Re: [Flightgear-flightmodel] Force instead of lift

[Bill G. <bi...@ho...>]

In this case, the Cl is roll moment coefficient, not CL, the lift
coefficient

The attached file shows a new format for JSBSim files that I came up with.
It works just as well as the older format, but the formulation of the
coefficients more closely matches classical aerodynamic textbook equation
buildup. Feel free to use this, or the older format. They are both equally
valid.

Bill



> -----Original Message-----
> From: Oleksiy Frolov [mailto:Ole...@ma...] 
> Sent: Saturday, October 01, 2011 12:03 AM
> To: Flight dynamics model discussions
> Subject: Re: [Flightgear-flightmodel] Force instead of lift
> 
> Hello Bill
> 
>  This is a good suggestion, thank you.
> 
>  I understand about calculating 2(4) different CL-s.
> 
>  Do I also understand correctly we will than have use 
> something you guys did to the flaps once:
> 
>      <axis name="ROLL">
>       .................
>          <function name="aero/coefficient/CldF3">
>             <description>
>                Roll Moment Coefficient due to Asymetrical 
> Fowler Flaps Deflection
>                calculated as difference between left and 
> right flap lift coef,
>                times distance from centerline to MAC of surface.
>             </description>
>             <product>
>                <value>     21.28</value>
>                <difference>
>                   <property>aero/coefficient/CLdF3R</property>
>                   <property>aero/coefficient/CLdF3L</property>
>                </difference>
>             </product>
>          </function>
> 
> 
> in order to calculate the moments due to difference in 
> individual CLs ?
> 
> With best regards,
> Oleksiy Frolov
> 
> >
> >
> >> -----Original Message-----
> >> From: Oleksiy Frolov [mailto:Ole...@ma...]
> >> Sent: Friday, September 30, 2011 3:43 PM
> >> To: fli...@li...
> >> Subject: [Flightgear-flightmodel] Force instead of lift
> >>
> >> Hello
> >>
> >>  I am trying to simulate the effects of the differential 
> wing lift. 
> >> Such as single wing stall due to the propwash loss at a low speed, 
> >> and the effect of the icing on a single wing (which can 
> happen during 
> >> a deicing failure on that wing). All of these are important 
> >> aerodynamic effects.
> >>
> >>  Now, we know we only have one wing in jsbsim currently, not 2. My 
> >> idea is therefor to try using 2 <force> records to 
> simulate the wings 
> >> separately, instead of the usual CL record.
> >> This however would require some kind of algorithm to 
> define how the 
> >> force origin moves to overlay with center of lift for each wing, 
> >> which is probably not an easy task
> >>
> >>  I was wondering if anyone have tried a similar approach 
> before, and 
> >> if this problem pechaps has an easier solution ?
> >>
> >> Thank you
> >>
> >> regards,
> >> Oleksiy Frolov
> >>
> >
> >
> > No reason that you couldn't build this inside of the 
> existing JSBSim 
> > format without using the external forces. Divide your wing into 
> > panels, maybe (on each side) one that is influenced by the 
> propeller 
> > slipstream, one not.
> > Sum
> > all of your lifts to apply them at the aero reference 
> point. So with a 
> > two engine aircraft, you might have a total of four panels, two per 
> > wing half, one inboard in the slipstream, one outboard in 
> clean air. A 
> > mismatch of forces left/right would normally shift the aero 
> reference 
> > point left or right, but that can be resolved with a moment.
> >
> > You have a couple advantages doing this. A force at a distance is a 
> > moment, so if the outer panels are experiencing different 
> lift forces, 
> > that lift times its arm creates a moment. If the aircraft 
> is rolling, 
> > each wing sees a different angle of attack, and therefore different 
> > lift. This is usually handled other ways, but your method has the 
> > advantage of spinning properly.
> > There are disadvantages, though.
> >
> > If you are going to that trouble, you might consider 
> keeping the flaps 
> > and ailerons seperate as well, unless the actuator mechanism is 
> > guaranteed to never give you different flap or aileron angles.
> >
> > Bill
> >
> >
> > 
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> 
> 
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> seriously valuable.
> Why? It contains a definitive record of application 
> performance, security threats, fraudulent activity, and more. 
> Splunk takes this data and makes sense of it. IT sense. And 
> common sense.
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