Leaking port fuel tank on landing and left rudder slip
- Thread starter Philly5G
- Start date
wireweinie
FOUNDER
Palmer, AK
Hard to say without seeing it in person.
Web
Web
My advice will make the snowball bigger. I would do the following. First, drain all fuel from both tanks. Second, take the cover off the right tank and inspect it also. Third, trace all fuel lines from the tanks to the valve (including path of vent lines) Once you do this you should understand exactly how the system works. Correct the low spot in the tubing in front of the valve, this is a water trap that should not be there. From what we can see I think that is a front header tank that is plumbed from the front of the valve and front vent on left tank. What I do not see in any pictures is a fuel line running down from the front of the tank. Where does the line from the front of the tank go? Across the front to the right tank or down the left side of the windshield or somewhere else? I think the header tank in this case is poorly designed, (it should have flow from both the bottom front and back of the tank, not from the vent. If you keep this system I would add a outlet to the left bottom front tank and run it to the header tank. Once again I am just taking my best guess because I am not at the plane. I would expect you will have to cut some fabric near the wing root and header tank to do this right.
DENNY
DENNY
TurboBeaver
Registered User
Northern Maine
Philly,
Denny is giving you excellent advise here. For what ever its worth once you add the front pick up points, in the Cub Crafters STC that gets rid of that potentially dangerous header
Tank, you wont need it anymore.
Good Luck.
E
Denny is giving you excellent advise here. For what ever its worth once you add the front pick up points, in the Cub Crafters STC that gets rid of that potentially dangerous header
Tank, you wont need it anymore.
Good Luck.
E
You're right Denny and thank you, the snowball is getting bigger and just finding the tank was leaking was an unwelcome start to all this :roll:
Tomorrow I'll be taking off the wing/fuselage fairings to see more of where the pipes are going and I will be looking at the starboard tank too, more work, but I think necessary too.
From what I've seen and traced so far, I THINK the rear port tank fuel pickup is plumbed into the fuel valve and I THINK the front port (vent?) connection is linking to one of the Y ends of the Y connector that links into the Starboard tank feed and the other Y connection from the Starboard tank is plumbed into the fuel valve.
It looks like we're all agreed the torpedo under the panel is a header tank BUT the BIG problem is that the header connections and most of the pipework is hidden under the Cowl Assembly (Univair Part#U10691-000 as Aircraft Serial No 12-2907) directly behind the firewall etc and from what I can see and research, to get that panel off is engine and engine mount out, windscreen off etc, which is obviously WAY beyond what I'm envisaging for this fuel tank leak work........
$64,000 Question: am I correct in saying there's no easy way to get the Cowl Assembly off and therefore get access to the header/plumbing, OR do we need to cut an access panel into the Cowl Assembly to get to the header (have other people done this?) OR, do we trace what we can, get the tank fixed and carry on flying until major tear down time and then get the Cowl Assembly off and see the plumbing in detail - and to be clear, other than the fuel tank leak, there have been NO other fuel feed problems...........
Last edited:
skywagon8a
MEMBER
SE Mass MA6
Philly, Don't get too deep in the weeds. So far we know only that the left fuel tank is leaking. Fix it and go from there. You have seen no evidence that the header tank has an issue. Let it be.
Thanks for this skywagon8a!!! I'm going to take the advice from all and as sketched in my plan above, stop short of making holes in the Cowl Assembly for now...
Left tank drained and no cross feeding happening
Wing fairings removed, fairings and inner surfaces cleaned and front connection looking even more like a vent.
All 4 fuel tank gauge screws badly rusted in and dremelling out tomorrow required, this is the pattern for this work-big struggle to get the panel off initially, cleaned and refitted with new screws and MUCH easier next time
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Wing fairings removed, fairings and inner surfaces cleaned and front connection looking even more like a vent.
All 4 fuel tank gauge screws badly rusted in and dremelling out tomorrow required, this is the pattern for this work-big struggle to get the panel off initially, cleaned and refitted with new screws and MUCH easier next time
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Hi Web, I've just found this document http://www.knightglider.com/assets/supercubpilotmanual.pdf and the fuel diagram on Page 9 looks PRETTY MUCH like what I've found so far.......... I got the left fuel tank out today, but next time I'l be taking a look at the right tank and trying to find the rear header
On the fuel tank, this is some corrosion and repairs on it, but no real obvious leak signs, I noticed the cork fuel cap "seal" was really hard when I first looked at it, as there's no obvious source of leaks on taking the tank out (although I am still sending it to the tank hospital for an inspection/refurb) I'm wondering whether the pretty serious leak I saw could possibly have come from the filler cap seal........ any thoughts anybody?
