Homebuilt Fuel Tank ("Cell") Design and Fabrication

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Mac790

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re: Homebuilt Fuel Tank ("Cell") Design and Fabrication

If I can't restrain an engine that weighs the same as me, how on earth am I going to restrain ME in a crash?

Wow, Jarno I didn't know that you weight over 200kg (E-racer has Lycoming 0-540) :gig: but seriously, like I said in context of fuel cells, attach (design) it properly. They (E-racer designers) didn't, and this is what happend. There is nothing wrong with things behind your back, every F1 car (just watching race) has engine and gearbox behind driver, and I haven't seen any problems related to that.

SVSUSteve said:
Honestly, in a lot of these case where the family goes looking for a medical excuse, it's because they don't want to admit that their loved one screwed up.
Yes, I have same opinion, but the point was to show how important it's to design "attachments" properly. Even small improperly mounted battery at +20g's can make serious damage.

Seb
 
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Vigilant1

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re: Homebuilt Fuel Tank ("Cell") Design and Fabrication

I was wondering, are going to build an airplane from a kit, or do you think about a "custom" design. If you are going to design it from scratch, you could design it with fuel in the wings, and eventually put a small fuel cell in the fuselage, which willl feed an engine.
I'd love to design a plane and I definitely have ideas I'd like to try, but I think I'll probably be using a standard design and modifying it. I haven't settled on a design. I like the Sone*x a lot, it is very close to what I need for the type of flying I'd like to do. I think the Thatcher CX5 is going to be a very nice plane, but I wish it were stressed for mild acro. But neither these planes nor any other airplane is quite perfect. As designed, the Sone*x carries all its fuel between the instrument panel and the firewall. There are lots of opinions pro and con on header tanks (if the plane can operate on gravity feed alone--and the Sone*x can). A Sone*x with 10 gallons in each wing would be a pretty good single-place cross-country machine (better yet with a small turbonormalized engine!).

Slosh baffles: Yes, I plan to put 'em in to reduce "regular" slosh but also to reduce peak hydraulic forces on the leading tank wall in an impact.

Thanks for the links, interesting testing.
Drop testing: The US Army standard for helicopter fuel tanks used to be 65 feet (which exceeded the civilian testing height), and they used water instead of fuel (denser, so it stressed the tanks a bit more--plus lots safer for the testers). I think/hope it's gotten more stringent than that.

A good friend of mine crashed three USAF helicopters of various types and for various reasons (tranny failure,etc) over the course of his career--and he's still in good shape. The DoD has done a pretty good job of protecting crews in those contraptions.
 
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karoliina.t.salminen

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re: Homebuilt Fuel Tank ("Cell") Design and Fabrication

Are you trying to solve the right problem?
I was looking at fuel cell fabrication and the challenge was that there was a membrane (proton exhange membrane fuel cell)
required for the function of the fuel cell that costed millions for a very small piece and was only available in minimal scientific sample sizes. I do not know a way to produce (or have it produced by some company) such membrane and it is not commercially available, especially at prices that would lead to practical implementation possibilities. The problems associated looked big enough challenge for not being worth looking any further.

Or are you considering using high temperature fuel cells? How are you going to achieve +800 degree Celcius temperature in flight without melting or burning anything?

I am not wanting to be a nay-sayer for fuel cells - if you would have a solution in mind for either of these (IMO huge) problems (that are not safety but actual fuel cell function related challenges), I would be very interested to hear about it. If you can produce a prototype fuel cell (even on the ground, and not requiring flying it) with a budget of up to couple of thousands of dollars rather than tens of millions to hundreds of millions of dollars, that would be totally awesome.
 

autoreply

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re: Homebuilt Fuel Tank ("Cell") Design and Fabrication

Karoliina, Vigilant is going for the "real" fuel cell, the fuel "storing" ones, not the power producing ones ;)
 

Vigilant1

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re: Homebuilt Fuel Tank ("Cell") Design and Fabrication

Moderators: I caused the confusion with the unintentionally ambiguous title for this thread. If desired, please revise to something like "Homebuilt Fuel Tank ("Cell") Design and Fabrication"

Mark
 

skeeter_ca

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Wouldn't some kind of blow-off valve be useful. During an impact the fuel tank could deform and as pressure built up the blow-off would open and purge the fuel overboard. Of course that in itself could lead to other problems. Or purge the fuel into some kind of bladder to keep it contained.

skeeter
 

SVSUSteve

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skeeter_ca said:
Wouldn't some kind of blow-off valve be useful. During an impact the fuel tank could deform and as pressure built up the blow-off would open and purge the fuel overboard. Of course that in itself could lead to other problems. O

Purging it overboard is a good way to aerosolize it and nearly guarantee a fire. There are some in the safety community who argue that Cirrus actually went with wet wings (which is effectively a system that relies on "dumping the fuel" in a crash scenario) to try to ensure a post-crash fire so that the lacking structural design of the cockpit would be largely hidden from anyone interested during an investigation.

skeeter_ca said:
r purge the fuel into some kind of bladder to keep it contained.

