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welded fuel tank?

Spartan939

Spartan939

Member
I've been lurking here for a few years now, and one thing that i haven't seen come up is if it is possible to weld the fuel tank,
I can understand for most people this would not be realistic due to cost and skill required to do so, but i happen to be an aluminum TIG welder :D so my question is if there is any reason that a welded tank would be out of the question.

i'd rather work with the heat of a weld and never have a leak then that goo stuff.
 
Jesse
I have no expertice as to whether a welded tank is a good or not good idea.
If it turns out it is a good idea, there is probably a substantial demand out there for an aluminium TIG welder to supply such a standard size welded tank, plus an option for an after market larger tank then the standard RV-12 tank.
I look forward to expert replies to your question
John

Melbourne
Australia
 
Not with the "as engineered" materials

Jesse,
The issue would be with the 2024 T3 alloy. It is not considered a "weldable" alloy. Welding would change it's characteristics. 6061 T6 would allow welded tanks to be made. However, thicker material would have to be used, to compensate for the reduced strength [for aircraft use] that 6061 T6 offers.
So, you could do it, but it would require careful engineering to calculate the thickness needed with a weldable alloy. The fuel tanks would also be slightly heavier.
Another possible issue would be how the welding would hold up over time, due to thermal cycling of the metal. Parking on a hot, sun lit ramp, then climbing to 12,000 feet would stress the welds. I suspect that sometime during the life of the plane, a leak issue would occur. That's just my opinion, and worth what you paid for it.
Charlie Kuss
 
Tank

Jesee points out something some of us have discussed before; namely, that a drop-in replacement tank that had a 25-gallon capacity would be welcome. An extra hour of range would make the plane a lot more adaptable to cross county use...fewer stops. I think the existing aluminum used for the stock tanks migh be a bit too thin for welding, but an after market drop-in tank could use a thicker metal. I am still looking for someone to offer something.
 
I used to be certified aircraft tig welder

Weldable aluminum alloys are 1100, 3003, 4043 and 5052. The 6053, 6061 and 6151 can also be welded if they are re-heat treated. TIG would be preferred for anything under .125". It helps to pre-heat the aluminum and tooling to 350-400F prior to welding. It is possible to distort the heat-affected zones. During WWII gas shielded arc welding was very popular due to speed.

RV-10 tanks cannot be welded due to their size, complexity and the need for them to flex with the wing. A welded tank would crack in a short period of time.

I don't have the RV-12 tank dimensions or location in the plane so can't offer any advice. If located in a rigid area(no flexing) I would run it by Van's engineers then go for it.

As far as cost for a TIG welder to build with the proper machine/skills/materials it would be cheaper. As far as Van's having them built and shipped to the builder it would cost more. The materials take up much less space than a completed tank in storage or shipment.
 
so my question is if there is any reason that a welded tank would be out of the question.
Click to expand...

You mean other than the tendency of them to burst open along welded seams (those being the "weakest point" when subjected to the hydraulic forces induced by impact applied to a vessel filled with a non-compressible fluid? Honestly, single ply fuel tanks are just asking for trouble but they persist due to cost issues and ease of construction.
 
There's also the issue of the change itself - it would remove the aircraft from being an E-LSA. It would be an E-AB, I think.

Dave
 
A better solution?

IMHO, a molded polyethelyne fuel tank "a la Sonex" would be a better solution to the fuel tank issues.
 
a molded polyethelyne fuel tank "a la Sonex" would be a better solution to the fuel tank issues.
Click to expand...

You still get the same issue of hydraulic rupture (although somewhat lessened dependent upon how it's molded) not to mention if you have a fire start from a source other than spilt fuel the tank will melt. It's also more prone to abrasive failure if the aircraft impacts and skids along a hard surface, such as a runway.
 
