Call me a worrying ninny but isn't the fuel tank a bit exposed on your average seven? I'm concerned that a rear impact would burst the tank
and cover me and my passenger with it's contents.
Has anyone thought about this and come up with any good ideas? (Other than moving the tank, which isn't possible in my case). I was browing the
MNR website the other day and read something about a deformable structure - presumably some extra tubes - used on the Vortx for this purpose.
I've heard they use some fancy foam filled tanks in racing, but hey are expensive ( try demon tweeks ) or a much cheaper solution is to fit
cortina brakes. This works on the theory that the guy behind you will have stopped long before you do
If you were feeling paranoid you could use a bagged fuel cell inside the aluminium shell.
But it isn't a real problem (for some value of real problem) as the car that burst the tank would be embedded in your spine before it caught
fire.
7's aren't the safest design in a shunt.
My chassis is outside this moment for storage, I turned it upsides down to so it rests on the roll bar and noticed that at that angle any fuel leaking
from the tank would pour on to the drivers head 
how lovely 
Yeah it's a crazy old place to put a tank and I thought the landys were bad with their ejector seat
did you know that when cars were first being made to run on petrol, you had to obtain a licence to handle the stuff due to the extreme danger...how
times have changed 
[Edited on 18/12/07 by Mr Whippy]
I think you are being overly cautious. Petrol tanks only explode on impact in amercian tv and films, if petrol was that easy to ignite, there would be no need for the AA, RAC or Green flag.
quote:
Originally posted by 02GF74
I think you are being overly cautious. Petrol tanks only explode on impact in amercian tv and films, if petrol was that easy to ignite, there would be no need for the AA, RAC or Green flag.
If someone has just rear ended you the last thing i would be worrying about would be gettting covered in fuel, as the next thing they are going to hit
it u!
Have you thought about side impact protection yet? 
quote:
Originally posted by RichieW
Have you thought about side impact protection yet?
quote:
Originally posted by ash_hammond
quote:
Originally posted by RichieW
Have you thought about side impact protection yet?
Dont forget air bags
quote:
Originally posted by RichieW
Have you thought about side impact protection yet?
(I have this obsession with side pods ) but it didn't work out as I could
find no way of dealing with the exhaust system. I'll post a pic tonight to show you what it looked like. say's Mr twelve crashes and counting
This is where we get into the old chestnut of passive vs active safety.
Passive safety - crumple zones, air bags, side beams, roll cages etc.
Active safety - better breaking, abs, acceleration and steering agility.
Passive is good once you're in the accident, Active means you don't have the accident in the first place...
7's (and classic mini's) have better active safety so aren't in so many accidents, but once you've hit/been hit things are worse
than if you are in a modern tin-top.
The car that's hitting me has to travel through a couple of feet of steel tube, suspension gubbins, diff and the mighty strength of my ali
bulkhead and seats before it'll touch me or my passenger. The fuel tank, on the other hand, is the first solid thing it'll meet. So whilst
I'll be demolished in any kind of high-speed impact, I think there are a whole range of situations where I could be the receiver of a nice
refreshing petrol shower yet be otherwise uninjured.
I guess it comes down to how much force it would take to burst a tank and whether there's any practical way of mitigating the risk.
Foam fuell cells sound good, but presumably eats a huge amount of tank capacity and is not cheap?
quote:
Foam fuell cells sound good, but presumably eats a huge amount of tank capacity and is not cheap?quote:
Not so, I have this stuff in my Falcon's tank, it looks very like bath sponge and weighs very little. The biggest down side is it take absolutely ages to fill the tank, I mean like 5 minutes to put 30 litres in
[Edited on 18/12/07 by Mr Whippy]
iank - 18/12/07 at 04:02 PMDon't think I agree about there being much of anything to absorb a crash between the fuel tank and your back, in fact some of those 1" steel tubes could even turn into spears. But there you go, if you're happy that's a good thing
Rubber bladder fuel cells are best. Can't find an easy UK link, but this US one has the theory and they have a catalogue full of pictures etc.
http://www.racerpartswholesale.com/fsafe12.htm
Foam to fill fuel tanks is easily available - even in little cubes to stuff down the filler pipe, but it can degrade over time and doesn't do much more than preventing it sloshing around. It takes up a surprisingly small volume of the tank.
bonzoronnie - 18/12/07 at 04:16 PMIf you are fabricating your own tank.
How about making the tank base from thinner material !!?
Design the inner baffle plates so as they will puncture the bottom of the tank in the event of a rear impact.
Just a thought
Ronnie
Bluemoon - 18/12/07 at 04:25 PMMy indy has a mod at the back to take it's roll bar back braces, and spare wheel carrier. It also has the old hoop around the top of the boot (as I'm using a ali back panel). There is a H arrangement of RHS with a spare wheel before you get to the tank...
In addition I have a removable tow bar across the back from 50mm x 50mm RHS (4mm thick), in a U that sits in a socket of RHS, weld to a strengthening plate at the back on each side of the chassis. The U is held in with 2 12mm pins on each side.
