Tank conversion options?

As the following pictures will show, I'm converting an old tank for use in my Walter Umland All-American Sr. It's an old tank, and as you can see, it originally had some (to me) fairly bizarre plumbing. The filler/overflow tubes were on the same side, and neither extended into the tank. As well, there is some kind of baffle inside the tank, separating the pickup tube from the "main" tank. There are a few holes in this baffle near the front of the tank, the picup tube ends about 3/8" from the back wall of the tank, and it looks like there'd be a small gap between the baffle and the back wall (the end that is off the tank), so there are a number of ways for fuel to get behind the baffle from the "main" tank.

As you can see in the last couple of pictures, the tank is a pretty snug fit, and has to be slid in from the front, so I want to make this into a "tubes forward" configuration. My question is, how should I plumb this tank? Can I make it a uniflow? For that to work, I think I would have to cut away part of the baffle at the back - I don't think it'll be doing any good anyway, I just want to accomplish this with as little major surgery as possible (laziness). I think I could make it a two-tube configuration, i.e. just have the pickup and uniflow tubes, and when filling, use one for the filler, one for the overflow. It would be a bit of a pain in the neck, but I think it would work.

Opinions? Thanks.

Tim

Tim, I would plumb the tank as a uniflow. I would leave the baffle in and seal off the two top vents shown and replace them with a single vent (to be capped off after filling) pointing forward at the upper inboard end of the tank front. Going JUST inside the tank so that bt tipping the plane nose up and slightly outboard wing down you will get a full tank of fuel.
I would leave the baffle in and run the uniflow vent through the baffle 3/8ths to 1/2 inch forward of the end on the feed line end. Be sure that the feed line goes to the back of the tank and is SOLDERED to the tank at the rear so that no vibration can affect the feed line. Angle the end of the feed line at appx 45 degree angle. Where the uniflow line passes through the baffle, solder it there. The end of it should JUST clear the feed line and be dead level with the feed line.

CAUTION!!! WARNING!!!WARNING (phrase from "Lost in Space") Be sure that ALL lines inside the tank are COPPER. NO brass feed or uniflow lines.

On my AAsr I had the tank permanently installed and mounted up on 1/16 inch spacers over the mounts. then I put 1/16 th aluminum spacers under my engine to get it in line with the tank. That way, I could either remove the spacers under the engine or add to them to adjust the engine to tank alignment. I never had to however. 2 1/2 ounces would get me through the modern AMA pattern with a Fox 35 Hemi head/stuffer backplate setup. Thet was with a Fox NVA too. 10 X 5 APC 7 1/2 % nitro and 25 % castor oil. Combo lasted 12 years of HARD flying and still had good compression but the shaft was getting fairly loose in the case.

Bigiron

If you have questions and want to, give me a call at (316)838-8494
Marvin Denny

Hi Tim, Marvin,
Help me out, Marvin, memory is fading.....
That tank looks a lot like an old Veco Pressure tank, or team race tank, like I said, I haven't "seen" one in years. (about 30)
Thanks!
Bill <><

LAST EDITED ON Feb-28-04 AT 04:32 PM (CDT)
 
>That tank looks a lot like an old Veco Pressure tank, or team race tank; like
>I said, I haven't "seen" one in years. (about 30)

It was their "T-31" series for combat, and had four tubes going in & out of it. Sometimes there was a ball-check device in the one at the front center, where the crankcase pressure was attached. The two on top were filler/overflow, and would be capped with a single piece of tubing in a "U". It had only two real failings; the tubes were all brass, not copper, and with most of the usual pressure fittings, you needed a necked-down restrictor piece added to the plumbing (someone in the late 50's, early 60's sold a pressure fitting with a pinhole size outlet {possibly Veco themselves} that worked the best with tanks like this one).

It makes up into as good of a stunt tank as any other if you yank out all the brass and use copper instead. The pressure fitting hole can be plumbed to a Uniflow tube that will in turn be plumbed to a muffler pressure fitting. That hole is in a poor location for a Uniflow tube open to the atmosphere, of course.

.