In airliners, they use something kind of like this called a "bay" but it really would take up more space and add more weight than just building a "basic" tank that isn't likely to rupture in a reasonable crash. Also a secondary "overflow" bladder would have to be similarly constructed to a crashworthy primary tank and itbecome an area that could accumulate water condensation from the atmosphere and cause more problems than it solves.
 

bmcj

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Honestly, in a lot of these case where the family goes looking for a medical excuse, it's because they don't want to admit that their loved one screwed up.

Not as likely in this country. If they call it a medical cause, then it's all due to pilot incapacitation, whereas if they say it was the plane or some other external source, then they have an avenue to a lawsuit. Even in an over-gross situation as you described, a good lawyer can spin a jury in the plaintiff's favor.
 

SVSUSteve

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Not as likely in this country. If they call it a medical cause, then it's all due to pilot incapacitation, whereas if they say it was the plane or some other external source, then they have an avenue to a lawsuit.

Well, it happens all the time in the US. Probably at least half of the crashes that I deal with, I hear the family say something like "Dad was such a great pilot. He never would have stalled/flown into a mountain/etc" and start looking for an excuse. Often this message is put forth by the family's lawyer especially if the case involved non-family passengers to minimize legal liability. You put those two together (perceived liability and not wanting to admit that your dad/brother/mother/sister was, as a point of fact, a marginal pilot) and you hear this a lot more often than one would assume.

In fact, in one deposition I gave for a case, I spent the better part of three hours being grilled over whether I could tell if the injuries to the pilot were inflicted peri-mortem or post-mortem. The defense was trying to argue that the pilot was already dead or close to it when all of the evidence (presented by two pathologists and myself) said he was as alive as you or I at the time of impact. This is one reason why I have come to despise most liability and personal injury attorneys.

Even in an over-gross situation as you described, a good lawyer can spin a jury in the plaintiff's favor.

Most judges honestly put their foot down on crap like that. The public only hears about the few times you get a judge with his or her head up their ass. Usually those are quickly reversed on appeal.
 

gschuld

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I apologize for the minor thread drift, but on the subject of fuel tank safety considerations...

Does anyone have an opinion on the Aeroquip breakaway fuel hose fittings?

http://www.herberaircraft.com/pdf/Oth Prod_Eaton Couplings (new)/Break-away Coupling Catalog.pdf

They are light in weight, and combined with the recommended AE701 flexible fuel hoses with the stainless braided outer cover allows flexibility in case of structural deformation during a crash. This should go a long way toward preventing or at least drastically reducing fuel spillage during a crash. This does not however help if the fuel tanks themselves rupture!

Using these fittings and hoses would make it a little safer though for a situation with fuel in the wings that must have fuel lines routed through the cockpit, correct?

George
 

SVSUSteve

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gschuld said:
They are light in weight, and combined with the recommended AE701 flexible fuel hoses with the stainless braided outer cover allows flexibility in case of structural deformation during a crash. This should go a long way toward preventing or at least drastically reducing fuel spillage during a crash. This does not however help if the fuel tanks themselves rupture!

Aeroquip has a good reputation with regards to fuel lines. I have never heard anything about their breakaway fuel valves (although these may be the valves currently called "Stratoflex" by Eaton since the catalog you posted appears to be rather old) but if they are of similar quality, I would definitely consider them.

gschuld said:
Using these fittings and hoses would make it a little safer though for a situation with fuel in the wings that must have fuel lines routed through the cockpit, correct?

Right, but I would still put some structure around the lines to shield them further if absolutely necessary to route them through the cockpit (which is seldom necessary for anything other than convenience).
 

GESchwarz

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I kinda like the idea of an integral fuel tank located between the fwd and aft spars, outboard of the fuselage at least three feet.

