A Smoke System

[GraemeSmith]

With more than a little help from:

Marvin Homsley
http://www.smoke-system-helper.com
419 360-7414

I got a smoke system up and running this weekend. Marvin was kind enough to provide a general schematic and design advice. Given that he only got to sell me $170 worth of parts and I sourced everything elsewhere - it was extraordinarily generous of him.

Schematic

Key points
=========

- Injectors must be as near the hottest point in the exhaust system as possible (JUST below the EGT probes).
- The oil must spend the longest amount of time possible in the pipes to fully oxidize and reduce risk of fire. So on the AeroVee - the injectors go in the front pipes
- A minimum volume of 1/2 Gall of oil a minute per 100hp is needed to get decent smoke volume.
- If ordering Marvin's injectors - be sure to ask for the "Rotax" injectors which are sized for the smaller AeroVee exhaust pipes.

Looking at complete systems - I was pretty sure that most of the pumps on offer were simply RV type fresh water pumps that the smoke system folks oversticker and reprice at aircraft pricing. My past life boatbuilding tells me these pumps use neoprene impellers or valves and can run dry, self prime and will pump just about any liquid. So I used a simple $30 Shur-Flo type that pumps 1 gall per min. Between losses from sucking oil from the tank and back pressure from pushing the oil into the injectors I just about got 1/2 gall per min (more about that in a moment).

The actual equipment came in at 5lb total weight and consisted of:

- 1 Gall "oil" header tank from Aircraft Spruce with a Venting Cap. As this is all positive G acro - no flop tube needed. Mounted on two aluminium straps in the back of the baggage compartment
- Some reinforced hose
- Pump which went under the seat pan with some wiring, in line fuse and a switch to activate. There are some fancy PTM/PTB switches and relays to be had that fit on your stick. But I just used a toggle switch next to the mixture control. As my hand is on the throttle for acro - it's easy enough to extend a finger to flick the switch on and off as needed.
- Needle valve to control pressure
- Bulkhead fitting to get through the firewall
- Aeroquip Stainless reinforced hose on the engine side to deliver the oil to the injectors on the pipes.

Equipment Locations in aircraft

For Weight and Balance - Smoke Oil comes in at about 7lb per US Gall.

--

Testing
======

Test 1

- Safe the engine, initially you don't want it running.
- Fill oil tank
- Place a bucket under your tail pipes
- Turn on pump
- Time how long it takes to get a gallon of oil to pump through the system - catching it in bucket.
- Adjust needle valve and repeat test as necessary.
- After a few runs check whole system for leaks.

Test 2

- Move plane to the downwind corner of the ramp - away from everyone.
- Warn airport management that some people outside the fence may call saying an aircraft is on fire (glad I did - someone did!).
- Volunteer standing by with a large fire extinguisher
- Run engine up to good and hot and set EGT's to hottest setting.
- Briefly turn pump on and immediately off - volunteer to confirm you got smoke and not fire.
- Try longer bursts till you are happy it works and stop before you annoy the neighbors!

Test 3

- Air test!



Observations
===========

- A half gallon a minute means you get 2 mins endurance out of a 1 Gall tank. I could have fitted a bigger tank but that's more weight to haul around.
- EGT's decay a little as you make smoke so get them good and hot. I make sure I am at peak EGT for a complete oil burn. Doing this there is almost no residue on the plane.
- Fly faster and the smoke gets spread out thinner. Fly slower and you get more density / apparent volume.
- It looks a little disappointing sitting in the cockpit - but it looks fine to the observers on the ground. In fact I've found that a third of a gallon a minute gives decent enough smoke and gets you more smoke time.
- Set your expectations a bit lower. You are not going to get massive volume like a Pitts or an Extra at an airshow. We don't have the horsepower and sufficent waste heat to burn enough oil or the ability to carry enough. But flick the switch while sitting idling on the ramp and you will instantly find yourself IFR on the ramp. It's pretty good. Fly slower and don't smear it out too much!
- Fellow pilots immediately accuse you of helping keep up the Chem Trail work - as the airlines are not flying as much and are not doing as much Chem Trail work..... (Peter Anson!)

