Fuel Tank Question

On a profile model, with "standard" tank configuration (not uniflow) would this tank...
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...be better than this tank...
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...for minimizing the pressure change or leaning of the engine during flight?

Thanks,

Jim

Yes.

Like Lou said "yes".
However I would add the caveat that it still won't be very good.
That tank plumbed for uniflo will be much better.

Randy C [photo not recovered: sipcof.gif]

And the pick-up tube coming out the top of the tank means you have to use a long S-shaped piece of fuel tubing (unless the needle value is reversed, where you can't reach it from the top). Short, direct fuel routes are better.

Kim

If I wanted to convert a tank to uniflow, where would I put the end of the vent tube in relation to the pickup? I assume the pickup tube goes to the rear-outside corner of the tank, and I understand that the idea of the uniflow is to have the vent tube end near the pickup tube end, but do I put them side by side, or should there be some separation?

Thanks again,

Jim

Jim,
The uniflo vent should enter the tank in roughly the area where the fill tube on top is now. It should face into the airstream to avoid vacuum siphoning and provide a small amount of "pitot" pressure to the tank. Muffler pressure if desired can be run to this vent. Personally I prefer not to use it (muffler pressure). Inside the tank the uniflow vent should run to and roughly parallel with the fuel feed tube. It should be securely soldered to the feed tube and end about 3/8 to 1/2 inch in front of the pickup end of the feed tube. This is to prevent air bubbles going directly into the feed tube. Air coming into the tank must then pass through the fuel in the tank to allow equalization of pressure and fuel to exit the tank through the feed tube. This creates the compensation that allows a more constant needle setting throughout the flight. all other openings in the tank like the overflow etc must be capped so that air enters the tank only through the uniflo tube. Any leaks, even very small ones will upset the pressure equalization and create problems with fuel flow.
Be sure to pressure test the tank under water for leaks after all rework.
Works pretty well in most cases.

Randy C

Thanks - I think I'll try the conversion to uniflow.

I've got the taller tank (2nd tank pictured above) in my Mustang with the Brodak .049 MK II and my engine run goes from just enough power to make it around the circle in the beginning, to "I need longer lines!" by the end.

Jim

In a uniflow tank, the engine "thinks" it is sucking fuel from the uniflow. Position of the fuel pickup is not important so long as it picks up fuel. It is conventional to position the end of the uniflow as said above. I use a one way valve on my open-air uniflow vents to prevent siphoning and to shield the uniflow from changes in air pressure. I've also used a cap with a tiny hole for the uniflow. The hole in the one way valves I use (KK, Kustom Kraftsmanship) is smaller than a #80 drill.

The pic below is of a well known KK tank from a Joker and similar kits from yesteryear with a more conventional positioned uniflow vent. To convert this little sucker to uniflow required a small length of copper tube chamfered on the end. The hole is pushed through the side of the tank with a scriber point to give a better solder joint. The chamfer stops blocking of the vent if too close to the outside edge of the tank.. Block off the vents with whatever method you like. Maybe a lot quicker, neater and definitely works for a better run.

HH




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I did my uniflow conversion tonight. Just punched a hole in the tank with a roofing nail and slid in my tube. Tried to solder it with with a 100 watt iron but that wasn't enough. Hit it with the torch and it was done in a second. I pressure tested it by forcing air into it with my fueling bulb and holding it underwater with all the holes plugged. No bubbles so I think I'm good to go. I might get to try it out on Saturday if the weather cooperates.

[photo not recovered: uniflow.jpg]

Jim

>I did my uniflow conversion tonight. Just punched a hole in
>the tank with a roofing nail and slid in my tube. Tried to
>solder it with with a 100 watt iron but that wasn't enough.
>Hit it with the torch and it was done in a second. I pressure
>tested it by forcing air into it with my fueling bulb and
>holding it underwater with all the holes plugged. No bubbles
>so I think I'm good to go. I might get to try it out on
>Saturday if the weather cooperates.
>
>[photo not recovered: uniflow.jpg]
>
>Jim




I'm surprised that the 100w didn't have enough heat Jim. I do all of my soldering of tanks etc with an 80w iron. Is the tip you are using tapered too much to a point and the heat is being sucked away too quick?

Report back and let us know if the run changed for the better.

HH

Uniflow works properly if the "exposed to air end" of the vent is inboard of the inside wall of the tank. Your's looks to be about halfway across the tank. With that position fuel weight MAY force fuel out the vent when flying until the fuel level is outboard of the end of the vent. Also, yours is above the top of the tank. That's good in that it prevents fuel siphoning out when sitting on the ground.

don Burke
Menifee, CA
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways - body thoroughly used up, totally worn out and screaming, WOO HOO, What a Ride!

