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How to Make MORE
SMOKE!
(or Zen and the Art of Smoke System Installation)
by Robert Osorio - The Flying Penguin
Okay, let's talk smoke systems. I know, most of you
are thinking "hey, I haven't got a giant scale plane
with a gas engine, so I can't make smoke." NOT!" I
don't fly anything bigger than a .90 four-stroke, all my
engines run on glow, and many of my planes have
smoke systems onboard. I just love to burn up a clear
blue sky with some smoke, and we're not talking
about a piss-ant dribble that can be mistaken for a rich engine run. No sir! I'm talking nice, thick, white smoke thick enough to lay a haze across the runway on a low pass. I've rigged many of my planes with smoke and I've
learned a lot from it. I'll be happy to share some of my hard earned insights with you (feel free to ignore them if
you're feeling smug and superior, won't bother me). The most important thing is this: be prepared to experiment! If
you don't like to experiment you're in the wrong hobby anyway - take up stamp collecting. If you don't like to fiddle
around with a plane once it's airworthy then forget this. Trust me, you'll do nothing but tinker with a smoker. Get into
that Zen Mad Scientist Mode, and prepare yourself for the grim truth that nothing really comes easy in this hobby,
but you can have a whole lot of fun getting there if you're patient. As with most suggestions you're likely to hear
about this hobby, take anything you read here with a grain of salt. None of this is the gospel truth, it's not written in
stone or any such thing. If you ask four different people at the field about smoke systems, they'll probably tell you
four entirely different things. It's not that any of them are entirely wrong (and probably they aren't entirely right
either), but that smoke systems, like many things having to do with modeling, are an engineering challenge that can
be approached from different angles. No two engines, installations, planes, prop/engine combos, mufflers, etc. are
the same. What worked for me and your friend Joe Blow, may not do squat for you. I'm here to give you a starting
point by telling you what's worked for me, and hopefully this can save you some aggravation. I've had luck getting
engines as small as .40 size to smoke, but .60's are better. I've found four-strokes smoke better than a comparably
sized two-stroke. My personal theory on this is that the smaller muffler on four-strokes in combination with the
longer pause between exhaust cycles allows the smoke fuel to get hotter. You engineering types out there are
more than welcome to comment.
Smokin'!
All smoke systems work essentially in the same way: pumping a smoke fuel from a separate tank into the muffler.
The smoke fuel, on contact with the hot exhaust gases and muffler walls, burns creating smoke. Same thing is
happening in that wreck you got stuck behind on the interstate the other day. You know the one, belching big
clouds of smoke for your lung's appreciation (you gotta wonder how some of those things pass inspection), except
in that case engine oil is unintentionally (I hope) leaking into the exhaust system through a worn seal, bad ring, or
cracked engine block (and the slob wonders why he has to pour two quarts of motor oil in it each week!).
In general, a smoke system consists of the following: a separate smoke fuel tank and associated tubing, a smoke
pump, a smoke valve that can be controlled via a spare servo channel on you radio system (needless to say, you
need at least a five channel radio), a one way check valve, a needle valve to control the flow of smoke fuel into the
muffler, and an optional fuel filler valve (if the pump isn't buried under a cowl you could just pull the intake line and
fill it from there). This basic system diagram in shown in Figure 1:
The smoke fuel is drawn from the tank by the pump, and forced through the lines until it gets to the smoke valve.
When the smoke valve is opened via remote control, it allows the smoke fuel to continue on down the line through
the one way check valve and needle valve. The one way check valve allows fuel to flow in only one direction (Duh!)
and is necessary to prevent muffler pressure from forcing the smoke fuel back up the lines. Many other modelers
and some pump manufactures consider the needle valve unnecessary or optional, but I consider it a must. It's the
simplest way to control the flow, and it's just not worth the hassle to do without it for the sake of a few dollars. Keep
your fuel lines as short and straight as possible. Long lines make it harder for the pump to prime itself and reduces
the flow rate, leading to long delays between the time you turn on the smoke, and when it actually starts coming
out. Excessively long and twisty lines can render a smoke system totally useless.