Kiwi

Thanks, guys, I'll have to plan out what I'm going to do and how. I'm not sure I'll be able to find copper tubing around here, I've looked before without luck, so I may be stuck with brass. As you can see, I've already removed the two vent tubes that were pictured in the first couple of pictures, and filled the holes. Marvin, I will see if I can implement what you've recommended. Not real sure how I'm going to drill a hole in that baffle, but I guess at this point I might as well go whole hog and remove the front of the tank as well. That'll let me get where I need to, and clean all the rust and gunk out, and I should be able to get it all back together.

Tim

>As you can see in the last couple of pictures, the tank is a
>pretty snug fit, and has to be slid in from the front, so I
>want to make this into a "tubes forward" configuration. My
>question is, how should I plumb this tank? Can I make it a
>uniflow? For that to work, I think I would have to cut away
>part of the baffle at the back - I don't think it'll be
>doing any good anyway, I just want to accomplish this with
>as little major surgery as possible (laziness). I think I
>could make it a two-tube configuration, i.e. just have the
>pickup and uniflow tubes, and when filling, use one for the
>filler, one for the overflow. It would be a bit of a pain
>in the neck, but I think it would work.
>
>Opinions? Thanks.

Ay Carumba! That's one nasty-looking tank. For sure, before you spend any time modifying it, use some plumbers rust dissolver (the kind you put in the toilet tank, not acid) and following with soap/water and lacquer thinner. I do not suggest, at all, spending any time modifying the tank or using it unless you can get the insides completely clean - i.e., completely pristine with no spots of anything.

Then, as Marvin suggests, remove all the tubes and replace them with copper. They have it in Canada, or you can order it on-line, I suppose. While you have the tubes out, use a desoldering bulb and quick wipes with a paper towell over the molten solder to to remove all excess solder from around the tube holes and backplate.

The unilflow line can go in one of the holes and then solder the far end to the baffle right at the point of the wedge. Put the pickup in the same hole it was, and then solder the far end of that to the wall of the tank, right in the peak of the wedge.

You can stop there, and then fill through the uniflow vent, but I don't recommend that. Just put in an overflow tube through an available hole (or make another) and run it to the inside/top/front corner of the tank right in the corner. Fill through the uniflow, allow overflow through the overflow, and then cap it off airtight when you are done. Block all the other holes with patches made of tin-plated steel.

When you go to solder, you may be able to solder effectively to the remaining tin plate protected by the old solder. The tin is completely gone from the body of the tank. If you have to solder in new holes that you just made, you may have to solder using acid flux like StaBrite or plumber's flux. Solder all the holes first, the rinse and rinse and rinse with lots and lots of running water, and then follow with laquer thinner. Then put the backplate on and check for leaks. Then beat it on a table for a while in various positions to break any weak joints and solder balls loose, then recheck for leaks.

I can tell you right now. I wouldn't even begin to mess with it. By the time you rework this tank, you could have called Brodak and bought one, or made one from scratch that's already clean and tight. THAT's how a REALLY lazy guy such as myself would do it.

>replace them with copper. They have it in Canada, or you can
>order it on-line, I suppose...
>

Of course they do have it in Canada, I just haven't found any locally - the LHS doesn't carry it, and I haven't seen it at the local hardware store, either. Guess I'll have to order some online, and I guess while I'm at it, I'll order some K&S tinplate, and get enough of both to make several new tanks.

>
> You can stop there, and then fill through the uniflow
>vent, but I don't recommend that. Just put in an overflow
>tube through an available hole (or make another) and run it
>to the inside/top/front corner of the tank right in the
>corner. Fill through the uniflow, allow overflow through the
>overflow, and then cap it off airtight when you are done.
>

Thanks - that sounds like a better solution...

>... The tin is completely gone from the body of the
>tank.

I'm not sure it ever had any tin plating on it. The body of the tank is so uniformly the same color and texture, I'm pretty sure it came that way new.

Tim

>>... The tin is completely gone from the body of the
>>tank.
>
>I'm not sure it ever had any tin plating on it. The body of
>the tank is so uniformly the same color and texture, I'm
>pretty sure it came that way new.

