Why you don't trust new old-stock fuel tanks

[Dennis Vander Kuur]

Yesterday I was looking for a tank to put in a BiSlob that I am scratch building from plans. In my tank stash box I found a very shiny and nice looking new and unused 3.5 ounce VECO T-21 tank still in the box (bought recently at a swap meet). I was all set to put it in the BiSlob's nose and sheet it over when I vaguely remembered someone's words of caution to not trust old tanks. Because the tank would be built in when the model was finished, it would not be accessible for repair without butchering the plane. Therefore, I reluctantly decided to open up this new tank and check it out, however, I didn't expect to find any problems. I used a propane torch to heat the solder around the rear end cap and carefully removed the cap. WOW!!! Was I surprised at what I found. Two pictures are attached. The first picture shows the amount of surface rust on the tank's interior and the amount of powdered rust that was laying loose in the tank. The second picture shows the large amount of white-colored corrosion that had built up on the brass vent tubes. Needless to say, if I had actually used this tank without checking it then I would have suffered significant engine run problems.
DennisV

[Tim Wescott]

Ugly.  Good thing you checked.

I'm not even sure if that's a good candidate for derusting and re-soldering, or even with all that brass and solder if the more aggressive de-rusting procedures would work without dissolving something you care about.

It occurs to me that a quick check would have been to shake the thing up and blow on one port -- if a bunch of rusty dust comes out the other, then you know you're in trouble.  Of course, the right answer after doing that is probably "then take an end off and check anyway".

I'm still working at graduating from RC to something more recent and advanced, so it's still plastic tanks for me.

[Chucky]

This is what one typically sees in an old metal tank that been sitting empty here in Florida.  I recall Larry Cunningham recommending an tank interior inspection in one of his Mo' Best articles and believe it's good practice to pop the back off of any metal tank before using it -- new or otherwise.  Considering who's building 'em these days, it's all the more appropriate.  If you plan on flying it for any appreciable length of time, a tank hatch on the Bislob would make fuel problems a whole lot easier to deal with.

[Alan Hahn]

Dennis,
I would consider adapting the tank hatch from the ARF Bislob version.  Very convenient. Also lets you use a plastic tank. I crammed a soft rectangular 4oz Sullivan in mine.


All that corrosion probably came from the soldering flux--which wasn't cleaned out completely. As a matter of fact ( = conjecture  ), the old age probably contributed to the problem. If it had been used soon after purchase, the normal fueling (not to mention initial cleaning) would have removed the flux. That's my guess.

[Tim Wescott]

Dennis,
I would consider adapting the tank hatch from the ARF Bislob version.  Very convenient. Also lets you use a plastic tank. I crammed a soft rectangular 4oz Sullivan in mine.

I'm new to this game, but the notion of burying a fuel tank into a plane that you're going to finish up all nice and pretty just gives me spasms.

All that corrosion probably came from the soldering flux--which wasn't cleaned out completely. As a matter of fact ( = conjecture  ), the old age probably contributed to the problem. If it had been used soon after purchase, the normal fueling (not to mention initial cleaning) would have removed the flux. That's my guess.

I'll bet you're right.  It would explain why the outside of the tank looks so good and the inside so horrid.  This probably wasn't a big deal in the heyday of build-your-own, as few tanks would have stayed on the shelf long enough to corrode.

I was looking at the photo thinking that were I buy a metal tank I'd want it to come inside a plastic bag with a little packet of indicating desiccant just to let me know where things stood with the thing.

[Jim Thomerson]

I would never use a metal tank without taking a look inside.  I've been amazed at where some of the tubes went, particularly on the old Perfect tanks. 

[Phil Coopy]

Great post Dennis!!

Phil

[Alan Hahn]

I'm new to this game, but the notion of burying a fuel tank into a plane that you're going to finish up all nice and pretty just gives me spasms.

...<snip>

Tim,
I am not sure spending a lot of time putting a nice finish on a Bi-slob is worth it in the long run! Yes a fuel/oil proof finish is very useful for that slobbering Fox35.

However the TBCEWG  (Time Between Close Encounters With Ground   -excluding wheels) tends to be rather short if you are wringing it out!

[Harleyman]

Yesterday I was looking for a tank to put in a BiSlob that I am scratch building from plans.

A new Slob huh?  We hooked you at the Cheesehead fly-in, didn't we?  Slobs are just too much fun.  I was hooked when I gave it a try two summers ago.

"I GOTTA GET ME ONE OF THESE!"    

Great post BTW, good information here that I'm sure not many of us were aware of.

