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Aluminum vs Plastic Fuel Tanks

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Posted (edited)

I am going to begin rebuilding my Merlin GT very soon.  The Merlin has an aluminum tank in each wing.  From your experiences which is a better tank. Plastic or ALuminum.  I have read some stories of seams splitting on aluminum tanks.

 

Thanks

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Edited by AVID STOL HH

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Posted (edited)

I think a lot of the choices have to do with your spar construction - Evidently the Avids and Foxes wings flex more and the aluminum tanks don't last - However, there are thousands of Pipers, Maules, Champs, and so on, flying with aluminum tanks in the wings without any problems.

How are the spars made in your Merlin wings?

EDMO

Edited by Ed In Missouri

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Posted

Sonex switched from Aluminum to plastic.  The owner called it the biggest safety improvement they'd ever made......

Mark

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Posted

My Kitfox I/II has aluminum Tanks, It has 700 Hours on the airframe and no leakage. The tanks are set with RTV I believe this was to prevent the flexing issue.

Dave

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Posted

I will take a picture of my wing without the cover and you can comment on the construction and how the tanks are situated.  I am completely unfamiliar with a Merlin GT so everything is new to me.

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Posted

Dave,

My fg tanks in my KF1&2 were set in GE Silicone 2 - I used it on the new one too.

EDMO

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Posted

I just looked at one of the Sonex plastic tanks and it is really nice! I can see why they switched, it sits right over your legs, bad place for a leak!

The plastic looks like the same stuff the kitfox is using and the other plastic tanks guys are using in the Avids.

I think I would go plastic. They are now ethanol friendly and flexible.

I used the fiberglass tanks in my Magnum, but only because the original builder had already glassed them in, otherwise, starting from scratch, I would have used plastic.

Good luck,

Ron

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Posted (edited)

Okay, I have posted the pictures up top.  Please comment on construction and the tanks.  The wing is a single strut system. 

 

Here is the description of the wing construction I found on the Blue Yonder website.

 

Wing construction on the Merlin is very sturdy and rugged. The leading edge is built of 2024T6 aircraft aluminum. The strong 9" aluminum "I"-beam main spars (O.080" laminated) and wing leading edges ("D-cells") are completely pre-built by the Merlin Aircraft factory. The wing ribs are constructed by the builder, using high-density foam for lightweight and strength. These easily assembled ribs are capped with heavy-duty 0.040" aluminum "U" channels. These "U" channel rib caps are joined from top to bottom of the rib by 1 " straps of aluminum. There is no structural wood in the aircraft anywhere, thus eliminating the worry of rot and the eventuality of warping. Foam has been chosen because of its durability. Fewer ribs are required due to the exceptional rigidity they provide, simplifying construction and installation. The foam ribs can be repaired, if necessary, much more easily and affordably than either wood or aluminum stamping. Slotted full span ailerons have been incorporated into the design, resulting in excellent slow flight control and a responsive roll rate. The aileron horns are made of heavy aluminum and have never experienced any cracking or in-flight failures. The ailerons are controlled by push rods inside the cockpit, not by cables in the wing. This system eliminates high maintenance pulleys, hardware, bell cranks and control cables. The aileron control rods are easily accessible for routine inspection. Combined with the pre- fabricated "D" cells and aluminum capped foam ribs, these simple wings are the key to the Merlin GT's well established 350 hour quick build time. Each Merlin GT also comes with simple "folding-wing" capability, to facilitate trailering and road transport.

Edited by AVID STOL HH

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Posted (edited)

Ron,

I am not aware that there are plastic wing tanks available for any Avid or Kitfox, just header tanks, and some plastic inserts that go in the fiberglass tanks.

EdmO

Edited by Ed In Missouri

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Posted

Ed,

 

Wingtanks.com have the plastic tanks for the Avid / Kitfox, I know several guys that have them, I also know of a couple who are not real happy as they have a lot of plumbing and lots of potential leaks. That is what has Jack grounded right now till they can get the leaks to seal up on all the plumbing. 

 

Jeff,  Those tanks are not part if the wing structure like the Avids / Kitfox, I would not think twice about using them.  If it is a potential issue, you can put a hinged lid on the top op the wing so you can take them out and get them welded up at some point in the future should the need come up, just like the pipers have.

 

:BC:

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Posted (edited)

Avid had/have plastic tanks that slip into the old tanks, or can be mounted by themselves I believe. The website is wingtanks.com Jim Chuk

Leni, you hit send while I was still typing. ;-)

Edited by Jim Chuk
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Posted

Lenny.  What does that mean that the wing has a .080 laminated wing I beam.  I am not sure what the laminated means.

 

Thanks

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Posted

I am pretty sure its a couple pieces of the aluminum bent to shape and riveted together.  It looks like it may have some angle riveted along the top and bottom as well.  I did a little research and it seems that everyone pretty much agrees that the plane is built hell for stout and is a great performing little bird!  I think After COMP quit making it I think there is a factory in Canada producing it now called the Merlin EZ.  You may try to get ahold of them if you need any parts that you cant make yourself.

