FUEL TANK COMPOSITES

[Steve L]

I'm about to build two fiberglass auxiliary tanks for my Explorer, they will only be about 15-16 liters each. Can anyone tell me what composites I need to purchase that will be immune to ethanol and adhere to aluminium which I plan to glass in for the fittings.

 

Thanks in advance

 

Steve

 

 

[Old Koreelah]

I'm about to build two fiberglass auxiliary tanks for my Explorer, they will only be about 15-16 liters each. Can anyone tell me what composites I need to purchase that will be immune to ethanol and adhere to aluminium which I plan to glass in for the fittings.Thanks in advance

 

Steve

This topic has been discussed before, Steve. A search of old threads might reveal more.

Acting on advice from a chemical engineer, I built mine from vinyl ester, because he said it was pretty much ethanol proof, and resistant to most fuel additives. Epoxy is less resistant, but can be used to add fittings because it sticks to vinyl ester (but not vice-versa).

 

 

[kgwilson]

Use Vinyl Ester resin with glass CSM or woven cloth. There are a lot of grades of Vinyl Ester & the one recommended by Nuplex who manufacture the resin has a code PVR 6001. This one has a higher resistance to heat than the others although all are impervious to most chemicals and all those found in petrol including the aromatics and ethanol.

 

 

[Mike Borgelt]

Use vinylester but use kevlar cloth instead of glass. Will eggshell but not shatter in event of accident. Also lighter than glass.

 

 

[Oscar]

Phil Rockstroh at: http://www.cgcomposites.com.au/ is excellently helpful - and cgcomposites is great to deal with - PLUS they sell in small quantities, great service, very reasonable transport charges. Nuplex / FGI often won't sell less than a LARGE quantity, plus they charge as if you are Boeing...

 

 

[Old Koreelah]

Use vinylester but use kevlar cloth instead of glass. Will eggshell but not shatter in event of accident. Also lighter than glass.

Agreed, but Kevlar is a bugger to work with. Hard to see if it has been wetted out and hard to cut (will blunt scissors after a metre or so- buy a box of cheap Xmas scissors). Might be better to use light fibreglass fabric for the first layers then laminate Kevlar over the top; that's what I did.

 

 

[Litespeed]

Yep Kevlar is a absolute bugger to cut- exactly why you want to use it.

 

A well designed kevlar and glass or kevlar and carbon tank is damn tuff and far stronger than the human body can sustain in a crash. Assuming a fuselage mounted tank- your tank will be the last of your problems. Even in wing mounts they are still far superior.The ultimate is a kevlar based tank and a bladder inside, this may include a sandwich composite of suitable foam.

 

If designed well it should be able to drop when filled 100ft and not rupture or leak, pretty much a gold standard and almost impossible with any other materials. Often tanks split from Gshock of the fuel moving in a collision, baffles help as does fuel tank foam but not enough in many cases of alloy or steel tanks.

 

Even with a bladder inside a steel or alloy tank will rupture at high G impacts- unless it is far too heavy to be for aircraft use. The Poly tanks tend to be better but will never come close to a kevlar one.

 

This has been a item of much discussion by many and considerable design effort and testing by a forum member who is a crash safety expert on Homebuiltairplanes forum. He is even patenting his tank design. Tanks are something that are rarely designed well - especially in home built aircraft and there rupture is often just considered natural in a heavy crash.

 

It is certainly a area worth the effort for enhanced safety- no one wants to survive the arrival with terra firma and be burnt. The materials are easily available, the techniques understood and the extra cost over a simple glass tank is tiny compared to the cost of everything else in a aircraft.

 

Kevlar is wonderful stuff when used for it benefits, the toughness and ability to absorb shock loads, puncture and abrasions are the stuff of legend. Yes it is a pain to cut- high quality scissors or disk cutters are the answer. A really good pair of dress maker style scissors that can be sharpened are worth the money. It is also a bugger to repair but that's fine- if it needs repair (tank) then the aircraft is crumpled anyway.

 

As far as wetting out goes - try this. Use sandwich film to really force all the resin in, you will be able to see the excess sitting under the film. Or/and just use peelply over the top to absorb the generously applied excess resin. If you are using fiberglass as a outside layer- this will help with seeing the resin penetration.

 

The advantage of using kevlar as the main structure of a tank far outweigh any hassles in making it.

 

I guess I am always concerned about the fuel thing- a inflight fire or upon crashing is my greatest fear. Being burnt to death is probably the worst possible way.

 

I will post a relevant link to the tank idea.

 

Phil

 

 

[Litespeed]

here is the related link- includes overall safety discussion

 

http://www.homebuiltairplanes.com/forums/aircraft-design-aerodynamics-new-technology/22774-design-safety-3.html

 

 

[Steve L]

Thanks guys, I know which way I'm heading now . . . Kevlar. . . That's what's great about this forum. After contacting a few suppliers here in adelaide I was none the wiser, one even suggested I do my own testing, I guess I could have been talking to the wrong people, I contacted Phil Rockstroh yesterday he put me straight and can supply everything.

 

Thanks Phil the link is most interesting.

