Fuel Tanks and Fuel.

[Warren Leadbeatter]

Hi All,

I have a couple of questions about fuel tanks and fuel.  I've been making my own control line clunk tanks recently and while researching different designs I keep seeing, "use copper tubing and not brass". Can anyone tell me why this is? Is it really that important?

Secondly on fuel, most of the hobby shop fuels here these days are only 18% oil, with most having 16% synthetic and 2% castor for 2 stroke and 4 stoke is all synthetic.  The other day I got some 4 stroke fuel that is 15% nitro and 15% synthetic oil.  I have been told by many that I should be using 20 to 22% oil for control line.  Why is this and what are the ramifications?  Aside from the obvious additional engine wear, does it have any impact on how the 2 stoke engines 4-2 break?

Any comments would be appreciated.

Regards,
Warren

[Phil Bare]

Hi Warren, I do not claim to be an expert on the subject of fuel and fuel tanks but I can tell you of my own experiences of about a half a hundred years of messing with model airplanes and glow engines. The main thing with brass is the fact that it will corrode a little faster then copper will and it tends to be more prone to splitting then copper. With that said, I have all ways used brass tubing and never seem to have experienced any fuel tank problems directly related to it.
Now, on the matter of fuel, again, I do not claim to be any sort of expert but can only tell you of my own experiences and knowledge gained from a life long interest in all sorts of aviation and education in the field of mechanical engineering..
First of all, I personely would NOT use synthetics in any of my engines and that would include four strokes, If I had any, for a couple of what I think, are real and valid reasons. No 1 being the simple fact that castor has a considerabley higher flash point then synthetics and No 2 being the simple fact that castor does NOT (wash) like synthetics do. In our model engines, it is this non washing property of castor, even under high heat conditions such as experienced in a lean run, that makes castor a far superior choice over synthetics. I have found that for most general sport flying, Fox Super Fuel works well in most all of the engines that I own, both c/l and r/c. I will admit that 29% castor is more then some engines need, BUT, I have never seen an engine burnt up or fried from having an over supply of oil....
I will say that if you are a competative flyer and looking for that last 1% of performance and the life of your engines are a second consideration, then by all means, adjust the oil content as well as the nitro to suite ever you think will deliver that last bit that the engine is capable of. I have and use a wide variety of engines and for the kind of sunday fun flying that I do, I use one fuel in every thing except for my .020 and .049 stuff and then the only change is in the nitro content. 29% castor protects all of my lapped iron piston engines and certainly does my ringed engines no harm....Phil

[Bill Little]

Since forever, I have heard that the brass can develop stress cracks/splits.  This would cause extremely hard to catch problems in the engine run department that I do not wish to experience.

Like Phil, I like some castor in my fuel.

Bill <><

[Garf]

I have some very old engines and fuel tanks. On the tanks, old brass tubing doesn't just split. I had a tank start giving me trouble, I pulled it apart, and the brass feed line had SHATTERED. That is not an exaggeration. It came out in several pieces. As far as fuel, I use castor almost exclusively. Synthetic has a lower vapor point than castor, and has a high detergent level. Fox at one time added 1% synthetic to Superfuel as a detergent. I used to run K&B 100 in my Fox stunt engines. I couldn't figure why I only got 2 or 3 seasons out of one before it lost compression. Then during the sale of K%B I found out. I called K&B and talked to someone there that told me they used 17% castor in the 100. That in an engine that needs at least 25% castor to survive.

[Marvin Denny]

  Warren, I wrote an article on the cracking brass tubing for an article in the PAMPA newsletter a few years back.  You might get one of the PAMPA guys to give you a copy of it or at least the month and year it came out in.  I won't go into the causes of why the brass tends to crack, but it does.  There are numerious people with theories of the mechanism that causes the cracking and virtually everyone of them will swear that either their theory is right OR that they heard it from someone who they say  his word is impeccable and above question.  To each, his own theory.
  I may still have a copy around here if you can't find it in the PAMPA sources.  Copper don't crack.
  As to the amount of oil in the fuel, I think that our engines are loaded in hard turns more than RC engines, and they are run at a constant speed throughout the flight without a way to throttle back for cooling that the RC engines can do. Maybe just a safety item, but we can't throttle back if we happen to go lean for some reason during a flight,
  The oil quantity definitely does have some bearing on the engine's tendency to hold a good four and to transition back and forth  between a two and four run during maneuvers.  Not enough oil, and they tend to break into a two and not return to the four.

  Bigiron

[rob biddle]

    G'day Warren,
                                                                                                                                                   
 I have been using brass tubes in my tanks for years with no problems, as nothing else was available locally.

 Many people have reported having brass tubes split at bends over time, which maybe encouraged by vibration.