The layout shown in Figure 1, while not critical, is ideal. As a general rule of thumb, you want the pump as close to
the tank as possible to reduce delay times and make it easy for the pump to self prime. The smoke valve should be
located after the pump so that the pump never goes dry, again, to prevent priming problems (it won't hurt most
pumps to pump against a closed valve and the slight buildup in pressure gives the pump an assist when the valve
is opened). The one way check valve is next, followed by the needle valve which should be the final stop before the
muffler. I do not recommend the plastic valves that come with some pumps instead of needle valves. The hot
exhaust will damage a plastic valve, they're not very accurate, and I've never seen one that doesn't leak anyway. I
personally prefer to mount the needle valve right to the muffler, and some specialty smoke mufflers actually come
this way. Don't bother pressurizing the smoke tank with muffler pressure like you do on the fuel tank. Gut instinct
would tell you that pressurizing the tank to the same ambient pressure as the outlet of the system would help, but
I've found it makes no difference. Just have it dump out underneath the engine somewhere so that when filling the
tank, the overflow will just drain out onto the ground or into a reclamation tank. I've started saving my own overflow.
That smoke fuel is expensive and probably eco-unfriendly, so is glow and gas for that matter. With all of us
becoming more environmentally aware (are we?) we should all think of ways to clean up our acts before some
government agency comes along and uses this as an excuse to close down fields. I understand this practice is
already very popular in many parts of Europe. (Okay, I've said my green thing for the day, you can all tune back in
now).
There is a simpler smoke system that eliminates the need for a smoke pump, although it can only be used on twostroke engines, and it has some drawbacks. This system necessitates the installation of a pressure fitting on the
back crankcase cover of the engine (this pressure fitting is also necessary when using a smoke pump that runs off
crankcase pressure, mentioned later). The diagram for this simplified smoke system is shown in Figure 2:
With the downward movement of the piston, an engine draws the air and fuel mixture through the carburetor, the
crankcase and, via the ports, into the combustion chamber. The pressure fitting provides a means of tapping into
the substantial positive air pressure created in the crankcase which can be used to pressurize the smoke tank to
force the smoke fuel through the system. A four-stroke engine does not draw fuel and air through the crankcase
and most four-strokes don't even have an airtight crankcase, so this method can't be used on a four-stroke engine.
The check valve is still required, but now it's installed immediately after the engine pressure tap to prevent smoke
fuel from backing up into the crankcase due to gravity or while fueling.
The major drawback with this system is that when the smoke valve is closed, the tank swells because of the
unrelieved pressure. This makes it necessary to mount the tank loosely so the swelling doesn't crack open your
fuselage (I've seen it happen!). Occasionally a tank will burst a seam, spilling smoke fuel all over the interior of your
aircraft (I've seen this happen too). This problem could be eliminated by installing a second smoke valve between
the pressure fitting and the tank, but the valve would have to be a more expensive air pressure valve, and the
additional mechanics aren't worth it (you'd have to use both valves as the air pressure valve alone wouldn't prevent
smoke fuel from siphoning out of the tank under gravity). With this system you must also make certain not to
throttle back to idle while the smoke is on (something hard to keep track of during some aerobatic maneuvers)
otherwise it will kill the engine, as engines don't idle too well with a compression leak (this is not a problem with a
pump driven by crankcase pressure as in that case the pump provides a closed system which prevents the
crankcase pressure from leaking away). The only benefit of this system is that it saves you the cost of the smoke
pump. I've used this system successfully, but I only use it on throw away planes, never on a scale model. I used to
have a 40 size Ugly Stick (yes, I actually did own an Ugly Stick once, we all go through that phase) that used this
system when I was experimenting with wing-tip smoke. The plane was rigged with tubing that would carry the
muffler exhaust through the wing and out the wing-tips - looked cool, but I didn't want a complex smoke system,
and there wasn't much room in the plane anyway. To keep it simple I attached the smoke tank to the outside of the
fuselage just behind the engine on the side opposite the muffler (ala control line style), with velcro and rubber
bands. To keep it cheap and simple I didn't even use a smoke valve, I'd just pinch off the line with a pair of forceps
and have someone hold the plane for me on the runway. When I was ready to take off, I'd run up the engine and
signal my helper who'd remove the forceps and let go of the plane. I didn't even use a one way check valve since
the smoke was never turned off, and I'd take great care not to let fuel get into the crankcase. Needless to say,
without a reliable idle, all landings were dead stick, but it did work.
