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Old 01-18-2011, 02:13 AM   #1
vicky_molokh
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Default [Spaceships] Gasbag system - size modifier?

Greetings, all!

Spaceships #7 has stats for gasbags, and RPK mentioned that (for example) an SM+10 craft with appropriate-sized gasbags is the SM of folded, deflated state. So . . . what is the necessary SM adjustment for craft featuring gasbags?

Thanks in advance!
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Old 01-18-2011, 05:11 AM   #2
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Default Re: [Spaceships] Gasbag system - size modifier?

Quote:
Originally Posted by vicky_molokh View Post
Spaceships #7 has stats for gasbags, and RPK mentioned that (for example) an SM+10 craft with appropriate-sized gasbags is the SM of folded, deflated state. So . . . what is the necessary SM adjustment for craft featuring gasbags?
Assuming the rest of the craft is "typical", you could use the relative static lift of the contents of the gas bag and the craft's (full) mass to determine the volume of the gas bag; then… Well, that's probably going to dwarf the rest of the craft, so you could take that volume to the equation in VE, or figure some proportions and use the table in Basic.



But Spaceships does not adjust for volume; its SMs are determined by mass. Consider these two craft:

SM: +8 Ballistic Escape Pod, 1 core Habitat, 19 Exotic Laminate Armor systems

SM: +8 Park Trailer, 1 core Engineering Room, 19 Open Space systems

Those should not have the same SM for targeting purposes.

Now, somebody could make a list of systems and the volume they come out to under VE(which would require some extrapolation and interpolation), and you could then add up volumes and use the equation in VE to find the SM. But that's a bit too complex for Spaceships.
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Old 01-18-2011, 06:04 AM   #3
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Default Re: [Spaceships] Gasbag system - size modifier?

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Originally Posted by jacobmuller View Post
Vehicles 3e rates hot air as 60x volume and lifting gas as approx 15x.
S7 needs 20% of vehicle as lifting body.
Am I wrong to think
Hot air: .2 x 60 + .8 x 1 = 12.8 x volume or SM+2 or 3?
Lifting Gas: .2 x 15 + .8 x 1 = 3.8 x volume or SM+1 or 2?
Well, that 60 is 60cf/lb. The rest of the ship isn't 1cf/pd; the spaceship in VE has a density of 11.93463pd/cf.

So, let's see… a 300T ship, as in, with the gasbag deflated, requires 600 000lb of lift in 1G. At 60cf/lb, that requires 36 000 000cf. Using the spaceship in VE as "typical" density, the volume of a 300T non-gasbag ship would be about 50 274cf. The non-gasbag portion of the ship with a gasbag is about 40 219cf. So about ×717 volume, or +6 SM by the table in VE. (+5.7 SM by the equation, which I guess I derived from the table.) The same with lifting gas is about ×180 volume, or +5/+4.5 SM.
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Last edited by Darekun; 01-18-2011 at 06:31 PM. Reason: Slept, checked my math.
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Old 01-18-2011, 03:03 PM   #4
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Default Re: [Spaceships] Gasbag system - size modifier?

Yes, ever so slightly failed to read...
Would 300 tons @ 1 ton per cubic metre be about 11,000cf?
If so, I get lifting gas +6SM and hot air +7SM? Probably wrong again.
Funniest thing is, the first time I worked it out, I used the wrong scaling (read linear for volume) which gave the sort of numbers I just got...

But, Wow, an increase by a factor of 1,000? And that's just for enough gas to lift the ship.
And a zeppelin would be SM+11 (30ton? They had about a 9 ton cargo capacity...)
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Old 01-18-2011, 04:06 PM   #5
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Default Re: [Spaceships] Gasbag system - size modifier?

Quote:
Originally Posted by Darekun View Post
Now, somebody could make a list of systems and the volume they come out to under VE(which would require some extrapolation and interpolation), and you could then add up volumes and use the equation in VE to find the SM. But that's a bit too complex for Spaceships.
It must be possible to make a quick-and-dirty solution that's better than the RAW, at handling these kinds of "edge cases".
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Old 01-18-2011, 04:22 PM   #6
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Default Re: [Spaceships] Gasbag system - size modifier?

Quote:
Originally Posted by vicky_molokh View Post
Greetings, all!

Spaceships #7 has stats for gasbags, and RPK mentioned that (for example) an SM+10 craft with appropriate-sized gasbags is the SM of folded, deflated state. So . . . what is the necessary SM adjustment for craft featuring gasbags?
+5 to +6 (x300-x1,000 volume); the assumed density of normal craft is on the order of 320 kg/m^3 (20 lb/cf), the density difference between a gasbag and the surrounding air is on the order of 0.5-1 kg/m^3 depending on what the gasbag is filled with, so the gasbag needs to be 320-640x the volume of the craft.
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Old 01-18-2011, 05:34 PM   #7
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Default Re: [Spaceships] Gasbag system - size modifier?

You could just treat them as Exposed Systems (p. SS66), targeted at the spacecraft's SM +3.
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Old 01-18-2011, 06:53 PM   #8
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Default Re: [Spaceships] Gasbag system - size modifier?

Quote:
Originally Posted by jacobmuller View Post
Would 300 tons @ 1 ton per cubic metre be about 11,000cf?
Ish, yeah. Try Google Calculator :J

Quote:
Originally Posted by jacobmuller View Post
If so, I get lifting gas +6SM and hot air +7SM? Probably wrong again.
Pretty close; I just double-checked my numbers above, and so long as my assumptions are valid, it holds. (Note that among those assumptions are operation in 1G and 1atm.)

Quote:
Originally Posted by jacobmuller View Post
But, Wow, an increase by a factor of 1,000? And that's just for enough gas to lift the ship.
Sounds about right. Pick a hot air balloon, note that the balloon is thicker in Z than the gondola, and compare the total volume to the gondola volume.

Quote:
Originally Posted by Peter Knutsen View Post
It must be possible to make a quick-and-dirty solution that's better than the RAW, at handling these kinds of "edge cases".
Plural? Doubt it. This particular edge case is so extreme that it dwarfs any normal variation, but what happens if you add radiator fins to the Ballistic Escape Pod?

Also, I suspect something like the volume-adding system would probably be needed as a stepping stone to such a system.
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