Mounting method - 100litre LPG tank on 110 wheelbox

LPG cylinders don't actuall do a lot of propelling (the pressures a bit low), but if they're emitting liquid LPG they do a lovely line in cryogenic burns.

Sheesh! It's not going to go - I'm gonna put gaffer tape all over it :0)

In message , Badger writes

[sniperoo]

Out of curiosity, any takers on how many g is developed by our friend's half-full 100-litre LPG tank when his LR is in a head-on collision with, say, a Mondeo sized car, with each vehicle doing 20mph? More than 7g?

Well, a lot of cars can reach 100% braking efficiency when doing a decelerometer test for an MOT, and that's done at 20mph, 100% efficiency for a given vehicle mass being equivalent to 1g I assume?? (assumption, the mother of all f*ck-ups!). Highest reading I've seen recently was a P38 rangie which achieved a decel rate of 155% (1), but that's emergency stop stuff, not head-on collision. I'd imagine the impacting of a Mundane might add another 2g, possibly, bringing the total to approx 3.5g?? Badger.

(1). Most vehicles will give considerably higher brake force on the road than on the test rollers, due to weight transfer under braking.

1g is an acceleration of 32 feet per second per second (approximate round figure) and 20mph is just short of 30 feet per second. So we're not going to be far wrong if we say 32 feet per second for the vehicle speed, which simplifies the arithmetic slightly.

v**2 = 2*a*s

v=32 a=32 s=distance. Re-arrange and we get:

v*v/a = 2*s which means v/2 = s

So 1g at 20mph is a stopping distance of 16 feet, plus thinking.

Doubling the acceleration halves the distance.

Follow this through, and a 7g limit on those tank fittings gives you a distance of 28 inches, which is about what you might expect for a car's crumple zone.

Fortunately, there is an answer to this apparent safety problem.

And if I knew who was driving over that crest into a crossroads at 60mph I'd tell them to take their bloody foot off the accelerator too.

If I've done the sums correctly, a 7g stop is the result of stopping from 30 mph in around 4.3 ft. That doesn't seem too improbable for a head on into a standard collapsible car.

Hmm. So I need to fabricate a mount to survive +7g (extra for safety margin) longitudinal deceleration and, say half that for the inverse and the same for lateral and vertical.

It's going to take some intelligent triangulation back to the chassis to do that - considering that the extremities of the mount will be 18" above and outboard of the chassis rail ...

It just so happens that while I was sitting on the porcelain recliner in the 'library' at home this morning (on the bog), I saw something interesting in the LRM November 2003 issue. On page 67, there's a picture of a wheelbox mounted tank in the back of what looks like a Series from the side windows? Or maybe a panel with aftermarket side- windows. Anyhoo, (million-to-one shot) anyone know anything about it?

/Simon

I'd think you needed more than this, humans survive much more than this

So it'd be a shame if they were then crushed by a heavy object.

AJH