Fuel tank and venting

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CanadianSheepHunter
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Re: Fuel tank and venting

Post by CanadianSheepHunter »

Here’s both my fuel caps now with the holes drilled vertically, right beside where the original hole went horizontally, drilled with a 5/64” drill bit. I only drilled the very first layer, if you drill the next layer I’m certain you would come out the topside...after I drilled the hole I could feel the drill bit hit the top if I move it in and out without rotation.
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SheepdogRD
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Re: Fuel tank and venting

Post by SheepdogRD »

There was a recent discussion on the Facebook Just Aircraft thread. A couple people wished it was on the forum and searchable, so here's a lightly edited transcript:

Dennis Rowe
Has anyone else with the 13.5 gallon Highlander aluminum tanks and a header tank had an issue with them feeding uneven or cross feeding and over filling one wing in flight?

Over the last several hours I noticed my right tank empties in flight while the left one fills up. I’ve shut the right one off and confirmed the left one still draws fine, I’ve checked the tank caps and swapped them and the problem does not follow the caps. No kinks in hoses and cycled valves, since it’s cross feeding I don’t think it’s a restriction. Also made damn sure we were flying coordinated and wings level and the issue remains.

Pretty sure this problem was here all along but only noticing it now that we’re doing longer flights and boarding more fuel.

Also noticed last night that the left wing is venting fuel from the cap vents probably because it was pretty full in flight, this problem was also evident on our ill-fated trip to Lakeland last year as we had full tanks and it was evident that the left wing had vented fuel in flight.

I think it’s time for better caps with the forward facing periscope vent tubes. Anyone know of a source for those or the parts to make them?

Steven Deckard
Kitfox has those caps.

Dennis Rowe
Will Kitfox caps fit Just tanks?

Steven Deckard
Yes, a friend is building a KitFox and I tried them on my aluminum tanks. They are the exact same cap that has been modified with the tube coming out the center.

Dennis Rowe
Can you get me the part number?

Steven Deckard
I will contact my friend to see if he can get it.

Patrick Armstrong
#27012 from KF

Steven Deckard
Kitfox Fuel Caps Label.jpg
Kitfox Fuel Caps.jpg

Dennis Rowe
The buggers at Kitfox won’t sell me a set of these caps since it’s for a Highlander.
It really sucks as they only want $64 for a set of two.
I guess they don’t like money, and they also guaranteed I’ll never buy a kit from them.🤬

Dennis Rowe
Anyone know where I can buy a set of these caps without the pressed in vents on the bottom side?
I figure I can weld on the periscope tubes myself.

Steven Deckard
Kit Fox Welds vents shut on the underside of the cap. If you can weld the periscope you certainly can weld the vents shut. This is my plan.

Kenny Kitzmann
Even though you changed caps I’ve seen two sets of caps that the tiny vent holes were not all the same as they are stamped holes and I had to drill some of them out as the stamp never fully opened some of the holes. I told this to a friend and he checked his caps and found the same. We both haven’t flown ours yet so that’s all I know at the moment, but I ran a vent from header to each wing tank.

Michael Caffrey
I also had my left wing tank drain 3 times faster than my right tank.
I switched left cap to right tank and problem switched sides.
Looking in the cap the vent holes were not stamped all the way and I drilled them out .
Problem solved for me.
Plus now I have on off valve on each tank so I can keep them balanced on longer flights.
I was flying one day and had one tank almost empty before I made it back to the airport.
Not a good feeling. When I can't shut off that tank

Shawn Taplin
I had same problem
Drilled vent holes in cap out fixed it
One cap not venting

Mark Machado
This is a common problem. Had to carefully drill mine out. Poor manufacturing/quality control…..if any!

Debby Mairs Griewahn
You're just a little uncoordinated. Trust me it doesn’t take much. One thing that might make it better is your fuel line routing. Make sure one is not higher than another.

Dennis Rowe
My lines are routed as exactly the same as I can figure.
Swapping caps didn’t change sides for the problem, and I’m definitely keeping the ball centered.

Debby Mairs Griewahn
Call Kris to discuss

Thomas Moore
A bunch of left pattern turns?

Dennis Rowe
Problem shows up on long flights or in pattern work.

Don Blossom
Had exact issue, but left tank would empty first. During build put in flapper style check valves between main & header tanks to eliminate cross over-fill issue. THAT WORKED. Still had issue of ALL feed to header from LH wing only. Put a hose pinch plier clamp on LH wing tank feed. Then RH wing fed header fine. Next went to 2 each goose neck caps from A/C Spruce. Put in a 90 degree bend in the 1/4 tube faced into slip stream. So both tanks identical, but had varying head pressures depending on airspeed. LH wing still drained way down first with no feed from RH wing. Next config was a goose neck cap RH wing only & 'Just' vented cap on LH wing. This config drained only the RH wing. At this point the problem had swapped sides but things were getting in the ball park. So in that config, a reducer plug was installed in RH goose neck inlet with approx 50% reduction. THAT FIXED both feeds, from full to low with even feed both sides. Now I fly the max endurance. There's your sign.....
https://www.aircraftspruce.com/catalog/ ... ckkey=7373
Vented Cap - Aircraft Spruce 05-08077.jpg

Dennis Rowe
They are proud of them 😂
But they look good!

