[simpits-tech] Motion cues - a start

[Marv De Beque]

Alex,

When I fly, most of the motions that I perceive are much more subtle 
than that.  First, rolling the sim in the direction of the turn is the 
wrong thing to do (unless it is simply to provide a little roll 
acceleration and a few inches of roll is all you should need).  It may 
sound right, but you really have to think about what is happening to you 
and your craft in flight and the forces acting on it.

If you think back to what actually turns an aircraft it is not the 
rudder, but the wings.  In order to get the wings to turn the craft you 
must bank the aircraft.  At the point you bank the aircraft, G forces 
build up and pull you downward into the center of the seat.  The 
increase of G force is matched by external forces on the wings that keep 
the aircraft tracking in the turn. It neither slips downward nor upward 
out of the bank.

As a pilot you do not feel any lateral forces to either side of your 
body, just increased G loading.  What you propose would lean the sim 
over and you would feel a corresponding lateral force into the turn 
which you ABSOLUTELY will not get in a real plane.  That is, it would be 
unnatural.  For that matter, you almost never feel a lateral component 
of G force in an aircraft unless something horrible is happening.

I like your idea for modeling turbulence.  I think that is where you 
will get the most bang for the buck.

If you can develop acceleration cues based on changes in aircraft 
position (pitch, yaw, roll, etc.) you can add another element of reality 
to the sim.   However, rolling the aircraft side to side should only be 
used to give you a little kick and be quickly (not too quickly) returned 
to level position or you will get a lateral influence from Earth's 
gravity that will be unwanted.

Good luck.  I hope to hear more on your experiment as you go!

Marv



On Friday, April 12, 2002, at 12:36 PM, Wiebe, Alex wrote:

> Off and on, I brainstorm the requirements for a motion based sim, and 
> will now perform a brain dump:
>
> Assuming a simple platform with only pitch and roll capabilities and 
> also assuming a simple aircraft. By simple I mean, not rolling past 
> +/-60 degrees, not pitching past +/- 45 degrees and not equiped with 
> function after burners (or JATO bottles :-). I realize that might cause 
> all the military guys to stop reading, but I'm thinking baby steps here.
>
> As mentioned, having a pit follow the joystick is inaccurate. However, 
> it should possible to approximate the motion.
>
> To start, a really simple algorithm could match the roll of the pit to 
> the Ball on the TC. The ball already determines the left / right 
> direction of the force vector on the aircraft.
>
> The next stop would be to add the pitch information. Baring any other 
> type of acceleration, the pitch of the aircraft should match the 
> front / back component of the force vector.
>
> Now throw in acceleration / deceleration. Most sim software should be 
> able to generate ground speed. A simple algorithm that compares the 
> ground speed every fraction of a second should be able to compute the 
> linear acceleration. Add the gravity vector and via some basic trig you 
> have the angle the pit needs to pitched to replicate the front / back 
> component of the force vector +/- the aircraft's current pitch.
>
> Once again, this should be sufficient for civilian sims not lighting up 
> the after burners...
>
> Once these are incorporated, it should be a matter of trial and error 
> to produce a 'wash out' algorithm that brings the pit back to centre 
> ready for the next 'cue'.
>
> Adding roll cues probably is where things start getting messy, and 
> without heave capabilities on your sim, turbulance and rate of climb 
> fluctuations are probably out of the question.
>
> Another thought regarding adding heaving capabilities (to the sim, not 
> your gut) to simulate some turbulance, ground roll vibrations and 
> landing contact, would be to take the pitch/roll only pit and mount it 
> to another frame via those automotive air ride shocks someone mentioned 
> a few days ago.
>
> I agree that we'd all love to get our hands on a 6 cylindar fullmotion 
> platform and download the motion driver for MSCFS, F4, etc. from 
> Boeing, etc., but that's not likely to happen. So why not start simple 
> and build a driver that generate the various force vectors that occur 
> in the plane, and let other build drivers that take that information 
> and move their pit?
>
> Just some thoughts...
> Alex
>