The tank to be lined with a single ply of Kevlar cloth and an elastomeric material like Proseal. This liner would serve the purpose of preventing or at least restricting the flow of fuel from the tank in the event of a rupture of the aluminum tank itself.
 

Vigilant1

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I kinda like the idea of an integral fuel tank located between the fwd and aft spars, outboard of the fuselage at least three feet.

The tank to be lined with a single ply of Kevlar cloth and an elastomeric material like Proseal. This liner would serve the purpose of preventing or at least restricting the flow of fuel from the tank in the event of a rupture of the aluminum tank itself.
Do you mean "integral" to the wing (e.g the forward wall of the tank is the main spar, the rear wall of the tank is the rear spar) or integral to itself? Those parts are going to flex and bend a lot in a crash, I'd think you'd significantly reduce the chance of fuel leakage with a tank that was independent from the aircraft structure.

Kevlar--I like the strength a lot, but wonder how it will hold up to fuel, and if it is compatible with Proseal. It is absorbent stuff. Even Kevlar body armor has to be replaced regularly due to contamination/weakening from sweat, body oils, etc. If you aren't going to have the inner layer be a true bladder (i.e. reduce in size as fuel is used in order to reduce the volume of flammable vapors in the tank), maybe consider putting the Kevlar/Proseal layer outside the AL tank to serve as the container in the event the AL tank is compromised.
 

DesertFlier

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What about building a tank using Kevlar or carbon fiber with a flexible resin? That would make the tank flexible and crush/cut/burst resistant. The problem is figuring out what resin to use.
 

SVSUSteve

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What about building a tank using Kevlar or carbon fiber with a flexible resin? That would make the tank flexible and crush/cut/burst resistant. The problem is figuring out what resin to use.
I would give Kevlar preference for the middle layers (to give "structure" to the tank for ease of handling) but on the inner and outer layers, I would use mil-spec 1050 denier double weave ballistic nylon as the primary fabric for cut or burst resistance. As for "resins", on the outer and inner (penetration and rupture prevention) layers it might be plausible to use an urethane elastomer similar to the sealants used for more traditional fuel tanks.

Most "resins" as we think of them in composite aircraft is not the best idea if you're trying to produce a flexible tank. They are simply too rigid and prone to more or less brittle fracture or delamination. The other issue is whether you really want a truly 'flexible tank'. You really have to find a happy medium between a glorified water balloon (very flexible) and a rigid tank as we traditionally think of fuel storage. If you make the tank too flexible, it poses a greater risk of hydraulic blowout opposite the point of impact not to mention it would be a pain in the butt to install in the aircraft. We built a "bag" style tank of Kevlar, ballistic nylon and a for drop testing and it ruptured after a 15 ft drop and gave us a 60+ ft geyser from the tank's contents (in this case, it was water dyed to make it more visible). I should also point out that it was a major pain to hoist it and move it for the drop, akin to moving a 20 gallon lightly reinforced water balloon (or a two-man tent filled with water with the frame attached). A design using a more rigid design but built to crumple without rupturing was dropped from a height that exceeded even the US Army's somewhat rigorous drop testing standards and some of the more "inventive" torture tests we could come up with.
 
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We built a "bag" style tank of Kevlar, ballistic nylon and a for drop testing and it ruptured after a 15 ft drop and gave us a 60+ ft geyser from the tank's contents (in this case, it was water dyed to make it more visible).

Way off topic but this reminded me to ask:

Are you recording these tests with high speed camera? If so I'd be interested in what hardware you are using. I'm looking for an adequate slow motion digital camera for a reasonable (translation - as cheap as I can get it) price to record some similar testing.
 

SVSUSteve

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Are you recording these tests with high speed camera? If so I'd be interested in what hardware you are using. I'm looking for an adequate slow motion digital camera for a reasonable (translation - as cheap as I can get it) price to record some similar testing.

We have recorded them but I don't know what camera was used specifically. An engineering student friend of mine (actually the husband of an ex-girlfriend I have remained friends with) provided the cameras and operated them. From the way he described them, it sounds like they were the property of the department he is affiliated with and he simply kissed the ass of the right folks to get permission to use them. I keep telling him he needs to kiss up some more to get me access to a wind tunnel (even if I have to nominally make the Praetorian's aerodynamic testing a student's project).

However, I do believe one can rent the sort of technology you are looking for. That would honestly probably be the cheapest way to obtain this sort of thing under normal conditions. Another option might be looking into local colleges or universities with a film or audiovisual program to see if they might be willing to partner with you in exchange for the "hands on" experience for their students. Often they have some really nice technology at hand.