Don Blossom
https://madracingparts.com/products/ear ... -251006erl
Earls Check Valve 251006ERL.JPG

Craig Timm
You could always just switch tanks every 15-30 minutes OR put one way valves in the fuel lines.

Dennis Rowe
I’m forgetful so I’m fixing the source

Shawn Taplin
Dennis -- Take metal cap that comes w tank, turn upside down, the little wrinkles around the outside edge are the vent holes
Use very small drill to oversize and enlarge vent holes

Dennis Rowe
I’ll definitely give it a try,

Keith Showalter
I had the same problem but after a few years I stopped worrying about it. I prefer to have a little more fuel on the right side because I sit on the left, keep it even. It seems to move around depending on coordination and so on.

Hubert P Davis Jr
I have 13.5 gallon wing tanks in my SuperSTOL XL, and it uses slightly more fuel out of the left wing than the right. I am going to try switching the caps and see if it makes any difference. I put in a Steve Henry 5 gallon header tank. The only valves in the system are the shut off on the floor by the tailwheel lock toggle, and the shut off between the low point on the header tank, and the test drain.

Dennis Rowe
Hubert P Davis Jr keep us informed how it goes, I have a header tank like yours but have shutoff valves between it and the wings

Stephen Gromak
It’s from flying uncoordinated, if you don’t believe me, give Gary a call at Just, he’s the one that told me. 🤷🏻‍♂️

Don Blossom
So I guess changing the fuel cap configuration on my Highlander centered the ball, let's go with that....

Dennis Rowe
They definitely vent fuel when flying with close to full tanks.

Stephen Gromak
Don Blossom what was wrong with the cap?

Don Blossom
Maybe nothing, but there is no set method of modulating or matching the fuel consumption if it is uneven, without valves for each tank. So getting equal feed seemed important. If the issue where unbalanced flight, say ball to the left, then flying with ball to the right should reverse the problem & the opposite tank should deplete faster. After numerous test flights (I had 40 hours to kill) with the ball out left and then right, I could see NO consumption from the right side. So what I discovered is this - increasing the air pressure above the fuel in a wing tank slightly will create a slight increase in the fuel that exits that tank. Since this is an EXPERIMENTAL aircraft, I did just that. I'm not piloting any better now, ball out wise, yet this aircraft now consumes equally from either side.

Stephen Gromak
I’ve flown mine with full tanks, on the SS, and haven’t had any venting out on the wings in over 550 hrs. I’ve filled them to the top for long flights and the wing wasn’t perfectly level and had fuel leak out on the lower wing. 😡

Don Blossom
If there was no fuel 'venting out on the wings', where did the 'fuel leak out on the lower wing' originate?

Stephen Gromak
One was a comment about flying, no fuel weeped out during flight, the other was on the ground sitting after a few minutes on the ground and not level. Yes, they do have to vent, obviously but I’ve never had one blow fuel out during cruise.

Shawn Taplin
The vented caps on these tanks are in the low pressure boundary layer on top of wing
So…
The better the vent, the lower the pressure in the tank? Vacuum?
Unless you have a forward facing tube on cap for more pressure??
Just thinking out loud.
I know I “vent” fuel like crazy anywhere near full, more than fuel transferring

Don Blossom
You are spot on concerning the low pressure area down low at the cap lip near wing upper surface. I have an idea that prop thrust/wash is altering that pressure on the left side, increasing the pressure in relation to the same area on the right wing. Maybe residual P-factor? Always more dirt & bugs on the left wing in this area, so? Also, with the goose neck tube, the vent is 2 inches higher, which should help with over-serviced spillage. Still need to allow an air pocket for expansion though.

Shawn Taplin
I agree with prop wash effect.
Do you have VGs on the wing?

Don Blossom
Yes

Don Blossom
https://www.flightliteracy.com/.../uplo ... 1/5-48.jpg
Prop Wash Effect.JPG

http://avstop.com/.../flighttraingha... ... ffect.html
Corkscrewing Slipstream.jpg

Shawn Taplin
Don this is why I have fences on my flaps

L.A. Gibson
I have forward facing vented caps, and my right tank uses fuel faster than my left tank. It will also bleed fuel out of the left vent if they are both full and sitting level. I have about 10x as many hours in planes that require swapping tanks in flight as I do in planes that don’t, so running a 30 minute alarm on my watch is an old habit that makes keeping up with fuel levels very easy.

Dennis Rowe
I talked with Kris G this morning and he assured me that Kim is correct and my wing tank plumbing is probably causing the issues.
I’m going to take a hard look at them on my next outing.

L.A. Gibson
Anyone who can sit in a Highlander seat for a full fuel burn, is way tougher than me. 🤣

Dennis Rowe
These things have really long range with the big header tank and wing tanks.👍🏻
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Richard Holtz
Highlander N570L -- Ms. Tonka -- in gestation

If just enough is really good, then too much ought to be perfect.
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