pressure with a one-way valve. The
advantage of this method is that it is very light but a major drawback is that the
pressurized tank inevitably will spring a leak and soak the inside of the airframe.
Believe me, you don't want this to happen! For this reason, I don't recommend this
method.

5) Control Systems
Small engine smoke systems will use 2 to 3 ounces of fluid per minute whereas some
of the larger gas engine set-ups will use 4 or more ounces per minute. For this reason
as well as esthetics, we want to emit smoke only during maneuvers. Therefore we
need a means to turn the flow of smoke fluid on and off at will. The system used will
determine the items needed to accomplish this.

A servo actuated control valve is used with the diaphragm pump, oscillating pump
and the pressurized tank. The servo plugs into either the retract channel or an
auxiliary channel of your receiver. This is a simple piston type on-off valve. The one
I'm using was supplied by B & B Specialties.

The electric "Simple Smoke Pump" plugs directly into the receiver and has an
electronic switch that controls the pump. A second connector hooks up to a battery
pack. Usually, 500 mah is sufficient. Either the retract or an auxiliary channel works
well.

Another item that is required is a flow control valve. This valve controls the amount
of fluid going to the muffler. Too little fluid results in thin, wispy smoke. Too much
fluid can cause the same problem in addition to the problem of wasted fluid that
accumulates on the airplane exterior. This can be a simple clamp type valve that
remains hidden away in the innards of the airframe or it can be a needle valve that
can be adjusted from the outside of the model. Originally, the valve on my Chipmunk
was accessible only when the wing was off. This certainly does not facilitate fine
tuning the flow rate. I've since changed the set-up so it can be adjusted while the
engine is running.

Finally, a one way check valve is required. Consider that the pump is trying to pump
fluid in to a muffler that is, in effect, pressurized. This pressure will try to push the
fluid back into the tank. Both the diaphragm and oscillating pump have pressure
pulses. It's between these pulses that the muffler pressure can reverse or retard the
flow of fluid. For quite some time, I was getting excellent smoke from my Chipmunk.
But recently, the smoke was thin at full throttle. I didn't think that I changed
anything and was puzzled as to the cause of the problem. Finally, it dawned on me
that I had made a change. I was having a problem with the muffler bolts becoming
quite loose. This problem was solved only recently, with much help from Richard
Majors. I wasn't using a check valve and when the muffler bolts were loose, the
muffler pressure was reduced. Now that they remain tight, the pressure is higher.
I've since installed a check valve and it appears that the problem has been eliminated.
When an electric pump is off, the muffler pressure can reverse the fluid flow in the
pump - even to the point that the pump can lose its prime.

Finally, I've tried to cover the high lights and provide the information needed but
space and limited knowledge prevents me from getting into further detail. For more
information, I highly recommend a pamphlet published by Tejera Microsystems
Engineering titled "Secret Smoke Success Tips". Also, I'll try to answer any questions
that you come up with. Good luck!