Things I’ve learned today:
it’s an aluminium tank and therefore not original
The forward pipe connection is very high, so more likely a vent.
Research I’ve done leading to more questions!! :
Is this a header tank?
Am I right in thinking the right tank feed is connected to the fuel tap and also the left tank vent pipe?!!
View attachment 38531View attachment 38532View attachment 38533View attachment 38534View attachment 38535View attachment 38536
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Hmmmmmmm, the other Pa-12 owner on the field today has been away on holiday, when he saw my tank today, he says it's an original and therefore tin..........
mike mcs repair
Registered User
chugiak AK
the caps DON'T seal really, they are vented(or your tank will collapse as you use fuel)
Thanks Mike(?) so even if the sealing rubber washer in the cap is cracked, there wouldn't be a big leak if the fuel level was over the cap in a sideslip for example?
Cheers
P
The tank is now at the tank hospital, a place where tin and soldering are both understood
A tank being freed from its mounting and years of accumulated grime!!
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Attachments
cubpilot2
SPONSOR
Anchorage Alaska
I’ve found the other header tank Web
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Something about that looks quite scary to me.
Electrical connections, solenoids, loose looking attachments right close to a thin walled tank.....
TurboBeaver
Registered User
Northern Maine
Gosh thay positive lead cable looks like it might be from a 1961 Rambler car??? Is that automotive? Now if the fire dont get ya the fumes will??:x
cubdriver2
FRIEND
upstate NY
TurboBeaver
Registered User
Northern Maine
Lol. Guess your right there Glenn. Bet your more firmilar with a 49 DeSoto????
skywagon8a
MEMBER
SE Mass MA6
DENNY, That front outlet is the vent to the header tank and needs to be on the top. If it is not on top it could cause the header to fill with vapors leading to the engine stopping. He could add a lower fitting with a line joining the feed to the on/off valve which would give positive fuel flow in nose low conditions.
mike mcs repair
Registered User
chugiak AK
Ummmmm. EVERY stock pa-18 has it on the bottom So many varieties of fuel systems I don’t think it matters much.
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Here is a link to a digram of the stock system. http://www.lbfk.com/wp-content/uploads/2015/12/PA-18_Information_Manual.pdf You have to go down a bit to find it. The vent line (or forward fuel pickup) also provides fuel in the nose down position. I agree it should work fine the way it is, as long as caution with prolonged nose down flight is observed. I noticed fuel valve seems to be rotated also. Like Mike said LOTS of varieties in the fuel systems.
DENNY
DENNY
wireweinie
FOUNDER
Palmer, AK
I’ve found the other header tank Web
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That solenoid needs to move.
Web
skywagon8a
MEMBER
SE Mass MA6
Mike, It may not matter much. I had a T-craft with the 12 gallon main tank in the nose and one 6 gallon wing tank which fed the main at the bottom. There was a slight rise in the fuel line from the wing tank just after the shut off valve. When the wing tank had been completely used and then refilled there would be an air bubble in that raised section of tubing. When the fuel valve was turned on the fuel would not flow until the wing was raised the rudder was pushed skidding the plane to get a greater head of pressure to push that air bubble out of the line to get the gas flowing. My point is when a bubble is in the line it shuts down the fuel flow.
If for some reason a large air bubble is formed in the header tank with the vent connection on the bottom of the main tank, it could prevent the header from refilling itself.
Thanks Web. Do you mean a movement away from the header, although staying in the same bay (battery compartment) or moving it nearer to the starter end of the plane?
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Thanks sw8a this makes sense, I was wondering whether a lower fitting front connection would actually “T” into the same feed line as comes from the rear feed, as the top mounted connection does look definitely like a vent connection
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skywagon8a
MEMBER
SE Mass MA6
Not suction but head pressure trying to push the air bubble through the line. The air bubble would have needed to move down through almost three feet of gas before it could get out of the fuel line. The flat tank in the wing only has about four inches of head pressure. Unless there was enough pressure to move the bubble all the way it would just stay at the top of the rise in the fuel line. By banking and skidding the plane the wing tank would generate about five feet of head pressure which did the job. I have no way of knowing whether the bubble went down to the main tank or back up into the wing tank. Either way the obstruction was cleared. If I managed to shut off the wing tank before it emptied this was not an issue.
