OS FSa-56 and smoke

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!

Marty

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.

Good luck.

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!!)

Thanks, Steve

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:

Smoke pretzel Cool! mk

Very interesting stills and videos. Thanks for posting the info. Very entertaining and well done.

Ed Cregger

FWIW Dept.

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 stroke. If you get any smoke from a 2 stroke glow, it will be pure luck.

My $.02 FWIW

Great info, thanks.

Here is a photo of what I think is very decent smoke from an OS .91 Surpass without a smoke muffler or pump:

Another shot, in flight detail

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 the muffler?

- 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.

-Dave

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 out.

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.

Steve