So I think this could stop someone crushing the fuel tank. Trouble is there is so much metal I will probably get bad whip lash in the event of rear end crash!
Dan
britishtrident - 18/12/07 at 04:32 PMNothing you can do will protect the tank in a Locost the up side is it so low it will probably not get craushed, however you can cover the outside of the tank with grp (best to use woven fibre glass) to prevent the tank splitting. This tip used to be in the MSA Blue Book.
Syd Bridge - 18/12/07 at 05:20 PMThe only problem with laminating grp over a tank, is that it will delaminate with time. And if any moisture gets in between, you've got a bigger problem than when you started.
One way I've seen used in my youth was to put foam sheet around the outside of the tank. If the tank is hit, the impact will be absorbed to a certain extent, and the foam stops the contents spewing everywhere, giving you time to get clear.
Cheers,
Syd.
Confused but excited. - 18/12/07 at 05:36 PMquote:
Originally posted by Mr Whippy
(I have this obsession with side pods
Who would have guessed?
JB - 18/12/07 at 05:44 PMBasically if you are worried about vehicle safety drive the biggest newest car around or a Saab.......
For good fuel system integrity you need a deformable structure to absorb energy and the petrol tank enclosed in a survival area to minimise fuel tank crush. The pipes must also be protected. There should be no sharp protrutions towards the tank or pipes. This will be difficult on a Seven.
Your best bet would be a bladder cell (such as ATL) with foam filling but this will cost in excess of £1,000.
If you could get the tank down the tunnel and behind the seats then that would be a positive step.
Side pontoons are a good idea for side impact.
Forget about airbags. An airbag system is a finely tuned interaction between vehicle pulse, steering column colapse and occupant kinamatics. There is no way you could get a safe system on a DIY basis.
kb58 - 18/12/07 at 07:10 PMI used a real fuel cell in my mid-engine Mini. Steel box, rubber bladder, and foam filled. It is placed approximately where the transmission goes in a Locost. It cost US$800 for a 10 gallon unit.
BTW, the foam in the cell is not to prevent fuel slosh, but to prevent fuel spray from being ejected violently in a crash. In fact I can hear the fuel sloshing around when it's partly full. I can fill the cell as fast as I want and the foam has never impeded fuel flow.
kb58 - 18/12/07 at 07:12 PMquote:
Originally posted by JB
Side pontoons are a good idea for side impact.
And if they're integrated into the design correctly they can add greatly to chassis stiffness.
Hammerhead - 18/12/07 at 07:23 PMI have thought about this to.
My only conclusion was to make a Kevlar box for the tank to live in, hopefully this would be strong enough. Could even cocoon the tank in a kevlar and expandable foam crush structure.
Syd Bridge - 18/12/07 at 07:41 PMIf you're gonna make a kevlar box, then you may as well go the one step on, and get a bladder to put in the box. Do away with the separate tank you're trying to protect, and ending up with a much better setup.
Cheers,
Syd.
procomp - 19/12/07 at 08:55 AMHi Having spent nearly 20 years with cars of this type crashing on a regular basis at quite high speed and sometimes above 100 mph. You learn a few things.
1. Never bolt a petrol tank direct to a frame/chassis. Mount it with straps over it. Gives it more chance to move rather than just getting sheared of it's mountings witch will always cause it to lose it's contents.
2. If independent mount it above the diff area. Not ideal for CoG. But it dose give better protection. And it is how the likes of westfield HAVE to mount it for there race championship to satisfy the MSA.
3. if live axle mount is either above the axle or a combo of in front and above. Again not ideal for CoG but it has proved to work very good on our own race cars.
4. Always if you can use a roll-bar that has rear stays as these will add strength to the rear section. But will still allow the rear to become a crush able area with the tank mounted above the rear diff.
5. Side impacts or a T-bone situation are not as bad as you might imagine. This is due to the fact that these type of cars are relatively light and means that they are more lightly to just get pushed sideways rather than remain stationary and absorb the impact. However side protection is required to stop the offending vehicle from reaching you. But the rear wheel/tyre will take a lot of the impact unless you get hit further forward toward the leg area. In which case one of the better ideas is to use the diagonal bar that most now fit as std ( and fitted by ourselves to every racing kitcar we have prepared for 20 years) to the top frame at the bottom of the dash area that goes to the tunnel/intermediate crossbar above your feet. This proved to be a good way of protecting that area from deforming when one of the locost race cars was hit in the drivers side by 4 cars all doing in excess of 50 mph. The car was relatively untouched and the driver only suffered a badly bruised foot from where it caught the brake pedal. Car was repaired and is back racing. But of-course if you are being assaulted by a large 4x4 then threes not a lot that will really help you if it's trying to climb over rather than push your vehicle.
HTH Cheers Matt
AdamR - 19/12/07 at 10:07 AMThanks for that Matt. Lot's of interesting stuff there. No tales of locost fireballs included which must be a good thing!