[Dennis Vander Kuur]

Harleyman,
Yep! I enjoyed watching the BiSlob antics at the last annual Cheesehead Flyin. One of our local club members also acquired a BiSlob this past summer. He was foolish enough to let me fly it and after just one flight I was hooked. I had to have one for myself so that's what I'm building during the cold, frozen tundra, Chicago winter. However, we have been known to also actually do some winter flying. Attached are two pictures of a few Chicagoland Circle Cutter members flying at the club field on New Years Day.
DennisV.

[Chuck Feldman]

Dennis,  At the last fly in in Merritt Island I sold a lot of Items including Veco Fuel Tanks. I do not know if you where there or not. But the pictures do prove that you need to take the metal tanks apart to be sure its OK. That is the worse looking internals  I ever saw. I always put alcohol in my tanks and shake them. Then I put acetone in there and shake again. Blowing the liquid that comes out into a glass jar indicates what the inside condition might be. Normally the acetone dissolves the flux and it is not uncommon to find little solder beads.  Next I shake the tank bang it around and then shake it and listen for loose items. If it passes all this I seal it up and use my fuel bulb to pressure test the tank while it is under water.

If you got that tank from me I am sorry it turned out to be so bad a shape.

[Glenn (Gravitywell) Reach]

Always exchange the brass tubes for copper.  Copper won't corrode as badly as brass does.  I always boil my tanks after buiolding them, blow them out and repeat, this gets rid of the flux.  You can see it float to the top of the pot.  Works good.

[Larry Cunningham]

My experience with a metal tank was even more horrifying (about 23 years ago) I couldn't find a metal tank in Las Cruces, so I went to El Paso. Of course, none of the "newer" hobby shops had any and couldn't feature why I wanted one. As a last resort, I went to the Five Points hobby shop, downtown. The guy has a lot of old stuff, some of it very interesting (like tons of aircraft decals).

Anyway, way back in the back was a Veco cardboard display stand with one metal 4 oz tank on it. The tank looked dusty, but otherwise immaculate. It had a price tag on it of $1.50 (original) but when I got to the counter, the guy could see I wanted it, and said the price would be $7.00.. I paid it anyway, having driven to El Paso to get a metal tank.

When I got home, I was preparing to modify the tank by moving the top vent, and when I punched it with an awl, it collapsed. I could see rust. So I started taking it down and the entire inside was filled with rust - it had grown, like a colony of coral! And the tank walls were entirely crusted and eaten away, they were paper thin. Yet it had looked so nice on the outside! ;->

I briefly considered taking it back to the guy at Five Points and demanding my money back..

I don't believe the brass tanks have this problem.

L.

"Ever notice how irons have a setting for *permanent* press? I don't get it." -Steven Wright

[Alan Hahn]

Guess I could have the same problem with old batteries!

[Dennis Vander Kuur]

Alan,
My BiSlob magazine plans don't show a tank hatch and so I've built the fuselage that way. However, after this enlightening  experience with the "new-old" tank I am going to take your advice and modify the fuselage to incorporate a tank hatch.
DennisV

[Alan Hahn]

Dennis,

I've got the Flying Model Plans too. Even bought some wood from LoneStar before the fire.

Decided to go with the ARF because I wasn't getting around to it, and Bislobbin' just looked like too much fun to wait. Plus I thought that terra firma contacts were a high probability, and that I might be more daring with the Arf. Actually crashes are not that frequent, once you get the hang of the thing.

Gee first we get you to waste time with 1/2A stunt and racing, now you are bislobbin, what's next----Combat?

[Dennis Vander Kuur]

"Gee first we get you to waste time with 1/2A stunt and racing, now you are bislobbin, what's next----Combat?"

Alan,
Shhhhhhhh!!!!! Don't tell anyone BUT......I am thinking of trying to fly some combat this summer. However, it'll only be at our CCC club combat contest. We had the biggest turnout in many years this past summer for the club combat contest. I was so jealous of all the fun they were having that I decided I should give it a try this summer. Rest assured I won't be flying my Pathfinder or PA .65-powered LEGACY in the combat contest. I tried my hand in combat back in high school in the early 60's when I was young and foolish. Now I'm old and still foolish, however, I still have a couple combat engines/planes left to sacrifice to the combat gods .
DennisV

[Dennis Adamisin]

D-VK:
THAT is a scarry fuel tank you almost used there!  I have never had that happen to me but have heard the stories - and your pix tell the proverbial 1000 words... Ugh.  Looking over a set of BiSlob plans, it looks like you could build it so the tank could slide out the front from behind the engine (after removing said engine).

Combat?     Yee haw!   

 

[Crist Rigotti]

"Gee first we get you to waste time with 1/2A stunt and racing, now you are bislobbin, what's next----Combat?"

