weight and balance?

A thread of 2 messages, 28 November 1992 to 30 November 1992, in the order they were sent.

#4993 weight and balance?

Jeff Zeitlin · 28 November 1992

  I was chatting with my father the other day, and we started
  discussing his favorite hobby - flying (he has a private pilot
  license).  One of the things we were discussing was the necessity
  and principles of weight and balance calculations.  The past couple
  of nights, I've been thinking about that, and realized (for no
  particular reason) that this concept seems to be absent from
  Traveller/Megatraveller.  I'd like some ideas on how to add it. My
  reasoning is as follows:

  Obviously, an aircraft, it's important.  You have a limited amount
  of power, and you must maintain a certain airspeed to stay up in the
  sky.  So, your weight must be below a certain limit, which, if you
  go above that limit, will cause the aircraft to be unable to achieve
  the necessary airspeed.  Balancing the load to keep the center of
  gravity at or below a certain point (center of gravity of the empty
  aircraft) ensures that you have the maneuverability required to
  provide full control over the aircraft (an improperly balanced load
  could make the plane tilt or flip).

  Similarly for a sea vessel:  If the load is centered too far above,
  ahead of, or behind the CG of the empty vessel, you could end up
  with one sunken wreck.  Too much weight, and you could find your
  decks awash when that big wave comes along.  That water will have to
  be bailed out really fast, because it's adding to your weight,
  compounding the problem.  Note that balance problems can be
  compensated for, to some degree, by taking on or dumping ballast
  (which is usually water) into the appropriate ballast tanks (of
  which there are several on your average cargo ship).

  Now, what about your spacegoing vessel?  Well, there are basically
  two cases to worry about here - 1) the vessel can not or does not
  enter atmosphere, or 2) the vessel can and does.

  In case 1), the issue of weight and balance would appear to be a
  non-issue.  The weight is in zero-gee, hence not a factor, and the
  center of gravity would be irrelevant, since there's no "preferred"
  attitude in space.  End of problem.  Or is it?  Well, not as
  _weight_, but as _mass_.  Mass possesses a quality called _inertia_.
  Inertia is why you can't get that big railroad car moving when you
  push on it with one finger, even though the brakes are off, the
  journals are properly lubricated, and you are on perfectly level
  track.  The formula (for you non-physicists out there) that
  describes this problem is F=ma (Force equals mass times
  acceleration).  Your one finger _F_ is pretty damn small, and the
  railroad car's _m_ is pretty large, which means that the _a_, for
  all practical purposes, is not distinguishable from zero.  An
  extreme example, but relevant:  Your maneuver drives, even though
  they violate Newton's second law, must be imparting an acceleration
  to the mass of your ship and everything aboard.  They are therefore
  applying a force.  Now, there is only a certain maximum level of
  force that they can provide.  How do you ensure that this level of
  force is going to be sufficient to move your ship?  If I don't have
  to worry about this, then obviously my drives can produce enough
  force to move my ship at its rated acceleration even if my cargo
  holds are packed to maximum capacity with pure osmium (the densest
  element known), or maybe the metal that is used for superdense
  armor, or maybe collapsium, or whatever the universe's densest
  material is.  O.K., I can accept that.  The logical implication is
  that when I am running with empty holds, or with holds filled or
  partially filled with materials less dense than those cited above, I
  have some extra acceleration available - since the drive can put
  out a maximum force _F_, and the mass of the ship _m_ has gone down,
  so _a_, the resultant acceleration, must go up.  Hmm, does that
  mean that my free trader rated at 1G acceleration can actually get
  1.5G or maybe 2G if I'm running empty?

  Now, case 2).  All of the comments above apply, once we get out of
  atmosphere.  In addition, we have the "conventional" issues to deal
  with, since when we are in atmosphere, we are far enough into a
  gravity well that there _is_ a preferred attitude for the ship to
  assume.  Which means that conventional weight and balance
  calculations must come into play.  I note that for all ships that I
  have seen deck plans for, if the ship was streamlined (or airframe),
  the internal arrangement appeared to be "acceptable" for "normal"
  weight and balance considerations.  Which would seem to me to be
  common sense, but still...

