Smoke System:

Starduster Too Smoke System

 

Somewhere around November of 2000 I saw, on the Starduster Bulletin Board, that Gary DeBaun was contemplating putting a smoke system on his Acroduster. I decided at that moment that I wanted to do exactly the same thing on my Starduster. Now neither Gary nor I had a clue as to what a smoke system looked like or what was entailed in creating one for an airplane. At that point both he and I began the long process (or at least it seemed long to us) of building a smoke oil injections system for our planes.  

We began with BB posts, asking those who had built smoke systems, ďHow do we make our birds smokeĒ. Answers to most of our questions were answered in bits and pieces. In retrospect I suppose the answers were quite succinct and to the point. However, not having a clue as to what we needed, it seemed like we were getting only about half of the answer many times.  

What I found is that the system really isnít very complicated, but if you donít know what it looks like and you donít have a parts list then the design of the system is daunting to say the least. I was also reminded several times that smoke oil IS flammable and you are exhausting a heated, vaporized, flammable substance right under your seat! I was also told to make absolutely sure I didnít cut the throttle WHILE injecting oil. I suppose a possible backfire could ignite the oil and make a really spectacular site from the ground, and a really big surprise in the air. The guys doing this professionally even suggest a Nomex suit before you turn the smoke on. I donít know whether all of that is necessary or not, but I am adding it as a caution and a reminder that making smoke may be pretty but it Ďainít without itís hazardísí.  

I knew from posts on the BB that a good system would probably put out in the neighborhood of 1 gal of oil per minute, and I would probably want 5 gallons of oil capacity to allow for 5 minutes worth of smoke. I didnít want any more of this tank intruding into an already small cockpit than was absolutely necessary and I wanted the tank as near to the firewall as possible because my bird is already way heavy on the tail. Various sources on the BB also suggested that I would need at least 15psi oil pressure to feed the system. With those design constraints in place I set about designing the system.


As the tank seemed to me to be the most complicated part I created it first. I designed a tank the fits partially below the front floorboards and partially above it. The dimensions of the tank are approximately 26 inches wide under the floor and 10 x 10 x 10 for the box, with the half moon shaped bottom area being 3 ľ inches deep. The 3 ľ depth is part of the 10 inch total height .I purchased a 9Ē flop tube for oil pickup. The fuel cap is a twist to lock non-vented cap.The tank has a side panel that is notched to fit around braces and longerons in the aircraft floor. These plates were made from .090 aluminum and just welded on the tank. The tank walls could probably be made out of .090 in this area and then the braces would become part of the tank proper. The 1-inch aluminum angle, also notched, has a 1/8 x 1 inch steel plate screwed on to the top for added strength. I placed small pieces of hard rubber around the notches to help prevent chaffing. This is the only portion of the installation I am not really happy with, so if someone comes up with a better installation method Iíd like to hear about it. The tank is vented with a piece of 1/8 in aluminum tubing welded through an AN816 fitting. This tube goes to within 1/8 inch of the top of the tank. It is screwed into a piece of ľ inch plate welded on the lower rear portion of the tank, which was drilled and tapped for the fitting. The flop tube should just barely clear it when you are finished. You will want to tack the tank together and make sure of clearances before final welding. It clears the bungee posts by about Ĺ inch in front and JUST clears the stick at the rear of the tank when the stick is in full aft position. As individual builders may have somewhat different dimensions in their plane than I did, you should fabricate the tank to fit you dimensional constraints. My tank holds almost exactly 5 gallons when full.I used a fuel tank sloshing compound (obtained at a local auto parts dealer) to help prevent any leaks along seams but if the tank is welded well that probably isnít necessary. I also welded baffle plates across the tank where the half moon section meets the square top. That was done to help stop sloshing of oil in the tank when you roll the plane and the tank is not full. The baffles essentially continue the square top down to the bottom of the tank.






Forward of the tank, passing right between the triangular bungee cord attach bracing is a length of 601-6 Aeroquip hose. This hose connects to an AN833-6D bulkhead elbow. From that point 3/8 aluminum tubing, bent to clear firewall throttle and mixture components, connects to a filter and then a high pressure fuel pump. The pump I used does not have an internal filter screen and I have been warned that not using a filter will cause a lot of grief. The pressure relief valve inside the pump will plug and then one must disassemble the pump to clean the valve. The filter, with that thought in mind, seemed like a good idea. The pump itself is mounted on a piece of 4430 steel plate bolted onto the lower part of the battery box. From the output port of the pump more 601 hose connects to an inline check valve and further downstream an aluminum T Bock. This block has a 3/8 pipe input and 2 1/8 pipe thread exit ports. I used a piece of .060 4130 plate to attach the block to the engine using two of the studs covering the governor port on my engine. Those having constant speed props will need to find some other mount point for this block. To connect the T-block to the exhaust system I had 2 flexible braided stainless steel Teflon lined brake lines made at a local auto parts store. So far they seem to be holding up very well. The injector nozzle was placed right after the 2 in one header meet the collector past the swivel joint. I welded stainless steel bung onto the SS header system right over a quarter inch hole I predrilled in the exhaust collector. An AN816-2 nipple was welded shut on the pipe-threaded end and then drilled through with a 1/16-inch drill to be used as an injector nozzle. The beauty of this is that if you are too small or too large you just drill it larger or weld it up and redrill. The injector nozzle is easily removable. Photos accompanying the article should clarify any questions about the setup.

