Fiberglass or Plastic fuel tanks?

23 posts in this topic

Posted

I am building a set of wings for a guy's Avid Magnum. He has a set of large fiberglass tanks and a set of plastic tanks. The plastic tanks look to be 5 gallons a piece and there are 6 of them. He planned on either running the fiberglass as mains and two of the plastic tanks in each wingtip. He asked me if he should use the fiberglass tanks or use all six of the plastic tanks. I've heard of people having issues with the fiberglass tanks so I wanted to get some input.

If I were to use the plastic tanks I would need a plumbing diagram.

The plane with have an 0-320 for a power plant. I'm sure he will be running AV-GAS.

Thank you for any input you may provide. My name is Vance Simons. I live in Post Falls, Idaho. You can call or text me at (509) 599-9477. I do have photos I can send.

Thank you

Vance

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Posted

Hi Vance, first of all I don't have a finished flying Magnum so there might be more expertise out there. The fiberglass tanks are glued in place and have a couple layers of glass around them which also encapsulates the spars. Therefore they could have a degree of structrual integrity built in for the entire wing. Before I installed my tanks, I did a low pressure check (using a baloon) to see if there were any obvious leaks then did a thorough physical inspection and patched any defect I found. I haven't filled these tanks yet so the jury is still out. To install a bunch of plastic tanks would take a lot of fittings, clamps, and inspection holes. Not knowing the shape or configuration of your tanks makes it difficult to assess. Can you post some photos? Fuel systems can be tricky!

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Posted

Vance the issue with the fiberglass tanks is the use of ethanol fuels otherwise they are great, and some of the tanks (mine are good) are ok to use with ethanol. the plastic tanks would require lots of fittings ie. places to leak. i would stay away from them. if your tanks are not ok for ethanol and you want them to be you could cut the top off and coat them with the new resins and glass them back together. another option (read that $$$) would be to have Rod at performance products make new ones, that's the route I went. 

 

-Robert-

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Posted

Vance,

      Avgas should not harm the fiberglass tanks.

THEY TELL ME THAT CAPS ON PUTERS IS "CURSING", so turn your hearing aid down low-  I have the early Avid Magnum Builders' Manual - I could not believe the STUPID IDEA OF TIP TANKS in those Avid Wings!!!! 

IMO, that is the most dangerous, stupid thing that they could have tried - not only does it induce more stress on the outer part of the wing, but adds inertia which can inhibit recovery, and could cause a fuel starvation problem - and a few other problems.

I have 2, 12 gallon fiberglas tanks in each of my wings, all at the root of each wing.

My 5 cents worth!

EDMO

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Posted

Thank you for the reply. Ed I told the owner he might want to do some homework on installing the wing tip tanks. I personally would not install them but it's his plane. I'm just getting paid to build the wings.

Thank you

Vance

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Posted (edited)

Vance,

     It would be very simple to relocate the tip tanks to the next bay near the root tanks, but would require moving a drag brace.

My tanks have separate fuel lines, each going to a separate shut-off valve inside the cabin, and T'd together after that to the header tank - but you could always use the more expensive multi-tank shut-off valves.

EDMO

Edited by Ed In Missouri

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Posted

Ed, except in landing and taxiing, tip tanks actually reduce the stress on the wing spar.  They spread the load out over the whole wing instead of concentrating it all near the center.  Remember the wing lifts over the entire length, not just the center.

 

Mark

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Posted (edited)

Mark,

I've been taught that wings do not lift equally the length of the span - they are braced by the struts across the area with about 67 to 75% of total lift, depending on planform - and the outer half is free to float. Also, check out the formula for inertia, or kinetic energy - like taking a pencil by one end and moving it up and down, then adding a weight to the other end and trying the same thing.

I still say that the tanks should not be at the tips of these wings - and I wont build that way.

EDMO

Edited by Ed In Missouri

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Posted

I agree putting weight at the wing tips is not a good idea.  Think spin recovery.  If you are thinking about putting weight at any extreme point on the airplane, ie nose, tail, or wing tips, do the math for the moment of inertia.  The formula is arm SQUARED times weight.  It is not as simple as weight and balance calculations.

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Posted

What about Lears, Comanches, and many others with tanks hanging off the wing tips? Not arguing just curious.

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Posted

"Non-Aerobatic Spam Cans for straight and level flights"!

EDMO

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Posted

Ok then, how about the sia marchetti?

Mark

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Posted

I sealed the inside of my fiberglass tank with a product from KBS coatings. It is a fuel tank sealer for steel or fiberglass tanks. It is not effected by ethanol and was easy to use with the tank out of the wing. There was an extensive washing and etching process and then the sealer was poured in and the tank was rotated until the entire inside was coated. I haven't reported on it until now because I wanted to make sure it worked, I have had fuel in it for a few months with no leaks and no softening of the fiberglass. So far ao good. I will let you all know if it fails in the future.

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Posted

Thanks, cliff. That's good to know information. Can you give any more details on the product?

I have then factory installed "Cream" in my yellow plane. So far, no worries, but it has never seen ethanol, either...

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Posted

The KBS sealer is silver. I have been painting motorcycles for over 30 years and have seen every type of tank sealer known to man. I have seen the off white cream sealer fail many times. There is a red product that looks like transmission fluid, It works well but It wasn't known if it would work in fiberglass tanks. The KBS Coatings product had specific instructions for use in fiberglass tanks. One of the custom bike builders that I did paint work for had been using the KBS for years with no problems. I just figured I would try it. I have a fiberglass right tank and a metal left tank. I sealed them both with KBS sealer. We will see if it holds up. I am running clear fuel lines so I can keep an eye out for any break down of the sealer. I will post the name of the product when I go back out to the shop.