Fuel for Thought
What is smoke fuel? In most cases it's a light fuel oil. Let me warn you right now, friend; cleaning a plane with a
smoker is a messy job. It's worth it, it really is, but it's a real mess on the plane. That mess need not be limited to
the exterior of the plane either. Leaks always develop - plan for them! Fuel proof the compartment you install the
smoke tank in, and make sure anything that has to be mounted along side, like the receiver or battery is wrapped in
plastic. While we're on the subject, remember that you'll need a separate fuel container and filler pump for your
smoke fuel, and that they have to be compatible with gasoline fuel. Most smoke fuels are petroleum based and will
destroy glow pumps and silicon fuel lines. Even if you're not sure, get a gas compatible system anyway, as you can
pump anything through it. For those of you fellow environmentalists out there who may feel that making smoke is
going to contribute to global warming, I suggest you go fly electrics and ride a bicycle to work. Yes, partially burning
a petroleum based oil is probably not great for the environment, but I doubt you'd be contributing much more
pollution than the engine's exhaust is already putting out. I doubt these small engines contribute much at all to the
problem, and as long as I'm choking on a cloud of diesel exhaust behind a city bus at the traffic light, I'm not going
to feel too guilty about it.
Full scale planes can burn almost any sort of oil for smoke, or even just plain water. Unfortunately, our engines are
too small for that trick. Model engines certainly get hot enough, but the smoke oil acts as a coolant. On a full scale
plane that little squirt of smoke fuel hardly has any effect on the exhaust temperature at all. Our small engines get
their fire doused in a hurry, though, and keeping the heat on is the secret to a good smoke system. As long as you
can maintain a high exhaust temperature, you'll get good smoke. This is why some modelers suggest you preheat
the smoke fuel by running it through a marine engine cylinder head or by wrapping aluminum tubing around the
engine cylinder. I've tried all that and I've found that you don't get enough improvement to offset the money or the
extra plumbing the pump has to work against. Later, I'll make some suggestions on how to keep your muffler hot.
There are lots of different smoke fuels available and some I've tried while others I've only heard about. Diesel fuel
(straight from the gas station pump) works, but it doesn't smoke very much. If you're running a big, cowled in
engine, you may be able to get some decent smoke out of diesel alone, but adding a bit of kerosene (some gas
stations still sell it, especially near camp grounds) will make it smoke a whole lot better. From long experiment I've
found that the best mixture is three or four parts diesel mixed with one part kerosene. This can smoke from okay to
great depending on your setup and how high an exhaust temperature you can maintain. It's cheap and easy to
make, but it can stink pretty bad and the kerosene eats up some painted finishes like dope and enamel. My guess
is epoxy based paints would work best, but I've never tried. Kerosene also dissolves Styrofoam as well as some
iron-on coverings so don't even think about using kerosene on a plane with a foam wing. I don't care how well you
think you've sealed it, smoke fuel will always get into the wing. Next thing you know, you've got a hollow wing (I
know, it's happened to me). I've found Monokote to hold up well, Black Baron melts, and I haven't tried any other
coverings yet. Make sure all edges are ironed down tight as this stuff attacks the glue holding down the covering as
well, and soaks into balsa. By the way, if you ever need to get oil out of balsa, and you will someday, spray on
some K2r spot remover. Let it sit overnight, and vacuum up all the white powder the next morning. Repeat again if
necessary. Somebody once turned me on to this, and it really works. This procedure is mandatory when you try to
re-cover that plane somewhere down the road, as you'll find that somewhere fuel got under the skin.
Please remember to use a filter when you fill your smoke tank, Smoke pumps are easily clogged, and
smoke fuel seems to have even more junk floating around in it than glow fuel does (you are filtering your
glow fuel, aren't you?)
Engine
Yeah, well sure, you already have one, but I want you to be sure you've got the right one. A smoke system adds a
good deal of extra weight; you're doubling the amount of onboard fuel (and smoke usually weighs more than glow).