 

Steve

 

 

[Oscar]

Phil Rockstroh and cgcomposites are excellent to deal with; I found them through an aero- modeller's thread, actually, and they are very cheerful about supplying small quantities, and they stock a very good range of the top-end stuff one might need for aircraft work.. They are helpful like FGI was about 30 years ago, when it was trying... Paul Kulmar at Gurit ( Mona Vale) is also really helpful on technical stuff, but Gurit doesn't do retail... and many of their distributors don't handle small quantities of the higher-tech stuff, unfortunately; most will order but you're looking at many, many litre pail sizes. ATL Composites are also good but again, I think have now moved to a 'distributor/dealer network' sales model ( I haven't used them for quite some years now, so I may be wrong there).

 

 

[robinsm]

Made tank extensions for my Xair tanks ( resined onto the back of the existing

 

tanks like a camel hump)...vinyl ester and fibreglass. Light, no problems and now 6 years old and going perfectly. I use both mogas and avgas. No leaks. Carbon fibre is great but its a bit like squashing a bug with a sledgehammer for normal and small size tanks. Make sure you get all of the air out when laying up and bobs your proverbial.....

 

 

[Oscar]

Choice of materials ( e.g. cloth glass vs in particular c/f) should be considered with respect to the specific situation of the tank in question. Thin c/f structures have great strength to thickness (and hence weight) ratios - but c/f can shatter like plate glass.

 

Take, for example, the cabin-mounted tank in a Jab. LSA55/120. Because of the nature of the airframe, in an accident it will flex a great deal and if the tank itself is extremely rigid it may be broken by the transmission of flex in the accident whereas a more flexible tank constructed of cloth glass or Kevlar will distort with the airframe but not be cracked. If you mix flexible with non-flexible components, you will inevitably get high levels of stress in the non-flexible components. I am not aware of ANY tank failures in Jab. cabin-mounted tanks even in really severe cases of crash damage where the airframe has been really severely damaged: ( and if anybody has contrary information, I would be really interested to know, as I have an LSA55). For example see: http://www.jabirucrash.com/jabiru-crash-site-photos.html

 

If you are going to build a new tank, it is important to be 'sympathetic' to the nature of the airframe in which it is mounted in relation to the materials you might choose for its construction. The expression 'horses for courses' applies.

 

 

[Litespeed]

As a extra for protection- which can be used on any type of tank is amazingly Ute bed liner. Eg Rhino liner or Line-X.

 

This will if applied correctly at 6mm thick, will literally make your tank Bomb proof. Or when combined with Kevlar - ballistic penetration proof. I do not suggest you shoot your tank but it will survive it and not leak.

 

Check out vids on youtube, such as this

 

 

 

[Geoff13]

Made tank extensions for my Xair tanks ( resined onto the back of the existingtanks like a camel hump)...vinyl ester and fibreglass. Light, no problems and now 6 years old and going perfectly. I use both mogas and avgas. No leaks. Carbon fibre is great but its a bit like squashing a bug with a sledgehammer for normal and small size tanks. Make sure you get all of the air out when laying up and bobs your proverbial.....

So what capacity do you have now. Do you have any photos?

 

 

[robinsm]

I will post some, I went from 54 lts over 2 tanks to 93 lts over the 2 tanks.

 

 

[Kitplanes]

Hi Steve, you can use Derakane 470, it's what we use at the factory and has excellent properties. You can use Kevlar but we use glass (160gr and 300gr) in combination. When you use alli then turn some rings on the lathe around the surface that will be glassed in. This will help prevent leaks and will also make the fittings adhere properly.

 

 

[Kitplanes]

http://www.nuplex.com/composites/products/browse-products/epoxyvinylesterresins/novolacbasedepoxyvinylesterresin/derakanemomentum470-300

[Steve L]

Hi Stefan, just spoke to Nuplex and they told me that Derakane 470 is about the best composit to use for aircraft

 

tanks so I'll order some, you don't cut any corners eh. . . Would the seat be the same material as I'm going to fit two

 

compartments under seat cushions to carry the heavier equipment like a few tools, tent and tie down pegs, couple cans of bakes beans, spam and don't forget the Vegemite haha! I'm presently in central QLD working at the moment which now they look like extending a few extra weeks buggarit, so no building for awhile.

 

Steve

 

 

[Oscar]

Steve - be a bit careful about storing lumpy and sharp stuff beneath your seat. In the event of a seriously hard landing, it is the deflection of the seat that may well be the difference between being a paraplegic and being able to walk out of the arrival bruised but complete. 25-30mm of Temper-foam (or Memory-foam) will NOT save your spine in a solid crash, and if the seat structure collapses or deflects sufficiently to put your spine in contact with something really hard, you could be in DEEP physical trouble.

 

I can't remember offhand the FAA requirement for travel for an impact-absorbing seat structure, but vague memory says around 12cm! Seriously, don't have sharp/hard stuff anywhere less than at least 50-80mm underneath your spine..

 

 

[Litespeed]

Hi Steve,

 

I am with Oscar- do not put baked beans etc under your seat- unless you want it permanently inserted in your rear end upon crashing.

 

Seats are another area that can be done much better than is average in light aircraft. Have a read through the entire thread on HBA as mentioned above- lots of seat design discussion. The thread is long but worth it.

 

 

[Steve L]

Of course I should have know that, thanks fellas.

 

 

[Kitplanes]

Very sound advice regarding the seats. It's one of the reasons we do not install a small toolbox there. You luggage bay can structurally carry 40kg so rather use that. (Staying within the CG limit off course). I will e-mail you a spreadsheet of the Explorer CG and you can then fiddle with that a bit. Installing a slightly heavier prop will also expand your CG envelope a bit more. (Obviously loosing a bit in MAUW)