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Posted

The original Avid Magnum fiberglass tanks have a very sophisticated venting system unlike all other Avid tanks. It works very well. I would not recommend coating the inside of the tanks unless you are willing to cut them open to do it. Even then that should only be done to repair a leak.

 

No coating you can put on the inside of the tanks will prevent eventual deterioriation if the underlying material is subject to decay with ethanol. There will always be one spot that was missed or some exposure of the substrate at the filler or drain penetrations.

 

The original glass tanks ar far and away the best solution asuming 1) you test them for leakage prior to install and fix any leaks, 2) never use ethanol. Ethanol is not compatible with rubber parts in the lycoming anyway. I had great luck with non ethanol auto fuel in my Magnum tanks.

 

Another option might be to fit current kitfox tanks in if the wing profile is similar, but they won't have the superior venting system the Avid Magnum tanks have.

 

 

Chris

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Posted (edited)

Speaking of "fiberglass" tanks, what about the late 80's / early 90's era C model fiberglass tanks? Are these the "original" glass referred to by Chris?  My '92 build was done with no venting other than the caps. Venting the header is presently in the works however as suggested in the '91 C Heavy Hauler Build Manual -- out through the right cabin side of the wing-root.   Indeed ventin a critical topic addressed by Avid Service letter.

 

Too bad the glass tanks appear susceptible to ethanol.  There's numerous threads addressing it in boating forums as well. It seems the optimum construction material (indeed especially for the HH wing from what I can see in the plans) with respect to max strength and the least weight for aircraft. Fortunately where I am NC, we have an abundance of 93 non-ethanol available. 

 

Apologies to Vance for hijacking the thread. :news:

 

btw - My aircraft has only been serviced w/100LL all it's life until I purchased it last year and they appear immaculate especially inside fwiw. I plan on burning 93 non-ethanol however mostly.

 

 

Paul

Edited by allonsye

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Posted

Chris, I knew I shouldn't have posted anything about sealing my tanks. Thank you for letting me know that there is no coating that will seal a tank. 

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Posted

Clif my apologies if my comment offended. I know there are people who have coated tanks and had no problem. Some have had problems. What I said is my opinion and I should have been more sensitive to the fact what I say might offend others. I try not to dis other's approaches to problem solving but I failed here. My apologies again.

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Posted

Hi Paul,

The Magnum tanks are different that other Avid tanks. Filler is different, venting is way different and outlet size is larger all to accomodate the up to 180 HP engine the Magnum can support. The tanks are however the same size and shape externally and could be interchanged. Internally there is all of the tank vent and cross-tank vent plumbing in the Magnum tanks that the regular Avid tanks don't have, and the internal baffling is different. The The Magnum tanks have three internal bays and all other Avid tanks have four smaller bays.

 

Dos this answer your question?

 

Chris

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Posted (edited)

My Kitfox tanks only have two baffles making three sections - the venting is KISS and works!

I have the diagrams of the Magnum vents - they are like some I have seen on spam cans - they should work for tank pressures and overflow, but cant see where they would help a header tank vent back to the wings...Maybe I missed something...

EDMO

Edited by Ed In Missouri

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Posted

@Cliff,

I'm interested to see how the KBS holds up! We need a sealant to work, because if AV gas disappears it might be the only solution that doesn't require us removing our fiberglass tanks. So, we have to keep trying.

@everyone else

I looked into everything...sealants, aluminum, plastic, but when everything weighed out I decided to go with plain fiberglass. Sealant can cause clogging/venting issues, welded aluminum tanks can have rupture problems due to vibration/prop wash, and the plastic tanks are having issues with fuel line attachment leaks (I read one post on that, my original problem was loosing a few gallons of usable fuel because the plastic tanks went inside the fiberglass tanks.)

The real solution is for somebody to spend the money to mold a plastic tank that completely replaces our fiberglass tanks.

So, I'm running straight fiberglass until somebody (Cliff) has a good experience with a sealant, or I get a fuel leak.

Ron

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Posted

Speaking of "fiberglass" tanks, what about the late 80's / early 90's era C model fiberglass tanks? Are these the "original" glass referred to by Chris?  My '92 build was done with no venting other than the caps. Venting the header is presently in the works however as suggested in the '91 C Heavy Hauler Build Manual -- out through the right cabin side of the wing-root.   Indeed ventin a critical topic addressed by Avid Service letter.

 

Too bad the glass tanks appear susceptible to ethanol.  There's numerous threads addressing it in boating forums as well. It seems the optimum construction material (indeed especially for the HH wing from what I can see in the plans) with respect to max strength and the least weight for aircraft. Fortunately where I am NC, we have an abundance of 93 non-ethanol available. 

 

Apologies to Vance for hijacking the thread. :news:

 

btw - My aircraft has only been serviced w/100LL all it's life until I purchased it last year and they appear immaculate especially inside fwiw. I plan on burning 93 non-ethanol however mostly.

 

 

Paul

Paul, I Sure hope you have success venting the header tank through the right wing root.  Jeff's Avid was vented that way when I started flying it; it kept the tail well coated with fuel and wrecked the turtle deck.  We changed it to just vent through the tanks like mine is. Have never had a problem with 3 planes vented this way.

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