>Uniflow works properly if the "exposed to air end"
>of the vent is inboard of the inside wall of the tank. Your's
>looks to be about halfway across the tank. With that position
>fuel weight MAY force fuel out the vent when flying until the
>fuel level is outboard of the end of the vent. Also, yours is
>above the top of the tank. That's good in that it prevents
>fuel siphoning out when sitting on the ground.
>
>don Burke
>Menifee, CA

Hmmm...thanks for the comment! Indeed I was concerned about fuel siphoning out while on the ground, which is why I put it up high. I hadn't considered fuel being forced out because of centrifugal force. Simple for me to hit it with the torch and rotate it inward a bit. Won't be completely to the inboard side, but I can get it closer.

Jim

>I did my uniflow conversion tonight. Just punched a hole in
>the tank with a roofing nail and slid in my tube. Tried to
>solder it with with a 100 watt iron but that wasn't enough.
>Hit it with the torch and it was done in a second.

I am very surprised at that. One of the best tank builders I knew (Ed Robbert) did his tanks with a 25 watt or so "pencil" iron. 100 W ought to be *plenty* of power, if it's working properly.

Torches are risky for something like this. A second or so it all you dare, because if you have it just a teeny bit too high or a teeny bit too long and you boil off all the tin plating and then you are forced to use a very strong flux to get it to stick to the bare steel.

Brett

>>Hmmm...thanks for the comment! Indeed I was concerned about fuel siphoning out while on the ground, which is why I put it up high. I hadn't considered fuel being forced out because of centrifugal force. Simple for me to hit it with the torch and rotate it inward a bit. Won't be completely to the inboard side, but I can get it closer.<<

You can just drill a 1/8" hole through the fuz side at top level of tank and cyno a piece of copper tube in. On the inboard side bend it forward and connect the outboard side to the uniflow tube you have. You could cut quite a bit off the one you have on the tank if you want to save weight.

HH

>
>You can just drill a 1/8" hole through the fuz side at
>top level of tank and cyno a piece of copper tube in. On the
>inboard side bend it forward and connect the outboard side to
>the uniflow tube you have. You could cut quite a bit off the
>one you have on the tank if you want to save weight.
>
>HH

So a short piece through the fuse, and cut the one down on the tank, and then I can just connect them with some fuel line, right?

Jim

>>
>>You can just drill a 1/8" hole through the fuz side
>at
>>top level of tank and cyno a piece of copper tube in. On
>the
>>inboard side bend it forward and connect the outboard side
>to
>>the uniflow tube you have. You could cut quite a bit off
>the
>>one you have on the tank if you want to save weight.
>>
>>HH
>
>So a short piece through the fuse, and cut the one down on the
>tank, and then I can just connect them with some fuel line,
>right?
>
>Jim


Right on Jim.

H

I've got an old 100 watt soldering gun from Radio Shack with the trigger. Maybe it's not getting as hot as it should. I could get it to melt the solder right where I touched it to the tank, but I couldn't get the big tip in between the two tubes so I had a spot that wasn't taking any solder. I thought holding it there for a minute would heat the tube up enough to melt the solder all the way around, but it didn't happen, so I hit it with the torch, which took less than two seconds.

Thanks for the info though, I didn't realize there was a danger of damaging the tank.

Jim

The "guns" don't work well for tanks. The iron types work better. If you're good at it, the small torches also work well.

>The "guns" don't work well for tanks. The iron
>types work better.

That's all I use, and I can't see what the problem would be.

Brett

The old Weller guns always worked well for me; the tips tend to get eroded where they make contact, so it is always good to check the two screws if there is a question. In a pinch, you can use some heavy gauge copper wire for a tip.

As with all this stuff, you'll have better luck with resin core solder and clear paste flux, to get proper heat flow, and your tip must be tinned and clean. That's the nice thing about the clean flux, you can dip the hot tip in it and it will flow and clean. Use a damp sponge to wipe the hot tip. Be sure to hold the tank in a vise or clamp, unless your fingers are not made of flesh.

I've also used a torch on tanks with very little problem. Just go easy. The end of a metal tank pops off easily using a torch, it can be almost impossible with a low watt pencil iron, since the heat area is small. I know it easier to use a low watt iron for re-assembly, since larger areas need not be molten.

The real secret to tin/lead soldering is to keep it all clean, of course.

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"It's not over till it's over." -Yogi Berra

So I flew with the uniflow tank tonight. It definitely made a difference. I didn't notice it leaning out during the flight at all.
Thanks for all the pointers!

Jim

Another happy customer! That's what the group is generally about with helping each other to try and solve a problem. Enjoy flying it Jim.

HH