SteveinIndy said:
You still get the same issue of hydraulic rupture (although somewhat lessened dependent upon how it's molded) not to mention if you have a fire start from a source other than spilt fuel the tank will melt. It's also more prone to abrasive failure if the aircraft impacts and skids along a hard surface, such as a runway.
Click to expand...

if you have a fire that melts the fuel tank i think the airplane is already totaled and you are either totaled as well or have un-assed the fire zone.

aluminum if it skids down the runway will get worn through probably as fast as a plastic tank, some plastics actually resist abrasion wear fairly well. i didn't think the tank really was that exposed to the exterior to be a skid plate anyway...
 
if you have a fire that melts the fuel tank i think the airplane is already totaled and you are either totaled as well or have un-assed the fire zone.
Click to expand...

...or you've been knocked out and are unable to escape but could otherwise survive. It's not a "you either survive to evacuate or you're dead on impact" sort of dichotomy. The use of non-protected fuel lines and single wall (or fiberglass lined metal) tanks likely explains in part why there is such a high rate of post crash fire in EAB crashes. The number of folks running their engines on mogas probably contributes to this as well, but that's a topic for another discussion.

aluminum if it skids down the runway will get worn through probably as fast as a plastic tank, some plastics actually resist abrasion wear fairly well. i didn't think the tank really was that exposed to the exterior to be a skid plate anyway...
Click to expand...

You'd be surprised. That's one of the major drawbacks of a lot of EABs is that they tend to crack up rather easily and expose things that aren't overtly exposed to begin with. Then again, I'd still rather fly in almost any homebuilt over a Cirrus for that very reason. There's a reason why some of my friends who work for the NTSB and FAA not so jokingly refer to Cirrus aircraft as 'Ronsons' after lighter brand whose slogan was (is?) "It lights the first time, every time".
 
so anyway, you mention parts get exposed to runway surfaces, ok. but you don't mention the difference in abrasion resistance from al to whatever plastic would be used.

and in a fire, say you are knocked out. Do you really think a fire directly behind your seat that is hot enough to melt plastic isn't going to kill you by poisonous gases or heat? the scenario where you are in the plane with a hot enough fire to melt the tank just doesn't seem very livable to me, even before the tank melts
 
but you don't mention the difference in abrasion resistance from al to whatever plastic would be used
Click to expand...

Are you a materials engineer because I can get pretty technical on this and was trying to refrain from pointing out that polyethylene doesn't have better abrasion resistance than aircraft grade aluminum and making you look rather foolish. You can take most industrial grade polyethylene containers, put a weight in them such as water and drag them behind you at a walking pace on concrete and have a visibly appreciable loss of thickness.

Do you really think a fire directly behind your seat that is hot enough to melt plastic isn't going to kill you by poisonous gases or heat?
Click to expand...

Probably not (assuming that the aircraft stays intact enough for the fuel tank to actually remain in its original position) but then again a crash hard enough to knock a person unconscious is going to make it pretty **** likely that the fuel lines are going to separate and that fuel directly behind your seat is going to wind up in the cockpit with you. The point that fuel systems can and should be improved stands. That is my point, nothing more and nothing less. For starters, having a fuel tank behind the seat is questionable from an engineering standpoint but I digress.
 
SteveinIndy said:
Are you a materials engineer because I can get pretty technical on this and was trying to refrain from pointing out that polyethylene doesn't have better abrasion resistance than aircraft grade aluminum and making you look rather foolish. You can take most industrial grade polyethylene containers, put a weight in them such as water and drag them behind you at a walking pace on concrete and have a visibly appreciable loss of thickness.
Click to expand...

I am certainly not a materials engineer. i hearby give you permission to make me look foolish, i would like to see an examination of the difference in abrasion resistance between the two materials at the thicknesses that would be used.
 
2 concerns

WingedFrog said:
IMHO, a molded polyethelyne fuel tank "a la Sonex" would be a better solution to the fuel tank issues.
Click to expand...

