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Leaking port fuel tank on landing and left rudder slip

P

Philly5G

Registered User
England
Since day one, (4 months ago) my PA12 has had a fuel leak from the port tank, when landing, when the tank is relatively full (90%+).

The fuel filler cap has a homemade cork seal, which I've never liked and want to replace with a rubber one and I've kind of suspected the leak is coming from the tank filler, so I've fed from the port tank mainly and landed with it <75% full, which has meant no leaks........

On a test flight today, to re-test the fixed:

Charging system
ASI
CHT
Trim

in addition to the main test item-the new diaphragm in the starboard brake master cylinder (all tests went pretty much perfectly!!) I practiced some slips, left aileron/right rudder went perfectly, as did right aileron/left rudder UNTIL I noticed the stream of blue fluid (fuel) hitting the port perspexes!!!! Clearly fuel leaking from the port tank!!!! The tank was about 60%+ full, but it looked like someone was throwing buckets of fuel at the port windows!!!

Has anyone had a similar experience and was it the tank filler, or something more sinister?!!!

Also, another question please-the fuel selector is VERY stiff to turn, any tips for freeing it up please??

Thanks!!!

Philly
 
Last edited:
Philly5G said:
Since day one, (4 months ago) my PA12 has had a fuel leak from the port tank, when landing, when the tank is relatively full (90%+).

The fuel filler cap has a homemade cork seal, which I've never liked and want to replace with a rubber one and I've kind of suspected the leak is coming from the tank filler, so I've fed from the port tank mainly and landed with it <75% full, which has meant no leaks........

On a test flight today, to re-test the fixed:

Charging system
ASI
CHT
Trim

in addition to the main test item-the new diaphragm in the starboard brake master cylinder (all tests went pretty much perfectly!!) I practiced some slips, left aileron/right rudder went perfectly, as did right aileron/left rudder UNTIL I noticed the stream of blue fluid (fuel) hitting the port perspexes!!!! Clearly fuel leaking from the port tank!!!! The tank was about 60%+ full, but it looked like someone was throwing buckets of fuel at the port windows!!!

Has anyone had a similar experience and was it the tank filler, or something more sinister?!!!

Also, another question please-the fuel selector is VERY stiff to turn, any tips for freeing it up please??

Thanks!!!

Philly
Click to expand...

Fuel selector need to be taken apart and cleaned. Best to just buy the new style one from Dakota cub, it comes with stc to give you both position.

Open tank lid and look before you burn up.

Get a GOOD annual inspection done.


Sent from my iPhone using SuperCub.Org mobile app
 
What Mike says. We recently had a Dakota Cub tank leak. Some reasonably experienced folks were sure it was the quick drain or the rubber hoses. It turned out to be a welded seam on the back edge. Tank removal/replacement was fairly easy, but I farmed out the actual removal and installation to a couple of very young and agile A&Ps. I did the easy stuff, like opening, finding the leak, closing, test flight.

Owner's wife is much happier - no gas smell in the cockpit. Yow!
 
Re very stiff fuel selector, there is a Piper Service Instruction (or bulletin or letter or whatever) on it.

But what Mike says. Last year when I sold our Cub, I put a new Dakota fuel selector in. What a beautiful bit of gear. I walked away thinking why didn't I do that 17 years earlier.
 
Philly5G said:
Since day one, (4 months ago) my PA12 has had a fuel leak from the port tank, when landing, when the tank is relatively full (90%+).

The fuel filler cap has a homemade cork seal, which I've never liked and want to replace with a rubber one and I've kind of suspected the leak is coming from the tank filler, so I've fed from the port tank mainly and landed with it <75% full, which has meant no leaks........

On a test flight today, to re-test the fixed:

Charging system
ASI
CHT
Trim

in addition to the main test item-the new diaphragm in the starboard brake master cylinder (all tests went pretty much perfectly!!) I practiced some slips, left aileron/right rudder went perfectly, as did right aileron/left rudder UNTIL I noticed the stream of blue fluid (fuel) hitting the port perspexes!!!! Clearly fuel leaking from the port tank!!!! The tank was about 60%+ full, but it looked like someone was throwing buckets of fuel at the port windows!!!

