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04-06-2020, 10:46 AM | #21 |
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Re: Vent Line Overflow Header Tank Setup
I believe the vent pick-up line in the secondary tank really should be in the centre of the tank. If the vent in the secondary tank only goes into the tank the amount shown in Primo's drawing then as soon as fuel began to accumulate in the secondary tank, wouldn't it then immediately start to vent out the bottom of the plane on a down-line?
Isn't the point of the vent pick-up line being in the centre of the tank so that the secondary tank can fill up to half way before becoming submerged in fuel and then venting outside the airplane? For the same reason I'd be concerned about the method in Jim's drawing. As soon as fuel started to fill the secondary tank (while inverted) the vent would be submerged and potentially be venting fuel outside the airframe, no? For some reason I thought the fuel pick up line in the secondary tank should be rigid. I can't remember why, at the moment but, I thought that was how Rick explained it to me. I'd check my plane but, it's no accessible at the moment. Where is Rick btw? Need him here to clear the air Cheers, Dave
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04-06-2020, 02:42 PM | #22 |
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Re: Vent Line Overflow Header Tank Setup
Dave - when I looked at it I thought the vent in the header tank should go back further ie middle probably. I don't have Primo's email or I would ask him. I might just try to scrounge it out or message him on the IMAC site.
I think as Dennis said there are likely several ways of doing this as hopefully the header tank only gets a shot of fuel overflow. I have not done this yet but I would like to find a way to see the header tank when I am filling the system, so I know when the main tank overflows. Or else I have to fill the header tank too and then back off and siphon a few ounces back out. However I have a feeling that I have 3 or more months to decide what setup I want to try. Going to be tough if my caller has to stand 6 feet away. With my hearing deficit they are going to have to yell out the maneuvers.
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04-06-2020, 05:43 PM | #24 |
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Re: Vent Line Overflow Header Tank Setup
Hmm interesting thread.. I can see the purpose of the header tank.. to prevent fuel from getting sucked out.. provided that whatever is causing the suction does not continue to long..
In my case I had this little sport plane I liked.. and as normal the vent line stuck out the bottom about and inch, which was just a piece of tigon tubing.. As it turned out.. every time I took the plane up.. about 5 minutes into the flight and almost exactly to the second, the engine would quit.. Turns out that the fuel tubing was bending back due to the high airflow and creating a venturi effect.. it increased the vacuum in the tank to the point where the pumped carb could not overcome the vacuum and basically ran out of fuel.. cut the fuel line off short on a 45 angle facing forward so that the airflow would be caught and directed into the tubing.. plane flew great after that..
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04-06-2020, 08:13 PM | #25 | |
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Re: Vent Line Overflow Header Tank Setup
Quote:
We both use those things "hearing aids", but I can yell at you. Your aids have bluetooth?
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04-06-2020, 08:41 PM | #26 |
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Re: Vent Line Overflow Header Tank Setup
There are several of us in this club it appears. Could not hear any of the alarms on my radios anymore so it was time.
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04-06-2020, 08:52 PM | #27 |
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Re: Vent Line Overflow Header Tank Setup
Yeah I got those things but I hate wearing them at the flying field because of the engine noise - don't need that amplified. I think they have BT.
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04-06-2020, 08:55 PM | #28 |
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Re: Vent Line Overflow Header Tank Setup
so true - I cannot hear the radio alarms or my wife's voice - just a question of priorities LOL
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04-06-2020, 09:07 PM | #29 |
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Re: Vent Line Overflow Header Tank Setup
Basically it's what Denis has covered so some of the following is redundant.
What I've done, 4 oz tank, need an additional longer piece of brass tube. Vent line from the main tank goes to the longer tube that normally would have been the clunk line... I use no clunk. In the upright orientation bend the tube so that it gets to the bottom back of the tank as close as possible. I file mine on a 45 to avoid it getting bumped and potentially sealing itself off on the back of the tank. Wouldn't be a good thing. The second line, the vent for this tank. Is bent and positioned such that the pickup point is exactly centered in the tank x-y-z. No matter the orientation of the plane that tip of tube will never be in the fuel until the tank is at least half full.(2oz) Any negative G that would normally cause fuel to go out the vent tube is held on board. Doesn't seem like any event causes more than 2 oz to go back. Once back to upright the tube at the bottom scavenges the fuel back to the main tank. Yes a clunk would make the scavenge happen in all orientations but I wasn't keen on having any moving parts. Not a potential failure point nor requires any maintenance this way. The added bonus to this system is when a plane is full of fuel in the hot sun the fuel expands and can go overboard as well. This catches that. We have observed less or no fuel spray over the bottom of the planes and flight times are up about 2 minutes per tank. I don't think the position of the header tank is too sensitive. Mine sits on top of my main tank. I would not be inclined to mount it below the main tank out of concern for siphoning. I've seen that happen with a full tank and a normal vent line. Siphon started and was draining the tank (sitting on the ground) For function think is terms of this being a 2 oz tank not a 4 oz. Agreed, the standard vent line loop is eliminated.
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04-10-2020, 11:07 AM | #30 |
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Re: Vent Line Overflow Header Tank Setup
Can't wait to try this out down here. (colorado). And the comments from the others "what the heck is that for???"
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