Softened plastic fuel tank

[Tree top pilot 13]

I have made it to the point now that taxi tests have been done...pretty much ready to fly...more than a few yards above the grass. So being happy with that i left the plane in the hangar for about 6 days with a half tank of fuel remaining last week. Came into hangar and first thing I see is wrinkled fabric behind the tank....something obviously has happened. After checking it out the tank is soft as rubber and has drawn down in the top of the tank and sagged wherever fuel was touching the tank. It even pushed itself up in the back near the rear spar. Yes it it the cream colored, welded together 5 gallon tank from stace at Rocky mountain wings. Seems he has struck a last parting shot at me. It seems to be soft only where fuel has had stood. So the one and only tank was removed from a newly completed plane today and will be replaced by a 5053  aluminum tank soon as I can get it made. After the hangar chat session about it i know i can't be the only one. Granted it has been in my closet for 8 years before it was installed ...100LL and mogas  half and half shouldn't have made it buckle and become soft. Another couple days and I am sure it would have been more than just soft. It was the first time the tank had ever had fuel in it by me. Just wanted to see if anyone else has had this problem with those type plastic tanks. New fuel cap with a new open vent tube , fresh fuel no ethanol and atmosphere pressure only. We would really like to know why this happened.  I was hoping to fly this thing this fall. 

[marksires 484]

You never know what is in mogas - they can put anything in it as long as it meets the relatively weak specifications for automobile useage.  It may be fine, and it may contain some nasty solvents they needed to get rid of when mixing up the next batch.  

[Klmt101 5]

Please keep us uptaded, left a voice mail with him yesterday asking about new tanks. 

[Allen Sutphin 705]

I have one plastic/ one alum so I will pay close attention to the plastic one. A lot of Stace's tanks out there so if there is a problem, it affects a lot of aircraft. That would probably be the end of Stace and his business. Contrary to what some say, a properly welded alum tank will not just up and spring a leak so I have no concerns with them. I do have concerns about ANY fiberglass tank using auto fuel. Plastic? Well, time will tell.

[akflyer 1427]

is it ethanol free mogas?  

Welded aluminum tanks in the wings have proven to be problematic as they are built as an integral part of the KF / Avid wings.  The flexing is what tends to crack the aluminum tanks.  If you were to install them like a piper tank and not have them as an integral part of the wing structure, I don't see aluminum as being an issue at all.

Any pics of the tanks you have that are wrinkled up and buckled?

 

[Tree top pilot 13]

Yes. Pics soon...almost back together. Fuel issue is over ...made a new 5 gallon tank...Fuel in it for a week no swelling or leaks. Used slightly higher test pressure @ 1.7 or near psi over night

[Tree top pilot 13]

This is what was ringing the alarm something isn't copo

[Tree top pilot 13]

Turned to jelly like elasticity

[Tree top pilot 13]

[Tree top pilot 13]

Made new shock cords as well out of 1/2 material from ACS. Made tools to stretch and make new units. Thank you to the folks that were here before me...new cords were 64" long and seem just right. Taxi tests soon

[Tree top pilot 13]

Ready to go now

[Tree top pilot 13]

I also noticed a certain website was not active this evening.....

[Tree top pilot 13]

It may seem trivial but a little curl of the end of that .041" safety wire keeps everything nearby from being punctured...mainly my paws