Re: Force instead of lift

On Friday 30 September 2011 13:43:24 Oleksiy Frolov wrote:
> 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

A better place to ask might be on the JSBSim user list
JSBSim user questions <[email protected]>

In the aerodynamics section of a JSBSim configuration you are only allowed one 
force vector, applied at aerorp, and consisting of lift, drag and side or 
normal, axial and side.  You can also specify the moments for yaw, pitch and 
roll.

An alternative is to use the 'external force' section of JSBSim. This allows 
you to specify an arbitrary number of forces, each of which can be applied at 
separate points on the airframe and can be computed in different axis 
systems.

I've played a little with doing the vertical stabilizer as external forces in 
the JSBSim config I did for the Gloster Meteor:
https://gitorious.org/ron-s-hanger/gloster-meteor

The JSBSim config is here:
https://gitorious.org/ron-s-hanger/gloster-meteor/blobs/master/gloster-meteor-jsb.xml
And the systems file that computes the external force is here:
https://gitorious.org/ron-s-hanger/gloster-meteor/blobs/master/Systems/external_reactions.xml

This was a quick exercise, and I didn't fully validate the trig used to 
compute the axial/normal/side components.

Ron

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