Has anyone had a similar experience and was it the tank filler, or something more sinister?!!!

Also, another question please-the fuel selector is VERY stiff to turn, any tips for freeing it up please??

Thanks!!!

Philly
Click to expand...

Are the tanks original terne plate? If so, I’d suspect a crack in the tank. Those tanks can be very hard to repair, or at least hard to keep repaired.

MTV
 
mike mcs repair said:
Fuel selector need to be taken apart and cleaned. Best to just buy the new style one from Dakota cub, it comes with stc to give you both position.

Open tank lid and look before you burn up.

Get a GOOD annual inspection done.
Click to expand...

Thank you for that Mike!! GREAT advice and I'm on my way to the the airfield a bit later to open the lid and take a good look at the tank!!!!

I love the look of the Dakota fuel selector.

On the annual inspection, I bought this aircraft with about 6 months remaining on the (signed off) mandatory annual inspection and it had flown a handful of hours since that inspection. I knew it was a TLC fixer upper and needed a new radio and some work on the tailwheel steering locking, but the list of faults I've found and am working through is, shall we politely say, "rather a surprise" on a supposedly signed off aircraft.

Cheers

Philly
 
Philly,
Please let us know what you find about the leak. All too often requests for advice are responded to, but we don't get feedback on the results. It helps all of us.

Jim
 
Um - an IA would be wise to fill all fuel tanks and check for leaks, but it isn't done often. The aircraft I mentioned above - I signed the annual, then the owner filled the tanks for a trip, and I happened to see rivulets of blue dye on the fuselage. Trip canceled.

Do your mechanic a favor - if you know of a problem, mention it.
 
bob turner said:
Um - an IA would be wise to fill all fuel tanks and check for leaks, but it isn't done often. The aircraft I mentioned above - I signed the annual, then the owner filled the tanks for a trip, and I happened to see rivulets of blue dye on the fuselage. Trip canceled.

Do your mechanic a favor - if you know of a problem, mention it.
Click to expand...

I work very closely with the Chief Engineer at the airfield where I'm based and discuss 100% of the issues with him and work the fixes under his supervision as required. To be honest, I wouldn't dream of buying such an aircraft without the expert help and support I have, both from a wanting to understand how the aircraft works IN DETAIL and keeping the costs under control angles. I did my Pitts S-1S and Andreasson BA4B in the same way and the questions I now need to ask are just on new issues and techniques, as I've already learned a LOT about aircraft from the other 2 projects and also my time in the Air Force as a Flight Systems Technician. I dread to think of the cost of doing the (extensive) work I've/we've done so far if I'd just taken it to an aircraft shop..........:roll:
 
55-PA18A said:
Philly,
Please let us know what you find about the leak. All too often requests for advice are responded to, but we don't get feedback on the results. It helps all of us.

Jim
Click to expand...

THANK YOU Jim and everyone else who's commented on this post (and my other ones), it is BRILLIANT to be amongst so many good and happy to help people and I've literally just upgraded my subscription to paid "Friend", which hopefully is a tangible expression of my thanks and eagerness to belong and contribute :) I particularly appreciate the comments and concerns above on fixing before next flying :)

On progress, I got the tank cover open yesterday, 75% of the screws were easy, but the rest were badly rusted and "graunched" and had to be Dremelled and then persuaded out :roll: Immediately it was obvious that there was a LOT of filler/tank fixing gloop at the aft/top right corner of the port tank, which of course is where the leak would be if it manifested on landing (high AOA) and right stick/left rudder slips as it does. Next step is to get the tank drained and out and off to the tank experts for either repair or replace. I couldn't see where the 2 tank straps ends meet and can be unfastened? Is it under the 2 inspection panels at the front and under the leading edges, or somewhere else? Or is there another way to release the tank from the straps? - I was also refitting the gascolator yesterday and ran out of time to check.
 
Again, IF your tanks are the originals, they are soldered terne plate. Those tanks are okay once settled in, but difficult to repair. Years ago, I owned a 12 with these tanks, and one started to leak. Had a mechanic repair it and very carefully re installed it. Shortly it started to leak again. The mechanic had warned me and he was right. Replaced the tank with a Super Cub tank and never looked back. The next owner replaced the other tank not long after he bought it.

