Re: Force instead of lift

 

> -----Original Message-----
> From: Oleksiy Frolov [mailto:[email protected]] 
> Sent: Friday, September 30, 2011 3:43 PM
> To: [email protected]
> 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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