Alan,
Shhhhhhhh!!!!! Don't tell anyone BUT......I am thinking of trying to fly some combat this summer. However, it'll only be at our CCC club combat contest. We had the biggest turnout in many years this past summer for the club combat contest. I was so jealous of all the fun they were having that I decided I should give it a try this summer. Rest assured I won't be flying my Pathfinder or PA .65-powered LEGACY in the combat contest. I tried my hand in combat back in high school in the early 60's when I was young and foolish. Now I'm old and still foolish, however, I still have a couple combat engines/planes left to sacrifice to the combat gods .
DennisV

I vote that Dennis does use his Pathfinder and Legacy in the combat contest!   

[Dennis Vander Kuur]

I received the following email regarding this post from Eric Rule. I post it here with Eric's permission so that all may benefit from it.


Hello Dennis;

I was "lurking" on Stuka Stunt and saw your posting.

Since I own GRW Fuel Tanks I have some idea of what caused your problem.

Most fuel tanks are soldered up using tin plated steel sheet material which has the coating applied to one side only. This gives a very nice and shiny finish on the outside of the tank. Unfortunately the uncoated surface of the steel is subject to corrosion. This is what happened to your tank.

At RSM we use a 75# tin plated steel which is coated on both sides. In addition we use only annealed copper tubing and a very expensive electroronic solder which will not discolor when it comes into contact with fuel. Although the use of these materials increases our cost in building the tanks we feel strongly that when our customers purchase a fuel tank from GRW they should get a tank that has the proper material used in it's construction.

In addition to the use of this more expensive material we pressure test each tank then soak the insides to clean out any residue left from the soldering process. Once the tank is soaked we then pressure test again (sometimes the flux residue will fill in a small hole; therefore, when the residue is flushed out the tank will have a leak) prior to packaging the tank for shipment.

If you decide to take the advice of one of the respondents and build your own fuel tank please be sure to obtain only tin plated steel which has the coating on both sides. Since most folks purchase their copper tubes from the K&S rack in the hobby shop please make sure that you anneal the tube before soldering it into the tank. You can anneal copper tubing by heating it up with a torch until it just becomes red in color and then letting it cool naturally.

I hope that this note will be of some assistance to you

Regards
Eric Rule

[Mark Misegadis]

Tanks Alot!

Here in Colorado where its dry we don’t see the rust issues.  If you’re a fan of old cars its yet another good reason to vacation elsewhere and Live Here.
I have been cleaning out old fuel tanks and using them. I actually have been putting them in a Crockpot with Antifreeze and cooking them on low. I "Do Not" use Alcohol to clean them out as it really doesn’t have the bite to do much. If I were to have had water in something I would however as Alky will absorb the water.  For a solvent I use Laquer Thinner.  Laquer Thinner fix everything!
Now having said that I also use this to clean off the acid flux on the Slot Car chassis that I built and it works great. (I soak them in it for a few mins, A tank would get more time)

I am pretty happy with my little recipe above and have had great success. I’ll be building tanks in the future for myself and as I learned to do my more serious soldering helping a friend in a radiatior shop and have built various tanks etc for 1-1 racecars I think they will turn out great.

So..based on all of that.. and I hope some of you can use it for success..I am sitting her wondering about the following:

1)   Why is brass not a good choice for the tubes in a model airplane tank?
2)   Why would you use Copper instead?
3)   Why if you used Copper why would you anneal it?

On #3 I can see only one reason and that would be to “work” the material so that you can get the shape you want to snake it around somewhere to meet the design that your after. As you work the material it will work harden and then its not annealed anymore.

Sometimes I wonder if we all just get lost in the terminology and the recipe for something that works well. I had a salesman try to sell me a Moutain Bike years ago he had this line that sounded very cool to most folks. “Well you see these frames are welded with an Inert Gase..blah blah blah….”    So I said.. Great.. does that mean they were MiG’d or TIG’d…knowing the answer as its obvious if you weld. I just received a blank expression. I am however sure this guy sold a lot of bikes though.

Mark

[Mark Misegadis]

Nice Post Ty,

You gave me a good laugh to start the day off with that last part!

The splitting part makes me wonder what the source would have been for any splitting brass tube. I am pretty sure that the K&S stuff (today..anyway) is DOM (Drawn Over Mandrel) tubing so there isnt a seam.  I was out in the garage flaring two short sections via a very crude method. Ballpeen hammer and a punch. I would have thought this would have split if there were a tendancy for the material.   I can however see where the alcohol could attack the material but I havent seen that before with Brass.  I have a really nice blue anodized billet fuel filter that was attacked from the inside out and is now in the scrap metal bin from Alky. Its still pretty from the outside..LOL

All good stuff in this post that will keep folks from making a mistake.

Mark