So, if your tanks are originals, you may want to consider replacement vice repairs.

FWIW.

MTV
 
mvivion said:
Again, IF your tanks are the originals, they are soldered terne plate. Those tanks are okay once settled in, but difficult to repair. Years ago, I owned a 12 with these tanks, and one started to leak. Had a mechanic repair it and very carefully re installed it. Shortly it started to leak again. The mechanic had warned me and he was right. Replaced the tank with a Super Cub tank and never looked back. The next owner replaced the other tank not long after he bought it.

So, if your tanks are originals, you may want to consider replacement vice repairs.

FWIW.

MTV
Click to expand...

thanks for this! and how do I tell if they’re original?!!

Philly
 
Consirning Terne Plate tanks in actual fact sorta like changing bungees.......... Lots of misconception about both of these on PA12,s .
#1 rule on tanks if they have never been repaired over the
Years they WILL leak. However IF you understand how to fix them they are actually quite easily repaired. The problem is when a leak is found modern day mechanics
want to simply replace them........ Because they are often
not firmilar with the correct way to fix them. They will 99%
of the time try to fix JUST the spot thats leaking. It almost
never works........... The tank needs to come out onto the bench and ALL the seams need to be resoldered with an old fashioned LARGE iron heated up with a torch. Reflux and release all the seam and reseal the tank is less than one hours work total time. Its common to get 10 years out
Of one that is redone correctly........ Or spend $1500 for cub tank installed. We used to solder in two stubs of copper tubing
In the end plate and install 18 sight gauges that are huge
Safer set up. 100,s done and field approved. But doubt if
You could ever get em approved today? So its like saying its simpler to install $3000 18 landing gear than change your bungees...........omg.
 
Thanks everyone, looks like it’s time to get the tank out!!

I’ve been searching for the PA-12 maintenance manual, but no luck so far. I’ve bought the Univair parts list and downloaded a PA-18 instructional build doc, both of which have been some help.

My plan was/is to remove the left tank and while it’s being repaired/replaced just use the right tank BUT on taking off the wing root panel to be able to open the tank flap, I saw there were two pipes. From the univair parts list drawing, the rear one looks to be the feed and the front one some kind of combination of vent and MAYBE some kind of tanks contents levelling connection?? Is this the case? (Sorry for the real newbie question!!) and if it IS the case, I’m assuming I’ll need to blank it off if flying with just one tank?

If it IS a fuel levelling connection, this seems to imply that the Left/Right positions on the fuel selector are simply choosing which feed circuit is in use and NOT using that tank and keeping the other tank “full”??

#IsAnythingEasy!!!


Sent from my iPhone using SuperCub.Org
 
There should be a forward and an aft fuel pickup. The vents are in the caps.

I would not even consider flying one of these airplanes with one tank removed, especially not the left tank, which is generally uses for takeoff and landing. In any case, the FAA would never consider the airplane to be airworthy with one tank removed. Maybe under a ferry permit, but......

MTV
 
mvivion said:
There should be a forward and an aft fuel pickup. The vents are in the caps.

I would not even consider flying one of these airplanes with one tank removed, especially not the left tank, which is generally uses for takeoff and landing. In any case, the FAA would never consider the airplane to be airworthy with one tank removed. Maybe under a ferry permit, but......

MTV
Click to expand...

Ok, 100% clear on no Flying with one tank!!! But is IS there some kind of cross feed? Which means the remaining tank will Flow its fuel across and onto the hangar floor when the left tank’s removed?!!


Sent from my iPhone using SuperCub.Org mobile app
 
I think Cub cross-feed only occurs with a "both" position on the fuel selector.

When you pull the tank, be aware that if the diagonal wing brace tube bolts are tough to get to, you can probably un do the one at the butt rib, then rotate and slide the tank off the tube. The posters above alerted me to that fact in another thread, and it made what looked impossible at least doable.

Also, after re-installing, getting those straps back together appears to be a two-man job.
 