The pump I used pulls only 2 amps. I used a combination switch/circuit breaker mounted in the panel to turn the smoke on. I suppose an on/off button could also be mounted on the stick but I havenít done that and at this point it doesnít really seem necessary. I also added a cutoff micro-switch that shuts the pump off when the RPM drops below 1500. This was a safety item added in deference to the concern I had for pulling the throttle back while in smoke mode without having time to otherwise switch the system off. By doing this I donít even have to think about it. The switch is adjustable by moving the mounting position for different RPM ranges or it could be mounted as a normally open switch that is only closed when the Rpmís reach a certain point. In this configuration it would need to be placed, of course, on the opposite side of the throttle arm. This switch is mounted on a bracket made from 1 inch angle aluminum cut to fit on the firewall throttle mixture control arm bracket.

Thatís all there is to it. Anyone who is reasonably competent in fabrication should have no problems duplicating my system. The aluminum tank was the only thing that was the least bit tricky and with a little planning it should present no major problem.  

Now on the subject of which oil to use Ė I have used both the cheapest hydraulic oil that WalMart sells ($7.50 for 2 gal) and Canopus 13 oil. Canopus 13 was formerly known as Corvus oil. It is made by Texaco and is sold in 5 gal buckets and 55 gal drums. Itís cost was about the same as the WalMart oil, at the time this article was written I paid $19 for 5 gallons. Canopus 13 is a very clear light mineral oil with a high paraffin content (reminds me of baby oil). I donít think there is much difference in the amount/type of smoke between the two but the Canopus oil may be a little less polluting. Just a guess on my part, nothing to back that one up. I do use the 2 gallon container that the WalMart oil came in to fill my oil tank. It IS a mess when you spill it so go slow and be careful when filling the tank!  

Most of my parts were purchased from Aircraft Spruce. The parts list will include AS part numbers if they are AS purchased parts. Other parts will have a manufacturers part number or description where available. There are no special purchase parts, everything is available from any aircraft parts supplier, your local auto parts dealer(and Summit or Jeggs or some similar source), and nearby electrical supply house. Builder should verify all lengths and sizes before beginning construction. These parts worked for my plane but may need to be modified for your installation. The check valve would be better if it was spring loaded. Mine is free flow and will not actually stop the oil flow, only prevent backflow.  

I would like to thank Buck Roetman, Frank Gorham, and Gary DeBaun for all their encouragement, insights, and support during this project. And a big thanks to the folks at Starduster for providing a Bulletin Board, without which, the project would have most probably never been finished.

 

Bob Perkins

24BX

 

 

 

 


Parts List

 

1.        1.        .050 and .090 Aluminum plate  - amount will vary on final tank dimensions

2.        2.        8 ft of 1 x 1 inch angle aluminum

3.        3.        6 x 6 x .060 4130 plate to fabricat mounting plates

4.        4.        4 ft 1 x 1/8 mild steel plate for angle reinforcing material

5.        5.        assorted nuts and bolts for mounting hardware

6.        6.        3/8Ē aluminum tube approximately 2 feet       S# 03-40600

7.        7.        ľĒ aluminum tube approximately 1 ft        (vent)                     AS# 03-39300

8.        8.        Aluminum Manifold         AS# 04-00126

9.        9.        ACS twist to lock non vented cap   AS# 10600

10.     10.     ACS Free flow check valve    AS# 10630

11.     11.     Flop tube    AS# 05-20509

12.     12.     Flop tube adapter    AS# 10380-1                         

13.     13.     Aluminum Welding Flange   AS # AN867-8      I found the 1 inch thread size was needed to be able to pass the flop tube through it           

14.     14.     Aeroquip 601 hose -  3/8 i.d. approximately 4 ft     AS# 601-6

15.     15.     6 Aeroquip hose fittings AS# 816-6D                          

16.     16.     Fuel pump from Summit Racing 140gph, 18psi      Summit # SUM-G3134 

                  an alternative pump is a Blue Holly fuel pump 

17.     17.     Fuel filter 390 gph, 60 micron, 100psi    Summit # SUM-G1516-6

18.     18.     Micro switch - Selecta straight lever SPDT 15A  UPC#71180       mfg# BZ-2RW80-A2-BG

                  This switch can be configured for either normally closed or normally open

19.     19.     30 Ft of 16 gauge electrical wire

20.     20.     W31 series 5 amp circuit breaker                 AS# W31X2M1G5

21.     21.     AN fittings

                  2 AN816-2D

                  2 AN816-2     steel for injector nozzles

                  4 AN816-6-6D       one is used for vent

                  1 AN833-6D

                  1 AN822-6-6D

                  4 AN818-6D         

                  4 AN819-6D         

 

Also look at http://musclebiplane.org/htmlfile/tanks.htm