Fighter fuel criticals

[Acolyte]

So, I asked this in the rules forums, but they're busy making cool products so I thought I'd ask here in hopes of a faster answer.

When you get a fuel critical on an aerospace fighter and it doesn't blow up, are there any other effects? There would seem to be, as it's one of the forced withdrawal conditions listed, but I can't seem to find any other effects.

Anyone got an idea?

   - Shane

[NullVoid]

The effects of critical hits on aerospace units is described in page TW240; there's also a Fuel Tank Leak/Explosion Table on page TO136, but that's related more to refueling station buildings rather than unit tanks.  According to Rules As Written (RAW), the tank seems to be self-sealing, so if it doesn't blow, the hole is immediately plugged. 

You can always houserule an arbitrary number of thrust points to be expended each round by units that suffered a fuel tank critical hit.  That'd force such a unit to hightail it out of there or end up either standed in space or spread in a stain across a few kilometers of ground terrain.

[Arkansas Warrior]

ASF "fuel" isn't actually fuel as we think of it, but rather reaction mass that's driven out the back of the ship to push it forward.  It could well be something completely inert like helium, so I wouldn't be as worried about it exploding as much as I would running out of propellant before I got to somewhere I could land and get it fixed.

[Weirdo]

Except we know for a fact that it explodes, otherwise it wouldn't have rules stating it does.

I believe that even when no boom occurs, a fuel crit drains 2d6 points of fuel.

[Arkansas Warrior]

Huh.  Shows you how much I game on the aerospace side of things.  So nobody learned from the Hindenburg disaster?

[Auren]

The fuel itself doesn't even have to be flammable. It could just be that when the tank is breached, the pressure is terrifying. See Mythbusters Scuba tank versus the brick wall.  :o

[cray]

ASF "fuel" isn't actually fuel as we think of it, but rather reaction mass that's driven out the back of the ship to push it forward. 

Yes, it is fuel. The hydrogen used by aerospace fighters is fused in large quantities in their fusion rockets, producing helium and (unfused) hydrogen exhaust. It thus serves as both reaction mass and propellant. See p. 141 Strategic Operations.

[CloaknDagger]

The fuel explosions have to be pressure. Yes, hydrogen explodes, but in space there would be no oxygen to explode with.

[Acolyte]

Except we know for a fact that it explodes, otherwise it wouldn't have rules stating it does.

I believe that even when no boom occurs, a fuel crit drains 2d6 points of fuel.

Cool, thanks! Do you happen to know where the fuel loss rule is? I can't seem to find it in the current volumes....

   - Shane

[Weirdo]

...turns out I was wrong on the fuel loss. I must have been remembering how it was back in the days of AT2r.

[Acolyte]

Doh! OK, so the tanks are self sealing and/or re-enforced. Well, they'd really have to be. Still, I don't see why a fuel tank hit would then necessitate a retreat if you survive the hit.

Maybe I'll house rule something like NullVoid suggested.

Thanks
   - Shane

[Tai Dai Cultist]

Except we know for a fact that it explodes, otherwise it wouldn't have rules stating it does.

I believe that even when no boom occurs, a fuel crit drains 2d6 points of fuel.

A boom doesn't mean the fuel is explosive.

A tank of any inert material will explode if it's sufficiently pressurized when damaged.
(Given the difficulties ASFs have in packing their mass into their fluffy dimensions, those tanks must be VERY pressurized indeed)

[pensiveswetness]

can you imagine how you do confined space maintenance on ASF's? or do OSHA standards differ greatly from House to House?  >:D

[Acolyte]

A boom doesn't mean the fuel is explosive.

A tank of any inert material will explode if it's sufficiently pressurized when damaged.
(Given the difficulties ASFs have in packing their mass into their fluffy dimensions, those tanks must be VERY pressurized indeed)

True enough, like a balloon, except a lot more pressure in a confined space. One thing though, I've always assumed the tonnage for "fuel" also included the tonnage of the tanks used to contain said fuel. Robust tanks in and of themselves are heavy. So 80 points of thrust isn't 1 ton of hydrogen, but maybe a tank weighing 900kg and 100kg of hydrogen packed into it. Keeping 100 kg of hydrogen liquid takes a robust tank. :)

So, in essence, you've got a chance to crack the tank, then it goes BOOM due to pressure? I can see that. Also means you're not losing fuel if it doesn't crack, although the hit might activate an overpressure vent to keep the BOOM from happening, and that's why you lose some fuel....