There's also the extra weight of the pump, servo, tubing and batteries (if you're using an electric pump). If you're
one of those people who likes to buy the minimum recommended engine size for a kit, learn to break that habit right
now. If the box says you can use a .40 to .60, stick a .65 in it. Remember, also, that because of the extra weight of
the smoke system and the greater torque of a larger power plant, you may have to go back and beef up the
structure of the plane in critical areas to handle the load. Flimsy tail feathers should be reinforced with wire struts,
and small wing bolts may need to be replaced with bigger ones. Is that landing gear gonna hold up under the extra
weight, or will the plane go into bouncing oscillations on landing? Think ahead.
Spend the money on a good quality engine. A smoke system puts additional stress on an engine, making it work
harder and run hotter, and that cheap Taiwanese copy might not cut the grade. Don't skimp on your glow fuel
either. I'm not talking nitro, I never use more than five percent, and anything more will only make your engine run
hotter. No, I'm talking oil. Buy a good quality fuel with castor or castor/synthetic lubrication. I always add an extra
ounce of castor oil to my fuel because you never know what you're getting and it only helps. Lean runs aren't
unusual with the extra burden of a smoke system.
Tanks for the Memories
Whatever you wind up using for fuel, you'll need a second tank to carry it in. One about the same size as your glow
tank, give or take a couple of ounces, will work just fine. If you've got no room for the smoke tank, forget it and try it
in a roomier bird. It's pretty tight in some of those .40 size kits, but there's tons of room in a Goldberg Cub for
instance. BIG WARNING: As mentioned above, most smoke fuel is petroleum based and will make silicon
swell up. You can't use the silicon tank stopper and pickup line that comes with a standard glow fuel tank. Buy a
gas conversion kit which consists of a neoprene stopper and pickup. Same goes for fuel lines. I don't suggest you
use neoprene here, though, as it's too soft and crimps easily. I've found the yellow Tygon gasoline tubing works the
best, but it's a little stiff. You may need to use a short piece of neoprene tubing, an inch or two long, to make the
final connection at the muffler, as exhaust heat can melt Tygon tubing.
The tank needs to be mounted, physically, as close to the engine as possible. The ideal location is right along side
the glow tank. I've found in some situations that it's necessary to mount the smoke tank as high in the fuselage as
possible, in order to give the pump a little gravity assist in priming. Sometimes you can get creative. I installed a
smoke system in an Ultra Sport .40, a plane notorious for it's tight tank compartment. I used two, four ounce tanks,
connected in series (See Figure 3), with the pickup line of the first tank connected to the vent line of the second. I
mounted them in the radio compartment right in front of the servos. This worked okay, although there was a notable
delay when turning on the smoke. A year later I crashed that plane and rebuilt it with an eight ounce tank mounted
in the cockpit area, and I blacked out the canopy. This worked great, and the high position of the tank improved fuel
flow. The lesson is, don't be afraid to experiment!
Pump it Up!
Again, you have to buy a pump that's designed to be compatible with gas, as glow pumps will be destroyed by
petroleum based fuels.
Remember not to use muffler pressure when using a glow pump, it's not necessary and you may make the engine
run too rich. Just vent the line out under the engine compartment somewhere and use it as an overflow. Oscillating
pumps take advantage of the fact that the engine rocks slightly as the crank turns to produce the pumping action.
I've found that motor mounts that flex some allow the pump to do a better job. I couldn't get much smoke out of a
bipe I had that used wooden engine mounts attached to a false profile cowl. When I sawed them off and installed a
glass-filled motor mount, things improved quite a bit (I've never tried soft mounts, but I'd guess they'd work great).
I've also used the Varsane two-stroke pump that runs off crankcase pressure with good results. Using this pump
will require the installation of a crankcase pressure tap on the engine to power the pump. Please keep in mind that
this modification will probably void your warranty, but then again, so will flying your plane into a concrete runway. If
you ever want to use the engine in a plane without smoke, in the future, just attach a short piece of plugged fuel
line to the pressure tap to prevent leaks.
