Fuel tank and venting

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BDA
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Fuel tank and venting

Post by BDA »

I have used a few tanks worth of fuel now, and have noticed that with both tanks full it only uses fuel out of the right tank untill it is empty then it will pull from the left tank and or equalize between tanks.
No problem but I was hoping for equal usage.

I do not have a vent from my header tank.

I do have “vented” caps that came with the tanks.

After I land I can hear the tanks burp, and gurgle. Sounds like there is a vacuum in the tank. When I remove a cap air is sucked in, there is a vacuum in there.

I am going to try different caps.

I dont think it is a header vent issue, I think the caps do not vent easy enough.
SuperStol XL Alaskan With Titan 340
N331AK. Shawn Taplin
Wing extensions,Symetrical Airfoil tail ribs (NACA 21)
Mods in progress: Heavier struts, Double slotted flaps
Goal: 15mph no wind
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alan
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Re: Fuel tank and venting

Post by alan »

I went to the factory for some guidance on installing the new aluminum fuel tanks from Jak. He was installing the first of those in a factory built Highlander and I was doing so as a replacement for my dissolving fiberglass tanks. For the cap vent issue, he said to make sure to increase the vent hole size with a drill bit as the stock holes were much too small. Also, I had installed a shutoff valve on each tank during the build and always fly using one tank at a time for the first hour from each tank and then open both.

Alan
If I had known I would live this long I would have taken better care of myself.
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BucF16
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Re: Fuel tank and venting

Post by BucF16 »

OK, SERIOUSLY? When did that MEMO come out? I love my Highlander. I have enjoyed the build process. BUT SUCKING tanks scares the shit out of me. SO. how much larger do I drill. And I can't drill out the bend.

Thanks for letting me rant.

Bruce
Bruce Johnson Highlander # 393
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danerazz
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Re: Fuel tank and venting

Post by danerazz »

If it is sucking air when you open a cap, it is NOT venting.

There was something about increasing the vent hole size in the caps, but I don’t remember where.

Just out of curiosity, you DID drill through BOTH the top and bottom pieces of the cap, right? If you don’t drill through the plate that pulls up against the big O-ring, it will not vent.

I installed AN nipples in my wings near the caps, and then installed the vent tubes onto those. I didn’t want to use vented caps mostly so I was not tempted to use the vent tube for leverage to remove the caps. Hindsight would have had me position them elsewhere, but I would have liked aluminum tanks, too. I would have changed the whole venting system.

Also, my caps were not drilled when I got my kit.

Here is the sentence from my manual describing the cap vent holes.
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Dane

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Tralika
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Re: Fuel tank and venting

Post by Tralika »

I drilled my caps as described in the build manual. No air would pass thru the vent. I drilled through the bottom part and it vented. I'm not sure why the build manual said to only drill through the top part but it obviously would not work. If a vacuum is created in the wing tanks the problem is in the fuel cap vent and should be easy to solve.

I originally built my fuel system with no vent from the header tank to the wing tanks. I flew it that way for 80 hours or so and it worked fine under most circumstances. I found that when on a long descent (nose low) with the wing tanks low on fuel, the fuel would slosh forward and uncover the fuel ports at the rear of the tanks. This was not an immediate problem because the header tank would supply fuel to the engine during the descent. However when I leveled off and fuel moved back in tank to the fuel ports, the fuel would not always start to flow to the header tank right away. For the fuel to flow into the header tank that was not full, the air in the tank had to be displaced. With no vent that means the air had to go back up one of the fuel lines while fuel flowed down the other fuel line. I have fuel filters on the fuel lines between the wing tanks and the header tank so I think that bit of restriction prevented the air from moving up the fuel line past the filter. I installed a 1/4" vent line from the header tank to the right wing tank and that problem is solved. If I had to do it over I would probably use 3/16" or even 1/8" for the vent line.
John Nealon
Wasilla, Alaska
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danerazz
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Re: Fuel tank and venting

Post by danerazz »

I think the build manual is right, just poorly worded. It has you drill a 3/16” hole all the way through the assembled cap (that would be top and bottom) then I think they want you to basically counterbore the top to allow the 1/4” tube to be inserted.

This is one of those “a picture is worth...” moments.

I added a 3/16” line as a header vent exactly the same way you described. I know there was a bulletin a few years ago for the same thing on Kitfox, for exactly why you added the vent.
Dane

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BDA
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Re: Fuel tank and venting

Post by BDA »

I was told at the factory that these caps were vented and needed no mods.
SuperStol XL Alaskan With Titan 340
N331AK. Shawn Taplin
Wing extensions,Symetrical Airfoil tail ribs (NACA 21)
Mods in progress: Heavier struts, Double slotted flaps
Goal: 15mph no wind
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danerazz
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Re: Fuel tank and venting

Post by danerazz »

Are there holes?

You say that they are clearly not venting, and regardless of what the factory said, you should be able to pull a cap, look at it for 5 seconds, and determine if it is or is not venting. Based on your description I would guess one cap is not venting. Could be both but I think you would have other problems. The cap might be set up right but the vent might be blocked.

Or you can speculate on the forum for days and then go tempt fate that you will have adequate fuel flow on your next flight.
Last edited by danerazz on Tue Aug 25, 2020 10:38 am, edited 1 time in total.
Dane

Paralysis by analysis
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kenryan
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Re: Fuel tank and venting

Post by kenryan »

Or just install caps with snorkel vents.
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Tralika
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Re: Fuel tank and venting

Post by Tralika »

BDA wrote:I was told at the factory that these caps were vented and needed no mods.
I don't know if we are talking about the same fuel caps. The attached photo is what mine look like. The vent tube was supplied with the kit but not installed. I drilled the cap and installed the tube with hysol per the build manual instructions. I know it's vented because I can blow air through the tube. My fuel tanks are different than yours so it's likely your fuel caps are different as well. Every vented fuel cap I've seen has a hole in it. If you can't find a hole in yours I'd call Just and ask how they are vented.
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John Nealon
Wasilla, Alaska
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mykitlog.com/jnealon
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Tralika
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Re: Fuel tank and venting

Post by Tralika »

danerazz wrote:I think the build manual is right, just poorly worded. It has you drill a 3/16” hole all the way through the assembled cap (that would be top and bottom) then I think they want you to basically counterbore the top to allow the 1/4” tube to be inserted.

This is one of those “a picture is worth...” moments.
"I see," said the blind man. You're right, that's what it says.
John Nealon
Wasilla, Alaska
Highlander Extreme #191
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Clark in AZ
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Re: Fuel tank and venting

Post by Clark in AZ »

Ok, you guys have me wondering now. Here is a pic of my SuperSTOL gas cap.
Fuel Cap - 1024x576.jpg
It does not have the vent tube and I can't find any reference in the manual saying I need one? Are all you guys building Highlanders? Is the vent in the cap specific to the Highlander? Anyone with a SuperSTOL care to comment?

Thanks,
Clark
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SheepdogRD
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Re: Fuel tank and venting

Post by SheepdogRD »

That appears to be the same as the caps delivered with my Highlander tanks. Mine were among the first tanks for the Highlander.
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Clark in AZ
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Re: Fuel tank and venting

Post by Clark in AZ »

My kit is a Nov. 2017 kit.

Clark
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danerazz
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Re: Fuel tank and venting

Post by danerazz »

So the aluminum tanks have a very different cap. Still should be easy to check the vent.
Dane

Paralysis by analysis
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