Originally posted by RichardPrice
And I totally disagree - whats it going to do, rise 30 ft and *then* decide to burn? I think not.
Again with the 'above the plane' rubbish - if its bioling off of spilt liquid hydrogen, the plane and ground is most likely going to be soaked in
it. Its not going to be burning above the plane, its going to be burning around the plane.
Another extract from another paper that has studied this then.
Will hydrogen fueled aircraft be safe?
AIAA - 82 - 1236
"Liquid hydrogen was shown to pose substantially less hazard to passengers as well as to persons and property in surrounding areas in the event of a
crash. This conclusions stems from the following considerations: one, in event of a crash in which passengers can reasonably be expected to survive
the impact, LH2 tanks are less apt to be ruptured, thus minimizing spillage potential; two, in the event a tank is ruptured and fuel is spilled,
LH2 evaporates almost immediately, the gas becomes buoyant very quickly and it dissipates into the atmosphere so rapidly the time and the area exposed
to flammable mixtures are both quite small compared to the other candidate fuels;
three, if the spilled fuel is ignited, the duration of the
hydrogen fire would be so brief that it would not heat the fuselage to the point of collapse, as would be the case with the other fuels and the
heat-affected area would be substantially smaller.
For reference the other fuels considered were liquid methane, Jet A and JP-4.
There are more details in the paper dealing with the spread and vapourisation of the fuels - in each case considered, the models predicted the LH
spill radius was between 3.5 and 9.5 times smaller than JP-4 and Jet A. The time to max spill radius was also much lower, between 25 and 125 times
quicker than both conventional fuels. All a result of quicker dissipation into the atmosphere.
If your going to persist in saying that hydrogen won't quickly vapourise and rise above the aircraft, your going to have to provide some evidence of
studies indicating such is the case (thats 2 papers I've cited versus nothing but inherent belief).
I am reading your stuff, you obviously are not reading mine - replacing JetA with LH does not reduce the weight, while it does increase the volume.
You have three to four times more LH to do the same job, which means three to four times more fuel tank capacity.
I have said in terms of energy content, if the airframe weight was the same you would carry the same regardless of the fuel used.
I have also pointed out, that since LH will require more weight for the fuel tanks, you will need more energy, and hence more LH to fly the plane the
Safe is a matter of degree, theres nothing to suggest a plane flying using hydrogen is any *more* safe than a current JetA fueled aircraft.
Except pretty much everything I've read on it.