If you don't like the idea of drilling a hole in your engine, take it down to your hobby store and I'm sure they'll do it
for you for a reasonable price. It's a ten minute job if you've got the right tools and have done it before. To install a
pressure tap, remove the engine back plate, usually held on with four metric hex socket-head bolts. Some engines
use a clear plastic gasket between the back plate and the crankcase, take care not to tear it or lose it. Du-bro
Products sells a pressure tap fitting that fits a 6-32 threaded hole. Do yourself a favor, if you haven't got a tap and
die set go out and buy one. It's a must-have tool for fixing bad threads or cutting new ones. Most hobby stores sell
individual taps along with the proper size drill bit to go with it, if you don't want to shell out the dough for a complete
set. Drill a hole in the back plate, I don't really know if the exact location makes a difference, but I usually drill it low
and to the side. For you drill novices, use some 3-in-1 oil - just squirt a good gob on the spot you'll be drilling - it'll
help make the bit last longer. Use a the tap to cut the threads. They sell some neat alignment blocks out there that
help you tap the hole straight, I just go for it. Aluminum is soft, just keep the tap straight and steady. Wash off the
back plate so there are no metal cuttings left (you don't need any of those going through the engine), and screw in
the pressure tap. It's very important that you make certain the pressure tap doesn't extend past the inside wall of
the back plate, otherwise it may interfere with the crank. Just use a Dremel sanding drum (you do have a Dremel,
don't you?) and grind that puppy down flush. Wash it off again, and bolt it back onto the crankcase (don't forget that
gasket!).
I've recently been trying out the TME Simple Smoker in my Aeromaster Bipe. This pump greatly simplifies
installation because it eliminates the need for a smoke valve and servo. The pump plugs directly into a receiver
channel, but runs off a separate battery pack. The only downside is the weight of the extra battery pack, but in my
experience most planes can carry it comfortably. Also, you'll have to invest in a fast charger as I've found I have to
recharge the pump battery after every few flights (if you fly all day like I do!). A fast charger can set you back
anywhere from $40 to $90, but is well worth having. I fast charge all my radios at the field, and I never allow myself
to get into the situation where I want to fly, but my battery voltage is iffy. TME claims the pump will run off a four cell
receiver battery, but I've found it works better with a five cell pack. A little pricey, but I like it so far, it's very reliable.
Smoke Valve
The smoke valve is a mechanical valve, connected via a linkage to a servo, that actually turns the smoke fuel flow
on and off by remote control. The simplest one is made by Du-bro. It's a plastic assembly that pinches a neoprene
tube to shut off the flow. The more expensive ones look like reactor valves on nuclear powered subs. You can also
make your own if you've got the time and inclination (I have neither), and save a little money. It's by far the simplest
part of a smoke system, but can cost from $10 to $20.
Needle Valve in a Haystack
As I said before, the needle valve is a must, and don't let anybody tell you otherwise. Once you've got your smoke
system installed, it's going to take a few flights to adjust it properly. You want to set the needle valve for a
compromise between the thickness of the smoke and the longest possible run time. You're going to be switching
the smoke on and off during flight, so you don't need a full flight's worth of smoke. Mine usually set up with seven to
nine minutes of continuous smoke, which is fine for a twelve minute flight.
You can purchase a remote engine needle valve, which almost all engine manufacturers make, from nearly any
hobby shop. I personally like to use the replacement needle valve assembly for an Enya TV60 engine. It's business
end (the outlet that normally screws in the carburetor) is threaded for an 8-32 hole. I drill and tap a hole this size
and screw the needle assembly right into the side of the muffler, this nicely solves the problem of mounting it. Most
mufflers have thick enough walls to let you do this. On four-stroke mufflers, drill into the angled flanged area where
the pressure tap is usually located - it's thicker there than at the sides. You can also mount the needle valve away
from the muffler. In this case a strap, and a big blob of PFM glue is usually enough to hold it in place. Remember,
you will have to add an extra pressure tap in addition to the one already on the muffler, unless you're using a pump
for the glow fuel system as well, in which case the existing pressure tap will be available for your use. If you do
decide to use the TME electric pump, throw away the plastic valve it comes with, it's worthless.
