I'm planning on using an OS FS-56 engine on my next plane (VR Models
Pitts) and one of the reasons for the choice is I wanted to use smoke
on it. I've tried smoke on 2 strokes and it didn't work all that well
and I've been told 4 strokes are the way to go for smoke. I can't
seem to find a smoke muffler for it though, and I'm wondering if I'm
missing something. Is the engine too small? Can I just tap the
On Thu, 3 Dec 2009 15:35:38 -0800 (PST), Steve wrote in
No harm in trying. If it doesn't work, just seal the
hole with a short bolt.
I tried to do smoke once. I still fantasize about trying
it again. I had a hand-me-down pump that was unreliable.
It was no fun and the experiment did not last long. But
I love to see smoke!
There are two problems with smoke in model airplanes.
The first is the delivery of the fluid to the exhaust. Various pumps fix
that leaving the second challenge to be worked around. I don't think there
is enough available vacuum to run the smoke pump and supply the 4 stroke
with fuel, but I have not tried that yet.
Most model aircraft SMOKE mufflers (see, they recognized the 2nd problem and
tried a solution - that sort of works) have a coiled tube inside to preheat
the smoke since our engines operate at significantly lower temperatures than
rider scale engines and have shorter exhaust systems.
I have seen a modeler put a single coil of 1/8 brass tubing around the head
of a 2 stroke engine to preheat the fluid, but *I* wouldn't for fear of
cooking the top end of the engine. However, you can put a wire inside the
tubing and wrap a couple of turns around the exhaust header of most 4 stroke
engines before the fluid is injected into the muffler. Once the wraps are
made, pull the wire out since it was just there to keep the walls of the
tubing from collapsing. I would buy some JB Weld suitable for heat and use
it to try to control, stop, or prevent the metal to metal vibration you may
get to protect the integrity of the radio system. Pump the fluid through
the tube and then into the exhaust muffler and you should get smoke.
Smaller engines may need more wraps to get the oil hot enough for the short
time it is in the exhaust chamber.
I did this on a 2 stroke and it barely worked. I wrapped a 12" length
of 1/8" copper tubing around a dowel aa few times and stuck the whole
thing inside the muffler. I drilled out the muffle and had one end
sticking out (with the requisite JB Weld....) and had the other end
positioned right in front of the exhaust. It wasn't hard to do, and
might've worked better with a bigger engine (I was using a .46) but I
wasn't impressed. I was hoping to do better with a 4 stroke, but
maybe I just need a much bigger engine (and a bigger plane!!)
I have used smoke very successfully on OS FS .52 and FS .91 engines.
You do not need a smoke muffler, or a pump, or a coil.
You use the muffler pressure and a one-way valve to pressurize the smoke
tank. One servo to actuate a switch to allow the oil into the muffler.
Details on my website:
Here is a photo of my Smith Miniplane with a FS .52 and smoke:
In the order of ranking of least to the best for smoke is; 2 stroke
glow engine, 4 stroke glow engine, Gasoline engine.
I have not done smoke, but I have measured exhaust gas temperatures.
On a 2 stroke the most I found was 450 degrees F at the exit of the
engine. I could move the thermal couple inside the muffler a 1/4 inch
and get a 50+ degree change. By the time the exhaust exits the muffler
is is very cool.
A 4 stroke with range over 700 degrees F at the muffler. A gasoline
engine can be up to 1600 degrees. You can see which one will produce
the best smoke.
The reason for the coolnest of the 2 stroke glow is some of the
incoming fuel goes out the exhaust for cooling reasons whereas it
doesn't in the 4 stroke.
I have seen excellent smoke from a gasoline engine. Decent smoke from
a Saito 100 with a smoke muffler (coil inside) and no smoke from a 2
If you get any smoke from a 2 stroke glow, it will be pure luck.
My $.02 FWIW
Nice smoke, Mike! Some questions:
- What do you use for smoke fluid?
- Is the oil injected thru any kind of spray nozzle, or just dribbled into
- I'm surprised there's enough pressure differential between the "Muffler
Pressure to Smoke Tank" and "Smoke Oil to Muffler" lines to pump the fluid.
I use SuperDri smoke oil. No spray nozzle, just a regular nipple (like
the pressure out to the vent) into the muffler.
As far as the pressure differential is concerned, the pressure in a
4-stroke engine muffler is not constant but "in-out". When the pressure
is negative, the smoke oil is sucked in; when positive it gets pushed
It works very well. I never tried it with a 2-stroke.
Again, 4-stroke .90, no pump or coils:
You can use a check valve to prevent the pressure from "backing" out
of the tank.
The smoke system I have has a tiny electric pump that hooks into a
spare receiver channel. You can put it on a channel with a switch and
turn it on and off.
The real fancy guys put it on a switch and mix it to the throttle
channel so that, even if you turn the switch on, it'll only start the
pump above half throttle.