I'm not familiar with the fuel tank location in a Sonex. For wing mounted tanks, the material would need to have UV protection. I think that the effects of the fuel on the plastic would mean that sort of fuel tank would have a shorter life expectancy, compared to aluminum/ProSeal.
Charlie
 
With all this talk of alternate tanks we need to remember that RV tanks are a structural component. I suspect that the tank area endures significant twisting forces.
 
we need to remember that RV tanks are a structural component. I suspect that the tank area endures significant twisting forces.
Click to expand...

Seriously? Just out of curiosity why would they design it as a structural component from an integrity standpoint?
 
i hearby give you permission to make me look foolish, i would like to see an examination of the difference in abrasion resistance between the two materials at the thicknesses that would be used
Click to expand...

I'm not a materials engineer either although I am an engineer in training and materials factors very heavily into the education I am getting.

I don't know of a strict comparison between the two from a scientific standpoint although I will call around to try to find it once I get back from Oshkosh, but I will tell you what. Later this year we (myself and a couple of colleagues) are going to be testing the integrity of some standard designs versus what we are currently developing. I will try to include a poly tank and an aluminum welded tank and do an abrasion test so we will have some hard and fast numbers under simulated crash conditions to compare.
 
SteveinIndy said:
....I will try to include a poly tank and an aluminum welded tank and do an abrasion test so we will have some hard and fast numbers under simulated crash conditions to compare.
Click to expand...

I wasn't thinking of comparing to a welded tank (which i think would have thicker walls), i was thinking of comparing to the standard vans sheet metal with sealant tank. It would be interesting to see what you come up with in a comparison of any of them.
 
Missed the point.

I think everyone has missed the point here.

The pseron who posted this thread is a welder.

Welders like to weld. They don't like to pro-seal. He did not ask to redesign the brakes, or get an injection system. He wants to weld on his plane.

This has nothing to do with an improvement its just someone wanting to do their trade. I am sure if he was a cloth guy he would be asking has anyone ever done the mep kit with cloth.

Re-design has a purpose, he just wants to do his thing.
 
GusBiz said:
I think everyone has missed the point here.

The pseron who posted this thread is a welder.

Welders like to weld. They don't like to pro-seal. He did not ask to redesign the brakes, or get an injection system. He wants to weld on his plane.

This has nothing to do with an improvement its just someone wanting to do their trade. I am sure if he was a cloth guy he would be asking has anyone ever done the mep kit with cloth.

Re-design has a purpose, he just wants to do his thing.
Click to expand...


Finally.
Thank you.
 
Tanks

GusBiz said:
I think everyone has missed the point here.

The pseron who posted this thread is a welder.

Welders like to weld. They don't like to pro-seal. He did not ask to redesign the brakes, or get an injection system. He wants to weld on his plane.

This has nothing to do with an improvement its just someone wanting to do their trade. I am sure if he was a cloth guy he would be asking has anyone ever done the mep kit with cloth.

Re-design has a purpose, he just wants to do his thing.
Click to expand...

I concure...!!! Exactly what the gentleman asked!
 
thank you all for the information. I'm definitely giving this a try. I'm not worried about lsa, e/ab issues. I'm going E/AB anyway because i like the freedom of choices that comes with it. van's kit is excellent but not perfect. any design can benefit from trying something new.
i'm going to try for a 25-30 gallon tank. it will probably be a few lbs heavier plus the added fuel weight. but with the added power of the viking engine. this probably wouldn't make a huge difference. more of an incentive to eat healthy and get more exercise :)
a good weld is stronger then glued rivets any day.
 
Good luck with the build.
Any chance of getting some pictures posted of the tank when its all done?
You just may have a market out there for it .......... ya' never know.
 
Baggage limit

Bit of a digression, but a bigger tank when full will obviously weigh more. Does anyone know what drives the 50 lb weight limit in the luggage area (conservatism?)? Under some loading conditions it may well be possible to add weight here without impacting the max gross or the CofG.