One Way Street
No pump can fight the substantial back pressure from the muffler's exhaust, so you need a one-way check valve to
keep exhaust gases from backing up the line. A one-way check valve allows fuel to flow in one direction, but
prevents fuel or exhaust gases from traveling in the other. TME claims you can do without one with their electric
pump, but recommends you use one. Use it, it really is necessary. Don't use the ones made for high performance
pattern engines with pressurized fuel systems, as these are intended for glow fuel and smoke oil will destroy them.
TME makes a check valve to go with their smoke pumps, and so do a couple of other manufacturers.
Most check valves have an arrow drawn on them to indicate flow direction. You should be able to blow through it in
one direction, but not the other. Also make sure you can blow through it hard, without any resistance. I've gotten a
few defective ones that seemed to work okay when I blew through them, but they wouldn't work under the higher
pressure from the pump. Spend a day taking an entire smoke system apart, until I narrowed it down to the check
valve, which seemed to be working, until I blew through it real hard.
The check valve should be the last thing in line before the muffler, or it can be installed right before the needle
valve. I've found that the exact placement of the check valve can be very critical, especially with the Varsane
pumps. It's best to have a few inches of tubing between the valve and the muffler otherwise the higher back
pressure nearer the muffler can force the check valve to stay closed (the valve is actually only opening between
combustion cycles when the exhaust pressure drops briefly). If there's no smoke, but there's plenty of smoke fuel
squirting out of the check valve when you disconnect it from the muffler (and you're certain the check valve is
working), you can bet your check valve is too close to the muffler. Check valves also go bad over time, and hot
exhaust gases can melt the internal parts during a lean run, so pickup a spare and keep it in your flight box.
Keeping the Heat Turned Up
As I said earlier, the secret to a great smoke system is maintaining a high exhaust temperature. This isn't always
easy to do, as a good muffler is usually designed to keep the exhaust temperatures down below where we want it.
If the engine is going to be cowled in then all the better, just make sure there aren't too many holes that allow
cooling air to pass over the muffler. Do make sure, though, that the engine's cylinder head is getting plenty of
cooling. Since we're running up the exhaust temperature a bit, the engine is going to tend to run hot. Remember,
also, that you may not get as much smoke during test flights with the cowl off as with it installed. If the muffler has
cooling fins on it, you may want to grind them off with a Dremel tool. In general what you want to do is to try and
keep cooling air off the muffler entirely, or if that's not possible, at least make that cooling ineffective. I like to slip a
tight sleeve of silicon tubing (the kind used for connecting tuned pipes to headers) over my four-stroke mufflers, to
help keep them hot. Remember that the engine will be running hotter, so you want to run it a little richer than you
normally would to keep it from overheating. As I mentioned earlier, I like to add an extra ounce of castor oil to every
gallon of fuel I buy. Our engines can always use the extra lubrication, and the extra oil helps carry heat away. Most
hobby stores sell castor oil.
Some muffler manufacturers make a special muffler, or sell a retrofit kit, that adds a coil of tubing inside that the
smoke fuel has to pass through before being injected into the exhaust. This allows the fuel to stay in the muffler
longer and, subsequently, get hotter, giving better smoke. I've never bought one of these, but I built my own once
by modifying a J-Tec muffler. It works, and it's worth it if it can make a difference between a lame and a great
smoker. Don't forget, though, you're also adding more plumbing for the smoke fuel to travel through, which will
increase delay times when turning on the smoke, and make the pump work harder. These mufflers aren't cheap
either, so you'll have to decide if your budget can afford it. Some modelers also suggest soldering a piece of tubing
to the pressure tap, on the end inside of the muffler, and crimping it and cutting small notches in it with a razor saw.
The idea is to make an atomizer of sorts that sprays the smoke fuel into the muffler as a fine mist. I've never had
any luck making one of these, but I can see why it should help. Experiment!
Before installing a smoke system, I like to have an idea of how well a particular engine/muffler combination will
smoke. I connect the filler line from my smoke fuel storage container directly to the muffler pressure tap through a
needle valve, and pump a small quantity of fuel into the muffler with the engine running (I use a Du-bro squeeze
pump, so it's pretty easy to meter it out). Ideally, it shouldn't take much fuel to make it smoke. Despite the fact that
smoke fuel has the side affect of cooling the muffler, some engines want a large quantity of fuel before they'll
smoke worth a damn. All that fuel in there, I'm guessing, loads the engine down, which increases the engine
temperature, which also increases the exhaust temperature. So sure, you could put a sixteen ounce tank in there if
you've got the room, and increase the flow, but it's a waste of smoke fuel, you'll really slime up the plane now, and
all that puts a heck of a load on the engine. While you could drown the muffler to achieve your goal, you're only
going to choke the engine on it's own exhaust, and performance will suffer. You should always strive for fuel
efficiency by doing anything you can to keep the exhaust temperature high (within reason), while keeping the
required fuel flow as low as possible.
