Diesel fiberglass tank question

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Arfang

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Hello everyone,

I have decided to build a fiberglass diesel fuel tank for my Ka 8 motorglider conversion.

I've contacted my local composite supplier and the contact person told me that I need two different resin (epoxy) and hardener, one pair for the shell and one, called ''chemical-proof'', to coat the inside after the shell has cured.

Since I didn't find any mention of two separate resin and hardener being used in Sportplane Construction Techniques or Understanding Aircraft Composite Construction, I start having doubts about what type of resin and hardener to use for a fuel tank.

What building technique would you recommend me to use? Do I have to coat the inside?

Your comments are as always very appreciated.
 

wsimpso1

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Sounds fishy to me. Look up most epoxy systems, and they are usually minorly affected by gasoline and usually less by Jet A, but not fine with gasoline containing ethanol.

Vinylester resin is proof against all fuels. Build the portion of the airplane that will be fuel tank using vinylester. It does have a few foibles to know when you build with it, but it works.

The solution I liked for my airplane is Dow-Corning's silicone primer and flurosilicone sealant. Absolutely proof against ethanol. My glass epoxy panels were already built, so that was my solution.

I can share more if you want to talk about.

Billski
 

Arfang

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Thank you for your input Billski.

So epoxy resin is fuel proof as long as there is no ethanol mixed in and the only way to prevent any damage by ethanol is either to use vinylester or a coating or sealant like you described. I would gladly learn more about the use of vinylester since you proposed to talk about it.

To give you more details, the tank contains approximately 3 gallon, it will be empty after about 15 minutes of flight, I don't know if having the tank almost empty would reduce the damage.
 

proppastie

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You said "diesel fuel tank" so do you have to worry about ethanol?....what are you using for an engine?
 

Arfang

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From what I could find there may be a small percentage of ethanol in some ''regular'' gasoline, but I don't know about diesel. Since Billski mentioned the ethanol issue I'm worried there could be some in diesel also.

I'm using a jet engine.
 

proppastie

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From what I could find there may be a small percentage of ethanol in some ''regular'' gasoline, but I don't know about diesel. Since Billski mentioned the ethanol issue I'm worried there could be some in diesel also.

I'm using a jet engine.
Hope you post the details....of the engine installation....I think I might use an "off the shelf" plastic (polyethylene) tank..... boat or ultra light, but I am sure you have good reasons.
 

pictsidhe

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Ethanol has a dreadful cetane number so you shouldn't find it in diesel. On the other hand, if the diesel engine doesn't work out, having a gasoline compatible tank will make a swap much less hassle.
 

datadriver

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Hello everyone,

I have decided to build a fiberglass diesel fuel tank for my Ka 8 motorglider conversion.

I've contacted my local composite supplier and the contact person told me that I need two different resin (epoxy) and hardener, one pair for the shell and one, called ''chemical-proof'', to coat the inside after the shell has cured.

Since I didn't find any mention of two separate resin and hardener being used in Sportplane Construction Techniques or Understanding Aircraft Composite Construction, I start having doubts about what type of resin and hardener to use for a fuel tank.

What building technique would you recommend me to use? Do I have to coat the inside?

Your comments are as always very appreciated.
Use Rhino 9700 (sometimes called Jeffco) from aircraft spruce. The hardener is an amber color and the resin is grey. This is what Velocity builders such as myself use.
 

Arfang

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An off-the-shelf tank would be great, however I have two reasons to look at the custom-build option:

The space in which the tank must be fitted is quite small and crossed by steel tubes.

20180708_163003.jpg

The engine will be located on top of the fuselage, in front of the spar, mounted to the horizontal V-shaped frame. It would be neat to have the tank play the role of an aerodynamic fairing like in the pictures below. Of course, if I find a suitable off-the-shelf tank, I might reconsider.

csm_Ventus_CTT_jet_01_90ea076a1b.jpg csm_Ventus_CTT_jet_02_7f8138644d.jpg

If vinylester resist both ethanol and ethanol-free fuel, the safest option would be to build with vinylester. I'll see what I can find about vinylester-fiberglass construction. Thanks for your input.
 

proppastie

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Of course, if I find a suitable off-the-shelf tank, I might reconsider.
The RC Model guys have small tanks where perhaps you could fit several in the small spaces available. Your ideas are good and very workable.
 

Markproa

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My homebuilt holds 80 litres of diesel in the wings. Although the plane is all epoxy/ply and foam the tanks are made with kevlar and vinylester, as Bilski proposed.

Mark
 

Arfang

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My homebuilt holds 80 litres of diesel in the wings. Although the plane is all epoxy/ply and foam the tanks are made with kevlar and vinylester, as Bilski proposed.

Mark
Thanks Mark. Care to share any tips on working with vinylester and Kevlar? I'm used to epoxy and fiberglass, how does the two compare in terms of construction?
 

Markproa

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Thanks Mark. Care to share any tips on working with vinylester and Kevlar? I'm used to epoxy and fiberglass, how does the two compare in terms of construction?
Sorry, I can't help. The Tanks were done when I bought the project and I must be one of the only boatbuilders who has never used polyester or vinylester. Actually I did once build some cat hulls out of vinylester but that was infused.
 

Marc W

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Vinylester works much like polyester or epoxy resin depending on viscosities. It has been over 30 years years since I used it, but I don't remember catalyzation ratios to be as critical as epoxy. I don't know how you buy small quantities but we bought it by the drum and mixed cobalt into the resin to "activate" it before use. I believe you can buy it already activated too. The resin has a limited shelf life after it is "activated". Once activated it is catalyzed with MEKP like polyester resin and, like polyester, gel times can be varied by adjusting the amount of catalyst. Gel times are similar to polyester resin. Use acetone or MEK for cleanup.
 

BJC

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I would add that gel times are also affected by the amount of cobalt used to promote the resin, and that another chmical, DMA, may be used to have a resin that will cure in lower temperatures. Typical catalyst to resin ratios are in the 1 to 2 % range. If you find small quantities, you can greatly extend the shelf life by storing it in a refrigerator. Some products have wax in them to help the surface cure. Avoid those.

The inside of the tank should be resin rich.


BJC
 

Arfang

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Thanks a lot for all the information about vinylester. On the other hand, proppastie might be right about the simplicity of an ''off-the-shelf'' solution. I will give it some thought.
 

proppastie

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Thanks a lot for all the information about vinylester. On the other hand, proppastie might be right about the simplicity of an ''off-the-shelf'' solution. I will give it some thought.
linking several tanks together for filling and moving fuel may not be trivial. A single tank probably it is not much of an issue. The model guys, I think, have caps you can buy that fit standard containers such as anti-freeze containers or the gallon jugs their fuel comes in. I am not a model guy so others might be able to help more.
 

Cozyflier

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I have also used EZ Poxy from Aircraft Spruce on a number of my builds. The fuel cells used 100 LL and also Gas station diesel depending on a piston or jet power plant. The EZ Poxy is commonly used by the Long EZ and Cozy builders for the fuel tanks and fuel sumps. As mentioned, as long as your fuel does not contain any ethanol the EZ Poxy systems should work for your fuel tanks.
 
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