Thanks...Keith
 
the tank on the '12 is in the cabin, so i assume CofG will not be an issue per say.
correct me if I'm wrong but an extra 5 gallons of gas would be about 30 lbs i believe. this probably would have to be negated from baggage unless you or your passenger weigh in at less then 190 lbs each.
i know i can't speak for everyone, but losing 30 lbs for another hour of flight would be a welcome tradeoff to me
 
SteveinIndy said:
You mean other than the tendency of them to burst open along welded seams (those being the "weakest point" when subjected to the hydraulic forces induced by impact applied to a vessel filled with a non-compressible fluid?
Click to expand...

only a poor/inexperienced welder makes a weld weaker then the parent material

David Paule said:
There's also the issue of the change itself - it would remove the aircraft from being an E-LSA. It would be an E-AB, I think.
Click to expand...

i plan on going e-ab anyway. i like the idea of building my plane the way i like it, since its gonna be mine and all :)
 
Bursting? The current issue of Sport Aviation says Maule fuel tanks are welded aluminum (page 52.) Regarding weight in the baggage area, the floor support on both sides is symmetrical. A full tank weighs ~123 pounds. However, there seems to be some clearance underneath the tank, it is supported by 2 AN3 bolts to the main fuselage member and one AN4 bolt at the back to the rear bulkhead. Anything heavy placed on top of the tank is thus supported by the tank and by those bolts (and what they are connected to), not the baggage floor. Run your own scenarios.
 
Welded Fuel Tank

Go for it. No reason not to try a welded fuel tank for the RV-12.

We used to use 5052-H32 when I designed highway tanker trucks and trailers. English racing cars of the 1960s used welded aluminum tanks on the spaceframe cars. They held up pretty well to crash impacts. Early ones were just plain aluminum. Later ones had fiberglass overlay outside and fuel cell foam inside. My Cessna 150 has welded aluminum tanks. They are made from two pressings, a top and a bottom with a turned out flange on the centerline which is then welded. My tanks are over 40 years old and there were over 15,000 Cessna 150s and 152s manufactured.

Consider making the RV-12 tank with turned out flanges wherever it is welded, this makes a pretty easy weld.
 
Spartan939 said:
the tank on the '12 is in the cabin, so i assume CofG will not be an issue per say.
correct me if I'm wrong but an extra 5 gallons of gas would be about 30 lbs i believe. this probably would have to be negated from baggage unless you or your passenger weigh in at less then 190 lbs each.
i know i can't speak for everyone, but losing 30 lbs for another hour of flight would be a welcome tradeoff to me
Click to expand...

Why don't you put a aux tank?
 
We made an aux tank and it works great! It can be taken out to the gas station at your destination for fueling at out stations and used as a fueling tank or put back in for travel. There is a thread somewhere on this forum.
 
Diamond DA20 Welded Tank

This is probably not relevent, but I currently fly a Diamond DA20-C1. It's fuel tank is behind the seats, like the RV12. However, it extends the full width of the baggage compartment, so that baggage compartment is not very deep. It is a welded 25 gallon tank. As far as I know, it has proven to be very reliable with no instances of post-crash fires.
 
Slips

How long do you fly in a slip? Probably way less than the time it takes to use the fuel already in the lines
 
How long do you fly in a slip?

All the way from the end of the base leg to the runway, and sometimes that's not long enough. In those cases a stopped engine might be just what I need to hit the numbers ;-)

Cheers...Keith
 
Check the summit racing web site

There are a number of aluminium welded fuel tanks through RCI and Summit Racing. Take a peek...most are 1/10 th of an inch thick...welded...my next 12fuel tank will be too!

Jay Sluiter
N124CS
Albany, OR
 
That depends.

David Paule said:
How much unusable fuel is there in a slip?

Dave
Click to expand...

That would depend on the number of internal baffles that were installed in the tank. The wider and shorter the fuel tank is, the more critical it would be to install baffles in the tank. A fuel tank which spans the entire width of the fuselage, but has no internal baffles, could also create weight transfer issues.
Charlie
 
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