The smallest details can make the difference between good and bad smoke. If the fuel is chilled, it'll cool your
muffler and won't smoke very well. Keep your fuel storage container in a warm place for a few hours before flying
(car trunks in the summer are just fine). Weather conditions can affect smoke thickness and persistence. Smoke
looks best against a clear blue sky and when lit by the sun from the front. Smoke also looks better against the
darker azure blue directly overhead than against the light aqua marine sky on the horizon. Don't even bother
packing the smoke fuel on an overcast day, unless you like to do simulated crop dusting (which is actually a lot of
fun). Each flight, I spend the first few minutes flying around looking for the best patch of sky to make smoke in. I
make most of my impressive (at least to me) aerobatic maneuvers in that "sweet spot" where the sun hits the
smoke just right, and the sky is clear blue behind it.
You'll be surprised what you can do with a smoke system. Low passes look even sexier with smoke. Some
aerobatic maneuvers that you know are impressive but look ho-hum normally, suddenly stand out as a crowd
pleaser with smoke. Try a flat spin with smoke, and just listen to the oohs and ahhs from behind you. That tail slide
really looks like a tail slide when you can see the plane actually back into the smoke. Smoke can also make your
mistakes stand out. That four point roll that you thought was perfectly axial, might prove to have a little burp in it
that shows up in the smoke trail. This is good, it helps make you a better pilot. I set up a Skyward .60 ARF trainer
with a smoker once, and I found that the smoke trail helped student pilots tell their orientation easier.
I hope you've found this article useful, or at least entertaining. I hope I haven't scared any of you away from trying
smoke, because that would be a shame. Yes, a smoke system does require you to do some extra fiddling at the
field, but so do retracts or, for that matter, any scale feature you add to a plane. If you're just starting out in the
hobby, you've got lots of other fun and interesting challenges ahead, don't worry about smoke right now (you want
real fun, wait until you tear your first set of retracts out of an EZ kit on a grass landing!). But, if you're like me, and
feel like a new challenge, then smoke may be the ticket for you. With some experimentation, advanced planning,
and a whole lot of patience, you can enjoy the thrills of a smoke system. Go on, show off!
Good luck, and keep Smokin!
July 1996
Updated March 1997
Robert Osorio - The Flying Penguin
[email protected]
Smoker Info
My big Sukhoi have been smoking up the sky around for 4 seasons now with very few problems and
ridiculous amounts of smoke. I'm almost afraid to do tail slides since I can't see the plane ;)
I use a Slimline muffler but not the smoker version. I inject into the exhaust port right above the exhaust port on
the cylinder.
A piece of 1/8" copper tube is J&B welded into the port and flattened slightly to make the liquid spray a bit of a fan
pattern
when it hits the exhaust. The copper tube is more than an inch long so that the Tygon line that carries the liquid
from the valve
does not have to be too close to the muffler and will hence not melt.
The real secret of my success is the liquid. Basically you have to use a mineral oil based smoke fluid. MDW
Super Dri both make fluids, both are ridiculously overpriced but work magnificently. Start with these mixes and
when happy, then start playing with other liquids to reduce the cost. Basically if you cannot get SuperDri to work
well you will never have much luck with anything else.
A 4.2 will burn between 8 and 10oz of fluid a minute for good smoke. I use a 24oz tank for an 8 minute flight with
careful control of when it is on and off.
Peter
Smoke Mixtures:
The Mix that everyone should be Using!!!!!!
Peter wrote:
When I tried Diesel and various ratios of Auto Transmission fluid in my Sachs 4.2, I got
a) smelly smoke and plane and
b) the smoke was a kind of light grey instead of puffy white.
