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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?
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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.

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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.
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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!

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    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.
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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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    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.
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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

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    Hey Guys,

    My tanks are always on both, unless I am parked on a hill and then they are off. It would be great to read a list of pro's and con's to running Left and Right or Both.

    thanks,

    Jonny Olson

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    skywagon8a's Avatar
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    Quote Originally Posted by Jonnyo View Post
    Hey Guys,

    My tanks are always on both, unless I am parked on a hill and then they are off. It would be great to read a list of pro's and con's to running Left and Right or Both.

    thanks,

    Jonny Olson
    Are you referring to a Left, Right, Both, Off valve in a Cub? If so both the Both and Off positions allow cross feeding. Off just means fuel doesn't flow to the engine. For hill parking it would be better to leave it on Left or Right where it can not cross feed.
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    Quote Originally Posted by Jonnyo View Post
    Hey Guys,

    My tanks are always on both, unless I am parked on a hill and then they are off. It would be great to read a list of pro's and con's to running Left and Right or Both.

    thanks,

    Jonny Olson
    As stated above, the off position doesn't isolate the tanks from each other. Selecting one or the other does. As far as in flight, I almost always run on both. If I need maximum range I'll stair-step them down in 30 min increments until I'm roughly 1/2 tank on both sides (standard 18 gal tanks) and then I'll run the next one until it sputters. That way I end my flight with a visible/measurable amount on one side, instead of both balls sitting at the bottom of the tube.
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  20. #20
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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.
    Guys donít forget as you skid, crab or slip thru the air, one can feed the other and one will be noticeably lower because of it. See it a lot. MK


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    More to it then that, and besides we all fly perfectly coordinated at all times! I think the most likely culprit is the P factor, the prop swirling air over the wing, whatever it's called, which somehow makes one tank drain quicker then it's mate. Does anyone with this "problem" (it's only a problem if you want to make it one, I sure can't tell the difference in how it flies when one wing tank is fuller then the other) ever notice the phenomenon is utterly consistent? My bird anyway, ALWAYS drains the right tank first, always, if it was a sloppy flying, crabbing, slipping issue, the results would vary, they don't. Your results will differ, the Rotax spins assbackwards I believe.
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    Just to add fuel to the fire, i have the CC headerless system, and it feeds more from the right tank than the left until the fuel is down to about 3/4 tanks, then it feeds evenly. I suspect it's feeding from the right tank through the vent line. It's not a big problem - just switch to left for a little while.
    Idaho drinks more wine per person than any other state in the country.

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    Quote Originally Posted by courierguy View Post
    More to it then that, and besides we all fly perfectly coordinated at all times! I think the most likely culprit is the P factor, the prop swirling air over the wing, whatever it's called, which somehow makes one tank drain quicker then it's mate. Does anyone with this "problem" (it's only a problem if you want to make it one, I sure can't tell the difference in how it flies when one wing tank is fuller then the other) ever notice the phenomenon is utterly consistent? My bird anyway, ALWAYS drains the right tank first, always, if it was a sloppy flying, crabbing, slipping issue, the results would vary, they don't. Your results will differ, the Rotax spins assbackwards I believe.
    You fly an S7, if anything on a Super Cub which I thought this thread was about it tends to drain out of the left wing first, more direct line to the fuel valve and the gascolator. I have left, right both and a Lycoming with standard fuel caps, no snorkles so don't see P factor having an influence.
    Steve Pierce

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    In every Cub I'm familiar with, the tanks are tied together by an overhead vent line so head pressure is always going to be equal. On long, smooth, coordinated flights my left tank always burns a little faster than the right and I've always thought it was due to it being the path of least resistance (shortest run).
    After Monday and Tuesday, even the calendar says WTF !
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  25. #25
    Steve Pierce's Avatar
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    Quote Originally Posted by sjohnson View Post
    Just to add fuel to the fire, i have the CC headerless system, and it feeds more from the right tank than the left until the fuel is down to about 3/4 tanks, then it feeds evenly. I suspect it's feeding from the right tank through the vent line. It's not a big problem - just switch to left for a little while.
    I have not experienced the right tank tendency before on a Cub or Pacer but like your experience they even out pretty soon. Was flying a Top Cub today and noticed more fuel in the right and then as I got into the flight they burned down even.
    Steve Pierce

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    PerryB's Avatar
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    Dang it Steve, you type faster than I do.
    After Monday and Tuesday, even the calendar says WTF !

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