Possibly, but I doubt it. I've seen a lot of these old Veco tanks that looked exactly like that - bare steel. The plating was really thin and it just fell off/wore away. I bet you will find that where the solder was it's significantly brighter because the solder protected the tin. If you sand/abrade on it, you'll find out very quickly!

I agree with Brett on the tin plating . It was so thin that it didn't take long for it to disappear.

Kiwi you are correct on the number T31 was used quite a lot in Combat and Rat Race. There was a letter following the number A,B,C, D etc. The letter was for the size in ounces (or in length, measured in 1/2 inch increments. I think The C was 3 inches long and held 3 oz of fuel.
Bigiron

All things considered, I think I'll just pitch this tank (and a couple others I have that are like it) and go for a few Brodak tank kits instead... Thanks for the education!

Tim

Tim, Before you pitch it, package it up with the end cap and ship it to me. I will see if I can configure it for you and ship it back (no charge)

Bigiron

I have too many tanks that look about like yours as to general state of disrepair. One point, which I think Brett made, should be emphasized. I have uniflowed a number of tanks with that sort of baffle and placed the uniflow on the inside of the baffle, not outside with the pickup, with fine results. So no need to drill holes in the baffle for the uniflow to get through. Do solder the ends of the tubes well so that they don't vibrate around.

Thanks, Jim, I was kind of thinking along the same lines... since the baffle doesn't actually go all the way to the back wall, it didn't really seem necessary to put the uniflow outlet on the same side of the baffle as the pickup tube. I wonder just what that baffle does, anyhow...

Tim

>Thanks, Jim, I was kind of thinking along the same lines...
>since the baffle doesn't actually go all the way to the back
>wall, it didn't really seem necessary to put the uniflow
>outlet on the same side of the baffle as the pickup tube. I
>wonder just what that baffle does, anyhow...

Tim,
My understanding is that the baffle is intended to reduce the variance in fuel pressure at the pickup tube from full to nearly empty tank (and therefore help steady the engine run) by having the centrifugal weight of the fuel press mostly against the baffle rather than the outer wall and the pickup tube. The gap between baffle and tank back allows fuel to flow into the pickup area slowly as it is used up.

The principle is similar to the chicken hopper tank discussed previously, but with simpler construction and better space utilization inside a built-up fuselage.

The baffle is similar to those described by Brian Eather as used in his custom tanks sometime back on the board.

The use of these baffle tanks in combat and racing as mentioned by Big Iron makes sense when you think about the greater sensitivity of large-bore venturis to changes in fuel pressure.

Jim T, Big Iron,
Is my brain in the right gear here?

>>Thanks, Jim, I was kind of thinking along the same lines...
>>since the baffle doesn't actually go all the way to the back
>>wall, it didn't really seem necessary to put the uniflow
>>outlet on the same side of the baffle as the pickup tube. I
>>wonder just what that baffle does, anyhow...
>
>Tim,
>My understanding is that the baffle is intended to reduce
>the variance in fuel pressure at the pickup tube from full
>to nearly empty tank (and therefore help steady the engine
>run) by having the centrifugal weight of the fuel press
>mostly against the baffle rather than the outer wall and the
>pickup tube.

No, I don't think so. The baffle is intended to reduce the tendency of the fuel to slosh away from the baffle under hard maneuvering. That IS the same idea as a chicken hopper. But it can't do anything about the change from beginning to end.

I might add that I have flown a lot of this shape tank. I have taken the baffles out, and put them in, and couldn't tell a lick of difference, on stunt planes at least.

Marvin, you don't pitch tanks- you pitch props! You go around saying things like that and people will think you're a Texan. Again. By the way, we've got this painting of the sunset that Rhea did and it's hanging on our wall- it is beautiful! ooos and xxxs,

You are WRONG OLE DAD!! I PITCH tanks !!! PITCH !!! GOT IT!!! Like TAR!!! Like tar and feather!! you want some tar !! y'all .

See you at VSC.

Bigiron