Have to think about that.
   - Shane

[pensiveswetness]

True enough, like a balloon, except a lot more pressure in a confined space. One thing though, I've always assumed the tonnage for "fuel" also included the tonnage of the tanks used to contain said fuel. Robust tanks in and of themselves are heavy. So 80 points of thrust isn't 1 ton of hydrogen, but maybe a tank weighing 900kg and 100kg of hydrogen packed into it. Keeping 100 kg of hydrogen liquid takes a robust tank. :)

So, in essence, you've got a chance to crack the tank, then it goes BOOM due to pressure? I can see that. Also means you're not losing fuel if it doesn't crack, although the hit might activate an overpressure vent to keep the BOOM from happening, and that's why you lose some fuel....

Have to think about that.
   - Shane

i like that idea. It on itself could be fluff specific to a type of fighter (or manufacturer, with their line of products using that particular type of Fuel Containment system on their products)

[cray]

A tank of any inert material will explode if it's sufficiently pressurized when damaged.

For example, here's what happens when a 3000psi natural gas tank lets go a car, note the lack of flame damage:
http://4.bp.blogspot.com/-fK_KBbAEXPs/TlJPWtuJqHI/AAAAAAAAAHo/3th_eTsFFCw/s1600/cng-car.jpg

(Given the difficulties ASFs have in packing their mass into their fluffy dimensions, those tanks must be VERY pressurized indeed)

Condensed states of matter (i.e., solids and liquids) don't compress significantly. Thus, there's no appreciable* compression of liquid hydrogen to even several million psi, and BT spacecraft use liquid hydrogen as reaction mass. You could significantly compress gaseous hydrogen, but the limit of pressurization is liquid density. You'd get a larger enhancement in hydrogen density by switching to a slushy or fully solid (icy) state, which can use tanks that are very light due to their low pressure.

*Some tens of percent.

So 80 points of thrust isn't 1 ton of hydrogen, but maybe a tank weighing 900kg and 100kg of hydrogen packed into it. Keeping 100 kg of hydrogen liquid takes a robust tank. :)

The shuttle's external tank uses about 10 tons* of tankage and insulation to keep 100 tons of hydrogen liquid. It's not particularly robustly built since its pressurization limit, with a factor of 2 safety margin, is about 35psi. It's made of thin aluminum and fancy styrofoam. The driving factor behind its mass is still the pressurization, which greatly exceeds other loads (even weight during the shuttle's 3G launch). Switching to a slush or hydrogen ice tank at a few psi would let you use a very thin-walled, ultra-light tank and, better yet, conform to unusual aerospace fighter shapes. Higher pressures tend to use spheres or cylinders (or fancy lobed things like the VentureStar's composite hydrogen tank abomination) to minimize hoop stresses from pressurization and thus structural weights.

*After removing the external tank's intertank, SRB thrust member, LOX tank, and other trimmings to guess the hydrogen tank's mass.

[Lord Cameron]

The fuel explosions have to be pressure. Yes, hydrogen explodes, but in space there would be no oxygen to explode with.

Unless of course the pressured fuel line vented into the cabin/interior or perhaps the damage also ruptured an oxygen line.   ;)

[DaveMac]

Unless of course the pressured fuel line vented into the cabin/interior or perhaps the damage also ruptured an oxygen line.   ;)

Nasty!

[Lord Cameron]

Nasty!

Well we've (most unfortunately) seen the consequences of what happens with minor* problems on the shuttle with failed O-rings or foam strikes -- now imagine that someone was actually shooting at the shuttle engines during launch.  :o

*dismissed as a "minor" problem until the disaster happened of course.