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Fuel Tanks

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paul.mcallister

Joined: 09 Jan 2006
Posts: 177
Location: Waukesha, WI USA

Posted: Sun Jun 17, 2007 5:25 pm Post subject: Fuel Tanks

Hi all,



I recall watching Ivan Shaw's impromptu demonstration of a Landrover driving

over a Europa fuel tank.



I remember thinking at the time, wondering if it would fare as well if it

was full of liquid.  I suspect that the hydraulic pressure would easily

rupture the tank, no matter what it was constructed of.



I would offer up a hypothesis that a full tank in a Europa that was

subjected to a high G load would rupture, but one that has had fuel burnt

off would have sufficient airspace in it that could be compressed and not

cause the tank to burst.



Just a theory.



Paul

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asarangan(at)YAHOO.COM
Guest

Posted: Sun Jun 17, 2007 7:02 pm Post subject: Fuel Tanks

I am not sure about that theory. It is easier to crush an empty soda

can than a full one. Air is more compressible than liquid. When a full

tank is impacted, the liquid will transfer that energy to all surfaces

with little or no compression. A partial tank on the other hand will

compress until the air inside is squeezed to match the liquid. By then

the tank might have undergone enough bending stress to break it. Again,

just a theory.



--- Paul McAllister <paul.mcallister(at)qia.net> wrote:



 	  Quote: 	
		   

 <paul.mcallister(at)qia.net>

 

 Hi all,

 

 I recall watching Ivan Shaw's impromptu demonstration of a Landrover

 driving

 over a Europa fuel tank.

 

 I remember thinking at the time, wondering if it would fare as well

 if it

 was full of liquid.  I suspect that the hydraulic pressure would

 easily

 rupture the tank, no matter what it was constructed of.

 

 I would offer up a hypothesis that a full tank in a Europa that was

 subjected to a high G load would rupture, but one that has had fuel

 burnt

 off would have sufficient airspace in it that could be compressed and

 not

 cause the tank to burst.

 

 Just a theory.

 

 Paul

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davidjoyce(at)doctors.org
Guest

Posted: Mon Jun 18, 2007 12:52 am Post subject: Fuel Tanks

Paul, Being in the process of building a long range fuel tank at present, I

have had to look out the VLA regs for this, which will be applied by the PFA

before approval. Key requirements are: The tank needs to be able to

withstand a pressure of 24 kPa (about 3.48 lbs/sq. in) without rupture or

leakage. The tank must have an expansion space of minimum 2% of volume. The

tank must be restrained to resist inertial forces in forced landings, etc -

I have not got precise figures to hand but believe this to be to withstand

10g.

         3.48 psi may not sound a lot but a tank with a side measuring 18 by

24 ins will need to withstand1503 lbs on that side to give an idea of the

strength required, and a 110 litre tank weighing about 200 lbs full should

have a restraining system of 2000 lbs strength. I wonder whether  any system

sitting in the luggage bay can meet these requirements, as opposed to one

sitting in the passenger seat and using the passenger seat belt system as

restraint

 Regards, David Joyce G-XSDJ

---

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asarangan(at)YAHOO.COM
Guest

Posted: Mon Jun 18, 2007 11:11 am Post subject: Fuel Tanks

I think you have a point. I just spoke to one of my students who does

failure analysis of aircraft parts. They have giant machines that pulls

and pushes a part until it breaks, and they take high speed photos

during the process for analysis. He seems to think that the tank being

full or not can go either way depending on the construction. In an

empty tank, the impact will tend to buckle the walls until the

structure collapses. In a full tank the fluid will equalize the forces

on all contacting surfaces, and will cause it to fail at the weakest

point, usually a weld joint. He seems to think that on welded

structures a full tank is probably worse, in agreement with Paul's

message.



--- Jeremy Davey <europaflyer_3(at)msn.com> wrote:



[quote] 

 <europaflyer_3(at)msn.com>

 

 Andrew,

 

 I think Paul is right. There is a direct parallel in the mechanism he

 refers

 to in the Concorde accident in Paris - there debris hit the very full

 tank

 causing a segment of the wall to be blown out at the weakest point.

 It might

 not have happened had the tanks not been brimmed.

 

 With the Europa tank, what the Land Rover unscientific demonstration

 tells

 us is that the tank can flex hugely without splitting. What any

 materials

 scientist will tell us is that the material will have a limit to the

 tension

 loads it can take: it is possible for a full tank taking an impact to

 split

 in tension; that tension arises because the contents will not allow

 if to

 flex.

 

 Taking your can analogy: fill it with a dense foam (compressible) and

 throw

 it against a wall, hard. It will likely not split. Fill it with

 liquid and

 throw it similarly: it will likely split.

 

 If the above stands scrutiny, it does tell us that brimming the tanks

 "just

 because there is space so I might as well use it" is not always the

 wisest

 policy if that fuel is not required.

 

 Regards,

 Jeremy

 

 --

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