Is one gallon worth it?

Discussion in 'Firewall Forward / Props / Fuel system' started by cdlwingnut, Jan 15, 2019.

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  1. Jan 15, 2019 #1

    cdlwingnut

    cdlwingnut

    cdlwingnut

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    I have a 6 gallon boat tank in the fuselage of the ultra-piet that I'm building. I am putting a rotax 503 on the front of it so I'm guessing a fuel burn between 3 and 4 gallons an hour. that means 6 gallons will give me around 1 1/2 to 1 3/4 hours. I don't have much room for more fuel but could fit the one gallon tank bellow up front to give me an extra 15 mins. My question is do you think the extra gallon is worth the effort and added complexity to the fuel system? I figure the plane will cruise at about 60-65mph so I'm not going far with 15 mins but if winds pick up it may be nice.

    here's the tank I'm thinking about
    https://www.usplastic.com/catalog/item.aspx?itemid=104079&catid=578
     
  2. Jan 15, 2019 #2

    blane.c

    blane.c

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    It'll fly with extra weight but it won't fly out of gas.
     
  3. Jan 15, 2019 #3

    Aerowerx

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    How will the CG change as you burn fuel?
     
  4. Jan 15, 2019 #4

    don january

    don january

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    A 6 gallon boat fuel tank as far as I know has no reserve capability that I'm aware of so a gallon tank plumbed in for a backup might be a safe idea. Also if a Ultra piet staying with Par 103 reg. can only carry 5 gallons but yours appears to be over 245lb. empty so 5 gallons in the center section of wing and a 5 gallon header tank will give you fair range. I don't know if UL specs can even be met with a 503 mounted up front?
     
  5. Jan 15, 2019 #5

    cdlwingnut

    cdlwingnut

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    I have no intention of making 103 weights, specially with douglas fir for wood. so if i can get weight and balance then extra fuel is ok. the plans call for a 6 gallon tank behind the cockpit. without weighing it yet but by estimating weights I figure i should be ok with full 6 gallons maybe a tad nose heavy with the tank empty but the matco tailwheel should even that out, if i put a gallon in the nose i may have to burn that first then to to the aft tank
     
  6. Jan 15, 2019 #6

    Toobuilder

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    --The weight fraction of a one gallon tank is going to kill you as a function of packaging efficiency (much lighter to add a touch of raw material to enlarge the main tank by a gallon).

    --The added valving complexity may actually make the airplane LESS safe overall

    --The unusable fuel in two tanks is going to be greater than if using one tank of the same total capacity.

    At first blush it seems hard to justify a second tank with only one gallon capacity.
     
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  7. Jan 15, 2019 #7

    Rockiedog2

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    If I couldn't figure out a way to get 6 gallons in one tank I would reevaluate the need for 6 gallons.
     
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  8. Jan 15, 2019 #8

    blane.c

    blane.c

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    HMMM. Bigger fuel tank = more better. Grunt!
     
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  9. Jan 15, 2019 #9

    Topaz

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    +1. One more gallon, on an airplane like the Ultra Piet, seems like needless complexity on an airplane that's intended to be simple. Personally, I wouldn't bother.
     
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  10. Jan 15, 2019 #10

    Rockiedog2

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    I dunno why but that cracked me up.
    Something about "grunt".
     
  11. Jan 15, 2019 #11

    blane.c

    blane.c

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    I've been known to clear a room with the other end.
     
  12. Jan 15, 2019 #12

    Rockiedog2

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    Too much info!

    LOL
     
  13. Jan 15, 2019 #13

    radfordc

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    If you look at the extra gallon as a "reserve", that gives you a nice safety margin. I would plumb the tank with a valve so that it dumps into the main tank only when you need it. On a cross country leg with a head wind and you're thinking "maybe...maybe not" you use it.
     
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  14. Jan 15, 2019 #14

    radfordc

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    There were times when I would have sold a kidney for an extra 15 min's of gas!
     
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  15. Jan 16, 2019 #15

    Armilite

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    ======================================================

    Install a Ecotrons or Mega Squirt EFI Setup and get on Average a 1.0 gph Savings. Also a Better Starting, Smoother Running Engine, with No Carb Icing.
     

    Attached Files:

  16. Jan 16, 2019 #16

    Dana

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    Adding one gallon and teeing into the existing plumbing with the added complication and room for error I'd say isn't worth it. If you can plumb it so it drains into the main tank when the main is partly empty than it makes sense.

    My Ultrastar originally had two 1.75 gallon tanks teed together for a total of 3.5 gallons. I added an additional 1.5 gallon tank draining into the existing tanks for a total of 5 gallons. Later, I replaced all three tanks with a single custom made 7 gallon aluminum tank which greatly simplified things and added to my peace of mind on longer flights.
     
  17. Jan 17, 2019 #17

    mcrae0104

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    Please cite a source.
     
  18. Jan 17, 2019 #18

    Armilite

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  19. Jan 18, 2019 #19

    pictsidhe

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    Hmmm, rebuild a worn engine and get 12% more power. Increase jet size and see CHT go down... That article doesn't mention EFI, so it's pretty poor evidence as to the possible BSFC reduction.
     
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  20. Jan 18, 2019 #20

    radfordc

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    Actually, the article does mention EFI in the last couple of paragraphs. I don't remember all the details but he converted his Rotax engine from normal carbs to dual port EFI using a Hirth EFI system. He had a lot of issues getting it to work correctly but eventually got them all sorted out and working.
     

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