I've done (back to back) show the Super Dri to be twice as good as any Diesel/oil mix and a pure white non
smelly color compared to a light grey, smelly. Admittedly on a clear blue day with no wind 100% Diesel or various
Diesel/oil mixes look not too bad.
Smoke Mufflers/Installation:
Here’s what you need for a smoke setup.
1.) A pump for oil delivery. TME makes one that plugs right into your Rx on a spare channel .
2.) An extra fuel tank for the smoke oil. Use one as big as you can fit into your fuselage as it goes quick
NOTE:
if your gonna use diesel or kerosene you will have use a stopper on the fuel tank that is compatible.....along with
fuel lines in the plane. The normal fuel lines will rot with this stuff.......also make previsions for the fueling tank and
a means to fuel or pump the stuff in.
3.) A smoke muffler.
and more HEAT!
You can either buy one or make your own.
However the key here is HEAT HEAT HEAT
The key to making smoke is partly pre-heating (I used to think pre-heating was # 1 a while back), and the major
concern is how it is injected (where) and in what manner. A large pressure tap does you no good. For a smoke
system to work properly, you have to atomize the fluid as much as possible. In order to do this, you need to have a
small, I mean small hole on a pressure tap or a sort of is that will spray your fluid into the muffler at the hottest part.
Think about it. If you take a spray bottle and shoot a stream on something, how fast does the water evaporate? If
you then set it to a finer mist, or spread the water molecules apart into smaller droplets, they will dissipate faster.
I've had good luck with pre-heaters in the past, but I found a noticeable difference in the amount of smoke if you
flare the end of a copper tube to make a spray (if it's an internal pre-heater) or get a really small pressure tap.
I just finished a Midwest Super Stinker this year with a Moki 1.8 on it. I used Bisson's injector nipple which uses
this same sort of principle. Granted, there is no pre-heater on this engine and I doubted it would be a very
impressive system. Boy, was I shocked.. The key is atomizing and getting the right amount of fluid injected into a
muffler. Too much does no good.
Try the super dri liquid. As for having a gas engine, my Moki proved this wrong :)
Run the TME smoke pump on a Saito .91 with good success. I inject the smoke oil into the header just before here
the muffler attaches, instead of into the muffler itself. I this helps give it a little more time to heat up and smoke. If
you can, wrap a copper or brass tube around the header a few turns then feed it into the header. This will also
help.
I had the TME pump, a 10oz smoke tank, 500mah battery all tucked into the empty space under the fuel tank on a
Sig Astro Hog Bipe. It hardly noticed the extra weight, and it looked great doing snaps or tail slides with the smoke
on.
All in all, it provided good smoke. Nothing like a G62 blowing full smoke, but a nice pleasing effect overall.
The secret to good smoke is
a) heat and
b) the proper fluid. The answer to the proper fluid is SuperDri by MDW. This stuff is twice as good as any other
combination you can mix yourself and makes no smell and very little mess.
Ok, that aside the next problem is heat. A big engine like the 1.8 should be not bad. I'd suggest simply running
some kind of copper piping around the head of the motor before injecting it directly into the muffler just slightly aft of
the engine's exhaust port. There are other options like coils that are snaked up inside the muffler but I don't think
that's such a good idea, mine just broke on both my smoker mufflers but my application has more vibration than
yours. The larger the volume of your muffler the better the smoke because it has longer to smolder in the muffler
before hitting the cold outside air.
Slimline style pitts smoker mufflers work really well but don't go out and buy one if you already have a slimline non
smoker muffler. Instead, run copper tubes from one end of the muffler to the other and connect them with external
pieces of neoprene in a U. Make sure you give yourself a good inch of copper sticking out of the canister so that
the neoprene is not too close to the muffler. You can stick the copper tubes with JB weld which will hold up well to
the heat. You probably only need one or two runs back and forth through the canister before the final injection but
you can experiment with more runs if the results are not good.
I go through 20oz in 3 minutes. You could probably get 5 minutes on 15 oz but you're still gonna spend some
money. Certainly more than the cost of your glow fuel.
As far as pumps are concerned I have no experience with small glow engine based systems but many folks like
the TME electric system since it requires no fancy mods or plumbing.