In the original tanks there will only be Aft feed points. (Ditto for Wag Aero replacement ones as well)If yours has original tanks, the only fittings in the forward part of the tank is from the top, and that is for the balance tube. There will be a header tank by your left foot.
If you desire a 18 style selector: instead of the factory double " On/Off" selectors. Then at that point you can ditch the header tank, But you will need to modify your tanks, with forward bottom of the tank feed points. If your "well placed"; just grab some 24gal Dakota tanks and their 4 way valve, at bout $5,000 plus installation??? Or on a more "streamlined budget". Solder up your seams, and live with the header tank.........
 
Last edited:
When you pull the tank, be aware that if the diagonal wing brace tube bolts are tough to get to, you can probably un do the one at the butt rib, then rotate and slide the tank off the tube. The posters above alerted me to that fact in another thread, and it made what looked impossible at least doable
Click to expand...
The stock PA-12 wings/tanks do not use that diagonal tube. There are drag and anti-drag brace wires under the tank saddle.
 
TurboBeaver said:
In the original tanks there will only be Aft feed points. (Ditto for Wag Aero replacement ones as well)If yours has original tanks, the only fittings in the forward part of the tank is from the top, and that is for the balance tube. There will be a header tank by your left foot.
If you desire a 18 style selector: instead of the factory double " On/Off" selectors. Then at that point you can ditch the header tank, But you will need to modify your tanks, with forward bottom of the tank feed points. If your "well placed"; just grab some 24gal Dakota tanks and their 4 way valve, at bout $5,000 plus installation??? Or on a more "streamlined budget". Solder up your seams, and live with the header tank.........
Click to expand...

Interesting as these tanks definitely have fuel type hoses front and rear and they’re also drawn in the Univair parts catalogue. There’s a cylinder, running horizontally the width of the fuselage to the rear of the firewall and below the instruments, which I’m guessing might be a header tank? But I can’t get to the hangarvthis week to check the connections and confirm.

I do have some pics and I’ll try to post them later :)


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Philly5G said:
Interesting as these tanks definitely have fuel type hoses front and rear and they’re also drawn in the Univair parts catalogue. There’s a cylinder, running horizontally the width of the fuselage to the rear of the firewall and below the instruments, which I’m guessing might be a header tank? But I can’t get to the hangarvthis week to check the connections and confirm.

I do have some pics and I’ll try to post them later :)


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Click to expand...

IMG_2625.JPGIMG_2626.JPGIMG_2627.JPGIMG_2631.JPGIMG_2632.JPG

As you can also see, this is the kind of dirt I’ve found behind each panel I’ve taken off, easy to wash off and no apparent corrosion, just not a nice sight



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Didn’t take a before shot, but this is the after, after replacing the fuel selector to gascolator pipe and gascolator and cleaning off the same type of crud as in the tank picsIMG_2624.JPG


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It depends on the type of selector you have and if someone modified it in the past. If you have a left/right/off/off you should be able to isolate right or left tank at the valve, but the balance tube is another issue. You said the selector was stiff so I would drain both tanks and pull lube/replace the fuel selector while the tank is getting fixed. I had mine pulled and lubed and it is smooth as silk. I prefer a prefer a left/right/off/off valve (no both) myself. Lots of modified PA12/18 fuel systems out and about so my advice may not work on yours.
DENNY
 
DENNY said:
It depends on the type of selector you have and if someone modified it in the past. If you have a left/right/off/off you should be able to isolate right or left tank at the valve, but the balance tube is another issue. You said the selector was stiff so I would drain both tanks and pull lube/replace the fuel selector while the tank is getting fixed. I had mine pulled and lubed and it is smooth as silk. I prefer a prefer a left/right/off/off valve (no both) myself. Lots of modified PA12/18 fuel systems out and about so my advice may not work on yours.
DENNY
Click to expand...

Thanks Denny, I'm starting to wonder about this fuel system. The aeroplane was used for aerial photography in Portugal, so extra big tanks would make sense, does anyone recognise the tank from the part of it visible in the pic? It has "corrugations" inset and running from left to right, maybe 4" apart?

I'm also wondering whether the "header tank" under the panel really is a header, as looking at the fuel pipes going to the selector, they seem to come direct from the wings, although I haven't traced the front pipes through yet..........
 
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