 Now there is a local source of 1/8" copper tube (a refrigeration parts supplier) which sells a 12' roll for about $18 Aud, so this will be the way of the future for me.

 I used to run a commercial premix fuel in my fp .40 and other abc engines it was 10% nitro, 20% all castor. I found that the engines ran well but glazed up after some time.

 At the time I was flying 3-4 times a week and the cost of pre-mixed fuel was getting out of hand, so I started mixing my own.

 The brew that I am currently using is 10% nitro, 22% oil (50/50, castor/synthetic) the engines seem to be very happy on it and the synthetic has stopped them from glazing up. The cost has gone from $11 per litre to about $6.

 Cheers, Rob.

P.s  Hope you had a good trip back from the Nats, I only managed to get there for one day (bloody work!), I was going to catch up with you but ran out of time in the end.
 

[Bill Adair]

Hi Warren,

Can't help with the tank question, because I don't make my own.

Some years ago I did some testing of off the shelf model fuel, and what I found scared hell out of me!  Some of the store bought fuel was short of even the scant amount of lube indicated on the labels!!!

I've always added castor oil to my fuel, with the amount based on engine type, and the lube quantity indicated by the manufacturers. For ABC, and ring type engines around 20 percent oil was the minimum I'd use, but I wasn't flying anything else at the time.

Later, after seeing a few sport engines ruined while trying to break in with commercial fuel, I decided to do some testing. I copped one of the wife's muffin tins and poured three measured (medical syringe) samples of each type of fuel into the cups, and set the pan in the garage to let the volatiles evaporate. A few days later, the remaining lube was drawn back into the syringe, and measured. (I tried burning the fuel samples earlier, and found it often caused the fuel to boil off some of the lube, not to mention the fire hazard involved.)

What I found was that one of the more popular (then) local brands of 2-stroke fuel contained less than 15 percent lube by volume, and a couple others were higher, but still short of the advertised levels. The fuels that measured right on the money were made by Fox, SIG, and one other US manufacturer (that slips my mind at the moment).

Might not be a bad idea to test the fuel for any of your iron piston engines, because they are much more vulnerable to damage by insufficient castor content. The better ABC and ring type engines seem to get by on most commercial fuel blended for them.

Bill

[Keith Spriggs]

  Warren, I wrote an article on the cracking brass tubing for an article in the PAMPA newsletter a few years back.  You might get one of the PAMPA guys to give you a copy of it or at least the month and year it came out in.  I won't go into the causes of why the brass tends to crack, but it does.  There are numerious people with theories of the mechanism that causes the cracking and virtually everyone of them will swear that either their theory is right OR that they heard it from someone who they say  his word is impeccable and above question.  To each, his own theory.


  Bigiron

You obviously know more about brass tubing than I do, however I know that when brass is formed as in the making tube, it will "work harden". It can be softened again or more correctly annealed by heating it until it starts to glow and then sticking in to cold water.  If I was going to use brass tubing for a tank I would at least anneal it. Once it is annealed you can bend it pretty easy, however it is still subject to collapsing when you make a sharp bend in it. As you said copper does not crack. The only problem I can see is that I think copper tubing has a thicker wall and therefore a smaller inside diameter.

[Bill Little]

Hi Warren,

After reading Bill Adair's post it got me to thinking (OH NO!).

Bill is right, the newer ABC, AAC, etc., engines and those that are ringed and/or ball bearing, do not really need the castor in as high quanities as the older iron/steel p/s engines that had bronze shaft bushings.  A fox 35 or McCoy Red Head, etc., needed the castor in 25% or more to last anylength of time for most pwople.  Fox recommended 29% for their engines in Stunt use (Fox Superfuel) which also served to cool the engine.  The down side to 29% all castor is varnish build up.  I guess that is why they started using 1% synsthetic in the Superfuel, to help clean up the varnish.  If you take a well run in old engine that lived on high "all castor" fuel, and run it with a lot of synthetic oil, you sometimes remove the varnish to the point that there is little to no compression!

For LAs, and similar modern engnies, 20%-22% 1/2 and 1/2 should give you an engine that will run a LONG tme and run well.  That is what we run in the PAs, and such which really take a LONG time to "wear out"!

[Marvin Denny]

You obviously know more about brass tubing than I do, however I know that when brass is formed as in the making tube, it will "work harden". It can be softened again or more correctly annealed by heating it until it starts to glow and then sticking in to cold water.  If I was going to use brass tubing for a tank I would at least anneal it. Once it is annealed you can bend it pretty easy, however it is still subject to collapsing when you make a sharp bend in it. As you said copper does not crack. The only problem I can see is that I think copper tubing has a thicker wall and therefore a smaller inside diameter.

