Mark Simmons (scorpio@best.com)
Sun, 29 Oct 2000 11:29:51 -0800


Lim Jyue writes,

>>The mass ratio specs provided for Z and ZZ mobile suits - which
>>represent the ratio of full weight to unfueled weight (i.e. base
>>weight plus weapons)
>
> I don't recall ever seeing such figures -- not that I was actively
>looking for them -- but where did they originate from?

  They were originally published in Z and ZZ reference books from The
Anime, NewType, Animedia, et cetera. I don't think most of the fans &
publishers ever figured out what they signified, and they've been omitted
from recent reference books like the Entertainment Bible series and MS
Encyclopedia... and since most publishers just get all their specs from
the MS Encyclopedia nowadays, as well as echoing all its numerous errors,
they've also lost this useful data.

  Basically, "mass ratio" is a rocket-science term. It indicates the
ratio between the fully-fueled and un-fueled weight. There's a formula -
9.8 m/sec^2 x specific impulse x natural log of mass ratio - that
predicts what the final velocity of any rocket-propelled vessel will be.
(Or, as Dafydd would put it, the total "delta-v". :-)

  From a specs perspective, you can divide the full weight by the mass
ratio to find the weight without propellant. The resulting number is
always greater than the base weight, and the difference between these two
numbers is the weight of the mobile suit's carried weapons. Take the Rick
Dias as an example...

  Full weight = 54.7 t
  Dry weight = 32.2 t
  Mass ratio = 1.43

  Thus, unfueled weight is roughly 38.3 tons. The net weight of
propellant would be 54.7 - 38.3 = 16.4 tons, and the weapons would be
38.3 - 32.2 = 6.1 tons. (In most cases, the weapon weights seem to be
whole numbers of tons. I've experimented with different values, and
almost all the published specs work with whole numbers - so you still get
a mass ratio of 1.43 if the Rick Dias has exactly 6.0 tons of weapons.)

  You can perform this calculation for any mobile suit from Z Gundam or
Gundam ZZ, and the results are consistent enough that it's easy to
extrapolate to other series. I've wasted many hours playing with weapon
weights and mass ratio values for One Year War mobile suits. :-)

> Oh, now I see where I went wrong. To get T/W ratio in Gs, I'll need
>to up the ratio I have by a factor of 9.8.

  No, not necessary - the numbers you have are _already_ expressed in
terms of Gs. To convert Gs to meters/second^2, _then_ you'd multiply by 9.8.

-- Mark

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Mark Simmons / scorpio@best.com / http://www.gundamproject.com/
"If you can kill it, it's not a god, just a good old-fashioned monster."

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