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Thread: CC fuel system cross feeding

  1. #1

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    CC fuel system cross feeding

    Having some issues with cross feeding with CC fuel system. When on the off position with one DC 24 gallon tank full it will balance out overnight or after several hours. In flight on both the right tank sight gauge starts to go up as the left goes down. Running on the right tank seems to keep the sight gauges more even. Yes I know sight gauges can not always be trusted just wanted to know if anyone running the CC fuel system is having the same issues. The system is installed correctly with the cross over vent to top of sight gauges and the pressure vented fuel caps. My concern is that while trying to manage fuel by running on L or R it will still possibly be cross feeding a little bit.
    Last edited by Supercub Works; 03-14-2019 at 11:53 AM.

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    skywagon8a's Avatar
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    Are you flying with a heavy left foot?
    N1PA

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    Well now I just got it in the air after a rebuild, the wings seem to be rigged ok but it does want a little left rudder running at high power settings breaking in the engine. May be possible the pressure on the caps are not exactly equal as a cub does not fly perfectly straight. I need to burn some more fuel and watch it close and make sure the rigging is true.
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    skywagon8a's Avatar
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    Usually when running at high power settings more right rudder is wanted. This is true on right hand turning engines as are built in the USA. Is your slip indicator level in the airplane?
    N1PA

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    Yes the TC is level with the airplane. My thoughts exactly, should have needed a little right rudder. I guess it's not allot different that some 180/182's that always seem to want to feed of one side more than the other. Aligning the vent correctly helps but never solves it. More time in the plane will help, have not stalled or done any slow flight yet.

  6. #6
    RaisedByWolves's Avatar
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    Cc headerless, one tank will burn more when in the both. Only time itís cross fed on me is if I was parked on a not level surface and one wing was much lower


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    Rans s7 are notorious for the same issue, not a big deal if you don't fully fuel and then park angled. In flight, I can tell no difference via rudder pedal when one tank is fuller then other, a non issue to me and not worth chasing it around with valving.

  8. #8

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    Quote Originally Posted by RaisedByWolves View Post
    Cc headerless, one tank will burn more when in the both. Only time it’s cross fed on me is if I was parked on a not level surface and one wing was much lower


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    I really don't think there is fault in the "Both" thing but likely a combination of the variables related to the close-quarters hydraulics. Tom, you know my system. Belts and suspenders all the way with header tanks, Dakota 24's and a Dakota Cub valve and it draws more from one side than the other up until the low tank is down to around 1/3 vs 2/3 for the high then it more balances out down as low as I've ever taken it (1/4 x1/4). This happens no matter up high or weed-wacken. Typically, if I let it do it's thing for say 3+ hours it gets a bit wing low noticeable in calm air so if I want it balanced I fly on one tank awhile. No surprise, cub's aren't NASA accurate and I doubt that the intricate hydraulics involved were truly studied since line sizes appear to have stayed the same and there are no control orifices that I know of, My guess is these systems were likely tested to show equal or greater fuel flow to the engine than stock in all normal attitudes and fuel loadings with no adverse performance problems.
    Last edited by OLDCROWE; 03-15-2019 at 10:18 AM.
    Remember, These are the Good old Days!

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    RaisedByWolves's Avatar
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    With that being said, I havenít flown not on both sense the rebuild. It draws more from one side but not really that bad or noticeable besides looking at the gauges


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    I've always thought it's due to some combination of prop swirl, and maybe the Corialis Effect, ( kidding,maybe) as hydraulically, at least on my bird, I can't account for it. I know when I up pump the wing tanks with my floor mount transfer pump from a fuel jug, they fill exactly evenlly. I have flushed toilets in Ecuador and observed the C Effect in action. I need to fly down there and see if the tanks reverese how they drain first!

  11. #11
    PerryB's Avatar
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    Quote Originally Posted by courierguy View Post
    I've always thought it's due to some combination of prop swirl, and maybe the Corialis Effect, ( kidding,maybe) as hydraulically, at least on my bird, I can't account for it. I know when I up pump the wing tanks with my floor mount transfer pump from a fuel jug, they fill exactly evenlly. I have flushed toilets in Ecuador and observed the C Effect in action. I need to fly down there and see if the tanks reverese how they drain first!
    Off topic I realize, but many years ago my Mom and I stayed in a lodge located on the equator while on an African safari. I don't recall exactly where, but the subject of coriolis effect came up. When we got back to our room we conducted an experiment by filling the sink, letting it settle and then opening the drain. We did 5 runs. Got 2 lefts, 2 rights and 1 no-rotation. No kidding.
    After Monday and Tuesday, even the calendar says WTF !

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    I have heard that Ansys has a CFD test model that can simulate fuel flows in flight. Would be interesting to some of us but darn those software seats are spendy, not to mention the time involved to model it.
    Remember, These are the Good old Days!

  13. #13
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    Quote Originally Posted by RaisedByWolves View Post
    With that being said, I havenít flown not on both sense the rebuild. It draws more from one side but not really that bad or noticeable besides looking at the gauges


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    Ed Doyle flew cuzuum that way once. Remember the end of the story?


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    Likes Supercub Works liked this post

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    Steve Pierce's Avatar
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    Quote Originally Posted by SteveE View Post
    Ed Doyle flew cuzuum that way once. Remember the end of the story?


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    Made for a cool picture in Smithsonian Air and Space.
    Steve Pierce

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    Steve Pierce's Avatar
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    Quote Originally Posted by OLDCROWE View Post
    I really don't think there is fault in the "Both" thing but likely a combination of the variables related to the close-quarters hydraulics. Tom, you know my system. Belts and suspenders all the way with header tanks, Dakota 24's and a Dakota Cub valve and it draws more from one side than the other up until the low tank is down to around 1/3 vs 2/3 for the high then it more balances out down as low as I've ever taken it (1/4 x1/4). This happens no matter up high or weed-wacken. Typically, if I let it do it's thing for say 3+ hours it gets a bit wing low noticeable in calm air so if I want it balanced I fly on one tank awhile. No surprise, cub's aren't NASA accurate and I doubt that the intricate hydraulics involved were truly studied since line sizes appear to have stayed the same and there are no control orifices that I know of, My guess is these systems were likely tested to show equal or greater fuel flow to the engine than stock in all normal attitudes and fuel loadings with no adverse performance problems.
    I have the stock fuel system and the both valve and my experience is the same as yours. Having flown several super Cubs with the CC headerless fuel system I never noticed aN imbalance in the tanks. I do know that I am bad about forgetting to switch tanks with the left right system.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
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