  Comments, anyone?

  J/
  [email removed]

 * QMPro 1.0 30-0183 * REALITY.SYS Corrupted: Re-boot universe?
- --
Executive Network Information System  [phone removed]
International ILink Host

#4996 RE: Weight and Balance.

Carl Makin · 30 November 1992 · reply to #4993

[email removed] (Jeff Zeitlin) writes:

>  license).  One of the things we were discussing was the necessity
>  and principles of weight and balance calculations.  The past couple
>  of nights, I've been thinking about that, and realized (for no
>  particular reason) that this concept seems to be absent from
>  Traveller/Megatraveller.

Yes it's missing as, I suspect, it's too complicated and difficult
to calculate accurately in a gaming situation and the vast majority
of gamers arn't interested in that level of detail.

The problem is that weight and balance calculations are different for
every aircraft type, and often for individual aircraft of the same
type if they've had modifications.  This would become very unweildy in
a game (such as one I'm currently playing in) where aircraft are a
major part of the equipment of the characters.

> I'd like some ideas on how to add it. My reasoning is as follows:

You can do it either of two ways.
1) Make the players calculate it out, or

2) Create a preflight "check" roll against the pilot's (and in fact,
all pilots in the aircraft) skill level.  Make it a normal task.

Also, for those situations where the pilot doesn't load the aircraft
make the "loadmaster" do the roll against their skill (work out which one
applies).  It should be an normal task for one with experience.  Give the
pilot (or pilots) a chance to detect problems on their "preflight check"
roll.  This would encampass more than just weight and balance though.
Is the cargo properly secured?  Did the ground handlers forget to put the
fuel cap back on?  Are the tyres/wings/control surfaces/air intakes/
instrumentation probes and holes in good condition, not blocked etc.
NOTE most of these a non-pilot just wouldn't think of.

Consequences.
Out of balance:  The aircraft will either want to turn towards the
heavier side, or raise/lower the nose.  It will require some control
input to override this however it may be masked by the trim controls.
Often, in light aircraft the weight and balance shifts as fuel burns off
so the problem may get worse (rarely better though. :-() the longer you
fly.  This problem may not manifest itself until the aircraft is in the
air and climbing to the desired altitude.

Overweight:  Sluggish climb performance.  How badly overweight will
determin how badly it performs.  This problem would tend to get better
as fuel burns off.  An overweight aircraft also won't climb as high as
a lightly loaded one.  This probably wouldn't be detected until aircraft
rotated off the runway.  As soon as it's in the air the pilot will know
something is wrong (but it could be a bad engine!).

The GM can devise other "problems" as needed. :-)

>  Obviously, an aircraft, it's important.  You have a limited amount
>  of power, and you must maintain a certain airspeed to stay up in the
>  sky.

There is a saying in aviation circles, "Takeoff is optional, Landing
is compulsory". :-)

>  Now, what about your spacegoing vessel?  Well, there are basically

>  force that they can provide.  How do you ensure that this level of
>  force is going to be sufficient to move your ship?  If I don't have
 ...
>  so _a_, the resultant acceleration, must go up.  Hmm, does that
>  mean that my free trader rated at 1G acceleration can actually get
>  1.5G or maybe 2G if I'm running empty?

That depends on how you specify the drives work.

I've never been satisfied with Traveller drives (either maneuver or jump)
because of these inconsistancies, however it does make the game a little
easier to play.  Less worrying about practicalities and more emphasis
on situations.

BTW the "Hooded Swan" series by Brian Stableford has a very interesting
universe with a number of maneuver and translight drives with different
characteristics.  Have a look for some ideas. :-)

Carl.