> From: Jon Berndt <[EMAIL PROTECTED]>
> Reply-To: FlightGear developers discussions <flightgear-devel@flightgear.org>
> Date: Mon, 17 Jan 2005 22:00:28 -0600
> To: FlightGear developers discussions <flightgear-devel@flightgear.org>
> Subject: RE: [Flightgear-devel] Antonov AN-225.
> 
>> Does anyone know if there is something similar in JSBSim?  It seems that the
>> spoilers there are only symmetric, so are useful for landing, but not for in
>> flight use?
>> 
>> -- Adam
> 
> It hasn't been done, yet - I was just discussing this offline with someone.
> Let me say
> that, yes, it certainly CAN be done, without question. At one time years ago I
> modeled
> certain aerodynamic aspects of a military aircraft and great pains were taken
> to model
> similar things, and other much smaller effects.
> 
> The effect cannot be modeled without some thought, though. Remember that
> JSBSim models
> aerodynamic forces and moments using aerodynamic coefficients and stability
> derivatives.
> By calculations, empirical data, flight test data, etc. one can usually
> determine the
> total (symmetric) effects of spoilers which will generally be:
> 
> 1) effect on lift
> 2) effect on drag
> 3) effect on pitching moment
> 
> If the spoilers are deployed asymmetrically, the effects are wider:
> 
> 1) effect on lift
> 2) effect on drag
> 3) effect on pitching moment
> 4) roll
> 5) yaw
> 6) side force
> 
> ... all six axes ...
> 
> If we can determine the symmetric case, we can figure out the asymmetric case.
> 
> Jon
> 
> 


That sounds to me like the difficulty is in choosing (finding?) the
coefficients, rather than in the coding of JSBSim?
I don't mean to minimize the difficulty of finding all of those
coefficients, but in some sense that is really a different problem than "can
JSBSim do it?"  
Lot's of aircraft use spoilers for some part of roll control, so it seems to
me that would be an important addition to JSBSim.  Typically the spoilers
will only deploy above some yoke position threshold (maybe actually a roll
rate?), and then they can, of course, only deploy "up", so only one is
involved at a time.  This all does make it somewhat ugly.
But often, for modeling, finding the correct parameters is the hardest part,
once the code can handle what is needed.
So, please add me to the requesters, and add me to the offline discussion.

Thanks,

--Adam





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