 

Are the wings hammered on it or was it just a little bit of fuse / gear damage? 

 

:BC:

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Posted

The plastic insert tanks can be used as main tanks also. The main tanks on my SkyRaider are the same tanks I put inside my crap fiberglass tanks on my Avid.

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Posted

If you contact Merlin, be sure to also ask about the tank mounting - Piper has two straps that hold the tank in the wing. The removable cover that Leni mentioned is also used in some models.

EDMO

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Posted (edited)

I am pretty sure its a couple pieces of the aluminum bent to shape and riveted together.  It looks like it may have some angle riveted along the top and bottom as well.  I did a little research and it seems that everyone pretty much agrees that the plane is built hell for stout and is a great performing little bird!  I think After COMP quit making it I think there is a factory in Canada producing it now called the Merlin EZ.  You may try to get ahold of them if you need any parts that you cant make yourself.

 

Are the wings hammered on it or was it just a little bit of fuse / gear damage? 

 

:BC:

The only damage is to one wing.  Trailing edge on one rib got bent and the aileron attachments got bent to one side.  I am golden otherwise.  You would not believe the amount of cabin space in this plane.  I could take a 6' 6" 500 lb guy with me if it could get off the ground.  I think the cockpit is 42" wide. 

Edited by AVID STOL HH
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Posted

sweet, that is a quick easy fix!  I know, I drooled over one that was at the Soldotna airport years ago.  Lots of room and built pretty stout.  I am not sure why there are not more of them flying up here.  After Merlin folded the first time, a guy in Canada started making the lil buzzard.  It is pretty much a copy of the Merlin GT.  I tried to get ahold of the guys that make the lil buzzard a few years ago as I wanted to be a dealer for them up here and buy one for myself, but I could never get the guy to call me back or answer an email...

 

:BC:

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Posted

sweet, that is a quick easy fix!  I know, I drooled over one that was at the Soldotna airport years ago.  Lots of room and built pretty stout.  I am not sure why there are not more of them flying up here.  After Merlin folded the first time, a guy in Canada started making the lil buzzard.  It is pretty much a copy of the Merlin GT.  I tried to get ahold of the guys that make the lil buzzard a few years ago as I wanted to be a dealer for them up here and buy one for myself, but I could never get the guy to call me back or answer an email...

 

:BC:

And when they go out of business he'll blame bad economy, cheap pilots, etc etc.  Couldn't possibly be he wouldn't return a simple phone call.

Mark

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Posted

Leni,

I was wondering about the plumbing on thes tanks at wingtanks.com

The plumbing looks like clear tubing pushed in a drilled hole! Is that right? And is that what is causing the problems?

That has to be frustrating after using those because the old tanks were leaky!

Ron

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Posted

Ron,

 

On my Avid Plus the fuel tanks leaked because I used brass fittings with O-rings against the tank, pressed in place with alarge area washer and coated with fuel resistant sealer.  The problem was that I couldn't tighten the nut on the fitting tight enough without forcing the O-ring out from behind the washer that was pushing it against the tank, and the sealer couldn't make up for the loosness.  When I screwed the barb fitting into the end of the bulkhead fitting that went through the tank it broke the seal and caused the leaks.

The reason I went with the bulkhead fitting instead of the  grommet was there were some problems with the grommets being attacked by the ethenol in the fuel and leaking. 

Although it looks like the tubing is just pushed into the plastic tank, usually there is a grommet inserted into a hole drilled in the side or bottom of the tank, a metal fitting with a barb on one end is inserted into the the grommet, then the fuel line is attached to the barb end of the fitting.

What Randy and I have done is, after talking to the rep from Lock-tite, is to use, in place of the O-ring, a flat washer with an O-ring bonded to the inner opening of the washer, completely coated with swimming pool under water sealant, followed with a flat washer to mash it all against the tank.  Randy was able to really tighten the nut on the bulkhead fitting and then form the sealant that was forced out from around the washers, into a filet to seal the outer edge of both washers. 

This has been a very trying effort because the fiberglass tanks weren't leaking to start with! I was trying to prevent a problem.

We'll see how successful our efforts have been when we service the tanks.

 

Jack 

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Posted

Interesting.

 

I have a Merlin GT and the tank split at the forward seam last winter

. But my tank fits inside a single rib bay and holds 8 gallons. Obviously something has changed over time - Mine first flew in 1998 (If I rememember correctly) - would yours be newer or older? Larger than 8 gallons?

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Posted

I wonder if it would help to keep the tank from flexing and breaking if one was to wrap fiberglass around the edges of the tanks. That would support the edges of the tank I would think. Any opinions on that? Jim Chuk

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