Re: [Jsbsim-users] Problems with ground reactions and crash detection

[Ronald J. <rj...@tq...>]

JSBSim is normally run at 120 Hz (0.00833 ms/frame) and that's way slow for crashing shocks, the model tends to be unstable at slower rates.

When I'm trying to tune ground reactions I'll often raise the model rate by one or two orders of magnitude, up to 10 kHz (0.0001 ms/frame) or more. I'll graph the contact response curve and try and get the slower model rate response to be similar. I think I worked the bogeys (gears) in the c172x model that way but did not do it for the structural contacts.

Speaking of Bogeys and Structural contacts, I just noticed the c172p model has all of its contacts defined as type="BOGEY". Try changing everything but the 3 gears to type "STRUCTURE" and see if that helps. The BOGEY type needs to limit its contact angle to much less than 45 degrees or it misbehaves. The STRUCTURE type does not have that limitation.

See the wiki at http://wiki.flightgear.org/JSBSim_GroundReactions

Good luck,

Ron


From: Carlos Vieira <carlos.vieira@gm...> - 2013-10-21 09:34
> Hi, i'm using jsbsim for a simulation project, and after integrating it
> with my project i'm doing some tests with existing aircrafts, namely c172p
> and c172r.
>
> I takeoff with no surprises and the flight it self is Ok as i expected...
> my problems comes with the ground contacts in plane crash situations.
>
> I can land also Ok in "normal" situations, but if the plane hit the ground
> with nose or wing tips instead of a crash detection situation, the plane
> "jumps" for hug altitudes... or simply gets into the ground and keeps
> falling for large negative altitudes until crash detection results Ok.
>
> I've played arround with ground reactions settings in the .xml file, but
> can't make it work correctly.
>
> Any idea of what i'm doing wrong? I'm using jsbsim got from master branch.
>
> Thanks in advance.
>
> Regards,
> Carlos V.
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