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Thread: Switching fuel selector valves

  1. #41
    Steve Pierce's Avatar
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    I have seen a couple of gauge lines with loops in them acting like a P trap.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
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  2. #42
    hotrod180's Avatar
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    A case of swollen balls?
    Cessna Skywagon-- accept no substitute!

  3. #43
    #JoeM8848 #JoeM8848's Avatar
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    It appears that the 40 year old Wag tank is simply higher than the sight gauge....so just marked the gauge for now.Click image for larger version. 

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    'Hard to see from the picture, but the bottom hose drops a couple inches to below the level of the bottom of the tank.

    Sent from my iPhone using SuperCub.Org mobile app
    Last edited by #JoeM8848; 09-23-2020 at 11:24 PM. Reason: bad picture
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  4. #44
    krines's Avatar
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    I discovered when draining fuel from my cub that my fuel selector was not left right off as placard said, but left both right off. There is 1/2 inch fuel line from the selector to gascolator. At one time my cub had 180hp installed by STC SA36RM. The 337 states the fuel system was altered IAW. I have front and rear headers. Currently I have a 160hp installed with 3/8 fuel line from gascolator to carb. I do not have the STC paperwork in my logs just the 337. I am wondering what my legal basis for having this both selector is as I would like to keep it. Ideas?

  5. #45
    Taledrger's Avatar
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    Got the CubCrafters STC in mine. Headerless and a BOTH position... Was a bit labor intensive to install but works great!!
    Bob D

  6. #46
    skywagon8a's Avatar
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    Quote Originally Posted by krines View Post
    I discovered when draining fuel from my cub that my fuel selector was not left right off as placard said, but left both right off. There is 1/2 inch fuel line from the selector to gascolator. At one time my cub had 180hp installed by STC SA36RM. The 337 states the fuel system was altered IAW. I have front and rear headers. Currently I have a 160hp installed with 3/8 fuel line from gascolator to carb. I do not have the STC paperwork in my logs just the 337. I am wondering what my legal basis for having this both selector is as I would like to keep it. Ideas?
    If that fuel selector was installed at the time and in accordance with STC SA36RM it is still approved, unless you specifically removed it on paper.
    N1PA
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  7. #47

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    In my humble opinion the right left off fuel selector is advantageous.

    1. It is easier when doing fuel burn calculations if the burn is done from one tank. While it can be done from two tanks it complicates the issue and is more prone to errors especially when cross feed causes some error.

    2. When running to nearly the end of fuel range it is advantageous to keep fuel reserves in one tank. This means running one tank dry then switching to the other tank. Piper stated that takeoff and landing should be done on the left tank. I am aware of several fuel starvation incidents resulting from takeoffs on the right tank. It is my understanding that in a climb with the aft header tank servicing the right tank low on fuel the fuel pressure may become inadequate. Keep in mind that a low wing can require use of a different than recommended tank. In a low dihedral wing such as a cub it is easy to pass the dihedral angle which keeps water in a tank flowing toward the inboard side. Example: if one walks out on a float to check fuel, it pushes that wing down causing water in the tank to move toward the outboard end of the tank. Same happens on a slanted beach. While an 18 has a sump stamped in the bottom of the tank that holds some water, additional water or water introduced while fueling in that configuration flows to the outboard side of the tank and can’t be drained. When flying it doesn’t stay in that end of the tank. The 12 has no sumps, a flat bottom and a boss for the quick drain is put in this flat bottom. After a water in the fuel engine failure on takeoff, prior to which I sumped my 12 not once but twice, I had significant time to experiment and learn and come up with a fix. During my rebuild I found that the numerous 12 tanks I examined ALL had the area surrounding the quick drain oil canned upward from years of people pushing up on the quick drain and it returning from the force of the spring. Water would sit in a ring around the quick drain or move toward the lowest point of the tank. In low dihedral wing it doesn’t take much rotation to pass the dihedral angle and allow water flow to the outboard side. On a 12 with cub gear that means if one axel is raise .62”, 5/8” higher than the other, any water in the fuel from the low wing can’t be drained when sumped. My fix was to change the 12 tanks and eventually install 18 wings and tanks and in all my cubs I have installed quick drains in not only the inboard sump but the outboard sump as well. I can sump from both quick drains even if one wing is low. The 18 has a tank bottom with a sump on the inboard and outboard side. This issue was pointed out to the NTSB, Piper while they were still making super cubs and to the FAA. John McCalis agreed to give a field approval for any fix I came up with.

    3. With a right left valve in the event of engine issues due to fuel contamination, at least there is a chance that you can switch tanks and perhaps if there is enough altitude and time, get good fuel to the carburetor. At least if your on one tank, not both, you know which the offending tank is and have a chance to go to the other tank.

    While the headerless fuel systems have the advantage of flying on a both position and the STC specifies that, it is easy and for someone who is inclined not to pay too much attention to fuel that may be fine, but I feel active management of fuel is a good thing. I’m not sure that the accident with the headerless fuel system that MTV talked about is the same one I’m familiar with, if so he was an experienced pilot, a coworker and a friend who was manuvearring at low altitude on the left tank af a headerless system as one would on the other standard cubs in that fleet.

    I might add that while I’m not fond of the headerless system I have it in both of my cubs. I am still not as comfortable with it as I am with the left right valve.

    Stu
    Last edited by reliableflyer; 09-30-2020 at 09:49 AM.
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