1,000ft AGL. Observer with cell phone camera

Smoke Oil
=========

For weight and balance - about 7lb / US Gall.

Man it's expensive! And every seller claims "Cleanest Burn", "Best volume", "Best hang time". "Cleanest Belly" Shipping costs are horrible.

Time for some "Home Brew". Many claim that filtered used brake fluid works and Concrete Release Agent also works. So I dug out the MSDS sheets for those and for actual smoke oils. Guess what? They are all at least 80% "Mineral Oil" Also sold as "Baby Oil" or the stuff you get at the drug store for constipation or used by food processing plants as a lubricant. Confusingly - in some parts of the world this is also called "Paraffin Oil" - but this is not Kerosene.

The Brake Fluid and Concrete release contain chemistry that it's probably not wise to burn.

The smoke oils are 80% mineral oil plus "proprietary secrets" that all have hazard codes similar to the actual mineral oil. A clue is in the "light yellow/straw color".

So the cheapest Mineral Oil in bulk that I could find was for food processors on Amazon at about $9 / US Gall.

A WAG said the other 20% was another hydrocarbon.

So I tested and flew:

- 100% Straight Mineral Oil - Not bad smoke

- 80% Mineral Oil / 20% Mineral Spirits (Odorless Paint Thinner / Turpentine Substitute). Nope bad idea - poor smoke.

- 80% Mineral Oil / 20% Kerosene. Good smoke - but Kerosene is expensive

- 80% Mineral Oil / 20% Low Sulphur diesel. Nearly as good as the Kerosene mix and better than 100% Mineral Oil. Hey! And also got me a light straw color mix.
Much cheaper than the Kerosene mix.

So I'm currently using the Mineral Oil and Diesel blend.

YMMV

Why Do it?
=========

With no ground observer to help me with acro critique in the area I have for practice. A burst of smoke helps you see how you are doing. A quick check shows that my barrel rolls look pretty good, aileron rolls are OK and loops - much more pinched than I thought they were...... :-(

[Rynoth]

Great write up Graeme, thanks! A couple comments/questions:

Would this be possible on the Aerovee turbo? Somehow I doubt that injecting near the EGT probes but prior to the turbo turbine is a good idea. And exhaust post-turbo is probably quite a bit cooler.

Heating oil is diesel with a red dye, might be a cheaper alternative? What about JetA (probably more expensive than Kerosene, but is basically the same thing.)

[GraemeSmith]

Great write up Graeme, thanks! A couple comments/questions:

Would this be possible on the Aerovee turbo? Somehow I doubt that injecting near the EGT probes but prior to the turbo turbine is a good idea. And exhaust post-turbo is probably quite a bit cooler.

Heating oil is diesel with a red dye, might be a cheaper alternative? What about JetA (probably more expensive than Kerosene, but is basically the same thing.)

No idea about the turbo. But the layout doesn't look promising. Ask Marvin - he is REALLY helpful!

Heating oil - not easy for me to find the odd gallon.

Jet-A - I was thinking about that. Next time our fuel truck is filling someone - I'll try and snare a gallon. Wonder if "Prist" will make a difference? ;-)

[John Monnett]

Sonex Smoke!

There is a good article on smoke systems in the Feb. 2010 EAA Sport Aviation. Alternates for smoke oil are discussed. No real good cheep substitutes except filtered used transmission oil. Jet A smokes but not good enough IMHO.

[GraemeSmith]

Ha! That article is written by Marvin who helped me come up with the system!

[GraemeSmith]

A little video

[GraemeSmith]

And the magic mix is:

80% Mineral Oil
20% Jet-A

The Jet-A gets the "hang" time.

[GordonTurner]

Nice!!!!!

[radfordc]

Getting the oil/diesel mix as hot as possible before it goes into the exhaust pipe definitely helps. For my large RC model I wrapped copper tubing around the exhaust several times so that the smoke mix is preheated just before being injected. Seems to work well.

[GraemeSmith]