[simpits-tech] May the Force Feedback be with you...

[Gordan Sikic]

  Hi Matt,


First, let me apologize for so late answer. It happened to me before, 
but this time, I decided to answer back ;)  BTW, when do you sleep?
The thread is over long time ago, but anyway... here I am

>	I dunno exactly what math is required although from the math you are doing 
>it looks like you're thinking the same method I was, but you know more of the 
>math required. :) This was actually my second choice, however......I was 
>thinking a much simpler way would be to use airfoil lift. Perhaps not as 
>accurate as the previous method but much easier to handle for a non-math dude 
>like me. :)
>  
>
There's always more than one way of  solving the problem, and at the 
beginning, it not easy to say which is better.  Solution I proposed was 
simplified view of "clasicall solution" used to predict stick force 
while constructing new aircraftes. It involves some math during design 
stage, but the resulting equations are quite simple to implement in 
hardware or in software.

I would like to see more about your proposal,  is it possible?

>	By dynamic pressure, are you referring to the pressure caused by the plabe 
>moving through the air, or the actual pressure on a control surface?
>  
>

What I had in mind was the pressure that might be presented as 
0.5*rho*V*V, where "rho" is air density at the altitude of flying, and V 
is airspeed. This pressure is commonly used to connect AD coefficients 
with actual forces. It is not actual pressure on the control surface.

>	FWIW, X-Plane does not model trim tabs. I've heard that Fly has a really 
>good trim system but I don't know if it models the physical trim tab.
>  
>
AFAIK it does, but on the other hand I don't own it, so I looked at the 
documentation about the exporting data (in the internet connection 
part), and the position of the trim is listed as variable that can be 
exported.

>	I believe X-Plane already considers downwash of the wing on the horizontal 
>stabilizer, although I don't know how well (it's not doing fluid dynamics, I 
>know that).
>  
>

Yes it does (and should), and (after bit oc checking) exports it as well :)

>	This is good as long as your sim supports it. The main difference I can 
>think of between having an actual simulated trim tab compared to just moving 
>the force feedback assembly is that changes in trim would affect how much 
>control authority you have........not by much, but theoretically it should 
>change. For instance, if you have full nose-down trim (trim tab deflected 
>upwards), you will have less pitch-down control possible than with the tab 
>neutral, and more pitch-up control. But I would think the difference would be 
>pretty small. But it would be nice to have it done right.
>  
>

Yes, you are right about that.
( I was inspired by the thread discussion, this is not directly the 
subject of the thread, but (very) closely connected.)

If the nforce on the stick is calculated, why adding aditional input 
directly, why not simply use output of the simulation program? 
 Generally, everything should be calculated within simulation program, 
and results exported. All input needed for stick force calculation 
should be feeded from program (if anybody is interested in theory, I'll 
explain  this in more details).  Doing otherwise almost certanly leads 
into problems .

Additionally, even if everything goes well, after while, one would like 
to feel (for example) subtle vibrations, or buffeting while approching 
stall AoA, or (for buster comands) hydro failure, and switch to manual 
forces......  If all calculations are made within software, it is not so 
hard to add all these features, hardware remains absolutely the same.

I have to say that I'm bit biased, I preffer software solution 'cause 
I'm software frick (maybe I should introduce myself?),  and think it is 
later much easier to recompile the program, compared to changing the 
hardware. I suppose that my opinion is not spread?


at the end ,
once more I'd realy like to see your "lift connection proposal"...

ciao,

Gordan