[Jsbsim-users] [Fwd: Re: [Flightgear-flightmodel] Force instead of lift]

[Oleksiy F. <Ole...@ma...>]

Hello Ron

 As suggested, I am moving this discussion to jsbsim-users.

 I've checked your links to the files.

It seems in this way we could also simulate sections of the wings with
forces which would give us some "YAsim" advantages, such as a realistic
behavior outside of the "programmed" profile.

Anyway, I will try the Bill's suggestion first cause its simpler and might
be sufficient, but will come back to the external forces if its not
working as expected.

Thank you very much for your help

With best regards,
Oleksiy



---------------------------- Original Message ----------------------------
Subject: Re: [Flightgear-flightmodel] Force instead of lift
From:    "Ron Jensen" <wi...@je...>
Date:    Fri, September 30, 2011 4:52 pm
To:      "Flight dynamics model discussions"
<fli...@li...>
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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 <jsb...@li...>

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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