I'd originally planned to build a tank to fit above the diff, but I don't think I've got enough space there to accommodate my rather tall in-tank pump. Will look at it again.
02GF74 - 19/12/07 at 11:01 AMquote:
Originally posted by procomp
Hi Having spent nearly 20 years with cars of this type crashing on a regular basis at quite high speed and sometimes above 100 mph.
some good points but presumably these are based are locost vs locost crashes?
On the road which I imagine is most folks concern, we are most likely to be hit by a montego, 4x4, lorry, bus etc that weigh considerably more than a locost and are much stronger.
the bottom line is, as someone already stated, drive a SAAB if safety is a concern.
AdamR - 19/12/07 at 11:27 AMI really don't understand that attitude. Obviously no one would reasonably expect to build a seven that is as anywhere near as safe as a bigger, heavier, more modern car. Therefore it's not worth thinking about at all?
It's a bit like saying "I notice that you're car has a passenger seat. What's the point in that when you could have bought a bus?"
[Edited on 19/12/07 by AdamR]
kb58 - 19/12/07 at 02:34 PMIt's worthwhile dicussing this. I think that far more frequent than catastrophic accidents will be fender benders or getting rear-ended at a light at 5-10mph. In this last case is exactly where the tank is most vulnerable. Having the tank compressed at the back pressurizes the contents until a seam bursts, spraying fuel into the air... bad news!
OTOH, many (most) "real" cars have bumpers so high that they'll completely miss the gas tank, and may in fact try to roll up and over the car
"You're jumping from a plane at 10,000 feet, why bother messing with a parachute that may not work." I'll take my chances with the chute.
procomp - 19/12/07 at 03:07 PMHi one other area of the fuel tank that is always going to be a problem. Is if you have the tank filler mounted to the body and connected to the tank via a joining hose. This will always be the weak link when the body and tank move in different directions.
This is why for MSA events the tank filler must not be connected to the bodywork of protrude through the bodywork.
Cheers Matt
David Jenkins - 19/12/07 at 03:37 PMI worried about this for a while - then decided that a balanced approach was required (for me, that is).
1. It's much, much safer than the motorbikes I used to ride (400+ miles per week).
2. It will be slightly less safe in an impact than an ordinary car.
On that basis, plus my intention to drive it like I used to ride the bikes (i.e. everyone else is an idiot, plus the 'see and be seen' philosophy), then I can accept the risks.
David
[Edited on 19/12/07 by David Jenkins]
kb58 - 19/12/07 at 03:55 PMquote:
Originally posted by procomp
Hi one other area of the fuel tank that is always going to be a problem. Is if you have the tank filler mounted to the body and connected to the tank via a joining hose. This will always be the weak link when the body and tank move in different directions.
Real fuel cells have a rubber flap that closes off the filler hose in case the cell is compressed or the car ends up upside down.
JB - 19/12/07 at 05:00 PMAs has been stated it is risk management.
A home built car will never be as safe as a developed and tested production car. Especially considering that the US fuel integrity requirement is a 1368kg honeycomb barrier travelling at 88kph hitting the rear of a stationary car 70% offset.
Production cars are designed to have the filler pipe detach from its mounting/s to the body.
Most production tanks also have a valve at the entrance of the tank, that prevents reverse flow in a roll over. These would be quite easy to retrofit into an aftermarket tank.
vinnievector - 22/12/07 at 12:45 AMGood discussion so far , some good ideas there.
I think you have two problems one is impact resistance and the other is fuel containment.
I to had some concerns with fuel splashing around in the event of a rear shunt ,so i put a stainless rear bulk head between driver and tank this should contain any fire long enough for you to get out and also wrap the tank in a fire blanket this should contain most of the fuel .
not sayin this by any means will save your life but some is better than nowt .
the impact side is a matter of weight to beef up the rear structure and is down to you .
[Edited on 22/12/07 by vinnievector]
[Edited on 22/12/07 by vinnievector]
Doug68 - 22/12/07 at 05:42 AMI'm looking into using a plastic fuel cell such as those made by JAZ. If I can get one to fit in my design.
If I had a bigger budget I'd go for a bladder tank, but the bladders have a fixed lifespan too.
Plastic tanks do not have seams to split and are highly deformable so I think that they are a good compromise between a plain welded item and a full race tank.
kb58 - 22/12/07 at 05:53 AMExcept that the plastic used is (I think, polyethylene) which is very slippery. What I mean is, you can easily stick a knife through it. This very topic is touted as a reason by the fuel cell companies why you're supposed to use only "real" cells.
It's always something.
Doug68 - 22/12/07 at 06:12 AMI guess you cant win.
KB58 what did your cell cost BTW?
kb58 - 22/12/07 at 06:08 PMAbout US$800. All my gloom and doom aside, I don't know if I'd spend that much next time. I may concentrate on protecting it to the point that I feel comfortable with a plain box (though it will still have a roll-over valve and foam.)
[Edited on 12/22/07 by kb58]