  I wouldn't say that,  it is just that I have tried to research out why the cracking was occurring.
True, if you intend to bend the brass tubing, it is almost mandatory to anneal it as it is "work hardened by the drawing (extruding) process of manufacture.
  I have seen more cracks in the brass tubing along straight (un-bent) portions than in bends.  I have seen it crack during heating to anneal it.
  I took some cracked brass tubing to an independent testing laboratory that specalizes in material failures and their causes (usually associated with A/C accidents  or fatal auto crashes).
  They took the pictures that accompanied the article that I submitted  to PAMPA newsletter. They seemed to think that the cracks started in  non-metallic inclusions caused by the extruding of the tubing . When impurities  (slag, dirt, or other impurities) are forced into the brass as it passes through the die, it is drawn into a long thin line within the brass and thus becoms a weak spot that then fails under vibration, or by being washed (dissolved) out by the fuel we use.  Once started, the ckack may continue in a straight line, or angle off into a different direction. That could explain the "shattering" condition stated by one poster.
  What ever does cause it, and I don't rule out ANY theory, is real, and brass tubing DOES crack occasionally and it DOES cause problems  when it does.
 You may be right in that the wall thickness of the copper being thicker--- I have never measured it.
  I just recently opened up an old tank that I had replaced because I couldn't get a consistant run and clean shutdown from it and a new tank cured the problem.  You guessed it--- cracks in all three tubes inside the tank.
 If ANYONE out there is having problems getting good consistant runs or good clean shutdowns in your flights, I urge you to get  a copy of the article that I got published in the PAMPA news letter.

  Bigiron

[minnesotamodeler]

I haven't seen any mention of aluminum tubing.  I've been using that for a couple-3 years, no problems.  Am I just dodging a bullet here, are there issues I need to be aware of?

--Ray

[Marvin Denny]

  Ray, not having ever used any Aluminum tubing, I can't say if that might crack under long time usage.  I kinda doubt thet it will crack however.

  Bigiron

[James Lee]

Just to keep the rumor going...  I was told years ago that the brass tubing was a seamed product, wheras the copper was not...
I have seen brass tubing in tanks with large splits and almost shattered as previously noted...   Tracking down run problems due to cracked brass tubing is a real hair puller!!   
Jim 

[Bill Adair]

Darn interesting reading.

Never had a problem in the limited C/L flying that I did years ago, but none of my C/L airplanes lasted long enough to wear out anything at all! Some even died with the original prop still installed! 

One of my R/C airplanes flew for ten plus years of frequent flying using a clunk tank and brass tubing, and never had a fuel feed problem that wasn't cleared up by flushing the carb/tank, or replacing split silicone fuel tubing.

What I'm thinking is that metal C/L tanks have very different vibration levels than R/C clunk tanks, which are often padded with foam to further limit vibration. No doubt hard mounted profile tanks are subjected to the most severe vibration levels of all, so it's no wonder that brass tubing subjected to who knows what vibration levels are prone to failure. Could also be a bad run of brass tubing, as that stuff is probably turned out in mega feet, from single batches of foundry ingots (or however it comes to the tubing makers).

Might be interesting to hear more details from those that experienced brass tubing failures, such as approximate number of flights, mounting systems used, and engine types (i.e. high vibration Fox engines, or???).

Bill

[Keith Spriggs]

it is just that I have tried to research out why the cracking was occurring.
  Bigiron

Thanks, Bigiron that is a lot of good information. I did a little checking on 1/8 inch tubing. You can get titanium for 53.31 per foot. Surprisingly stainless steel is not as expensive as I thought it would be 8.72 for 6 ft. You can get soft copper for 29.70 for a 50 ft roll. The ID is .065. I imagine that the freight on the 6 foot stainless would be pretty expensive and I have no idea how well it, or even the titanium would work.  The titanium would give you bragging rights. If I make any tanks I think I would go with the copper.

[Warren Leadbeatter]

I had an old Perfect tank that started leaking fuel out the overflow when the tank was not even full. Unsoldering the tank revealed that the pipe was split.  This is the only occurence of a spilt pipe I've ever had.  I've also heard that the brass lines react with the methanol and they get corroded away - I have not seen this.

Not sure how I would be able to use aluminium or stainless though... how would you solder it in?

Cheers
Warren

[Keith Spriggs]

Not sure how I would be able to use aluminium or stainless though... how would you solder it in?

Cheers
Warren

They have a type of solder that works surprisingly well for fastening alum. to alum. It is used with a propane torch.
Stainless can be silver brazed to common materials that a tank would be made of . All of which would be more trouble than soft soldering in a copper tube.