From: knutson@mcc.com (Jim Knutson)
Newsgroups: rec.aviation,comp.sys.ibm.pc.games
Subject: Re: PC a step closer to realistic simulator (Thrustmaster)
Date: 11 Sep 92 22:09:15 GMT
Organization: MCC, Austin, TX

In article <5552@ssc-bee.ssc-vax.boeing.com> prang@ssc-vax.boeing.com (Ron Wanttaja) writes:
>Simulating G-forces, of course, is something even the big simulators can't
>do.

They can simulate it.  They can even duplicate it within a centrifuge.

>another thing.  Note that in "normal" flight this vector doesn't change
>much... not at all in a coordinated turn, for instance.  The easiest way to
>do this is to place the entire cockpit on a pivot and tilt it in the
>appropriate direction.  Suprisingly little tilt is needed... just the hint
>should be enough.  Ten to 30 degrees, maximum.

It's not just the tilt.  It's the lateral motion and accelleration
changes.  Really, the sensory input is only needed for a short period of 
time.  Just enough to get the mind thinking that something is going
on.  After that the mind takes over and the sensory input (i.e. motion)
can be cancelled.

I've flown two simulators.  One was an F15 simulator at NASA-AMES and
the other was an F4 simulator at a local AFB (helps to have a father in
the AF :-).

The F15 simulator was a Singer-Link trainer and was strictly instrument
flying as far as I could tell.  It had a 3 poster (as I recall)
hydraulic system for motion sensing as well as other sensory cueing
systems.  The hydraulic system was shut off.  When I asked why, they
said that it was prone to failure and maintenance was incredibly
expensive.  When it works, you are raised 15' or so off the floor.
When it fails, you fall like a rock.  You can understand why they
wouldn't want to use it that much.  The colonel that was with us said
he had forgot to put his helment on once and the hydraulics failed.  He
ended up with a concussion from slamming into the canopy during descent
and that was with his belts on.  My impression was the AF mainly uses
the simulators to keep pilots proficient in operational proceedures
(egress, flameout, instrument failure, instrument landings, etc.)  For
flight proficiency, they use the full scale birds.

The F4 simulator had 3 displays mounted stragically around the
simulator cockpit.  One in front and one on each side of the pilot.
I don't recall there being monitors for the back seat.  I
was flying at night, so I can't tell exactly how good the displays
were.  It did not have the full motion hydraulics.

Both simulators had buffet simulation and the F4 had a G force whoopee
cushion.  I've seen this type of thing at Disney Land.  Basically, it's
an air bag that you sit on.  As G increases, it starts inflating.  The
shape of the bag is such that it starts squeezing you as it inflates.
It also raises your body and when you have belts on, it feels like
something is pressing on your butt.  I thought that the buffet
simulation was much better at making me think I was really flying than
the G whoopee cushion.  Both also had feedback through the stick and
pedals.

Flying these simulators really makes you understand why pilots work so
hard at staying fit.  It takes an incredible amount of energy to horse
these planes through the air.  The F4 was heavier on the stick than the
F15, but I guess that would be expected.

It's also amazing how much simulation you are getting on a PC with Falcon
compared to these monsters.  Sure, we don't get all the fancy buttons and
dials, but most of the time, a pilot spends his time looking out of the
cockpit, not in it.  All we need is a bit more tactile feedback and
then you're set.

>Two things make Nitinol ideal for a home-grown simulator:  First, it can be
>bought in wire form; the wire itself acts as a resistor.  By hooking a
>variable-current power supply to it, you can shorten/lengthen the wire as
>desired (within a given range, of course).
>
>Second, its resistance changes linearly with length.  A simple voltmeter
>can be calibrated to give a direct readout of position.
>
>So you don't need LVDTs or other methods to determine the current
>position... feedback is built right into the system.
>
>It's easy to see how to mount your simulator's cockpit... a cruxiform
>base mounted on a center pivot, with springs supporting the arms of the
>cross.  Connect nitinol actuators inside each spring, and vary the
>current appropriately to get the desired combination of bank/pitch. 

I think it's a bit harder than this to get the feel you want.  For
instance, a roll to the right feels like a constant lateral
accelleration to the right (i.e. your head pulls to the left).  How
would I simulate this with your setup?

How's this for a low budget simulator:

1. Mount a chair on roller plates over a fixed base.  Attach some kind
   of actuators to give the chair X and Y motion.  Only a few inches of
   mobility would be needed.

   Roll changes and side slip are done by moving the chair in the X
   direction with a slow return to center after the initial
   displacement.

   I believe the sit down version of the Stunt Driver arcade game does
   this.  Nice effect!

   Acceleration changes (AB, brakes, etc.) are done by displacing the
   chair in the Y direction.  Actually, these forces are smaller than
   lateral motion and don't occur as often, so this motion could
   probably be eliminated with little degradation in the feel.

2. Add an air bladder whoopee cushion and belts.

   The air bladder would multiplex the G and buffet signals.

3. Sound card of one sort or another.

At this point, you have your visual, auditory, and some tactile feedback
taken care of.  Now let's get fancy.

Put the setup in an enclosure designed to divorce your senses from your
real environment (dark room, model cockpit, closet, etc.).

Put on your flight suit with oxy mask and helmet.  The helmet adds mass
to your head and intensifies any X/Y motion that the chair makes.  The
oxy mask has a regulated oxygen supply which reduces oxygen flow during
high G manuevers thereby making you dizzy (can you say liability?  Sure
I knew you could. :-).  The mask could be as simple as a rebreather
type setup with a valve that regulates how much of your own breath you
rebreath.  The flight suit would have 4 small wires running to each
elbow and wrist.  These wires would run to 4 take up spools that keep
tension on the wires.  As G increases, so does the tension.

Then, in your back yard, take your playground's merry-go-round, motorize
it and mount the setup on it for your centrifuge, and, oh ya, put 40MM
shells and armor plate under the seat for ejection simulation, and, 
ooooh ...

-- 
Jim Knutson
knutson@mcc.com
cs.utexas.edu!milano!knutson
Wk: (512) 338-3362
Newsgroups: rec.aviation