Re: FTFB Turn Arcs

On Fri, 27 Nov 1998, Laserlight wrote:
> > "Realistically", a change of facing for a starship takes on the
order of
> > one minute to execute.
> Based on what?  I'm not arguing, just asking.

hmm, yes. to say 'realistic' implies that you have figures for mass,
size
and thrust in real-world units for starships. if i recall, there was
only
weak consensus last time this was debated.

>  It would make more sense to
> me that a dreadnought isn't going to be able to flip as fast as a
corvette.
>  More mass, and a longer axis to rotate.

i'm not so sure about this. as part of my continuing program to
rehabilitate the battleship, i gave this some thought.

executive summary: big ships turn faster than little ships.

you will be pleased to hear that i will spare the algebra this time! my
physics is a bit weak as far as angular motion is concerned, though, so
if
the wiser on the list could check this, it'd be nice.

the speed of turning depends on the ratio of turning thrust to the
angular
inertia of the ship. turning thrust depends on drive power, which
depends
on drive mass, which (for ships with a constant fraction of their mass
in
the drive), so turning thrust is proportional to mass. assuming all
ships
are similar shapes (eg spheres, cylinders of a given length-to-radius
ratio, scale models of halibut, etc) angular inertia is proportional (i
think) to the radius of the object. radius is proportional to the cube
root of the mass. thus, the speed of turning varies as mass (for thrust)
divided by cube-root-of-mass (for inertia), which gives the two-thirds
power of mass. according to this simple (but, as far as i can see,
waterproof) analysis, larger ships turn faster than small ships.

in short, you have two choices: (a) rethink your assumptions on size and
maneuverability (b) ignore physics in favour of playability. i find the
second option very attractive myself.

>  If it is below the grain of the
> gamescale, that's okay, but I'm curious to see why.

herein lies the rub; if the ft2 turn is indeed 15 minutes, then any ship
is going to be able to execute a 720 without too much difficulty. maybe
we
should give up any limitations on turning? it would make things a little
simpler and more hard-sf.

Tom