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  • October 14, 2019, 01:29:46 PM

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Author Topic: fuel tank configuration  (Read 681 times)

Offline Jim Kraft

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fuel tank configuration
« on: November 04, 2018, 01:41:57 PM »
Is it better to have a long skinny tank, or a short fat tank, or does it matter. Not sure it makes any difference, but some of you guys may know better than I. I have 4 and a half to 5 ounce tank in my ignition planes, and am going to change to camp stove fuel. Not sure That an ounce and a half will be enough for the pickup before take off with the tanks I have in them. After running many hours with camp stove fuel and Walmart 2 stroke oil, the engines stay perfectly clean, run great, stay cool, and I never have to clean plugs. The engines show no signs of wear.

I know guys run the plastic tanks which are usually shorter and larger than our usual 2" by what ever tanks. So does it make a difference?
Jim Kraft

Offline Brett Buck

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Re: fuel tank configuration
« Reply #1 on: November 04, 2018, 01:55:03 PM »
Is it better to have a long skinny tank, or a short fat tank, or does it matter. Not sure it makes any difference, but some of you guys may know better than I. I have 4 and a half to 5 ounce tank in my ignition planes, and am going to change to camp stove fuel. Not sure That an ounce and a half will be enough for the pickup before take off with the tanks I have in them. After running many hours with camp stove fuel and Walmart 2 stroke oil, the engines stay perfectly clean, run great, stay cool, and I never have to clean plugs. The engines show no signs of wear.

I know guys run the plastic tanks which are usually shorter and larger than our usual 2" by what ever tanks. So does it make a difference?

   It can make a huge difference, you want a long, skinny tank rather than a short fat one. One of the keys to the 20FP run is to make sure the tank is no more than 1 1/2" wide if it is mounted on the outboard side of a profile fuselage.  Too wide, and the engine has to draw fuel too far "uphill". Fortunately, it also only uses about 2 ounces per flight, so you can pretty easily fit a narrow tank. Of course, you can make it as wide as you want with the tank mounted inboard.

  For RC clunk tanks, mount them so the flat part of the tank is up against the fuselage, making it "narrow" from the top view.

      Brett

     

Offline Jim Kraft

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Re: fuel tank configuration
« Reply #2 on: November 04, 2018, 02:10:00 PM »
Thanks Brett. That is what I thought, but was not sure. I will make some long skinny tanks of about 2 ounces. I think that is about all a big sparker will use at the most for 7 minutes. I only need enough for the old time pattern. My Orwick uses the most, but I think 2 ounces will be plenty. The Spitfires, Super Cyclones and Atwoods do not take so much. These are all on full fuselage planes, so I can mount them to the inboard side of the fuselage so that they do not have to draw uphill.
Jim Kraft

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Re: fuel tank configuration
« Reply #3 on: November 04, 2018, 02:44:43 PM »
I would suggest you copy the proportions of your existing tank and just make it smaller. You don't want to get too extreme with any one dimension.

Motorman 8)
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Offline Jim Kraft

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Re: fuel tank configuration
« Reply #4 on: November 04, 2018, 02:56:41 PM »
I believe that will work fine as the tanks I have been running work great Motorman. Just need way less than fuel.
Jim Kraft

Offline Curare

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Re: fuel tank configuration
« Reply #5 on: November 04, 2018, 05:04:18 PM »
This does raise a bit of a question that's been floating around in the back of my mind: Why are stunt tanks (generally) long and skinny? What's the reasoning for having a 1" or so thickness?
Greg Kowalski
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Re: fuel tank configuration
« Reply #6 on: November 04, 2018, 05:22:48 PM »
You could make it 7/8" deep, 1-1/2" wide and 3-1/4" long and that will give you about 2 oz.

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Offline Jim Kraft

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Re: fuel tank configuration
« Reply #7 on: November 04, 2018, 06:12:21 PM »
I was just going through my tank stash, and found a couple of three inch tanks is had built. They are a little less than 2" wide and 1" deep. Should be about three ounces, but I can short tank those and try them. Sparkers usually hold very study all through the flight since they have controlled timing. I should be able to get away with an ounce and a half plus without losing the prime before takeoff.

Most of my old time planes with spark engnes set pretty nose high on the ground to clear the large props I run. 13" on most.
Jim Kraft

Offline Dan McEntee

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Re: fuel tank configuration
« Reply #8 on: November 04, 2018, 08:12:04 PM »
This does raise a bit of a question that's been floating around in the back of my mind: Why are stunt tanks (generally) long and skinny? What's the reasoning for having a 1" or so thickness?

    If you have a fuel pick up too far outboard of the engine center line, the fuel draw has to go "up hill" or against centrifugal force to get to the needle valve assembly. That is why I don't like really wide wedge tanks or chicken hopper tanks. I have had several profiles in my time that were using typical wide wedge tanks, and had to set the needle ridiculously rich on the ground to keep it from going too lean in the air. I like to have narrow as possible tanks, and if using plastic on a profile, I mount them as Brett describes. On a full fuselage, they can be mounted wide side down because the engine center is usually in line with the tank center and the affect is minimal.
  Type at you later,
   Dan McEntee
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Offline Brett Buck

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Re: fuel tank configuration
« Reply #9 on: November 04, 2018, 08:27:32 PM »
This does raise a bit of a question that's been floating around in the back of my mind: Why are stunt tanks (generally) long and skinny? What's the reasoning for having a 1" or so thickness?

   Because that was the size of the Veco T21 series tanks. About the right height for a Fox 35 when placed flat on the bearers (although it won't fit in a Green Box Nobler...). If you are going to make a generic tank in 1956, that's a pretty good place to start.

    I haven't used 1" thick or 2" wide tanks since the early 90s, you just can't get enough fuel in a short enough space. My 7.6 ounce tanks are 1 3/8 deep and 2 3/16 wide, 6" long, and tapered in two dimensions.

    Brett

Offline Jim Kraft

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Re: fuel tank configuration
« Reply #10 on: November 04, 2018, 09:00:35 PM »
The fuselage front ends are usually wide because of the width of the spark engines crank case width on most old time planes that ran ignition. They also have short front ends because you do not need much tank space for gasoline, and of course the engines are heavier and can get nose heavy. I set them in a good 4 stroke on the ground and in level fight they will break a little in to two. Most will hold that setting from beginning to end breaking in maneuvers to keep constant speed.
Jim Kraft

Offline Curare

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Re: fuel tank configuration
« Reply #11 on: November 04, 2018, 09:07:03 PM »
   Because that was the size of the Veco T21 series tanks. About the right height for a Fox 35 when placed flat on the bearers (although it won't fit in a Green Box Nobler...). If you are going to make a generic tank in 1956, that's a pretty good place to start.

    I haven't used 1" thick or 2" wide tanks since the early 90s, you just can't get enough fuel in a short enough space. My 7.6 ounce tanks are 1 3/8 deep and 2 3/16 wide, 6" long, and tapered in two dimensions.

    Brett

I suspected that it was a bit of a legacy to a particular engine and mounting arrangement, but was't sure whether there was some secret reasoning, such as minimizing fuel head from full to empty, but uniflow should negate that anyway.
Greg Kowalski
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