You would be amazed what you can get access to simply by asking nicely in a lot of cases. Our two series of drop tests were conducted using either a crane or a fire department ladder truck. In the former case, the fact that we wanted to break something ended up with the company agreeing to do it for a minimal fee and the cost of a good lunch so long as we agreed to do the test on their property (to prevent the need to drive the crane elsewhere, thereby saving fuel costs). The volunteer fire department offered their services simply for a small donation ($100) and a lunch of pizza from one of the better places in the area. The announcement that we were going to break stuff for the test and that there would be food present resulted in us having all the manpower and equipment we could need.
 

Mac790

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Ok, my last response to this topic. Just few things.

First, when I asked about size of your fuel tank, it wasn't actually only about crash safety issue (as it's not problem at all, if designed correctly) I don't know how many changes do you want to do compared to the original design. But for such a small airplane like Sone*x you may or may not have a problem with your C.G, if you decide to mount the fuel tank behind your back rather that in front of you, especially if it was designed that way. Of course you could redesign it... This is another reason, why the best place for the fuel is in the wings, as close to C.G as possible. For some ideas take a look at Midget Mustang (later they introduced also wet wing option), and Rv's family, but all those planes have fuel tanks front to the spar.

Resins, ethanol, etc.

I really don't know why someone would like to use epoxies, for their separate fuel tank instead of Vinyl esters resins. I could understand it, if someone was going to build composite wet wings, all those issues with second bonding of Vinyl esters, etc. but for separate fuel tanks, I really don't get it. Vinyl ester resins are much better for chemical applications, than epoxies (unless we are talking about exotics one, that I haven't heard of), not only because I'm saying it, Orion was saying it also.
Orion said:
In my opinion, the best resin choice for fiberglass fuel tanks is Vinylester.
If it's still not enough, take a look at those specifications, (ethanol page 13) DERAKANE Chemical Resistance guide pdf free ebook download from k.b5z.net

One of the best resin, that you can actually get is Derakane 470-300. There were some issues earlier with vinylester resins combined with carbon fibers etc. But it seems, that there is not a big problem any more (based on Orion post).

Some papers
Mechanical behavior and damage evolution in E-glass vinyl ester and carbon composites subjected to static and blast loads

there are also methods of additional surface preparation

CARBON FIBER-VINYL ESTER INTERFACIAL ADHESION IMPROVEMENT BY THE USE OF A REACTIVE EPOXY COATING

etc

Another advantage of VE is HDT (high distortion temperature), even for room cured resin, for some +100 C deg. So in short, if you put a composite fuel cell in an aluminum wing, you could paint that wing with whatever color, without worrying that it might become really hot inside of it (wing).

Of course it's really depend from what type of fuel you are going to use. Someone might say, epoxy resin and proper sealant. But even good sealant can't give you guarantee. Take a look here, Auto fuel troubles I've seen more cases like that, but unfortunately forum I was seeing it, is gone, so I can't give links for it.

Just in case if you decide to build ballistic proof tanks :gig: Woven fabrics for ballistic protection

Testing.

Assuming that you are in very early stage at the moment (still deciding what to build), probably I won't be far from true, if I say that you won't fly your airplane in the next 4-5 years. Make tests now. Call guys at Ashland (derakane producers), ask them what is the best option for your application. Buy samples of resin (even here I can buy 1kg without any problem at all). Make specimens, and put them into a jar (turn jar upside down, to be sure is properly sealed, and nothing is going to vapor quickly) with different petrols (you could replace petrol every couple months or so, to make those test even more realistic). If you make samples big enough, you could cut them in half, put one half into jar with petrol, other into for example a cardboard box (hide it from UV). And compare it after a year, two, etc. Thanks to that you will have first hand experience, even before making molds for your tank.

It really amaze me, that some people here and not only here first builds things next, test them. Personally I have two rules, first I always calculate/test everything before, not after. Thanks to that I'm able to build things cheaper and better, just recent tool (3 shafts [4140 heat treated] driven system, 1.1KW, 340-350 kg, tube roller bender, 25-30 pages of hand calculations and some FEA) that I had to build for myself. Total cost of completed tool with cover, painted, etc 1700-1800 euro, for very same (slightly thinner shafts) tool I would have to pay here 5000 euro, and just for comparison local guys asked me about 1000 euro, just for bending a couple of pipes, I laughed straight at them.
Second, well I'll keep for myself:).

Seb
 

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